WO2008097534A1

WO2008097534A1 - Hydraulic control unit for vehicular brake system

Info

Publication number: WO2008097534A1
Application number: PCT/US2008/001497
Authority: WO
Inventors: Christopher Roberts; Westley Wilke
Original assignee: Kelsey-Hayes Company
Priority date: 2007-02-05
Filing date: 2008-02-05
Publication date: 2008-08-14

Abstract

A hydraulic control unit for controlling fluid flow between first and second passageways includes a valve housing having a valve bore defining an axis. The control unit further includes a valve assembly mounted within the bore. The valve assembly carries an annular resilient lip seal having a lip portion moveable between a sealed position wherein the lip portion sealingly engages a cooperating sealing surface of the valve bore when fluid pressure in the first passageway is greater than fluid pressure in the second passageway, and an unsealed position wherein the lip portion is separated from the sealing surface when fluid pressure in the second passageway becomes greater than the fluid pressure in the first passageway to permit fluid flow past the lip seal. The lip seal is further provided with an angled lip and the sealing surface of the valve bore is formed in a frusto-conical manner for cooperating sealing engagement with the angled lip in the sealing position.

Description

TITLE

HYDRAULIC CONTROL UNIT FOR A VEHICULAR BRAKE SYSTEM

Inventors: Westley J. Wilke and Christopher J. Roberts.

BACKGROUND

[001] Various embodiments of a vehicular brake system are described herein. In particular, the embodiments described herein relate to a control valve having an improved lip seal and mounted in an improved hydraulic control unit (HCU) of an electronically controlled brake system. [002] Electronically controlled brake systems for vehicles are well known. One type of electronically controlled brake system includes an HCU connected in fluid communication between a master cylinder and a plurality of wheel brakes. The HCU typically includes a housing containing control valves and other components for selectively controlling hydraulic brake pressure at the wheel brakes.

[003] Control valves for HCU' s are commonly formed as electronically actuated solenoid valves. A typical solenoid valve includes a cylindrical armature slidably received in a sleeve or flux tube for movement relative to a valve seat. A spring is used to bias the armature in an open or closed position, thereby respectively permitting or blocking fluid flow through the valve. A coil assembly is provided about the sleeve. When the valve is energized, an electromagnetic field or flux generated by the coil assembly causes the armature to respectively slide from the biased open or closed position to a closed or open position, respectively.

[004] Control valves mounted in an HCU are actuated by an electronic control module to provide desired braking functions such as anti-lock braking, traction control, and vehicle stability control. To provide desired braking responses, fluid flow must be maintained from the wheel brakes to the master cylinder during all fluid pressure conditions during brake release.

SUMMARY

[005] The present application describes various embodiments of a hydraulic control unit (HCU) for controlling fluid flow between first and second passageways includes a valve housing having a valve bore defining an axis. One embodiment of the HCU includes a valve assembly mounted within the bore. The valve assembly carries an annular resilient lip seal having a lip portion moveable between a sealed position wherein the lip portion sealingly engages a cooperating sealing surface of the valve bore when fluid pressure in the first passageway is greater than fluid pressure in the second passageway, and an unsealed position wherein the lip portion is separated from the sealing surface when fluid pressure in the second passageway becomes greater than the fluid pressure in the first passageway to permit fluid flow past the lip seal. The lip seal is further provided with an angled lip and the sealing surface of the valve bore is formed in a frusto-conical manner for cooperating sealing engagement with the angled lip in the sealing position.

[006] Other advantages of the HCU and lip seal will become apparent to those skilled in the art from the following detailed description, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[007] Fig. 1 is a schematic diagram of a prior art vehicular braking system. [008] Fig. 2 is an enlarged sectional view of a prior art normally closed control valve. [009] Fig. 3 is an enlarged sectional view through a portion of a first embodiment of the HCU of Fig. 1 showing the normally closed control valve in the checked position.

[010] Fig. 4 is an enlarged sectional view of the first embodiment of the

HCU and the normally closed control valve illustrated in Fig. 3, showing the valve under vacuum.

[011] Fig. 5. is an enlarged sectional view of the lip seal shown in Figs. 3 and 4, shown prior to being installed on the control valve.

DETAILED DESCRIPTION OF THE INVENTION

[012] An exemplary vehicular brake system is indicated generally at 10 in Fig. 1. The brake system 10 includes valves and other components described below to provide anti-lock braking (ABS), traction control (TC), and vehicle stability control (VSC) functions.

