Braking device

Abstract

To provide a braking device capable of saving a space around a wheel in a vehicle capable of independently steering and independently driving and braking.SOLUTION: In a vehicle 100 in which wheels 91-94 can be steered independently by steering actuators 71-74 and can be braked / driven independently by braking / driving forces outputted by braking / driving actuators 81-84, a braking device 50 brakes the vehicle 100. When a braking request is generated, the used brake determination unit 56 of the braking device 50 calculates the braking force distribution of longitudinal force braking and lateral force braking of each wheel, and determines the type of brake to be used. The used brake determination unit 56 can use at least the regenerative brake by the braking / driving actuators 81 to 84 for the longitudinal force braking of each of the wheels 91 to 94. Further, the used brake determination unit 56 can use at least the turning brake for setting the left and right pair of wheels to the toe-in or the toe-out by the turning actuators 71 to 74 for the lateral force braking of each of the wheels 91 to 94.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a braking device. [Background technology]

[0002] BACKGROUND ART Conventionally, there is known a technique used in an independently steering vehicle to reduce the space around the wheels.

[0003] For example, in the industrial vehicle disclosed in Patent Document 1, the rotation angle detection device is formed as part of the steering drive unit, thereby realizing a space-saving and inexpensive rotation angle detection device. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2023-547472 Summary of the Invention [Problem to be solved by the invention]

[0005] Compared to a typical vehicle in which the left and right wheels are steered in common via a connecting shaft, an independently steered vehicle in which a steering actuator is mounted on each wheel faces the challenge of reducing the space around the wheels. Furthermore, the need for space reduction is even greater in an independently braking / driving vehicle in which each wheel is provided with a braking / driving actuator. In particular, there is room for improvement in reducing the space around the wheels in braking devices that use braking means such as friction brakes.

[0006] The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a braking device that saves space around the wheels in a vehicle that is capable of independent steering and independent braking and driving. [Means for solving the problem]

[0007] A vehicle (100) to which the braking device of the present invention is applied has three or more wheels (91-94) including one or more pairs of left and right wheels that are not mechanically constrained to one another, and which can be independently steered by steering actuators (71-74) corresponding to each wheel, and can be independently braked and driven by braking and driving forces outputted by braking and driving actuators (81-84) corresponding to each wheel. The braking device brakes the vehicle in this vehicle.

[0008] The braking device includes a brake application determination unit 56, a steering control unit 57, and a braking / driving control unit 58. When a braking request is generated, the brake application determination unit calculates a braking force distribution between longitudinal force braking acting in the longitudinal direction of each wheel and lateral force braking acting in a direction perpendicular to the longitudinal direction of each wheel, and determines the type of brake to be used.

[0009] The steering control unit controls the steering actuators to steer each wheel in response to instructions from the brake application determination unit, and the braking / driving control unit controls the braking / driving actuators to brake / drive each wheel in response to instructions from the brake application determination unit.

[0010] The brake application determination unit can use at least a regenerative brake by a braking / driving actuator for longitudinal force braking of each wheel, and can use at least a steering brake that sets the pair of left and right wheels to a toe-in or toe-out position by a steering actuator for lateral force braking of each wheel.

[0011] The braking system of the present invention uses regenerative brakes and steering brakes in coordination depending on the vehicle state, thereby ensuring the necessary braking force while traveling without using friction brakes or even by reducing the braking force distribution by friction brakes. This makes it possible to eliminate friction brakes or downsize them, thereby realizing space savings around the wheels. Furthermore, eliminating friction brakes or downsizing them also leads to weight and cost reductions. [Brief explanation of the drawings]

