Vehicle speed estimation device and brake control device

Abstract

The objective is to accurately estimate vehicle speed when the drive wheels are spinning. [Solution] The vehicle speed estimation device (control unit 20) is a device for estimating the estimated vehicle speed of a front-wheel drive or rear-wheel drive vehicle. The vehicle speed estimation device has a maximum wheel speed determination means 21, a minimum driven wheel speed determination means 22, and a vehicle speed estimation means 23. The maximum wheel speed determination means 21 determines the maximum wheel speed, which is the highest among the wheel speeds of all wheels. The minimum driven wheel speed determination means 22 determines the minimum driven wheel speed, which is the lowest among the wheel speeds of multiple driven wheels, by limiting it with a lower limit calculated based on the previously estimated vehicle speed. The vehicle speed estimation means 23 uses the smaller of the maximum wheel speed and the minimum driven wheel speed as the estimated vehicle speed.

Description

Technical Field

[0001] The present invention relates to a vehicle body speed estimation device and a brake control device.

Background Art

[0002] Conventionally, as a vehicle body speed estimation device, there is known one that estimates the vehicle body speed as a value obtained by imposing a limit on the acceleration or deceleration of the wheel speed of the front wheels (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in the prior art, even when the front wheels are driving wheels and the front wheels are wheel-spinning, it is desired to accurately estimate the vehicle body speed.

[0005] Therefore, an object of the present invention is to accurately estimate the vehicle body speed when the driving wheels are wheel-spinning.

Means for Solving the Problems

[0006] In order to solve the above problems, a vehicle body speed estimation device according to the present invention is a vehicle body speed estimation device that estimates an estimated vehicle body speed of a vehicle with front-wheel drive or rear-wheel drive. The vehicle body speed estimation device includes a maximum wheel speed determination means, a minimum driven wheel speed determination means, and a vehicle body speed estimation means. The maximum wheel speed determination means determines a maximum wheel speed that is the maximum among the wheel speeds of all the wheels. The minimum driven wheel speed determination means determines the minimum driven wheel speed by limiting the minimum wheel speed, which is the smallest among the wheel speeds of multiple driven wheels, by a lower limit calculated based on the previously estimated vehicle speed. The vehicle speed estimation means uses the smaller of the maximum wheel speed and the minimum driven wheel speed as the estimated vehicle speed.

[0007] With this configuration, if the drive wheels spin, the minimum driven wheel speed becomes the estimated vehicle speed, allowing for accurate estimation of the vehicle speed.

[0008] Alternatively, the minimum driven wheel speed determination means may determine the minimum driven wheel speed by limiting the minimum wheel speed with upper and lower limits calculated based on the previously estimated vehicle speed.

[0009] Furthermore, the upper limit may be calculated by adding a predetermined first value to the previously estimated vehicle speed.

[0010] Furthermore, the lower limit may be calculated by subtracting a pre-set second predetermined value from the previously estimated vehicle speed.

[0011] Furthermore, the vehicle speed estimation device according to the present invention may be a vehicle speed estimation device that estimates the estimated vehicle speed of a front-wheel drive vehicle. The vehicle speed estimation device includes a means for determining the maximum wheel speed, a means for determining the minimum driven wheel speed, and a means for estimating the vehicle speed. The maximum wheel speed determination means determines the maximum wheel speed among all the wheel speeds. The minimum driven wheel speed determination means determines the minimum driven wheel speed by limiting the minimum wheel speed, which is the smallest of the multiple rear wheel speeds, by a lower limit calculated based on the previously estimated vehicle speed. The vehicle speed estimation means uses the smaller of the maximum wheel speed and the minimum driven wheel speed as the estimated vehicle speed.

[0012] With this configuration, if the front wheels, which are the drive wheels, spin, the minimum driven wheel speed, based on the minimum wheel speed of the rear wheels, becomes the estimated vehicle speed, allowing for an accurate estimation of the vehicle speed.

[0013] Alternatively, the minimum driven wheel speed determination means may determine the minimum driven wheel speed by limiting the minimum wheel speed with upper and lower limits calculated based on the previously estimated vehicle speed.

