Braking control device for vehicle

Abstract

To provide a braking control device of a vehicle capable of restraining excessive torque from acting on a drive shaft in response to a variation in frictional force acting on a tire when traveling on a rough road by braking.SOLUTION: The braking control device for the vehicle is provided with a drive shaft to which a motor is connected at one end and a drive wheel is connected at the other end, and a braking mechanism for applying braking torque to the drive wheel, and determines that the vehicle travels on a rough road (step S2), and increases the braking torque by the braking mechanism when the angular speed of the drive wheel increases (step S7 and step S9) and decreases the braking torque by the braking mechanism when the angular speed of the drive wheel decreases (step S6 and step S10) in the case that the vehicle travels on the rough road.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a device for controlling a braking device that applies braking torque to a wheel. [Background technology]

[0002] Patent Document 1 describes a braking control device for an electric vehicle in which a motor and drive wheels are connected via a drive shaft. This braking control device is configured to prevent excessive torque from acting on the drive shaft when the electric vehicle is decelerating on a rough road. Specifically, the braking control device determines whether the electric vehicle is decelerating on a rough road, and, if the electric vehicle is decelerating on the rough road, increases the braking torque applied to the drive wheels to prevent fluctuations in the rotation speed of the drive wheels. Note that, if anti-lock brake system control (ABS control) is activated while the electric vehicle is decelerating on a rough road, this braking control device is configured to increase the braking torque reduced by the ABS control to a braking torque equivalent to the braking torque corresponding to the driver's brake operation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2024-048550 Summary of the Invention [Problem to be solved by the invention]

[0004] The rotational speed of a wheel when a vehicle is braking is determined by the brake torque acting on the wheel, the frictional force acting on the tire from the road surface, and the inertial torque of the tire and wheel. When a vehicle is traveling on a rough road, the tire's contact load or the friction coefficient between the tire and the road surface fluctuates, causing the frictional force acting on the tire from the road surface to fluctuate. Therefore, the rotational speed of the wheel may fluctuate (pulsate) when the vehicle is braking on a rough road. Meanwhile, the rotational speed of the input side of the driveshaft fluctuates depending on the inertial torque of the components connected to the input side of the driveshaft and the torque input from the driveshaft. Therefore, when the rotational speed of the wheel fluctuates, the rotational speed of the input side of the driveshaft changes with a delay compared to the rotational speed of the wheel due to factors such as the torsional rigidity of the driveshaft. Therefore, when the rotational speed of the wheel is increasing, the rotational speed of the input side of the driveshaft may decrease, and conversely, when the rotational speed of the wheel is decreasing, the rotational speed of the input side of the driveshaft may increase.

[0005] The braking control device described in Patent Document 1 is configured to increase the braking torque applied to the drive wheels when braking on a rough road. Therefore, even if the frictional force between the road surface and the tires increases while the rotational speed of the input side of the drive shaft is decreasing, the increase in the rotational speed of the drive wheels can be suppressed. On the other hand, if the frictional force between the road surface and the tires decreases, the rotational speed of the drive wheels decreases rapidly. Therefore, while the rotational speed of the input side of the drive shaft is increasing, the rotational speed of the drive wheels may decrease rapidly. In such a case, the torque (torsion torque) acting on the drive shaft may become excessive, potentially reducing the durability of the drive shaft.

[0006] The present invention has been made with a focus on the above-mentioned technical problems, and aims to provide a braking control device for a vehicle that can suppress excessive torque from being applied to the drive shaft due to fluctuations in the frictional force acting on the tires when braking while driving on rough roads. [Means for solving the problem]

[0007] In order to achieve the above-mentioned object, the present invention provides a braking control device for a vehicle having a rotating shaft having a drive side rotating member connected to one end and a wheel connected to the other end, and a braking mechanism that applies braking torque to the wheel, and further comprising a controller that controls the braking mechanism, wherein the controller determines that the vehicle is braking on a rough road where the friction force between the wheel and the road surface fluctuates as the vehicle travels by applying braking torque to the wheel using the braking mechanism, and when the vehicle is braking on the rough road, if the angular velocity of the wheel is increasing, the braking torque by the braking mechanism is increased, and if the angular velocity of the wheel is decreasing, the braking torque by the braking mechanism is decreased. [Effects of the Invention]

