228Service.Variable Automatic Gearbox multitronic® 01JDesign and FunctionSelf-Study Programme 228For internal use onlymultitronic®The name multitronic® stands for the new variable automatic gearbox developed by Audi. The variable automatic gearbox is commonly known as the CVT gearbox. The CVT concept improved by Audi is based on the long-established principle of the “chain drive transmission”. According to this principle, the reduction ratio between the shortest and the longest ratio can be controlled steplessly by means of a so-called “variator”.CVT is the English abbreviation for “Continuously Variable Transmission”.228_023The new Audi multitronic® with Tiptronic function offers a synergy of the best possible dynamics, optimal fuel utilisation and the highest possible level of drive comfort.2ContentsPage Introductionmultitronic® ............................................................................ 2 The gearbox concept .............................................................. 9 Specifications ........................................................................10Gearbox modulesThe flywheel damper unit .................................................... 11 Sectional view of gearbox ....................................................13 The forward clutch/reverse clutch with planetary gear train ..................................................... 14 The clutch control ................................................................. 20 The clutch cooling system.................................................... 28 The auxiliary reduction gear step ....................................... 31 The variator ............................................................................32 The transmission control ..................................................... 35 The torque sensor ................................................................. 38 The splash oil cover .............................................................. 43 The chain ............................................................................... 44 The oil supply .........................................................................47 Electrohydraulic control .......................................................52 Selector shaft and parking lock ...........................................56 Gearbox housing/ducting and sealing systems ................ 57 Hydraulic chart .......................................................................60 ATF cooling system ............................................................... 62Gearbox controlControl unit for multitronic J217 ......................................... 63 Sensors .................................................................................. 66 CAN information interchange, multitronic® ...................... 75 Auxiliary signals/interface ....................................................76 Function diagram ................................................................. 80 Dynamic control program (DCP) ......................................... 82ServiceTowing ....................................................................................91 Update programming (flash programming) ...................... 92 Special tools/workshop equipment .................................... 96The Self-Study Programme contains information about designs and functions.The Self-Study Programme is not a Workshop Manual!New! Note!Important! Note!Please refer to the relevant Technical literature for all maintenance and repair instructions. 3IntroductionGearboxes are required in order to match the torque characteristic of the internal combustion engine to the vehicle. In the main, multi-step reduction gears are used such as manual gearboxes, automated manual gearboxes and multi-step automatic reduction gears. A multi-step reduction gear always represents a compromise between handling dynamics, fuel economy and driving comfort. In an internal combustion engine, torque flow is not intermittent, rather it is continuous. A variable ratio is, therefore, ideal with regard to engine power utilisation. The CVT concepts which have been available on the market until now are also based upon the "chain drive principle“. On account of their limited power transmission, however, they are only suitable for subcompact cars and vehicles in the lower mid-range segment with low engine performance. As the results of independent tests show, these CVT concepts have yet to impress in terms of driving performance. Audi also chose the belt/chain drive principle for the development of its CVT gearbox, since it is the most advanced form of transmission available today. Audi's objective was to develop a CVT gearbox for high-performance premium segment vehicles that sets new standards in terms of driving performance and fuel economy, as well as in handling dynamics and comfort.Manual gearboxR 1 3 5 2 4CVT stepped modemultitronic®P P R N R ND4 3 2D228_0024The innovations incorporated by Audi and its development partners in the course of advanced development work will surpass existing gearbox concepts with regard to all the characteristics mentioned above.Audi is therefore the first car-maker to present a CVT gearbox which can be used in combination with 2.8-ltr. V6 engines for power and torque ratings of 200 bhp and 300 Nm respectively.Basic principle The key component part of the multitronic® is the variator. It allows reduction ratios to be adjusted continuously between the starting torque multiplication ratio and the final torque multiplication ratio. As a result, a suitable ratio is always available. The engine can always operate within the optimum speed range regardless of whether it is optimised for performance or fuel economy. The variator comprises two tapered disc pairs - a set of primary pulleys (pulley set 1) and a set of secondary pulleys (pulley set 2) - as well as a special chain which runs in the V-shaped gap between the two tapered pulley pairs. The chain acts as a power transmission element. Pulley set 1 is driven by the engine by means of an auxiliary reduction gear step. Engine torque is transmitted via the chain to pulley set 2 and from here to the final drive. One of the tapered pulleys in each of the sets of pulleys can be shifted on the shaft for variable adjustment of the chain track diameter and transmission ratio. The two sets of pulleys must be adjusted simultaneously so that the chain is always taut and the disc contact pressure is sufficient for transmission purposes.228_043 Set of primary pulleys (pulley set 1) Set of secondary pulleys (pulley set 2)Drive Downforce NarrowWideThis gearbox a is known as a chain drive transmission because of its design.5Introductionmultitronic® for maximum comfort In automatic mode, any ratio is possible within the bounds of the control map. The factors that determine rpm are driver input (accelerator pedal position and actuation rate) and traction resistance. Transmission ratios are adjusted completely free of jolts and without any interruption in tractive power flow. In the tiptronic function, there are 6 defined shifting characteristics for manual gear selection. The driver can therefore choose handling dynamics to suit his/her personal preferences. This feature is particularly useful on downhill gradients for example, as the driver can personally determine the engine braking effect by selective down-shifting. Top speed is achieved in 5th gear. 6th gear is configured as an economy gear or overdrive. The tiptronic can be operated from the steering wheel at option.This makes the tiptronic function very user-friendly indeed.228_007228_038228_015Transmission ratio diagrams of multitronic® 01J in the 2.8-litre Audi A6 V6 developing 142 kW228_01660001st gear2nd gear3rd gear4th gear5th gear6th gear50004000Unavailable rpm range3000Engine speed rpm20001000228_07250km/h 100km/h 150km/h 200km/h 250km/hRoad speed 6vmax = approx. 