Brake system

Abstract

This invention provides a braking system that can improve driving stability when the parking brake is applied. [Solution] The brake system is a brake system having a service brake capable of generating a first braking force on a vehicle and a parking brake capable of generating a second braking force on the vehicle, and further comprising a first control unit that controls the first braking force according to the vehicle speed and a second control unit that controls the second braking force according to the vehicle speed.

Description

[Technical Field]

[0001] This disclosure relates to a brake system. [Background technology]

[0002] Vehicles are equipped with service brakes used for deceleration and stopping, and parking brakes used for parking. Generally, service brakes apply fluid pressure (e.g., air pressure) when used. Parking brakes release fluid pressure to apply force such as a spring when used. In the following explanation, service brakes may sometimes be referred to as "service brakes."

[0003] Furthermore, the vehicle is equipped with an Antilock Brake System (ABS) that, in the event of emergency braking, automatically releases and re-engages the brakes repeatedly, even if the brake pedal is still pressed, to restore wheel grip and maintain vehicle stability.

[0004] For example, Patent Document 1 discloses a braking system that includes an electric parking brake, and in the event that the service brake fails or deteriorates, the electric parking brake is activated as a substitute for the service brake to supply braking torque to the wheels.

[0005] Furthermore, for example, Patent Document 2 discloses a braking system that, in the event of an electronic malfunction in the service brake, allows the driver to perform the requested braking action via the parking brake. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2016-68940 [Patent Document 2] German Patent Application Publication No. 102014006615

Summary of the Invention

Problems to be Solved by the Invention

[0007] By the way, in the braking system described in Patent Document 1, when a failure or the like occurs in the service brake, when the parking brake is actuated to decelerate and stop the vehicle, the vehicle is not decelerated and stopped according to the vehicle body speed. Therefore, the wheels may lock, and there is a problem that the running stability during the operation of the parking brake is reduced.

[0008] Similarly, in the braking system described in Patent Document 2, when braking is performed via the parking brake, the vehicle is not decelerated and stopped according to the vehicle body speed. Therefore, the wheels may lock, and there is a problem that the running stability during the operation of the parking brake is reduced.

[0009] An object of the present disclosure is to provide a braking system capable of improving the running stability during the operation of the parking brake.

Means for Solving the Problems

[0010] To achieve the above object, the braking system in the present disclosure is a braking system having a service brake capable of generating a first braking force for the vehicle and a parking brake capable of generating a second braking force for the vehicle, a first control unit that controls the first braking force according to the vehicle body speed of the vehicle, a second control unit that controls the second braking force according to the vehicle body speed, and is provided with.

Effects of the Invention

[0011] According to the present disclosure, the running stability during the operation of the parking brake can be improved.

Brief Description of the Drawings

[0012] [Figure 1] Figure 1 is a diagram showing the relationship between longitudinal slippage and the longitudinal coefficient of friction. [Figure 2] Figure 2 is a diagram showing the relationship between longitudinal slippage and the lateral coefficient of friction. [Figure 3] Figure 3 is a block diagram functionally representing an example of a braking system in an embodiment of the present disclosure. [Figure 4A] Figure 4A is a diagram schematically representing an example of a braking system during driving in an embodiment of the present disclosure. [Figure 4B] Figure 4B is a diagram schematically representing an example of a braking system during service brake operation in an embodiment of the present disclosure. [Figure 4C] Figure 4C is a diagram schematically representing an example of a braking system during parking brake operation in an embodiment of the present disclosure. [Figure 5] Figure 5 is a block diagram showing an example of an FF control device in an embodiment of the present disclosure. [Figure 6] Figure 6 is a diagram schematically representing an example of a parking brake in an embodiment of the present disclosure. [Figure 7] Figure 7 is a block diagram functionally representing a modified example of the braking system in the present embodiment.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0014] Figure 1 shows the relationship between longitudinal slip and longitudinal braking friction coefficient at various lateral slip angles. The vertical axis of Figure 1 shows the braking friction coefficient μ of the tire (wheel), and the horizontal axis shows the slip ratio (percentage of the difference between vehicle speed and wheel speed divided by vehicle speed). The lateral slip angle is the angle between the direction the tire is pointing and the direction the tire is traveling. In Figure 1, the relationship between the two at lateral slip angle β (=0) is shown by a solid line, the relationship at lateral slip angle β (=0.1) is shown by a dashed line, the relationship at lateral slip angle β (=0.2) is shown by a dotted line, and the relationship at lateral slip angle β (=0.3) is shown by a dashed line. As shown in Figure 1, at each of the multiple lateral slip angles β, the longitudinal grip force of the tire is maximum when it is slightly slipped longitudinally (slip ratio between 10 and 20%), and even when it is slipped further, the grip force remains high for a considerable period of time.

