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  1. OBJECTIVES After studying Chapter 4, the reader should be able to: • Describe the power flow through a planetary gearset. • Identify the components of a multiple-disc clutch and describe how it operates. • Identify a one-way clutch and describe how it operates. • Identify a band and servo and describe how they operate.

  2. INTRODUCTION • There are several paths for power to flow through an automatic transmission, and each path provides a different gear ratio. • These power paths are controlled by the driving and reaction devices, also called driving and reaction members. • The driving devices connect the turbine shaft from the torque converter to a member of the planetary gear train. • The reaction devices connect a member of the gear train to the transmission case.

  3. FIGURE 4-1 The 4L60 (THM 700) has one band, five multiple-disc clutches, and two one-way clutches to control the power flow. The reverse input, overrun, forward, and 3–4 clutches along with the forward sprag clutch are driving members. The 2–4 band, low roller clutch, and low-reverse clutch are reaction members. INTRODUCTION

  4. DRIVING DEVICES • The driving devices provide the input to the gearset. • The turbine shaft is normally built as part of or splined to one or more of the driving devices. • Driving devices are usually multiple-plate disc clutches. • In most cases, they will be at the front of the transmission, just behind the pump.

  5. DRIVING DEVICES • An example of this involves the two clutches in front of a Simpson gear train transmission. • Chrysler Corporation calls the first clutch the front clutch; • Ford Motor Company calls it a high-reverse clutch; • General Motors Corporation and Toyota call it a direct clutch; • Toyota uses the term direct clutch but more commonly calls it C2. • Synchronizing Shifts • Synchronous • Nonsynchronous

  6. MULTIPLE-DISC DRIVING CLUTCHES • The parts of a clutch assembly are: the drum, hub, lined plates, unlined plates, pressure plate, apply piston, and piston return springs. • The drum, also called a housing, has splines inside its outer edge for the externally lugged plates, usually the unlined plates. • The inner diameter of the drum is machined for the apply piston and its inner and outer seals.

  7. FIGURE 4-2 A sectioned view (a) and exploded view (b) of a multiple-disc clutch. Note the piston to apply the clutch and the spring(s) to release it. (b is courtesy of Chrysler Corporation) MULTIPLE-DISC DRIVING CLUTCHES

  8. FIGURE 4-3 A 4L60 input clutch assembly has three separate clutch packs:202 is the overrun clutch; 607 is the forward clutch; and 228 is the 3–4 clutch. The input sprag assembly is at the bottom left. (Courtesy of Slauson Transmission Parts, MULTIPLE-DISC DRIVING CLUTCHES

  9. FIGURE 4-4 The apply piston is released (left) by the coil springs. Fluid pressure moves the piston to apply the clutch (right). MULTIPLE-DISC DRIVING CLUTCHES

  10. FIGURE 4-5 Clutch piston return springs can be a single large spring (a), a group of small springs (b), or a single Belleville spring (c). (Courtesy of Chrysler Corporation) MULTIPLE-DISC DRIVING CLUTCHES

  11. MULTIPLE-DISC DRIVING CLUTCHES • Clutch Plates • Double- and Single-Sided Friction Plates • Clutch Operation • Wet Friction • Open Pack Drag

  12. FIGURE 4-6 Any fluid left in the apply chamber of a spinning clutch will be pushed outward by centrifugal force. This force can cause the fluid to push on the piston and partially apply a clutch. FIGURE 4-7 A close-up view of the surface finish on a steel plate. Note the small nicks and grooves that tend to hold fluid. MULTIPLE-DISC DRIVING CLUTCHES

  13. FIGURE 4-8 Friction plates often have a groove pattern to help wipe fluid away, dissipate heat, eliminate clutch noise, and change friction qualities during apply and release. A smooth plate is the coolest and slowest to apply; the waffle plate will apply the fastest, but it will have less heat removed by the oil. (Courtesy of Raybestos) MULTIPLE-DISC DRIVING CLUTCHES

  14. FIGURE 4-9 This friction plate has directional grooves. The lugs (center inset) are assymmetrical, so the plate cannot be installed incorrectly. (Courtesy of Raybestos) MULTIPLE-DISC DRIVING CLUTCHES

  15. FIGURE 4-10 A microscopic view of the surface of paper friction plate lining. Friction material is formed on the lined plate to establish a crosslinked matrix. Note the large cavities between the paper fibers that can store relatively large amounts of fluid. (Courtesy of Raybestos) MULTIPLE-DISC DRIVING CLUTCHES

