Method of controlling a vehicle parking brake

Abstract

Method for controlling a vehicle parking brake configured to apply a friction means on a braking member, comprising the following steps: - detecting (22) a request to apply the brake, - depending on the parking conditions of the vehicle, determining a target application force value making it possible to keep said vehicle stationary, - actuating the brake so as to provide an application force corresponding to the target value, characterized in that the step of determining a target application force value comprises the following steps: - determining a first application force value, making it possible to keep said vehicle stationary for an unlimited period, even after releasing the brake, - verifying (23) the presence of a driver at the driving position of the vehicle, - if the driver is present at his driving position, using (24) as the target application force value,of a second value strictly lower than the first clamping force value, - otherwise, use (25), as the target clamping force value, of the first clamping force value. Figure 3,

Description

Title of the invention: Method for controlling a vehicle parking brake

[0001] The invention relates to a method for controlling a parking brake, also called a parking brake, for a motor vehicle.

[0002] A brake generally comprises friction means and an actuating member, also called an actuator, capable of moving the friction means towards a braking member fixed to a wheel of the vehicle. The purpose of the actuator is to place the friction means, for example linings of a drum brake or pads of a disc brake, in contact with the braking member to brake the vehicle by friction and to move them away from the braking member in order to stop braking. When the braking system is a disc brake, the braking member is formed by a disc rotating integrally with the wheel. In the case of a drum brake, the braking member is formed by a drum rotating integrally with the wheel.

[0003] The parking brake is constituted by the combination of friction means and an actuator which can be controlled outside the rolling phases of the vehicle, to block at least some of its wheels - in general, the rear wheels - using the friction means and thus keep the vehicle stationary.

[0004] For many years, the actuator was mechanical. It is now electric and consists of an electric motor with its electronic control device, which has many advantages.

[0005] First of all, the electric actuator parking brake has a reduced size compared to the mechanical parking brake.

[0006] Furthermore, the electrically actuated parking brake can be used not only for parking, but also as an emergency means for dynamic braking while the vehicle is moving.

[0007] Using an electric parking brake is also simpler for the vehicle user. When a user wishes to immobilize his vehicle while parked, he simply has to command the brake to be applied, a command which can be explicit, by pressing a button for example, or implicit, by detecting a zero speed and an engine stop. Conversely, to get the vehicle moving again, he simply has to release the electric parking brake, a command which can again be explicit, such as pressing a button, or implicit, such as accelerating and engaging the clutch.

[0008] For its use as a parking brake, the electric actuator is pre-set to ensure that the vehicle is held in position whatever the circumstances, taking into account its weight and possibly the slope of the road surface on which the vehicle is located. The tightening takes into account in particular the drop in brake temperature which occurs following the stopping of the vehicle, since it is known that this drop in temperature can lead to a release of the tightening force.

[0009] To eliminate the risk of the clamping force becoming too weak to prevent unwanted movement of the vehicle, the brake is therefore applied at a clamping force greater than strictly necessary, to provide a safety margin such that the release over time of the initial clamping force does not cause it to fall below a minimum clamping force necessary to retain the vehicle.

[0010] A disadvantage of this preset tightening is that it is often excessive, especially when the vehicle is parked for only a few seconds, for example at a traffic light. The inventors have studied the impact of this excess. They discovered that it results in premature wear of the brake and significant excess energy consumption. Safety must of course take precedence, but the present invention aims to solve this problem of premature wear and excess energy consumption without degrading the safety of the parking brake function.

[0011] Furthermore, using a high clamping value lengthens the time required to release the brake when the vehicle needs to start moving again. This long time can cause a jerk that is detrimental to passenger comfort and can be annoying to the driver, who may expect better responsiveness from the vehicle.

[0012] To this end, the invention relates to a method for controlling a vehicle parking brake configured to apply a friction means to a braking member, comprising the following steps:

[0013] - detection of a brake application request,

[0014] - depending on the parking conditions of the vehicle, determination of a target value of clamping force allowing said vehicle to be kept stationary,

[0015] - actuation of the brake so as to provide a clamping force corresponding to the target value,

[0016] characterized in that the step of determining a target tightening force value comprises the following steps:

[0017] - determination of a first clamping force value, making it possible to maintain said vehicle stationary for an unlimited period, even after releasing the brake,

[0018] - verification of the presence of a driver at the driving position of the vehicle,

[0019] - in case of presence of the driver at his driving position, use, as value clamping force target, of a second value strictly lower than the first clamping force value,

[0020] - otherwise, use, as target tightening force value, of the first value of clamping force.