[013] The exemplary brake system 10 includes a brake pedal 12 connected to a master cylinder 14 for providing pressurized brake fluid to a plurality of wheel brakes 16, only one of which is shown. The wheel brake 16 is schematically illustrated as a disc brake. The wheel brake 16 however, may be any type of wheel brake found on vehicles, including a drum brake. The master cylinder 14 is in fluid communication with a master cylinder brake fluid reservoir 15. The reservoir 15 is a source of brake fluid for the master cylinder 14.

[014] The brake system 10 also includes a hydraulic control unit (HCU) 18 connected in fluid communication between the master cylinder 14 and the wheel brake 16. The HCU 18 includes a housing 19 having bores for receiving control valves and other components described below. Fluid 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 is illustrated in Fig. 1. Typically, however, the HCU 18 also houses corresponding components for other brake circuits and/or wheels of the vehicle.

[015] The HCU 18 includes a normally open control valve 20, commonly known as an isolation valve, disposed between the master cylinder 14 and the wheel brake 16 and at least one low pressure accumulator (LPA) 22. A check valve (not shown) may be disposed in parallel to the isolation valve 20. A normally closed control valve 24, commonly known as a dump valve is disposed between the wheel brake 16 and the LPA 22. A check valve (not shown) may be disposed in parallel to the dump valve 24. A hydraulic pump 26 has an inlet connected to the LPA 22, and a pump discharge connected to the fluid conduit between the master cylinder 14 and the isolation valve 20. The HCU 18 may also include other fluid flow devices such as an attenuator, restricted orifices, and check valves (none of which are illustrated), depending upon the system design.

[016] The illustrated isolation valve 20 and dump valve 24 are formed as solenoid valves switchable between two positions. The valves 20 and 24 include a coil subassembly that creates an electromagnetic flux to slide an internal armature between the two positions. The valves 20 and 24, as well as the pump 26, are electrically connected to an electronic control unit (ECU) (not shown), and operated to provide desired system braking in a well-known manner. The illustrated ECU receives electronic inputs from various sensors (not shown) in the vehicle.

[017] The brake system 10 illustrated in Fig. 1 may be any desired brake system, such as for example, a diagonally split system, wherein the right front wheel RF and the left rear wheel LR are included in a circuit, and the left front wheel (not shown) and the right rear wheel (not shown) are included in a second circuit. Other configurations of the brake system 10 may be provided. [018] A sectional view of a first embodiment of the normally closed control valve 24 is illustrated in Fig. 2. The control valve 24 is received in a bore 30 formed in the housing 19. As described below in detail, the control valve 24 includes a valve body 32 having a valve seat 34 and a flux tube or sleeve 36. As described below in detail, the control valve 24, being a normally closed valve, includes an armature 38 biased toward the valve seat 34 when the control valve 24 is not energized. A coil assembly 40 is disposed about the sleeve 36. When the coil assembly 40 is energized to produce an electromagnetic field, the armature 38 is pulled away from the valve seat 34 to allow fluid flow through the control valve 24.

[019] The valve seat 34 includes a longitudinal (axial in the illustrated embodiment) fluid passage 42 that terminates in a reduced diameter bore 44 extending to an opening 46. A seat 48 is formed on an outer surface of the valve seat 34. In one embodiment, the seat 48 has an angle al within the range of from about three degrees to about five degrees, as measured from a plane P 1 perpendicular to an axis A of the passage 42. In another embodiment, the seat 48 has an angle al of about four degrees. The valve seat 34 may be formed from any desired material, such as polyphenylene sulfide (PPS), polypthalamide (PPA), or polyetheretherketone (PEEK), however such materials are not required. The valve seat 34 can also be formed from any other desired non-ferromagnetic material or ferromagnetic material, such as steel.

[020] In the illustrated embodiment, the sleeve 36 is formed as a single piece from ferromagnetic material, such as steel. The sleeve 36 includes a first ferromagnetic portion defining a closed end portion 50, a second ferromagnetic portion or flux ring portion 52 adjacent the valve seat 34 and defining an open end, and a central portion or region of increased magnetic reluctance 54 between the flux ring portion 52 and the closed end portion 50. The region of increased magnetic reluctance 54 defines a substantially cylindrical outer surface 56. The region of increased magnetic reluctance 54 further defines a sleeve wall having a substantially uniform wall thickness T and an outside diameter Dl .

