Method for determining a hydraulic pressure value to be supplied in a braking device

Abstract

The invention relates to a method for determining a hydraulic pressure value to be provided in a braking device (6) of a motor vehicle, comprising the following steps, during a tightening: - determining a target total tightening force value to be exerted on the piston, - determining a main force value that the screw / nut system is capable of exerting alone on the piston - determining a missing force value to be exerted on the piston in addition to the main force - determining a future loss of tightening force value corresponding to the force exerted less by the screw / nut system as soon as, after the hydraulic system (8) has exerted an additional tightening force on the piston, this hydraulic system (8) no longer exerts this additional tightening force on the piston;- from the missing force value, the future clamping force loss value and a piston dimension, determination of a target hydraulic pressure value to be provided by the hydraulic system Figure for abstract: figure 1;

Description

Title of the invention: Method for determining a hydraulic pressure value to be supplied in a braking device

[0001] The invention relates to braking devices for motor vehicles, in particular parking brakes.

[0002] A parking braking device is already known in the prior art, comprising a brake lining, a braking piston intended to clamp the lining, a screw / nut system, which is by definition dimensioned to be irreversible and which is actuated by an electric gear motor to exert a main clamping force on the piston, and a hydraulic pressure generation and modulation system to exert an additional, optional, clamping force on the piston. When the vehicle is parked, the piston is clamped against the brake lining. For this purpose, a target clamping force value to be exerted on the piston is determined. If the screw / nut system alone cannot exert the target clamping force on the piston, in particular due to stalling of the electric motor, then a hydraulic pressure request is sent.The hydraulic system responds by providing a hydraulic pressure of 100 bars on the piston for a certain period of time so that, once this hydraulic pressure is released, the irreversible screw / nut system continues to exert a force on its own so great that it necessarily exceeds the target value of the clamping force.

[0003] A disadvantage of this technique is that each 100 bar hydraulic pressure phase wears out the hydraulic pressure system. As a corollary, it is recommended, or even required in some standards, not to accumulate more than 1000 100 bar pressure phases per 100,000 tightening cycles. Thus, it can become difficult to systematically achieve the target tightening value while respecting these recommendations. In addition, each 100 bar hydraulic pressure phase is energy-intensive.

[0004] The invention aims in particular to make it possible to achieve the target value of clamping force on the piston while reducing wear on the hydraulic system, as well as the energy used by this system. It also aims to allow compliance with the recommendations while still achieving the target clamping value.

[0005] To this end, the invention relates to a method for determining a hydraulic pressure value to be supplied in a motor vehicle braking device,

[0006] the braking device comprising:

[0007] - a brake piston intended to tighten a brake lining,

[0008] - a screw / nut system operated by an electric motor to exert a force main clamping on the piston, and

[0009] - a hydraulic system for generating and modulating hydraulic pressure to exert additional clamping force on the piston,

[0010] the method comprising the following steps, during tightening:

[0011] - determination of a target total clamping force value to be exerted on the piston,

[0012] - determination of a main force value that the screw / nut system is capable of exert alone on the piston when the hydraulic system has not yet provided additional clamping force during this clamping,

[0013] - determination of a missing force value to be exerted on the piston in supplement of the main force, to reach the target total clamping force value;

[0014] - determination of a value of future loss of clamping force corresponding to the less force exerted by the screw / nut system as soon as, after the hydraulic system has exerted an additional clamping force on the piston, this hydraulic system no longer exerts this additional clamping force on the piston;

[0015] - from the missing force value, the future force loss value of clamping and a dimension of the piston, determining a target hydraulic pressure value to be provided by the hydraulic system to exert the additional clamping force on the piston so that, after the hydraulic system has exerted this additional force on the piston, when the hydraulic system no longer exerts this additional clamping force on the piston, the screw / nut system alone exerts on the piston a clamping force equal to the total target clamping force value.

[0016] Thus, the target value of additional hydraulic pressure is no longer an arbitrary value of 100 bars. It is determined in such a way as to allow the screw / nut system, once this pressure is released, to exert the target clamping force without exceeding it.

