GB2305478A

GB2305478A - Brake system for a motor vehicle

Info

Publication number: GB2305478A
Application number: GB9519590A
Authority: GB
Inventors: Jacques Loche
Original assignee: Delphi Automotive Systems France
Current assignee: Delphi Automotive Systems France
Priority date: 1995-09-26
Filing date: 1995-09-26
Publication date: 1997-04-09
Anticipated expiration: 2015-09-26
Also published as: GB2305478B; GB9519590D0

Abstract

A brake system for a motor vehicle comprises a first, electrically, or electro-hydraulically, operated brake apply system 12; a second, hydraulically operated brake apply system 18 including a master cylinder 20; a brake pedal 10 for actuating the first and second brake apply systems; means 22 for detecting a fault in the first brake apply system; and means 24 whereby the master cylinder is actuated by the pedal on detection of a fault in the first brake apply system, the means also providing a reaction force or feel on the brake pedal on depression of the brake pedal when the first system is operative. Feel is provided by fluid in chamber 58 being displaced back into reservoir 64 via a restriction 68 and a solenoid operated valve 70. When a fault is detected, valve 70 closes so that pistons 38,42 move together to actuate the master cylinder 20.

Description

BRAKE SYSTEM The present invention relates to a brake system for a motor vehicle which includes an electrically operated or electro-hydraulically operated brake apply system.

Electrically operated or electro-hydraulically operated brake apply systems in motor vehicles are known. Such systems include a standard brake pedal by which the operator applies the brakes. The problem with such an arrangement is that the vehicle operator receives little or no feel or feedback, on depression of the brake pedal, to indicate the value of the braking force that is being applied when the operator presses the brake pedal. Such systems may also include a known hydraulically operated brake apply system which actuates the brakes should the electrically operated or electro-hydraulically operated system fail or develop a fault. The hydraulic system includes a master cylinder which is connected to and operated by the brake pedal.The master cylinder is therefore operated on depression of the brake pedal irrespective of the status of the electrically operated or electro-hydraulically operated system. An example of an electro-hydraulically operated system is described in US-A-5,246,283.

The present invention aims to overcome the above mentioned disadvantages.

A brake system for a motor vehicle in accordance with the present invention comprises an electrically operated or electro-hydraulically operated brake apply system; a hydraulically operated brake apply system including a master cylinder; a brake pedal for actuating the electrically operated or electro-hydraulically operated brake apply system, or the hydraulically operated brake apply system; means for detecting a fault in the electrically operated or the electro-hydraulically operated brake apply system; and means positioned between the brake pedal and the master cylinder for actuating the master cylinder on detection of a fault in the electrically operated or the electro-hydraulically operated brake apply system and for providing a reaction force on the brake pedal on depression of the brake pedal.

The present invention provides feel or feedback to the vehicle operator on depression of the brake pedal which is the same as or similar to the feel when the brake pedal is depressed on a hydraulically operated brake apply system. This provides the vehicle operator with an indication, at the brake pedal, of the value of the braking force being applied to the brakes of the motor vehicle. Also, in a preferred embodiment, the arrangement is such that the master cylinder of the hydraulically operated brake apply system is only actuated when the electrically operated or the electro-hydraulically operated brake apply system fails.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional view of a brake system in accordance with the present invention when the brakes are not being applied; Figure 2 is a similar view to that of Figure 1 when the electrically operated or the electro-hydraulically operated brake apply system is actuated by depression of the brake pedal; and Figure 3 is a similar view to that of Figure 1 when a failure is detected in the electrically operated or the electro-hydraulically operated brake apply system and the hydraulically operated brake apply system is actuated by depression of the brake pedal.

Referring to Figure 1, the brake system in accordance with the present invention comprises a brake pedal 10; an electrically operated or electro-hydraulically operated brake apply system 12 including a controller 14 and a pedal position monitoring device 16 (such as a potentiometer or switch); a hydraulically operated brake apply system 18 including a master cylinder 20; fault detection means 22 for detecting a fault in the electrically operated or the electro-hydraulically operated brake apply system 12; and pedal force application means 24 for providing a force on the brake pedal 10 on depression of the brake pedal.

The brake pedal 10 is pivotally mounted on the firewall 26 of the motor vehicle in the usual manner. The pedal position monitoring device 16 is connected to the brake pedal 10 and provides a signal to the controller 14 which is dependent on the pivotal position of the brake pedal relative tb the firewall 26. The controller 14 controls the operation of the electrically operated or electro-hydraulically operated brake apply system 12 in accordance with the signal received from the pedal position monitoring device 16 to apply the vehicle brakes (not shown) as required.

