Brake system

• US 4,261,624 A
• Filed: 05/10/1979
• Issued: 04/14/1981
• Est. Priority Date: 05/10/1979
• Status: Expired due to Term

• Current Assignee: Volvo GM Heavy Truck Corp. (AB Volvo)
• Original Assignee: White Motor Corporation
• Inventors: Plantan, Ronald S.
• Primary Examiner(s): Reger, Duane A.
• Application Number:
  US06/037,537
• Time in Patent Office: 705 Days
• Field of Search: 303/7, 303/22 R, 303/13, 303/40, 303/47
• US Class Current: 303/7
• CPC Class Codes: B60T 13/263 specially adapted for coupling with dependent systems, e.g. tractor-trailer systems
• CPC Class Codes: B60T 13/268 using accumulators or reservoirs
• CPC Class Codes: B60T 8/26 characterised by producing differential braking between front and rear wheels using electrical circuitry or regulation means B60T8/17

Abstract

A braking system for the tractor unit of a tractor trailer vehicle in which the ratio of the pressure applied to the front brakes to the pressure applied to the rear brakes changes automatically when a trailer is connected to or disconnected from the tractor. The brake system includes two dual mode relay valves and feedback conduits which convey feedback pressures between the front and rear dual mode valves and between a trailer brake service conduit and the front valve. The brake system includes brake pressure proportioning apparatus which is operative to reduce brake pressures on the rear tractor brakes, during normal brake applications, when the tractor is operated bobtail but which can be overriden by a vehicle operator if conditions warrant. The pressure feedback and system hysterresis cooperate to produce balanced braking and the proper sequence of brake application under a variety of vehicle operating conditions.

Claims

1. A brake system for the tractor unit of tractor-trailer vehicle adapted to be connected to a trailer carried brake system, the system comprising:

(a) a source of pneumatic pressure;

(b) friction brakes mounted on each wheel of the tractor unit, each of said brakes being energized by an associated pneumatically operated brake actuator;

(c) an operator controlled treadle valve adapted for generating a signal pressure in proportion to the amount of treadle valve depression;

(d) two dual mode relay valves for controlling the flow of pneumatic pressure, one for the front brake actuators, the other for the rear brake actuators, each dual mode relay valve including;

(i) non-communicating signal pressure, proportioning pressure, and delivery pressure chambers;

(ii) a flow passage for conveying pneumatic pressure from a reservoir port communicating with said source of pneumatic pressure to the delivery pressure chamber;

(iii) an inlet/exhaust valve interposed in said flow passage adapted to interrupt the pressure flow therethrough when said valve is seated and concurrently exhaust pressure from the delivery pressure chamber;

(iv) a biasing spring tending to seat said inlet/exhaust valve;

(v) an annular control piston with respective surface portions communicating with said non-communicating signal pressure, proportioning pressure, and delivery pressure chambers, the movement of said control piston being in response to the combination of the pressures in said chambers acting upon the respective surface portions of said control piston, the control piston further including a projecting portion, which upon movement of the control piston, abuttably engages and unseats said inlet/exhaust valve;

(e) conduits communicating the treadle valve with the signal pressure chamber in each dual mode relay valve;

(f) conduits communicating the delivery chambers of the front and rear dual mode relay valves with the front and rear brake actuators respectively;

(g) a trailer brake system conduit for conveying pneumatic pressure from the tractor brake system to a trailer brake system, said conduit being generally at atmospheric pressure when not connected to a trailer brake system and said conduit being at a pressure proportional to the amount of treadle valve depression when said conduit is connected to a trailer carried brake system;

(h) a conduit communicating the delivery chamber of the front dual mode relay valve with the proportioning chamber of the rear dual mode relay valve; and

(i) a conduit communicating the trailer brake system conduit with the proportioning pressure chamber of the front relay valve.

2. In a tractor-trailer vehicle of a type in which the application of the trailer brakes is controlled by fluid pressure supplied by the tractor unit, a tractor brake system comprising:

(a) a source of pressurized fluid;

(b) friction brake means on at least one front and one rear wheel, each brake means energized by a fluid pressure operated brake actuator;

(c) a front valve means and a rear valve means for controlling the flow of pressurized fluid to the front and rear brake actuators respectively, the output pressure of said front and rear valve means being responsive in part to an operator applied force;

(d) means communicating the input of said rear valve means with the output of the front valve means such that the output pressure of said rear valve means is modified by the output pressure of said front valve means;

(e) a connectible conduit means for conveying operator controlled fluid pressure to a trailer brake system, said conduit means being generally at atmospheric pressure when not connected; and

,

(f) means communicating the input of the front valve means with said conduit means such that the output pressure of the front valve means is modified by the pressure in the conduit means.