[0015] Figure 2 shows the relationship between longitudinal slip and lateral braking friction coefficient at various lateral slip angles. The vertical axis of Figure 2 shows the lateral braking friction coefficient μ of the tire, and the horizontal axis shows the slip ratio (%). In addition, the relationship between the two at a lateral slip angle β (=0.1) is shown by a dashed line, the relationship at a lateral slip angle β (=0.2) is shown by a dotted line, and the relationship at a lateral slip angle β (=0.3) is shown by a dashed line. As shown in Figure 2, at each of the multiple lateral slip angles β, the lateral grip force of the tire is maximum when there is no longitudinal slip, and decreases rapidly when longitudinal slipping begins.

[0016] Incidentally, if the braking force exceeds the tire's grip, the tire will lock up and slip, making it difficult to maintain the vehicle's driving stability. Service brakes are equipped with an ABS (Antilock Brake System) that can control the braking force according to the slip ratio when they are activated. The ABS can adjust the braking force so that the slip ratio is between 10 and 20%. This makes it possible to maintain the vehicle's driving stability. On the other hand, conventional parking brakes are mainly used to prevent the vehicle from moving while parked. Parking brakes have a parking brake chamber. The parking brake is activated by setting the pressure in the parking brake chamber to a predetermined pressure, and the parking brake is released by setting the pressure in the parking brake chamber to atmospheric pressure.

[0017] When slowing down or stopping a vehicle, the parking brake may be used as an alternative to the service brake. However, conventional parking brakes do not have ABS, which can control the braking force according to the slip ratio. Therefore, when the parking brake is applied, it is not possible to control the braking force according to the slip ratio, which makes it difficult to maintain the vehicle's driving stability.

[0018] Figure 3 is a block diagram functionally representing an example of a brake system in an embodiment of this disclosure. In the brake system 100 shown in Figure 3, pneumatic circuits are shown with solid lines and signal circuits are shown with dashed lines. Furthermore, the control unit 110 shown in Figure 3 represents a functional unit configuration, not a hardware (device) unit configuration. Therefore, functional blocks may be implemented in a single device or may be implemented separately in multiple devices. Data exchange between functional blocks may be performed via any means, such as a data bus or a controller area network (CAN bus).

[0019] Brake system 100 includes separate brake systems for the front and rear wheels. The front brake system includes a service brake 100S. The rear brake system includes a service brake 100S and a parking brake 100P. The following description will primarily focus on the rear brake system, omitting the description of the front brake system. The rear brake system may also be simply referred to as the "brake system" or "brake system 100." Furthermore, the rear wheels may be simply referred to as "wheels."

[0020] The Service Brake 100S comprises a tank, a Foot Brake Modulator (FBM), a Pressure Control Module (PCM), and multiple Brake Chambers with Parking Brakes (BC / wP). The number of BC / wP corresponds to the number of wheels to which the parking brake circuit's air pressure is supplied. The multiple BC / wP have the same configuration and are shared by both the Service Brake 100S and the Parking Brake 100P. Figure 3 shows one representative example of the multiple BC / wP.

[0021] Tank TNK stores compressed air (hereinafter referred to as air). The foot brake module FBM is, for example, the brake pedal located at the driver's feet and operated by the driver. The pressure control module PCM controls the pressure of the air flowing in from Tank TNK according to the amount the brake pedal is pressed. The pressure-controlled air is supplied to the service brake chamber SBC of the composite brake chamber BC / wP. This activates the service brake 100S. Details of the composite brake chamber BC / wP will be described later.

