lectronic controls were first intro- GETTING UP TO SPEED ON duced on a widespread GETTING UP TO SPEED ON basis in the late 1970s, as EPA regulations for emissions and fuel economy grew more stringent. The first Eelectronically controlled transmissions included simple systems that controlled only the operation of the torque con- verter clutch (TCC). The rest of the transmission’s operation remained un- der the valve body’s hydraulic control. TRANSMISSIONTRANSMISSION The ability to “lock” the torque con- verter in the higher eliminated nearly all of the power losses inherent in automatic transmissions equipped with hydraulic torque converters. This was considered a big step forward at the DIAGNOSIS time. But these early systems were pret- DIAGNOSIS ty crude by today’s standards and even then, many customers complained about their operating characteristics. BBYY KKARLARL SSEYFERTEYFERT Some clutches pro- duced a noticeable driveline shock when they engaged, while others were RegulationsRegulations forfor emissionsemissions andand fuelfuel responsible for a juddering sensation if they remained engaged for too long as economyeconomy havehave becomebecome increasinglyincreasingly engine and road speed dropped. stringent, making electronically Things have certainly progressed in stringent, making electronically the intervening years. Electronic trans- controlled,controlled, multispeedmultispeed transmissionstransmissions mission controls today are every bit as so- phisticated as the electronic systems that aa necessity.necessity. AndAnd itit allall startedstarted withwith control the engine management and oth- er vehicle systems. Unlike the stand- thethe torquetorque converterconverter clutch.clutch. alone control systems of the past, today’s are now fully integrated. The engine Photoillustration: Harold A. Perry; images: BMW & Thinkstock BMW & Thinkstock images: Harold A. Perry; Photoillustration: management system knows what the transmission control unit is doing and the mum efficiency. More ratio choices ley system to deliver the advantage of a operation of both systems is optimized to equals better fuel economy, higher per- seemingly limitless number of potential achieve the best possible fuel economy formance and lower emissions. gear ratios. Consequently, the engine al- and engine performance, while produc- Passenger vehicle designers have ap- ways operates at the most efficient rpm, ing the lowest possible emissions. plied these lessons to current automatic regardless of load or vehicle speed. The best way to achieve the seeming- transmission design. Today we see CVT designs offer a gear ratio spread in ly conflicting goals of high fuel economy, torque converter the range of 7:1 and are said to reduce high performance and low emissions is designs with six, seven and eight speeds internal friction while minimizing en- to ensure that the engine is always oper- in widespread use. Ford and GM recent- gine noise at higher vehicle speeds. ating in its most efficient rpm range. ly announced they’ll collaborate on the Some manufacturers have turned to This is why vehicles equipped with mul- design of nine- and 10-speed automatic dual-clutch transmission (DCT) de- tispeed manual transmissions used to be transmissions. ZF is working on a nine- signs. These transmissions take the ad- able to deliver better fuel economy than speed torque converter automatic, which vantages of manual transmissions and similar vehicles equipped with three- or will feature a gear ratio spread of 9.84:1, combine them with electronic controls, four-speed automatic transmissions. and Hyundai will offer a 10-speed torque which allow fully automatic operation. Semitractors, with more than a dozen converter automatic in the next-genera- Semiautomatic operation is also an op- different gear ratios to choose from, can tion Genesis. Will they stop at 10? tion if the driver wishes to select his efficiently move extremely heavy loads Other manufacturers have turned to own gears via a control lever or steering over very long distances because their continuously variable transmission wheel paddles. DCTs require no torque engines are always operating at maxi- (CVT) designs. CVTs use a belt and pul- converter, which results in a significant