[021] An annular portion 58 adjacent the open end of the sleeve 36 is crimped onto a radially outwardly extending flange 60 formed on the valve seat 34. In the illustrated embodiment, the sleeve 36 is retained within the bore 30 by clinching, wherein material of the housing 19 is forced into a groove 61 formed in the outer surface of the sleeve 36, as shown in Fig. 2. The valve body 32 (the combined sleeve 36 and valve seat 34) can be retained in the bore 30 by any desired mechanical or chemical means operative to retain the sleeve 36 within the bore 30, such as a threaded engagement. [022] In the illustrated embodiment, the armature 38 is formed from ferromagnetic material, such as steel. The armature 38 can also be formed from other ferromagnetic materials. The armature 38 includes a first end or axial pole face 62, and a second end 64, and has an outside diameter D2. As shown in Fig. 2, the first end 62 and the second end 64 may be generally planar surfaces. The armature 38 is slidably received in the sleeve 36. [023] As shown in Fig. 2, part of the flux ring portion 52 defines a radial magnetic pole 66 for the generally radial transmission of magnetic flux from the armature 38 to the sleeve 36 through a generally radial flux flow path. The radial magnetic pole 66 is defined as the gap between an inside diameter of the sleeve 36 and an outside diameter of the armature 38. [024] As shown in Fig. 2, the outside diameter D2 of the armature 38 is within the range of from about 84 to about 88 percent of the outside diameter Dl of the sleeve 36.

[025] A portion of the closed end portion 50 of the sleeve 36 adjacent the first end 62 of the armature 38 defines an axial magnetic pole 70 for the generally axial transmission of magnetic flux from the closed end portion 50 of the sleeve 36 to the first end 62 of the armature 38 through a generally axial flux flow path. As used herein, a magnetic pole is defined as a region wherein magnetic flux enters and/or leaves a body.

[026] The armature 38 is disposed at an extreme of travel toward the valve seat 34 when the coil assembly 40 is de-energized, such that the control valve 24 is in a closed position, as shown in Fig 2. A spring 72 engages the first end 62 of the armature 38 to urge the armature 38 toward the valve seat 34 when the control valve 24 is in the closed position. When the coil assembly 40 is energized, the armature 38 is disposed at an extreme of travel away from the valve seat 34, such that the control valve 24 is in an open position. [027] When the control valve 24 is in the closed position as shown in Fig. 2, fluid flow through the control valve 24 is blocked. When the control valve 24 is in the open position (not shown), fluid flow through the control valve 24 is not blocked. When the coil assembly 40 is energized, flux flow through the generally axial flux flow path and the generally radial flux flow path at the axial and radial magnetic poles 70 and 66, respectively, generates a force urging the armature 38 from the closed position toward the open position. [028] The second end 64 of the armature 38 acts as a valve sealing element and engages the seat 48 when the armature 38 is in a closed position; e.g. when the coil assembly 40 is not energized. When the second end 64 engages the seat 48, the fluid passage 42 and opening 46 is blocked. When the coil assembly 40 is energized, the armature 38 is pulled away from the valve seat 34 so that fluid can flow through the fluid passage 42 and the opening 46 in the valve seat 34.

[029] The armature 38 provides a responsive, economical element that reciprocates in the sleeve 36 during operation of the control valve 24 to provide desired braking responses in the brake system 10.

[030] An internal band filter 74 may be placed between the sleeve 36 and the valve seat 34, although such is not required. In the illustrated embodiment, the band filter 74 is received in a pocket 76 formed between the sleeve 36 and the valve seat 34.

[031] A lip seal 78 may be provided about an outer diameter of the valve seat 34 in a reduced diameter portion 3OA of the bore 30. Any other desired type of fluid sealing means can also be used.

[032] Referring now to Figs. 3 and 4, and using like reference numbers to indicate corresponding parts, there is illustrated generally at 120, a sectional view of a portion of a first embodiment of an improved lip seal 174 mounted in an improved hydraulic control unit (HCU). As shown in Figs. 3 and 4, the control valve 24 is received in a bore 140 formed in the housing 120.

