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

Abstract

The invention relates to a method for determining a value of hydraulic pressure to be supplied in a braking device (6) of a motor vehicle, comprising the following steps, during a tightening: - determination of a value of total target tightening force to be exerted on the piston, - determination of a value of principal force that the screw / nut system is capable of exerting alone on the piston - determination of a value of missing force to be exerted on the piston in addition to the principal force - determination of a value of future loss of tightening force 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 supplied by the hydraulic system Figure for the abbreviation: figure 1;

Description

Title of the invention: Method for determining the 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 achieve the target 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 ensure compliance with recommendations while still achieving the target clamping force.

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

[0006] the braking system comprising:

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

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

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

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

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

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

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

[0014] - determination of a future clamping force loss value corresponding to the force exerted less 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 missing force in the electric motor; it is greater. It has been observed that when the additional force from the hydraulic system, due to this pressure, ceases to push the piston, the screw / nut system, although irreversible, loses some of this additional force exerted on the piston. This lost force is therefore taken into account in advance to determine the required hydraulic pressure value.

[0018] By adjusting the pressure supplied to the piston to achieve the target clamping force without exceeding it, pressure phases well below 100 bar can be required. This saves on the hydraulic system and reduces energy consumption. Furthermore, it allows compliance with relevant recommendations. It also becomes possible, with equal wear, to increase the number of pressure requests since the required pressures are much lower than 100 bar. The hydraulic system can therefore be used more frequently, and Therefore, the target clamping force is reached 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 pressure on the piston alone during tightening before the electric motor actuating the screw / nut system is locked in place.

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

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

[0025] In this variant, a maximum power output for the electric motor is determined in advance, and the use of hydraulic pressure to exert additional force is therefore planned in advance. This variant is notably implemented when tightening a parking brake after a predetermined period of time, to anticipate any loosening due to cooling of vehicle components.

[0026] Advantageously, 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.

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

[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 required hydraulic pressure, corresponds to an observed phenomenon whereby some 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, lead the computer 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] The invention also provides a computer-readable recording medium comprising instructions which, when executed by a computer, lead the computer to implement the steps of the method for determining a hydraulic pressure value described above or 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 force 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 process described above.

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

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

[0043] The invention also provides for a vehicle comprising a braking system as described above. Brief description of the figures

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

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

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

[0047] [Fig.3] is a logic diagram of a process according to one implementation method of the invention. Detailed description

[0048] A braking system 1 according to an embodiment of the invention is shown on a [Fig.1].

[0049] It includes a data processing system 2. The processing system 2 includes a processor 3 configured to implement the steps of the process 100 described below. To this end, the system 2 also includes a computer-readable storage 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 process 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 process 100 described below. This data processing system 2 enables the implementation of the process 100 by obtaining the necessary data and providing the necessary data to the components described below.

[0050] The braking system 1 also includes an electromechanical braking actuator 6 for a vehicle, which will also be referred to hereafter as the "braking device." This actuator 6 is known to those skilled in the art; it is conventional. Thus, this actuator 6 includes, as not shown, a brake piston for clamping a brake lining on a wheel of a vehicle 9. This actuator 6 also includes a screw / nut system actuated by an electric motor to exert a primary clamping force on the piston. This actuator 6 includes 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 actuator piston.Thus, the actuator piston is configured to receive a primary clamping force from the screw / nut system, powered by an electric motor, and an additional clamping force from a hydraulic source; the two forces combine to clamp the piston onto the brake lining.

[0051] The braking system 1 also includes, but is not shown, at least one brake disc, the piston of the actuator 6 being configured to exert a clamping force on the disc during application. The brake lining is indeed placed on this disc. This brake lining can therefore be called, in this case, a "pad".

[0052] Alternatively, the braking system could include a drum. The brake lining would then be a "segment". Method 100 applies in the same way to a drum brake.