[0012] [Figure 1]1 is a diagram of a four-wheel vehicle equipped with a braking device according to an embodiment of the present invention; [Figure 2] FIG. 2 is a diagram illustrating the principle of steering braking. [Figure 3] A diagram showing four patterns of toe-in / toe-out for the front and rear wheels. [Figure 4] FIG. 4 is a diagram illustrating braking force distribution according to a required deceleration. [Figure 5] 4 is a flowchart of a brake application determination process according to the first embodiment. [Figure 6] 10 is a flowchart of a brake application determination process according to a second embodiment. [Figure 7] 11 is a flowchart of a brake application determination process according to a third embodiment. [Figure 8] 10 is a flowchart of a brake application determination process according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of a braking device will be described with reference to the drawings. The braking device of this embodiment is mounted on a vehicle in which three or more wheels, including one or more pairs of left and right wheels, which are not mechanically constrained from one another, can be steered independently and can be braked and driven independently. As a typical example, the braking device of this embodiment is mounted on a four-wheel vehicle including left and right front wheels and left and right rear wheels. The four wheels can be steered independently by steering actuators corresponding to each wheel, and can be braked and driven independently by braking and driving forces output by braking and driving actuators corresponding to each wheel. The braking device brakes this vehicle.

[0014] The configuration of a vehicle 100 equipped with a braking device 50 of this embodiment will be described with reference to Figure 1. The vehicle 100 has four wheels 91-94. The left front wheel 91 is labeled "FL," the right front wheel 92 is labeled "FR," the left rear wheel 93 is labeled "RL," and the right rear wheel 94 is labeled "RR." The numbers "1" to "4" at the end of the reference numerals of the following elements correspond to FL, FR, RL, and RR, respectively.

[0015] Steering actuators 71-74 and braking / driving actuators 81-84 are provided corresponding to the wheels 91-94. In the drawing, "actuator" is written as "Act." The steering actuators 71-74 are typically constituted by motors. The braking / driving actuators 81-84 are constituted by in-wheel motors, for example.

[0016] Battery 88 is a rechargeable secondary battery. Braking / driving actuators 81-84, which are connected in parallel to common battery 88, exchange power with battery 88. When power is supplied from battery 88 and vehicle 100 operates for power running, driving force is generated in braking / driving actuators 81-84, causing vehicle 100 to accelerate. When battery 88 is charged by regenerative operation, braking force is generated in braking / driving actuators 81-84, causing vehicle 100 to decelerate.

[0017] With regard to overall control of the driving of vehicle 100, vehicle operation determination unit 65 determines a target vehicle operation based on current vehicle information such as actual steering angle and vehicle speed, and turning instructions and acceleration / deceleration instructions from the driver or an automatic driving device. When functioning as part of a vehicle driving control device, the steering control unit controls steering actuators 71-74 to steer each of wheels 91-94 in accordance with instructions from vehicle operation determination unit 65. The braking / driving control unit controls braking / driving actuators 81-84 to brake / drive each of wheels 91-94.

[0018] However, in this embodiment, functions related to vehicle driving control other than braking are omitted, and attention is focused only on the function as a "brake device." Brake device 50 includes a brake application determination unit 56, a steering control unit 57, and a braking / driving control unit 58. When a braking request is generated, brake application determination unit 56 calculates the braking force distribution between longitudinal force braking and lateral force braking (see FIG. 2) for each wheel 91-94, and determines the type of brake to be used. The types of brakes used in this embodiment include at least regenerative brakes and steering brakes. Furthermore, friction brakes and parking brakes may be used depending on the braking configuration of the vehicle.

[0019] More specifically, the brake application determination unit 56 acquires information on the vehicle speed, the required deceleration, and the remaining battery charge (SOC) of the battery 88. The vehicle speed is input directly or via the vehicle operation determination unit 65 from a vehicle speed sensor (not shown). Alternatively, the vehicle speed may be calculated based on the rotation speed of the braking / driving actuators 81-84. The required deceleration is input from the vehicle operation determination unit 65. Here, the required deceleration is expressed as a negative value, and the greater the absolute value of the required deceleration, the greater the braking force required. Based on this information, the brake application determination unit 56 calculates the braking force distribution between longitudinal force braking and lateral force braking for each wheel and determines which brake to use.

[0020] Steering control unit 57 controls steering actuators 71-74 to steer each of wheels 91-94 in response to instructions from brake use determination unit 56. The purpose of steering here is not to perform a turning operation, but to set the pair of left and right wheels to toe-in or toe-out and use the "steering brake." In Figure 1, BrSt represents the steering brake.