  16. FIGURE 4-11 In this clutch assembly, clutch stack clearance is adjusted using either the large or small flange (backing plate). Other clutches may use a selective snap ring. (Courtesy of Toyota Motor Sales USA, Inc.) MULTIPLE-DISC DRIVING CLUTCHES

  17. FIGURE 4-12 The ZPAK is a single-sided clutch design (a). Both sides of the two different plates show a lined and unlined side (b). The clutch pack requires proper placement of the end plates (c). (Courtesy of Raybestos) MULTIPLE-DISC DRIVING CLUTCHES

  18. FIGURE 4-13 When this transmission is in first gear, the sun gear and unlined plates of the front clutch rotate counterclockwise while the hub and lined plates of this clutch rotate clockwise. Any drag will produce heat that can cause clutch burnout. MULTIPLE-DISC DRIVING CLUTCHES

  19. FIGURE 4-14 If you push against a stationary book, you will notice the static friction that resists motion. Pushing against the same book while it is sliding is easier because the dynamic friction is somewhat less. MULTIPLE-DISC DRIVING CLUTCHES

  20. FIGURE 4-15 A comparison of the dynamic and static coefficients of friction with motor oil and three types of ATF. (Courtesy of Raybestos) MULTIPLE-DISC DRIVING CLUTCHES

  21. FIGURE 4-16 The clutch apply curves of five different clutches. The dynamic friction is the rate of torque increase, whereas the static friction is the amount of torque at the left. (Courtesy of AFM) MULTIPLE-DISC DRIVING CLUTCHES

  22. FIGURE 4-17 The four slots in this steel plate, called a turbulator plate, promote a fluid layer on each side of the stationary plate. (Courtesy of Raybestos) MULTIPLE-DISC DRIVING CLUTCHES

  23. ONE-WAY DRIVING CLUTCHES • Two styles of one-way clutches are used in automatic transmissions: • Roller clutches • Sprag clutches • Mechanical Diode • Clutch Operation

  24. FIGURE 4-18 This overrunning clutch assembly is a roller clutch with the clutch cam secured to the transmission case (a). It uses a set of springloaded rollers in the retainer (b). (Courtesy of Chrysler Corporation) ONE-WAY DRIVING CLUTCHES

  25. FIGURE 4-19 If this inner race tries to turn counterclockwise, the rollers will wedge at the narrow part of the cams and lock the clutch. Movement of the inner race in a clockwise direction will move the rollers to the wide part of the cams, where they will roll freely. (Courtesy of Chrysler Corporation) ONE-WAY DRIVING CLUTCHES

  26. FIGURE 4-20 Each sprag has a major and minor diameter. The major diameter is greater than the distance between the two races (right); the minor diameter is smaller (left). (Courtesy of Toyota Motor Sales USA, Inc.) ONE-WAY DRIVING CLUTCHES

  27. FIGURE 4-21 A mechanical diode. The struts can move out of the pocket plate to engage the notch plate, and this will lock the pocket plate. The pocket plate can overrun in the opposite direction. ONE-WAY DRIVING CLUTCHES

  28. FIGURE 4-22 This clutch hub and sprag clutch should rotate freely in a clockwise direction but should lock up in the opposite direction. (Courtesy of Toyota Motor Sales USA, Inc.) ONE-WAY DRIVING CLUTCHES

  29. HOLDING/REACTION DEVICES • A holding member acts as a brake to hold a planetary gearset member in reaction. • Three types of holding devices are used: • Multiple-disc clutches • Bands • One-way clutches

  30. MULTIPLE-DISC HOLDING CLUTCHES • A multiple-disc holding clutch is quite similar to a driving clutch. • The difference is the transmission case is the drum, and the clutch plates splined to it do not rotate. • Some manufacturers call these clutches a brake. • The lugs on the outside of the unlined plates fit into slots built into the case.

  31. FIGURE 4-23 The 41TE transaxle low/reverse clutch is a holding clutch. Note the splines in the case for the clutch plates. (Courtesy of Chrysler Corporation) MULTIPLE-DISC HOLDING CLUTCHES

  32. FIGURE 4-24 The plates of the O/D brake are splined to the transaxle O/D case. The first and reverse brake and the second brake are multiple-disc clutches that are splined to the transaxle case. (Courtesy of Toyota Motor Sales USA, Inc.) MULTIPLE-DISC HOLDING CLUTCHES

  33. ONE-WAY HOLDING CLUTCHES • One-way clutches are commonly used as reaction devices. • The outer race is often secured directly to the transmission case so it cannot rotate.