[0014] The brake control device according to the present invention includes a vehicle speed estimation device that estimates the estimated vehicle speed of a front-wheel drive vehicle. The brake control unit controls the parking brake mechanism that applies braking force to the rear wheels. The brake control device can determine whether the rear wheels are about to lock up based on the estimated vehicle speed estimated by the vehicle speed estimation device and the wheel speed of the rear wheels. If it determines that the rear wheels are about to lock up while the vehicle is in motion and braking force is being applied to the rear wheels by the parking brake mechanism, it releases the braking force applied by the parking brake mechanism.

[0015] With this configuration, for example, even if braking force is applied to the rear wheels by the parking brake mechanism immediately after the front wheels spin, the estimated vehicle speed, which was accurately estimated during the wheel spin, can be used to determine whether the rear wheels are locked by the parking brake mechanism, thus enabling accurate determination of whether the rear wheels are locked by the parking brake mechanism. [Effects of the Invention]

[0016] When the drive wheels are spinning, the vehicle speed can be estimated with high accuracy. [Brief explanation of the drawing]

[0017] [Figure 1] This is a diagram showing the configuration of a vehicle equipped with an electric parking brake control device according to an embodiment of the present invention. [Figure 2]It is a diagram showing a drum brake and a parking brake mechanism, including diagram (a) showing the state where no brake is applied and diagram (b) showing the state where the brake is applied by the parking brake mechanism. [Figure 3] It is a cross-sectional view showing the electric actuator of the parking brake mechanism, including diagram (a) showing the release state and diagram (b) showing the apply state. [Figure 4] It is a block diagram showing the configuration of the control unit. [Figure 5] It is a flowchart showing the operation of the control unit. [Figure 6] It is a graph showing the relationship between the wheel speed of each wheel and the estimated vehicle body speed when the parking brake is actuated while the vehicle is traveling on a low μ road. [Figure 7] It is a graph showing the relationship between the wheel speed of each wheel and the estimated vehicle body speed when brake hydraulic pressure is generated while the vehicle is traveling on a high μ road. [Figure 8] It is a graph showing the relationship between the wheel speed of each wheel and the estimated vehicle body speed when the front wheels experience wheel spin on a low μ road. [Figure 9] It is a graph showing the relationship between the wheel speed of each wheel and the estimated vehicle body speed when the vehicle accelerates on a high μ road.

Best Mode for Carrying Out the Invention

[0018] Next, embodiments of the present invention will be described in detail with appropriate reference to the drawings. As shown in FIG. 1, the vehicle CR includes a drum brake D, a parking brake mechanism 200, and a vehicle brake hydraulic pressure control device 100. The vehicle CR of the present embodiment is a front-wheel drive vehicle.

[0019] The drum brake D is provided on each of the four wheels W. The parking brake mechanism 200 is a mechanism that mechanically operates the drum brake D of the rear wheels (the two rear wheels W) to apply a braking force to the rear wheels. The parking brake mechanism 200 is provided for each of the drum brakes D provided on the left and right rear wheels.

[0020] The vehicle brake fluid pressure control device 100 is for appropriately controlling the braking force applied to each wheel W of the vehicle CR, and mainly comprises a hydraulic unit 10 equipped with oil passages (hydraulic passages) and various components, and a control unit 20 for appropriately controlling the various components within the hydraulic unit 10. The hydraulic unit 10 is connected via an oil passage to the master cylinder MC, which generates brake fluid pressure when the brake pedal BP is pressed, and is also connected via an oil passage to the wheel cylinder D4 of each drum brake D. The hydraulic unit 10 is equipped with valves, pumps, etc., for controlling the brake fluid pressure applied to the wheel cylinder D4.

[0021] The control unit 20 is an example of a vehicle speed estimation device and brake control device, and has the function of controlling valves and pumps in the hydraulic unit 10 and the function of controlling the parking brake mechanism 200. The control unit 20 is connected to a wheel speed sensor 91 for detecting the wheel speed of the wheel W and a parking switch 92 for switching the state of the drum brake D between the apply state and the release state. Here, the apply state refers to the state in which braking force is generated from the drum brake D. The release state refers to the state in which the braking force of the drum brake D is released.

[0022] The parking switch 92 is switchable between an apply position and a release position. When the parking switch 92 is in the apply position, it outputs an apply signal to the control unit 20 to set the drum brake D to the apply state, and when the parking switch 92 is in the release position, it outputs a release signal to the control unit 20 to set the drum brake D to the release state.

