5107 Description and function of pump and hydraulic valves

Pump (P) (Fig. 5.39) This internal gear crescent-type pump consists of an internal toothed-spur ring gear which runs outside but in mesh with a driving external toothed-spur gear, so that its axis of rotation is eccentric to that of the driving gear. Due to their eccentricity, there is a space between the external and internal gears which is occupied by a fixed spacer block known as the crescent whose function is to separate the inlet-output port areas. The rotation of the gears creates a low pressure area at the inlet suction end of the crescent which draws in fluid. As the gear wheels rotate, oil will be trapped between the teeth of the inner driver gear and the inside crescent side walls, and between teeth of the outer gear and the outside crescent side wall. These teeth will then carry this fluid around to the other end of the crescent where it will then be discharged at pressure by both set of teeth into the output port.

Selector position valve (SPV) (Fig. 5.39) This valve is indirectly operated by the driver to select the forward and reverse direction of drive and the neutral or park positions.

Main pressure valve (MPV) (Fig. 5.39) The main pressure valve 'MPV' regulates the fluid pressure supply produced by the internal gear crescent pump; it is a variable pressure limiting valve which relates to driving conditions and the driver's demands.

Pressure reduction valve (PRV-1) (Fig. 5.39) The pressure reduction valve 'PRV-1' reduces the main fluid pressure supply to an approximate constant 5 bar output pressure which is the necessary fluid pressure supply to operate the solenoid valves MV1, MV2 and MV3.

Pressure reduction valve (PRV-2) (Fig. 5.39) The pressure reduction valve 'PRV' reduces the main fluid pressure supply to an approximate constant 5 bar output pressure which is the necessary fluid pressure supply to operate the electronic pressure regulation valves EPRV-1, EPRV-2, EPRV-3 and EPRV-4.

Modulation pressure value (MOD-PV) (Fig. 5.39) The modulation pressure valve is actuated by the electronic pressure regulator valve EPRV-1, it produces an output pressure which rises proportional to engine torque. The modulation pressure is conveyed to the main pressure valve and to each of the clutch valves, its purpose being to raise the system's pressure and to maximize the opening of the clutch valves with increased engine load so that a higher supply pressure reaches the appropriate multiplate clutch or/and brake.

Shift valves (SV-1, SV-2 and SV-3) (Fig. 5.39) The shift valves are actuated by the various solenoid valves MV1, MV2 and MV3: the function of a shift valve is to convey system pressure to the relevant operating circuit controlling the application or release of the various multiplate clutches/brakes.

Reverse gear valve (RGV) (Fig. 5.39) The reverse gear valve functions as a shift valve for selecting reverse gear; it also acts as safety valve for the forward gears by interrupting system pressure reaching clutch 'A', thus preventing the reverse gear being accidentally engaged whenever the vehicle is moving in a forward direction.

Clutch/brakes (CV-A, CV-B, CV-C, CV-D/BV-E, BV-F and BV-G) (Fig. 5.39) The clutch valves control the engagement and disengagement of the multiplate clutches and brakes. These valves are variable pressure reduction valves which are actuated by the appropriate solenoid valves, electronic pressure regulator valves, traction valves and shift valves and are responsible for producing the desired clutch pressure variations during each gear shift phase. Clutch valves CV-B, CV-C and CV-F are influenced by modulation pressure which resists the partial closure of the clutch valves, hence it permits relatively high fluid pressure to reach these multiplate clutches and brake when large transmission torque is being transmitted.

Retaining valves (RV-E and RV-G) (Fig. 5.39) In addition to the electronic pressure regulator valve which actuates the clutch valves, the retaining valves RV-E and RV-G modify the opening and closing phases of the clutch valves in such a way as to cause a progressive build-up or a rapid collapse of operating multiplate clutch/brake fluid pressure during engagement or disengagement respectively.

Traction/coasting valve (T/C-V) (Fig. 5.39) The traction coasting valve T/C-V cuts out the regulating action of the traction valve TV (5-4) and shifts the traction valve TV (4-5) into the shut-off position when required.

Traction valve (TV) (4-5) (Fig. 5.39) The traction valve TV (4-5) controls the main system fluid pressure to the multiplate-clutch MPC-B via the traction valve TV (5-4) and clutch valve CV-B and hence blocks the fluid pressure reaching the multiplate clutch CV-B when there is a upshift from fourth to fifth gear.

Traction valve (TV) (5-4) (Fig. 5.39) The traction valve TV (5-4) is another form of clutch valve, its function being to supply system pressure to the multiplate clutch MPC-B via clutch valve CV-B when there is a downshift from fifth to fourth gear.

Converter pressure valve (CPV) (Fig. 5.39) The converter pressure valve 'CPV' supplies the torque converter with a reduced system pressure to match the driving demands, that is, driving torque under varying driving conditions, it also serves as a pressure limiting valve to prevent excessive pressure build-up in the torque converter if the system pressure should become unduly high. The valve in addition vents the chamber formed on the drive-

plate side of the lock-up clutch when the torque converter pressure control valve is actuated.

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