3. The brake system of claim 2 wherein the operator applied force is a signal pressure generated by an operator controlled treadle valve.

4. A brake system for the towing unit of an articulated vehicle, said brake system comprising:

(a) a source of pressurized fluid;

(b) fluid pressure operated friction brake means on at least one front and one rear wheel;

(c) conduit means for conveying fluid pressure to the brake system of a towed unit, said conduit means being generally at atmospheric pressure when not connected to the towed unit;

(d) a brake proportioning means including front and rear valve means for controlling the flow of fluid pressure to the front and rear brake means respectively, the fluid pressure output of one of the valve means being a function of the combination of an operator applied force and the output pressure of the other valve means, and, the output pressure of the other valve means being a function of the combination of operator applied force and the pressure in the conduit means.

5. The brake system of claim 4 wherein the operator applied force is a signal pressure generated by an operator controlled treadle valve.

6. A brake system for the towing unit of an articulated vehicle, the brake system comprising:

(a) a source of pressurized fluid;

(b) fluid pressure operated brake actuators for engaging friction brakes on at least one front and one rear wheel;

(c) conduit means for conveying fluid pressure to a brake system of a towed unit;

(d) brake proportioning means, responsive to pressure in said conduit means;

(e) said proportioning means including front and rear valve means for controlling the flow of pressurized fluid to the front and rear brake actuators, respectively; and

,

(f) pressure feedback means between the front and rear relay valve for modifying the output pressure of said rear valve means until a predetermined output pressure is reached wherein said feedback means has a diminishing affect on said output of said rear valve means.

7. A dual mode relay valve for controlling the flow of pressurized fluid to a fluid pressure operated brake actuator, comprising:

(a) a housing;

(b) flow passage means for conveying fluid from a reservoir port to a delivery port;

(c) an inlet valve member interposed in said flow passage means and operative to interrupt fluid flow therethrough when said valve is seated;

(d) a biasing means tending to seat said valve member;

(e) non-communicating signal pressure, proportioning pressure, and delivery pressure chambers, said delivery pressure chamber communicating with said delivery port;

(g) a control piston means with respective surface portions communicating with said non-communicating signal pressure, proportioning pressure, and delivery pressure chambers, the movement of said control piston means being in response to the combination of the pressures in said chambers acting upon the respective surface portions of said control piston means, the control piston means further including an abutment means for unseating the inlet valve member; and

,

(g) exhaust valve means for exhausting the fluid pressure in the delivery pressure chamber when said control piston means is not abutting the inlet valve member.

8. A dual mode relay valve for using a fluid pressure operated brake proportioning system, comprising:

(a) a valve means for controlling the flow of pressurized fluid from a reservoir port to a delivery port;

(b) a housing with a control piston slidably received therein, the movement of said control piston being in response to the combination of an operator controlled signal pressure, a proportioning pressure, and the pressure at the delivery port, the control piston further including an abutment means for unseating said valve means to allow fluid flow between said reservoir and delivery ports upon movement of said control piston, said abutment means spaced from said valve means when said operator controlled signal pressure is below a predetermined level.

9. A brake proportioning system for the tractor unit of a tractor-trailer type vehicle comprising:

(a) a source of pressurized fluid;

(b) fluid pressure operated brake actuators on the front and rear wheels of said tractor;

(c) front and rear valve means for controlling the flow of pressurized fluid to the front and rear brake actuators respectively; and

(d) feedback means communicating with the front valve means for reducing the output pressure of the front valve means to effect increased braking on the rear wheels of the tractor unit when operating with a trailer.

10. In a tractor-trailer vehicle of a type in which the application of the trailer brakes is controlled by fluid pressure supplied by the tractor unit, a tractor brake system comprising:

(a) a source of pressurized fluid;

(b) friction brake means on at least one front and one rear wheel, each brake means energized by a fluid pressure operated brake actuator;

(c) a front valve means and rear valve means for controlling the flow of pressurized fluid to the front and rear brake actuators respectively, the output pressure of said front and rear valve means being responsive in part to an operator applied force;

(d) means communicating the input of said rear valve means with the output of the front valve means such that the output pressure of said rear valve means is reduced by the output pressure of said front valve means;

(e) a connectible conduit means for conveying operator controlled fluid pressure to a trailer brake system, said conduit means being generally at atmospheric pressure when not connected; and

,

(f) means communicating the input of the front valve means with said conduit means such that the output pressure of the front valve means is reduced by the pressure in the conduit means.

11. The brake system of claim 10 wherein the operator applied force is a signal pressure generated by an operator controlled treadle valve.

