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Title:
AIR BRAKE SYSTEM WITH THREE CHAMBER BRAKE ACTUATOR
Document Type and Number:
WIPO Patent Application WO/1991/006458
Kind Code:
A1
Abstract:
A vehicle air brake system (180) includes a novel three chamber brake actuator (182) having a service brake, chamber (8), a spring brake chamber (10) and a supplemental chamber (212). A conventional modulated spring brake control valve (78) is used to supply pressurized air to the spring brake chamber. The service brake chamber is supplied with air through the outlet of a conventional service brake application valve (68). The force applied to the actuator piston (198) can be changed to a lower force for parking and a higher force for emergencies according to the pressure applied to the spring brake and supplemental chambers.

Inventors:
Graham, John M. (930 Peninsula Avenue, #205 San Mateo, CA, 94403, US)
Application Number:
PCT/US1990/006334
Publication Date:
May 16, 1991
Filing Date:
October 31, 1990
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
Graham, John M. (930 Peninsula Avenue, #205 San Mateo, CA, 94403, US)
International Classes:
B60T13/26; B60T15/04; B60T17/08; (IPC1-7): B60T13/22
Foreign References:
US3719125A
US4003606A
US3926094A
US3943830A
US4564088A
US4589704A
Attorney, Agent or Firm:
Hann, James F. (Townsend and Townsend, One Market Plaza 2000 Steuart Towe, San Francisco CA, 94105, US)
Download PDF:
Claims:
WHAT IS CLAIMED IS;
1. A vehicle air brake system comprising: a combination brake actuator including a spring brake chamber, a supplemental chamber, a spring brake spring operably positioned between the spring brake chamber and the supplemental chamber, a push rod operably coupled to the spring brake spring and a service brake chamber; a pressurized air source; a spring brake control valve means for selectively fluidly coupling the spring brake chamber to the pressurized air source and to atmosphere; a service brake actuation valve means for selectively fluidly coupling the service brake chamber to the pressurized air source and to atmosphere; and a user actuated force control valve means for selectively fluidly coupling the supplemental chamber to the pressurized air source whereby the force exerted on the push rod can be changed according to the pressurization of the spring brake chamber and of the supplemental chamber to accommodate different braking forces desired during parking and emergency situations.
2. The system of claim 1 wherein the spring brake spring is a coil spring.
3. The system of claim 1 wherein the force control valve is placeable in at least first and second states, said first state coupling the supplemental chamber to the source of pressurized air and the second state coupling the supplemental chamber to the ambient atmosphere.
4. The system of claim 1 wherein the combination brake actuator includes a first pistontype element driven by air in the supplemental chamber for movement between a first position, corresponding to first and second deflected states of the spring brake spring, and a second position, corresponding to a third deflected state of the spring brake spring, the first and third states being compressed states relative to the second state.
5. The system of claim 4 wherein: the combination brake actuator includes a second pistontype element driven by air in the spring brake chamber; and the spring brake spring is a compression spring captured between the first pistontype element and the second pistontype element.
6. The system of claim 1 wherein the spring brake control valve means includes a spring brake control valve having a first inlet coupled to the first pressure source, a first outlet and a first exhaust port opening into the ambient atmosphere, and wherein the force control valve includes a second inlet coupled to the third pressurized air source, a second outlet and a second exhaust port opening into the ambient atmosphere, the spring brake control valve operable to fluidly connect the first inlet and the first outlet when in a first state and to fluidly connect the second outlet and the first exhaust port when in a second state, the force control valve operable to fluidly connect the second inlet to the second outlet when in a third state and to fluidly connect the second outlet to the second exhaust port when in a fourth state.
7. The system of claim 1 including means for supplying pressurized air from the pressurized air source to the service brake chamber and the supplemental chamber at the same pressure.
8. A combination air brake actuator comprising: a service brake portion including a service brake chamber and a push rod actuator responsive to pressurization of the service brake chamber; a spring brake portion including a spring brake chamber and a spring brake actuator element, responsive to pressurization of the spring brake chamber, operably coupled to the push rod actuator; a supplemental portion including a supplemental chamber and a supplemental actuator element responsive to pressurization of the supplemental chamber; and a spring brake spring, operably positioned between the spring brake actuator element and the supplemental actuator element, biasing the spring brake actuator element and the supplemental actuator element against any forces applied thereto by pressurizing the respective spring brake and supplemental chambers.
9. The system of claim 8 wherein pressurizing the spring brake chamber, depressurizing the spring brake chamber, and pressurizing the supplemental chamber while depressurizing the spring brake chamber places the spring brake spring in first, second and third deflected states, respectively, the first and third states being compressed states relative to the second state.
10. The actuator of claim 9 wherein the supplemental actuator element moves between a first position, corresponding to the first and third deflected states of the spring brake spring, and a second position, corresponding to the second deflected state of the spring brake spring.
11. The actuator of claim 10 wherein the spring brake spring is a compression spring captured physically between the spring brake actuator element and the supplemental actuator element.
12. The actuator of claim 8 wherein the spring brake actuator element includes an actuator piston.
13. The actuator of claim 12 wherein the supplemental actuator element includes a supplemental piston.
14. An improved combination air brake actuator of the type including a push rod, a service brake portion and a spring brake portion, the spring brake portion including a housing, an actuator element mounted within the housing, a spring brake chamber defined by the housing and the actuator element, and an actuator spring positioned between the actuator element and a housing wall, the improvement comprising: a supplemental actuator ovably positioned within the housing between the actuator spring and the housing wall, the actuator spring captured between and biasing the actuator element and the supplemental actuator away from one another; the supplemental actuator and the housing configured to define a variable volume supplemental chamber between the supplemental actuator and the housing wall as the supplemental actuator moves between first and second positions; and a supplemental port opening into the supplemental chamber; whereby the force exerted on the push rod can be changed according to the pressurization of the spring brake chamber and the supplemental chamber to accommodate different braking forces desired during different situations.
Description:
AIR BRAKE SYSTEM WITH THREE CHAMBER BRAKE ACTUATOR

