FR3124467A1 - CONTROL DEVICE FOR AN ELECTRO-MECHANICAL BRAKE OPERATING AS AN EMERGENCY BRAKE - Google Patents

Abstract

Controls (38, 41) for controlling the movement of an electro-mechanical brake actuator, operating as an emergency brake during vehicle driving, are provided to alternately apply and reapply the brake according to a difference in speed ( Δω) between the wheel equipped with the brake and another wheel. The release commands (38) are interrupted as soon as the intensity value (I) of the electric current driving the actuator stabilizes, in order to avoid idle strokes of the actuator and to allow rapid re-tightening afterwards. Figure for abstract: Figure 5.

Description

CONTROL DEVICE FOR AN ELECTRO-MECHANICAL BRAKE OPERATING AS AN EMERGENCY BRAKE

The invention relates to a device for controlling an electro-mechanical brake operating as an emergency brake.

Some motor vehicles are equipped, in addition to main service brakes controlled directly by a driver wishing to slow down, with brakes used as emergency brakes, supplementary to the previous ones and automatically controlled under certain driving conditions of the vehicle when the main brakes are activated. Such emergency brakes can be, according to significant existing achievements, electro-mechanical brakes fitted to the non-driving wheels and used primarily as parking brakes. The invention could nevertheless be applied to other braking configurations.

A problem that appears with these emergency brakes relates to possible locking of the wheels fitted to them. It is normal to interrupt the braking of these wheels if a lock is noticed, and to resume it only when the lock stops. A usual procedure is to compare the speed of the wheel concerned with the speed of the wheel of the other axle, generally therefore the driving wheel, on the same side of the vehicle; wheel locking is assumed to be present if the speed difference exceeds a determined threshold. However, it is observed that the resumption of emergency braking is not immediate with the existing emergency brake control strategies, when the locking has ceased. The overall braking of the vehicle is therefore degraded.

This disadvantage is aggravated by the impossibility of unequivocally determining the occurrence of a blockage. The wheel speed comparison process is often faulty in slippery road conditions (wet, icy or muddy) for example, because the drive wheel can race while the wheel equipped with the emergency brake turns normally. The incorrect blockage detection that is then made may persist for a long time before the wheel is racing and regains grip on the ground; and the resumption of emergency braking is even slower.

The object of the invention is to allow rapid resumption of the application of electro-mechanical brakes used as emergency brakes while driving the vehicle, as soon as the detection, possibly incorrect, of a locking of the wheel fitted to the emergency brake ceased.

The invention applies mainly, but not exclusively, to braking systems in which the service braking is provided hydraulically while the parking and emergency braking is provided by the electric motor.

In a general form, the invention relates to a braking device for a vehicle comprising a first wheel and a second wheel, the device comprising:

- a first brake associated with the first wheel and which is a main brake controlled directly by the driver of the vehicle,

- a second brake associated with the second wheel and which is an additional brake,

- a second brake actuator,

- an electric motor moving the actuator in a direction of braking of the second brake, and in a direction of release of the second brake, opposite to the direction of braking,

- a motor control unit of the electric motor, comprising:

- a module for supplying brake and release commands to the electric motor to move the actuator either in the direction of braking or in the direction of release of the second brake,

- a module for measuring the speeds of the first wheel and of the second wheel, and for comparing said speeds of the wheels,

- a decision module connecting the rotation speed measurement module to the command supply module and designed to order the latter to supply the commands to the electric motor according to the wheel speed comparisons,

characterized in that the motor control unit comprises an electric current intensity measurement module supplied to the electric motor during the control commands; and in that the decision module is designed to stop the commands for releasing the second brake according to a criterion of level or level variation of said intensity.

The release commands are in fact prolonged, according to the existing strategies, as long as the difference in the speeds of the two wheels is greater than a second threshold, much lower than the previous one, that is to say until that the speeds of the two wheels have again become almost identical. The invention is based on the observation that it is in fact not useful to prolong the release commands beyond the time necessary to effectively release the emergency brake and that extensions of the release commands no longer have any effect. anti-lock effect then, but only produce idle strokes of the actuator which prevent immediate resumption of additional braking afterwards. We therefore hope to reduce the duration of degraded braking by anti-lock controls on the emergency brake when these degraded braking operations are no longer useful.

In another aspect, the invention also relates to the electro-mechanical vehicle brake motor control unit in accordance with the foregoing, therefore comprising:

- a module for supplying braking and release commands to an electric motor for moving a brake actuator either in a braking direction or in a brake release direction,

- a module for measuring the speeds of a first wheel and a second wheel of the vehicle, and for comparing said speeds of the wheels,

- a decision module connecting the rotation speed measurement module to the command supply module and designed to order the latter to supply the commands to the electric motor according to the wheel speed comparisons,

characterized in that it comprises a module for measuring the intensity of electric current supplied to the electric motor during commands; and in that the decision module is designed to stop the brake release commands according to a criterion of level or level variation of said intensity.