[0017] It should be noted that this pressure value is not equal to the force missing from the electric motor, it is greater. It has in fact been found that, when the additional force coming from the hydraulic system thanks to this pressure ceases to push the piston, then the screw / nut system, although irreversible, loses part of this additional force exerted on the piston. This lost force is therefore taken into account in advance to determine the hydraulic pressure value to be provided.

[0018] By adapting the pressure to be supplied to the piston so as to reach the target clamping force value without exceeding it, it is possible to require pressure phases well below 100 bars. The hydraulic system is therefore saved, as is the energy deployed. In addition, this makes it possible to comply with the recommendations in this area. It also becomes possible, with equal wear, to multiply the number of pressure requests since the required pressures have values ​​much lower than 100 bars. The hydraulic system can therefore be used more often, and therefore reaches the target clamping force more often.

[0019] Other optional features, taken alone or in combination, follow.

[0020] Advantageously, to determine the main force value that the screw / nut system is capable of exerting alone on the piston when the hydraulic system has not yet provided any additional clamping force during this clamping, the method comprises the following steps:

[0021] - initialization of the tightening and,

[0022] - determination of a maximum force value that the screw / nut system can exert alone on the piston during tightening before stalling the electric motor actuating the screw / nut system.

[0023] Thus, it is the stalling of the electric motor that defines the maximum main force value that the screw / nut system can exert. A current measurement is used to determine the value of this main force that is being applied by the entire geared motor to the screw / nut system, just before stalling. If the motor does not stall, then hydraulic pressure is not required. The method is therefore implemented during full tightening, depending on whether or not the motor stalls.

[0024] Alternatively, the method comprises, to determine the force value that the screw / nut system is capable of exerting alone on the piston when the hydraulic system has not yet provided any additional clamping force during this clamping, a step of predetermining a force value to be reached by the screw / nut system during clamping.

[0025] In this variant, a maximum power that the electric motor will produce is determined in advance, and it is therefore planned in advance to use hydraulic pressure to exert an additional force. This variant is notably implemented in the context of re-tightening a parking brake after a predetermined period of time, to anticipate any release due to cooling of the vehicle elements.

[0026] Advantageously, the value of future loss of clamping force is determined from a percentage, in particular 30%, of an additional clamping force value exerted by the hydraulic system.

[0027] Thus, it has been found that, with respect to the total force applied by both the screw / nut system and the hydraulic system, the loss of tightening once the hydraulic pressure is released is a function of the tightening force applied by the hydraulic system before this release. This loss is generally of the order of 30% of the additional hydraulic force applied before deactivation of the hydraulic system.

[0028] Preferably the hydraulic pressure value is determined from the following formula:

[0029] hydraulic pressure = tolerance + missing force value l piston diameter \\ ■ r \ (------5—- j '"Fri 1-future loss of strength] Or tolerance is a predetermined tolerance value, for example 10 bars.

[0030] This tolerance value, added to the necessary hydraulic pressure, corresponds to a phenomenon observed according to which part of the hydraulic pressure is sometimes lost in the braking device.

[0031] The invention also provides a method for applying a parking brake, characterized in that it implements a method described previously.

[0032] The invention also provides a computer program comprising instructions which, when the program is executed by a computer, cause the latter to implement the steps of the method for determining a hydraulic pressure value described above or of the method for applying a parking brake described above.

[0033] Also provided according to the invention is a computer-readable recording medium comprising instructions which, when executed by a computer, cause the latter to implement the steps of the method for determining a hydraulic pressure value described above or of the method for applying a parking brake described above.

[0034] The invention also provides a processing system comprising a processor configured to implement the steps of the method for determining a hydraulic pressure value described above or of the method for applying a parking brake described above.

[0035] According to the invention, a braking system is also provided comprising:

[0036] - a brake piston intended to tighten a brake lining,

[0037] - a screw / nut system operated by an electric motor to exert a force main clamping on the piston, and

[0038] - a hydraulic system for generating and modulating hydraulic pressure to exert additional clamping force on the piston,

[0039] - the processing system described above.

