Patent GB-624685-A (GB)
Title: Improvements in or relating to power units
IPC: B60T8/20
Filed: 1944-09-20
Abstract: 624,685. Fluid-pressure servomotor-control systems. ROCKWELL, E. A. Sept. 20, 1944, No. 17964. Convention date, April 11, 1941. [Class 135] [Also in Group XXXIV] A pneumatic power unit for connection between a manually-operated hydraulic master cylinder and a brake or other device to be operated comprises a control plunger acted upon by the master cylinder pressure to operate valves controlling the application of pneumatic pressure to a diaphragm which applies hydraulic pressure to the brake &c. through a power plunger, the valves being connected to the diaphragm so that there is a " follow-up " action. The pressure applied to the brakes by the power plunger reacts on the control plunger the resistance to movement of which thus increases with the degree of application of the brake. The power unit shown comprises a housing 25 having a clamp 33 for mounting it on the steering column of a motor vehicle. It is connected to a pedal operated master and to the vehicle brakes by pipes 16, 18, respectively. A two-part control plunger comprises a piston 54 slidable on a rod 51 having a piston 59 and a valve head 52. The chamber 49 of this plunger is connected by port 55 to the chamber 56 of a power plunger 120 having a piston head 126, the chamber 56 being connected to the pipe 18. The plunger 120 is slidable in a fixed part 121 and is engaged at its end 118 by a tubular rod 99 secured to a diaphragm 38 mounted in a casing 35, 39. The rod 99 slides in a bush 109 within a fixed sleeve 110 carrying a cap 111 which serves as a stop for the diaphragm and to hold a seal for the rod 99, as shown. A rod 113 extending loosely through the plunger 120 and screwed to a plug 114, has its end 115 formed as an abutment for a return spring 117 seated also on the end 118 of the plunger 120. An air inlet 105a carries a filter 105b. A spring 125 abuts on seals 123, 124, in the chamber 56. The diaphragm 38 comprises plates 72, 73 secured by a plug 98 to the tubular rod 99 and forming a chamber 97 which is constantly open to atmosphere through the rod, ports 103 and inlet 105a. The plunger 51 acts through a rod 106 and a lever 68 pivoted at 76 on the diaphragm plate 73, on the stem 82 of a vacuum valve 84 slidable in an air valve 93 attached by a flexible piece 86 to the diaphragm plate 72. The valve 93 is balanced as regards the air pressure acting on it. The diaphragm chamber 39 is connected by a pipe 42 to a vacuum source and the chamber 35 is normally open to chamber 39 by the valve 93. Upon operation of the master cylinder, liquid initially flows from pipe 16 past the valve 52, passage 46, ports 48, chambers 49, 56 and pipe 18 to the brakes until the pressure is sufficient to move the piston 59 and thus to seat the valve 52 on piston 54 and also to close the vacuum valve 84. Movement of the plunger 51, 54, 59 as a whole then opens the valve 93 to admit air from the chamber 97 to the diaphragm chamber 35, thus moving the plunger 120 to force liquid to the brakes from chamber 56. If the pedal movement ceases the diaphragm movement effects the re-closing of the air valve 93 so that the brake pressure can thus be graduated. This pressure reacts in chamber 49 on the piston 54 and thus on the pedal. The air inlet 105a may be provided with a valve, Fig. 8, for limiting the maximum pressure that that may be built up in the diaphragm chamber 35. When it is desired that full atmospheric pressure may be available for this chamber, the thumb-screw 137 is adjusted to permit the plate 145 to be raised by spring 147, as shown above the diaphragm 130. If, however, the plate 145 is depressed by the screw so as to engage the diaphragm 130 and compress the spring 151, the diaphragm 130 will be depressed to admit air through the inlet 105a to the diaphragm chamber 35 when the valve 93 is opened only until the pressure in the chamber reaches a value less than that of the atmosphere by an amount corresponding to the compression of the spring 151. The power device may be operated by compressed air instead of vacuum, the inlet 105a being then connected to the compressed air supply and the pipe 42 to atmosphere.