[0021] The braking / driving control unit 58 controls the braking / driving actuators to brake / drive each of the wheels 91-94 in response to instructions from the brake application determination unit 56. However, even though it is called braking / driving, the operation based on instructions from the brake application determination unit 56 is braking mainly by regenerative braking. In Figure 1, BrRg represents the regenerative brake.

[0022] The steering brake will be explained with reference to Figures 2 and 3. In Figure 2, the steering angles δ1-δ4 of each wheel 91-94 are defined, for example, with a counterclockwise direction from the neutral position being positive and a clockwise direction from the neutral position being negative. In the toe-zero state shown in the upper part of Figure 2, each wheel 91-94 faces in the fore-and-aft direction of the vehicle, and all steering angles δ1-δ4 are 0. In this state, running resistance is small.

[0023] Toe-in is a state in which the front ends of the pair of left and right wheels point inward, and toe-out is a state in which the front ends of the pair of left and right wheels point outward. The lower part of Figure 2 shows the toe-in state of left and right front wheels 91, 92 and left and right rear wheels 93, 94. When four wheels are toe-in, the steering angles δ1-δ4 are "δ1<0, δ2>0, δ3<0, δ4>0". When four wheels are toe-out, the steering angles δ1-δ4 are "δ1>0, δ2<0, δ3>0, δ4<0". A braking method that uses the running resistance generated by toe-in or toe-out is the steering brake.

[0024] The target braking force in the longitudinal direction of the vehicle for each wheel 91-94 is divided into longitudinal force braking acting in the longitudinal direction of the wheel, and lateral force braking acting in a direction perpendicular to the longitudinal direction of the wheel. Brake application determination unit 56 can use at least regenerative braking by braking / driving actuators 81-82 for longitudinal force braking of each wheel 91-94, and can use at least steering brakes for lateral force braking of each wheel 91-94. When using steering brakes, brake application determination unit 56 sets the pair of left and right wheels to toe-in or toe-out by steering actuators 71-74.

[0025] Figure 3 shows the following four patterns for the toe-in / toe-out of the front and rear wheels. In addition to these, it is also possible to have a pattern in which only the front or rear wheels are toe-in or toe-out. Pattern 1: Front wheel toe-in, rear wheel toe-in Pattern 2: Front wheel toe-in, rear wheel toe-out Pattern 3: Front wheel toe-out, rear wheel toe-in Pattern 4: Front wheel toe-out, rear wheel toe-out

[0026] Of these, the second pattern is preferable for steering braking while the vehicle is moving. Brake use determination unit 56 instructs steering control unit 57 to set the front wheels to toe-in and the rear wheels to toe-out for lateral force braking of each wheel 91-94 by steering braking while the vehicle is moving. Furthermore, the third pattern is preferable for steering braking while the vehicle is stopped. Brake use determination unit 56 instructs steering control unit 57 to set the front wheels to toe-out and the rear wheels to toe-in for lateral force braking of each wheel 91-94 by steering braking while the vehicle is stopped.

[0027] Next, with reference to Figure 4, the concept of selecting the brake to be used by the brake to be used determination unit 56 will be explained. Generally, in vehicles equipped with friction brakes, the friction brakes are used for longitudinal braking of each wheel 91-94. With friction brakes, the wheels are braked by the friction force generated when, for example, the brake pads are pressed against the disc rotor. However, to provide the target braking force using friction brakes alone would require large friction brakes, which would occupy space around the wheels and increase weight and cost.

[0028] In particular, in vehicle 100 capable of independent steering and independent braking / driving, steering actuators 71-74 and braking / driving actuators 81-84 are provided for each of wheels 91-94, so there is a greater need to save space around the wheels, reduce weight, and reduce costs. Therefore, there is a demand to reduce the distribution of braking force by friction brakes by using regenerative brakes and steering brakes as much as possible, and to eliminate friction brakes or downsize them to smaller, lighter brakes.

[0029] In Figure 4, the horizontal axis shows the absolute value of the required deceleration, and the vertical axis shows the target braking force. Assume that the remaining battery charge is below the threshold at which charging is possible, and that regenerative braking can be used. When the absolute value of the required deceleration is below the deceleration threshold Xs, the target braking force can be secured by regenerative braking alone. In braking force distribution example 1, when the absolute value of the required deceleration is greater than the deceleration threshold Xs, the target braking force can be secured by using the regenerative braking and the steering brake in combination. Because there is no need to use friction brakes, it is possible to eliminate friction brakes, i.e., achieve "friction brake-less."

