Getting up to Speed on Getting up to Speed
Total Page：16
File Type：pdf, Size：1020Kb
lectronic transmission 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 gears 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 torque converter 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 gear 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 automatic transmission 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.