BACKGROUND OF THE INVENTION This invention relates in general to a hydraulic control unit (HCU) for use in a vehicular anti-lock brake system (ABS). More specifically, this invention relates to a HCU having a pair of normally open control valves for controlling fluid pressure to a corresponding wheel brake during an ABS event.

An ABS monitors wheel rotation and selectively reduces, increases and holds the braking pressure to a particular wheel brake in order to maximize the braking pressure while maintaining the wheel speed within a designated slip range.

A typical ABS comprises a HCU including control valves for controlling the pressure to corresponding wheel brakes. The control valves are comprised of a plurality of normally open solenoid valves and a plurality of normally closed solenoid valves. The normally open solenoid valves or isolation valves modulate the flow of hydraulic fluid to the corresponding wheel brakes by switching between a normally open position and a closed position. The normally closed solenoid valves or dump valves modulate the flow of hydraulic fluid from the corresponding wheel brakes by switching between a normally closed position and an open position. The HCU further includes a pump for transferring hydraulic fluid from the dump valves to the isolation valves during an ABS event. The isolation and dump valves work in concert to control wheel

brake pressures. The isolation valves allow fluid to flow to the corresponding wheel brake when in the normally open position. Conversely, the isolation valves prevent fluid from flowing to the corresponding wheel brakes when in the closed position. In contrast, the dump valves prevent fluid flow from the corresponding wheel brake when in the normally closed position. Conversely, the dump valves allow fluid to flow from the corresponding wheel brakes when in the open position. In order to reduce the pressure to a particular wheel brake, the isolation and dump valves corresponding to the particular wheel brake are placed in the closed position and the normally open position, respectively. This arrangement prevents fluid from flowing to the particular wheel brake while allowing the pump to draw fluid from the particular wheel brake, thereby reducing the pressure to the particular wheel brake. In order to increase the pressure to a particular wheel brake, the isolation and dump valves corresponding to the particular wheel brake are placed in the normally open position and the normally closed position, respectively. This arrangement prevents fluid from flowing from the particular wheel brake while allowing additional fluid to be supplied to the particular wheel brake, thereby increasing the pressure to the particular wheel brake. In order to maintain the existing pressure to a particular wheel brake, the isolation and dump valves corresponding to the particular wheel brake are placed in the closed position and the normally closed position, respectively. This arrangement prevents fluid from flowing to the particular wheel brake from the isolation valve and from the particular wheel brake to the dump valve provided that the force applied to the brake pedal is not reduced, thereby holding the pressure to the particular wheel brake.

A noted concern associated with the HCU of the typical ABS involves the evacuation and fill procedure required to make the ABS ready for use.

When installing the ABS to a vehicle and/or when making repairs to an installed ABS, the air in the ABS must be removed and hydraulic fluid must added to the ABS. However, in order to perform the evacuation and fill of the ABS the

dump valve of the HCU must be switched from the normally closed position to the open position. This switching requirement adds to the time and cost to perform the evacuation and fill procedure. Additionally, equipment for switching the position of dump valve must be made available.

Furthermore, there is an on-going objective to reduce the cost of the HCU.

SUMMARY OF THE INVENTION This invention concerns a hydraulic control unit for use in a vehicular anti-lock brake system. The hydraulic control unit includes a housing having desired bores and fluid conduits. A plurality of first control valves are disposed in the housing for modulating the flow of hydraulic fluid to a plurality of corresponding wheel brakes during an anti-lock brake system event. A plurality of second control valves are disposed in the housing for modulating the flow of hydraulic fluid from a plurality of corresponding wheel brakes during an anti- lock brake system event. At least one of the first control valves and at least one of the second control valves are normally open solenoid valves for movement between a normally open position and a closed position. A pump disposed in the housing is in fluid communication with the first and second control valves.

The pump transfers hydraulic fluid from the second control valves to the first control valves during an anti-lock brake event.

This invention eliminates the need for switching at least one second control valve from a normally closed position to an open position when performing an evacuation and fill procedure for the system. Consequently, the evacuation and fill procedure can be performed in a simplified and efficient manner. In addition, the equipment required to switch normally closed second control valves to the open position in the evacuation and fill procedure can be eliminated provided that each of the second control valves is a normally open solenoid valve. Furthermore, this invention allows for the first and second control valves to be common parts, resulting in further cost reductions.