The electrically operated or electro-hydraulically operated brake apply system 12 and an associated fault detection means 22 may be any system known to those skilled in the art and will not be described herein in detail.

The hydraulically operated brake apply system 18 may be any system known to those skilled in the art and will not be described herein in detail. The master cylinder 20 includes a piston 28 which is axially slidable in a bore 30 in a housing 32. The hydraulically operated brake apply system 18 is used to apply the vehicle brakes when a fault is detected in the electrically operated or electro-hydraulically operated brake apply system 12, as will be described in more detail below.

The fault detection means 22 monitors the operation of the electrically operated or electro-hydraulically operated brake apply system 12 and sends a signal to the controller 14 when a fault is detected in the electrically operated or electro-hydraulically operated brake apply system. On detection of a fault, the controller 14 acts (as will be described in more detail below) to ensure the operation of the hydraulically operated brake apply system 18.

The pedal force application means 24 is a hydraulic device and comprises a housing 34 having an axially extending through bore 36. The housing 34 is secured to the firewall 26 by screws 33 and to the housing 32 of the master cylinder 20 by screws 35. The longitudinal axes of the through bore 36 and the bore 30 of the master cylinder 20 are substantially aligned on axis A. Two pistons 38,42 are positioned in the through bore 36. The first piston 38 is connected to the brake pedal 10 by way of a push rod 40, and the second piston 42 which is connected to the piston 28 of the master cylinder 20. The first and second pistons 38,42 make a sealing sliding fit with the through bore 36 and are slidable in an axial direction relative to each other and relative to the housing 34. The push rod 40 passes through an aperture 44 in the firewall 26. Movement of the first piston 38 towards the firewall 26 is restricted by a ring stop 46 secured in the through bore 36 adjacent the aperture 44. The first and second pistons 38,42 are linked together by a pin 48 which is secured to two longitudinally extending, spaced apart, arms 50 integral with the second piston 42, such that the pin extends in a radial direction. The first piston 38 has a corresponding longitudinally extending arm 52 which is positioned between the arms 50 on the second piston 42. The arm 52 has a slot 54 there through which extends in a radial direction and which has a predetermined axial length L. The pin 48 is positioned in, and extends through, the slot 54. A helical coil spring 56 extends between and engages the first and second pistons 38,42 to bias the first and second pistons away from one another in the axial direction.A pressure chamber 58 is defined between the first and second pistons 38,42 inside the through bore 36. A second chamber 60 is defined in the through bore 36 between the second piston 42 and the master cylinder 20 and is connected to air at atmospheric pressure by an aperture 62 passing through the housing 34. Hydraulic fluid is supplied to the pressure chamber 58 from a fluid reservoir 64 (which may be integral with the fluid reservoir - not shown - for the master cylinder 20).

Hydraulic fluid can flow from the fluid reservoir 64 to the pressure chamber 58 by way of a one-way valve 66.

Hydraulic fluid can flow from the pressure chamber 58 to the fluid reservoir 64 by way of a restriction orifice 68 and a solenoid controlled valve 70, which is shown in a closed position in Figure 1. Operation of the valve 70 is controlled by the controller 14, as will be described in more detail below.

When the brake pedal 10 is not depressed by the vehicle operator, the brake system of the present invention is at rest and assumes the arrangement shown in Figure 1.

When the brake pedal 10 is depressed, the pedal position monitoring device 16 sends a signal to the controller 14. The controller 14 signals the electrically operated or electro-hydraulically operated brake apply system 12 to actuate the vehicle brakes.

The braking force applied by the vehicles brakes is dependent on the amount of depression of the brake pedal 10. Substantially simultaneously, the controller 14 sends a signal to the solenoid operated valve 70 to move the valve to the open position as shown in Figure 2. As the brake pedal 10 is depressed, the first piston 38 moves towards the second piston 42 against the bias of the spring 56. The length L of the slot 54 is such as to substantially allow the first piston 38 to move towards the second piston 42 without the first piston engaging and moving the second piston. The second piston 42, and hence the piston 28 of the master cylinder 20, remain substantially stationary relative to their respective housings 34,32. Hydraulic fluid in the pressure chamber 58 passes from the pressure chamber to the reservoir 64 by way of the restriction orifice 68 and the open valve 70.This arrangement provides the vehicle operator with feel or feedback at the brake pedal 10, the value of the force of which increases as the brake pedal is further depressed. In this way, the vehicle operator can gauge the force being applied by the vehicle brakes. The amount of feel at the brake pedal 10 is dependent on the biasing force of the spring 56 and the size of the restriction orifice 68.