[0022] The parking brake 100P includes a multi-protection valve (MPV), a hand control valve (HCV), a double check valve, a relay valve, and multiple composite brake chambers (BC / wP). As mentioned above, the multiple composite brake chambers (BC / wP) have the same configuration and are shared brake chambers for both the service brake 100S and the parking brake 100P. In the following explanation, the chamber of the service brake 100S will be referred to as the "service brake chamber" and represented as the service brake chamber SBC. The chamber of the parking brake 100P will be referred to as the "parking brake chamber" and represented as the parking brake chamber PBC.

[0023] The Multi-Protection Valve (MPV) supplies air pressure from the Tank (TNK) to the Hand Control Valve (HCV). The Hand Control Valve (HCV) is located next to the driver's seat and, via driver operation, controls the parking brake control pneumatic circuit that runs from the Multi-Protection Valve (MPV) to the Double Check Valve. The Double Check Valve is a valve with a high-priority function that supplies the relay valve with the higher of the air pressure supplied from the Foot Brake Module (FBM) to the Relay Valve (RV) and the air pressure supplied from the Hand Control Valve (HCV). The Relay Valve (RV) is a valve that amplifies the air flow rate. Based on the command pressure supplied from the Double Check Valve, the Relay Valve (RV) amplifies the flow rate and supplies air into the Brake Chamber (PBC), and also discharges air from the Parking Brake Chamber (PBC) to the outside. When the Parking Brake (100P) is not operated (for example, while driving), air is supplied to the Parking Brake Chamber (PBC) via the Relay Valve (RV), and the Parking Brake Chamber (PBC) is kept under high pressure. When the parking brake 100P is applied, air is discharged from the parking brake chamber PBC to the outside via the relay valve RV, and the pressure in the parking brake chamber PBC is reduced. The relay valve RV is controlled by the control unit 110.

[0024] The brake system 100 controls the braking force independently for each of the multiple wheels. In the following description, the control of the braking force for one wheel will be described as a representative example. Figure 4A is a schematic diagram showing an example of the brake system during driving in an embodiment of the present disclosure. Figure 4B is a schematic diagram showing an example of the brake system when the service brake is applied in an embodiment of the present disclosure. Figure 4C is a schematic diagram showing an example of the brake system when the parking brake is applied in an embodiment of the present disclosure. Figures 4A to 4C show the wheel brake systems used for decelerating and stopping the wheels. In Figures 4A to 4C, the side of the wheel closer to the brake disc BD is called the front side, and the side of the wheel further from the brake disc BD is called the rear side.

[0025] As shown in Figure 4A, the brake system 100 includes a case CS, a service brake chamber SBC, a parking brake chamber PBC, a brake pad BP, a rod LD, a first spring SPR1, and a second spring SPR2.

[0026] Case CS has a front wall FW located on the front side, a rear wall BW located on the rear side, and a peripheral wall SW that surrounds the interior from the outside. A service brake chamber SBC is located on the front side of case CS. A parking brake chamber PBC is located on the rear side of case CS.

[0027] The case CS and the service brake chamber SBC are separated by the service brake chamber wall SBCW. The case CS and the parking brake chamber PBC are separated by the parking brake chamber wall PBCW. The service brake chamber SBC and the parking brake chamber PBC are separated by a partition wall PW. Air (AirSB) can be supplied to / discharged from the service brake chamber SBC. Air (AirPB) can be supplied to / discharged from the parking brake chamber PBC.

[0028] The first spring SPR1 is positioned in a compressed state between the front wall FW and the service brake chamber wall SBCW. The second spring SPR2 is positioned in a compressed state between the rear wall BW and the parking brake chamber wall PBCW.

[0029] One end of rod LD is connected to the service brake chamber wall SBCW. The middle section of rod LD passes through the front wall FW and is positioned to reciprocate between the front and rear sides of the front wall FW. The other end of rod LD is connected to the brake pad BP.