BACKGROUND OF THE INVENTION Trucks, buses and other such vehicles typically use air brake systems. These brake system includes air actuated service brakes coupled to service brake actuators. Pressurized air, typically at 100 psi, is applied to the service brake chambers of the service brake actuators to apply the service brakes. To keep the brakes applied while parked, combination brake actuators are usually used. The combination brake actuators include a spring brake portion and a service brake portion. The spring and service brake portions include respective spring and service brake chambers. The spring brake portion also includes a heavy actuator spring coupled to the brake through an actuator piston. The actuator spring tends to apply the brakes. Supplying pressurized air to the service brake chambers applies the brakes (as discussed above) while supplying pressurized air to the spring brake chambers moves the actuator piston to compress the actuator spring to release the brakes. Thus, when parked, air is exhausted from both the spring brake chambers and the service brake chambers which allows the actuator springs to apply the brakes according to the force of the actuator springs.

One of the problems with these conventional air brake systems is that the braking force generated by the spring brake portion of the combination brake actuator is only about 50% of the maximum braking force generated by an applied service brake. Therefore, each axle with combination brake actuators has only about half of the braking force which is available with the service brake. Conventional combination brake actuators may be designed to provide this lower force during parking is to protect the brakes. That is, if the vehicle is parked and drum brakes are set or parked while the drums are warm, upon cooling the drums have a tendency to contract which can, if the braking force is too high, result in damage to the brakes. Also, not all of

the axles have combination brake actuators; often no more than half of the axles are so equipped. Although the resulting braking force is sufficient for parking purposes, in an emergency when service brake air pressure is lost, the braking force available is woefully inadequate.