[0023] The control unit 20 includes, for example, a CPU, RAM, ROM, and input / output circuits, and performs control by processing various calculations based on inputs from the wheel speed sensor 91 and parking switch 92, as well as programs and data stored in the ROM.

[0024] As shown in Figures 2(a) and (b), the drum brake D comprises a drum D1, a brake shoe D2, a return spring D3, and a wheel cylinder D4. The drum D1 is a member having a cylindrical portion that rotates integrally with the wheel W.

[0025] The brake shoe D2 is an arc-shaped member that extends along the inner circumferential surface of the drum D1, and applies braking force to the wheel W when pressed against the inner circumferential surface of the drum D1. Two brake shoes D2 are provided along the inner circumferential surface of the drum D1. Each of the two brake shoes D2 is rotatably supported at one end by a support member D5, allowing them to rotate toward and away from each other.

[0026] The return spring D3 biases the other ends of the two brake shoes D2 toward each other. The wheel cylinder D4 biases the two brake shoes D2 toward the inner surface of the drum D1 by the brake fluid pressure supplied from the hydraulic unit 10.

[0027] The parking brake mechanism 200 comprises a strut 210, a parking lever 220, a wire 230, and an electric actuator 240 shown in Figure 3. The strut 210 engages with the other end of each of the two brake shoes D2.

[0028] One end of the parking lever 220 is rotatably supported by a pin 221 on one of the brake shoes D2. A wire 230 is connected to the other end of the parking lever 220. The portion of the parking lever 220 between the two ends, closer to the one end, is engaged with the strut 210.

[0029] When the wire 230 is pulled to the right in the diagram, the parking lever 220 rotates around the pin 221, causing the parking lever 220 to press the other brake shoe D2 against the inner surface of the drum D1 via the strut 210. Furthermore, when the wire 230 is pulled, the parking lever 220 rotates around the engagement point with the strut 210, causing the parking lever 220 to press the other brake shoe D2 against the inner surface of the drum D1 via the pin 221.

[0030] As a result, the tension of the wire 230 presses each brake shoe D2 against the inner surface of the drum D1. When the wire 230 is loosened in the left direction shown in the diagram, the biasing force of the return spring D3 causes each brake shoe D2 to move away from the inner surface of the drum D1.

[0031] As shown in Figure 3, the electric actuator 240 is a device for pulling the wire 230. The electric actuator 240, together with the control unit 20, constitutes the electric parking brake control device 1. The electric parking brake control device 1 is a device that changes the state of the drum brake D between the applied state and the released state. The electric actuator 240 comprises a motor 241, a conversion mechanism 2, a screw shaft 244, a housing 245, a retainer 246, and a plurality of disc springs 247.

[0032] The conversion mechanism 2 is a mechanism that converts the rotational motion of the motor 241 into linear motion, and comprises multiple gears 242 and nuts 243. The nut 243 is connected to the motor 241 via a plurality of gears 242. The nut 243 has a female threaded portion 243A that meshes with the male threaded portion 244A of the screw shaft 244.

[0033] The screw shaft 244 is a component that moves linearly by the conversion mechanism 2. The screw shaft 244 is supported in the housing 245 so as to be movable in the axial direction, and a wire 230 is fixed to its tip. A flange portion 244B that protrudes radially is formed at the end of the screw shaft 244 opposite to the tip.

[0034] The retainer 246 is a disc-shaped member with a hole in the center, and engages with the flange 244B of the screw shaft 244 from the tip side of the screw shaft 244. Multiple disc springs 247 are positioned between the retainer 246 and the nut 243 in the axial direction of the screw shaft 244.

[0035] In this electric actuator 240, when the motor 241 is rotated forward, the screw shaft 244 moves in a direction that is housed within the housing 245, pulling the wire 230 and putting the drum brake D into the applied state. Conversely, when the motor 241 is rotated backward, the screw shaft 244 moves in a direction that is protruding from the housing 245, loosening the wire 230 and putting the drum brake D into the released state.

[0036] In the following explanation, the position of the screw shaft 244 when the drum brake D is in the applied state will also be referred to as the "applied position," and the position of the screw shaft 244 when the drum brake D is in the released state will also be referred to as the "released position." Specifically, the released position is the position shown in Figure 3(b), and the applied position is the position shown in Figure 3(a).