[0021] Thus, it is possible to reduce the application force of a parking brake when the driver is present in the vehicle. It is thus possible to avoid providing an excessively high application force contributing to premature wear of the brake, more particularly of the friction means. Thanks to the proposed method, it is therefore possible to increase the service life of the brake while reducing energy consumption during braking.

[0022] The step of determining a first clamping force value makes it possible to evaluate a minimum force required to keep the vehicle stationary regardless of the vehicle's parking conditions, for an unlimited duration. Advantageously, the worst possible conditions are considered so that the minimum force determined is high enough to ensure the vehicle is immobilized safely. The first clamping force value may come from charts or tables pre-recorded in a digital computer of the vehicle.

[0023] Next, the presence of the driver at the driving position is verified. By this step, it is understood that the vehicle does not need to be kept stationary on its own, that is to say without human supervision. Indeed, the presence of the driver deduces that the latter is able to intervene if necessary.

[0024] Once the presence of the driver is confirmed, a second clamping force value is determined, which is used as a target value for performing the clamping. This value is strictly lower than the first value, it is chosen to avoid the use of excessive clamping force and to reduce energy consumption without compromising braking safety. It is understood that the driver in the driving position ensures braking safety because the driver can intervene if necessary, for example when the chosen target clamping value becomes insufficient.

[0025] Thanks to the reduced clamping effort and this reduced clamping force, the time required to release the brake, when the vehicle has to start moving again, is also advantageously reduced.

[0026] Furthermore, in the case where the driver is not present at the driving position, the parking braking follows the usual procedure, that is to say that the first determined force value is used as the target value for keeping the vehicle stationary. Indeed, without the supervision of the driver, the clamping force must be high to ensure the safety of the vehicle and prevent it from accidentally starting to move.

[0027] The braking method may further comprise one or more of the following optional features, taken alone or in combination:

[0028] - The parking conditions of the vehicle are at least the slope of the road on in which the vehicle is located and the temperature of the friction means and / or the friction member.

[0029] - The slope is determined by a tilt sensor, called an inclinometer, or by a vehicle's on-board computer.

[0030] - The slope value is an absolute value.

[0031] - The temperature is determined by estimation based on a command from braking applied by the driver on the parking brake. Alternatively or in combination, the temperature is determined by means of a temperature sensor, advantageously located close to the wheels.

[0032] Thus the target clamping force value varies according to the slope and temperature conditions, in order to optimize the clamping force required for immobilizing the vehicle, for example when it must be kept stationary on a zero or slight slope having a slight inclination, for example an inclination of less than 13%. In this case, the first determined clamping force value is low, for example around 10 kN, and the second value is advantageously reduced compared to the first value. Energy consumption is therefore optimized by avoiding providing excessive clamping force and over-using the brake to immobilize the vehicle.

[0033] Similarly, for a low temperature, for example below 150°C, the target clamping force value is optimized.

[0034] - The difference between the second clamping force value and the first force value tightening force is between X% and Y% of the first tightening force value, preferably at least Z%.

[0035] A considerable reduction in the clamping force is thus noted.

[0036] - The step of verifying the presence of the driver at his driving position is carried out continuously.

[0037] This verification step constitutes a safety step. It is carried out continuously to ensure that the driver is present to intervene if necessary, for example in the event of accidental release of the clamping. This step is all the more important for cars comprising an electric parking brake configured to activate braking when zero speed is detected. Indeed, the continuity of the verification step indirectly makes it possible to distinguish between parking and momentary braking, for example when the vehicle is held stationary at a traffic light. Depending on this distinction, the vehicle is held with a high safety clamping force (first braking force value) or with a reduced clamping force (second clamping force value) whose safety is ensured by the driver.