235 kphmultitronic® for maximum dynamics Multi-step reduction gear: The coloured fields show the ranges within which maximum engine power is not available. The result is a loss of acceleration. multitronic®: The gearbox input speed control maintains engine performance at maximum. The vehicle accelerates with no interruption in tractive power flow. The result is an optimum acceleration characteristic.Control map Gearbox input speed control is used to vary maximum road speed as a function of tractional resistance.Depending on tractional resistance, it is necessary to shift down from the longest ratio sooner or later.Shifting characteristics of tiptronic 01JMost economical characteristic Sporty characteristicComparison of ratios: • 5-speed automatic gearbox 01V (gearbox code DEU) • multitronic® 01J (gearbox code DZN)rpm range not available for stepped gearboxes Shifting characteristics of 01V1st gear60002nd gear3rd gear4th gear5th gear500040003000Engine speed rpm2000100050km/h100km/h150km/h200km/h250km/h228_073Road speed7Introductionmultitronic® for high fuel economy As a result of the long ratio, a large reduction in engine speed is possible in the economy driving mode. In comparison with the 5-speed manual gearbox, engine speed for example is reduced from approx. 3200 rpm to approx. 2450 rpm at a road speed of 130 kph so as to increase fuel economy. Through continuous transmission ratio adjustment, the engine always runs within the optimum operating mode, regardless whether it is optimised for performance or fuel economy. The green area shows the engine speed reduction within the "Economy" operating mode.Most economical characteristic Sporty characteristic Transmission ratios on 01WComparison of ratios: • 5-speed-manual gearbox 01W (gearbox code DHY) • multitronic® 01J (gearbox code DZN)1st gear6000Engine speed reduction within "Economy" operating mode Example 130 kph2nd gear3rd gear4th gear5th gear5000400001W3000Engine speed rpm01J2000100050km/h100km/h150km/h200km/h250km/h228_074Road speed 8130 kphvmax = approx. 235 kphThe gearbox conceptEngine torque is transmitted to the gearbox through either a flywheel damper unit or a two-mass flywheel depending on engine output. There is one "wet“ plate clutch for forward travel and one for reverse travel; both act as starting clutches. The rotational direction for reverse is changed by means of a planetary gear train. The engine torque is transmitted to the variator via an auxiliary reduction gear step and transferred from there to the final drive. It is worth mentioning the innovative concept for torque transfer by means of a pull chain (refer to description of variator and pull chain). The electro-hydraulic control, together with the gearbox control unit, forms a unit which is accommodated in the gearbox housing. The Tiptronic function provides 6 "speeds“ for manual gear selection.Reverse gear clutch Flywheel damper unit Auxiliary reduction gear step Variator with chain228_003Planetary gear train Forward clutchHydraulic control unitGearbox control unit9IntroductionSpecificationsDesignation: Factory designation: Code: Max. transferable torque: Range of ratios of the variator: Spread: Ratio of auxiliary reduction gear step: Final drive ratio: Operating pressure of oil pump: Delivery rate of oil pump: ATF for multitronic®: Axle oil for multitronic®: Gear oil quantities: ATF new filling (incl. ATF cooler and ATF filter) ATF change Axle oil Gross weight (without flywheel): Overall length: multitronic® 01J VL 30 DZN max. 310 Nm 2.40 - 0.40 6 51/46 = 1.109 : 1 43/9 = 4.778 : 1 max. approx. 60 bar 10 rpm @ 1000 rpm G 052 180 A2 G 052 190 A2approx. 7.5 litres approx. 4.5 litres approx. 1.3 litres approx. 88 kg approx. 610 mmAll the sizes specified in this SelfStudy Programme refer only to the multitronic® with the code DZN.228_001 10Gearbox modulesThe flywheel damper unitIn reciprocating engines, the unevenness of the combustion sequence induces torsional vibration in the crankshaft. This torsional vibration is transmitted to the gearbox and results in resonant vibration here, producing noise and overloading components in the gearbox. The flywheel damper unit and the two-mass flywheel dampen torsional vibration and ensure the engine runs quietly. In the 2.8-litre V6 engine, engine torque is transmitted to the gearbox through a flywheel damper unit. As four-cylinder engines do not run as smoothly as 6-cylinder engines, a two-mass flywheel is used in 4-cylinder engines.228_032Damper unitFlywheelTwo-mass flywheelFor more detailed information, please refer to Self-Study Programme 142.228_00411For better representation, the oil pump and the transfer case are shown folded on the cutting plane.228_04012Gearbox modulesSectional view of gearboxColour definitionsHousing, screws, boltsHydraulic parts/controlElectronic gearbox controlShafts, gearsPlate clutchesPistons, torque sensorsBearings, washers, circlipsPlastics, seals, rubberOrder No.: 507.5318.01.00 This figure can be ordered as a size A0 poster through Bertelsmann Distribution for a net price of DM 10.00. Direct ordering through Bertelsmann only applies to Germany. Dealers in export markets are requested to contact their importer.13Gearbox modulesThe forward clutch/reverse clutch with planet gear setIn contrast to multi-step automatic transmissions, which use a torque converter for torque transmission, separate clutches are used for forward and reverse travel in the Audi CVT concept. These clutches, so-called “wet plate clutches”, are also used to execute gearshifts in multi-step automatic transmissions. They are used for driving off and transmitting the torque to the auxiliary reduction gear step. The drive-off process and torque transmission are monitored electronically and regulated electro-hydraulically. The electro-hydraulically controlled plate clutch has the following advantages over a torque converter: • Low weight • Very little installation space is required • Adaptation of drive-off characteristic to driving situation • Adaptation of creep torque to driving situation • Protective function in the event of overloading or misuseGearbox input shaftRing gear Planetary gearsForward clutch/reverse clutch with planetary gear trainInput pulley set 1 (auxiliary reduction gear step) Planet carrier Forward clutch 228_005 Reverse clutch 14The planetary gear train The planetary gear train is constructed as a planet reversing gear set and its only function is to change the rotational direction of the gearbox for reversing. The reduction ratio in the planetary gear train is 1:1 when reversing.Assignment of components The sun gear (input) is linked to the gearbox input shaft and the steel plates on the forward clutch. The planet carrier (output) is linked to the drive gear the auxiliary reduction gear step and the lined plates on the forward clutch. The ring gear is connected to the planetary gears and the lined plates on the reverse clutch.Steel plates and lined plates on forward clutchPlanet carrier with planetary gearsGearbox input shaft Sun gearInput pulley set 1 (auxiliary reduction gear step)228_008Steel plates and lined plates on reverse clutchRing gear15Gearbox modulesForce path in the planetary gear train Torque is transferred to the planetary gear train via the sun gear connected to the input shaft and drives the planetary gears 1. Planetary gears 1 drive planetary gears 2, which are in mesh with the ring gear. The planet carrier (output planetary gear train) is stationary because it acts as the input for the auxiliary reduction gear step and the vehicle is still not moving. The ring gear idles and rotates at half engine speed in the direction of engine rotation.Planetary gear 1 Planet carrier Planetary gear 2Ring gear228_033Gearbox input shaft with sun gearDirection of rotation of components when engine is running and vehicle is stationary16Force path during ahead travel The steel plates on the forward clutch are linked to the sun gear and the lined plates are linked to the planet carrier.When the forward clutch is positive (engaged), it connects the gearbox input shaft to the planet carrier (output). The planetary gear train is locked and rotates in the same direction as the engine; the torque transmission ratio is 1:1.Forward clutchPlanetary gear train228_009 Oil pressure for clutch