[0008] According to the present invention, when a vehicle is braking on a rough road, the braking torque applied by the braking mechanism is increased when the angular velocity of the wheel increases, and the braking torque applied by the braking mechanism is decreased when the angular velocity of the wheel decreases. That is, the braking torque applied by the braking mechanism is increased or decreased according to the angular velocity of the vehicle so as to suppress fluctuations in the angular velocity of the wheel. This suppresses changes in the angular velocity of the wheel caused by changes in the frictional force between the wheel and the road surface. In other words, an increase in the amount of torsion of the rotating shaft is suppressed. As a result, excessive torque such as resonance torque is suppressed from acting on the rotating shaft. Furthermore, because an increase in the amount of torsion of the rotating shaft is suppressed, a change in the angular velocity of the drive-side rotating member connected to the input side of the rotating shaft caused by torsion of the rotating shaft is suppressed. As a result, the difference between the angular velocity of the input side and the angular velocity of the output side of the rotating shaft is reduced, and excessive torque such as resonance torque is suppressed from acting on the rotating shaft. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram schematically illustrating an example of a vehicle according to an embodiment of the present invention. [Figure 2]FIG. 1 shows a time chart (a) illustrating the changes in motor rotation speed and wheel speed when braking on rough roads, a time chart (b) illustrating the changes in drive shaft torque, and a time chart (c) illustrating the changes in the control amount of the actuator of the braking mechanism. [Figure 3] 4 is a flowchart illustrating an example of control executed by the braking control device according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described based on the embodiments shown in the drawings. Note that the embodiments described below are merely examples of specific implementations of the present invention and are not intended to limit the present invention.

[0011] In an embodiment of the present invention, the vehicle has a rotating member and wheels connected by a rotating shaft, and when the wheels function as drive wheels, the rotating member may be any rotating member on the input side of the rotating shaft including the drive power source. When the wheels function as non-drive wheels, the rotating member may be a differential mechanism in which the wheel and its paired wheel are connected to each other so as to rotate differentially.

[0012] 1 shows an example of a vehicle Ve in which a motor 2 provided at the lower end of a vehicle body 1 and drive wheels 3 are connected via a drive shaft 4, which corresponds to the rotating shaft in an embodiment of the present invention. The drive shaft 4 and motor 2 are connected via a constant velocity joint 5, and similarly, the drive shaft 4 and drive wheels 3 are connected via a constant velocity joint 6.

[0013] Like motors used as driving power sources in conventional electric vehicles and hybrid vehicles, motor 2 is capable of outputting driving torque according to the power supplied thereto, and is configured to function as a generator that converts the power of the torque transmitted from drive wheels 3 into electric power by being rotated by the torque. Specifically, it is configured as a synchronous motor with a permanent magnet in the rotor, an induction motor, or the like.

[0014] The drive wheels 3 are provided with braking mechanisms 7. The braking mechanisms 7 can be configured similarly to brake mechanisms installed in various conventional vehicles. For example, the braking mechanisms 7 may be configured to clamp a brake disc installed on the drive wheels 3 with a caliper to generate friction between the brake disc and the caliper, thereby braking the drive wheels 3, or to press a brake shoe against a brake drum integrated with the drive wheels 3, thereby generating friction between the brake drum and a brake chute, thereby braking the drive wheels 3. The caliper and brake shoe (hereinafter referred to as "pressing members") are configured to be actuated by hydraulic pressure or electromagnetic force corresponding to the driver's brake pedal depression force or depression amount. Furthermore, the hydraulic pressure or electromagnetic force can be increased or decreased based on a control example described later. That is, an actuator for operating the braking mechanism 7 and controlling its braking torque is configured to control the pressing force of the pressing member by a hydraulic actuator or an electromagnetic actuator, thereby controlling the braking torque of the drive wheels 3. Hereinafter, the brake disc and the brake drum will be referred to as "pressed members."

