HYDRAULIC CONTROL UNIT WITH FLUID COMPENSATOR TO ACCOMMODATE TRAVEL OF MASTER CYLINDER PISTON

Abstract: A fluid compensator (100, 225, 325) is provided in a hydraulic control unit (18, 218, 318) of vehicular brake system (10, 200). The fluid compensator permits additional displacement of a master cylinder piston during anti-lock braking events only by storing fluid in the hydraulic control unit (18, 218, 318). The additional displacement moves a seal mounted on the master cylinder piston away from a compensator port orifice, thereby preventing repeated "nibbling" of the seal which can cause premature seal failure.

Description: 1 TTΠ E HYDRAULIC CONTROL UNIT WITH FLUID COMPENSATOR TO ACCOMMODATE TRAVEL OF MASTER CYLINDER PISTON BACKGROUND OF THE INVENTION This invention relates in general to vehicular brake systems, and in particular is concerned with a fluid compensator provided in a hydraulic control unit to accommodate travel of a master cylinder piston- Hydraulic braking systems for vehicles are well known. A typical hydraulic brake system includes a master cylinder, fluid conduit ^ranged into a desired circuit, and wheel brakes. The master cylinder generates hydraulic forces in the fluid circuit by pressurizing brake flmd when the driver steps on the brake pedal. A piston in the master cylinder travels in response to the brake pedal. The pressurized fluid travels through the fluid conduit in the circuit to actuate brake cylinders at the wheel brakes and slow the vehicle. Anti-lock braking systems (ABS) for vehicles are also well known hydraulic systems. A hydraulic control unit HCU) or housing, containing control valves and other components such as control valves and pumps, is located between the master cylinder and the wheel brake assemblies. Through an electronic controller, the control valves and other components selectively control pressure to the wheel brake assemblies to provide a desired braking response of the vehicle. A seal is provided about the master cylinder piston. Preferably, this seal is formed as a one-way seal commonly known as a lip seal. During a braking event, this seal can be positioned nearby a compensation port orifice of the master cylinder. Repeated passes of a seal holding pressurized fluid across the compensation port orifice as the master cylinder piston is stroked can result in deterioration of the seal and shortened effective life of the seal. Known braking 2 systems can provide additional displacement of the master cylinder piston to move the seal away from the compensation port orifice, but such systems add extra pedal stroke to every braking event, i.e., normal (base) braking as well as anti-lock braking. Additional pedal stroke is generally not desired in many brake systems. SUMMARY OF THE INVENTION This invention includes a fluid compensator provided in a hydraulic control unit of vehicular brake systems. The fluid compensator permits additional displacement of a master cyhnder piston during anti-lock braking events only by storing fluid in the hydraulic control unit. The additional displacement moves a seal mounted on the master cylinder piston away from a compensator port orifice, thereby preventing repeated 'nibbling" of the seal which can cause premature seal failure. One advantage provided by this fluid compensator is that additional pedal stroke is not present during normal base braking, since this fluid compensator has no effect during normal braking. The fluid compensator is provided in a hydraulic control unit and can be used with many variations of anti-lock brake systems. In a first preferred embodiment, a fluid compensator to accommodate piston displacement of a master cylinder in a vehicular brake system includes a body formed from a resilient material having a gas trapped in pores. The body includes a fluid impermeable outer surface. The body can be positioned in a bore of an attenuator downstream of a pump outlet As fluid enter the bore, the body compresses to permit additional displacement of a master cylinder piston. In a second preferred embodiment, a fluid compensator to accommodate piston displacement of a master cylinder in a vehicular braking system includes a fluid chamber formed between an end wall of a bore mounting a slidable piston in a low pressure accumulator and a seal mounted about the piston. A fluid 3 passageway intersects a side wall of the bore at a predeteπnined distance away from the end wall. At predeteπnined positions of the piston, fluid flow out of the fluid chamber is restricted as a suction force from a pump inlet draws the piston against the fluid passageway. In a third preferred embodiment, a fluid compensator is formed in a manner similar to the second embodiment with the inclusion of an undercut provided about an outer surface of the piston. The undercut increases the annular restriction between the piston and the bore at the area where the fluid passageway intersects the side wall. Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic circuit diagram of a vehicular brake system according to this invention illustrating a first embodiment of a fluid compensator provided on a high pressure side of a pump in a hydraulic control unit FIG. 2 is a sectional view through the fluid compensator of FIG. 1. FIG. 3 is a schematic circuit diagram of a vehicular brake system according to this invention illustrating a second embodiment of a fluid compensator provided on a low pressure side of a pump in a hydraulic control unit. FIG. 4 is a sectional view through a third embodiment of a fluid compensator according to this invention provided on a low pressure side of a pump in a hydraulic control unit. 4 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A vehicular brake system according to this invention is indicated generally at 10 in FIG. 1. System 10 includes valves and other components described below to provide anti-lock braking functions. In other embodiments, system 10 can also include components to provide traction control functions and/or vehicle stability control functions. In system 10, a brake pedal 12 is connected to a master cylinder 14 to provide pressurized brake fluid to a wheel brake 16. In the embodiment illustrated in FIG. 1, the wheel brake 16 is illustrated as a disc assembly; however, wheel brake 16 may be any type found on vehicles. As is well known in the art, the master cylinder 14 includes a piston (not illustrated) which moves in response to application of the brake pedal 12. The master cylinder piston (not illustrated) includes seals (not illustrated) which separate fluid into various chambers in the master cylinder 14. It is known to use Up seals about the master cylinder piston- A hydraulic control unit (HCU) 18 is a housing having bores for receiving control valves and other components described below. Fluid passageways or conduits are provided between the bores to provide fluid communication between the valves and other components. For purposes of clarity of illustration, only one set of components are illustrated in the schematic of FIG. 1. However, it is understood that the HCU 18 can also house corresponding components for other circuits and/or wheels of the vehicle. The HCU 18 includes a normally open control valve 20, commonly referred to as an isolation valve, and a normally closed control valve 22, commonly known as a dump valve, disposed between the master cylinder 14 and the wheel brake 16. A low pressure accumulator 24 is disposed between the dump valve 22 and a reciprocating hydraulic pump 26. The pump 26 is driven by an electric motor (not illustrated) in a well known manner. A fluid 5 compensator 100, described in detail below, is provided in the HCU 18 between an outlet of the pump 26 and an inlet to the isolation valve 20. In tins position, the fluid compensator 100 can be said to be mounted on a high pressure side of the pump 26. 5 The isolation valve 20 is preferably formed as a solenoid valve switchable between two positions. The dump valve 22 is preferably formed as a solenoid valve switchable between two positions. Valves 20 and 22, as well as pump 26, are electrically connected to an electronic control module (not illustrated) and operated to provide desired braking in a well known manner. i o A schematic sectional view of a portion of the HCU 18 is presented in FIG. 2. As stated above, the HCU 18 is formed as a housing containing valves and other components described below. The HCU 18 includes bores for receiving die isolation valve 20, the dump valve 22, the low pressure accumulator 24, and the fluid compensator 100. The fluid compensator 100 15 accommodates additional displacement of a master cylinder piston (not illustrated) during anti-lock braking only, thereby moving seals of the master cylinder piston away from a compensator port orifice (not illustrated) of the master cylinder 14. The fluid compensator 100 is mounted in the HCU 18 that can be used 0 with various anti-lock brake systems. A bore 102 is provided in the HCU 18. The bore 102 and its interior volume can be referred to as an attenuator to damp fluid pulses entering the bore 102. A resilient body 104 is fitted within the bore 102. The body 104 is retained within the bore 102 by an end plug 106. The end plug 106 is secured to the HCU 18 by any desired means. 