WO2011064481A1

WO2011064481A1 - Method for controlling a motor vehicle braking system

Info

Publication number: WO2011064481A1
Application number: PCT/FR2010/052353
Authority: WO
Inventors: Arnaud Lizot
Original assignee: Peugeot Citroën Automobiles SA
Priority date: 2009-11-24
Filing date: 2010-11-03
Publication date: 2011-06-03
Also published as: FR2952885A1; EP2504601A1; FR2952885B1

Abstract

The invention relates to a method for controlling a motor vehicle braking system including disk brakes (31, 41), controlled by means of a main hydraulic circuit comprising a brake pedal (14), and at least one automatic actuator (38) for a parking brake, said actuator applying brake linings onto the disks (4) for motor-driven brakes (31), the automatic actuator (38) reducing the play between the linings and the disks (4) for the motor-driven brakes (31). When the accelerator pedal of the vehicle is released, the displacement of the hydraulic pistons (8) of the motor-driven disk brakes (31) is greater than the displacement of the hydraulic pistons (8) of the non-motor-driven disk brakes (41).

Description

CONTROL METHOD FOR A BRAKING SYSTEM OF A

MOTOR VEHICLE

The present invention relates to a control method for a braking system of a motor vehicle, comprising a hydraulic control actuated by a brake pedal, it also relates to a braking system comprising such a method, and a motor vehicle comprising this braking system.

The braking systems of motor vehicles generally comprise a brake control comprising a brake pedal acting on a master cylinder, for transmitting by hydraulic circuits a pressure of a fluid to receivers braking the different wheels of the vehicle.

The brake systems may further include driving assistance devices, such as an anti-lock brake system "ABS" modulating the brake pressure, or a vehicle stability control system "ESP".

The hydraulic brake pressure is transmitted to the receivers having brake linings, which are pressed on discs or drums linked in rotation to the wheels to deliver a braking torque.

In the case of disc brakes, each brake comprises two brake pads comprising linings which are clamped in opposition on both sides of the disk connected in rotation to a wheel, by a piston of a jack receiving the hydraulic pressure. The piston is guided in a bore of a stirrup, comprising a groove receiving an elastic annular seal enclosing the piston to ensure a dynamic seal when sliding the piston.

For small strokes of the piston, the annular seal undergoes an elastic deformation between its portion held in the groove of the stirrup, and its inner face which remains substantially bonded to the piston. This elastic deformation of the annular seal applies a biasing force which tends to roll back the piston, returning the brake fluid to the master cylinder when the hydraulic pressure drops. The recoil of the piston separating the lining of the disk and releasing the rotation of the wheels, is generally of the order of 0.3 mm.

Optimum release of the brake discs is important to reduce the wear of these brakes, and to reduce the consumption of vehicles by reducing the losses due to residual braking that may remain on these discs after braking.

It has been calculated that for a vehicle comprising four disc brakes, a residual torque of 10 mN on each brake generally considered as a maximum allowable value, corresponds to an additional emission of 20 gr of carbon dioxide per kilometer.

For various reasons such as manufacturing dispersions, a slight sail of the brake discs, deformations due to overheating during braking, or deflections in the turns, it is possible to obtain a residual torque greater than this maximum admissible value.

It is possible, according to a known solution, to reduce the losses with an increase in the recoil of the piston, brought for example to 0.5 mm, by modifying the annular seal of the piston making the return of this piston, and the groove receiving it.

The dead stroke of the brake pedal necessary to bring the linings in contact with the faces of the disc being related to the recoil of the piston, is significantly increased to move a larger volume of liquid. A problem that arises is that this increase in dead travel of the brake pedal modifying the pedal feel, is not comfortable, and can further disturb the driver.

It is also known in particular from US-A-5251968, to use an electric actuator for clamping the parking brake, to add a braking force of the vehicle to that controlled by the main hydraulic brake control. However nothing is planned in this braking system to reduce residual friction of brake linings.

The present invention is intended in particular to avoid these drawbacks of the prior art, and to bring to the problem of reducing the residual friction of the brakes of a vehicle, a simple, economical and effective solution, without noticeably modifying the sensation at the brake pedal.

It proposes for this purpose a control method for a braking system of a motor vehicle, comprising disc brakes controlled by a main hydraulic circuit comprising a brake pedal, and at least one automatic parking brake actuator tightening trims. brake system on the motorized brake discs, characterized in that when the accelerator pedal of the vehicle is released, the automatic actuator reduces the clearance between the linings and the discs of the motorized brakes.

An advantage of the control method according to the invention is that it is generally possible to roll with a large clearance between the brake linings and the discs of the motorized brakes, resulting in energy savings, while allowing thanks to the reduction of the Trim set under conditions where braking may occur, brake pedal maneuver including reduced dead travel.

The control method according to the invention may further comprise one or more of the following features, which may be combined with each other.

Advantageously, the automatic actuator applies a preliminary force on the pads of the motorized disc brakes, when the brake pedal starts to be activated.

