Brake system including parking brake device with improved operational reliability

Abstract

The present invention relates to a parking brake system including a parking brake device for a motor vehicle, the braking system including at least a first electric parking brake (FP1) arranged on a first wheel, a second electric parking brake (FP2) arranged on a second wheel, a control unit (UC) configured to generate a command to the first and second parking brakes (FP1, FP2) to apply a predetermined parking brake force, and means (D1, D2) for detecting the operating state of each of the first and second parking brakes (FP1, FP2), wherein the control unit (UC) is configured to generate a command to the second parking brake (FP2) to apply at least the predetermined parking brake force in order to keep the motor vehicle stationary in the event of a failure of the first parking brake.

Description

[Technical Field]

[0001] The present invention relates to braking systems, including parking brake devices for motor vehicles, and to methods of operating such braking systems. [Background technology]

[0002] An automobile is equipped with a braking system that has brakes on each wheel.

[0003] The braking system is equipped with a service brake to slow down and stop the vehicle. The service brake is usually activated by stepping on the brake pedal. In some cases, the service brake is automatically controlled by the control unit, for example, in situations where the vehicle speed is automatically adjusted.

[0004] The braking system also includes a parking brake to keep the vehicle stationary when parking. The parking brake can also be used as an emergency brake in case of an emergency. According to ECE R 13-H regulation, the parking brake system must be able to keep a fully loaded vehicle stationary on an 8% gradient slope.

[0005] The braking system typically includes a parking brake located on each rear wheel, and the parking brake is typically integrated with the service brake.

[0006] Traditionally, parking brakes are activated by the driver pulling a brake lever, which is directly connected to the rear brake by a cable, and the harder the lever is pulled, the greater the braking force of the parking brake.

[0007] Recently, many vehicles have adopted electric parking brakes, which can be activated by pressing a button. When the driver presses the button, a signal is sent to a control unit, which starts the electric motors attached to each rear wheel and applies the brakes. In the case of disc brakes, the electric motor presses the brake pads against the brake disc, and in the case of drum brakes, it presses the brake linings against the brake drum.

[0008] If one of the two electric parking brakes fails, the other electric parking brake is disabled and the driver is notified of the malfunction in the parking brake system, but as a result, the vehicle cannot be held stationary in park. Summary of the Invention [Problem to be solved by the invention]

[0009] An object of the present application is to propose a parking brake system with improved operational safety. [Means for solving the problem]

[0010] The above object is achieved by a parking brake system including at least two electric parking brakes (one provided on one rear wheel and the other on the other rear wheel), a control unit for controlling the electric parking brakes, and sensors for detecting the actuation states of each electric parking brake, wherein the control unit is configured to compare the actuation states of each electric parking brake during a parking brake phase and adjust the actuation of one electric parking brake according to the actuation of the other electric parking brake, thereby keeping the vehicle stationary.

[0011] In one operating mode, if one electric parking brake fails (malfunctions), the other electric parking brake is controlled to at least partially compensate for the malfunction, thereby increasing the braking force of the normally functioning electric parking brake. Such a braking system can be used in accordance with ECE R 13-H regulation.

[0012] In one embodiment, if a fault occurs while the other electric parking brake is about to apply or is being applied, the application command is changed during application to provide a braking level that takes into account the fault.

[0013] Alternatively, a fault occurs while the other electric parking brake is already applied, in which case a new application phase of the other electric parking brake is initiated to take the fault into account.

[0014] In other words, a parking brake system is proposed in which each parking brake can be individually activated taking into account the activation state of the other parking brakes, thereby ensuring the vehicle's ability to stop even if the other parking brake fails.

[0015] The subject of the present invention is a braking system including a parking brake device for a motor vehicle, comprising at least a first electric parking brake arranged on a first wheel, a second electric parking brake arranged on a second wheel, a control unit configured to generate commands to apply a predetermined parking brake force to the first and second parking brakes, and means for detecting the operating state of each of the first and second parking brakes, wherein the control unit is configured to generate a command to the second parking brake to apply at least the predetermined parking brake force in order to ensure the stationary state of the motor vehicle in the event of a malfunction of the first parking brake.