[0037] When the screw shaft 244 is in the release position, multiple disc springs 247 are held in a deformed state between the retainer 246 and the nut 243. When the screw shaft 244 is in the apply position, the retainer 246 is prevented from moving by contact with the housing 245, and the flange portion 244B of the screw shaft 244 is separated from the retainer 246. During the process of the screw shaft 244 moving from the apply position to the release position, the disc springs 247 are deformed by the screw shaft 244.

[0038] The control unit 20 controls the drive of the motor 241 based on the signal from the parking switch 92. The control unit 20 has the function of performing apply processing and release processing. In the following description, the output of the apply signal from the parking switch 92 will also be referred to as the "apply command," and the output of the release signal from the parking switch 92 will also be referred to as the "release command."

[0039] The apply process is the process of driving the electric actuator 240 so that the drum brake D is in the apply state. In other words, the apply process is the process of controlling the electric actuator 240 to move in a direction that presses the brake shoe D2 against the drum D1. Specifically, when the control unit 20 receives an apply command, it rotates the motor 241 in the forward direction to move the screw shaft 244 to the apply position, thereby changing the state of the drum brake D to the apply state.

[0040] The release process involves driving the electric actuator 240 so that the drum brake D is in the released state. In other words, the release process involves controlling the electric actuator 240 to move the brake shoe D2 away from the drum D1. Specifically, when the control unit 20 receives a release command, it reverses the rotation of the motor 241 to move the screw shaft 244 to the release position, thereby putting the parking brake mechanism 200 into the released state.

[0041] As shown in Figure 4, the control unit 20 includes a maximum wheel speed determination means 21, a minimum driven wheel speed determination means 22, a vehicle speed estimation means 23, and a rear wheel lock suppression means 24.

[0042] The maximum wheel speed determination means 21 has the function of acquiring wheel speeds from all wheel speed sensors 91 and determining the maximum wheel speed V4 which is the highest among the wheel speeds of all wheels W. Once the maximum wheel speed determination means 21 has determined the maximum wheel speed V4, it outputs the determined maximum wheel speed V4 to the vehicle speed estimation means 23.

[0043] The minimum driven wheel speed determination means 22 acquires wheel speeds from wheel speed sensors 91 of the two rear driven wheels and has the function of determining the minimum driven wheel speed Vr based on the minimum wheel speed Vrp, which is the smallest of the two rear wheel speeds. Specifically, the minimum driven wheel speed determination means 22 determines the minimum driven wheel speed Vr by limiting the minimum wheel speed Vrp with an upper limit value Vru and a lower limit value Vrd calculated based on the previously estimated vehicle speed V(i-1).

[0044] The minimum driven wheel speed determination means 22 calculates the upper limit value Vru by adding a preset first predetermined value Gu to the previously estimated vehicle speed V(i-1). Here, the first predetermined value Gu can be set to a value corresponding to the vehicle's acceleration when the vehicle accelerates to its maximum on a high-friction surface, for example.

[0045] The minimum driven wheel speed determination means 22 calculates the lower limit value Vrd by subtracting a preset second predetermined value Gd from the previously estimated vehicle speed V(i-1). Here, the second predetermined value Gd can be set to a value corresponding to the magnitude of the vehicle's deceleration when the vehicle decelerates to its maximum on a low-μ surface, for example.

[0046] The minimum driven wheel speed determination means 22 determines the minimum driven wheel speed Vr and outputs the determined minimum driven wheel speed Vr to the vehicle speed estimation means 23.

[0047] The vehicle speed estimation means 23 has the function of estimating the vehicle's estimated vehicle speed. Specifically, the vehicle speed estimation means 23 uses the smaller of the maximum wheel speed V4 and the minimum driven wheel speed Vr as the estimated vehicle speed V(i). Once the vehicle speed estimation means 23 has determined the estimated vehicle speed V(i), it outputs the determined estimated vehicle speed V(i) to the rear wheel lock suppression means 24.

[0048] The rear wheel lock suppression means 24 has the function of suppressing rear wheel lock by releasing the application of braking force by the parking brake mechanism 200 when it is determined that the rear wheels are about to lock up while the vehicle is in motion and braking force is being applied to the rear wheels by the parking brake mechanism 200. When the control unit 20 receives an apply command from the parking switch 92, it controls the left and right parking brake mechanisms 200 to set the left and right drum brakes D to the apply state.