30 June 2013 weight savings. These transmissions ef- posed to work. The remainder of this ar- gaged again, the engine automatically fectively shift into Neutral when the ve- ticle will be devoted to explaining how starts up. Even at standstill times of just hicle is standing still, so the engine isn’t the major transmission designs de- 10 seconds, switching off the engine fighting against an inefficient torque scribed above actually work, and to cov- cuts average consumption and CO2 converter. This saves additional fuel. ering diagnostic strategies as well. emissions noticeably. Volkswagen recently announced it The start-stop function is enabled by will produce a 10-speed dual-clutch Multispeed Automatic Transmissions the development of the hydraulic im- transmission with an extremely wide The ZF eight-speed-automatic trans- pulse oil storage (HIS). It supplies the gear ratio spread of 10:1. This design is mission (8HP) is claimed to achieve an hydraulic oil that the transmission’s shift said to be suitable for a torque range of additional 6% fuel saving over its six- elements need for starting. When the more than 369 ft.-lbs. Six- and seven- speed designs, which also reduces CO2 engine is switched off, it allows for a speed DCTs are already in production. emissions. The 8HP is a completely quick start—as is required with the What does all of this transmission in- new transmission concept with four start-stop function. Only 350 millisec- novation mean to service technicians? gear sets and five shift elements, a high- onds after starting the engine, the vehi- Put simply, the more complicated some- er overall gear ratio, a variable oil pump, cle is ready for setting off. With the thing becomes, the more complicated a new torque converter and optimized start-stop function of the hydraulic im- and difficult it gets to diagnose and re- hydraulic and transmission control. An pulse oil storage, it’s possible to reduce pair it when something goes wrong. It’s optional stop-start function is also of- fuel consumption by another 5%. always easier to fix something if you first fered. Idling at a standstill, the engine There are only five shift elements— have an understanding of how it’s sup- automatically switches off; when en- multidisc clutches and brakes in the

June 2013 31 GETTING UP TO SPEED ON TRANSMISSION DIAGNOSIS heart of the transmission—and only two the arc radius of the belt on the drive On the other hand, when the gear ra- are open in each gear. The fewer open pulley gets wider. At this point, manual tio runs at a higher gear, the engine ro- shift elements there are, the fewer or automatic transmission vehicles would tation decreases, meaning there’s better transmission parts there are rotating rel- be in a higher gear, such as 5th or 6th. fuel combustion and less noise. In a ative to one another. This results in a The steel belt serves to bridge the similar fashion on a manual transmis- significant reduction of drag losses in two pulleys as they change the diame- sion vehicle, the engine rotates at a the transmission. The development en- ter. If the gear ratio at low gear is low- slower speed when in 5th gear at high- gineers were also able to increase the ered even more, acceleration improves. way speed than in 4th gear. gear-meshing efficiency with the new This is similar to starting in 1st gear with In addition to the acceleration, the transmission concept. Energy is lost in more power than starting in 2nd. Vehi- fuel combustion and engine noise levels some gears when power is transmitted cle response improves at lower speed can be improved by making the low and through gear wheels. In the 8HP, these and on takeoffs. high gear ratio range (called transmission losses are below 2% through- gear ratio range) larger. out—a further factor helping Through the use of a narrow- to reduce consumption. er pulley axle and newly de- veloped belt, the New Gener- Continuously Variable ation XTRONIC CVT has ex- Transmissions panded the transmission gear The continuously variable ratio range from 6.0:1 to transmission is a “stepless” 7.0:1. It also includes adaptive gear transmission whose shift control, which interprets merits include lower fuel the driver’s intentions from consumption and seamless the acceleration and steering acceleration. As opposed to inputs to provide optimum manual or automatic trans- shift control. Coordinated missions, the CVT can auto- control between the engine matically select the most and transmission delivers op- suitable transmission gear ra- timal fuel consumption and tio without any steps. Vehi- The ZF eight-speed-automatic transmission (8HP) has just driving performance. five shift elements—multidisc clutches and brakes—and cles with CVT can run on the only two are open in each gear. The fewer open shift ele- most efficient engine rpm ments there are, the fewer transmission parts to rotate Dual-Clutch Transmissions (i.e., with the best fuel com- relative to one another. This results in a significant reduc- A dual-clutch transmission bustion) for regular velocity. tion of drag losses in the transmission. can be considered two tradi- The technology delivers tional manual transmissions, seamless performance with- each with its own clutch op- out shift changes when accel- erating in parallel and alter- erating and decelerating. nating shifts. The Ford Pow- On recent Nissan CVT erShift is a six-speed trans- designs, the low-to-high gear mission with one clutch act- ratio range is expanded, de- ing on gears 1, 3 and 5 and livering a significant reduc- the other used for 2, 4 and 6. tion in friction and up to As 1st gear is engaged, the 2- 10% improvement from the 4-6 clutch is disengaged and previous generation. the 2nd gear cogs are en- The CVT adjusts the width gaged. At the appropriate of two pulleys and changes time, the 1-3-5 clutch is dis- the arc radius of the steel belt engaged and the other is en- running between them in or- BMW courtesy Photo gaged. While in 2nd gear, the ZF courtesy Photo The control system of BMW’s eight-speed automatic trans- der to control the transmis- mission is claimed to predict and adapt gearshift com- other side moves from 1st to sion gear ratio. When driving mands dynamically according to the driving situation. The 3rd. The process is repeated at slow speeds, the arc radius control unit gathers inputs from the driver, scans the with quick, smooth shifts and of the belt for the engine topology of the road ahead and relates all of it to traffic data none of the efficiency losses shaft pulley gets narrower. At to anticipate the ideal gear for the circumstances. Using an normally associated with this point, manual or auto- interface that includes data from the traction and stability torque converter-equipped matic transmission vehicles control systems, navigation, radar sensors and cameras, transmissions. are in a lower gear (e.g., 1st or the system takes into account things like surface friction The PowerShift transmis- 2nd gear). At higher speeds, coefficient, radius of a corner, cars ahead and more. sion is a joint development