[0040] Thus, this braking system is capable of, and even configured to, implement the steps of the method described previously.

[0041] Advantageously, the braking system comprises at least one braking disc, the piston being configured to exert a clamping force towards the disc during a tightening.

[0042] Preferably, the braking system comprises a floating caliper.

[0043] According to the invention, a vehicle is also provided comprising a braking system as described above. Brief description of the figures

[0044] The invention will be better understood on reading the following description, given solely by way of example and with reference to the appended drawings in which:

[0045] [Fig-1] is a diagram of a braking system according to one embodiment of the invention;

[0046] [Fig.2] is a diagram of a vehicle according to one embodiment of the invention;

[0047] [Fig.3] is a flowchart of a method according to an embodiment of the invention. Detailed description

[0048] [Fig.l] shows a braking system 1 according to an embodiment of the invention.

[0049] It comprises a data processing system 2. The processing system 2 comprises a processor 3 configured to implement the steps of the method 100 described below. For this purpose, the system 2 also comprises a computer-readable recording medium 4 comprising instructions which, when executed by a computer, more specifically by the processor 3, cause the latter to implement the steps of the method 100 described below. Specifically, the medium 4 contains a computer program 5 comprising instructions which, when the program is executed by a computer, here by the processor 2, cause the latter to implement the steps of the method 100 described below. This data processing system 2 allows the implementation of the method 100 by obtaining the necessary data and by providing the necessary data to the components described below.

[0050] The braking system 1 also comprises an electromechanical vehicle braking actuator 6, an actuator which will also be referred to hereinafter as a “braking device”. This actuator 6 is known to those skilled in the art and is conventional. Thus, this actuator 6 comprises, in a manner not illustrated, a braking piston intended to clamp a brake lining of a wheel of a vehicle 9. This actuator 6 also comprises a screw / nut system actuated by an electric motor to exert a main clamping force on the piston. This actuator 6 comprises a floating caliper. This actuator 6 also contains a hydraulic receiver for receiving hydraulic pressure, so as to exert an additional clamping force against the piston of the actuator.Thus, the actuator piston is configured to receive a main clamping force from the screw / nut system, powered by an electric motor, and an additional clamping force from a hydraulic source, the two forces adding together to exert a clamping of the piston on the brake lining.

[0051] The braking system 1 also comprises, in a manner not illustrated, at least one braking disc, the piston of the actuator 6 being configured to exert a clamping force towards the disc during clamping. The brake lining is in fact placed on this disc. This brake lining can therefore be called, in this case, a “pad”.

[0052] Alternatively, the braking system could comprise a drum. The brake lining would then be a “segment”. The method 100 applies in the same way to a drum brake.

[0053] The braking system 1 also comprises a system 7 for controlling the electric motor of the actuator. This control system 7 is configured to send, to the data processing system 2, data such as voltage and current values ​​of the electric motor of the actuator 6. This control system 7 is also configured to receive from the processing system 2 instructions for controlling the motor, which it converts into intensity and voltage to be supplied to the electric motor of the actuator 6.

[0054] The braking system 1 also comprises a hydraulic system 8 for generating and modulating a hydraulic pressure to exert an additional clamping force on the piston of the actuator 6. This pressure system 8 is configured to send to the data processing system 2 pressure data from the hydraulic receiver of the actuator 6. This pressure system 8 is configured to receive the hydraulic pressure instructions issued by the processing system 2 and to generate the hydraulic pressure to be exerted on the hydraulic receiver of the actuator 6, so as to exert the additional clamping force on the piston of the actuator. In a variant not illustrated, the system 8 further comprises vehicle stabilization means, or stabilization system, usually designated by the brand name “ESP” (for “Electronic Stability Control” in English).