Torque flow 17Gearbox modulesForce path when reversing The lined plates of the reverse clutch are connected to the ring gear and the steel plates are connected to the gearbox housing. When the reverse clutch becomes positively engaged, it holds the ring gear and thereby prevents the gearbox housing from rotating on starting. Torque is then transmitted to the planet carrier, which begins to rotate in the opposite direction to the engine. The vehicle reverses. When reversing, road speed is limited electronically. The variator remains in the starting torque ratio.Reverse clutchRing gear228_010 Oil pressure for clutch Torque flow18Notes19Gearbox modulesThe clutch controlThe drive-off process During the drive-off process engine speed is primarily used for clutch control. Depending on the starting characteristic, the gearbox control unit defines a nominal engine speed at which engine speed is regulated as a function of clutch torque. The driver input and the internal demands in the gearbox control unit are the factiors that determine the starting characteristic. In an economy driving mode, which is characterised - for instance - by a small accelerator pedal angle during the driveoff process, the transition from engine idling speed to drive-off engine speed is performed at low revs. Short clutch slip times and low engine speed allow for higher fuel economy. For a performance start, the transition from engine idling speed to drive-off engine speed takes place at higher revs. The higher engine torque leads to correspondingly higher vehicle acceleration. Several engine variants (petrol/diesel, torque and torque curve) also have an effect on the starting characteristic.100 80 60 40 20 0Accelerator pedal 60% depressedEngine speed4000 3000 2000 1000 012345678910Time in seconds228_053Accelerator pedal 100% depressed100 80 60 40 20 0Engine speed4000 3000 2000 1000 012345678910Time in seconds228_052Accelerator pedal 100% depressed + kickdown100 80 60 40 20 06000 5000Engine speed4000 3000 2000 1000 012345678910Time in seconds228_054Accelerator pedal angle Engine speedGearbox input speed, pulley set 1 Gearbox output speed, pulley set 2Nominal engine speed 20Electronic control The following parameters are used for clutch control: • Engine speed • Gearbox input speed • Accelerator pedal position • Engine torque • Brake pressed • Gearbox oil temperature The gearbox control unit calculates the nominal clutch pressure from these parameters and determines the control current for pressure regulating valve N215. The clutch pressure, and therefore also the engine torque to be transmitted by the clutch, changes almost in proportion to the control current (refer to “Hydraulic control”, page 22). Hydraulic pressure sender 1 G193 registers the clutch pressure (actual clutch pressure) in the hydraulic control. Actual clutch pressure is continuously compared to the nominal clutch pressure calculated by the gearbox control unit. The actual pressure and specified pressure are checked continuously for plausibility and corrective action is taken if these two values deviate from one another by more than a certain amount (refer to “Safety shut-off”, page 23). To prevent overheating, the clutch is cooled and clutch temperature is monitored by the gearbox control unit (for more detailed information, refer to “Clutch cooling”, page 28, and “Overload protection”, Page 23).G193 multitronic control unit228_075N21521Gearbox modulesHydraulic control Clutch pressure is proportional to engine torque and is not dependent on the system pressure. A constant pressure of approx. 5 bar is applied by the pilot pressure value (VSTV) by the pressure regulating valve N215. N215 produces a control pressure which controls the position of the clutch control valve (KSV) depending on the control current calculated by the gearbox control unit. A high control current results in a high control pressure. The clutch control valve (KSV) controls the clutch pressure and therefore also regulates the engine torque to be transmitted. The clutch control valve (KSV) is supplied with system pressure and produces clutch pressure in accordance with the activation signal from N215. A high control pressure result in a high clutch pressure. The clutch pressure flows via the safety valve (SIV) to the manual selector valve (HS). The manual selector valve transfers clutch pressure either to the forward clutch (position D) or to the reverse clutch (position R), depending on the selector lever position. The non-pressurised clutch is vented into the oil sump. In selector lever positions N and P, the supply is shut off via the manual selector valve and both clutches are vented into the oil sump.RK HSVKP RN DSIVKSV VSTVN215228_011ATF depressurised Clutch pressure Supply pressure 22Pilot control pressure Control pressure In the oil sumpSafety shut-off A safety-critical malfunction has occurred if actual clutch pressure is clearly higher than specified clutch pressure. In this case, the clutch is depressurised regardless of the manual selector valve position and other system states. A safety shut-off is implemented via the safety valve (SIV) and enables the clutch to open quickly. The SIV is activated by solenoid valve 1 N88. At control pressures upwards of approx. 4 bar, the supply to the clutch control valve (KSV) is shut off and the connection to the manual selector valve in the oil sump is vented.Overload protection Using a model calculation, the gearbox control unit calculates the clutch temperature from clutch slip, engine torque to be transmitted and gearbox oil temperature. Engine torque is reduced if the measured clutch temperature exceeds a defined threshold because of excess load on the clutch. Engine torque can be reduced to the upper end of the idling speed range. It is possible that the engine will not respond to the accelerator pedal for a short period of time. The clutch cooling system ensures a short cooling-down time. Maximum engine torque is quickly available again. Overload of the clutch is almost impossible.Switched position after safety shut-offHS VK P RN D KSV SIVN88 228_082Vented into oil sump/depressurised Clutch pressure Supply pressurePilot control pressure Control pressure In the oil sump 23Gearbox modulesClutch control when vehicle is stationary (creep control) The creep control function sets the clutch to a defined slip torque (clutch torque) when the engine is running at idling speed and a drive position is selected. The vehicle behaves in the same way as an automatic transmission with a torque converter. Selective clutch pressure adaptation results in an input torque which causes the vehicle to “creep”. Input torque is varied within defined limits depending on vehicle operating state and vehicle road speed. The contact pressure applied by the taper pulleys - as determined by G194 - is used for precision clutch torque control. Creep control allows the vehicle to be manoeuvred (when parking) without pressing the accelerator pedal and therefore enhances driving comfort.As contact pressure is proportional to the actual engine input torque present at pulley set 1, clutch torque can be precisely calculated and controlled using G193 (for more detailed information, refer to “The torque sensor”, page 38).G193 G194228_013 Brake not pressed 40 Nm24Special feature of the creep control A special feature of the creep control is the reduction of creep torque when the vehicle is stationary and the brake is actuated; as a result, the engine is not required to develop so much torque (the clutch is also open wider). This has a positive effect on fuel economy and comfort, as the vehicle's acoustics (humming of the engine running at idling speed when the vehicle is stationary) are improved and much less pressure has to be applied to the brake to stop the vehicle. If the vehicle rolls back when standing on a slope with only light pressure applied to the brake, the clutch pressure is increased so as to immobilise the vehicle (“Hill-holder” function). By using two gearbox output speed senders G195 and G196 - it is possible to distinguish between ahead travel and reverse travel, which makes the hillholder function possible (for further information, please refer to the chapter on “Sensors”).G194G193228_012 Brake pressed15 Nm25Gearbox modulesThe micro-slip control The micro-slip control serves to adapt the clutch control (see description of adaption process) and dampen the torsional vibration induced by the engine. In the part-throttle range, the clutch characteristics are adapted up to an engine torque of 160 Nm. In the rev range up to approx. 