[0015] An electronic control device (hereinafter referred to as a controller) 8 is provided for controlling the braking mechanism 7. Similar to a controller that controls a braking mechanism provided in a conventional vehicle, this controller 8 is configured to receive signals from various sensors provided in the vehicle Ve, determine the braking torque to be applied by the braking mechanism 7 based on the received signals and a pre-stored arithmetic expression, and output a signal for generating the braking torque to an actuator provided in the braking mechanism 7.

[0016] An example of sensors connected to the controller 8 is shown in Fig. 1. In the example shown in Fig. 1, the controller 8 is connected to a resolver 9 that detects the angular velocity of the motor 2 (hereinafter referred to as the motor rotation speed), a wheel speed sensor 10 that detects the angular velocity of the drive wheels 3 (hereinafter referred to as the wheel speed), and a torsion angle sensor 11 that detects the torsion angle of the drive shaft 4.

[0017] In the vehicle Ve configured as described above, braking torque is applied to the drive wheels 3 by the braking mechanism 7 in response to the driver's brake operation, etc. The magnitude of this braking torque is, for example, the product of the hydraulic pressure or electromagnetic force supplied to the actuator, the pressure-receiving area where the pressing member and the pressed member come into contact, and the effective diameter of the contact point between the pressing member and the pressed member. The braking force of the drive wheels 3 is the value obtained by dividing the braking torque by the tire diameter (diameter) x 2, in other words, the braking force obtained by dividing the braking torque by the tire radius.

[0018] Furthermore, a frictional force, the magnitude of which is the product of the load on the tire (normal force) and the coefficient of friction between the tire and the road surface, acts on the drive wheel 3 in a direction that changes the angular velocity of the drive wheel 3. Specifically, the frictional force acts in a direction that reduces the difference between the angular velocity of the drive wheel 3 in the event that there is no slippage between the drive wheel 3 and the road surface and the actual angular velocity of the drive wheel 3. Therefore, for example, when braking and there is slippage between the drive wheel 3 and the road surface, the actual angular velocity of the drive wheel 3 becomes slower than the angular velocity of the drive wheel 3 in the event that there is no slippage between the drive wheel 3 and the road surface, and so the frictional force acts in a direction that increases the angular velocity of the drive wheel 3.

[0019] As described above, during braking, braking force and frictional force act on the drive wheels 3, and the angular velocity of the drive wheels 3 increases or decreases depending on the magnitude relationship between these forces. That is, when the braking force is greater than the frictional force, the angular velocity of the drive wheels decreases, and conversely, when the braking force is smaller than the frictional force, the angular velocity of the drive wheels increases.

[0020] Therefore, for example, when braking on a rough road such as a cobblestone road or a wavy road, or a road surface with an uneven coefficient of friction between the tire and the road surface such as a sandy road, while maintaining a constant braking torque by the braking mechanism 7, the angular velocity of the drive wheel 3 pulsates as shown by the solid line in Figure 2(a) as the friction force acting on the drive wheel 3 fluctuates.

[0021] As described above, because the drive wheels 3 and the motor 2 are connected via the drive shaft 4, fluctuations in the angular velocity of the drive wheels 3 cause fluctuations in the angular velocity of the motor 2. On the other hand, when the angular velocity of the motor 2 fluctuates, an inertia torque corresponding to the moment of inertia, which is determined by the configuration of the motor 2, and the angular acceleration of the motor 2 is generated in a direction that suppresses the fluctuations in the angular velocity of the motor 2. Therefore, when the angular velocity of the drive wheels 3 fluctuates, an inertia torque of the motor 2 is generated in a countering direction, and the drive shaft 4 twists according to the torsional rigidity determined by its shape and material. As a result, the angular velocity of the motor 2 fluctuates with a delay relative to the angular velocity of the drive wheels 3, as shown by the dashed line in Figure 2(a). In other words, when the angular velocity of the drive wheels 3 pulsates, the angular velocity of the motor 2 pulsates out of phase with the angular velocity of the drive wheels 3. Such a phase shift causes fluctuations in the angular velocity between the drive wheels 3 and the motor 2, and as a result, a relatively large torsional torque acts on the drive shaft 4, as shown in FIG. 2(b).