34 June 2013 GETTING UP TO SPEED ON TRANSMISSION DIAGNOSIS

produced by a torque converter in a conventional automatic transmission. Volkswagen has also introduced a seven-speed DSG. In comparison to the six-speed DSG, there’s no “wet” clutch in the new transmission. The clutch is not immersed in an oil bath— rather, a “dry” clutch is used. Under “normal,” progressive and lin- ear acceleration and deceleration, the DSG shifts in a “sequential” manner, (1st > 2nd > 3rd > 4th > 5th > 6th). The sequence is reversed for deceleration. However, the DSG can also skip the normal sequential method, by “missing

out” adjacent gears, and shift two or Ford courtesy Photo more gears. This is most apparent if the In addition to quicker reaction times, Photo courtesy Nissan courtesy Photo vehicle is being driven at sedate speeds dual-clutch transmissions are typically The CVT adjusts the width of two pul- in one of the higher gears with a light lighter than traditional automatic trans- leys and changes the arc radius of the throttle opening, and the accelerator missions because they do not need a steel belt running between them in or- torque converter. They’re also more effi- der to control the transmission gear pedal is then pressed down, engaging cient, providing better fuel economy ratio. When driving at slow speeds, the the “kick-down” function. than conventional automatic or manual arc radius of the belt for the engine During kick-down, the DSG will skip transmissions. With companies like Fer- shaft pulley gets narrower; at higher gears, shifting directly to the most ap- rari switching to transmissions of this speeds, the arc radius of the belt on propriate gear, depending on speed and design, the end of conventional manual the drive pulley gets wider. throttle opening. This kick-down may transmissions could be very near. be engaged by any increased accelera- among Ford, Getrag and LuK and was tor pedal opening, and is completely in- to be found when the pedal is pressed first introduced in Europe. Both Volvo dependent of the additional resistance fully to the floor, which will activate a and Ford have used wet clutches and similar kick-down function when in hydraulic actuation on their previous Manual operation mode. DCT designs. However, the new Power- Porsche AG offers a series production Shift gearbox used in the Ford Fiesta of two variants of the longitudinally in- and Focus uses dry clutches and electric stalled, ZF Friedrichshafen AG designed motor/solenoid actuation. The Power- and built 7DT. These are wet-clutch ver- Shift transmission is claimed to improve sions of the previously race-only Porsche fuel efficiency by as much as 10% over a Doppelkupplungsgetriebe (PDK) trans- conventional automatic transmission. mission. Both variants use seven forward Volkswagen refers to its dual-clutch speeds, and it’s believed the PDK trans- transmission by the acronym DSG, mission will replace the outgoing conven- which stands for a direct-shift gearbox tional Tiptronic automatic transmissions. (Direkt-Schalt-Getriebe). The DSG is However, the eight-speed ZF 8HP may an electronically controlled dual-clutch continue to be used in some applications. multiple-shaft manual gearbox, in a Like all DCTs, the Porsche PDK transaxle design—without a convention- transmission is fundamentally two sepa- al clutch pedal, and with full automatic rate manual transmissions in one. The or semimanual control. The first actual 1st, 3rd, 5th, 7th and Reverse gears are dual-clutch transmissions derived from Ford courtesy Photo available on one shaft, and 2nd, 4th and Porsche’s in-house development for its Dual-clutch transmissions combine 6th gears are available on the other shaft. some of the best attributes of manual 962 racing cars in the 1980s. Porsche claims improvements in CO2 Like the Ford design, a DSG consists and automatic transmissions. The two emissions of around 15% when compar- clutches allow two gears to be selected of two separate manual gearboxes (and at once. When the transmission shifts, it ing DCT installations against its former clutches), contained within one housing needs to open only one clutch and close automatic transmission, half of which and working as one unit. By using two another, saving time. Quick, smooth can be directly attributed to the DCT. independent clutches, a DSG can shifts mean none of the efficiency losses When compared directly with a manual achieve faster shift times, and elimi- normally associated with torque con- transmission, a 16% improvement can nates the weight and efficiency losses verter-equipped transmissions. be directly attributed to the DCT.

