chap100 pps Automotive technology at University of Cambridge

start Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 100, the reader should be able to: • • • Prepare for the ASE Automatic Transmission/Transaxle (A2) certification test content area “A” (General Transmission/Transaxle Diagnosis) Explain how a torque converter can transmit and multiply engine torque Describe how a planetary gear set can be used for gear reduction and reverse Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 OBJECTIVES: After studying Chapter 100, the reader should be able to: • Explain how automatic transmission fluid is circulated through the system and how it is cooled Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: compound planetary gear set • coupling phase flexplate impeller • input member lapelleties gear set • lube oil output member pump ravigneaux gear set • reaction member Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 KEY TERMS: simpson gear set • stall speed • stator torque converter clutch (TCC) • torque multiplication phase • turbine Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Automatic transmissions were first used on a large scale in the late 1940s, and now about 85% of the vehicles in North America are so equipped Unlike manual transmissions, most automatic transmissions not actually “shift gears” but apply clutches (or bands) to hold various sections of two or more planetary gear sets The torque converter is attached between the engine and the transmission/ transaxle and transmits and multiplies engine torque Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 TORQUE CONVERTERS The impeller, also known as the pump, is the driving member and rotates with the engine. The impeller  vanes pick up fluid in the converter housing and direct it toward the turbine Fluid flow drives the turbine, and when the flow between the impeller and turbine is adequate, the  turbine rotates and turns the transmission input shaft. A torque converter contains the stator, or reactor,  a reaction member mounted on a one­way clutch The vanes used in each of the three elements of a torque converter are curved to increase the diversion  angle of the fluid. This also increases the force exerted by the fluid and improves the hydraulic  advantage. See Figure 100–1 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 100–1 A cross-sectional view of a Chrysler Power Flight 2-speed automatic transmission used in the 1950s Most of the heat generated in an automatic transmission is created in the torque converter This air-cooled unit has a vent to allow hot air to escape Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 The outlet side of the impeller vanes accelerates the fluid as it leaves the impeller to  increase torque transfer to the turbine See Figure 100–2 The inlet side of the turbine vanes absorb shock and limit power loss that occurs when  flow between the impeller and turbine suddenly changes. The curve of the stator vanes is  opposite to the curve of the impeller and turbine vanes See Figure 100–3 Since the stator is located between the impeller and turbine, it adds to the original  impeller flow and multiplies the force delivered to the turbine. See Figure 100–4 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 100–2 Fluid flow within a torque converter The stator redirects the fluid that is thrown out by the turbine, thereby improving efficiency Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 This combination is capable  of providing three forward  gears, as well as neutral and  reverse Operation, construction, and  methods of obtaining  various gear ratios with a  simple planetary gear set  also apply to the Simpson  gear set The main difference is the  number of gear ratios Figure 100–19 A Simpson planetary gear set is composed of two ring gears and two planet carrier assemblies that share a common sun gear Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 RAVIGNEAUX GEAR SET Another popular compound planetary design is the Ravigneaux gear set. The Ravigneaux system has two sun  gears; two sets, one longer than the other, of planet pinions supported in one carrier; and a single ring gear.  This design provides four forward gears, two in reduction, one direct, and one overdrive, as well as neutral and  reverse. Basic planetary gear set operation, construction, and control methods also apply to the Ravigneaux gear  set Both of these compound planetary gear set designs have been used over the years by import and domestic  manufacturers See Figure 100–20.  Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 100–20 A Ravigneaux gear set is composed of two sun gears, one carrier that supports two sets of pinion gears, and a single ring gear Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 LAPELLETIES GEAR SET The Lapelleties (pronounced La­plet­e­ay) gear set was invented by Pierre Lapelleties, a  retired engineer who figured out a unique way to create a simple and efficient six­speed  automatic transmission gear set It was first produced by ZF in 2002. The Lapelleties gear set is constructed by connecting a  planetary gear set in front of a Ravigneaux gear set Besides ZF, General Motors uses the Lapelleties gear set in the 6L45, 6L50, and 6L90 rear­ wheel­drive transmission and Ford uses it in their 6R60, 6R75, and 6R80 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 CONTINUOUSLY VARIABLE TRANSMISSION A continuously variable transmission (CVT) is usually found on front­wheel­ drive vehicles, which use a transaxle Instead of using three or more gears, a continuously variable transmission uses two  variable width pulleys sometimes called variators to change the gear ratio from  about 2.5:1 to an overdrive ratio of 0.5:1.  