In an important embodiment of the invention, the criterion corresponds to a decrease in a time derivative of said intensity below a determined threshold.

Stabilization of the intensity of the emergency brake actuator command actually corresponds to the start of an idle stroke of the actuator, which it is therefore useful to interrupt.

Similarly, the criterion corresponds to a decrease in a value of said intensity below a determined threshold. This criterion is little different from the previous one in practice, because it has similar effects on the control.

The emergency brake can be, as already mentioned, a parking brake.

According to other optional features: the decision module is designed to stop the braking commands when a first wheel speed difference threshold is reached; or the decision module is arranged to initiate release commands when a second wheel speed difference threshold is reached.

Another aspect of the invention is a vehicle comprising such a braking device; where for example the first wheel is a front wheel, and the second wheel is a rear wheel.

Yet another aspect of the invention is a method of braking a motor vehicle comprising a first wheel, a second wheel, a main brake controlled by a driver of the vehicle and a second brake which is an electro-mechanical brake controlled by a engine control unit as an emergency brake, the method comprising issuing commands to apply or release the second brake as a function of braking by the main brake and continuous comparisons of speeds of the first wheel and of the second wheel, characterized in that it comprises continuous measurements of intensity values of an electric current supplied to the electric motor, and of interruption of the release commands as soon as said intensity stabilizes during the release commands.

The invention will now be described in its various aspects, characteristics and advantages, by means of the following figures, annexed for purely illustrative purposes, which represent a preferred embodiment thereof:

- there schematically represents an automobile;

- there schematically represents an exploded view of an electro-mechanical brake;

- there represents the motor control unit of the brake;

- there illustrates an existing strategy and its effects;

- there illustrates a strategy according to the invention and its effects;

- there illustrates a particular case of an existing strategy;

- and the illustrates a particular case of strategy according to the invention.

There represents an automobile 1 equipped with two driving and steering front wheels 2 on a front axle 3, and two non-driving and non-steering rear wheels 4 on a rear axle 5. Each of the front wheels 2 is here equipped with a main brake 6 service actuated directly by the driver, and each of the rear wheels 4 is equipped with a brake 7 described below in detail, and which is associated with an actuator 8 capable of making it work as a parking and emergency brake. The actuators 8 of the two brakes 7 are controlled by the same engine control unit 9 according to various information relating to certain parameters of the vehicle 1 and its driving condition. The engine control unit 9 is active when emergency braking becomes necessary or parking is requested.

There schematically illustrates a known and non-limiting embodiment of the brake 7, based on an exploded view. The brake 7 comprises a caliper 11 joined to a casing 12 of cylindrical shape. It also includes a gearmotor 60, one flange 61 of which is joined to a flange 62 on the rear face of the casing 12 by screws (not shown here). The geared motor 60 contains an electric motor 18 and gears for reducing the rotational speed of said electric motor 18. The housing 12 comprises a hydraulic cavity 13 called a cylinder, open towards the front (on the right at the ) and in which slides a piston 14 carrying a movable pad (not shown). Braking is carried out by causing the piston 14 to slide forwards, to bring the movable pad closer to a fixed pad located at the front end of the caliper 11 and grip a disc of the rear wheel 4 between these pads. This movement of the piston 14 is obtained, when the brake 7 works as a service brake, by the application of hydraulic pressure in the hydraulic cavity 13 while driving the vehicle: this pressure is exerted on the rear face of the piston 41 and pushes him forward. If, however, the brake 7 is controlled as a parking brake or as an emergency brake, the braking is carried out by the use of the electric motor 18 according to strategies imposed by the motor control unit 9. The electric motor 18 sets movement the gears of the geared motor 60, which causes a screw 15 which extends in the hydraulic cavity 13 to turn. The screw 15 engages with a nut 16 on which a rear face of the piston 14 is then in abutment. The rotations of the screw 15 are converted into translations of the nut 16 and of the piston 14, which moves according to the duration of actuation of the electric motor 18. The actuator 8 considered here comprises in particular the geared motor 60 and therefore its electric motor 18, and the system 17 made up of screw 15 and nut 16.

The invention could be applied to other vehicles and other brakes than these.

There illustrates in more detail the engine control unit 9: it comprises a command supply module 19 which supplies commands to the electric motor 18 by being connected to a battery or another source of energy on the vehicle 1, a intensity measurement 20 which measures the intensity I of the electric current flowing in the supply circuit of the electric motor 18, and a speed measurement module 25 informed by sensors 21 and 22 for respective measurement of the speeds of rotation of the rear wheel 4 fitted with the brake 7 and of the front wheel 2 on the same side (left or right) of the vehicle 1, and which calculates the difference Δω of their speeds of rotation, and a decision module 23 which connects the modules of provision of commands 19 and measurement of intensity 20 and speeds 25. The decision module 23 uses the outputs of the modules for measuring intensity 20 and speeds 25 to control the delivery of the commands.