[0038] - The driver's presence at his driving position is checked at with regard to a signal based on at least one of the following criteria: a. detection of vehicle ignition, b. detection of an open or closed state of the driver's side door, c. visual detection of the driver, d. detection of a driver's side seat belt lock, e. detection of a mass on the driver's side seat, f. detection of a force exerted on the accelerator and / or brake pedal.

[0039] Detection based on these different criteria is carried out by means of different sensors integrated into the vehicle. The above list not only allows for the verification of driver presence, but also for confirmation of active and operational driver presence, i.e., that the driver is present in the vehicle during driving or in such a way that he or she can intervene in the braking process if necessary. For example, when the seat belt is unlocked, it could be deduced that the driver is not present or is about to get out of the vehicle and therefore that a high clamping force value would be required to immobilize the vehicle.

[0040] - The signal is for example the signal PbcInDriveAwaylntentionlndication, of the re VDA305-100 v3 v2018 order from the German Automotive Industry Association.

[0041] Recommendation VDA305-100 is a generally known recommendation that explains the integration of brake controls into an electronic trajectory corrector (or "ESC" for "Electronic Stability Control") which is an active anti-skid safety device intended to improve the trajectory control of the vehicle. The PbcInDriveAwaylntentionlndication signal is cited as an example, another type of signal fulfilling the requirements of the recommendations related to brake controls, can be considered.

[0042] The invention also relates to a digital computer comprising a memory and a processor connected to this memory, characterized in that said memory contains a series of instructions which, when executed by said processor, implement the method described above.

[0043] The invention also relates to a memory medium containing a series of instructions for implementing the method 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.l] is a bottom view of a motor vehicle fitted with its brakes,

[0046] [Fig.2] is a side view of the vehicle of [Fig.l] parked on a slope,

[0047] [Fig.3] is a flowchart illustrating the algorithm executed by the digital computer to implement the method according to the invention. Detailed description

[0048] Figures 1 and 2 show a vehicle 1 parked on a slope 2. The vehicle is equipped with four wheels, two front wheels 5, 6 and two rear wheels 7, 8, mounted respectively on two axles 3 and 4. At least the two rear wheels 7 and 8 are equipped with parking brakes according to one embodiment of the invention. Each parking brake comprises an electric actuator 16 and friction means 14 acting on a disc 12 secured to the corresponding wheel.

[0049] A digital computer 20 is connected to the two electric actuators 16 to send them control signals intended to control the motor (not shown) of the friction means 14. A parking brake control member 18 is represented by a switch in the figure. This member is not necessarily a physical member. It can be constituted by a logic signal from an on-board computer. For example, the vehicle's on-board computer can be programmed to activate the parking brake when the driver switches off the engine and the vehicle speed is zero.

[0050] As is known, when a parking brake request is provided by the control member 18, the digital computer 20 detects this brake application request and retrieves the information reflecting the parking conditions of the vehicle, namely in particular the inclination of the road on which the vehicle is located, as seen in [Fig. 2]. This inclination information can come from the vehicle's on-board computer or be measured by an inclinometer specifically provided for this purpose. From these parking conditions, the digital computer determines a first target application force value making it possible to keep said vehicle stationary for an unlimited period. The value thus determined can come from charts or tables pre-recorded in the computer.

[0051] For example, if the vehicle weighs 2500 kg and the slope on which it is parked has an inclination of 10% (i.e. approximately 5.7 degrees from the horizontal), the first target value is 18.5 kN. With such a clamping force, even with a release over time due to the cooling of the friction means, the locking of the wheels would be ensured.

[0052] According to the invention, instead of sending this first clamping force value as a setpoint to the actuators 16, the digital computer 20 carries out a check of the presence of a driver in the driving position of the vehicle. This check is not carried out directly by the digital computer 20. The information of the presence of the driver is provided by the on-board computer (not shown) or by specific sensors (not shown) provided for this purpose in the passenger compartment or on the pedals, levers, buttons and steering wheel likely to be manipulated by the driver. Different signals can reflect the presence of the driver in the driving position of the vehicle: a. detection of vehicle ignition, b. detection of an open or closed state of the driver's side door, c. visual detection of the driver, d. detection of a driver's side seat belt lock, e. detection of a mass on the driver's side seat, f. detection of a force exerted on the accelerator and / or brake pedal.