[0030] The pressure control module PCM supplies / discharges air to the composite brake chamber BC / wP, which is the chamber for the wheel brakes, in response to the foot brake module FBM being pressed.

[0031] (When the service brake is released, while driving) Next, the operation of the service brake 100S during driving will be explained with reference to Figure 4A. During driving, air is discharged from the service brake chamber SBC, and the pressure in the service brake chamber SBC is reduced. As a result, the service brake chamber wall SBCW collapses from the front to the rear due to the restoring force of the first spring SPR1. Simultaneously, the rod LD and brake pad BP move from the front to the rear, causing the brake pad BP to separate from the brake disc BD on the wheel. Note that the parking brake chamber PBC is maintained at high pressure during driving.

[0032] (When the service brake is applied) Next, we will explain the operation of the service brake with reference to Figure 4B. When the service brake 100S is activated, air is supplied to the service brake chamber SBC so that the pressure in the service brake chamber SBC increases. As a result, the service brake chamber wall SBCW bulges from the rear to the front against the restoring force of the first spring SPR1. Simultaneously, the rod LD and brake pad BP move from the rear to the front, pressing the brake pad BP against the brake disc BD of the wheel. This generates braking force on the wheel. Note that even when the service brake 100S is activated, the parking brake chamber PBC is maintained at high pressure.

[0033] Furthermore, when the service brake 100S is activated, the vehicle has an anti-lock braking system (ABS) that controls the braking force of the wheels by controlling the pressure of the service brake chamber (SBC) in order to maintain the vehicle's driving stability. The anti-lock braking system (ABS) corresponds to the "first control unit" in this disclosure. The anti-lock braking system (ABS) also independently controls the braking force of each of the multiple wheels.

[0034] (When the parking brake is applied) Next, we will explain the situation when the parking brake is applied, referring to Figure 4C. When the parking brake 100P is activated, the control unit 110 controls the relay valve RV so that air is discharged from the parking brake chamber PBC. This reduces the pressure in the parking brake chamber PBC. Note that when the parking brake 100P is activated, the pressure in the service brake chamber SBC is also reduced. As a result, the parking brake chamber wall PBCW is displaced from the rear side to the front side by the restoring force of the second spring SPR2. At the same time, the rod LD and brake pad BP move from the rear side to the front side, pressing the brake pad BP against the brake disc BD of the wheel. This generates a braking force on the wheel.

[0035] The brake system in the embodiment of this disclosure has a feedforward control device that controls the braking force of the wheels (second braking force) by controlling the pressure of the parking brake chamber PBC in order to maintain the driving stability of the vehicle when the parking brake is applied. The control unit 110 shown in Figure 3 has a feedforward control device. The control unit 110 (feedforward control device) corresponds to the "second control unit" in this disclosure. In the following description, the feedforward control device may be referred to as the "FF control device". The FF control device also controls the relay valve RV so that it adjusts the braking force of the wheels. The FF control device is able to control the pressure of the parking brake chamber PBC by feedforward control according to the vehicle speed. Furthermore, the FF control device is able to control the pressure of the parking brake chamber PBC by feedforward control according to the wheel speed.

[0036] Figure 5 is a block diagram showing an example of an FF control device in an embodiment of the present disclosure. The FF control device comprises a memory unit and a control unit. The memory unit includes a ROM (Read Only Memory) for storing the computer program that implements the FF control device, and a RAM (Random Access Memory) which serves as the working area for the control unit 110. It also includes interfaces such as an AD converter, a DA converter, I / O ports, and CAN. The ROM may be a storage device such as an HDD (Hard Disk Drive) or SSD (Solid State Drive) that stores the OS (Operating System), application programs, and various information referenced when the application programs are executed.

[0037] The control unit 110 is a processor such as the CPU (Central Processing Unit) or GPU (Graphics Processing Unit) of the FF control device, and functions as follows by executing a program stored in the memory unit. Note that the FF control device is not limited to being composed of a single device. The FF control device may be implemented by computing resources such as multiple processors and memory. In this case, each part constituting the control unit is implemented by at least one of the multiple different processors executing a program.