SUMMARY OF THE INVENTION The present invention is directed to a three chamber brake actuator constructed to permit the actuator spring to exert a higher force during emergency situations and a lower force during parking.

The three chamber brake actuator can be made to be substantially identical to conventional combination brake actuators but with a minor modification. With conventional combination brake actuators, the actuator spring is captured between the rear face of the actuator piston and the spring brake cover. However, by providing a supplemental piston between the actuator spring and the spring brake cover, a supplemental chamber is created between the supplemental piston and the service brake cover.

The area of the supplemental piston is preferably less than the area of the actuator piston so that when both the spring brake and supplemental chambers are pressurized to the same pressure, the force exerted on the actuator piston by the pressurized air in the spring brake chamber is greater than the force exerted on the supplemental piston by the pressurized air in the supplemental brake chamber. Therefore, during normal operation the supplemental chamber can be pressurized or not pressurized. In either case the actuator spring is fully compressed between the actuator piston and the supplemental piston with the supplemental piston being forced against the spring brake cover.

To apply the brakes for parking, the spring brake chamber and the supplemental brake chamber are both vented to atmosphere. This allows the actuator spring to expand and drive the actuator piston towards the push rod to apply the brakes; the supplemental piston does not move since before venting the spring

brake chamber, the supplemental piston was already against the spring brake cover.

To apply the brakes in an emergency situation, the spring brake chamber is vented to atmosphere and the supplemental chamber is pressurized. The actuator spring expands and drives the actuator piston towards the push rod to apply the brakes. However, since the supplemental chamber is pressurized, the supplemental piston moves against the actuator spring to at least partially recompress the actuator spring; this increases the force applied by the actuator piston to the push rod over that applied during parking situations discussed above. In this way problems caused by excessive force on the brakes while parked can be avoided while providing additional braking force when emergency braking is needed. One of the primary advantages of the invention is that it can be carried out with very few modifications to a conventional air brake system. In particular, conventional actuator springs can be used with the invention. Also, since the spring brake can provide enough force to act as an emergency brake, as well as a parking brake, a single service brake application valve, as opposed to the dual pedal valves used with conventional split axle air brake systems, can be used. This further reduces costs, complexity, expense and weight of an air brake system made according to the invention. Also, little air is needed to pressurize the supplemental chamber so that its pressurization will not affect the pressure of the system to any substantial degree.

The invention can be used with braking systems which allow or prevent compounding of service brake force with parking/emergency brake force.

Other features and advantages of the invention will appear from the following description in which the preferred embodiment has been set forth in detail in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a conventional dual axle air brake system. Fig. 2 shows an air brake system made according to the invention. Fig. 3 is a cross-sectional view of a three chamber brake actuator used with the system of Fig. 2.

Fig. 4 shows the brake actuator of Fig. 3 in the parking brakes applied configuration with the spring brake and supplemental chambers vented to atmosphere. Fig. 5 shows the brake actuator of Fig. 3 in the emergency brakes applied configuration with the spring brake chamber vented to atmosphere and the supplemental chamber pressurized.

Fig. 6 is a simplified cross-sectional view of a normally open shut off valve mounted to the modulated spring brake control valve.

Fig. 7 is an end view of the shut off valve of Fig. 6 taken along line 7-7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

At Fig. 1 a conventional dual axle air brake system 2 is shown to include service brake actuators 4 at the front axle and combination brake actuators 6 at the rear axle. Combination actuators 6 include a service brake chamber 8 and a spring brake chamber 10. Compressed air is supplied by a compressor 12 which feeds a supply or wet tank 14 with pressurized air from a line 16. The pressure within tank 14 is regulated by governor 18 coupled to tank 14 through a line 20. Governor 18 maintains the pressure within wet tank 14 at about 100 psi. Wet tank 14 supplies pressurized air to a pair of supply tanks 22, 24 thorough lines 26, 28 and check valves 30, 32. Pressurized air within supply tanks 22, 24 is directed to a dual service brake application valve (dual pedal valve) 34 through lines 36, 38 to supply combination actuator 6 and service brake actuators 4 through lines 40, 42 and quick release valves 44. (Quick release valves 44 do not change the operation of air brake systems but permit faster operation by exhausting air from service brake chambers 8 through valves 44 rather than requiring