[0049] Furthermore, the rear wheel lock suppression means 24, upon receiving an apply command from the parking switch 92, has the function of determining whether the rear wheels are likely to lock up for each of the left and right rear wheels, based on the estimated vehicle speed V(i) and the wheel speed of the rear wheels. Specifically, the rear wheel lock suppression means 24 calculates the slip ratio (for example, the difference between the estimated vehicle speed and the wheel speed of the rear wheels divided by the estimated vehicle speed) based on the estimated vehicle speed V(i) and the wheel speed of the rear wheels, and determines that the rear wheels are likely to lock up if the slip ratio is greater than or equal to a predetermined value and the wheel acceleration of the rear wheels obtained from the wheel speed of the rear wheels is 0 or less.

[0050] If the rear wheel lock suppression means 24 determines that the left rear wheel is about to lock, it controls the left parking brake mechanism 200 to change the state of the left drum brake D from the applied state to the released state. If the rear wheel lock suppression means 24 determines that the right rear wheel is about to lock, it controls the right parking brake mechanism 200 to change the state of the right drum brake D from the applied state to the released state.

[0051] The rear wheel lock suppression means 24 stops the corresponding parking brake mechanism 200 and maintains the braking force of the corresponding rear wheel when the wheel acceleration of the rear wheel is greater than 0. The rear wheel lock suppression means 24 controls the corresponding parking brake mechanism 200 to transition the drum brake D to the applied state when the slip ratio is less than a predetermined value and the wheel acceleration of the rear wheel is 0 or less.

[0052] Next, the method for estimating the estimated vehicle body speed by the control unit 20 will be described. The control unit 20 repeatedly executes the process of FIG. 5 while the ECU of the vehicle is activated.

[0053] In the process of FIG. 5, the control unit 20 first acquires the wheel speeds of the four wheels from the four wheel speed sensors 91, and substitutes the maximum wheel speed among the four wheels into the maximum wheel speed V4 (S1). After step S1, the control unit 20 acquires the wheel speeds of the left and right rear wheels from the two wheel speed sensors 91 corresponding to the left and right rear wheels, and substitutes the lower wheel speed among the wheel speeds of the two rear wheels into the minimum wheel speed Vrp (S2).

[0054] After step S2, the control unit 20 determines whether there is a previous value V(i - 1) of the estimated vehicle body speed (S3). Here, the control unit 20 resets the estimated vehicle body speed when the ECU of the vehicle stops or the like. When the estimated vehicle body speed is reset, the control unit 20 determines No in step S3. Note that the reset of the estimated vehicle body speed may be performed, for example, when it is determined that the wheels are likely to lock by the hydraulic brake.

[0055] If it is determined in step S3 that there is a previous value V(i - 1) of the estimated vehicle body speed (Yes), the control unit 20 calculates an upper limit value Vru and a lower limit value Vrd of the wheel speed of the rear wheels based on the previous value V(i - 1) of the estimated vehicle body speed (S4). After step S4, the control unit 20 determines whether the minimum wheel speed Vrp is greater than the upper limit value Vru (S5).

[0056] If it is determined in step S5 that Vrp > Vru is not satisfied (No), the control unit 20 determines whether the minimum wheel speed Vrp is less than the lower limit value Vrd (S6). If it is determined in step S6 that Vrp < Vrd is not satisfied (No), or if it is determined No in step S3, the control unit 20 substitutes the minimum wheel speed Vrp into the minimum driven wheel speed Vr (S7).

[0057] If it is determined in step S5 that Vrp > Vru (Yes), the control unit 20 substitutes the upper limit value Vru for the minimum driven wheel speed Vr (S8). If it is determined in step S6 that Vrp < Vrd (Yes), the control unit 20 substitutes the lower limit value Vrd for the minimum driven wheel speed Vr (S9).

[0058] After step S7, step S8, or step S9, the control unit 20 determines whether the minimum driven wheel speed Vr is less than the maximum wheel speed V4 (S10). If it is determined in step S10 that Vr < V4 is not true (No), the control unit 20 substitutes the maximum wheel speed V4 for the estimated vehicle body speed V(i) and ends this process. If it is determined in step S10 that Vr < V4 (Yes), the control unit 20 substitutes the minimum driven wheel speed Vr for the estimated vehicle body speed V(i) and ends this process.