Accordingly, this invention provides a hydraulic control unit for use in a vehicular anti-lock brake system that can be evacuated and filled in a simple and efficient manner that is relatively inexpensive.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic circuit diagram of a vehicular anti-lock brake system according to a first embodiment of this invention.

FIG. 2 is a schematic circuit diagram of a vehicular anti-lock brake system according to a second embodiment of this invention.

FIG. 3 is a schematic circuit diagram of a vehicular anti-lock brake system according to a third embodiment of this invention.

FIG. 4 is a schematic circuit diagram of a vehicular anti-lock brake system according to a fourth embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A vehicular anti-lock brake system (ABS) according to a first embodiment of this invention is indicated generally at 10 in FIG. 1. The ABS 10 comprises a brake pedal 12 connected to a master cylinder 14 for providing pressurized fluid to a plurality of wheel brakes 16. The wheel brakes 16 are shown as a disc brake but may be of any well-known type.

A hydraulic control unit (HCU), indicated generally at 18, is connected in fluid communication with the master cylinder 14 and each of the wheel brakes 16. The HCU 18 controls the flow hydraulic fluid to and from the wheel brakes 16 during an ABS event.

The HCU 18 includes four first control valves 20 disposed in a housing indicated schematically at 19 of a well-known type and in a well-known manner. Each of the first control valves 20 is in fluid communication with the master cylinder 14 and a corresponding wheel brake 16. The first control valves 20 are normally open solenoid valves of a well-know type. The first control valves 20 modulate the flow of hydraulic fluid to the corresponding wheel

brakes by switching between a normally open position and a closed position.

Each of the first control valves 20 includes a first check valve 22 for preventing the flow of hydraulic fluid through the first control valve 20 to the corresponding wheel brake 16 when the first control valve 20 is placed in a closed position. As can be appreciated by one skilled in the art, a single first control valve could be arranged in fluid communication with a pair of wheel brakes rather than separate wheel brakes, thereby eliminating one first control valve for each such arrangement.

The HCU 18 further includes four second control valves 24 disposed in the housing in a well-known manner. Each of the second control valves 24 is in fluid communication with a corresponding wheel brake 16. The second control valves 24 are normally open solenoid valves of a well-known type. The second control valves 24 modulate the flow of hydraulic fluid from the corresponding wheel brakes 16 by switching between a normally open position to a closed position. Each of the second control valves 24 includes a disconnection 26 for preventing the flow of hydraulic fluid through the second control valve 24 when the second control valve 24 is placed in the closed position. As can be appreciated by one skilled in the art, a single second control valve could be arranged in fluid communication with a pair of wheel brakes rather than separate wheel brakes, thereby eliminating one second control valve for each such arrangement.

The HCU 18 further includes a pump, indicated generally at 28, disposed in the housing in a well-known manner. The pump 28 is of a well-known reciprocating piston type having a pair of pump chambers 30. A motor 32, of a well-known type, is disposed in the housing and is operatively connected to the pump 28 for driving the pump 28. Each of the pump chambers 30 includes an inlet 34 in fluid communication with a separate pair of second control valves 24.

Each of the pump chambers 30 further includes an outlet 36 in fluid communication with the master cylinder 14 and a separate pair of first control valves 20. During an ABS event, each of pump chambers 30 transfers hydraulic

fluid from the corresponding pair of second control valves 24 to the corresponding pair of first control valves 20.

In operation, the brake pedal 12 is depressed to actuate the master cylinder 14. In turn, the master cylinder 14 pressurizes fluid to the wheel brakes 16, thereby actuating the wheel brakes 16. During an ABS event, the first 20 and second 24 control valves corresponding to the particular wheel brake are selectively switched between the normally open and closed positions in varied combinations in order to control the fluid pressure to the particular wheel brake. At the same time, the motor 32 drives the pump 28, thereby producing a pumping action in each of the pump chambers 30. In turn, each of the pump chambers 30 draws fluid from the corresponding pair of second control valves 24 and supplies fluid to the corresponding pair of first control valves 20. The pressure to a particular wheel brake 16 is increased when the corresponding first 20 and second 24 control valves are placed in the normally open position and the closed position, respectively. This arrangement prevents fluid from flowing from the particular wheel brake 16 while allowing additional fluid to be supplied from the master cylinder 14 the particular wheel brake 16, thereby increasing the pressure to the particular wheel brake 16. The pressure to a particular wheel brake 16 is held at an existing pressure when both of the corresponding first 20 and second 24 control valves are placed in the closed positions. This arrangement prevents fluid from flowing to the particular wheel brake 16 from the corresponding first control valve 20, and prevents fluid from flowing from the particular wheel brake 16 to the corresponding second control valve 24. The existing pressure to the particular wheel brake 16 is thereby maintained provided that the force applied to the brake pedal 12 is not reduced. The pressure to a particular wheel brake 16 is reduced when the corresponding first 20 and second 24 control valves are placed in the closed position and the normally open position, respectively.