[0016] In one example embodiment, the control unit is configured to generate a command to the second parking brake to apply an additional parking brake force in addition to the predetermined parking brake force upon failure of the first parking brake.

[0017] As a further feature, the control unit may be configured to extend the power supply of the second parking brake if a failure occurs in the first brake during the power supply phase of the second parking brake, thereby applying an additional parking brake force in addition to the predetermined parking brake force.

[0018] As another feature, the control unit may be configured to re-energize the second brake, thereby applying an additional parking brake force in addition to the predetermined parking brake force, if a failure occurs in the first parking brake after the end of the powering phase of the second brake.

[0019] For example, the means for detecting the operating state of the first and second electric parking brakes may include means for measuring the power supply current of the electric motors and / or a sensor for detecting the position of a moving element coupled to a motor reducer of each of the first and second electric parking brakes.

[0020] Another subject of the invention is a braking system comprising a parking brake system according to the invention and at least two service brakes, the parking brake being integrated into the service brakes.

[0021] Another subject of the present invention is a method for operating a parking brake system including at least a first electric parking brake arranged on a first wheel, a second electric parking brake arranged on a second wheel, and a control unit connected to the first and second parking brakes and to means for detecting the operating states of each of the first and second parking brakes, the method comprising: a) generating by a control unit a command to each parking brake to apply a braking force appropriate to ensure stationary of the vehicle; b) detecting a malfunction of the first parking brake; c) generating by the control unit a command to the second parking brake to apply a parking brake force.

[0022] In one example of operation, in step c), the second parking brake is controlled to increase the braking force acting on the wheel to a predetermined value.

[0023] The method of operation preferably includes the step of determining, by the control unit, a value required for the vehicle to be stationary based on information relating to the parking state of the vehicle.

[0024] The determining step may also include the step of considering the braking force applied by the first parking brake in a failed state.

[0025] The method preferably includes the step of generating a message by the control unit to notify the driver of a malfunction of the first parking brake. [Brief explanation of the drawings]

[0026] The following description can be better understood with reference to the following drawings: [Figure 1] 1 is a diagram illustrating a brake system according to an embodiment. [Figure 2A] 6 is a graph showing changes in the supply current of the electric parking brake and changes in the brake application force of both parking brakes in a first operating state. [Figure 2B] 6 is a graph showing changes in the supply current of the electric parking brake and changes in the brake application force of both parking brakes in a first operating state. [Figure 3A]6 is a graph showing changes in the supply current of the electric parking brake and changes in the brake application force of both parking brakes in a second operating state. [Figure 3B] 10 is a graph showing changes in the supply current to the electric parking brake and changes in the brake application force of both parking brakes in a second operating state. DETAILED DESCRIPTION OF THE INVENTION

[0027] 1 shows a schematic representation of a vehicle V, which includes a braking system S with a brake F mounted on each wheel. Typically, hydraulic brakes provide the service braking.

[0028] The braking system further includes a parking device including a first parking brake FP1 provided on the right rear wheel and a second parking brake FP2 provided on the left rear wheel. Both parking brakes FP1 and FP2 are electric parking brakes. Generally, the parking brakes are integrated into the service brakes.

[0029] In the case of a disc brake, a motor reducer is integrated into the brake and moves a piston, for example, via a screw-nut mechanism.

[0030] In the case of drum brakes, a motor reducer attached to a plate presses the lining against the drum via, for example, a screw-nut mechanism.

[0031] If the parking brake system includes two parking brakes, they are usually arranged to act on two wheels on the same axle. Typically, parking brakes are only provided on the rear wheels. Brake systems with four parking brakes and / or electrically operated service brakes do not depart from the scope of this application.