A typical braking process of existing strategies is illustrated by the . The upper diagram 26 illustrates a series of commands (successively 27, 28 and 29) over time t, and the lower diagram 30 the difference Δω of the speeds of rotation of the wheels, calculated by the measurement module 25, during this period. The time t is represented on the abscissa, and the intensity I of the electric current as well as the difference Δω are represented on the ordinate for the diagrams 26 and 30. The first command 27 is a brake application command 7 which begins at a time t ₁ determined by a braking decision made by the driver. It continues until a time t ₂ of detection that the difference in speeds Δω exceeds a lower threshold Δ ₁ upwards, which suggests locking of the rear wheel 4. If the difference in speeds Δω later exceeds (at a time t ₃ ) and upwards an upper threshold Δ ₂ higher than the previous one, the second command 28 is given; it is a brake 7 release command, and it continues until a time t ₄ when the speed difference Δω goes back below the lower threshold Δ ₁ . If braking by the driver has continued and the difference in speeds Δω continues to decrease, the third command 29, which is a tightening command, begins shortly afterwards, at a time t ₅ , and it lasts until that the lower threshold Δ ₁ is still crossed upwards – which has been represented here at the instant t ₆ – or until the braking by the driver ceases.

The upper diagram 26 shows that the tightening commands 27 and 29 are expressed successively by a start-up peak 31 of high intensity, which corresponds to backlash in the mechanisms, then a flat portion 32 of low intensity which corresponds to an empty stroke of the actuator 8 before the disk is tightened, and finally a growing portion 33 which corresponds to a progressive tightening, increasingly strong, of the disk. The intensity I of the electric current which supplies the electric motor 18 is indeed correlated, even proportional, to the clamping force of the brake 7 applied by the screw 15; its value is not controlled, but it is measured by the module 20. And the release commands such as 28 are expressed successively by a starting peak 31 which again corresponds to a catch-up game, a decreasing portion 34 which corresponds to a gradual release of the disk, and a flat portion 35 of low intensity which again corresponds to an idle stroke of the actuator 8, this time in the direction of release. The tightening commands such as 27 and 29, and the releasing commands such as 28, therefore have total durations which vary according to the crossings of the thresholds Δ ₁ and Δ ₂ , and that their differences in duration relate above all to the durations respective flat portions 32 and 35.

However, the invention is based on the observation that the flat portion 35 of the release controls, corresponding to the release travels with no load, is useless and even becomes harmful when the brake 7 must be tightened. The invention is disclosed using the , which represents an upper diagram 36 and a lower diagram 37 respectively analogous to the previous ones (26 and 30), but which differ therefrom after time t ₃ : the release command, now 38 instead of 28, has a decreasing portion 39 analogous to that (34) of the , but a flat portion 40 of empty stroke much shorter than that (35) of the . This difference is produced by the motor control unit 9 and more particularly by the decision module 23, which interrupts the supply of electric current as soon as the intensity I measured by the intensity measurement module 20 stabilizes. A stabilization criterion that can be used is the passage of the time derivative (dI/dt) of the intensity I below a determined threshold. Other criteria could be envisaged, for example the passage of the value of the intensity I itself below a determined threshold. In other words, it is possible to exploit a level or a level variation of the intensity I of the electric current.

Let us examine the possible effect of this shortening of duration on the rest of the braking. As the idle travel of the release control 28 or 38 takes place when the brake 7 is already released, the lower diagram 37 of the difference Δω of the speeds remains unchanged until a new application control can be ordered at time t ₅ identical to that of the , or possibly a little earlier, as soon as the lower threshold Δ1 has been crossed downwards. The second tightening command 41 (instead of 29) is distinguished in that it comprises, after a starting peak 42, a growing portion 43, similar to the growing portion 33 of the tightening commands of the , but which is almost immediately obtained after the starting peak 42, which means that the application of the brake 7 resumes very shortly after the instant t ₅ , and is explained by the early interruption of the idle stroke at previous loosening; the flat portion 32 of the clamping controls 27 and 29 of the no longer appears here, or at least it is greatly shortened.

The almost immediate resumption of the tightening explains why the lower diagram 37 presents, after the instant t ₅ (at the portion 44), a decrease below the lower threshold Δ ₁ which is less marked than at the . The value of the difference Δω of the speeds can then rise more quickly and return to the lower threshold Δ ₁ at a time t ₇ prior to t ₆ , which means that the second clamping command 41 is interrupted at this time t ₇ and that it is shorter than the clamping control 29. We see that the invention makes it easier to resume braking by the emergency brake 7 when the situation is suitable, thus improving the overall braking and react better to road surprises.