Advantageously, the preliminary force delivered by the automatic actuator is calculated to compensate for the lack of braking of the non-motorized disc brakes during the approach time of their linings. Advantageously, the retraction of the hydraulic pistons of the motorized disc brakes is greater than the retraction of the hydraulic pistons of the non-motorized disc brakes.

In particular, the retraction of the hydraulic pistons of the motorized disc brakes may be greater than 0.4 mm.

According to a first embodiment, the braking system comprises an electric actuator on each disc brake of the rear axle of the vehicle.

According to a second embodiment, the braking system comprises a common electric actuator for the two disc brakes of the rear axle of the vehicle.

Advantageously, the control method is implemented by a control computer managing other braking functions, such as an anti-lock function of the "ABS" wheels, or an "ESP" vehicle stability control function.

The invention also relates to a braking system for a motor vehicle, implementing a control method comprising any one of the preceding features.

The invention furthermore relates to a motor vehicle having a braking system, implementing a control method comprising any one of the preceding features.

The invention will be better understood and other features and advantages will emerge more clearly on reading the following description given by way of example, with reference to the appended drawings in which:

- Figure 1 is a diagram of a brake control according to the prior art;

- Figures 2A and 2B are diagrams in axial section, respectively of a rear caliper and a front caliper at rest, a braking system comprising a control method according to the invention;

- Figures 3A and 3B are diagrams of these stirrups after a release of the accelerator pedal; - Figures 4A and 4B are diagrams of these stirrups at the beginning of actuation of the brake pedal; and

- Figures 5A and 5B are diagrams of these stirrups when maintaining the actuation of the brake pedal.

Figure 1 shows a brake control 1 comprising a brake caliper 2 covering a brake disc 4, and guiding two brake pads 6 arranged in opposition, each comprising a liner facing this disc.

The brake pads 6 are tightened on the brake disc 4 by a piston 8 guided in a bore of the stirrup 2, which presses directly on one of the plates. By reaction, the stirrup 2 which is slidably mounted relative to a support connected to the chassis of the vehicle, moves back and press the other brake pad 6 on the opposite face of the brake disc 4, so as to balance the pressures of the two platelets.

A brake pedal 14 acts by a control rod 16 on the piston

12 of a master cylinder 10, connected by a pipe to the piston chamber 8 of the caliper 2. The master cylinder 10 transmits the force of the brake pedal 14 with a certain reduction, to exert a significant effort tightening the brake disc 4.

The guide bore of the stirrup 2 comprises an annular groove receiving a seal 18, which seals the piston 8 during its sliding, and a return back of the piston when the brake pedal 14 is released.

The retraction of the piston 8 creates an overall axial clearance J shown to simplify only on the piston side, while it is distributed mainly between the brake disc 4 and the two brake pads 6.

According to the ratio of the sections of the piston 8 of the caliper 2, and the piston 12 of the master cylinder 10, the clearance J necessary to release the brake disc 4 gives a receding stroke C of the control rod 16, and therefore some dead travel of the brake pedal 14. For the whole of the brake control 1 it is necessary to add the games J necessary for the four stirrups 2 of the vehicle, in the case of a vehicle comprising four disc brakes, to obtain the total dead travel of the brake pedal 14 The dead travel of the brake pedal increases directly according to an increase in these games J.

FIG. 2A shows a stirrup 30 of a rear brake 31 of a vehicle, comprising axially at the end of the piston chamber 8, an electric parking brake actuator 38 comprising an electric motor.

The electric actuator 38 rotates an axial screw 32, which passes through the rear wall of the piston chamber with a seal 34. The axial screw 32 is screwed into a nut 36 housed in a cavity of the piston 8, to push the piston towards the brake disc 4 when this screw rotates in one direction. By reaction, the brake caliper 30 clamps the brake pad 6 located on the other side of the piston 8.

By providing an irreversible kinematic drive of the axial screw 32 by its electric motor, when the power supply of this electric motor is cut, we obtain a parking brake which is maintained permanently.

The driver maintaining pressure on the accelerator pedal, the piston 8 and its seal 18 of the rear brake caliper 31 are designed to obtain a significant return stroke of this piston as shown in FIG. 2A, in order to to obtain at rest a high clearance J which is advantageously of the order of 0.5 mm.

FIG. 2B shows a caliper 40 of a conventional front brake 41 of the motor vehicle, comprising the piston 8 which is recalled as shown in this figure, following a usual race giving a clearance J which can be of the order of 0.3 mm.

Figures 3A and 3B show the rear brakes 31 and before 41 when the driver releases the accelerator pedal, the brake pedal can then be operated at any time. A brake control computer of the vehicle which controls in particular the electric parking brake actuator 38, receives this information of release of the accelerator pedal, and has the rear brakes 31 in a braking waiting position. A rotation of the screw 32 advances the piston 8 so as to approach the linings of the brake pads 6 of the disc 4 by canceling the clearance J, but without exerting significant pressure on this disc.

