DAMPED HIGH PRESSURE FLUID PUMP

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to provisional patent application Serial No. 60/005, 125 filed October 12, 1995.

BACKGROUND OF THE INVENTION This invention relates in general to vehicular braking systems, and in particular to high speed, high pressure hydraulic pumping units, particularly opposed piston-type pumps for use in vehicular anti-lock braking systems ("ABS") including those having integrated traction assist ("TA") features, e. g., ABS/TA pumps. In conventional ABS in use on vehicles today, there is generally provided an electric motor-driven opposed piston-type pumping unit for supplying pressurized brake fluid to any one ofthe brakes on instant, automatically controlled demand. The electrically-driven motor is a part ofthe ABS unit and includes a driveshaft which will include one or more cam lobes. Transversely disposed ofthe driveshaft, generally at 180° from one another, are a pair of pumping pistons within a respective pump body. The output of each pumping piston provides high pressure brake fluid, generally in the order of 2500 psi, to a respective segment ofthe braking system. In other words, in a conventional braking system for a four-wheel vehicle, the braking system is divided into two separate braking segments beginning at a dual-chambered master cylinder. Each segment provides the braking force to a predetermined pair of wheels. One segment may be to the left front - right rear wheels, for example, while the other segment provides the braking power to the right front -left rear wheels. In this way, the vehicular braking system is generally considered fail-safe in that if

braking pressure were for any reason to be lost to one segment or pair of wheels, the remaining half of the brake system would be functional and sufficient to bring the vehicle under control. The ABS system is typically integrated into the vehicular braking system in the same manner, thereby providing anti-lock braking characteris- tics from each ofthe pair of pumping units to a respective one ofthe braking system segments. Likewise, traction assist capabilities are commonly added to the ABS system in such a manner as to use the pump output for applying brake pressure to a wheel or wheels to preclude wheel slip. This means increased use ofthe common pump, and added concern for the cost, performance attributes ofthe pump. Due to the performance demanded ofthe ABS unit, it is important that the pumping unit provide high pressure brake fluid to the system as efficiently and quickly as possible. Further, it is important that manufacturing costs be minimized and that performance reliability be maximized.

It is also important that the overall noise or decibel levels ofthe operating pump be kept to a πiinimum so as to be imperceptible to the operator. While braking situations requiring employment ofthe ABS/TA system are relatively infrequent, it is common practice to provide a diagnostic check ofthe system ,including operating momentarily the hydraulic pumps, each time the vehicle is started. It is important that the operator ofthe vehicle, when first starting the vehicle, not be concerned in any way with noise generated from the brake diagnostic checking system.

SUMMARY OF THE INVENTION This invention relates to a vehicular braking system and in particular to a hydraulic pump for use in a vehicular braking system, including an anti-lock braking system or a traction assist braking system, or both, operatively coupled therewith. The noise levels associated with this pump are j-nimized to as not to cause a distraction to an operator of a vehicle.

In a preferred embodiment, a vehicle braking system includes a hydraulic reciprocateably driveable dual-piston type pump. The pump is enclosed in a housing having a cavity for receiving a driveshaft. The system further includes a motor having an output driveshaft. The driveshaft has a cam for continuously engaging and driving the pump on demand. The cam extends into the cavity, and the cavity is filled with a viscous fluid. The viscous fluid dampens out noise that is generated by power transfer of inefficiencies when the motor drives the pump piston under load.

The advantages accruing to the present invention are numerous. For example, noise generated from the brake diagnostic checking system is damped by the viscous fluid in accordance with the present invention.

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 sectional view of an ABS/TA hydraulic control unit housing illustrating a first embodiment of a pump assembly in accordance with this invention.