This arrangement prevents fluid from flowing to the particular wheel brake 16 while allowing the pump 28 to draw fluid from the particular wheel brake 16,

thereby reducing the pressure to the particular wheel brake 16.

A vehicular anti-lock brake system (ABS) according to a second embodiment of this invention is indicated generally at 100 in FIG. 2. The ABS 100 is similar to the first embodiment of this invention except for one of second control valves 24 of each of the pairs of second control valves 24 in fluid communication with the corresponding pump inlets 34, as illustrated in FIG. 1, is replaced by a second control valve 138. The second control valves 138 are of a well-known type. Each of the second control valves 138 includes a second check valve 140 for preventing the flow of hydraulic fluid through the second control valves 138 to the corresponding wheel brake 116 when the second control valve 138 is in a first closed position. Each of the second control valves 138 further includes a disconnection 142 for preventing the flow of hydraulic fluid through the second control valve 138 when the second control valve 138 is in a second closed position.

The ABS 100 operates similar to the first embodiment of this invention as described above. The principle difference is the positioning of the second control valves 138 in controlling the pressure to the corresponding wheel brakes 116 during an ABS event. The second control valves 138 are placed in the first closed position when reducing the pressure to the corresponding wheel brakes 116. The second control valves 138 are placed in the second closed position when either applying supplemental pressure or holding pressure to the corresponding wheel brakes 116. In addition, the second control valves 138 prevent the flow of fluid through the second control valves 138 to the corresponding wheel brakes 116 when placed in either the first or second closed positions.

A vehicular anti-lock brake system (ABS) according to a third embodiment of this invention is indicated generally at 200 in FIG. 3. The ABS 200 is similar to the first embodiment of this invention except for one of second control valves 24 of each of the pairs of second control valves 24 in fluid communication with the corresponding pump inlets 34, as illustrated in FIG. 1,

is replaced by a one-way valve 244. The one-way valves 244 are of a well- known type. Each of the one-way valves 244 prevents the flow of hydraulic fluid to a corresponding wheel brake 216. In addition, an orifice 246 is placed in fluid communication between each of the one-way valves 244 and each of the wheel brakes 216 corresponding to the one-way valves 244. The orifices 246 are of a well-known type. Each of the orifices 246 restricts the flow of hydraulic fluid from the corresponding wheel brake 216 to the corresponding one-way valve 244. As can be appreciated by one skilled in the art, the orifices 246 may be eliminated.

The ABS 200 operates similar to the first embodiment of this invention as described above. The principle difference is the fluid from each of the wheel brakes 216 corresponding to the one-way valves 244 is allowed to continuously flow to the corresponding pump chamber 230, during an ABS event, unless the pressure at the corresponding pump inlet 234 is greater than the pressure between corresponding orifice 246 and the corresponding one- way valve 244.

A vehicular anti-lock brake system (ABS) according to a fourth embodiment of this invention is indicated generally at 300 in FIG. 4. The ABS 300 is similar to the first embodiment of this invention except for one of second control valves 24 of each of the pairs of second control valves 24 in fluid communication with the corresponding pump inlets 34, as illustrated in FIG. 1, is replaced by a second control valve 348. The second control valves 348 are normally closed solenoid valves of a well-known type. The second control valves 348 modulate the flow of hydraulic fluid from the corresponding wheel brakes 316 by switching between a normally closed position to an open position. Each of the second control valves 348 includes a disconnection 350 for preventing the flow of hydraulic fluid through the second control valve 348 when the second control valve 348 is in the normally closed position.

The ABS 300 operates similar to the first embodiment of this invention as described above. The principle difference is the positioning of the second

control valves 348 in controlling the pressure to the corresponding wheel brakes 316 during an ABS event. The second control valves 348 are placed in the open position when reducing the pressure to the corresponding wheel brakes 316. The second control valves 348 are placed in the normally closed position when either applying supplemental pressure or holding pressure to the corresponding wheel brakes 316.

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.