From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Description of the operation and installation of the Pendulum Valve for clutch control.
| Identifier | ExFiles\Box 128\2\ scan0201 | |
| Date | 12th October 1933 guessed | |
| -7- PENDULUM VALVE. Fig. 1 Front of car Fig. 2 Front of car This has been introduced to eliminate the usual difficulties associated with starting on a steep hill, and also smooths out the whole operation of the clutch control so that a good start is made even with careless handling of the accelerator pedal. It is placed in the "bleed line" between the end plate of the cylinder and the accelerator control valve. It consists of a weight W suspended by an arm A from a pivot S, so that the weight and arm are free to swing. Coupled to the arm is a plunger R, which slides across a port P interposed in the bleed line, and is cushioned by a spring C. As mounted on the car, compression of the spring moves the plunger to the right until the port is fully open. In this position the weight will hang at a slight angle from the vertical, taking up the position shown in the illustration Fig.1. On an incline the weight will take up a position near the vertical or even past it. Fig.2 (depending on the steepness of the slope) so that the bleed control port is partly closed, which limits the rate at which air can escape from the underside of the piston, thus securing very gradual clutch engagement. Similarly, whenever the car tends to lurch forward during the clutch engagement, the weight will swing back, close off the bleed port, and so ensure a gradual take up of the drive. When the unit system is employed, the pendulum housing is carried by a bracket clamped between the cylinder intake flange and the control valve. Its position can vary according to the space requirements, but it is essential that the centre line of the pendulum case should be truly vertical when the cylinder is at its cushion point. Sometimes the pendulum and control valve are separated from the cylinder and mounted on the dash. Again it is essential that the mounting be such as to set the pendulum case in a true vertical plane. It must always be mounted so that the plunger in its boss faces to the rear of the car. | ||