[033] As best shown in Figs. 3 and 4, the bore 140 bore is formed in a frusto-conical manner. The bore 140 includes a first groove surface or a transverse portion 142 substantially perpendicular to the axis A. The bore 140 further includes a second groove surface or tapered shoulder portion 144 adjacent the transverse portion 142. In the illustrated embodiment, the tapered shoulder portion 144 is disposed at an obtuse angle relative to the transverse portion 142. The transverse portion 142 and the tapered shoulder portion 144 cooperate to define a lip seal groove 146.

[034] In one embodiment, the shoulder portion 144 has an angle a2 within the range of from about 105 degrees to about 135 degrees, as measured from a plane P2 substantially perpendicular to the axis A of the passage 42. In the embodiment illustrated in Figs. 3 and 4, the shoulder portion 144 has an angle a2 of about 120 degrees.

[035] A low-cracking pressure lip seal 174, best shown in Fig. 5, may be provided about an outer diameter of the valve seat 34 and within the lip seal groove 146, such that the lip seal 174 is adjacent the transverse portion 142 and the shoulder portion 144 of the bore 140.

[036] The illustrated lip seal 174 is substantially V-shaped in section, and includes a resilient annular body 176 having an inner circumferential surface 183, a first end 178 (the lower end when viewing Fig. 5), and a second end 180. A resilient annular seal lip 182 includes an outer circumferential surface 184 and flares radially outwardly and upwardly from the body 176 in the general direction of the second end 180.

[037] As described in detail herein, the lip seal 174 may be described as moveable between three positions; (1) a first or static position wherein on forces are acting on the lip seal 174; (2) a second or checked position, wherein the seal lip 182 is supported on the shoulder portion 144, such that fluid is blocked; and (3) a third or under- vacuum position wherein the body 176 and the seal lip 182 are spaced apart from the transverse portion 142 and the shoulder portion 144, respectively, of the lip seal groove 146, such that fluid may flow.

[038] The lip seal 174 is disposed about the outer diameter of the valve seat 34, such that a portion 183 A (upper portion when viewing Figs. 3 and 4) of the inner circumferential surface 183 of the lip seal 174 engages the outer diameter of the valve seat 34 in a light interference fit. The outer circumferential surface 184 of the lip 182 engages shoulder portion 144. Advantageously, the shoulder portion 144 supports the lip 182 when under pressure from fluid (illustrated by the arrow 200) when the control valve 24 is in the checked position as illustrated in Fig. 3. Because the lip 182 of the lip seal 174 is support in the checked position, the lip seal 174 may be formed from an elastomer that is more compliant and pliable, and of a lower grade relative to the elastomers used in the known lip seal 78, shown in Fig. 2. [039] During an evacuation and fill cycle of the control valve 24 installed in the known HCU 19, as illustrated in Fig. 2, the lip seal 78 yields a vacuum differential within the range of from about 227 mm Hg to about 56.4 mm Hg after 10 seconds. Advantageously, when the control valve 24 is installed in the HCU 120, shown in Fig. 3, an improved vacuum differential such as within the range of from about 60.0mm Hg to about 20.0 mm Hg after 10 seconds may be achieved. It has been shown that an optimal vacuum differential is about 50.0 mm Hg after 10 seconds. Accordingly, the structure of the lip seal 174 allows fluid to flow (in the direction of the arrow 202 in Fig. 4) under a lighter vacuum differential relative to the vacuum differential required to cause fluid to flow around the lip seal 78 in the HCU 19.

[040] The fluid pressure (or cracking pressure) required to lift the seal 174 off the transverse portion 142 (upwardly as viewed in Fig. 4) is therefore minimal relative to the fluid pressure required with the known HCU 19 and lip seal 78. Such minimal fluid pressure, such as for example within the range of from about 60.0 mm Hg to about 20.0 mm Hg after 10 seconds, occurs when the control valve 24 is in a reverse fluid flow condition (see the arrow 202 in Fig. 4), such as during evacuation and fill and during an end of an ABS event. [041] Advantageously, the lip seal 174 and the lip seal groove 146 further provide an improvement in LPA 22 fluid evacuation efficiency. In the known HCU 19, if residual fluid is left in the LPA 22 following an ABS and/or "pressure dump" event, a return spring (not shown) of the LPA 22 piston (not shown) is required to push the residual fluid past the dump lipseal 78 and back to the master cylinder 14.