5 The body 104 can be formed as a molded member having an interior portion 108 having at least one pore or cavity 110. A membrane 112 is provided about the outer surface of the interior portion 108. The membrane 112 is formed from a material that prevents brake fluid from penetrating the porous interior 6 portion 108. The pores 110 are filled with a suitable trapped gas. The interior portion 108 and die membrane 112 are formed from suitable resilient materials- The body 104 can be formed by a method that utilizes a controlled porosity in a thermal plastic injection molding process. In such a process, closed-cell foaming agents are utilized during an injection process to produce controlled porosity (resulting in pores 110) in die interior portion 108. The pores 110 can be limited in size to provide controlled fluid displacement during ABS mode (to provide d e master cyhnder seal saver function). Also, porosity effectively reduces d e bulk modulus of die body 104, resulting in improved noise damping properties. The body 104 can also be formed by other means that produce a resilient interior portion having trapped gas. For example, a fluid impermeable outer surface of the body 104 can be integrally formed with the interior portion 108 having a lower modulus. The fluid compensator 100 is preferably located adjacent an outiet 113 of the pump 26 and adjacent an inlet 114 of a passageway 116 which leads to die isolation valve 20 (not illustrated in FIG. 2). Preferably, an end of die body 104 adjacent die outlet 113 is reduced. A restricted orifice 118 is preferably provided between bore 102 and the inlet 114. Preferably, a one-way check valve 120 is provided at the inlet 114. Naive 120 permits fluid flow from die fluid compensator 100 to the isolation valve 20 but not in the opposite direction The check valve 120 can be formed by a ball 122 retained by cold stakes 123 at one end of die inlet 114. A valve seat 124 is provided in die inlet 114 for seating the ball 122 to prevent fluid from flowing into the restricted orifice 118 from passageway 116. When system 10 is operating in normal braking (i. e. , not an ABS mode), die fluid compensator 100 has no effect on the system 10 as fluid from the master cylinder 14 is checked by die check valve 120. Thus, the fluid compensator 100 does not affect pedal stroke. 7 When the system 10 is operating in an ABS mode, i.e., when pump 26 is pumping brake fluid, die fluid compensator 100 permits die master cylinder 14 to continue to travel, thereby moving a seal of the master cylinder piston away from a compensator port orifice. As the pump 26 forces fluid into bore 102, body 104 compresses as its pores 110 collapse upon tiiemselves. Thus, additional fluid is stored within the borel02, and not routed to the master cylinder 14. When the pump 26 stops operating (i.e., when an ABS event is complete), the resilient body 104 expands to its approximate original configuration. The additional fluid tiiat had been stored in die bore 102 is returned to die master cylinder 14. As stated above, the resilient body 104 also improves noise damping in system 10 as fluid pulses exit the pump 26. The relatively soft interior portion 108 collapses as fluid enters bore 102 from the pump outiet 11 . A second embodiment of a vehicular brake system according to this invention is indicated generally at 200 and illustrated in Fig. 3. System 200 includes valves and other components described below to provide an anti-lock braking function In other embodiments, system 200 can also include components to provide traction control and vehicle stability control functions. In system 200, a brake pedal 212 is connected to a master cylinder 214 to provide pressurized brake fluid to a wheel brake 216. In the embodiment illustrated in FIG. 3, the wheel brake 216 is illustrated as a disc assembly; however, die wheel brake 216 may be any type found on vehicles. As is well known in the art, the master cylinder 214 includes a piston (not illustrated) which moves in response to application of die brake pedal 212. The master cylinder piston