[0038] As shown in Figure 5, the FF control device has three elements A, B, and C. The transfer function representing the input / output characteristics of element A is expressed by the following equation (1).

number

[0039] The transfer function representing the input-output characteristics of element B is expressed by the following equation (2).

number

[0040] The transfer function representing the input-output characteristics of element C is expressed by the following equation (3).

number

[0041] When the vehicle speed V is input to element A, an output signal is output from element A. An output signal is also output from element B. The output signal of element A is subtracted from the output signal of element B. The subtracted value is input to element C. As a result, the reference pressure P is output from element C as an output signal. ref_pb The following will be output.

[0042] The steering control valve HCV controls the parking brake chamber pressure P pb Reference pressure P ref_pb The relay valve RV is controlled to achieve this. Note that the parking brake chamber pressure P pb This is detected by a pressure sensor (not shown). The hand control valve HCV controls the relay valve RV based on the detection result of the pressure sensor.

[0043] When the parking brake 100P is activated, as described above, air is discharged from the parking brake chamber PBC so that the pressure in the parking brake chamber PBC decreases. Similarly, air is discharged from the service brake chamber SBC so that the pressure in the service brake chamber SBC decreases. As a result, the parking brake chamber wall PBCW is displaced from the rear side to the front side by the restoring force of the second spring SPR2. Simultaneously, the rod LD and brake pad BP move from the rear side to the front side, pressing the brake pad BP against the brake disc BD of the wheel. This generates a braking force on the wheel.

[0044] Next, parking brake chamber pressure P pbThe relationship with the pressing force of the brake disc and the like will be described with reference to FIG. 6. FIG. 6 is a diagram schematically showing an example of a wheel brake system. In FIG. 6, mainly, the parking brake chamber PBC and the second spring SPR2 in the wheel brake system are shown, and the case CS is shown as a cylinder. In FIG. 6, the service brake chamber SBC and the first spring SPR1 are omitted. In the following description, mainly, the parking brake chamber PBC, the second spring SPR2, and the cylinder (case CS) will be described, and the description of the service brake chamber SBC and the first spring SPR1 will be omitted.

[0045] In FIG. 6, A pb is the cylinder cross-sectional area, K pb is the spring constant of the second spring SPR2, P pb is the parking brake chamber pressure, q pb is the parking brake chamber flow rate, m pb is the brake pad mass, y pb is the displacement.

[0046] The equation of motion in the wheel brake system is expressed by the following formula (4).

Equation

[0047] Next, the state equation in the wheel brake system is expressed by the following formula (5).

Equation

[0048] Next, the output equation for the wheel brake system is expressed by the following equation (6).

number

[0049] As described above, in the wheel brake system, the FF control device (second control unit) controls the parking brake chamber pressure according to the vehicle speed. This makes it possible to adjust the brake disc pressing force due to the biasing force of the second spring SPR2. In this way, by adjusting the brake disc pressing force when the parking brake is applied, it is possible to improve driving stability.

[0050] The brake system 100 in the embodiment of the present disclosure is a brake system having a service brake 100S capable of generating a braking force on the wheels of a vehicle and a parking brake 100P capable of generating a braking force on the wheels of a vehicle, and further comprising an ABS device that controls the braking force on the wheels according to the vehicle speed and an FF control device that controls the braking force on the wheels according to the vehicle speed.

[0051] With the above configuration, the FF control device controls the braking force of the wheels according to the vehicle speed, thereby improving driving stability when the parking brake is applied.

[0052] Furthermore, the embodiments of this disclosure further include a parking brake chamber PBC configured to be pressure-adjustable to increase or decrease the braking force of the wheels, and the FF control device controls the pressure of the parking brake chamber according to the vehicle speed. As a result, the braking force of the wheels is increased or decreased by the FF control device controlling the pressure of the parking brake chamber. Consequently, it is possible to improve driving stability when the parking brake is applied.

