GB1044118A - Improvements in or relating to pressure transmitting devices for hydraulic brake systems - Google Patents

Abstract

1,044,118. Fluid-pressure brakes. KELSEY-HAYES CO. March 1, 1965, No. 8664/65. Heading F2F. A pressure-proportioning device for insertion between a master cylinder and wheel brake cylinders of a vehicle hydraulic brake system is adapted during initial brake application to apply a relatively large volume at reduced pressure to the front brake cylinders, as compared with a smaller, but unrestricted, volume at relatively high pressure to the rear brake cylinders, and during subsequent braking to deliver fluid to the front and rear brake cylinders in volumes having a fixed ratio such that front brake cylinder pressure then rises faster than rear brake cylinder pressure. As shown, a four-section differential piston 50, 58, 60, 62 is used, having a by-pass 70, 72 through it, whereby initially fluid can flow from the inlet 88 through the by-pass direct to the rear brake cylinders 20 at full master cylinder pressure, to enable relatively strong springs of duo servo type rear drum brakes to be overcome, and in order to rapidly take up clearance of the front brakes which are disc brakes, while avoiding too sudden a brake application, a relatively large volume of fluid at low pressure is supplied to the front brake cylinders 26 by the piston sections 58, 60, the reduction in pressure being determined by the ratio of the difference in area of sections 58 and 62 to the difference in area of sections 50 and 62. During this initial application the sections 58, 60 operate as one, since fluid can pass the oneway seal 66 (grooves 118 are provided in the cylinder to enable complete return of fluid on brake release). When master cylinder pressure reaches a predetermined value a valve 76 is closed, owing to movement of an inner piston 73 in the section 50 to the right against the force of a light spring 96. This checks the rate of rise of pressure in the rear brake cylinders. At about the same value of master cylinder pressure an additional change takes place in the volume relationship between front and rear brakes owing to the provision of a ball valve 126 controlling a duct 122 between bore 44, in which section 58 works, and the chamber between sections 50 and 58 which is at atmospheric pressure, via connection 30 to the master cylinder reservoir. Pressure in the front brake cylinders acts on a plunger 129 which controls the ball valve 126 such that the pressure in bore 44 gradually reduces to atmospheric pressure, thus effecting a transition whereby less and less fluid passes the seal 66 until a fixed volume relationship is established, by piston sections 60 and 62 only, between front and rear brake cylinders, this being arranged to take place when all pad clearance of the front disc brakes has been taken up, and being such that front wheel brake pressure then rises faster than rear wheel brake pressure. A check valve 142 ensures release of pressure in the front brakes during brake release.