[0032] The braking system further comprises a control unit UC which controls, inter alia, the actuation of the electric parking brakes FP1 and FP2.

[0033] In practice, the electric parking brake is activated by the driver's command, by activating a button, typically in the form of a small lever, or by other control means, for example a voice command, or automatically, for example when the engine is switched off. This activation signal is detected by a control unit, which sends a command to the motor reducers of each of the parking brakes FP1, FP2 to apply a braking force. The strength of the applied braking force depends on the inclination of the slope on which the vehicle is parked. For this reason, the brake system receives information about the parking state of the vehicle, in particular about the vehicle's inclination.

[0034] The braking system further comprises means D1 and D2 for detecting the operating state of each of the parking brakes FP1 and FP2. For example, these means measure the operating level of the brakes on the discs or drums. The operating state can be detected, for example, based on information about the brake level, which is obtained by measuring the supply current of the electric motor, which increases with increasing braking force. In another example, a sensor for detecting the position of a moving element connected to the motor reducer, such as a position sensor of a threaded shaft on a nut, is used.

[0035] According to the invention, the control unit is configured to take into account the activation state of one of the parking brakes FP1 and FP2 and to control the other, thereby ensuring stationary state of the vehicle.

[0036] When the control unit is notified of a failure of one of the parking brakes FP1 and FP2, it commands the other parking brake to at least partially compensate for the failure.

[0037] As used herein, a "failed parking brake" means a parking brake that is unable to apply any braking force to the wheels to which it is attached, or that is unable to apply sufficient braking force to bring the vehicle into park. Such a failure may be mechanical and / or electrical and / or electronic.

[0038] Two modes of operation of the parking brake system according to the present invention are described below.

[0039] 2A and 2B show graphs according to a first example of the operation of a parking brake system.

[0040] FIG. 2A shows the variation of the current I1 supplied to the motor of the electric parking brake FP1 as a function of time t and the variation of the braking force F1 applied by the parking brake FP1 as a function of time.

[0041] FIG. 2B shows the variation of the current I2 supplied to the motor of the electric parking brake FP2 as a function of time t, and the variation of the braking force F2 applied by the parking brake FP2 as a function of time t.

[0042] Each graph shows the braking forces that should be achieved during normal operation, denoted by FT1 and FT2, corresponding to brakes FP1 and FP2, respectively. These braking forces to be achieved are determined by the control unit UC based on the parking situation of the vehicle. Generally, FT1 and FT2 are equal.

[0043] The control unit issues a command to apply a parking brake force to both parking brakes FP1 and FP2, which causes current to be supplied to each brake. In this example, the supply of current to brake FP2 begins at time t1, which is before the start of the supply of current to brake FP1 at time t2.

[0044] The first current peak corresponds to the start of the electric motor and the loss of clearance, particularly between the gears of the electric motor, the screw-nut mechanism and the brake pads.

[0045] For brake FP1, no brake application force F1 is generated at all, and brake FP1 is therefore considered to be faulty. Such a lack of braking force can be caused, for example, by a malfunction of the electric motor and / or a malfunction of the screw-nut mechanism and / or a problem with the power supply.

[0046] On the other hand, for brake FP2, a brake application force is generated by supplying current I2, and a second current peak appears, which corresponds to the stage at which force is generated due to contact between the brake pad and the disc.

[0047] Upon detecting a malfunction of brake FP1, the control unit changes the command to brake FP2 so that the braking force applied by brake FP2 takes into account the malfunction of brake FP1 and at least partially compensates for it, and the electric motor of brake FP2 is then supplied with current I2 for a longer period, until the brake application force reaches the value FS2, ensuring that the vehicle is stationary as if both parking brakes had functioned normally.

[0048] The value of FS2 is calculated by the control unit UC based on the parking state of the vehicle or is obtained from a pre-built database.