[042] The low cracking pressure lipseal 174 provides two advantages: (1) when the lip seal 174 and the lip seal groove 146 are used in a brake system with a conventional LPA piston return spring, fluid is returned past the lipseal 174 more efficiently relative to a known lipseal 78; i.e., the lip seal 174 and the lip seal groove 146 provides for an improved drain rate in the LPA 22. It has been shown that this advantage or efficient fluid return past the lipseal 174 is particularly beneficial at relatively cold operating temperatures; and (2) the low cracking pressure lipseal 174 may allow for a reduction in the required LPA piston return spring force.

[043] Such a reduction in the required LPA piston return spring force provides the additional advantages: (1) of allowing for a relative less expensive spring having a reduced or lightened load-carrying ability, and a smaller wire diameter relative to a spring in the known LPA 22; and (2) a return spring having a relatively lower spring force allows the braking system to achieve lower "dump" pressures, thereby providing improved/faster wheel recovery. Such lower "dump" pressures are attainable because wheel pressure is "dumped" to the LPA, and the allowable dump-down pressure is dictated by the formula: (spring force x piston area). This advantage is most noticeable with surfaces having a relatively low coefficient of friction and/or vehicles with larger, high inertia, wheels (i.e., when it is very difficult to get the wheel to spin back up and/or recover again).

[044] The combination of the tapered shoulder portion 144 of the bore 140 and the low-cracking pressure lip seal 174 further reduces the amount of air trapped within the HCU 120 during an evacuation and fill cycle. [045] It will be understood that the improved lip seal 174 and/or the improved lip seal groove 146 may be used with valves other than the dump valve 24. For example, the lip seal 174 and/or the lip seal groove 146 may also be used with a supply valve and any other desired valve.

[046] The principle and mode of operation of the HCU and lip seal for a vehicle brake system have been described in its various embodiments. However, it should be noted that the HCU and lip seal described herein may be practiced otherwise than as specifically illustrated and described without departing from its scope.

Claims

CLAIMS What is claimed is:

1. A hydraulic control unit for controlling fluid flow between first and second passageways, the control unit including a valve housing having a valve bore defining an axis, and including a valve assembly mounted within the bore, the valve assembly carrying an annular resilient Hp seal having a lip portion moveable between a sealed position wherein the lip portion sealingly engages a cooperating sealing surface of the valve bore when fluid pressure in the first passageway is greater than fluid pressure in the second passageway, and an unsealed position wherein the lip portion is separated from the sealing surface when fluid pressure in the second passageway becomes greater than the fluid pressure in the first passageway to permit fluid flow past the lip seal, characterized in that the lip seal is provided with an angled lip and the sealing surface of the valve bore is formed in a frusto- conical manner for cooperating sealing engagement with the angled lip in the sealing position.

2. The hydraulic control unit according to claim 1 wherein the lip seal includes an inner portion connected to the lip portion and sealingly engaging an outer cylindrical surface of said valve assembly, the lip seal being capable of axially shiftable movement along the valve assembly when the lip portion moves between the sealed and unsealed positions.

3. The hydraulic control unit according to claim 2 wherein the valve housing or the valve assembly are provided with abutment surfaces for engagement with the inner portion to limit the axial movement of the lip seal along the valve assembly.

4. The hydraulic control unit according to claim 2 wherein the valve housing is provided with an abutment surface for engagement with the inner portion to limit axial movement of the lip seal in the sealed position.

5. The hydraulic control unit according to claim 2 wherein the valve assembly is provided with an abutment surface for engagement with the inner portion to limit axial movement of the lip seal in the unsealed position.

6. The hydraulic control unit according to any of claims 1 to 5 wherein the conical sealing surface is formed at an angle in the range from about 45 degrees to about 75 degrees relative to the bore axis.

7. The hydraulic control unit according to claim 6 wherein the conical sealing surface is formed at an angle of about 60 degrees.

8. The hydraulic control unit according to any of claims 1 to 7 wherein the lip portion is operative to move from the sealed position to the unsealed position when a fluid differential pressure between the second and first passageways is in the range of about 60 mm Hg to about 20 mm Hg.

9. The hydraulic control unit according to claim 8 wherein the fluid differential pressure is about 50 mm Hg.

10. The hydraulic control unit according to any of claims 1 to 9 wherein the valve assembly is an electromagnetic valve.

11. The hydraulic control unit according to any of claims 1 to 10 wherein the hydraulic control unit is adapted to form part of hydraulic vehicle brake system.