1800 rpm and at engine torques up to approx. 220 Nm, the clutch operates in what is known as “microslip” mode. In this operating mode, a slip speed (speed differential) of approx. 5 rpm to 20 rpm is maintained between the gearbox input shaft and pulley set 1. For this purpose, the gearbox control unit compares the signal generated by gearbox input speed sender G182 with the engine speed (making allowance for the auxiliary reduction gear step). Sender G182 registers the rpm of pulley set 1.As the term “micro-slip” suggests, clutch slip is kept at a minimum so no penalties in lining wear and fuel economy are noticeable.Clutch closed300250200Micro-slip control range150Engine torque in Nm100Adaption range during micro-slip control: up to approx. 160 Nm500 0 1000 2000 3000 4000 5000 6000 7000approx. 1800 rpmEngine speed in rpm228_09226Clutch control adaption To be able to control the clutch equally as comfortably in any operating state and throughout its service life, the relationship between control current and clutch torque has to be updated continuously. This is necessary because the coefficients of friction of the clutches are constantly changing. The coefficient of friction is dependent on the following factors: • Gearbox oil (quality, ageing, wear) • Gearbox oil temperature • Clutch temperature • Clutch slip To compensate for these influences and optimise clutch control, the relationships between control current and clutch torque are adapted in creep control mode and in the part-throttle range. In the part-throttle range, adaption.... ...... is performed in micro-slip control mode. In this operating mode the gearbox control unit compares the engine torque (from the engine control unit) to the control current to N215 and stores these data. The actual data are used for calculating new characteristics (see “Micro-slip control”). Here, “adaption” means learning new pilot control values.Summary: The adaption function serves to maintain a constant clutch control quality. The adaption data also have an effect on the calculation of clutch pressure at higher transmission torques (clutch fully positively engaged). High clutch pressures are not required, which ultimately has a positive effect on efficiency.Adaption in creep control mode (brake pressed): As mentioned already, a defined clutch torque is set in creep control mode. The gearbox control unit observes the relationship between the control current (from N215) and the data from pressure sender G194 (contact pressure) and stores these data. The actual data are used for calculating new characteristics.27Gearbox modulesThe clutch cooling systemThe clutches are cooled by a separate oil flow in order to protect them from exposure to excessively high temperatures (particularly when driving away in heavy conditions). To minimise power losses due to clutch cooling, the cooling oil flow is connected when required via a cooling oil control unit integrated in the valve body. The cooling oil quantity is also increased via a suction jet pump (entrainment pump) without placing a considerable higher demand on oil pump capacity. To optimise clutch cooling, the cooling oil flows only to the power-transmitting clutch pulley set. The cooling oil and the pressurised oil of the forward clutch flow through the hollow gearbox input shaft. The two oil circuits are separated from one another by a steel tube, the so-called “inner part”. An “oil divider” located at the oil outlet bores on the gearbox input shaft guides the cooling oil flow to the forward clutch and the reverse clutch.Distributor disc Diaphragm spring Oil divider with diaphragm spring and stop ring with openings228_064Inner part Stop ring Oil dividerReverse clutch Forward clutch 28Cooling the forward clutch If the forward clutch is engaged, the cylinder (thrust plate) of the forward clutch presses the oil divider back. In this position, the cooling oil flows past the front face of the oil divider and through the forward clutchCooling the reverse clutch If the forward clutch is not operated (when the engine is running at idling speed or when the reverse clutch is operated), the oil divider is in its basic position. In this position, the cooling oil flows to the oil divider and rerouted to the reverse clutch by means of a distributor plate. Branches in the distributor pulley duct a partial cooling oil flow to the planetary gear train and provide the necessary lubrication.Forward clutchReverse clutchCylinder228_014 Oil pressure for clutch Clutch cooling oil flow29Gearbox modulesHydraulic clutch cooling control The clutch cooling system cuts in at the same time as the clutch control is activated. The gearbox control unit applies a defined control current to solenoid valve 1 N88. This produces a control pressure which switches the clutch cooling valve (KKV). The clutch cooling valve (KKV) transfers pressure from the cooler return pipe to the suction jet pump (entrainment pump). The pressurised oil is used to operate the suction jet pump (entrainment pump) (for further details, refer to “Oil supply/suction jet pump (entrainment pump)”, page 51).to manual selector valve to cooler return pipeSIVKKVVSTVN215N88228_045Suction jet pump (entrainment pump) with non-return valve to the clutchesATF depressurised Cooling oil flow Oil from cooler return pipe 30Pilot control pressure Control pressure In the oil sumpThe auxiliary reduction gear stepDue to constraints on space, torque is transmitted to the variator through a auxiliary reduction gear step. The auxiliary reduction gear step has different ratios for adapting engine variants to the gearbox. As a result, the variator is operated within its optimum torque range.Planetary gear trainAuxiliary reduction gear stepPulley set 1228_01731Gearbox modulesThe variatorThe basic principle of the variator has already been explained on page 5. The special features and functions of the multitronic® variator are described on the following pages. Pulley sets 1 and 2 each have a separate cylinder for pressing home the taper pulleys (pressure cylinder) as well as a separate cylinder for transmission ratio adjustment (variable displacement cylinder). The dual-piston principle makes it possible to change the transmission ratio very quickly by applying a small amount of pressure; this ensures that the taper pulleys maintain sufficient contact pressure at a relatively low pressure level.The concept of the variator used in the multitronic® The mode of operation of the variator is based on what is known as the dual-piston principle. A further special feature of the variator is the torque sensor integrated in pulley set 1 (for more detailed information refer to “The torque sensor”, page 38).Starting torque ratio (underdrive)Torque sensor Chain Pulley set 1228_018Pulley set 2 32Adjustment A suitable supply of pressurised oil is required due to the heavy demands on the adjustment dynamics. To minimise the required quantity of oil, the variable displacement cylinders have a smaller surface area than the pressure cylinders. Therefore, the quantity of oil needed for adjustment is relatively small. This makes possible high adjustment dynamics and higher efficiency despite the low delivery rate of the oil pump. The diaphragm springs in pulley set 1 and the coil springs in pulley set 2 create a defined basic chain tension (contact pressure) when the hydraulic system is depressurised. In the depressurised state, the variator for the starting torque ratio is adjusted by the spring force of the coil springs in pulley set 2.End torque multiplication ratio (overdrive)Pressure cylinder Diaphragm spring Torque sensor Variable taper pulley Pulley set 1Variable displacement cylinder 228_019Pulley set 2 Variable displacement cylinder Pressure spring Pressure cylinder Variable taper pulley 33Gearbox modulesContact pressure High contact pressures are required between taper pulley and the chain to transmit the torques which the engine develops. The contact pressure is produced by adjusting the oil pressure in the pressure cylinder as appropriate. According to the Law of Hydraulics, a resultant force (contact pressure) can be varied as a function of pressure and effective area. The pressure cylinders have a larger surface area and can therefore apply the required contact pressure with less oil pressure. The relatively low oil pressure also has a positive effect on efficiency.Pressure 10 barEffective area 50 cm2 Resultant force 5000 NPressure 5 barEffective area 100 cm2 Resultant force 5000 N 228_080Towing When the vehicle is being towed, pulley set 2 drives pulley set 1 and there is a dynamic pressure buildup in the variable displacement cylinder and pressure cylinder of the pulley sets. The system is designed in such a way that the reduction ratio is adjusted to approx. 