the air to exhaust through valve 34.) Thus, actuation of valve 34 by the operator applies pressurized air to service brake chambers 8 at both the front and rear axles. Dual tanks 22, 24, dual application valve 34 and their associated lines are used to help prevent a loss of service brake air pressure at one axle from affecting the service brake air pressure at the other axle. Air passes through line 38, through lines 45, 48, and through a parking brake control valve 46 positioned along line 48. Line 48 couples control valve 46 with a first entrance port 49 of a two-way check valve 50. A line 51 couples a second entrance port 53 of two-way check valve 50 to line 40. Two-way check valve 50 supplies air to a quick release valve 52 through its exit port 55 and a line 54 so that pressurized air is supplied to spring brake chambers 10 along lines 56 when either line 48 or line 40 is supplied with pressurized air. Therefore, spring brake chambers 10 are pressurized, thus releasing the associated spring brakes, whenever the service brakes are applied to avoid compounding of the service and spring brake forces (that is the application of service and spring brake forces at the same time) . Compounding may be considered undesirable because the excessive braking force which would be applied could cause the operator to lose control of the vehicle and could damage the brake components.

The force required to stop a moving vehicle is much greater than that required to keep a stationary vehicle in place. Therefore, in some cases it is desired to be able to have the spring brake apply a higher force during emergencies and a lower force while parking. To accommodate this situation, an air brake system 180, shown in Fig. 2, can be used with a three chamber brake actuator 182, illustrated in Fig. 3. Actuator 182 is a rather modest modification of a conventional combination brake actuator such as that manufactured by M.G.M. Inc. of Cloverdale, California. Actuator 182 includes a service brake portion 184 defining service brake chamber 8 and a spring brake portion 186 defining spring brake chamber 10. Service brake portion 184 includes a diaphragm 188 against which an enlarged end 190 of a push rod 192 rests. A relatively weak return spring 194 keeps

push rod 192 in the retracted position of Fig. 3 until service brake chamber 8 is pressurized through a port 196.

Spring brake portion 186 includes an actuator piston 198 which rides within a spring brake housing 200. Piston 198 and housing 200 define spring brake chamber 10. Actuator piston 198 is connected to a push rod extension 202 having an enlarged end 204 opposite diaphragm 188. An actuator spring 206 presses actuator piston 198 thus tending to force end 204 of extension 202 against diaphragm 188. This tendency is opposed by high pressure air within spring brake chamber 10 which is applied through a port 208.

The above described structure of actuator 182 is generally conventional. However, actuator 182 includes a supplemental piston 210 which also moves within housing 200. Actuator spring 206 is captured between actuator piston 198 and supplemental piston 210. A supplemental chamber 212 is formed between supplemental piston 210 and the spring brake cover 214 of spring brake portion 186.

Actuator 182 is shown in Fig. 3 in a driving configuration with no brakes applied. This is achieved by pressurizing spring brake chamber 10, which drives actuator piston 198 to the right in the figure. Since the area of actuator piston 198 is greater than the area of supplemental piston 210, it does not matter if supplemental chamber 212 is pressurized or not so long as the pressures applied to each about the same; supplemental piston 210 will be forced against cover 214 by the pressurization of chamber 10. (In system 180, chamber 212 is pressurized in this configuration.) Pressurizing chamber 8, to apply the service brakes, drives enlarged end 190 and push rod 192 therewith to the left (not shown in Fig. 3) to apply the brakes.