Fig. 2 is a sectional view of an ABS/TA hydraulic control unit housing illustrating a second embodiment of a pump assembly in accordance with this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, there is illustrated in FIG. 1 a particular construction of a reciprocating dual-piston type pump assembly 10 of the present invention. The pump assembly 10 includes a hydraulic control unit (HCU) 12 formed as a housing to receive valves and other components. A pair of opposed pumping units 14 (each having a pump piston 24 and sleeve 26 assembly described

below) is concentrically received within a stepped counterbore 16 formed within the housing 12. Each pumping unit 14 is held axially in place within the housing 12 by means of an O-ring seal 17, a retaining plug type check valve assembly 18, and an end cap 20 which is threadily secured to housing 12 and bears against an end ofthe valve assembly 18, forcing it to seat a sleeve 26 upon one ofthe shoulders 22 within the stepped counterbore 16. To facilitate an understanding ofthe present invention, both pumping units 14 of dual-piston type pump assembly 10 are shown to be identical. It should be appreciated that in other embodiments, unlike the construction of FIG. 1, the pumping units 14 do not need to be identical. Each pumping unit 14 includes a piston 24 concentrically received in slidmg engagement with a sleeve 26. The piston 24 includes a drive or pilot section at one end operating off of a cam bearing surface 28 mounted on a driveshaft 27 of an electric motor 29 which is bolted at flange 31 to the housing 12. Each pump unit 14 has a pump section at its other end. The electric motor driveshaft 27 extends through a counterbored cavity 30 deiiiing with the housing 12 a heretofore urifilled (or air filled) motor bearing cavity 32. An O-ring 33 seals motor bearing cavity 32. With continuing reference to FIG. 1, a piston head 36 is provided at the pilots section of piston 24. Piston head 36 rides on cam bearing surface 28 ofthe driveshaft 27. Sleeve 26 has a bore defining a pump chamber 38 of the pumping unit 14. The pump end of piston 24 has a bore defining an inlet passage 40. Inlet passage 40 provides a seat 42 upon which is seated a ball valve 44, described below. In open communication with the fluid inlet passage 40 is a transversely oriented fluid inlet 46 which is an open fluid communication with an annular chamber defined by an annular groove 48 about the circumference of piston 24. The axial length ofthe annular groove 48 is such that it will always provide fluid communication through the sleeve 26 with an inlet passageway 50 formed in the housing 12.

Pump chamber 38 is closed at its other end by a ball valve travel limiting member 52 which additionally functions as a retainer for the coil type ball valve

return compression spring 54 which lightly maintains the ball valve 44 on seat 42 under a negligible force.

The pump assembly 10, other than the sleeve 26 and piston 24, which are preferably carbonized steel and springs 52 which are also steel, is preferably formed from aliiminum or other light weight alloy. Travel limiter 52 includes a concentrically located through port 60, and a stop shoulder 62 for engaging the ball valve 44. Sleeve 26 includes an open ended section at its one end nearest to the driveshaft 27 which is slidingly received within the least diameter section of stepped counterbore 16. This section includes an annular O-ring groove 70 for receiving an O-ring 72 to seal that end of the sleeve 26 from the low pressure brake fluid corning through inlet passage 50 to the pumping unit 14. The closed end ofthe sleeve 26 forms a seat 74 upon which a coil type compression spring 76 is captured between sleeve 26 and piston 24. At this end of sleeve 26, there is provided a radially extending O-ring flange 78 having an annular groove therein for receiving an O-ring 80. O-ring flange 78 provides a shoulder against which the sleeve 26 may be seated relative to housing shoulder 22, as earlier described. Fluid chamber 82 is provided between housing 12 and sleeve 26 near inlet passageway 50 as defined by a section of stepped counterbore 16 intermediate the open end and the closed end.

With continuing reference to FIG. 1, piston 24 has an annular groove 84 which receives an O-ring 86 which acts a seal between piston 24 and the open ended section of sleeve 26. Sleeve 26 further includes a low pressure inlet port 88 at its mid section communicating with housing 12, fluid inlet passageway 50, and transverse fluid inlet 46, as previously described. At the pump end ofthe sleeve 26, there is provided a ball valve 96 compressively seated against sleeve 26 by plug spring 98. Pump chamber outlet port 64 is in fluid communication with fluid chamber 100. An O-ring 102 is received in annular groove 104 formed about assembly 18, thereby acting as a seal for fluid chamber 100. An outlet passage way

106 formed in the housing 12 is in fluid communication with the annual fluid chamber 100 via outlet port 64.