The invention is particularly beneficial in certain particular situations illustrated by the , where the front wheel 2 races on slippery ground: the release control 49 which is then controlled, according to the same criterion as before, is powerless to bring the difference Δω of the speeds back below the upper threshold Δ ₂ , when the rear wheel 4 is not blocked by the brake 7. The release control can then comprise a very long flat portion 50, which results in a significant or even complete retraction of the screw 15, and a corresponding delay to re-tighten brake 7 afterwards.

And in certain favorable circumstances, represented by the , the value of the difference Δω of the speeds can remain between the thresholds Δ ₁ and Δ ₂ after the release control 38 has stopped (portion 51). This stable situation may correspond to slightly greater braking at the rear wheels 4, which is perfectly acceptable. It is then useless to re-tighten the brake 7, and the engine control unit 9 can then remain inactive, without unnecessarily stressing the rest of the device: the clamping control 41 of the is not ordered then.

Nomenclature

1 Automotive

2 front wheels

3 Front axle

4 rear wheels

5 Rear axle

6 Main brake

7 Emergency brake

8 Actuator

9 Engine control unit

10 Sensors

11 Caliper

12 Housing

13 Hydraulic cavity

14 Plunger

15 Screws

16 Nut

17 Screw-nut system

18 Electric motor

19 Order Delivery Module

20 Current intensity measurement module

21, 22 Wheel speed sensors

23 Decision Module

25 Speed measurement module

26 Intensity Diagram

27, 28, 29 Electrical power controls

30 Speed difference diagram

31 Boot Peak

32 Flat Portion

33 Growing Portion

34 Decreasing portion

35 Flat Portion

36 Intensity Diagram

37 Speed difference diagram

38 Release command

39 Decreasing portion

41 Tightening control

42 Boot Peak

43 Growing Portion

49 Release command.

50 Flat Portion

51 Stable portion of speed difference

60 Gearmotor

61 Bridle

62 Bridle

I Electric current intensity

dI/dt Time derivative of the intensity

t Time

t ₁ to t ₇ Threshold detection instants

Δ ₁ Lower speed difference threshold

Δ ₂ Upper speed difference threshold

Δω Speed difference

Claims (10)

Motor control unit (9) of an electro-mechanical brake (7) of a vehicle (1), comprising:
- a module for supplying brake and release commands (19) to an electric motor (18) for moving an actuator (8) of the brake (7) either in a braking direction or in a brake release direction (7),
- a speed measurement module (25) of a first wheel and a second wheel of the vehicle, and comparison of said wheel speeds,
- a decision module (23) connecting the rotation speed measurement module to the command supply module (19) and designed to order the latter to supply commands to the electric motor according to wheel speed comparisons,
characterized in that it comprises an intensity measurement module (20) of electric current (I) supplied to the electric motor during commands; and in that the decision module is designed to stop the brake release commands according to a criterion of level or level variation of said intensity. Motor control unit according to Claim 1, characterized in that the criterion corresponds to a reduction in a time derivative of the said intensity below a determined threshold. Motor control unit according to Claim 1, characterized in that the criterion corresponds to a reduction in a value of the said intensity below a determined threshold. Engine control unit according to any one of Claims 1 to 3, characterized in that the decision module is designed to stop the braking commands when a first wheel speed difference threshold (Δ1) is reached. Engine control unit according to any one of Claims 1 to 4, characterized in that the decision module is designed to start the release commands when a second threshold (Δ2) of wheel speed difference is reached. Engine control unit according to any one of Claims 1 to 5, characterized in that the second brake (7) is a parking brake. Braking device for a vehicle (1) comprising a first wheel (2) and a second wheel (4), the device comprising:
- a first brake (6) associated with the first wheel and which is a main brake controlled directly by the driver of the vehicle,
- a second brake (7) associated with the second wheel and which is an auxiliary brake,
- an actuator (8) of the second brake,
- an electric motor (18) moving the actuator in a direction of braking of the second brake, and in a direction of release of the second brake, opposite to the direction of braking,
-characterized by a motor control unit (9) of the electric motor according to any one of claims 1 to 6. Motor vehicle (1), characterized in that it comprises a braking device according to claim 7. Vehicle according to Claim 8, characterized in that the first wheel (2) is a front wheel, and the second wheel (4) is a rear wheel. Braking method for a motor vehicle comprising a first wheel (2), a second wheel (4), a main brake (6) controlled by a driver of the vehicle and a second brake (7) which is an electro-mechanical brake controlled by an engine control unit (9) as an emergency brake, the method comprising issuing commands to apply or release the second brake as a function of braking by the main brake and continuous comparisons of speeds of the first wheel and of the second wheel, characterized in that it comprises continuous measurements of intensity values of an electric current supplied to the electric motor, and of interruption of the release commands as soon as said intensity stabilizes during the release commands.