Braking control device

Abstract

Provided is a control device 16 that, during regenerative cooperative control, carries out one of: a first distribution adjustment in which, as an index value that indicates the degree of turning of a vehicle becomes higher, a regenerative braking force Fkr that is applied to a rear wheel 2r is increased while a regenerative braking force Fkf that is applied to a front wheel 2f is decreased, and a friction braking force Fmr that is applied to the rear wheel 2r is decreased while a friction braking force Fmf that is applied to the front wheel 2f is increased; and a second distribution adjustment in which, as the index value becomes higher, the regenerative braking force Fkr that is applied to the rear wheel 2r is decreased while the regenerative braking force Fkf that is applied to the front wheel 2f is increased, and the friction braking force Fmr that is applied to the rear wheel 2r is increased while the friction braking force Fmf that is applied to the front wheel 2f is decreased.

Description

Braking control device

[0001] The present invention relates to a braking control device for a vehicle that performs regenerative cooperative control.

[0002] Conventionally, there is known a technology related to regenerative cooperative control that applies regenerative braking force and friction braking force to vehicle wheels using a regenerative braking device and a friction braking device. For example, Patent Document 1 (Patent Document 1) describes a vehicle control device that changes the ratio of regenerative braking force and friction braking force when performing vehicle motion control, while the driver is performing a braking operation. This vehicle control device prevents the in-wheel motor from exceeding its control range by, for example, reducing the ratio of regenerative braking force on the wheel on the inside of a turn when braking the vehicle. Furthermore, this vehicle control device increases the recovered power and reduces friction loss by reducing the ratio of friction braking force on the wheel on the outside of a turn when braking the vehicle.

[0003] JP 2017-77753 A

[0004] When braking, the vehicle pitches, causing a change in vehicle posture, which in turn changes the load on the contact patches of the front and rear wheels. As a result, if the vehicle is turned and braked at the same time, the maneuverability desired by the driver may not be fully satisfied, and the change in posture may affect the driver's riding comfort.

[0005] The present invention has been made in consideration of these problems, and its purpose is to provide a braking control device that can appropriately adjust the maneuverability and ride comfort during cornering braking of a vehicle that performs regenerative cooperative control.

[0006] In order to achieve the above-mentioned object, the braking control device of the present invention uses a regenerative braking device that applies regenerative braking force to the front wheels and rear wheels of a vehicle, and a friction braking device that applies frictional braking force to the front wheels and rear wheels, and performs regenerative cooperative control to output the required braking force required for braking the vehicle by coordinating the regenerative braking force and the frictional braking force, and during the execution of the regenerative cooperative control, the larger an index value that represents the degree of turning of the vehicle, the larger the first distribution adjustment is that the regenerative braking force applied to the front wheels is reduced while the regenerative braking force applied to the rear wheels is increased, and the frictional braking force applied to the front wheels is increased while the frictional braking force applied to the rear wheels is decreased, and the second distribution adjustment is that the larger the index value is, the larger the regenerative braking force applied to the front wheels is increased while the regenerative braking force applied to the rear wheels is decreased, and the frictional braking force applied to the rear wheels is increased while the frictional braking force applied to the front wheels is decreased.

[0007] With this configuration, when the first distribution adjustment is performed, the larger the index value representing the degree of turning, the higher the grip limit of the front wheels, making it possible to improve the vehicle's maneuverability. Furthermore, when the second distribution adjustment is performed, the larger the index value representing the degree of turning, the higher the grip limit of the rear wheels, making it possible to suppress vehicle spin and improve the vehicle's maneuverability. Furthermore, by making it easier for the rear side of the vehicle to sink, it becomes possible to adjust the vehicle's pitch angle to approach 0 degrees. Therefore, the braking control device of the present invention makes it possible to appropriately adjust the maneuverability and ride comfort during cornering braking of a vehicle that performs regenerative cooperative control.

[0008] Furthermore, when the vehicle's driving mode is a sport mode that prioritizes improved maneuverability over ride comfort, it is preferable to execute the first distribution adjustment. In this case, it is preferable that the index value is at least one of the steering angle and the lateral angular velocity of the vehicle. With this configuration, the grip limit of the front wheels can be increased in the sport mode, improving maneuverability during cornering braking. Furthermore, by using the steering angle or the lateral acceleration as the index value, it is possible to realize distribution adjustment according to the degree of cornering of the vehicle.

[0009] Furthermore, when the vehicle's driving mode is a sport mode that prioritizes improved maneuverability over ride comfort, it is preferable to perform the second distribution adjustment. In this case, it is preferable that the index value is at least one of the yaw rate of the vehicle and the slip angle of the rear wheels. With this configuration, the grip limit of the rear wheels can be increased in the sport mode, and vehicle spin can be suppressed. Furthermore, by using the yaw rate or the slip angle of the rear wheels as the index value, it is possible to achieve distribution adjustment according to the degree of vehicle spin.

[0010] Furthermore, when the vehicle's driving mode is a comfort mode that prioritizes ride comfort over improved maneuverability, the second distribution adjustment is preferably performed. In this case, the index value is preferably at least one of the steering angle and lateral angular velocity of the vehicle. With this configuration, the rear of the vehicle tends to sink in comfort mode, and the vehicle pitch angle can be brought closer to 0 degrees. As a result, it is possible to suppress posture changes during cornering, when changes in ride comfort are easily felt, and improve the ride comfort for the driver. Furthermore, by using the steering angle or lateral acceleration as the index value, it is possible to achieve distribution adjustment according to the degree of turning of the vehicle.