36 June 2013 GETTING UP TO SPEED ON TRANSMISSION DIAGNOSIS

Diagnosis a major failure—either electrical or Electronic transmission control (ETC) mechanical. Limp-in mode usually systems are controlled by microproces- limits the transmission function to one sors, also referred to as control mod- gear and boosts system pressures to ules. The ETC module constantly mon- maximum. The strategies vary by itors inputs from various sensors. Mod- make, model and year. For example, ule programming then processes the Chrysler systems power the shift sole- input information and makes output noids through a module-controlled re- decisions for optimal transmission con- lay. Limp-in mode is accomplished by trol. The operation of the ETC system disabling the relay and removing pow- is well integrated with vehicle systems er from the system. On systems from by means of the vehicle’s communica- other manufacturers, limp-in mode tions network. ETC offers better shift may be accomplished by removing control, better transmission fluid pres- power or ground from certain actua- sure control, programmable software, tor components. The actual limp-in bidirectional scanner controls, adaptive function depends on the type of con-

learning and self-testing. Volkswagen courtesy Photo trol circuit used by the ETC system. While system components will vary Under normal, progressive accelera- An illuminated MIL is usually the by manufacturer and individual vehicle, tion and deceleration, the DSG shifts first thing a customer notices when an all ETC systems contain the same basic in a “sequential” manner, using all six ETC problem occurs and limp-in sensor and solenoid types. However, forward gears. The sequence is re- mode is triggered. The customer’s there are variations in the electrical op- versed for deceleration. However, un- complaint is often a lack of power eration of these systems. Most domestic der lighter loads, the DSG can bypass from a stop. At this point, the first vehicles use the ground side of their cir- the normal sequential method, by thing the technician must determine skipping over adjacent gears and cuits for circuit control, while most shifting two or more gears at a time. is whether the problem is electrical or Asian vehicles use the power side of mechanical. Most ETC systems are their circuits for control. •a throttle position sensor, very good at detecting faults in trans- Main ETC module inputs include: •a brake position sensor. mission operation, and a failure that •a gearshift lever position sensor, Depending on the vehicle, additional causes a limp-in condition will nor- •engine and transmission tempera- inputs may include: mally result in a diagnostic trouble ture sensors, •AWD/4WD, code (DTC) that will provide a diag- •a MAF or MAP sensor, •ABS/Traction Control, nostic direction. •a transmission input shaft speed sensor, •manual switch controls, ETC systems also have the ability •an output shaft rpm/vehicle speed •engine management. to adapt for component wear. The sys- sensor, Limp-in strategies are triggered by tem will raise or lower line pressure to meet various adaptive calculations. For example, an ETC system may compare actual shift times to desired shift times. The difference between the two is reported as shift time error. This is accomplished by comparing input and output shift sensor data. If the shift time is too long or too short, the controller can compensate by ad- justing line pressure. As with all diagnostic work, it pays to invest the time in observing and recording known-good readings on systems that are operating properly. This will make it much easier to spot out-of-spec data when it presents it- Photo courtesy Volkswagen courtesy Photo In 2008, Volkswagen added a seventh gear to its DSG transmissions, and in 2009 self on a vehicle that’s experiencing a a new model was introduced with greater power and torque-handling capacity. problem. This exploded view reveals the DSG’s internal similarity to a conventional manu- al transmission. The unit at the right handles shift execution. Since VW’s DSG This article can be found online at transmission design was introduced, more than 3.4 million of the units have www.motormagazine.com. been produced at the company’s Kassel, Germany, plant.

38 June 2013