Fig. 4 shows actuator 182 in a parking brakes applied configuration. Both chambers 10 and 212 have been placed at atmospheric pressure to permit actuator spring 206 to drive push rod 192 to the left and apply the brakes with the force exerted by partially expanded spring 206. Fig. 5 shows actuator in a emergency brakes applied configuration. While chamber 10 is at atmospheric pressure, supplemental chamber 212 is pressurized to

at least partially recompress spring 206 from the condition of Fig. 4. In this way, the force on push rod 192 is greater in the emergency brake position of Fig. 5 than the parking brake position of Fig. 4. System 180, as shown in Fig. 2, is somewhat similar to system 2, shown in Fig. 1, with like reference numerals referring to like elements. The primary differences, in addition to the use of three chamber brake actuators 182, are the inclusion of a single chamber service brake application valve 68, a modulated spring brake control valve 78, a force control valve 220, a pilot check valve 222, a supplemental tank 223, and check valves 224, 225, which will now be described.

Pressurized air from service brake supply tanks 22, 24 is supplied to service brake chambers 8 through the actuation of a service brake application valve (a single pedal valve) 68 which directs pressurized air, when actuated, through lines 70, 72 to quick release valves 44 and then to service brake chambers 8. Pressurized air is supplied from tank 24 along a line 74, through check valve 225, through supplemental tank 223, through an inlet 76 of a modulated spring brake control valve 78, thorough an outlet 80, and to the pilot inlet 226 of a pilot check valve 222. Supplemental tank 223 and check valve 225 provide a relatively small volume source of pressurized air for use in pressurizing supplemental chamber 212 (shown in Fig. 3 and discussed below) in the event pressure is lost in tanks 22, 24. Pilot check valve 222 includes a pilot outlet 228 coupled to a check valve inlet 230 of check valve 224 by a line 232, and a pilot control port 234 coupled to a check valve outlet 236 of check valve 224 by a line 238. Line 238 continues past outlet 236 to a quick release valve 240. Valve 240 couples line 238 to supplemental chambers 212 through lines 242 and ports 216.

Force control valve 220 includes an inlet 244 coupled to line 74 by a line 246, an outlet 248 coupled to line 238 and an exhaust port 250 opening into the ambient atmosphere. Quick release valve 52, which supplies spring brake chambers 10 with pressurized air, is coupled to line 232 by a line 252.

The operation of air brake system 180 is generally as follows. Assume system 180 is being used with a vehicle while

the vehicle is in motion and the brakes are off. In this situation service brake chambers 8 are exhausted to atmosphere through quick release valve 44 by the exhausting of air within line 72 through exhaust port 92 of valve 68. Spring brake control valve 78 is deactuated so that the high pressure air in line 74 passes through inlet 76, through outlet 80 and to inlet 226 of pilot control valve 222. Similarly, high pressure air in line 74 is provided to inlet 244 of force control valve 220 through line 246. Force control valve 220 is also deactuated at this time so that inlet 244 is connected to outlet 248 thus pressurizing line 238 and control port 234. Pressurizing line 238 causes supplemental chamber 212 to be pressurized with high pressure air from line 74. In addition, pressurizing line 238 pressurizes control port 234 thus fluidly coupling pilot inlet 226 with pilot outlet 228 so to supply pressurized air to line 232. The high pressure air in line 232 passes through line 252, quick release valve 52 and into spring brake chambers 10. As a result, brake actuator 182 is in the condition of Fig. 3.

Assuming an emergency arises, the vehicle operator can actuate spring brake control valve 78 thus allowing pressurized air within spring brake chambers 10 to pass through lines 56 and quick release valve 52 and into the ambient atmosphere. (The pressurized air can be only partially exhausted to the atmosphere if it is desired to apply the brakes in a controlled manner.) The pressurized air within line 238 remains at the elevated pressure because check valve 224 prevents the pressurized air from passing into line 232. This drives supplemental piston 210 from the position of Fig. 3 to the position of Fig. 5 while permitting actuator spring 206 to force actuator piston 198, and thus push rod 192, to the left in Fig. 3 thus applying the brakes with the force available from actuator spring 206 in the more fully compressed state. After being stopped, with spring brake chamber 10 having already been exhausted to atmosphere, the user can reduce the force exerted on the brakes by push rod 192 by actuating force control valve 244. Doing so couples outlet 248 to exhaust port 250 thus permitting pressurized air in line 238, line 242 and ultimately supplemental chamber 212 to be exhausted into the atmosphere through exhaust port 250 and quick release

