Electrical control method for parking brake with cooling estimation means

Abstract

A method for electrical control of a parking brake for a motor vehicle is provided by estimating the cooling of the braking members based on a cooling model that neglects conduction and radiation phenomena and exclusively uses a convection heat transfer model. The present invention relates to a method for electrically controlling a parking brake for a motor vehicle, said brake comprising at least one friction means connected to an electromechanical actuator capable of moving said friction means towards a braking member, the method comprising: - determining a clamping force for stopping the vehicle; - estimating the temperature fluctuations of the braking element based on a convective heat transfer model by neglecting the conductive and radiative heat transfer phenomena; - determining a fastening correction to be performed to maintain the determined fastening force based on an estimation of the temperature fluctuations; - applying a clamping force with clamping correction via an actuator; The following will be implemented.

Description

[Technical Field]

[0001] The present invention relates to a method for electrically controlling a parking brake (also called a parking brake) for a motor vehicle. [Background technology]

[0002] Disc or drum brakes are known from the prior art. Brakes generally comprise friction means connected to an actuating member (also called an actuator) that is capable of moving the friction means towards a braking member fixed to one of the vehicle's wheels. The purpose is to bring the friction means, for example a brake lining or brake pad, into contact with the braking member, thereby braking the vehicle by friction, or to move the friction means away from the braking member, thereby stopping braking. If the braking system is a disc brake, the braking member consists of a disc that rotates integrally with the rotation of the wheel. In the case of a drum brake, the braking member consists of a drum that rotates integrally with the rotation of the wheel.

[0003] The same brake can have multiple actuators. For example, the brake can include a hydraulic actuator used for the service brake and an electric actuator for the parking brake and emergency brake. In the latter case, it is also called an electrically controlled parking brake or an electric parking brake. Electric parking brakes are increasingly used as an alternative to manual parking brakes. Electric parking brakes are easier for the vehicle user to use and have smaller overall dimensions. When the user wants to stop parking the vehicle, they simply press the release button on the electric parking brake and, optionally, wait for a signal indicating that the electric parking brake has been effectively released before accelerating.

[0004] However, use of the brakes causes the braking members (discs if the brakes are disc brakes, or drums if the brakes are drum brakes) to heat up.

[0005] This heating must be taken into account when determining the parking brake application method, because once the vehicle is parked, the braking elements cool down, which can lead to the brakes releasing or over-application. For example, as the disc cools, its expansion decreases, which affects its contact with the friction means (pads or shoes) and reduces the application force. This loss of application force can then cause the vehicle to roll.

[0006] Therefore, estimating the cooling of the braking member is essential for determining an effective clamping force method.

[0007] It is known to estimate the cooling of braking components using a model that takes into account three heat transfer phenomena: convection, conduction, and radiation.

[0008] To estimate these three phenomena, a large number of parameters are required, which can only be determined by vehicle testing, in which case the following steps must be carried out: - implementing the equations with generic parameters - carrying out tests under various road conditions using temperature sensors - running a program (e.g., a Matlab script) that finds the best parameters to minimize the error between the estimated value and the actual temperature; - implementing a number of parameters in a software equation; - Carrying out a number of new tests in different road conditions to validate the temperature estimates.

[0009] Therefore, this type of method requires the management of a large number of abstract and model-dependent parameters and a large number of costly tests. This results in high estimation costs, especially in terms of time, while reducing the actual accuracy, which can lead to overestimating the engagement and shortening the brake life, or underestimating it and causing unexpected vehicle behavior. The engagement strategy takes into account the maximum temperature estimation error. That is, the engagement strategy corresponding to the temperature obtained by adding the maximum temperature estimation error to the temperature estimate is selected. Summary of the Invention [Problem to be solved by the invention]

[0010] The object of the present invention is to solve this problem in particular by proposing a method for the electrical control of a parking brake for a motor vehicle by estimating the cooling of the braking members based on a cooling model that neglects the conduction and radiation phenomena and exclusively uses a convection heat transfer model. [Means for solving the problem]

[0011] The object of the present invention is therefore a method for the electrical control of a parking brake for a motor vehicle, the brake comprising at least one friction means (pad / shoe lining) connected to an electromechanical actuator capable of moving said friction means towards a braking member (disk / drum) for braking, the method comprising: - determining a brake application force for stopping the vehicle; - estimating the temperature fluctuations of the braking element based on a convective heat transfer model by neglecting the conductive and radiative heat transfer phenomena; - determining a fastening correction to be performed to maintain the determined fastening force based on an estimation of the temperature fluctuations; - applying a clamping force with clamping correction via an actuator; The following will be implemented.

[0012] Such convective heat transfer models contain fewer parameters that depend primarily on the mechanical characteristics of the brake and are therefore known. No calibration of the parameters is required. Such models provide a more accurate estimation of the cooling, and therefore the actual temperature of the braking members.