In operation, the pump unit operates in a manner described earlier. Thus, when for example, wheel slip is sensed and the traction system is activated, low pressure fluid will be present at inlet passageway 50, and the sleeve 26 and pumping unit 14 will be generally filled. The pump unit 14 may be primed initially from a low pressure accumulator (not illustrated), but otherwise will suck fluid from a master cylinder (not illustrated) until the system is brought out to full outlet pressure. Within the single pump unit 14, as cam bearing surface 28 strokes piston 24 from no lift to maximum Uft, ball valve 44 will be forced into engagement with the seat 42 by fluid pressure by pump chamber 38 plus the spring force, and highly pressurized fluid will flow through port 64, unseating ball valve 96 and continuing to the housing outlet passageway 106 to provide braking force to a wheel.

On the downstroke, maximum lift to no hft, ball valve 96 will close under force ofoutlet spring 98. Also, ball check valve 44 will be momentarily lifted from seat 42 until its travel is stopped by stop shoulder 62 of travel limited 52. Then, when at or nearly at the no Uft point of crank shaft rotation, the force of spring 54 will be sufficient to return ball 44 to the seat 42. Then, pumping unit 14 may cycle again. Motor bearing cavity 32 is filled with a viscous fluid The viscous fluid dampens out noise that is generated by power transfer of inefficiencies when the motor 29 drives pump pistons 24 under load. In a preferred configuration, the viscous fluid is a has a viscosity of at least 50 centistokes. Glycerin or other gels are acceptable. A conventional silicon base lubricant, such as used to lubricate the ABS TC components, (e.g., the pump pistons 24) as part of standard assembly procedures, is quite acceptable, as is a 30 weight motor oil. By filling the motor bearing cavity 32 with high viscosity fluid, instead of air which is the convention, applicant has noted a substantial reduction in noise levels ofthe system.

A second embodiment of a reciprocating dual-piston type pump assembly 1 10 according to this invention is illustrated in FIG. 2. The pump assembly 1 10 includes a hydraulic control unit (HCU) 1 12 formed as a housing. The housing 1 12 includes bores for receiving valves and other components of a vehicular braking system. A pair of opposed pumping units 114 are received concentrically within a stepped counterbore 1 16 formed in the housing 112. The pumping units 1 14 are preferably positioned 180 degrees from one another. While each pumping unit 1 14 is illustrated as identical to the other pumping unit 1 14, such units do not have to be identical. Each pumping unit 1 14 includes a piston 124 concentrically received in sliding engagement with a hollow, cylindrical sleeve 126. Each piston 124 includes an inwardly directed drive or pilot section in contact with a cam 128. The cam 128 is mounted on a driveshaft 127 of an electric motor 129. The motor 129 is secured to the housing 1 12 by bolts (not illustrated) passing through respective apertures (not illustrated) in a mounting flange 131.

The motor 129 extends into a counterbored cavity 130 formed in the housing 1 12. An O-ring 133 is received in an annular groove 134 formed about the motor 129 and acts as a fluid seal between the motor 129 and the housing 1 12. The driveshaft 127 and the cam 128 extend into a cam cavity 132, wherein the cam 128 engages the reciprocable pistons 124.

Each sleeve 126 includes an annular groove 170 receiving an O-ring 172 to provide a seal between a sleeve 126 and the housing 1 12. Each piston 124 includes an annular groove 184 receiving an O-ring 186 to provide a seal between a piston 124 and a sleeve 126. Viscous fluid is contained in the cam cavity 132. Preferably, the viscous fluid substantially fills the cam cavity 132 and dampens noise which is generated as the motor 129 drives the pump assembly 110, particularly when loaded. As stated above for motor bearing cavity 32, the preferred viscous fluid has a

viscosity of at least 50 centistokes. A substantial reduction of noise from the pump assembly 110 has been achieved when the cam cavity 132 is filled with viscous fluid when compared to an empty (air-filled) cam cavity 132.

In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiments. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.