[0053] Thus, the digital computer executes the algorithm illustrated by [Fig.3].

[0054] In step 21, the brake is released. No parking braking is requested.

[0055] In step 22, the computer tests the state of the control member 18. If the latter is positioned to signal a parking brake request, the process continues to the next step 23. Otherwise, it loops to step 21.

[0056] In step 23, the computer determines whether the driver is in the cockpit of the vehicle. As already explained, this information is provided to the computer by external means. If this is the case, the method continues in step 24. Otherwise, it continues in step 25.

[0057] Step 24: The presence of the driver at his driving position is confirmed. The digital computer 20 reduces the first target tightening value by a predefined amount, to obtain a second target tightening value. It is this second target value which is sent as a setpoint value to the actuators 16.

[0058] Step 25: The presence of the driver is not confirmed, it is the first target value which is sent as the setpoint value.

[0059] The reduction applied to the first target value comes from a table of values, an example of which is provided in the following [table 1], where we see that not only the slope of the parking lot is taken into account, but also the temperature of the friction means.

[0060] [Tables 1] O"C-SO"C SO’C-IÛO’C wrc-iso-c 15O"C-2OO°C 2OO'C-25Û'C 250’0 300’0 ÎOO'C-ISOX 3sœc-400’c 4æ"C-4SÛ°C 450°C-5Û0°C 0%-l% | 0.34 0.36 0,39 0.42 0.46 0.50 0.55 0.61 0.® 0.80 l%-2% I 0.68 0.73 078 0.84 0.91 1.00 1.10 1.23 1.38 1.59 2%-3% i 1.02 1.09 1.17 1.26 1.37 1.50 1.65 1.84 2.08 2.39 3%-4% 1 1.36 1.45 1,56 1.68 1.82 1.99 2.20 2.45 2.77 3.18 4%-5% ! 1.70 1.81 1.95 2.10 2.28 2.49 2.7S 3.06 3.46 3.97 5%-6% | 2.04 2.17 2.33 2.52 2.73 2.99 3.29 3.67 4.15 4.77 6%-7% 1 2.37 2.54 2.72 2.93 3,18 3.48 3,84 4.28 4,84 5.56 7%-8% | 2.71 2.90 3.11 3.35 3.64 3.98 4.39 4.89 5.52 6.35 8%-9% 1 3.05 3.25 3.49 3.77 4.09 4.47 4.93 5.50 6,21 7.13 9%-10% 3.38 3.61 3.88 4.18 4.54 4.96 5.47 6.10 6.89 7.92 3.72 3.97 4.26 4.59 4.99 5.45 6.01 6.70 7.57 8.70 11%-12% 4.05 4.33 4.64 5.01 543 5.94 6.55 7.30 8 25 9.48 12%-13%| 4.38 4.68 5.02 5.42 5.88 6.43 7.09 7.90 8.93 10.26 13%-14%j 4.71 5.03 5.40 5.83 6.32 6.91 7.62 8.50 9.60 11.03 14%-15%| 5.04 5.39 5.78 6.23 6,76 7.40 8.16 9.09 10.27 11.80 15%-16%| 5.37 5.74 6.<h2 style=";text-align:left;direction:ltr">15 6.64 7.20 7.88 8.69 9.69 10.94 12.57 16%-I7% 5.70 6.08 6.53 7.04 7.64 8.36 9.22 10.27 11.61 13.33 17%-18% 6.02 6.43 6.90 7.44 8.08 8.83 9.74 10.86 12.27 14.10 18%-19%| 6.35 6.78 7.27 7.84 8.51 9.31 10.26 11.44 12.93 14.85 19%-20% 6.67 7.12 7.64 8.24 8.94 9.78 10.78 12.02 13.58 15.60 20%-21%| 6.99 7.46 8.01 8.63 9.37 10.25 11.30 12.60 14.23 16.35 21%-22% j 7.30 7.80 8.37 9.03 9.80 10.71 11.82 13.17 14.88 17.10 22%-23%| 7.62 8.14 8.73 9.42 10.22 11.18 12.33 13.74 15.52 17.83 23%-24%| 7.93 8.47 9.09 9.81 10.64 11.64 12.83 14.31 16.16 18.57 24%-25% 8.24 8.80 9.45 10.19 11.06 12.09 13.34 14.87 16.80 19.30 2S%-26% 8.55 9.14 9.80 10.57 11.47 12.55 13.84 15.43 17.43 20.02 26%-27% 8.86 9.46 10.15 10.9S 11.89 13.00 14.33 15.98 18.05 20.74 27%-28% | 9.17 9.79 10.50 11.33 12.30 13.44 14.83 16.53 18.67 21.45 28%-29%j 9.47 10.11 10.85 11.70 12.70 13.89 15.32 17.07 19.29 22.16 29%-30%| 9.77 10.43 11.19 12.07 13.10 14.33 15.80 17.62 19.90 22.86.<h2 style=";text-align:left;direction:ltr">