[0013] Furthermore, because this cooling estimation is more reliable, the vehicle's ECU can shut off the brakes more quickly. The ECU determines the initial engagement force depending on the gradient, and then adjusts the engagement / disengagement depending on the temperature. In other words, the engagement strategy is adapted to the actual temperature, avoiding oversizing the brakes. Furthermore, since re-engagement is not necessary in this case, the time the ECU needs to continue supplying the brakes after engagement can be shortened.

[0014] According to other optional features of the above method, taken alone or in combination, -Convection heat transfer model is based on the following parameters: -h: convective heat transfer coefficient of air -m: Mass of the braking member -c p : Heat capacity of the material of the braking member -A s : Contact area between air and braking member Includes: -The heat transfer model is expressed as follows:

[0015]

number

[0016] where dT conv is the temperature fluctuation due to convection heat transfer phenomenon, T disc is the temperature of the braking member, T amb is the temperature of the air at the level of the contact area between the air and the braking member, and v is the velocity of the air at the level of the contact area between the air and the braking member. -The convective heat transfer coefficient h is determined using a model such as the Jurges model. -The mass change of the damping element over time is taken into account in the convective heat transfer model. The braking force is determined based on the gradient on which the vehicle is positioned and the vehicle's mass. - A fastening correction is carried out by reducing the fastening. -The tightening correction is carried out by increasing the tightening. The brake is a drum brake, the braking member being a drum and the friction member being a shoe with a lining. The brake is a disc brake, the braking member is a disc, and the friction member is a brake pad.

[0017] The invention also relates to a motor vehicle comprising an electronic control unit adapted to implement the method according to the invention. [Brief explanation of the drawings]

[0018] The invention will be better understood from the following description, given by way of example only, with reference to the accompanying drawings, in which: [Figure 1] 2A-2D show diagrammatically the various steps of an embodiment of the electrical control method according to the invention; [Figure 2] 1 is a graph showing the actual temperature change of a disk over time and two estimated curves according to two different models. DETAILED DESCRIPTION OF THE INVENTION

[0019] FIG. 1 shows a schematic diagram of steps in one embodiment of the method for electrically controlling a parking brake for a motor vehicle according to the present invention.

[0020] The parking brake includes at least one friction means connected to an electromechanical actuator operable to move the friction means towards the braking member to apply the brake.

[0021] In a first variant embodiment, the brake is a drum brake, the braking member is a drum and the friction member is a shoe with a lining.

[0022] In a second variant embodiment, the brake is also a disc brake, the braking members being discs and the friction members being brake pads.

[0023] This method involves the following steps: - Determining the brake engagement force FS to stop the vehicle (Step 0), -estimating the temperature fluctuations (heating and cooling) of the braking element based on the convection heat transfer model by ignoring the conduction and radiation heat transfer phenomena (step 1); - determining the brake engagement correction to be performed to maintain the determined brake engagement force FS based on the above-mentioned temperature fluctuation estimation (step 2); - A brake engagement force FS accompanied by engagement correction is applied via an actuator (step 3).

[0024] In particular, according to this method, the braking force FS is determined depending on the gradient on which the vehicle is positioned and the mass of the vehicle (step 0). This force is determined by applying the following equation:

[0025]

number

[0026] where: -m: Mass of the vehicle -g: Gravitational constant -μ: Heat loss - "slope": road gradient - "static wheel radius": radius of the road, and - "effective wheel radius": the point at which the force is applied (the center of the piston at the center of the wheel).

[0027] Next, the temperature fluctuation of the braking member is estimated based on the convective heat transfer model by ignoring the conductive and radiative heat transfer phenomena (Step 1).

[0028] An estimate of these temperature variations in the braking members as a result of heating and cooling over time (preferably cooling when stopped due to application of the parking brake) allows the change in clamping force to be determined.

[0029] For example, if the brake is a disc brake, a drop in the temperature of the braking material reduces the expansion of the braking material, causing the pad and disc to move apart, resulting in a decrease in clamping force. In the case of drum brakes, the opposite occurs: a decrease in expansion brings the drum and shoe closer together, leading to an increase in clamping force. In either case, the real-time clamping force will be far from the clamping force FS mentioned above.

[0030] Following estimation of braking temperature fluctuations, the tightening correction to be made to maintain the determined tightening force is determined from this estimation (Step 2). As explained above, temperature fluctuations cause the tightening force to fluctuate and deviate from the tightening force FS. By quantizing the temperature fluctuations, the tightening force fluctuations can be quantized, and therefore the tightening correction to be made to result in the tightening force FS can be estimated.

[0031] For example, if the brake is a disc brake, cooling of the disc is estimated. The clamping correction corresponds to an increase in clamping (of the pads against the disc) to regain the originally determined clamping force by compensating for the separation of the disc from the pads (due to the reduced expansion).

[0032] If the brake is a drum brake, the cooling of the drum is estimated. The clamping correction corresponds to the reduction of the clamping (of the shoe on the drum) to regain the clamping force that was originally determined by correcting for the approach of the drum to the shoe (reduced expansion).