includes seals that separate fluid into various chambers in the master cylinder 214. It is known to use tip seals about die master cyhnder piston. A hydraulic control unit (HCU) 218 is a housing having bores for receiving control valves and other components described below. Fluid conduits 8 are provided between the bores to provide fluid communication between die valves and other components. For purposes of clarity of illustration, only one set of components are illustrated in die schematic of FIG. 3. However, it is understood tiiat the HCU 218 can also house corresponding components for other circuits and/or wheels of the vehicle. The HCU 218 includes a normally open control valve 220, commonly referred to as an isolation valve, and a normally closed control valve 222, commonly known as a dump valve, disposed between the master cylinder 214 and the wheel brake 216. A low pressure accumulator (LPA) 224 is disposed between die dump valve 222 and a reciprocating hydraulic pump 226. The pump 226 is driven by an electric motor in a well known manner. As described below, die LPA 224 includes a fluid compensator 225 that improves the operating life of seals mounted on a piston in the master cylinder 214. The isolation valve 220 is preferably formed as a solenoid valve switchable between two positions. The dump valve 222 is preferably formed as a solenoid valve switchable between two positions. Valves 220 and 222, as well as pump 226, are electrically connected to an electronic control module (not illustrated) and operated to provide desired system braking in a well known manner. The LPA 224 includes a bore 232 formed in die HCU 218. A cup-shaped piston 234 is slidably mounted in die bore 232. A spring 236 biases the piston 234 away from an end cap 238 that closes die bore 232. The end cap 238 can be retained in any desired manner. A seal 240 is received in a groove formed in an outer surface of the end cap 238 to seal the bore 232. A seal 242 is received in an groove formed in an outer surface of die piston 234. The fluid compensator 225 includes a fluid chamber 244 formed between an end wall 246 of the bore 232 and seal 242 placed about die piston 234. Fluid is routed to die chamber 244 via a passageway 248 intersecting a side wall 250 9 of the bore 232. The passageway 248 is spaced a predetermined distance away from the end wall 246. At predetermined positions of the piston 234, the piston 234 restricts fluid flow into and out of d e chamber 244. At outer predetermined positions of the piston 234, fluid travels freely into and out of die chamber 244 via passageway 248. Some fluid from me first few dump pulses remains in die chamber 244 during an ABS event During an ABS event, i.e., when die pump 226 is operating, a suction force to the pump inlet is generated in passageway 248. The suction force is applied against a side of die piston 234 and pulls die piston 234 against the side wall 250, thereby restricting fluid flow through passageway 248, and reducing fluid flow to the pump 226. This feature insures that a predetermined amount of fluid will be delayed (at least until die next dump sequence) in chamber 244 prior to returning to die master cylinder 14 during d e remainder of an ABS event. This storage of fluid in die HCU 18 provides a seal saver function for a seal on a master cylinder piston, since the stored fluid does not displace the master cylinder piston. Once the pump 226 is deactivated, i.e. , after an ABS event is completed, piston 234 will recenter in die bore 232, allowing fluid trapped in chamber 244 to drain out over lip seals (not illustrated) in the dump valve 222. When die system is operating in normal braking (i.e., not an ABS event), the fluid compensator 225 has no effect on die system 200. When the system 200 is operating in an ABS mode, i.e., when pump 226 is operating, die fluid compensator 225 permits a master cylinder piston to travel so that seals will be moved away from compensator ports in the master cylinder 14. A third embodiment of a fluid compensator according to this invention is indicated generally at 325 in FTG. 4. A low pressure accumulator (LPA) 324 is disposed between a dump valve (not illustrated) and a reciprocating hydraulic pump (not illustrated) in a hydraulic control unit (HCU) 318 in a manner similar 10 to corresponding elements of system 200 illustrated in FIG. 3. The LPA 324 includes a bore 332 formed in the HCU 318. A cup-shaped piston 334 is slidably