[0022] Therefore, the brake control device in this embodiment of the present invention is configured to control the braking torque in the brake mechanism 7 based on whether the angular velocity of the drive wheels 3 is increasing or decreasing. A flowchart for explaining an example of this control is shown in FIG. 3. This control example is executed when the brake pedal is depressed while the vehicle Ve is traveling, and first, normal brake control is executed (step S1). This normal brake control is similar to the control executed when braking a conventional vehicle. Specifically, the brake mechanism 7 is controlled based on a signal detected by a brake sensor (not shown). Note that when step S1 is executed, the brake mechanism 7 may be controlled so that the slip ratio between the tire and the road surface is within a predetermined range. In other words, conventional antilock brake system control (ABS control) may be executed.

[0023] The pulsation of the angular velocity of the drive wheels 3 as described above occurs when the vehicle is traveling on a rough road. Therefore, in the control example shown here, after step S1, it is determined whether the vehicle is traveling on a rough road (step S2). This step S2 can be determined, for example, based on whether the difference between the actual angular velocity of the drive wheels 3 and the motor 2 and the angular velocity according to the vehicle speed, tire radius, etc. is equal to or greater than a threshold value. Note that in step S2, it may also be determined whether the vehicle is traveling on a rough road based on a navigation system, etc.

[0024] If the answer to step S2 is YES because the vehicle is traveling on a rough road, it is determined whether the torsion angle (absolute value) of the drive shaft 4 is greater than a predetermined threshold value (step S3). This step S3 is a step for determining whether the torsion torque is acting to an extent that reduces the durability of the drive shaft 4. Therefore, the threshold value can be determined based on the rigidity of the drive shaft 4, etc.

[0025] The torsion angle in step S3 can be found based on the difference (absolute value) in angular velocity between both ends of drive shaft 4, and in the case of the configuration shown in Fig. 1, it can be found based on the difference between the motor rotation speed detected by resolver 9 and the wheel speed detected by wheel speed sensor 10. The torsion angle in step S3 may be the torsion angle detected by torsion angle sensor 11. If a speed change mechanism such as a reduction mechanism is provided between drive shaft 4 and motor 2, the angular velocity of the input side of drive shaft 4 may be found by multiplying the motor rotation speed detected by resolver 9 by the gear ratio, for example.

[0026] If the torsion angle of the drive shaft 4 is greater than the threshold value and therefore the answer to step S3 is affirmative, the braking torque of the braking mechanism 7 is changed to prevent excessive torque from acting on the drive shaft 4. In other words, the braking torque of the braking mechanism 7 is controlled in accordance with changes in the angular velocity of the drive wheels 3.

[0027] 2(a) and 2(b), a torsional torque corresponding to the difference between the wheel speed and the motor rotation speed acts on the drive shaft 4, and the wheel speed and the motor rotation speed are out of phase with each other, causing the angular velocity to fluctuate. That is, when the motor rotation speed is faster (high angular velocity) than the wheel speed or when the motor rotation speed is slower (low angular velocity) than the wheel speed, a torsional torque acts on the drive shaft 4.