[0030] In braking force distribution example 2, the vehicle weight is heavier than in example 1, and the target braking force relative to the absolute value of the required deceleration is greater. When the absolute value of the required deceleration is between the deceleration threshold Xs and the second deceleration threshold Xf, the target braking force can be secured by using both the regenerative brake and the steering brake. When the absolute value of the required deceleration exceeds the second deceleration threshold Xf, the friction brake is used in addition to the regenerative brake and the steering brake. However, even in this case, the braking force distribution of the friction brake is relatively small, so it is possible to downsize to a smaller, lighter friction brake.

[0031] Next, the brake application determination process of the first to fourth embodiments will be described with reference to the flowcharts of Figures 5 to 8. In the flowcharts of each embodiment, the symbol "S" indicates a step. The first to fourth embodiments differ in the braking configuration of the vehicle to which they are applied, and are divided into the following four embodiments depending on the combination of whether or not a friction brake and whether or not a parking brake is used. First embodiment: No friction brake, no parking brake Second embodiment: with friction brake, without parking brake Third embodiment: No friction brake, with parking brake Fourth embodiment: with friction brake and parking brake

[0032] S8A (when there is no friction brake) and S8B (when there is a friction brake) differ depending on whether a friction brake is present. S9A (when there is no parking brake) and S9B (when there is a parking brake) differ depending on whether a parking brake is present. Parking brakes include lever-type side brakes as well as stick-type and pedal-type brakes. The other steps S1 to S7 are common to the first to fourth embodiments. The same step numbers are used for common steps, and explanations will be omitted.

[0033] First, steps S1 to S7, which are common to all embodiments, will be described. In S1, it is determined whether the requested longitudinal acceleration is a negative value less than 0G, i.e., whether a braking request has occurred. If the requested longitudinal acceleration is a negative value less than 0G, the requested longitudinal acceleration corresponds to the requested deceleration. If a braking request has occurred and the answer is YES in S1, the process proceeds to S2. If a braking request has not occurred and the answer is NO in S1, the process ends.

[0034] In S2, it is determined whether the vehicle speed is greater than a vehicle speed threshold (for example, 0 km / h). If the vehicle is moving, a YES determination is made in S2 and the process proceeds to S3. If the vehicle speed is equal to or less than the vehicle speed threshold and the vehicle is deemed to be stopped, a NO determination is made in S2 and the process proceeds to S9A or S9B. Here, in this specification, the term "stopped" refers to a state in which the vehicle is physically stopped, regardless of the difference between "stopped" and "parked" under the Road Traffic Act, that is, regardless of whether the driver is in the vehicle or whether cargo is being loaded or unloaded within five minutes. If the vehicle has a parking brake, the parking brake can be used while the vehicle is stopped.

[0035] In S3, the brake use determination unit 56 calculates the braking force distribution according to the required deceleration. In S4, it is determined whether the remaining battery charge is equal to or less than the remaining charge threshold at which charging is possible. Specifically, it is determined by determining the SOC as a percentage or less. If the SOC is equal to or less than the remaining charge threshold and regenerative power can be used for charging, a YES determination is made in S4 and the process proceeds to S5. At least regenerative braking will be used after S5. If the SOC exceeds the remaining charge threshold and charging is not possible, a NO determination is made in S4 and the process proceeds to S8A or S8B. Regenerative braking will not be used in S8A or S8B.

[0036] In S5, it is determined whether the absolute value of the requested deceleration is equal to or less than a deceleration threshold value (corresponding to Xs in FIG. 4). The more sudden braking is requested due to emergency avoidance or the like, the larger the absolute value of the requested deceleration. If the braking request is relatively gentle and YES is determined in S5, in S6 brake use determination unit 56 determines to use the regenerative brake. If the braking request is relatively sudden and NO is determined in S5, in S7 brake use determination unit 56 determines to use the steering brake in addition to the regenerative brake. At this time, brake use determination unit 56 calculates the steering angle of steering actuators 71-74 in accordance with the braking force distribution.