[0053] Furthermore, in the embodiments of this disclosure, a relay valve RV is used to discharge air from inside the parking brake chamber PBC via the relay valve RV. The FF control device controls the relay valve RV to reduce the pressure in the parking brake chamber from a high-pressure state. As a result, the FF control device can adjust the pressure in the parking brake chamber by controlling the relay valve RV, thereby improving driving stability when the parking brake is applied.

[0054] Furthermore, in the above embodiment, the FF control device controlled the parking brake chamber pressure according to the vehicle speed, but in this disclosure, the FF control device may control the parking brake chamber pressure according to the vehicle speed and the wheel speed. In this case, the wheel speed is measured, for example, by a known wheel speed sensor capable of detecting the rotational speed of the wheel. This makes it possible to further improve driving stability when the parking brake is applied. Moreover, in this disclosure, the braking force may be controlled independently for each of the multiple wheels based on the vehicle's yaw rate (rotational angular velocity around the vertical axis passing through the vehicle's center of gravity). This makes it possible to suppress wheel spin and further improve the vehicle's driving stability. The vehicle's yaw rate can be detected by a sensor.

[0055] Furthermore, in the above embodiment, the FF control device may independently control the braking force of each of the multiple wheels based on the vehicle's lateral slip speed. This ensures that the braking force of each wheel is appropriately controlled, making it possible to recover from a lateral slip.

[0056] (modified version) Next, a modified example of the brake system in this embodiment will be described with reference to Figure 7. Figure 7 is a block diagram that functionally represents a modified example of the brake system in this embodiment. In describing the modified example, we will mainly describe the configurations that differ from the above embodiment, and omit the description of the same configurations.

[0057] As shown in Figure 3, the brake system in the above embodiment has a pneumatic circuit through which compressed air from the tank TNK flows into the relay valve RV via the multi-protection valve MPV, the hand control valve HCV, and the double check valve. In contrast, the brake system in the modified example shown in Figure 7 has a pneumatic circuit through which air from the tank TNK flows directly from the multi-protection valve MPV to the relay valve RV, and an electric parking brake switch EPS is also provided. The control unit 110 recognizes the state of the electric parking brake switch EPS and controls the relay valve RV based on the recognition result.

[0058] In the modified brake system, a simpler configuration than that of the above embodiment makes it possible to improve driving stability when the parking brake is applied.

[0059] Furthermore, the embodiments described above are merely examples of how the Disclosure may be implemented, and the technical scope of the Disclosure should not be limited by them. In other words, the Disclosure can be implemented in various ways without departing from its essence or its main features. [Industrial applicability]

[0060] This disclosure is preferably used in vehicles equipped with a braking system that requires improved driving stability when the parking brake is applied. [Explanation of Symbols]

[0061] BC Brake Chamber BC / wP composite brake chamber BD brake disc BP Brake Pads BW back wall CS Case EPS Electric Parking Brake Switch FBM Foot Brake Module FW front wall HCV Hand Control Valve LD Rod MPV Multi-Protection Valve PBC Parking Brake Chamber PBCW Parking Brake Chamber Wall PCM Pressure Control Module PW Bulkhead RV relay valve SBC Service Brake Chamber SBCW Service Brake Chamber Wall SPR1 First spring SPR2 2nd spring TNK Tank 100 Brake System 100P Parking Brake 100S Service Brake 110 Control Unit

Claims

1. A brake system comprising a service brake capable of generating a first braking force on a vehicle and a parking brake capable of generating a second braking force on the vehicle, A first control unit controls the first braking force according to the vehicle speed of the vehicle, A second control unit controls the second braking force according to the vehicle speed, Equipped with, Brake system.

2. The system further comprises a parking brake chamber configured to be pressure-adjustable to increase or decrease the second braking force, The second control unit controls the parking brake chamber pressure according to the vehicle speed. The brake system according to claim 1.

3. The second control unit further controls the second braking force based on the yaw rate of the vehicle. The brake system according to claim 1.

4. The second control unit further controls the second braking force based on the lateral skid speed of the vehicle. The brake system according to claim 1.

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