See Figure 100–21 Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 100–21 The belt-and-pulley CVT uses variable-width pulleys and a special steel belt to provide an infinite number of speed ratios Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Purpose and Function The purpose and function of a continuously variable  transmission is to allow the engine to operate in a speed range where it is most efficient Instead of causing the engine speed to vary as the transmission shifts gears, the  engine speed is more constant as the pulleys change to increase the speed of the  vehicle The result of using a CVT is improved fuel economy and reduced exhaust emissions Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Parts and Operation  Most CVT units use a conventional torque  converter with a torque converter clutch except the Honda Civic  CVT. In the Honda Civic CVT, a start clutch is used to apply  engine torque to the drive pulley The start clutch slips and provides a small amount of creep until  the driver releases the brake pedal. At this point, the start clutch is  fully applied and transmits torque to the drive pulley See Figure 100–22 NOTE:  Some vehicles equipped with a continuously variable  transmission (CVT) have shifter paddles on the steering wheel or a manual  shift mode on the gear selector. When using these paddles to upshift or  downshift, the transmission control module selects preprogrammed ratios,  which give the driver a sense that it is actively shifting gears Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Figure 100–22 Location of the Honda CVT start clutch Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 CAUTION: With any CVT unit, use of the specified fluid is critical to  its proper operation. Even a little dirt can cause wear to pulleys so be sure  to clean around the dip stick before removing it to check the level of fluid The two pulleys are moved at the  same time. One pulley is made  smaller in while at the same time the other pulley is enlarged This change in pulley width allows  the drive chain to move, thereby  changing the rate between the input  and output pulleys The chain is pushed rather than  pulled through the pulleys and is  made of hundreds of elements Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman Figure 100–23 Honda CVT drive belt construction ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 What Is It Like to Drive a Vehicle Equipped with CVT? For most, driving a vehicle equipped with a continuously variable transmission (CVT) is the same as driving the same vehicle equipped with a conventional automatic transmission/transaxle The vehicle creeps slightly when the brake is released and acceleration when the throttle is opened Because no shifts occur, the first thing the driver and passenger notice is that it is very smooth If the vehicle is equipped with a tachometer, the driver may notice that the engine speed increases when first accelerating and remains higher until speed increases During periods of rapid acceleration, the engine speed may be close to its maximum and thereby create noise and vibration often not experienced in a similar vehicle However, the fuel economy savings of a CVT compared to a conventional automatic transmission makes the slight difference a reasonable trade-off Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 Servicing Continuously Variable Transmissions  Routine service of a continuously  variable transmission/transaxle usually involves changing the fluid at regular intervals Always use the exact fluid specified by the vehicle manufacturer. The price of CVT fluid  is several times higher than conventional automatic transmission fluid but the special  additives needed by a CVT make it critical that the specified fluid be used Except for the replacement of the start clutch on a Honda Civic CVT, most continuously  variable transmissions are replaced as an assembly and not overhauled or repaired Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY The torque converter attaches to the engine and transmits  engine torque to the automatic transmission/transaxle  assembly The torque converter consists of three major components: the  impeller (driving member), turbine (driven member), and the  stator, which helps the torque converter double the available  engine torque at stall speed Since the early 1980s, a torque converter clutch has usually  been used on most automatic transmissions/transaxles to  increase fuel economy by locking the input and output  members of the torque converter together Continued Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 SUMMARY (cont.) A typical planetary gear set includes a sun gear in the center  surrounded by planet pinions attached to a planet carrier  assembly and a ring gear on the outside where internal teeth  mesh with the teeth of the planet pinions Most automatic transmissions/transaxles use a compound  planetary gear set to achieve the various forward gears as well  as reverse Automatic transmissions/transaxles use compound planetary  gear sets called Simpson or Ravigneaux Certain members of a gear set must be held to achieve a  particular gear ratio and direction Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 end Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition By James D Halderman ©©2008 2009Pearson PearsonEducation, Education,Inc Inc Pearson PearsonPrentice PrenticeHall Hall- -Upper UpperSaddle SaddleRiver, River,NJ NJ07458 07458 ... Vehicle manufacturers select torque converters to match the power train requirements and  operating demands? ?of? ?each application A vehicle with a large engine that produces a lot? ?of? ?torque? ?at? ?low RPM will often use a torque  converter that couples? ?at? ?low speeds for greater fuel economy... at? ?approximately the same speed. This is called the coupling phase The stator unlocks and freewheels once the angle? ?of? ?fluid flow changes enough to strike the  opposite side? ?of? ?the stator vanes and rotate the stator clockwise Continued Automotive Technology: ... Each member? ?of? ?a planetary gear set can play any one? ?of? ?these three roles to transmit torque. The various  combinations? ?of? ?drive, held, and driven members result in the number? ?of? ?gear ratios available. Certain  combinations? ?of? ?drive, hold, and driven can change the direction? ?of? ?rotation as well