[0033] Further, a clamping force with clamping correction is applied via the actuator (step 3). Thus, an optimal stopping of the vehicle is obtained by applying a clamping force FS, but this optimal stopping is obtained by applying a clamping force different from that which would have been applied without estimating the temperature fluctuations and different from that which would not have resulted in the clamping force FS, and which may be greater or less than the clamping force FS depending on the type of braking element, in particular.

[0034] For the convective heat transfer model used in step 1, this includes the following parameters: -h: convective heat transfer coefficient of air -m: Mass of the braking member -c p : Heat capacity of the material of the braking member -A s : Contact area between air and braking member According to one preferred embodiment, the heat transfer model is expressed as follows:

[0035]

number

[0036] where: -dT conv : Temperature fluctuation due to convective heat transfer phenomenon -T disc :Temperature of braking member -T amb : Air temperature at the contact area level between the air and the braking member -v: Air velocity at the contact area level between the air and the braking member Parameters v and T amb Since the values ​​come from the sensors, they are readily available.

[0037] Parameter T disc corresponds to an estimate of the temperature of the braking member (cooling plus heating).

[0038] Parameters m and c p and A s is known as a mechanical feature.

[0039] As an example, the table below shows various disc characteristics for three types of brakes.

[0040] [Table 1]

[0041] The parameter h, which is the convective heat transfer coefficient of the air, must be estimated according to the air velocity v at the level of the contact area between the air and the damping member.

[0042] According to one particular embodiment, the Jurges model is used.

[0043] Siv≦5m / s In that case: h=4xv+5.6 Siv>5m / s Then:h=7.1xv ∧ (0.78) Thus, the estimation of the temperature variation of the braking element is advantageously performed simply, quickly and accurately as shown in Figure 2. This figure shows the temperature change (°C) of the disk as a function of time (s). Thus, cooling is observed. Figure 2 has three curves:

[0044] a. Estimation using a heat transfer model that takes into account convective, conductive, and radiative heat transfer b. Estimation using the heat transfer model according to the present invention c. Actual temperature measured The following is confirmed:

[0045] -The average difference between the estimated and actual curves is 21.39°C for curve a, but only 14.15°C for curve b.

[0046] -The maximum difference between the estimated and actual curves is 46.65°C for curve a, but only 36.7°C for curve b.

[0047] According to a particular embodiment, the mass variation of the braking element over time is taken into account in the convective heat transfer model. Indeed, use of the brake leads to wear over time, particularly of the braking element. The braking element loses material through friction and corrosion, resulting in a loss of mass.

[0048] Therefore, the parameter m in the convective heat transfer model is a time-dependent parameter: m(t), which can then be estimated by a predictive wear model of the disk, just like the parameter h.

[0049] The invention also relates to a motor vehicle comprising an electronic control unit adapted to implement the method according to the invention.

Claims

1. 1. A method for electrically controlling a parking brake for a motor vehicle, said brake comprising at least one friction means connected to an electromechanical actuator capable of moving the friction means towards a braking member to apply braking force, comprising: - determining the braking force for stopping the vehicle without applying braking force; - estimating the temperature fluctuations of the damping member based on a convective heat transfer model by neglecting the conductive and radiative heat transfer phenomena; - determining the fastening corrections to be carried out to maintain the determined fastening force based on an estimation of the temperature fluctuations; - applying a first clamping force with clamping correction via an actuator; A method characterized by carrying out the steps of:

2. The convective heat transfer model is based on the following parameters: -h: convection heat transfer coefficient of air -m: Mass of braking member -c ｐ : Heat capacity of the braking material -A ｓ : Contact area between air and braking member The method of claim 1 , comprising:

3. The heat transfer model is expressed as follows: [Equation 1] Here, dT ｃｏｎｖ is the temperature fluctuation due to the convection heat transfer phenomenon, T ｄｉｓｃ is the temperature of the braking member, T ａｍｂ is the temperature of the air at the level of the contact area between the air and the braking member, and v is the velocity of the air at the level of the contact area between the air and the braking member. The method of claim 2.

4. 4. The method of claim 2 or 3, wherein the convective heat transfer coefficient h is determined using a model such as the Jurges model.

5. 5. The method according to claim 2, wherein the change in mass of the damping member over time is taken into account in a convective heat transfer model.

6. 10. A method according to any one of the preceding claims, wherein the application force of the brakes is determined as a function of the gradient on which the vehicle is placed and the mass of the vehicle.

7. 10. The method according to any one of the preceding claims, wherein the fastening modification is performed by fastening reduction.

8. 10. The method according to any one of the preceding claims, wherein the fastening correction is performed by increasing the fastening.

9. 10. A method according to any one of the preceding claims, wherein the brake is a drum brake, the braking member being a drum and the friction member being a shoe with a lining.

10. 10. A method according to any one of the preceding claims, wherein the brake is a disc brake, the braking members are discs and the friction members are brake pads.

11. A motor vehicle including an electronic control unit configured to perform the method according to any one of claims 1 to 10.

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