valve 240. Doing so permits supplemental piston 210 to move to the right to the position of in Fig. 4 thus reducing the force exerted by actuator spring 206 on actuator piston 198.

Force control valve 220 may be actuated (so to couple outlet 248 to exhaust port 250) while spring brake control valve 78 is deactuated thus continuing to supply pressurized air to pilot check valve 222. Actuating force control valve 220 drops the pressure in line 238 to reduce the pressure at control port 234 thus sealing pilot inlet 226 from pilot outlet 228. However, dropping the pressure in line 238 permits pressurized air in lines 232, 252, 56 and ultimately spring brake chambers 10 to pass through check valve 224 and out exhaust port 250. Thus, actuating force control valve 220 empties both spring brake chamber 10 and supplemental chamber 212 so that the lower, parking brake force is applied to the brakes. Using pilot check valve 222 prevents the unnecessary exhausting of compressed air in line 74, which could otherwise occur if valve 222 were not used in this situation.

The use of two-way check valve 50 is a simple way to prevent or limit compounding in system 2. If desired, system 180 could be modified to prevent the compounding which could occur when both valves 68 and 78 are actuated. For example, a normally closed shut off valve 102, shown in Figs. 6 and 7, could be used to control the exhausting of air through exhaust port 94 of valves 78 and 220. Valve 102 includes a body 104 having an inlet 106 and an outlet 108. A splined piston 110 has a head 112 which slides within the interior 114 of body 104 and a splined end 116b which slides within outlet 108. End 116 has axial splines 118 which guide end 116 within outlet 108 but permit air to easily pass from port 94, through interior 114 and out outlet 108.

Inlet 106 is coupled to line 72 by a connecting line 120. Actuation of valve 68 pressurizes lines 72, 120 so to push piston 110 to the right in Fig. 6 against the bias of a spring 122. Doing so causes rubber seal 124 to slide over and seal exhaust port 94. Therefore, if valve 78 is thereafter actuated, so to couple ports 80, 94, the pressure in line 54 will be maintained since the air in such line will be prevented from

escaping through exhaust port 94. Thus, complete anticompounding is achieved with valve 102 regardless of the pressures applied to service and spring brake chambers 8, 10.

If desired, complete anticompounding may be provided for system 180 using two shutoff valves 102 mounted to valves 78, 220 and coupled to line 72 as suggested in Fig. 6. When valve 68 is actuated, thus applying the service brakes, ports 94, 250 would be sealed to prevent application of the spring brakes in either the emergency mode or parking mode. Diaphragms, bellows, bladders or similar structure could be used in place of sealing pistons 198, 210. For example, a diaphragm, similar to diaphragm 188, could be used within either or both of chambers 10, 212 so to press against spring 206 through piston-like structures as appropriate. This would eliminate the need for sealing rings 215, 217 used with pistons 198, 210.

Other modifications and variations can be made to the disclosed embodiments without departing from the subject of the invention as defined in the following claims. For example, modulated spring brake control valve 78 may be made to be normally biased towards the deactivated position so that the spring brakes will be applied only while the handle of valve 78 is being held by the user. Valve 46 could be used instead of modulated valve 78 if desired. Also, a self-relieving pressure regulator could be used at port 216 to limit the pressure within supplemental chamber 212; this would enable the force on supplemental piston 21 applied by the pressurized air within chamber 212 to be easily adjusted without the need to change any mechanical components of actuator 184.