When the vehicle operator requires de-actuation of the vehicle brakes, the brake pedal 10 is allowed to return to its rest position (Figure 1) and the controller 14 de-actuates the vehicle brakes and closes the solenoid operated valve 70. The first piston 38 returns to its rest position by engaging the ring stop 46 (as shown in Figure 1) and fluid flows from the reservoir 64 to the pressure chamber 58 by way of the one-way valve 66 to replenish the pressure chamber.

In the case where a fault is detected in the electrically operated or electro-hydraulically operated brake apply system 12 by the fault detection means 22, and the vehicle operator depresses the brake pedal 10, the controller 14 does not open the solenoid operated valve 70. As a consequence, hydraulic fluid remains trapped in the pressure chamber 58 and cannot flow to the reservoir 64. Depression of the brake pedal 10 therefore causes the first and second pistons 38,42 to move substantially simultaneously relative to the housing 34 towards the master cylinder 20. Such movement also moves the piston 28 of the master cylinder 20 relative to the housing 32 to actuate the vehicle brakes by way of the hydraulically operated brake apply system 18.This arrangement therefore provides for vehicle brake actuation on failure of the electrically operated or electro-hydraulically operated brake apply system 12 with minimal or no travel loss despite the presence of the pedal force application means 24 between the brake pedal 10 and the master cylinder 20.

The brake system of the present invention therefore only actuates the master cylinder on detection of a fault in the electrically operated or electro-hydraulically operated brake apply system, and additionally provides the vehicle operator with pedal feel during operation of the electrically operated or electro-hydraulically operated brake apply system.

The controller 14 is preferably a microcomputer which additionally provides anti-lock braking for the braking system. The arrangement of the arms, slot and pin associated with the first and second pistons of the pedal force application means may be reversed. The pin 48 may be omitted. However, the presence of the pin 48 allows the pre-assembly of the first and second pistons 38, 42 and the spring 56 as a sub-assembly, and provides means for controlling the length of (and hence the force exerted by) the spring 56 in the rest, non-operating, position of the brake system.

Claims

Claims: -

1. A brake system for a motor vehicle comprising an electrically operated or electro-hydraulically operated brake apply system; a hydraulically operated brake apply system including a master cylinder; a brake pedal for actuating the electrically operated or electro-hydraulically operated brake apply system, or the hydraulically operated brake apply system; means for detecting a fault in the electrically operated or the electro-hydraulically operated brake apply system; and means positioned between the brake pedal and the master cylinder for actuating the master cylinder on detection of a fault in the electrically operated or the electro-hydraulically operated brake apply system and for providing a reaction force on the brake pedal on depression of the brake pedal.

2. A brake system as claimed in Claim 1, wherein the means positioned between the master cylinder and the brake pedal comprises a housing with a through bore; first and second pistons slidable in the through bore relative to each other and to the housing, the first piston being connected to the brake pedal and the second piston actuating the master cylinder, the first and second pistons defining a pressure chamber therebetween within the through bore, the pressure chamber containing hydraulic fluid; and valve means allowing restricted flow of fluid from the pressure chamber on depression of the brake pedal and when no fault is detected in the electrically operated or the electro-hydraulically operated brake apply system to provide a reaction force on the brake pedal.

3. A brake system as claimed in Claim 2, wherein the valve means comprises a solenoid operated valve which is opened on depression of the brake pedal and when no fault is detected in the electrically operated or the electro-hydraulically operated brake apply system; and a flow restriction orifice.

4. A brake system as claimed in Claim 2 or Claim 3, further comprising a fluid reservoir and a one way valve which allows flow of hydraulic fluid from the fluid reservoir to the pressure chamber.

5. r brake system as claimed in any one of Claims 2 to 4, further comprising a spring positioned in the pressure chamber and engaging the first and second pistons to bias the first and second pistons away from each other.

6. A brake system as claimed in any one of Claims 2 to 5, wherein the first and second pistons are linked by a pin which is secured to one piston and which limited axial movement in a slot in the other piston, the pin and the slot extending in a radial direction.

7. A brake system substantially as herein described with reference to, and as shown in, the accompanying drawings.