[0055] The braking system 1 is integrated into a motor vehicle 9. Specifically, the data processing system 2, the hydraulic system 8 for generating and modulating hydraulic pressure and the control system 7 of the electric motor are integrated into the electronic control unit ("ECU") of the vehicle 9. They could also be integrated into the stabilization system of the vehicle. The electromechanical actuator 6 is integrated into one of the wheels. Three other similar or identical actuators 6 are respectively integrated into the other three wheels of the vehicle 9. These four actuators are connected to the ECU and in particular to the control system 7 of their electric motors and to the hydraulic system 8. Naturally, the braking devices 6 could be connected to only two wheels to carry out parking only from these two wheels.

[0056] We will now describe the method 100 for determining a pressure value. hydraulic to be provided in one of the braking devices 6. It is implemented in the same way for the other devices 6 of the vehicle.

[0057] This method 100 is controlled by the data processing system 2, which implements it within the device 6 via the engine control systems 7 and pressure 8.

[0058] Step 101 is the initialization of the application. It occurs when a driver of the vehicle starts parking the vehicle 9 and requests the device 6 to apply the brake lining.

[0059] Step 102 is determining a target total clamping force value to be exerted on the piston. For the processing system 2, it consists of defining the force to be exerted on the piston for this clamping, based on known sizing data for the elements of the device 6, but also possibly based on other factors such as the force required by the driver during this clamping, regulations, and external factors specific to the time of parking.

[0060] Step 103 is the determination of a main force value that the screw / nut system is capable of exerting alone on the piston when the hydraulic system has not yet provided additional clamping force during this clamping. It consists of determining a maximum force value that the screw / nut system can exert alone on the piston during clamping, with a view to trying to reach the target total clamping force value, before stalling the electric motor actuating the screw / nut system. Thus, in particular as a function of the voltage and intensity values ​​obtained by the control system 7, the processing system 2 determines that the motor is about to stall and determines the maximum force value that it can exert without stalling.

[0061] Alternatively, this step 103 corresponds to a step of predetermining a force value to be reached by the screw / nut system during tightening. Thus, the system 2 defines in advance a main force value, lower than the target total tightening force value, which will be exerted on the piston by the screw / nut system without stalling the engine, and without necessarily seeking to approach a stall of the engine. This alternative is implemented in particular in the case of retightening the piston after a determined period of time. This retightening is intended to anticipate any loosening due to possible cooling of the elements. The value of the main tightening force exerted on the piston by the screw / nut system alone is thus determined in advance and when the hydraulic system has not yet provided additional tightening force during this tightening. The rest of the steps is the same regardless of the variant chosen in step 103.

[0062] Step 104 is the determination of a missing force value to be exerted on the piston in addition to the main force, to reach the target total clamping force value. Thus, the processing system 2 realizes the difference between the force total target determined, to be exerted on the piston to achieve this tightening, and the main force exerted by the screw / nut system on the piston. It deduces the missing force to be exerted on the piston.

[0063] Step 105 is the determination of a value of future loss of clamping force corresponding to the force exerted less by the screw / nut system as soon as, after the hydraulic system 8 has exerted an additional clamping force on the piston, this hydraulic system 8 no longer exerts this additional clamping force on the piston. Indeed, it has been found that, despite the irreversible nature of the screw / nut system, when the latter is first accompanied in its main force on the piston by an additional hydraulic force exerted on the same piston, after the additional hydraulic force fades, the clamping force exerted on the piston by the screw / nut system does not remain equal to the total of the main force and the additional force.This loss of force, despite the irreversible nature of the screw / nut system and therefore despite the fact that the clamping stroke of the piston is not modified, is due to a series of complex parameters including in particular the stiffness of the different elements of the device 6, between the brake lining and the electric motor of the device 6.

[0064] This future loss of clamping force is determined from a percentage of an additional clamping force value exerted by the hydraulic system 8. It has been found that a value of 30% is relevant.

