Empty-load fluid pressure brake system including proportioning valve

A fluid pressure brake system of the type including a changeover valve having a load and an empty setting, the system operable, when any given reduction in brake pipe pressure occurs, to remove a corresponding predetermined quantity of air from a supply reservoir and, in the load setting of the changeover valve to deliver said quantity of air to a brake operating motor and, in the empty setting of the changeover valve to deliver a part of said quantity of air to said motor through a proportioning valve and to deliver the balance of that air to a volume reservoir, the improvement comprising:

• a vent connection from said volume reservoir open when said brake system releases said brakes and closed when said valve is in empty setting,
• two paths in parallel flow relation with one another and through which said quantity of air removed from said supply reservoir may be delivered to said motor,
• one of said flow paths connecting said supply reservoir to said brake operating motor to provide at times the full pressure of the supply reservoir to the brake operating motor,
• the other of said flow paths connecting said supply reservoir to said brake operating motor, and including said proportioning valve and said volume reservoir in parallel relation with each other to provide at times a predetermined reduction of pressure at said brake cylinder,
• said changeover valve selectively rendering effective said one flow path when said changeover valve is in its said load setting and rendering effective the other flow path when said changeover valve is in its said empty setting.

An empty-load fluid pressure brake system of the type having a load and empty setting for vehicles comprising:

• (a) a brake operating motor,
• (b) an auxiliary reservoir for at times supplying fluid under pressure to a control valve for said brake operating motor,
• (c) a changeover valve operable between first-load and second-empty conditions,
• (d) means for supplying fluid pressure from said control valve to said brake operating motor when said changeover valve is in its first load condition, said fluid pressure being subject to regulation only by said control valve,
• (e) a proportioning valve located between said control valve and said brake operating motor, said proportioning valve including first and second pressure chambers communicating respectively with said control valve and with said brake operating motor and including also a piston means dividing said first and second pressure chambers,
• (f) means normally biasing said piston to a position which permits, in the unactuated non-braking conditon of the brake apparatus, free flow of fluid from said control valve to said brake operating motor only until the pressure in said brake operating motor reaches a predetermined value, said proportioning valve in response to a further increase in pressure from said control valve supplying to said brake operating motor a predetermined portion only of the pressure available from said control valve,
• (g) said piston means having a first pressure responsive surface enclosing said first pressure chamber which is of smaller area than a second pressure surface enclosing said second pressure chamber, said piston means being operable to close the proportioning valve at any time that the total force on said second surface is greater than the total force on said first surface.