  34. BANDS • A band is a circular strip of metal that has lining bonded to the inner surface. • It wraps around the smooth surface of a drum. • There are three types: • Single thick, heavy band • Single thin, light band • Split, double-wrap, heavy band

  35. FIGURE 4-25 A flex band (a) and a rigid band (b). Note the flex band has circumferential grooves for improved conformity, fluid flow, and performance. Note that this is a double-wrap rigid band. Single-wrap rigid bands are also used. (Courtesy of Raybestos) BANDS

  36. FIGURE 4-26 This band uses an adjustable anchor that allows the clearance to be easily adjusted. (Courtesy of Chrysler Corporation) BANDS

  37. FIGURE 4-27 A band is normally anchored at the trailing end so its rotation will pull the band tighter. Note that this servo is applied by fluid pressure and released by a spring. (Courtesy of Toyota Motor Sales USA, Inc.) BANDS

  38. FIGURE 4-28 Fluid pressure acting on the piston forces the piston and piston rod inward to apply the band. The band is released by the outer spring pushing outward on the piston. (Courtesy of Toyota Motor Sales USA, Inc.) BANDS

  39. FIGURE 4-29 This band apply lever increases servo force by about two and a half times. The apply speed will be decreased the same amount because the servo must travel a greater distance. (Courtesy of Chrysler Corporation) BANDS

  40. FIGURE 4-30 Air pressure can be used to apply the band while the length of the piston stroke is measured. Piston stroke is used to determine the correct piston rod and adjust band clearance. (Courtesy of Toyota Motor Sales USA, Inc.) BANDS

  41. BANDS • Band Operation • When fluid pressure enters the servo, the servo piston strokes to tighten the band around the drum. • The amount of torque that a band can absorb before slipping is determined by the band-to-drum contact area, type of band, drum diameter, fluid type, and the force squeezing the band onto the drum.

  42. FIGURE 4-31 This band is applied when 1–2 shift valve pressure pushes upward on the servo piston. It will release when 2–3 shift valve pressure pushes the piston downward. Note the larger area above the piston. BANDS

  43. SHIFT QUALITY • As a power shift occurs, there must be a smooth transition from one apply device to the next. • The smoothness of the shift is referred to as shift quality or shift feel.

  44. FIGURE 4-32 In second gear, the sun gear and front clutch drum are held stationary by the band (a). In third gear, the clutch is applied so drum and sun gear are rotating at engine speed (b). The driver feels this change as shift quality. (Courtesy of Nissan North America, Inc.) SHIFT QUALITY

  45. FIGURE 4-33 Two cushion plates: the Belleville plate has a coned shape. The wave plate has a wavy shape. Both of them will flatten slightly as the clutch is applied. SHIFT QUALITY

  46. FIGURE 4-34 This one-way clutch allows the shaft to overrun in a clockwise direction. (Courtesy of Toyota Motor Sales USA, Inc.) SHIFT QUALITY • Shifts Involving One-Way Clutches • Deceleration with One-Way Clutches

  47. SUMMARY • The power flow through a gearset is controlled by driving and reaction devices. • The driving and reaction devices are multiple-disc clutches, one-way clutches, and bands. • Multiple-disc clutches are the primary driving devices and are also used to hold planetary members in reaction. • One-way clutches primarily are used to hold planetary members in reaction, but can be used with a multipledisc clutch to be a driving device. • Bands are used to hold a planetary member in reaction. • The timing of the apply and release of the apply devices has a direct effect on shift quality.

  48. REVIEW QUESTIONS • The power flow through an automatic transmission is controlled by the _________ and _________ devices. • The most common driving member is the _________ _________ _________; a(n) _________ _________ is also used as a driving member. • List the seven major parts of a clutch assembly. • Usually the lined plates of a driving multiple-disc clutch are splined to the clutch _________, and the unlined plates are splined to the clutch _________. • List the four types of return springs used in a multiple-disc clutch are.

  49. REVIEW QUESTIONS • Piston travel or clutch plate clearance can be adjusted by replacing the _________ or _________. • The multiple-disc clutch torque capacity can be increased by increasing the _________ area, number of _________, _________ size, or by increasing the _________ pressure. • Shift quality is a term used to describe the _________ of a shift. • The two types of one-way clutches used in an automatic transmission are the _________ and _________. • One-way clutches _________ when turned in one direction and _________ when rotated in the other direction.