[0065] Step 106 is, from the missing force value, the future clamping force loss value and a dimension of the piston, the determination of a target hydraulic pressure value to be provided by the hydraulic system 8 to exert the additional clamping force on the piston so that, after the hydraulic system 8 has exerted this additional force on the piston, when the hydraulic system 8 no longer exerts this additional clamping force on the piston, the screw / nut system alone exerts on the piston a clamping force equal to the target total clamping force value.The processing system 2 thus determines the appropriate hydraulic pressure to be supplied so that the main tightening force exerted by the screw / nut system and the additional force exerted by the hydraulic system 8 add up and that, once the hydraulic system 8 no longer exerts any additional force, the force exerted by the screw / nut system alone is, after deducting the loss of force, equal to the total target tightening force value.

[0066] The treatment system 2 determines this pressure based on the following formula:

[0067] [Math.sl] hydraulic pressure = tolerance + missing force value piston diameter \ , r . , 1 -------------i '^*1 l-loss t ut ure of force] , where tolerance is a predetermined tolerance value, for example 10 bars. This tolerance value allows a slight margin to be taken in the case where the force exerted on the piston is partly lost in the other elements of the device 6.

[0068] Below is an example, taking into consideration consistent values ​​of the domain.

[0069] During a tightening operation, the processing system 2 determines that the total target tightening force of the piston is 18 kN (kiloNewtons). The processing system 2 determines, using data from the motor control system 7, that the motor stalls if the screw / nut system exerts a main tightening force, alone, greater than 14 kN. The main tightening force is therefore 14 kN, and the missing force value is therefore 4 kN. If the piston has a diameter of 36 millimeters, choosing a tolerance value of 10 bars and a future tightening force loss value of 30%, it follows from the previous formula that the hydraulic pressure to be supplied is 66 bars. For illustration purposes, it would be 35 bars if the piston had a diameter of 54 millimeters, all other values ​​being equal. These pressure values ​​are far from the pressures of 100 bars arbitrarily required in the state of the art.

[0070] This result can be read in the table below, which sets out the hydraulic pressure values ​​to be provided for tolerances of 10 bars, loss values ​​of 30%, for pistons ranging from 36 to 54mm in diameter (in line) and missing forces ranging from 1 to 10 kN (in column). The internal values ​​of the table are the hydraulic pressure values, in bar, therefore each corresponding to a diameter and a missing force. The values ​​of the example above, of 35 and 66 bars, are underlined in the table. [Tables 1] Missing force (kN) Piston diameter (mm) 36 38 40 42 44 46 48 50 52 54 1 24 23 21 20 19 19 18 17 17 16 2 38 35 33 31 29 27 26 25 23 22 3 52 48 44 41 38 36 34 32 30 29 4 66 60 55 51 48 44 42 39 37 35 5 80 73 67 62 57 53 49 46 44 41 6 94 86 78 72 66 62 57 54 50 47 7 108 98 90 82 76 70 65 61 57 54 8 122 111 101 92 85 79 73 68 64 60 9 136 123 112 103 95 87 81 75 71 66 10 150 136 124 113 104 96 89 83 77 72

[0071] It may be noted that, with respect to requests of 100 bars, in many configurations, the method makes it possible to require lower pressures. It therefore makes it possible to carry out more pressure requests with respect to the recommendations which cap the number of requests at 1000 per 100,000 tightening cycles, for requests of 100 bars. By carrying out pressure requests of less than 100 bars, the method also makes it possible to save the hydraulic system 8 and its energy. For cases where a pressure greater than 100 bars is necessary, the method makes it possible to achieve the target tightening force where a request of 100 bars does not make it possible to achieve it.

[0072] The formula and the values ​​in the table are naturally valid for the case of hydraulic tightening, the missing force being predetermined there.