1:1 by the dynamic pressure build-up in the variator. Pulley set 1 and the planetary gear train are thus protected from excessively high engine speeds. The diaphragm springs in pulley set 1 assist with this process.For more detailed information regarding dynamic pressure build-up, refer to the chapter on the “Splash oil cover”. Also observe the towing information given in the chapter on “Service”.Diaphragm spring in pulley set 1228_081 34The transmission controlElectronic control The multitronic® control unit has a dynamic control program (DRP) for calculating the nominal gearbox input speed. It is an improved version of the dynamic shift program DSP already being used in multi-step automatic transmissions. The driver input and vehicle operating state are evaluated in order to provide the optimal gear ratio in every driving situation (see description of DSP on page 82). The dynamic control program calculates a nominal gearbox input speed depending on the boundary conditions. Sender G182 registers the actual gearbox input speed at pulley set 1. The gearbox control unit calculates a control current for pressure regulating valve N216 based on an actual-value/setpoint comparison. N216 produces a control pressure for the hydraulic reduction valve which is almost proportional to the control current. Transmission control is monitored by checking the plausibility of the signals from G182 (gearbox input speed sender) and G195 (gearbox output speed sender) as well as the engine speed.multitronic control unit G195G182228_076 N21635Gearbox moduleHydraulic transmission control Pressure regulating valve N216 is supplied with a constant pressure of approx. 5 bar by the pilot pressure value (VSTV). N216 produces a control pressure corresponding to the control current calculated by the gearbox control unit, which influences the position of the reduction valve (ÜV).A high control current leads to a high control pressure. The reduction valve (ÜV) transfers the adjusting pressure to the variable displacement cylinder of pulley set 1 or 2, depending on the control pressure.Pulley set 1Starting torque ratio (underdrive)Pulley set 2ÜVN216 228_083VSTV From the oil pumpPilot control pressure Vented into oil sump oil supply 36 Control pressure In the oil sumpThe valve is closed at a control pressure of between approx. 1.8 bar and 2.2 bar. At a control pressure of less than 1.8 bar, the adjusting pressure is transferred to variable displacement cylinder / pulley set 1 and the variable displacement cylinder / pulley set 2 is simultaneously vented into the oil sump. The variator shifts the reduction ratio towards “Overdrive”.If the control pressure is greater than 2.2 bar, the adjusting pressure is transferred to the variable displacement cylinder / pulley set 2 and the variable displacement cylinder / pulley set 1 is simultaneously vented into the oil sump. The variator shifts the reduction ratio towards “Starting torque ratio”.Pulley set 1End torque multiplication ratio (Overdrive)Pulley set 2ÜVN216 228_084VSTV From the oil pumpPilot control pressure Vented into oil sump Oil supply Control pressure In the oil sump 37Gearbox modulesThe torque sensor(contact pressure control) As mentioned before, a suitable oil pressure in the pressure cylinder gives a resultant contact pressure of the taper pulleys. If the contact pressure is too low, slippage of the chain will occur and the chain and pulley sets will be damaged. An excessively high contact pressure, on the other hand, will result in loss of efficiency. The object, therefore, is to set the contact pressure of the taper pulleys as accurately and safely as possible according to requirements. A hydromechanical torque sensor integrated in pulley set 1 statically and dynamically registers the actual torque transmitted to a high degree of accuracy and sets the correct oil pressure in the pressure cylinders.The engine torque is transferred to the variator via the torque sensor only. The contact pressure is controlled hydromechanically by the torque sensor.Ramp shell 2Pulley set 1 Ramp shell 1228_021Ramp shell 2 38Design and function The torque sensor essentially comprises two shells with seven ramps between which steel balls are mounted in bearings. Ramp shell 1 is form-fitted to the output gear of pulley set 1 (output gear wheel of auxiliary reduction gear step). Ramp shell 2 is connected to pulley set 1 via a grooved gearing in such a way as to allow axial movement and is supported by the torque sensor piston. The torque sensor piston serves to regulate the contact pressure and houses torque sensor spaces 1 and 2. The shells can be rotated radially towards one another, converting the torque to an axial force (due to the ball and ramp geometry). This axial force acts upon ramp shell 2 and moves the torque sensor piston which is in contact with the shell. The control edge of the torque sensor piston now closes or opens the outlets in torque sensor space 1.The axial force generated by the torque sensor serves as a control force which is proportional to the engine torque. The pressure which builds up in the pressure cylinder is proportional to the control force.Grooved gearingRamp shell 2Ramp shell 1Torque sensor space 2 Torque sensor space 1Torque sensor piston228_02239Gearbox modulesTorque sensor space 1 is directly connected to the pressure cylinder.Control edge Torque sensor space 1The system is designed such that the axial force generated as a product of engine torque and the pressure in the pressure cylinder form a force equilibrium. In constant conditions of vehicle operation, the outlet bores are only partially closed. The pressure drop produced by opening the outlet bores (torque sensor) modulates the pressure in the pressure cylinder.Pressure cylinderOutlet bore228_056Pressure cylinderIf input torque increases, the outlet bores are initially closed further by the control edge. The pressure in the pressure cylinder rises until a force equilibrium again exists. If input torque decreases, the outlet bores are opened further. The pressure in the pressure cylinder decreases until the force equilibrium is restored.Outlet bore228_05740At peak torque levels, the control edge closes off the outlet bores. If the torque sensor moves any further, it acts as an oil pump. The displaced oil volume now causes a rapid rise in the pressure inside the pressure cylinder and thus adapts the contact pressure without delay.Pressure cylinderExtremely high peak torques can occur when the vehicle drives over a pot-hole or if the coefficient of friction of the road surface fluctuates considerably (transitions from black ice to tarmac) for example.Outlet bore 228_058Adaptation of contact pressure depending on transmission ratio The contact pressure exerted by the taper pulleys depends not only on the input torque but also on chain track radius and, therefore, on the actual reduction ratio of the variator. As the diagram shows, the