[0059] Next, a specific example of the method for estimating the estimated vehicle body speed by the control unit 20 will be described with reference to FIGS. 6 to 9. In FIGS. 6 to 9, FR represents the wheel speed of the right front wheel, FL represents the wheel speed of the left front wheel, RR represents the wheel speed of the right rear wheel, RL represents the wheel speed of the left rear wheel, and V(i) represents the estimated vehicle body speed.

[0060] As shown in FIG. 6, when the vehicle is traveling on a low-μ road and the occupant switches the parking switch 92 to the apply position, the parking brake mechanism 200 applies a braking force to the rear wheels, and the rear wheels tend to lock. When the rear wheels tend to lock, the minimum wheel speed Vrp of the rear wheels may become smaller than the lower limit value Vrd. In this case, the minimum driven wheel speed Vr is set to the lower limit value Vrd.

[0061] On the other hand, since the wheel speeds of the front wheels to which no braking force is applied rotate following the road surface, the values are larger than the wheel speeds of the rear wheels. Therefore, when the parking brake mechanism 200 applies a braking force to the rear wheels, the larger of the wheel speeds of the left and right front wheels is set to the maximum wheel speed V4.

[0062] The lower limit Vrd is obtained by subtracting the second predetermined value Gd, which is a relatively large value, from the previous estimated vehicle speed V(i-1). Therefore, when braking force is applied to the rear wheels by the parking brake mechanism 200, the minimum driven wheel speed Vr(Vrd) becomes smaller than the maximum wheel speed V4. Consequently, when braking force is applied to the rear wheels by the parking brake mechanism 200, the minimum driven wheel speed Vr, limited by the lower limit Vrd, is selected as the estimated vehicle speed V(i), as indicated by the sign Vr in the straight line portion of V(i) in the figure.

[0063] Based on the estimated vehicle speed V(i) set in this manner, the control unit 20 determines whether the rear wheels are about to lock up, and if it determines that they are about to lock up, it releases the braking force applied by the parking brake mechanism 200.

[0064] As shown in Figure 7, when a vehicle is traveling on a high-friction surface and the occupant presses the brake pedal BP, generating a brake fluid pressure high enough to prevent the wheels from locking, the wheel speed of each wheel may fall below the lower limit Vrd. In this case, the minimum driven wheel speed Vr, limited by the lower limit Vrd, becomes greater than the maximum wheel speed V4, so the maximum wheel speed V4 is selected as the estimated vehicle speed V(i).

[0065] As shown in Figure 8, when the occupant presses the accelerator pedal to accelerate the vehicle on a low-friction surface, the front wheels, which are the drive wheels, may spin. In this case, the wheel speed of one of the left or right front wheels becomes the maximum wheel speed V4, and since the maximum wheel speed V4 is greater than the minimum driven wheel speed Vr, the minimum driven wheel speed Vr is selected as the estimated vehicle speed V(i).

[0066] As shown in Figure 9, when the occupant presses the accelerator pedal to accelerate the vehicle on a high-friction surface, each wheel rotates in accordance with the road surface, so the wheel speed of each wheel at each point in time is approximately the same. In this case, the minimum driven wheel speed Vr(Vrp), which is not limited by the upper limit Vru and lower limit Vrd, is smaller than the maximum wheel speed V4, so the minimum driven wheel speed Vr is selected as the estimated vehicle speed V(i).

[0067] Depending on the setting of the upper limit Vru, the wheel speed of each wheel may exceed the upper limit Vru when the vehicle accelerates on a high-friction surface. In this case, the minimum driven wheel speed Vr, which is limited by the upper limit Vru, will be smaller than the maximum wheel speed V4. Therefore, if the minimum driven wheel speed Vr is selected as the estimated vehicle speed V(i), the estimation accuracy of the estimated vehicle speed V(i) will deteriorate. For this reason, it is preferable to set the upper limit Vru to a value corresponding to the maximum acceleration of the vehicle, as described above, so that the wheel speed of each wheel does not exceed the upper limit Vru when the vehicle accelerates on a high-friction surface.

[0068] As described above, the following effects can be obtained according to this embodiment. If the front wheels, which are the drive wheels, spin, the minimum driven wheel speed Vr, which is based on the minimum wheel speed of the rear wheels, becomes the estimated vehicle speed V(i), allowing for an accurate estimation of the vehicle speed.

