Primary pressure regulation valve

PRIMARY PRESSURE REGULATION VALVE

This valve continuously controls the transmission output speed, from minimum to maximum, whilst “D” or “L” are selected.

The pulley ratio is changed by varying the pressure in circuit (A), acting on the primary pulley, via the sliding bearing. The control inputs are the accelerator pedal position (read from the movement of the transmission control cam) and the engine RPM (calculated from the Pitot pressure).

At low speed, spring (2) pushes the transmission control valve towards the left. As the engine RPM increases the Pitot pressure (4) also increases; the transmission control valve moves towards the right and the pressure in circuit (B) is allowed to pass through the solenoid valve to be directed to the primary pulley.

At this point the transmission speed starts to change. The initial variation of the engine between N1 and N2 is calculated from the accelerator pedal position, connected to the transmission control cam. When the accelerator pedal is pressed, the transmission control valve moves towards the left. The pressure in circuit (B) cannot pass to the solenoid valve circuit until the Pitot pressure (which is proportional to the engine RPM) begins to increase. In this way the vehicle speed starts to increase from low speeds.

1. Primary pressure regulation valve
2. Spring
3. Spring
4. Modulator linkage
5. Pitot pressure
6. Safety valve
7. Spring
8. Plunger pin
9. Selector cam (connected to the accelerator pedal)
10. Compensating piston
11. Transmission retaining valve
12. Lubrication pressure
13. Engine braking valve
14. X: to outlet