drive-off ratio requires the greatest contact pressure. The radius of the chain is smallest in pulley set 1. For power transmission, only a small number of cradle type pressure pieces are in mesh despite the high input torque. Therefore, a higher contact pressure is applied by the taper pulleys until a defined reduction ratio (1:1) is exceeded.Contact pressure in %Required contact pressure for 100% torque requirementUnderdrive 10075 Overdrive 50 Underdrive 25 0 Overdrive2,410,4 228_046Variator ratioRequired contact pressure for 25% torque requirementContact pressure 41Gearbox modulesFunction and mode of operationTorque sensor space 2The ratio-dependent contact pressure is adapted in torque sensor space 2. The pressure level the pressure cylinder is varied by increasing or decreasing the pressure in torque sensor space 2. The pressure in torque sensor space 2 is controlled by two transverse holes in the shaft of pulley set 1. These holes are opened or closed through axial displacement of the variable taper pulley. The transverse holes are open when the variator is in the drive-off torque ratio (torque sensor space 2 is depressurised). When the variator changes the ratio to “High speed”, the transverse holes are shut off initially. As of a defined reduction ratio, the left-hand transverse hole is opened. Now this hole is connected to the pressure cylinder via corresponding holes in the variable taper pulley. The oil pressure is now transferred from the pressure cylinder into torque sensor space 2. This pressure counteracts the axial force of the torque sensor and moves the torque sensor piston to the left. The control edge opens up the outlet bores further, reducing the oil pressure inside the pressure cylinder. The main advantage of the two-stage pressure adaption process is that a low contact pressure which increases efficiency can be utilised in the mid-ratio range (refer to Fig. 228_046, previous page).Cross holes228_059 Variable taper pulley Torque sensor space 2 BoreBoreTorque sensor piston228_06042The splash oil coverA further special feature of the variator is the “splash oil cover” on pulley set 2 which counteracts the dynamic pressure build-up in the pressure cylinder. At high engine speeds, the gearbox oil in the pressure cylinder is subjected to high rotation-induced centrifugal forces, which leads to a rise in pressure. This process is known as “dynamic pressure build-up”. A dynamic pressure build-up is undesirable because it unduly increases the contact pressure and has an adverse effect on transmission control. The oil confined in the splash oil cover is subjected to the same dynamic pressure build-up as in the pressure cylinder. The dynamic pressure build-up in the pressure cylinder is compensated by this. The splash oil chamber receives its oil supply directly from the hydraulic control unit through an oil injection hole. Oil is continuously injected into the splash oil chamber inlet through this hole. A reduction in volume inside the splash oil chamber (when varying the transmission ratio) causes the oil to be discharged via the supply inlet.Oil injection holeSplash oil chamber228_061Pressure cylinder Pulley set 2 Splash oil cover43Gearbox modulesThe chainThe chain is a key component part of the variator of the multitronic®. This is the first time that a chain is for used as a driving means in a CVT gearbox. The chain is a new development and has the following advantages over previously conventional driving means such as sliding link belts or V-belts: • Very small track radii make possible a large “spread” despite the small size of the variator. • High transferable torque • High efficiency The spread indicates the range of ratios which a gearbox provides. The spread is specified as a ratio. The starting torque ratio divided by the spread amounts to the end torque multiplication ratio. In general a large spread is an advantage because both a high starting torque ratio (for good dynamics) and a low end torque multiplication ratio (for low consumption) are available. This applies in particular to the CVT concept, since practically all intermediate steps are available and no ratio steps are out of place.Pulley set 1Chain228_026Pulley set 2 44Design and function On a conventional chain, the chain link plates are interconnected non-rigidly via the joint pins. For torque transmission, a gear tooth moves into engagement with the pins between the chain link plates. The CVT chain uses a different technology. The CVT chain comprises adjacent rows of chain link plates linked continuously by means of cradle type pressure pieces (two per link).Taper pulley of the variatorCradle type pressure piecesOn the CVT chain, the cradle type pressure pieces are “jammed” between the taper pulleys of the variator, i.e. the taper pulleys are pressed against one another. The torque is transmitted only by the frictional force between the frontal areas of the cradle type pressure pieces and the contact faces of the taper pulleys. This is how it works:ShackleTop viewEach of the cradle type pressure pieces is permanently connected to a row of link plates in such a way that it cannot be twisted. Two cradle type pressure pieces form a so-called cradle type joint. The cradle type pressure pieces now roll off one another almost frictionlessly as they “drive” the chain within the track radius of the taper pulleys. In this way, lost power and wear are minimised despite the high torque and the large angle of bend. The result is long service life and optimal efficiency.Side view228_027Cradle type pressure piecesCradle type joint45Gearbox modulesAcoustic measures Two different lengths of link plate are used in order to ensure that the chain runs as quietly as possible. When using a constant length of link plate, the cradle type pressure pieces strike the taper pulleys at uniform intervals and induce vibrations which cause a noise nuisance. Using different lengths of link plate counteracts resonance and minimises running noise.228_028Different lengths of link plate46The oil supplyIn the multitronic®, power transmission is dependent on the power supply and also on the hydraulics. In order to work, an electric current and adequate oil supply are required. The oil pump is the main power consumer in the gearbox and its capacity is therefore important for overall efficiency. The systems described above have therefore been designed to run on a minimum of oil, and an innovative oil supply system has been developed.The oil pump The oil pump is mounted directly on the hydraulic control unit in order to avoid unnecessary interfaces. The oil pump and the control unit form a compact unit, which reduces pressure losses and production costs. The multitronic® is equipped with an efficiency optimised crescent pump. This pump produces the necessary pressures although it requires only a relatively small quantity of oil. A suction jet pump (entrainment pump) additionally supplies the oil quantity required for the clutch cooling at low pressure. The crescent-vane pump, as a compact component, is integrated in the hydraulic control unit and driven directly by the input shaft via a spur gear and pump shaft.Hydraulic control unit (valve body)Pressure tube routed to suction jet pump (entrainment pump)oil pumpIntake filter 228_034 47Gearbox modulesAs a special feature, the oil pump has axial and radial clearance adjustment. A pump with good “internal sealing” is required in order to produce high pressures at low engine speeds. Conventional type oil pumps do not meet these requirements due to component tolerances. What is meant by “internal sealing” is the inner leakproofing of the pump. The axial clearance between the gears and the housing, as well as the radial clearance between the gears and the crescent vane vary depending on the tolerance zone position of the component parts. The pressure generated can thus more or less escape “internally”. The result is a loss of pressure and a drop in efficiency.Segmental springs Sealing roller Inner segment Spring rod Stop pinOil pump housingOuter segment228_035 Driver Axial plates48Axial clearance