[0028] Therefore, in the control example shown in FIG. 3, if a positive determination is made in step S3, it is first determined whether the motor rotation speed is higher (high angular velocity) than the wheel speed (step S4). If a positive determination is made in step S4 because the motor rotation speed is higher than the wheel speed, the wheel speed may be decreasing, as shown by (I) in FIG. 2(a), or increasing, as shown by (II) in FIG. 2(a). If the wheel speed is decreasing, the motor rotation speed decreases with a delay from the wheel speed. Therefore, in order to reduce the angular velocity difference between the wheel speed and the motor rotation speed and thereby reduce the torsional angle of the drive shaft 4, it is sufficient to reduce the braking torque. Conversely, if the wheel speed is increasing, the motor rotation speed increases with a delay from the wheel speed. Therefore, in order to reduce the angular velocity difference between the wheel speed and the motor rotation speed and thereby reduce the torsional angle of the drive shaft 4, it is sufficient to increase the braking torque.

[0029] Therefore, if the answer in step S4 is YES, it is determined whether the wheel speed is decreasing (step S5). This step S5 can be performed, for example, by determining the time change (time differential) of the wheel speed detected by the wheel speed sensor 10, or based on the difference between the braking force and the friction force. The braking force can be estimated based on the braking torque applied to the drive wheels 3 by the braking mechanism 7, and the friction force can be estimated based on the ground load of the drive wheels 3 based on the deceleration of the vehicle Ve, etc., and the friction coefficient (estimated value) of the road surface.

[0030] If the wheel speed is decreasing and the answer to step S5 is affirmative, the braking torque is reduced to less than the braking torque (solid line) corresponding to the brake operation amount, as shown by the dashed line in Fig. 2(c) (step S6). That is, if the braking mechanism 7 is configured to be operated by a hydraulic actuator, the hydraulic pressure is reduced, and if the braking mechanism 7 is configured to be operated by an electromagnetic actuator, the current applied is reduced.

[0031] Conversely, if the wheel speed is increasing and the answer to step S5 is negative, the braking torque is increased (step S7) to be higher than the braking torque (solid line) corresponding to the brake operation amount, as shown by the dashed line in Figure 2(c). That is, if the braking mechanism 7 is configured to be operated by a hydraulic actuator, the hydraulic pressure is increased, and if the braking mechanism 7 is configured to be operated by an electromagnetic actuator, the current is increased.

[0032] On the other hand, if the motor rotation speed is lower than the wheel speed and the result of step S4 is negative, this may mean that the wheel speed is increasing, as shown by (III) in Figure 2(a), or that the wheel speed is decreasing, as shown by (IV) in Figure 2(a). When the wheel speed is increasing, the motor rotation speed increases with a delay from the wheel speed, so the braking torque can be increased to reduce the angular velocity difference between the wheel speed and the motor rotation speed and thereby reduce the torsional angle of the drive shaft 4. Conversely, when the wheel speed is decreasing, the motor rotation speed decreases with a delay from the wheel speed, so the braking torque can be reduced to reduce the angular velocity difference between the wheel speed and the motor rotation speed and thereby reduce the torsional angle of the drive shaft 4.

[0033] Therefore, if the determination in step S4 is negative, it is determined whether the wheel speed is increasing (step S8). This step S8 can be performed, for example, by determining the time change (time differential) of the wheel speed detected by the wheel speed sensor 10, as in step S5 above, or based on the difference between the braking force and the frictional force.

[0034] If the wheel speed is increasing and the answer to step S8 is affirmative, the braking torque is increased (step S9) to be higher than the braking torque (solid line) corresponding to the brake operation amount, as shown by the dashed line in Fig. 2(c). That is, if the braking mechanism 7 is configured to be operated by a hydraulic actuator, the hydraulic pressure is increased, and if the braking mechanism 7 is configured to be operated by an electromagnetic actuator, the current is increased.

[0035] On the other hand, if the wheel speed is decreasing and the result of step S8 is negative, the braking torque is reduced below the braking torque (solid line) corresponding to the brake operation amount, as shown by the dashed line in Figure 2(c) (step S10). That is, if the braking mechanism 7 is configured to be operated by a hydraulic actuator, the hydraulic pressure is reduced, and if the braking mechanism 7 is configured to be operated by an electromagnetic actuator, the current applied is reduced.