[0049] Parking brakes may be designed individually to hold a fully loaded vehicle to a standstill on slopes up to 8% gradient.

[0050] In another example of operation, a failure of brake FP1 occurs simultaneously with the application phase of brake FP2, followed by a modified application command to brake FP2, which allows the control unit to send two different commands to the same parking brake in succession.

[0051] Even if the supply of current to brake FP1 is started before the supply of current to brake FP2, this does not affect the progress of the parking brake phase.

[0052] According to the present invention, when parking braking, the vehicle is brought to a standstill in the same way as if all parking brakes were normally activated. Preferably, information about a malfunction in the parking brake system is communicated to the driver, prompting them to inspect the parking system. This notification is made, for example, by a message or a warning lamp displayed on the instrument panel and / or by an audio message or signal. As an example, it is envisaged that the vehicle is brought to a standstill after a malfunction of brake FP1 is detected. For this purpose, for example, parking brake FP2 is kept activated. To release the parking brake, a specialist must instruct the control unit.

[0053] 3A and 3B show another mode of operation in which detection of a fault in one parking brake occurs while the other parking brake is already applied.

[0054] FIG. 3A shows the variation of the current I1 supplied to the motor of the electric parking brake FP1 as a function of time t, and the variation of the braking force F1 applied by the parking brake FP1 as a function of time.

[0055] FIG. 3B shows the variation of the current I2 supplied to the motor of the electric parking brake FP2 as a function of time t, and the variation of the braking force F2 applied by the parking brake FP2 as a function of time t.

[0056] 3B shows the first application phase of brake FP2, in which the calculated braking force FT2 is reached, assuming normal operation of the brake system. The first application phase is labeled PHASE1. Braking force F2 reaches braking force FT2 at time t3, at which point the supply of current I2 is stopped. In practice, when the control unit sends the command, both parking brakes are considered to be normally applied.

[0057] 3A, the brake application force of brake FP1 is equal to Fi1, which is less than the brake force FT1 commanded by the control unit. The brake force FT1 is a calculated value assuming normal brake application of the parking brake system. The brake force Fi1 is detected, for example, by measuring the electric motor current, which is less than the current required to reach the brake force FT1. This causes brake FP1 to be considered faulty. Such a lack of brake force can be due, for example, to a malfunction of the electric motor and / or a malfunction of the screw-nut mechanism and / or a problem with the power supply.

[0058] The braking force Fi1 is detected at time t4 after time t3.

[0059] The control unit then issues a new command to brake FP2, adjusting its braking level accordingly to the fault in brake FP1. This new command initiates a second operating phase, PHASE2, in which the electric motor of brake FP2 is again supplied with current I2.

[0060] In one example, the control unit does not consider Fi1, i.e., brake FP1 is considered to be faulty and unreliable, providing maximum safety.

[0061] In another example, when brake FP2 is further activated, the braking force to be applied is adjusted taking into account the residual force Fi1 applied by brake FP1. The electric motor of brake FP2 is activated again and the braking force applied by brake FP2 reaches a value FS2 that ensures safe stationary of the vehicle.

[0062] Preferably, the control unit notifies the driver of a parking brake system fault condition, for example by displaying a message or warning light on the instrument panel and / or by issuing an audio message or signal, and may, for example, send a message to an organization that provides repair and / or maintenance for the vehicle.

[0063] In the above example, the normally operating parking brake is controlled to compensate for the failure of the other parking brake. Brake systems that control the normal parking brake to safely stop the vehicle and allow for repairs are within the scope of the present invention. For example, the control unit controls the normal parking brake so that it provides braking equivalent to that which would be provided if the other brake were normally operating. Nevertheless, the parking brake system of the present invention reliably stops the vehicle, unlike prior art parking brake systems.

[0064] In the case of a parking brake system including four parking brakes, the control unit is configured to control them to at least partially compensate for a failure of one or two of the parking brakes.