[0037] Next, steps that differ between the first to fourth embodiments will be described. In the first and third embodiments applied to vehicles not equipped with friction brakes, if the determination in S4 is NO, the process proceeds to S8A. In S8A, brake-to-be-used determination unit 56 determines that the steering brake will be used. At this time, brake-to-be-used determination unit 56 calculates the steering angle of steering actuators 71-74 in accordance with the braking force distribution.

[0038] On the other hand, in the second and fourth embodiments applied to vehicles equipped with friction brakes, if the determination in S4 is NO, the process proceeds to S8B. In S8B, brake use determination unit 56 determines that "the steering brake will be used and the friction brake will also be used," that is, that the steering brake and the friction brake will be used together. At this time, brake use determination unit 56 calculates the steering angle of steering actuators 71-74 in accordance with the braking force distribution.

[0039] Furthermore, in the first and second embodiments applied to vehicles not equipped with a parking brake, if the determination in S2 is NO, the process proceeds to S9A. In S9A, brake application determination unit 56 determines that the steering brake will be used while the vehicle is stopped. At this time, brake application determination unit 56 calculates a target braking force while the vehicle is stopped based on information on disturbances such as vehicle weight, road gradient, road surface friction coefficient, and wind force acquired or estimated from various sensors, and calculates the steering angle of steering actuators 71-74 according to the target braking force.

[0040] On the other hand, in the third and fourth embodiments applied to vehicles equipped with a parking brake, if the determination in S2 is NO, the process proceeds to S9B. In S9B, the brake to be used determination unit 56 determines that the parking brake or the steering brake will be used while the vehicle is stopped. In the case of a parking brake operated by the driver, the brake to be used determination unit 56 may display a message to the driver urging the driver to operate the parking brake, and if the driver does not operate it within a predetermined time, the process may switch to using the steering brake. An electric parking brake may be used in an autonomous vehicle, etc.

[0041] As described above, in this embodiment, regenerative braking is used preferentially in situations where battery 88 can be charged in response to a braking request while traveling, and steering braking is used when battery 88 cannot be charged and regenerative braking cannot be used, or when regenerative braking needs to be supplemented. By using regenerative braking and steering braking in coordination depending on the vehicle state, it is possible to ensure the braking force required while traveling without using friction brakes or even by reducing the braking force distribution by friction brakes. This makes it possible to eliminate friction brakes or downsize them, thereby realizing space savings around the wheels. Furthermore, eliminating friction brakes or downsizing them also leads to weight and cost reductions.

[0042] In addition, in this embodiment, the steering brake can be used in response to a braking request while the vehicle is stopped, regardless of whether the parking brake is applied. This allows the braking force to be secured by the steering brake while the vehicle is stopped, even if the driver does not operate the parking brake. Furthermore, if the parking brake can be eliminated under certain conditions, this can further contribute to saving space around the wheels, reducing weight, and reducing costs.

[0043] (Other embodiments) (a) The independently steering vehicle on which the braking device 50 is mounted is not limited to a four-wheel vehicle, but may be any vehicle having "three or more wheels that are not mechanically constrained to one another, including one or more pairs of left and right wheels." For example, a three-wheel vehicle with one front wheel and left and right rear wheels, or left and right front wheels and one rear wheel, may be used as long as the steering brake can be used by setting the left and right pair of wheels toe-in or toe-out. Furthermore, a six-wheel vehicle with three pairs of left and right wheels allows for a greater variety of steering brakes.

[0044] (b) The battery 88 may exchange power with other in-vehicle devices in addition to the braking / driving actuators 81-84. If the battery 88 has a surplus of chargeable power due to power consumption by other in-vehicle devices, the remaining charge threshold value in S4 of the flowchart may be changed to a higher value. Furthermore, the remaining charge threshold value may be changed according to the temperature based on the temperature characteristics of the battery 88.

[0045] The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit of the invention.