adjustment Two axial plates cover the pressure range of the pump and form a separate discharge casing inside the pump. They seal the pump pressure chamber laterally (axially). These plates, fitted with a special seal, are supported by the oil pump housing or the pump plate of the hydraulic control unit. The axial plates are designed so as to allow the pump pressure to act between the axial plates and the housing. The seal prevents pressure from escaping. As pump pressure increases, the axial plates are pressed more firmly against the crescent seal and the pump gears, which compensates for axial clearance.Thanks to axial and radial clearance adjustment, the pump is able to generate the required high pressures and simultaneously achieves high efficiency despite its compact design.Seal Axial plateOil pump housing228_051Axial plateAxial plate49Gearbox modulesRadial clearance adjustment The radial clearance adjustment feature compensates for the radial gap between the crescent seal and the gears (pinion and ring gear). For this purpose, the crescent seal is split in two segments, the inner segment and the outer segment. The inner segment seals the pressure chamber off from the pinion. It also holds the outer segment in a radial direction. The outer segment seals the pressure chamber off from the ring gear. The pump pressure flows between the two segments. The segments are pressed more firmly against the pinion and ring gear as the pump pressure increases, which compensates for radial clearance. When the pump is depressurised, the segmental springs provide the basic contact pressure of the segments as well as the sealing roller and improve the suction characteristics of the oil pump. They also ensure that the pump pressure can act between the segments and on the sealing roller.Pinion Inner segment Ring gear228_049Outer segmentCrescent seal50The suction jet pump (entrainment pump) A quantity of oil required to ensure sufficient cooling of the two clutches particularly when pulling away (there is high heat buildup due to slip) exceeds the capacity of the internal gear pump. A suction jet pump (entrainment pump) is integrated in the clutch cooling system in order to supply the quantity of oil required for cooling the clutch. The suction jet pump (entrainment pump) is of plastic construction and projects deep inside the oil sump. oil (pressurised oil) supplied by the oil pump is ducted through the suction jet pump (entrainment pump) in the form of a powerful jet. The oil flow through the pump vacuum result in a partial vacuum which “sucks” oil out of the oil sump and, together with the powerful jet, results in a large, almost depressurised quantity of oil. The quantity of cooling oil is almost doubled as required without additional pumping capacity. A non-return valve prevents the suction jet pump (entrainment pump) running dry and facilitates a quick response of the cooling oil feed.This is how it works: The suction jet pump (entrainment pump) operates according to the Venturi principle. When the clutch requires cooling, the coolingView of suction jet pump (entrainment pump)Suction jet pump (entrainment pump) shown in profile and folded outPressure tube routed to forward clutch228_036Venturi nozzlePressure tube routed from hydraulic control unit to suction jet pump (entrainment pump)Non-return valve228_037 Inlet pipeATF overflow pipe 51Gearbox modulesElectrohydraulic controlA new development is that the oil pump, hydraulic control unit (valve body) and gearbox control unit are combined as a compact, fully assembled unit.The hydraulic control unit comprises the manual selector valve, nine hydraulic valves and three electromagnetic pressure control valves. The hydraulic control unit and the gearbox control unit are interconnected electrically by direct plug-in contacts.Direct plug-in contact Hydraulic control unit Gearbox control unitSelector shaftManual selector valve228_063Oil pump52The hydraulic control unit executes the following functions: • Forward-reverse clutch control • Clutch pressure regulation • Clutch cooling • Pressurised oil supply to the contact pressure control • Transmission control • Supplying the splash oil cover The hydraulic control unit is connected directly to pulley set 1 or pulley set 2 via socalled “screw inserts”. The screw inserts are sealed by means of piston rings.Screw inserts for pulley set 1Piston ringOil injection hole for splash oil coverPiston ring 228_085 Screw inserts for pulley set 253Gearbox modulesThe description of the valves in the following refers to the valves which have still not been included in the module/function descriptions: To protect the component parts, pressure limiting valve DBV1 limits the pump pressure to max. 82 bar. The pressure control valves are supplied with a constant pilot control pressure of 5 bar via the VSTV pilot pressure value. The MDV minimum pressure valve prevents the oil pump drawing in engine air when the engine is started. When pump output is high, the MDV minimum pressure valve opens and allows oil to flow from the oil return pipe to the suction side of the oil pump; this improves efficiency.Hydraulic control unit (gearbox control unit removed)Sectional view of valve plateConnection to G193 Connection to G194 MDV minimum pressure valveKKV clutch cooling valveDBV1 pressure limiting valveKSV clutch control valveDBV1 pressure limiting valveConnector N215N215228_044 Connector N216228_047 N88 N216 VSTV pilot pressure valueConnector N8854The VSPV pressurising valve controls the system pressure so that sufficient oil pressure is always available for a particular function (application of contact pressure or adjustment). Solenoids N88, N215, and N216 are designed as so-called 'pressure control valves'. They convert an electric control current to a proportional, hydraulic control pressure.The N88 (solenoid valve 1) serves two functions: First, it controls the clutch cooling valve (KKV) and the safety valve (SIV). Solenoid N215 (pressure regulating valve 1 for autom. gearbox) actuates the clutch control valve (KSV). Solenoid N216 (pressure regulating valve 2 for autom. gearbox) actuates the reduction valve (ÜV).Sectional view of pump plateVSBV volumetric flow rate limiting valve HS manual selector valvePressure control valve (proportional valve)SIV safety valve228_101Diagram of pressure control valve228_048Control pressure in bar50 0 1000Current in mA228_100Pressurising valve VSPVÜV reduction valve55Gearbox modulesSelector shaft and parking lockA mechanical connection (cable pull) for transmission of selector lever positions P, R, N and D still exists between the gate selector lever and the gearbox. The following functions are executed via selector shaft: • Actuation of the manual selector valve in the hydraulic control unit, i.e. hydromechanical control of vehicle operating state (forward/reverse/neutral). • Operating the parking lock • Actuation of the multi-functional switch for electronic recognition of the selector lever position.In selector lever position P, the linkage with locking teeth is displaced axially in such a way that the parking lock ratchet is pressed against the parking lock gear and the parking lock is engaged. The parking lock gear is permanently connected to the drive pinion.Actuation of the outer selector mechanismSelector shaftManual selector valveMagnetic gate Parking lock gearDetent gate Drive pinionPulley set 2228_065Linkage with locking teethParking lock ratchet56Gearbox housing/ ducting and sealing systemsSheathed sealing ring system multitronic® is equipped with a new sheathed sealing ring system. The sheathed sealing rings seal the pressure cylinder and the variable-displacement cylinder of the primary pulley set, the secondary pulley set and the piston for the forward clutch. The O-ring has two tasks: To press down and seal the sheathed sealing ring. The oil pressure present assists the sheathed sealing ring with contact pressure application. Advantages of the sheathed sealing ring system: • Good antifriction properties • Low displacement forces • Wear • Stable at high pressuresSheathed