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

[0054] The braking system 1 also includes a hydraulic system 8 for generating and modulating hydraulic pressure to exert an additional clamping force on the actuator piston 6. This pressure system 8 is configured to send pressure data from the hydraulic receiver of the actuator 6 to the data processing system 2. 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 actuator piston. In an embodiment not shown, the system 8 further includes vehicle stabilization means, or a stabilization system, usually designated by the mark "ESP" (for "Electronic Stability Control").

[0055] The braking system 1 is integrated into a motor vehicle 9. Specifically, the data processing system 2, the hydraulic pressure generation and modulation system 8, and the electric motor control system 7 are integrated into the vehicle's electronic control unit (ECU) 9. They could also be integrated into the vehicle's stabilization system. The electromechanical actuator 6 is integrated into one of the wheels. Three other similar or identical actuators 6 are 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 perform parking using only those 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 principal force value that the screw / nut system is capable of exerting on the piston on its own when the hydraulic system has not yet provided any additional clamping force during this tightening. It consists of determining a maximum force value that the screw / nut system can exert on the piston alone during tightening, with the aim of reaching the target total clamping force value before the electric motor actuating the screw / nut system stalls. Thus, based in particular on the voltage and current values ​​obtained by the control system 7, the processing system 2 determines when the motor is about to stall and determines the maximum force value it can exert without stalling.

[0061] Alternatively, this step 103 corresponds to a predetermination step of a force value to be achieved by the screw / nut system during tightening. Thus, system 2 defines in advance a principal 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 attempting to approach engine stalling. This alternative is implemented in particular when the piston is retightened after a predetermined period of time. This retightening is intended to anticipate any loosening due to possible cooling of the components. The principal tightening force exerted on the piston by the screw / nut system alone is thus determined in advance, and this occurs when the hydraulic system has not yet provided any additional tightening force during this tightening. The subsequent steps are 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, in order to reach the target total clamping force value. Thus, the processing system 2 calculates the difference between the force The total target force to be applied to the piston to achieve this tightening is determined, along with the main force exerted by the screw / nut system on the piston. From this, the remaining force to be applied to the piston is deduced.

[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 supplied by the hydraulic system 8 to exert on the piston the additional clamping force 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 total target clamping force value.The processing system 2 thus determines the appropriate hydraulic pressure to be supplied so that the main clamping 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 deduction of the force loss, equal to the target total clamping 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 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] Here is an example below, taking into consideration consistent values ​​of the domain.

[0069] During tightening, the processing system 2 determines that the total target tightening force of the piston is 18 kN (kilonewtons). Using data from the engine control system 7, the processing system 2 determines that the engine will stall if the screw / nut system alone exerts a primary tightening force exceeding 14 kN. The primary tightening force is therefore 14 kN, and the missing force value is thus 4 kN. If the piston has a diameter of 36 millimeters, choosing a tolerance value of 10 bar and a future tightening force loss value of 30%, the preceding formula results in the hydraulic pressure to be supplied being 66 bar. For illustrative purposes, it would be 35 bar if the piston had a diameter of 54 millimeters, all other values ​​being equal. These pressure values ​​are far from the arbitrarily required pressures of 100 bars in the prior art.

[0070] This result can be seen in the table below, which shows the hydraulic pressure values ​​to be supplied for tolerances of 10 bar, loss values ​​of 30%, for pistons ranging from 36 to 54 mm in diameter (in rows) and missing forces ranging from 1 to 10 kN (in columns). The internal values ​​in the table are the hydraulic pressure values, in bar, each corresponding to a diameter and a missing force. The values ​​from the example above, 35 and 66 bar, 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 can be noted that, compared to 100-bar requests, in many configurations, the method allows for lower pressure requirements. It therefore allows for more pressure requests compared to the recommendations that limit the number of requests to 1000 per 100,000 tightening cycles for 100-bar requests. By using pressure requests below 100 bar, the method also saves on the hydraulic system 8 and its energy consumption. In cases where a pressure above 100 bar is required, the method makes it possible to achieve the target tightening force where a 100-bar request would not.

[0072] The formula and 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 shown and other embodiments will be obvious to a person skilled in the art. List of references

[0074] 1: Braking system 2: Data Processing System 3: Processor

[0075] 4: Data carrier

[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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