[0073] The invention is not limited to the embodiments presented and other embodiments will become clear to those skilled in the art. List of references

[0074] 1: Braking system 2: Data processing system 3: Processor

[0075] 4: Data support

[0076] 5: Computer program

[0077] 6: Electromechanical actuator / Braking device

[0078] 7: Electric motor control system

[0079] 8: Hydraulic system for generating and modulating pressure

[0080] 9: vehicle

[0081] 100: Method for determining a hydraulic pressure value

Claims

Claims

1. Method (100) for determining a hydraulic pressure value to be supplied in a braking device (6) of a motor vehicle (9), the braking device (6) comprising: - a brake piston intended to tighten a brake lining, - a screw / nut system operated by an electric motor to exert a main clamping force on the piston, and - a hydraulic system (8) for generating and modulating hydraulic pressure to exert an additional clamping force on the piston, the method (100) being characterized in that it comprises the following steps, during tightening: - determination (102) of a target total clamping force value to be exerted on the piston, - determination (103) of a main force value that the screw / nut system is capable of exerting alone on the piston when the hydraulic system (8) has not yet provided additional clamping force during this clamping, - determining (104) a missing force value to be exerted on the piston in addition to the main force, to reach the target total clamping force value; - determination (105) of a value of future loss of clamping force corresponding to the force exerted less by the screw / nut system as soon as, after the hydraulic system (8) has exerted an additional clamping force on the piston, this hydraulic system (8) no longer exerts this additional clamping force on the piston; - from the missing force value, the future clamping force loss value and a dimension of the piston, determining (106) a target hydraulic pressure value to be provided by the hydraulic system to exert the additional clamping force on the piston so that, after the hydraulic system has exerted this additional force on the piston, when the hydraulic system no longer exerts this additional clamping force on the piston, the screw / nut system alone exerts on the piston a clamping force equal to the target total clamping force value.

2. Method (100) according to the preceding claim, comprising, for determining (103) the main force value that the screw / nut system is capable of exerting alone on the piston when the hydraulic system (8) has not yet provided any additional clamping force during this clamping, the following steps: - initialization (101) of the clamping and, - determination of a maximum force value that the screw / nut system can exert alone on the piston during the clamping before stalling of the electric motor actuating the screw / nut system.

3. Method (100) according to claim 1, comprising, to determine (103) the force value that the screw / nut system is capable of exerting alone on the piston when the hydraulic system (8) has not yet provided any additional clamping force during this clamping, a step of predetermining a force value to be reached by the screw / nut system during clamping.

4. Method (100) according to any one of the preceding claims, wherein the future clamping force loss value is determined from a percentage, in particular 30%, of an additional clamping force value exerted by the hydraulic system (8).

5. A method (100) according to any preceding claim, wherein the hydraulic pressure value is determined from the following formula: . > , ,. , , missing force value hydraulic pressure = tolerance +----------t—---------------- 1 * xt piston diameter ± rtrl |------—>---। Vfuture force loss] , where tolerance is a predetermined tolerance value, for example 10 bar.

6. Method for applying a parking brake, characterized in that it implements a method (100) for determining a hydraulic pressure value according to any one of the preceding claims.

7. A computer program (5) comprising instructions which, when the program is executed by a computer, cause the computer to implement the steps of the method (100) for determining a hydraulic pressure value according to any one of claims 1 to 5 or of the method for applying a parking brake according to claim 6.

8. A computer-readable recording medium (4) comprising instructions which, when executed by a computer, cause the computer to carry out the steps of the method (100) for determining a hydraulic pressure value according to any one of claims 1 to 5 or the method for applying a parking brake according to claim 6.

9. A processing system (2) comprising a processor (3) configured to implement the steps of the method (100) according to any one of claims 1 to 5 or of the method of applying a parking brake according to claim 6.

10. Braking system (1) comprising: - a braking piston intended to clamp a brake lining, - a screw / nut system actuated by an electric motor to exert a main clamping force on the piston, and - a hydraulic system (8) for generating and modulating a hydraulic pressure to exert an additional clamping force on the piston, characterized in that it comprises a processing system (2) according to claim 9.

11. Braking system (1) according to the preceding claim, comprising at least one braking disc, the piston being configured to exert a clamping force towards the disc during clamping.

12. Braking system (1) according to the preceding claim, comprising a floating caliper.

13. Vehicle (9) comprising a braking system according to any one of claims 10 to 12.

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