In this way, with possibly a little additional friction on the rear brakes 31, during periods of limited duration, the stroke of the piston 8 is very small to prepare a next braking.

The positions of the pistons of the front brakes 41 are not modified under these driving conditions.

If the driver actuates the accelerator pedal again, the control computer returns the rear brakes 31 to the initial rest position shown in FIG. 2A.

Figures 4A and 4B show the rear brakes 31 and before 41 when the driver starts to operate the brake pedal.

The electric actuator 38 immediately applies a preliminary force F1 on the brake disc 4 of the rear brake 31, by turning the screw 32. The pressure P which enters the piston chamber 8 under the effect of the movement of the brake pedal , immediately begins to exert a braking force F2 on the brake disc 4 which adds to the effort F1 without delay, because the pads of the brake pads 6 are already in contact with this disc.

During this time the piston 8 of the front brakes 41 advance to fill the clearance J, putting the linings of the brake pads 6 in contact with the brake disc 4.

Advantageously, the force F1 delivered by the electric actuator 38 is calculated to compensate for the lack of braking of the front brakes 41 during the approach time of its linings, so as to give an additional braking torque on the rear wheels equivalent to that which would give the front brakes for the same actuation of the brake pedal, in the case where the pads would be in contact with their brake discs 4. There is thus delivered a global braking force on the vehicle corresponding to that expected by the driver who begins to brake.

Figures 5A and 5B show the rear brakes 31 and before 41 when the driver continues to operate the brake pedal. The pads of the brake pads 6 of the front brakes 41 which came into contact with their brake discs 4, begin to exert a force F3 on these discs.

Simultaneously, the electric actuator 38 removes the force F1 on the rear brake discs 31, by turning the screw 32 upside down, so that the effort F3 of the front brakes 41 which increases compensate for the decline of this effort F1 rear brakes.

This provides a level of overall braking of the vehicle that corresponds precisely to the demand of the driver according to the force exerted on the brake pedal, without abrupt departure of this level of braking.

In addition the braking of the vehicle arrives very quickly after a reduced dead stroke of the brake pedal, first on a single axle of the vehicle but with a demand for braking power still relatively low. Braking then increases in power, spreading over the four wheels of the vehicle to ensure both the requested power level and stability of the vehicle.

The braking system according to the invention is simple and economical to implement for a vehicle already equipped with one or more braking actuators that can be electric, or use another source of energy. In particular, it is possible to use electric actuators arranged on each rear wheel brake, or a common electric actuator which actuates the two brakes of the rear axle by means of a cable.

This braking system mainly requires a modification of the rear brakes 31 to have in the caliper 30, a groove receiving a seal 18 allowing a strong recoil of the piston 8.

Advantageously and economically, the control method is implemented by an existing brake control computer, for example in that managing braking functions such as ABS or ESP. In general, the braking system according to the invention may comprise motorized disc brakes implemented by the automatic actuator, arranged on the rear axle or on the front axle of the vehicle, or even on all axles of this vehicle.

The hydraulic braking circuit may comprise in particular two independent hydraulic circuits, each connecting the disc brakes of the two wheels arranged along a diagonal of the vehicle.

Claims

1 - Control method for a braking system of a motor vehicle, comprising disc brakes (31, 41) controlled by a main hydraulic circuit comprising a brake pedal (14), and at least one automatic parking brake actuator (38) clamping brake linings on the motorized brake discs (4) (31), characterized in that when the accelerator pedal of the vehicle is released, the automatic actuator (38) reduces the clearance between the linings and the discs (4) of the motorized brakes (31), characterized in that the retraction of the hydraulic pistons (8) of the motorized disc brakes (31) is greater than the recoil of the hydraulic pistons (8) of the non-motorized disc brakes ( 41).

2 - A control method according to claim 1, characterized in that the automatic actuator (38) applies a preliminary force (F1) on the linings of the motorized disc brakes (31), when the brake pedal (14) begins to to be activated.

3 - A control method according to claim 2, characterized in that the preliminary force (F1) delivered by the automatic actuator (38) is calculated to compensate for the lack of braking of the non-motorized disc brakes (41) during the approach time of their fittings.

4 - A control method according to one of claims 1 to 3, characterized in that the retraction of the hydraulic pistons (8) of the motorized disc brakes (31) is greater than 0.4 mm.

5 - Control method according to any one of the preceding claims, characterized in that the braking system comprises an electric actuator (38) on each disc brake (31) of the rear axle of the vehicle.

6 - A control method according to any one of claims 1 to 5, characterized in that the brake system comprises a common electric actuator (38) for the two disc brakes (31) of the rear axle of the vehicle. 7 - A control method according to any one of the preceding claims, characterized in that it is implemented by a control computer managing other braking functions, such as an anti-lock function of the wheels "ABS", or a vehicle stability control function "ESP".

8 - A braking system for a motor vehicle, characterized in that it implements a control method according to any one of the preceding claims.

9 - A motor vehicle comprising a braking system, characterized in that the braking system implements a control method according to any one of claims 1 to 7.