mounted in the bore 332. A spring 336 biases die piston 334 away from an end cap 338 that closes the bore 332. The end cap 338 can be retained onto die HCU 318 in any desired manner. A seal 340 is received in a groove formed in an outer surface of die end cap 338 to seal the bore 332. A seal 342 is received in a groove formed in an outer surface of die piston 334. The fluid compensator 325 includes a fluid chamber 344 formed between an end wall 346 of the bore 332 and the seal 342 placed about die piston 334. Fluid is routed to the chamber 344 via a passageway 348 intersecting a side wall 350 of die bore 332 The passageway 348 is spaced a predetermined distance away from the end wall 346. At predetermined positions of die piston 334, fluid is restricted from entering and exiting in the chamber 344. At otiier predetermined positions of die piston 334, fluid travels freely into and out of d e chamber 344 via passageway 348. An undercut or groove 352 is provided in an outer surface of die piston 334. Preferably, the undercut 352 is formed along a portion of the length of the piston 334 spanning die distance indicated at B in FIG. 4. The undercut 352 is formed between a portion of die length of die piston 334 indicated at A and between a portion of die piston 334 mounting seal 342. The undercut 352 improves the first dump performance by reducing die annular restriction between the piston 324 and die bore 332. The time to drain fluid trapped in chamber 344 at the end of an ABS event is reduced by minimizing the length of surface A and by maximizing the length of surface B. When a brake system is operating in normal braking (i.e., not an ABS event), the fluid compensator 325 has no effect on the system. When me system is operating in an ABS mode, i.e., when a pump operating, the fluid compensator 11 325 permits a master cylinder piston to travd so that seals will be moved a a from compensator port orifices in the master cylinder . In accordance with the provisions of the patent statutes, die principle and mode of operation of this invention have been explained and illustrated in its preferred embodiments. However, it must be understood tiiat this invention may be practiced otiierwise than as specifically explained and illustrated without departing from its spirit or scope.

Claims: 12 CLAIMS What is claimed is: 1. A fluid compensator to accommodate piston travd of a master cylinder in an anti-lock braking system, die compensator assembly comprising: a hydraulic control unit mounting a pump; and a fluid compensator formed by a compressible body provided downstream of me pump outlet 2. The fluid compensator defined in daim 1 wherein the fluid compensator includes a body formed from a resilient material having trapped gas in pores. 3. The fluid compensator defined in daim 2 wherein the body indudes a fluid impermeable outer surface. 4. A fluid compensator to accommodate piston travd of a master cylinder in an anti-lock braking system, the compensator assembly comprising: a hydraulic control unit mounting a pump; and a fluid compensator provided upstream of a pump inlet. 5. A fluid compensator to accommodate piston travd of a master cylinder in an anti-lock braking system, the compensator assembly comprising: a hydraulic control unit mounting a pump; and a low pressure accumulator having a slidable piston provided upstream of a pump inlet, wherein a fluid passageway is formed in a side wall of a bore which receives the piston so that a fluid chamber formed between an end wall of O 99/38740 13 the bore and the piston to restricts fluid between the piston and an end wall when a pump is operated. 6. The fluid compensator defined in claim 5 wherein die piston 5 includes an undercut in its outer surface which is in fluid communication with the passageway in die side wall of the bore during predetermined positions of the piston- 7. A vehicular brake system substantially as herein described witii l o reference to the accompanying drawings.

Inventors: CASSIDY JOHN M, KING JEFFREY, KNIGHT GARY R, SORENSEN RONALD L, TARDIFF PATRICK J, CASSIDY, JOHN, M., KING, JEFFREY, KNIGHT, GARY, R., SORENSEN, RONALD, L., TARDIFF, PATRICK, J.
Applicants: CASSIDY JOHN M, KELSEY HAYES CO, KING JEFFREY, KNIGHT GARY R, SORENSEN RONALD L, TARDIFF PATRICK J, CASSIDY, JOHN, M., KELSEY-HAYES COMPANY, KING, JEFFREY, KNIGHT, GARY, R., SORENSEN, RONALD, L., TARDIFF, PATRICK, J.
Application year: 1999
Main classification: B60T8
IPC codes: B60T8