[0065] In an example where both parking brakes are activated and parking braking is normal, it is assumed that the control unit will check the braking status of each parking brake to see if one is malfunctioning and activate the other parking brake accordingly.

[0066] The present invention has the advantage of significantly increasing the safety of the parking brake system by taking into account the risk of one of the electric parking brakes failing. [Explanation of symbols]

[0067] F: Brake FP1: First electric parking brake FP2: Second electric parking brake D1: Means for detecting the operation state of the first parking brake D2: Means for detecting the operation state of the second parking brake F1: Brake force applied by the first parking brake F2: Brake force applied by the second parking brake FT1: Braking force that the first parking brake should achieve during normal operation FT2: Braking force that the second parking brake should achieve during normal operation Fi1: Actual braking force applied by the first parking brake FS2: Braking force applied by the second parking brake to stop the vehicle I1, I2: Power supply current PHASE 1: First operation phase PHASE 2: Second operation phase S: Brake system CPU: Control Unit V: Vehicle

Claims

1. A parking brake system including a parking brake device for a motor vehicle, The vehicle includes at least a first electric parking brake (FP1) arranged on a first wheel, a second electric parking brake (FP2) arranged on a second wheel, a control unit (UC) configured to generate commands to the first and second parking brakes (FP1, FP2) to apply a predetermined parking brake force, and means (D1, D2) for detecting the operating state of each of the first and second parking brakes (FP1, FP2), 1. A parking brake system, wherein the control unit (UC) is configured to generate a command to the second parking brake (FP2) to apply at least the predetermined parking brake force in the event of a failure of the first parking brake to ensure stationary of the vehicle.

2. 2. The parking brake system of claim 1, wherein the control unit (UC) is configured to generate a command to the second parking brake (FP2) to apply an additional parking brake force in addition to the predetermined parking brake force upon a failure of the first parking brake.

3. 3. A parking brake system according to claim 1 or 2, wherein the control unit (UC) is configured to extend the power supply to the second parking brake if a failure occurs in the first parking brake during a power supply phase of the second parking brake, thereby applying an additional parking brake force on top of the predetermined parking brake force.

4. 4. A parking brake system according to any one of claims 1 to 3, wherein the control unit (UC) is configured to re-energise the second parking brake in the event of a failure of the first parking brake after the end of the powering phase of the second parking brake, thereby applying an additional parking brake force in addition to the predetermined parking brake force.

5. 5. The parking brake system according to claim 1, wherein the means for detecting the operating state of each of the first and second parking brakes includes a means for measuring the power supply current of the electric motor and / or a sensor for detecting the position of a movable element connected to a motor reducer of each of the first and second parking brakes.

6. A braking system comprising a parking brake system according to any one of claims 1 to 5 and at least two service brakes, the parking brake being integrated into the service brakes.

7. A method for operating a parking brake system including at least a first electric parking brake (FP1) arranged on a first wheel, a second electric parking brake (FP2) arranged on a second wheel, and a control unit (UC) connected to means for detecting the operation states of the first and second parking brakes and each of the first and second parking brakes, a) generating by said control unit a command to each said parking brake to apply a braking force appropriate to ensure stationary of the vehicle; b) detecting a malfunction of the first parking brake; c) generating by said control unit a command to said second parking brake to apply a parking brake force.

8. 8. The method for operating a parking brake system according to claim 7, wherein in step c), the second parking brake is controlled to increase the braking force acting on the wheel to a predetermined value.

9. 9. A method of operating a parking brake system as claimed in claim 8, including the step of determining, by said control unit, a value required to bring said vehicle to a standstill based on information relating to the parking state of said vehicle.

10. 10. The method of operating a parking brake system of claim 9, wherein said determining step includes taking into account the braking force applied by said first parking brake in a fault condition.

11. 11. A method of operating a parking brake system as claimed in any one of claims 7 to 10, including the step of generating, by the control unit, a message informing a driver of a malfunction of the first parking brake.

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