12. A brake system for the tractor unit of tractor-trailer type vehicle comprising:

(a) a source of pressurized fluid;

(b) frictional brake means on the front and rear wheels, said brake means applied by fluid pressure operated brake actuators;

(c) a front valve means and a rear valve means for controlling the flow of pressurized fluid to the front and rear actuators respectively; and

(d) front and rear pressure feedback means communicating with the front and rear valve means, responsive to the presence or absence of a trailer unit attached to said tractor unit, said pressure feedback means operative to effect a reduced braking on the rear wheels of the tractor unit when operating without a trailer.

13. A brake system for a tractor unit of a tractor-trailer vehicle, comprising:

(a) a source of pressurized fluid;

(b) fluid pressure operated brake actuators for engaging front and rear wheel mounted brakes;

(c) front and rear valve means, responsive to movement in an operator controlled treadle, for controlling the flow of pressurized fluid from the source to the front and rear brake actuators respectively;

(d) pressure feedback means communicating with said rear valve means, responsive to the absence of an attached trailer, for reducing the flow of pressurized fluid to the rear actuators for a range of treadle depression; and

(e) said feedback means having a diminishing affect on the flow of pressurized fluid to the rear brake actuators once said range of treadle depression is exceeded.

14. The brake system of claim 13 further including a feedback means communicating with said front valve means for increasing the crack-open pressure of said front valve means so that the rear valve means opens before the front valve means.

15. A brake proportioning system for a tractor unit of a tractor-trailer vehicle which proportions the brake application fluid pressure between front and rear vehicle braking means depending on the vehicle operational mode, the system comprising:

(a) a source of pressurized fluid;

(b) friction brake means operatively connected to each vehicle wheel and energized by fluid pressure operated brake actuators;

(c) a front relay valve and a rear relay valve for controlling the flow of pressurized fluid to the front and rear brake actuators respectively, the output pressure of said front and rear relay valves being responsive in part to a signal pressure generated by an operator controlled treadle valve;

(d) means communicating the input of said rear relay valve with the output of the front relay valve such that the output pressure of said rear relay valve is reduced by the output pressure of said front relay valve until the output pressure of the front relay valve equals the source pressure; and

,

(e) a connectable conduit means for conveying the operator controlled signal pressure to a trailer brake system, said conduit means being generally at atmospheric pressure when not connected.

16. The brake proportioning system defined by claim 15 further including means communicating the input of the front relay valve with the conduit means such that the output pressure of the front relay valve is reduced by the pressure in the conduit means.

17. A brake system for the tractor unit of a tractor-trailer vehicle having means for connecting to a trailer carried brake system, when a trailer is attached to the tractor, comprising:

(a) a source of pneumatic pressure;

(b) front and rear friction brakes mounted on front and rear wheels of the tractor unit, each of said brakes being energized by an associated pneumatically operated brake actuator;

(c) an operator controlled treadle valve for generating a signal pressure in proportion to the amount of treadle depression;

(d) two relay valves for controlling the flow of pneumatic pressure to associated output ports, each relay valve including;

(i) a signal pressure chamber for receiving signal pressure from the treadle valve;

(ii) a proportioning chamber which when pressurized produces a force which renders a force produced by the signal pressure in the signal pressure chamber partially ineffective;

(e) conduits communicating the treadle valve with the signal pressure chamber in each relay valve;

(f) conduits communicating the output ports of the front and rear relay valves with the front and rear brake actuators respectively; and

,

(g) a conduit communicating the output port of the front relay valve with the proportioning chamber of the rear relay valve.

18. The brake system of claim 17 further comprising:

(a) a trailer brake system conduit for conveying pneumatic pressure from the tractor brake system to a trailer brake system, the conduit being generally at atmospheric pressure when not connected to a trailer brake system and being at a pressure proportional to the amount of treadle depression when the conduit is connected to a trailer carrier brake system; and

,

(b) a conduit communicating the trailer brake system conduit with the proportioning pressure chamber of the front relay valve.

19. A brake system for the towing unit of articulated vehicle, said brake system comprising:

(a) a source of pressurized fluid;

(b) fluid pressure operated friction brake means on at least one front and one rear wheel;

(c) conduit means for conveying fluid pressure to the brake system of a towed unit;

(d) a brake proportioning means including front and a rear relay valves for controlling the flow of pressurized fluid to the front and rear brake means, respectively; and

,

(e) pressure feedback means between the front and rear relay valve and between the conduit means and the front relay valve for modifying the output pressures of said valves to effectively change the relative braking rate between the front and rear wheels of the towing unit when the towing unit is operated without the towed unit.

20. The brake system of claim 19 wherein said pressure feedback means reduces the output pressure of the rear valve means until the output pressure of the front valve means is substantially equal to the source pressure, when the towing unit is operated without the towed unit.