[0069] Since the estimated vehicle speed V(i) is accurately estimated when the front wheels spin, even if, for example, braking force is applied to the rear wheels by the parking brake mechanism 200 immediately after the front wheels spin, the accurately estimated vehicle speed V(i) obtained during the wheel spin can be used to determine whether the rear wheels are locked by the parking brake mechanism 200. Therefore, the parking brake mechanism 200 can accurately determine whether the rear wheels are locked.

[0070] The present invention is not limited to the embodiments described above, and can be used in various forms as illustrated below.

[0071] The vehicle speed estimation device may estimate the estimated vehicle speed of a rear-wheel-drive vehicle.

[0072] The vehicle speed estimation device and brake control device may be separate devices from the vehicle brake fluid pressure control device.

[0073] In the above embodiment, a parking brake mechanism 200 that drives a drum brake D was illustrated, but the present invention is not limited thereto, and for example, it may be a parking brake mechanism that drives a disc brake.

[0074] A single parking brake mechanism may be provided for each of the left and right rear wheels. In other words, the wires for each of the left and right drum brakes may be pulled by a single parking brake mechanism.

[0075] In the above embodiment, the minimum driven wheel speed was determined by limiting the minimum wheel speed with upper and lower limits calculated based on the previously estimated vehicle speed. However, the minimum driven wheel speed may also be determined by limiting the minimum wheel speed with at least a lower limit. Specifically, for example, in the process shown in Figure 5, the process in step S4 may be changed to a process that calculates only the lower limit Vrd, and steps S5 and S8 may be deleted.

[0076] The elements described in the above embodiments and modifications may be implemented in any combination. [Explanation of symbols]

[0077] 20...Control unit 21...Maximum wheel speed determination means 22...Minimum driven wheel speed determination means 23...Vehicle speed estimation means

Claims

1. A vehicle speed estimation device for estimating the estimated vehicle speed of a front-wheel drive or rear-wheel drive vehicle, A means for determining the maximum wheel speed which is the highest among all the wheel speeds, A minimum driven wheel speed determination means determines the minimum driven wheel speed by limiting the minimum wheel speed among multiple driven wheel speeds by a lower limit calculated based on the previously estimated vehicle speed, and A vehicle speed estimation device characterized by having a vehicle speed estimation means that uses the smaller of the maximum wheel speed and the minimum driven wheel speed as the estimated vehicle speed.

2. The vehicle speed estimation device according to claim 1, characterized in that the minimum driven wheel speed determination means determines the minimum driven wheel speed by limiting the minimum wheel speed with an upper limit and a lower limit calculated based on the previously estimated vehicle speed.

3. The vehicle speed estimation device according to claim 2, characterized in that the upper limit is calculated by adding a predetermined first value to the previously estimated vehicle speed.

4. The vehicle speed estimation device according to claim 1, characterized in that the lower limit is calculated by subtracting a pre-set second predetermined value from the previously estimated vehicle speed.

5. A vehicle speed estimation device for estimating the estimated vehicle speed of a front-wheel-drive vehicle, A means for determining the maximum wheel speed which is the highest among all the wheel speeds, A minimum driven wheel speed determination means determines the minimum driven wheel speed by limiting the minimum wheel speed among multiple rear wheel speeds by a lower limit calculated based on the previously estimated vehicle speed, and A vehicle speed estimation device characterized by having a vehicle speed estimation means that uses the smaller of the maximum wheel speed and the minimum driven wheel speed as the estimated vehicle speed.

6. The vehicle speed estimation device according to claim 5, characterized in that the minimum driven wheel speed determination means determines the minimum driven wheel speed by limiting the minimum wheel speed with an upper limit and a lower limit calculated based on the previously estimated vehicle speed.

7. A brake control device comprising a vehicle speed estimation device according to claim 5 or claim 6, and controlling a parking brake mechanism that applies braking force to the rear wheels, Based on the estimated vehicle speed estimated by the vehicle speed estimation device and the wheel speed of the rear wheels, it is possible to determine whether or not the rear wheels are likely to lock up. A brake control device characterized in that, when it is determined that the rear wheels are about to lock up while the vehicle is in motion and braking force is being applied to the rear wheels by the parking brake mechanism, the application of braking force by the parking brake mechanism is released.

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