[0036] On the other hand, if the answer to step S2 is negative because the vehicle Ve is not traveling on a rough road, if the answer to step S3 is negative because the torsion angle is equal to or less than the threshold, or if the answer to step S6, S7, S9, and S10 is negative, it is determined whether the vehicle has stopped (step S11). If the answer to step S11 is negative because the vehicle has not stopped, the routine returns to step S1. On the other hand, if the answer to step S11 is positive because the vehicle has stopped, the routine ends immediately. Whether the vehicle has stopped can be determined based on a vehicle speed sensor provided on the vehicle Ve or a vehicle speed sensor provided on each wheel.

[0037] The control amount of the actuator in steps S6, S7, S9, and S10 may be set to a value obtained by multiplying the angular velocity difference between both ends of the drive shaft 4 by a predetermined gain and subtracting the resultant value from the control amount corresponding to the brake operation amount, or may be set to a value obtained by band-pass filtering the detected wheel speed, multiplying the band-pass filtered fluctuation component by a predetermined gain, and subtracting the resultant value from the control amount corresponding to the brake operation amount. In this band-pass filtering, it is preferable to extract a frequency band including the resonance frequency band of the unsprung component provided closer to the road surface than the suspension.

[0038] As described above, when the vehicle Ve is braking and driving on a rough road and the wheel speed is increasing, the braking torque by the braking mechanism 7 is increased by steps S7 and S9. When the wheel speed is decreasing, the braking torque by the braking mechanism 7 is decreased by steps S8 and S10. That is, the braking torque by the braking mechanism 7 is increased or decreased so as to suppress the fluctuation of the wheel speed. Therefore, it is possible to suppress the change in the wheel speed accompanying the change in the frictional force between the drive wheel 3 and the road surface. In other words, it is possible to suppress the increase in the amount of twist of the drive shaft 4. As a result, it is possible to suppress the action of excessive torque such as resonance torque on the drive shaft 4. Further, since it is possible to suppress the increase in the twist angle of the drive shaft 4, it is possible to suppress the amount of change in the motor rotation speed accompanying the twist of the drive shaft 4. As a result, it is possible to reduce the difference between the angular velocity on the input side and the angular velocity on the output side of the drive shaft 4, and it is possible to suppress the action of excessive torque such as resonance torque on the drive shaft 4.

[0039] Note that the wheels in the embodiment of the present invention are not limited to the drive wheels connected to the motor as the driving force source as described above, and may be non-driving wheels in which a pair of left and right wheels are connected via a differential mechanism. In that case, the differential mechanism corresponds to the "driving side rotating member" in the embodiment of the present invention. Further, the drive wheel is not limited to one directly connected to the motor as the driving force source, and may be, for example, a drive wheel connected to the driving force source via a transmission mechanism or the like. In that case, the rotating member on the input side rather than the drive shaft such as the transmission mechanism including the driving force source corresponds to the "driving side rotating member" in the embodiment of the present invention.

Explanation of Signs

[0040] 2 Motor 3 Drive wheel 4 Drive shaft 7 Braking mechanism 8 Controller 9 Resolver 10 Wheel speed sensor 11 Twist angle sensor Ve Vehicle

Claims

[Claim 1] A braking control device for a vehicle, comprising: a rotating shaft having a driving-side rotating member connected to one end thereof and a wheel connected to the other end thereof; and a braking mechanism that applies a braking torque to the wheel, a controller for controlling the braking mechanism; The controller determining whether the vehicle is braking on a rough road where the frictional force between the wheels and the road surface fluctuates as the vehicle travels, by applying a braking torque to the wheels by the braking mechanism; When the vehicle is braking on a rough road, if the angular velocity of the wheel increases, the braking torque by the braking mechanism is increased, and if the angular velocity of the wheel decreases, the braking torque by the braking mechanism is decreased. A vehicle braking control device characterized by:

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