21. In a vehicle having towed and towing units in which the towing unit has front and rear road wheels and the towed unit has road wheels, the improved braking apparatus comprising:

(a) fluid pressure actuated brake assemblies, first and second of the assemblies being postioned selectively to arrest rotation of one of the front wheels and one of the rear wheels respectively, and at least one assembly being positioned selectively to arrest rotation of a towed unit road wheel;

(b) a source of fluid under pressure;

(c) a fluid supply system for selectively delivering fluid under pressure from the source to the brake assemblies in response to an operator supplied signal;

(d) said system including first and second valve means for controlling pressure delivery to the first and second brake assemblies, respectively;

(e) means for increasing valve hysteresis in said first and second valve means to effect an increase in the crack-open pressure of said first and second valve means such that a line delivering brake pressure to the towed vehicle brake assembly commences to receive fluid under pressure prior to lines connected to the towing vehicle brake assemblies in response to an operator supplied brake application signal.

24. The improved braking apparatus of claim 21 further comprising pressure feedback means for delaying the initial opening of said first valve means such that fluid under pressure is delivered to a pressure supply line connected to the rear wheel brake assembly after the towed vehicle line has commenced to receive pressure and prior to a time when a line connected to the front brake assembly commences to receive pressure.

25. The improved braking apparatus of claim 21 wherein said means for increasing valve hysteresis comprises a seal means.

27. The brake system of claim 25 wherein said front and rear valve means include seal means for increasing the crack-open pressures of said front and rear valve means such that said conduit means commences to receive pressure in response to the operator controlled braking force prior to opening of the front and rear valve means.

22. In a highway tractor adapted for towing a trailer and having at least one front and one rear brake actuator, the improved brake control system comprising:

(a) a source of air under pressure;

(b) a valve and conduit system connecting the source to the actuators;

(c) the valve and conduit system including trailer means to sense the absence of a trailer;

(d) an operator controlled treadle having a normal braking range and an override braking range; and

,

(e) valve means responsive to operator initiated treadle signals and to the trailer sensing means to provide a first ratio of pressures to the front and rear actuators during the normal range wherein the pressure supplied to the front actuator exceeds that supplied to the rear actuator and a different ratio when the treadle is in the override range wherein the pressure supplied to the rear actuator more closely equals the pressure supplied to the front actuator than when the treadle is in the normal range.

23. In a vehicle brake system having a source of pressurized fluid and fluid pressure operated friction brake means on at least one front and one rear wheel, a brake proportioning means comprising:

(a) a front valve means and a rear valve means for controlling the flow of pressurized fluid to the front and rear brake means respectively;

(b) at least one of said valve means having a valve operating means including a surface defining at least one effective pressure area;

(c) means communicating the output of the other valve means with the effective pressure area on said valve operating means such that the output pressure applied to said effective pressure area generates a force that opposes an operator applied force on said valve operating means, so that the output pressure of the one valve means will be a function of a combination of the operator applied force and the output pressure of the other valve means.

26. A brake system for the towing unit of an articulated vehicle, comprising:

(a) a source of pressurized fluid;

(b) fluid pressure operated friction brake means on at least one front and one rear wheel;

(c) conduit means for conveying fluid pressure to the brake system of a towed unit, said conduit means being generally at atmospheric pressure when not connected to a towed unit and being at a pressure proportional to an operator controlled braking force when said conduit is connected to a towed unit;

(d) front and rear valve means for controlling the flow of fluid pressure to the front and rear brake means respectively, as a function of the operator controlled braking force;

(e) pressure feedback means between said front valve means and said conduit means for delaying the initial opening of said front valve means when the towing unit is connected to a towed unit such that the rear valve means opens before said front valve means in response to the operator controlled brake force;

(f) pressure feedback means between the front and rear valve means operative when the towing unit is not connected to a towed unit to delay the initial opening of said rear valve means so that the front valve means opens before said rear valve means in response to an operator controlled braking force.

28. A braking system for a tractor unit of a tractor-trailer type vehicle, comprising:

(a) a source of pneumatic pressure;

(b) pneumatically operated friction brake means on at least one front and one rear wheel;

(c) conduit means for conveying pressure to the brake system of the trailer unit, said conduit means being generally at atmospheric pressure when not connected to the trailer and being at a brake pressure that is a function of an operator controlled braking signal when connected to the trailer;

p1 (d) front and rear valve means for controlling the flow of fluid pressure to the front and rear brake means respectively;

(e) means for increasing the crack open pressures of said front and rear valve means such that said conduit means commences to receive pressure in response to the operator controlled braking prior to the opening of said front and rear valve means;

(f) first pressure feedback means operative when said conduit means is connected to a trailer unit for further increasing the crack open pressure of said front valve means; and

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(g) second pressure feedback means for further increasing the crack open pressure of said rear valve means causing said front valve means to open prior to said second valve means, in response to the operator applied braking force, when the tractor unit is not connected to a trailer unit.