[0046] The disclosure that "The brake to be used determination unit is a braking device that uses the steering brake when the vehicle speed is equal to or lower than a vehicle speed threshold value" may be combined with the disclosure of any control device that cites the disclosure that "The brake to be used determination unit calculates the braking force distribution of longitudinal force braking and lateral force braking for each wheel based on the vehicle speed, the required deceleration, and the remaining battery charge of the battery that exchanges power with the braking / driving actuator, and determines which brake to use."

[0047] Each control unit (brake application determination unit, steering control unit, braking / driving control unit) and its method described in the present disclosure may be realized by a special-purpose computer provided by configuring a processor and memory programmed to execute one or more functions embodied in a computer program. Alternatively, each control unit and its method described in the present disclosure may be realized by a special-purpose computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, each control unit and its method described in the present disclosure may be realized by one or more special-purpose computers configured by combining a processor and memory programmed to execute one or more functions with a processor configured with one or more hardware logic circuits. Furthermore, the computer program may be stored in a computer-readable non-transitory tangible recording medium as instructions executed by a computer. [Explanation of symbols]

[0048] 50...braking device, 56... Brake use determination unit, 57···Steering control unit, 58 Braking / driving control unit, 71-74···Steering actuator, 81-84···Driving and braking actuator, 91-94...wheels, 100··· (four-wheel independent steering) vehicle.

Claims

1. A braking device for braking a vehicle (100) in which three or more wheels (91-94), including one or more pairs of left and right wheels, which are not mechanically constrained to one another, can be independently steered by steering actuators (71-74) corresponding to each wheel, and can be independently braked and driven by braking and driving forces outputted by braking and driving actuators (81-84) corresponding to each wheel, comprising: a brake application determination unit (56) that, when a braking request is generated, calculates a braking force distribution of longitudinal force braking acting in the longitudinal direction of each wheel and lateral force braking acting in a direction perpendicular to the longitudinal direction of each wheel, and determines the type of brake to be used; a steering control unit (57) that controls the steering actuators to steer each wheel according to an instruction from the brake application determination unit; a braking / driving control unit (58) that controls the braking / driving actuators to brake / drive each wheel according to an instruction from the brake use determination unit; Equipped with The brake application determination unit At least regenerative braking by the braking / driving actuator can be used for longitudinal force braking of each wheel, A braking device that can use at least a steering brake that sets a pair of left and right wheels to toe-in or toe-out by the steering actuator for braking the lateral force of each wheel.

2. 2. The braking device according to claim 1, wherein the brake application determination unit calculates a braking force distribution for longitudinal braking and lateral braking of each wheel based on the vehicle speed, the required deceleration, and the remaining battery charge of a battery (88) that exchanges power with the braking / driving actuator, and determines which brake to use.

3. The braking device according to claim 2, wherein the brake application determination unit uses the regenerative brake when the remaining battery charge is equal to or less than a threshold, and uses the steering brake when the remaining battery charge is greater than the threshold.

4. 4. The braking device according to claim 3, wherein in a vehicle equipped with a friction brake, the brake use determination unit further uses the friction brake when the remaining battery charge is greater than the remaining charge threshold.

5. The braking device according to claim 3, wherein the brake application determination unit calculates the steering angle of the steering actuator in accordance with braking force distribution when the steering brake is to be used.

6. The braking device according to claim 4, wherein the brake application determination unit calculates the steering angle of the steering actuator in accordance with braking force distribution when the steering brake and the friction brake are used in combination.

7. The braking device according to claim 2 , wherein the brake application determination unit applies the steering brake when the vehicle speed is equal to or lower than a vehicle speed threshold value.

8. Applies to four-wheel vehicles including left and right front wheels and left and right rear wheels, 8. The braking device according to claim 1, wherein the brake use determination unit instructs the steering control unit to set front wheels toe-in and rear wheels to toe-out for lateral force braking of each wheel by the steering brake while the vehicle is traveling.

9. Applies to four-wheel vehicles including left and right front wheels and left and right rear wheels, 8. The braking device according to claim 1, wherein the brake use determination unit instructs the steering control unit to set front wheels to a toe-out position and rear wheels to a toe-in position with respect to lateral force braking of each wheel by the steering brake while the vehicle is stopped.

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