[0061] By reducing the setpoint value, excessive strain on the brakes is avoided and their service life is increased. In addition, the energy required to operate the parking brake with a moderate application value reduces the amount of energy required for this operation. The energy saved has been estimated at more than 40% on average for a vehicle used under ordinary conditions.

[0062] For comparison, the following table shows the values ​​of clamping force, application time, release time and energy consumed in the case of the prior art and in the case of the invention. It can be seen in particular that in addition to the reduction in energy consumed, the brake release time is shorter thanks to the invention, which improves the vehicle's responsiveness to driver input.

[0063] [Tables2] Invention State of the art Target force value 9500N 14500N Clamping force 9769N 14552N Application time 0.87s 0.99s Release time 0.82s 1.04s Energy consumed (application + release) 33.05J 57.OR

[0064] The invention is not limited to the embodiment presented and other embodiments will become clear to those skilled in the art.

[0065] List of references 1: vehicle 2: slope 3: front axle 4: rear axle 5, 6: front wheels 7, 8: rear wheels 10: front brake disc 12: rear brake disc 14: means of friction 16: Electric parking brake actuator 18: parking brake control unit 20: digital calculator 21-25: Algorithm steps

Claims

Claims

1. Method for controlling a vehicle parking brake configured to apply a friction means (14) to a braking member (10, 12), comprising the following steps: - detecting (22) a request to apply the brake, - depending on the parking conditions of the vehicle (1), determining a target application force value making it possible to keep said vehicle stationary, - actuating the brake so as to provide an application force corresponding to the target value, characterized in that the step of determining a target application force value comprises the following steps: - determining a first application force value, making it possible to keep said vehicle stationary for an unlimited period, even after releasing the brake, - verifying (23) the presence of a driver at the driving position of the vehicle (1), - if the driver is present at his driving position, use (24),as the target clamping force value, of a second value strictly lower than the first clamping force value, - otherwise, use (25), as the target clamping force value, of the first clamping force value.,

2. Braking method according to the preceding claim, in which the parking conditions of the vehicle (1) are at least the slope (2) of the road on which the vehicle (1) is located and the temperature of the friction means (14) and / or of the friction member (10, 12).

3. A brake method according to any one of the preceding claims, wherein the difference between the second clamping force value and the first clamping force value is between X% and Y% of the first clamping force value, preferably at least Xl%.

4. Braking method according to any one of the preceding claims, according to which the step of verifying (23) the presence of the driver at his driving position is carried out continuously.

5. Braking method according to any one of the preceding claims, according to which the verification (25) of the presence of the driver at his driving position is carried out with regard to a signal based on at least one of the following criteria: a. detection of vehicle contact (1), b. detection of an open or closed state of the driver's side door, c. visual detection of the driver, d. detection of a driver's side seat belt lock, e. detection of a mass on the driver's side seat, f. detection of force exerted on the accelerator and / or brake pedal.

6. Braking method according to the preceding claim, wherein the signal is the signal PbcInDriveAwaylntentionlndication, of the recommendation VDA305-100 v3 v2018 of the German Association of the Automotive Industry.

7. Digital Computer (20) comprising a memory and a processor connected to this memory, characterized in that said memory contains a sequence of instructions which, when executed by said processor, implement the method according to any one of claims 1 to 6

8. 1 d. U. Memory medium containing a sequence of instructions for implementing the method according to any one of claims 1 to 6.

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