Land Rover Lesson 2 Auto Trans Coolingine Rover Manual
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Spool Valves The valve block contains twenty one spool valves which control various functions of the transmission. The spool valves are of conventional design and are operated by fluid pressure. Each spool valve is located in its spool bore and held in a default (unpressurised) position by a spring. The spool bore has a number of ports which allow fluid to flow to other valves and clutches to enable transmission operation. Each spool has a piston which is waisted to allow fluid to be diverted into the applicable ports when the valve is operated. When fluid pressure moves a spool, one or more ports in the spool bore are covered or uncovered. Fluid is prevented from flowing or is allowed to flow around the applicable waisted area of the spool and into another uncovered port. The fluid is either passed through galleries to actuate another spool, operate a clutch or is returned to the fluid pan. DRIVE CLUTCHES Multiplate Drive or Brake Clutch – Typical Input shaft1 Main pressure supply port2 Piston3 Cylinder – External plate carrier4 Clutch plate assembly5 Baffle plate6 Diaphragm spring7 Output shaft8 Bearing9 Dynamic pressure equalisation chamber10 Piston chamber11 Lubrication channel12 There are three drive clutches and two brake clutches used in the 6HP26 transmission. Each clutch comprises one or more friction plates dependent on the output controlled. A typical clutch consists of a number of steel outer plates and inner plates with friction material bonded to each face. The clutch plates are held apart mechanically by a diaphragm spring and hydraulically by dynamic pressure. The pressure is derived from a lubrication channel which supplies fluid to the bearings etc. The fluid is passed via a drilling in the output shaft into the chamber between the baffle plate and the piston. To prevent inadvertent clutch application due to pressure build up produced by centrifugal force, the fluid in the dynamic pressure equalisation chamber overcomes any pressure in the piston chamber and holds the piston off the clutch plate assembly. When clutch application is required, main pressure from the fluid pump is applied to the piston chamber from the supply port. This main pressure overcomes the low pressure fluid present in the dynamic pressure equalisation chamber. The piston moves, against the pressure applied by the diaphragm spring, and compresses the clutch plate assembly. When the main pressure falls, the diaphragm spring pushes the piston away from the clutch plate assembly, disengaging the clutch. Automatic TransmissionLesson 2 – Powertrain 265Technical Training (G421157)
PLANETARY GEAR TRAINS The planetary gear trains used on the 6HP26 transmission comprise a single web planetary gear train and a double web planetary gear train. These gear trains are known as Lepelletier type gear trains and together produce the six forward gears and the one reverse gear. Single Web Planetary Gear Train The single web planetary gear train comprises: •One sunwheel •Three planetary gears •One planetary gear carrier •One ring gear or annulus Cylinder1 Baffle plate2 Ring gear3 Planetary gear4 Planetary gear spider5 Torque converter input shaft6 (G421157) Technical Training266 Lesson 2 – PowertrainAutomatic Transmission
Double Web Planetary Gear Train Planetary gear spider1 Planetary gears (short)2 Ring gear3 Output shaft4 Planetary gear5 Sunwheel6 Double planetary gears (long)7 Sunwheel8 The double planetary gear train comprises: •Two sunwheels •Three short planetary gears •Three long planetary gears •One planetary gear carrier •One ring gear or annulus POWER FLOWS Operation of the transmission is controlled by the TCM which electrically activates various solenoids to control the transmission gear selection. The sequence of solenoid activation is based on programmed information in the module memory and physical transmission operating conditions such as vehicle speed, throttle position, engine load and selector lever position. Automatic TransmissionLesson 2 – Powertrain 267Technical Training (G421157)
Powerflow Schematic Torque input from engine1 Torque converter lock-up clutch2 Single web planetary gear carrier3 Single web planetary gears4 Single web sunwheel 15 Double web sunwheel 26 Double web planetary gears - Long7 Double web planetary gear carrier8 Double web planetary gears - Short9 Double web sunwheel 310 Torque output from transmission11 Multiplate clutchA Multiplate clutchB Multiplate brakeC Multiplate brakeD Multiplate clutchE Engine torque is transferred, via operation of single or combinations of clutches to the two planetary gear trains. Both gear trains are controlled by reactionary inputs from brake clutches to produce the six forward gears and one reverse gear. The ratios are as follows: Reverse6th5th4th3rd2nd1stGear 3.4030.6910.8671.1431.5212.3404.171Ratio The following table shows which solenoids are activated to produce the required torque output from the transmission. (G421157) Technical Training268 Lesson 2 – PowertrainAutomatic Transmission