sealing ringO-ring228_062Double-corrugated sealing ring 57Gearbox modulesDDV1 differential pressure valve with ATF strainer 1Pressure tube routed to reverse clutchInner sectionGroove for double-corrugated sealing ringOil drain screw Suction jet pump (entrainment pump) Fuel return hole 58 ATF inspection plugAxial sealing elementPressure tube routed to forward clutchTo save weight, the three-piece gearcase is manufactured from the AZ91 HP magnesium alloy. This alloy is highly corrosion resistant, easy to process and has an 8 kg weight advantage over a conventional aluminium alloy. As a special feature, the ATF pressurised oil is not distributed via housing ducts - as is usual on automatic gearboxes - but almost exclusively via pipes. So-called axial sealing elements are used to seal the pipe connections. The axial sealing element of the pressure pipes have two sealing lips which apply a higher contact pressure - as a result of the oil pressure - and therefore seal the pipes reliably. Diagonal pipe connections can also be sealed without difficulty using this technology (e.g. pressure tube connected to reverse clutch). The axial sealing element oil pump intake fitting has sealing beads which seal the fitting by virtue of their contact pressure. The double-corrugated sealing ring (see page 57) separates the ATF reservoir from the final drive oil reservoir. It prevents the ATF from entering the final drive and oil from the final drive entering the ATF reservoir. Leaks in the double-corrugated sealing ring become visible at the fuel return hole.228_041ATF levelIntake filter Pressure tube routed to suction jet pump (entrainment pump)Return pipe from ATF cooler with spray nozzles for chain and pulley sets59Gearbox modulesHydraulic chartPulley set 1 DBV2 Pulley set 2K DDV1 DDV2 F S1SB MP1 S2 1 VSPV N216 ÜVRKHSDBV1VSBVMP2 VK SIVP RN DS3KSV P VSTVKKVN215 MDV N882SSPSF228_03960Explanatory notes on the hydraulic chart (selector lever position P and engine “OFF”) DBV2 DBV2 DDV2 DDV2 F HS K KKV KSV MDV MP1 MP2 Pressure limiting valve 1 Pressure limiting valve 2 Differential pressure valve 1 Differential pressure valve 2 ATF filter Manual selector valve ATF cooler Clutch cooling valve Clutch control valve Minimum pressure valve Measuring point for contact pressure (registered via G194) Measuring point for clutch pressure (registered via G193) Solenoid valve 1 (clutch cooling/ safety shut-off) Automatic gearbox pressure control valve -1- (clutch) Automatic gearbox pressure control valve -2- (ratio) Oil pump Selector lever position Reverse clutch ATF strainer 1 ATF strainer 2 ATF strainer 3 4 Spray holes for pulley set lubrication/cooling ATF intake filter Safety valve Suction jet pump (entrainment pump) Reduction valve Forward clutch Volumetric flow rate limiting valve Pressurising valve Pilot pressure value In the oil sump228_071 Differential pressure valve DDV1 and ATF strainer 1N88 N215 N216Return pipe from ATF coolerP PRND RK S1 S2 S3 SB SF SIV SSP ÜV VK VSBV VSPV VSTVPressure limiting valve DBV2 in the gearbox housing1 To splash oil cover 2 To the clutchesHydraulic control unit Peripheral components in the vehicle61Gearbox modulesATF coolingThe ATF coming pulley set 1 initially passes through the ATF cooler. The ATF flows through the ATF filter before it is returned to the hydraulic control unit. As is the case with the CVT, the ATF cooler is integrated in the “engine cooler”. Heat is exchanged with the coolant in the engine cooling circuit (oil- coolant heat exchanger). The DDV1 differential pressure valve protects the ATF cooler against excessively high pressures (ATF cold). When the ATF is cold, a large pressure difference develops between the supply line and the return line. When a specific pressure differential is reached, the DDV1 opens and the supply line is shortcircuited with the return line. This also causes the temperature of the ATF to rise rapidly. The DDV2 differential pressure valve opens when the flow resistance of the ATF filter is too high (e.g. filter blockage). The prevents the DDV1from opening and the ATF cooling system from being disabled by the backpressure.If the ATF cooler is leaky, coolant can enter the ATF. Even small quantities of coolant in the ATF can have an adverse effect on clutch control.Peripheral components in the vehicle ATF cooler ATF filter DDV2 To hydraulic control unit ATF filter Return linemultitronic® S1 DDV1 From pulley set 228_090 Supply line Supply line Return line 62DBV2Gearbox controlmultitronic control unit J217A special feature of multitronic® is the integration of the electronic control unit in the gearbox. The control unit is attached directly to the hydraulic control with bolts. The connection to the three pressure regulating valves is made directly from the control unit by means of robust plug-in contacts (gooseneck contacts); there are no wiring connections. A 25-pin compact connector forms the interface to the vehicle. A further new feature is the integration of sensor technology in the control unit. • F125 - Multi-functional switch • G182 - Gearbox input speed sender • G195 - Gearbox output speed sender • G196 - Gearbox output speed sender -2• G93 - Gearbox oil (ATF) temperature sender • G193Automatic gearbox hydraulic pressure sender -1- (clutch pressure) • G194 - Automatic gearbox hydraulic pressure sender -2- (contact pressure)Multitronic control unit J217Gearbox output speed sender G195 and Gearbox output speed sender -2- G196Plug-in contact for N215Automatic gearbox hydraulic pressure sender -1- G193 (clutch pressure)Multi-functional switch F125 Plug-in contact for N216 (concealed by G182)228_055 Automatic gearbox hydraulic pressure sender -2- G194 (contact pressure) Gearbox input speed sender G182Plug-in contact for N8863Gearbox controlA strong aluminium plate acts as the base for the electronics and serves to dissipate heat. The housing is made of plastic and securely riveted to the base. It accommodates all the sensors, so neither wiring nor plug-in contacts are necessary. Since the majority of all electrical failures are attributable to faulty wiring and plug-in contacts, this construction offers a very high degree of reliability. The engine speed sender and the multifunctional switch are designed as Hall sensors. Due to the fact there are only a few interfaces to the gearbox control unit, the multitronic® does without a separate cable set. The wiring is integrated in the engine cable set. Hall sensors are free of mechanical wear. Their signal is immune to electromagnetic interference, which improves their reliability still further.25-pin connectorGearbox oil (ATF) temperature sender G93Gearbox input speed sender G182 (1 Hall sensor)228_077Multi-functional switch F125 (4 Hall sensors)64Gearbox output speed sender G195 and Gearbox output speed sender G196 (2 Hall sensors)Fault indication Faults in the multitronic® are to a high degree registered by the extensive self-diagnosis function. Faults are indicated to the driver via the selector lever position indicator in the dash panel insert depending on their effect on the multitronic® or on driving safety. In this case, the selector lever position indicator also serves as a fault indicator. As regards faults registered by the multitronic®, a distinction is drawn between 3 states: 1. The fault is stored and a subsitute program enables continued operation of the vehicle (with some restrictions). This state is not indicated to the driver, since it is not critical with regard to driving safety or multitronic®. The driver will notice the fault - if at all - by the way the vehicle handles and will automatically seek the assistance of an Audi service partner.When the display is flashing, vehicle operation will - in certain circumstances - only be maintained until the next time the vehicle stops. The vehicle can subsequently no longer be driven! In certain cases, vehicle operation can be resumed by restarting the vehicle.228_1022. As described item 1, the selector lever position indicator also indicates the presence of a fault by inverting the display. The situation is still not critical for dr