Electronic Pressure Regulator Solenoids (EPRS)Shift Control Solenoid Valve Gear Selector Lever Position654321 -ON-ONP -ON-ONONR -ON-ONN -ON--ON-ONOND 1 -ON--ON-ONOND 2 -ON--ON-ONOND 3 -ON--ON-ONONOND 4 -ON--ON-ONONOND 5 -ON--ON-ONONOND 6 ON = Active (pressure build up) OFF = Inactive -ON- = Inactive (pressure drain) The following table shows which clutches are operating for selected gear ratios to produce the required torque output from the transmission. BrakeClutchShift Control Solenoid Valve Gear Selector Lever PositionDCWKEBA XP XXR XN XXXD 1 XXXD 2 XXXD 3 XXXOND 4 XXXOND 5 XXXOND 6 X = clutch applied Automatic TransmissionLesson 2 – Powertrain 269Technical Training (G421157)
Shift Elements Turbine shaft1 Stator shaft2 Single web planetary gear train3 Ring gear 14 Clutch A5 Clutch B6 Clutch E7 Brake clutch C8 Fixed connection to transmission housing9 Shaft key10 Brake clutch D11 Double web planetary gear train12 Planetary gears - Long13 Ring gear 214 Sunwheel 215 Sunwheel 316 Double web planetary gear carrier17 Planetary gears - short18 Single web planetary gear carrier19 Sunwheel 120 The shift elements are three rotating multiplate clutches (A, B and E) and two fixed multiplate brakes © and D). All shifts from 1st to 6th gears are power-on overlapping shifts. Overlapping shifts can be described as one of the clutches continuing to transmit drive at a lower main pressure until the next required clutch is able to accept the input torque. The shift elements, clutches and brakes are actuated hydraulically. Fluid pressure is applied to the required clutch and/or brake, pressing the plates together and allowing drive to be transmitted through the plates. The purpose of the shift elements is to perform power-on shifts with no interruption to traction and smooth transition between gear ratios. (G421157) Technical Training270 Lesson 2 – PowertrainAutomatic Transmission
Power Flow 1st Gear The gear selector lever and the manual selector valve spool are in the D position. Engine torque is transmitted from the torque converter turbine shaft to the ring gear 1 of the single web planetary gear train and the outer plate carrier of clutch E. Ring gear 1 drives the planetary gears which rotate around sunwheel 1. This drives the planetary gear carrier 1 and also the outer plate carrier of clutch A and the inner plate carrier of clutch B. When clutch A is engaged, sunwheel 3 in the double web planetary gear train is driven and meshes with the short planetary gears. The double web planetary gear train is locked against the transmission housing by brake D. This allows ring gear 2 (output shaft) to be driven in the same direction as the engine via the long planetary gears. Automatic TransmissionLesson 2 – Powertrain 271Technical Training (G421157)
NOTE: Refer to Shift Elements illustration for key Power Flow 2nd Gear (G421157) Technical Training272 Lesson 2 – PowertrainAutomatic Transmission
The gear selector lever and the manual selector spool valve are in the D position. Engine torque is transmitted from the torque converter turbine shaft to the ring gear 1 of the single web planetary gear train and the outer plate carrier of clutch E. Ring gear 1 drives the planetary gears which rotate around sunwheel 1. This drives the planetary gear carrier 1 and also the outer plate carrier of clutch A and the inner plate carrier of clutch B. When clutch A is engaged, sunwheel 3 in the double web planetary gear train is driven and meshes with the short planetary gears. Sunwheel 2 is locked to the transmission housing by brake clutch C. The long planetary gears, which are also meshed with the short planetary gears, roll around the fixed sunwheel 2 and transmit drive to the double web planetary gear train carrier and ring gear 2 in the direction of engine rotation. NOTE: Refer to Shift Elements illustration for key Automatic TransmissionLesson 2 – Powertrain 273Technical Training (G421157)
Power Flow 3rd Gear The gear selector lever and the manual selector spool valve are in the D position. Engine torque is transmitted from the torque converter turbine shaft to the ring gear 1 of the single web planetary gear train and the outer plate carrier of clutch E. Ring gear 1 drives the planetary gears which rotate around sunwheel 1. This drives the planetary gear carrier 1 and also the outer plate carrier of clutch A and the inner plate carrier of clutch B. When clutch A is engaged, sunwheel 3 in the double web planetary gear train is driven and meshes with the short planetary gears. Sunwheel 2 is driven via clutch B which is engaged. The long planetary gears, which are also meshed with the short planetary gears, cannot roll around the fixed sunwheel 2 and transmit drive to the locked double web planetary gear train carrier in the direction of engine rotation. (G421157) Technical Training274 Lesson 2 – PowertrainAutomatic Transmission