[0011] According to the braking control device of the present invention, it is possible to appropriately adjust the maneuverability and ride comfort during cornering braking of a vehicle that performs regenerative cooperative control.

[0012] 1 is a schematic configuration diagram showing a vehicle equipped with a brake control device according to an embodiment. FIG. 1 is an explanatory diagram showing an example of time variations in required braking force, regenerative braking force, and frictional braking force in regenerative cooperative control. FIG. 2 is an explanatory diagram showing a schematic view of pitching motion when the vehicle is driven. FIG. 3 is an explanatory diagram showing a schematic view of pitching motion when the vehicle is braking. FIG. 4 is an explanatory diagram showing an example of an instantaneous center of rotation of the vehicle. FIG. 5 is a schematic diagram for explaining a load movement amount due to reaction torque. FIG. 6 is an explanatory diagram plotting an example of pitch angle when the regenerative ratio, friction ratio, front ratio, and rear ratio are changed. FIG. 7 is an explanatory diagram showing an example of time variations in pitch angle when regenerative cooperative control is performed. FIG. 8 is an explanatory diagram showing an example of pitching motion of a vehicle body when frictional braking force is applied only to the front wheels in a vehicle according to an embodiment. FIG. 9 is an explanatory diagram showing an example of pitching motion of a vehicle body when frictional braking force is applied only to the rear wheels in a vehicle according to an embodiment. FIG. 10 is an explanatory diagram showing a schematic view of a state when braking a vehicle in a turning braking mode by adjusting braking force with a first distribution adjustment. 10 is an explanatory diagram schematically showing a state in which the braking force is adjusted by the second distribution adjustment during cornering braking of the vehicle; FIG.

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0014] (Vehicle) FIG. 1 is a schematic diagram showing a vehicle equipped with a brake control device according to an embodiment. The vehicle 1 is a four-wheel-drive electric vehicle that travels by transmitting power from a front motor 10f, which serves as a power source, to left and right front wheels 2f and from a rear motor 10r, which serves as a power source, to left and right rear wheels 2r. The front motor 10f outputs driving power to the left and right front wheels 2f via a transaxle 12f, which includes a transmission and a differential gear. The rear motor 10r outputs driving power to the left and right rear wheels 2r via a transaxle 12r, which also includes a transmission and a differential gear. The vehicle 1 is equipped with a battery 14, which serves as a power source and is configured as a secondary battery such as a lithium-ion battery. Electric power from the battery 14 is supplied to the front motor 10f and the rear motor 10r via a power conversion device such as an inverter (not shown). The front motor 10f and the rear motor 10r are drive-controlled by a control device 16 (brake control device).

[0015] The vehicle 1 is also equipped with a braking device that applies braking force to the front wheels 2f and rear wheels 2r. The braking device includes a regenerative braking device 20 and a friction braking device 30. The regenerative braking device 20 is configured to include a front motor 10f, a rear motor 10r, a battery 14, and a power conversion device such as an inverter (not shown). When the vehicle 1 is decelerating with the accelerator released, the front motor 10f and the rear motor 10r are forcibly driven by the rotational force of the front wheels 2f and the rear wheels 2r to generate regenerative power and apply regenerative braking force to the front wheels 2f and the rear wheels 2r. The regenerative power generated by the front motor 10f and the rear motor 10r is supplied to the battery 14.

[0016] The friction braking device 30 is a disc brake device that applies friction braking force to each of the front wheels 2 f and each of the rear wheels 2 r by the friction force generated by pressing brake pads 34 driven by an actuator (not shown) against disc rotors 32 provided corresponding to each of the front wheels 2 f and each of the rear wheels 2 r. The actuator may be either hydraulic or electric. The friction braking device 30 is driven and controlled by the control device 16.

[0017] The control device 16 is configured to include input / output devices, storage devices (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), etc., and performs overall control of the vehicle 1. The control device 16 receives detected quantities and various operational information detected by various sensors (not shown), such as accelerator opening, brake stroke, vehicle speed, and wheel speed. Based on the input detected quantities and operational information, the control device 16 calculates information necessary for controlling the vehicle 1, such as the required driving force and the required braking force required for the vehicle 1 to travel, and controls various devices of the vehicle 1 based on the calculated information. For example, the control device 16 uses the regenerative braking device 20 and the friction braking device 30 to perform regenerative cooperative control, which outputs the required braking force required for braking the vehicle 1 in a coordinated manner using regenerative braking force and friction braking force.

[0018] 2 is an explanatory diagram showing an example of time variations in the required braking force, regenerative braking force, and friction braking force in regenerative cooperative control. The control device 16 calculates the required braking force Fb according to the amount of brake application by the driver, and based on the calculated required braking force Fb, sets the regenerative braking force Fkf to be applied from the front motor 10f to the front wheels 2f, the regenerative braking force Fkr to be applied from the rear motor 10r to the rear wheels 2r, the friction braking forces Fmf to be applied from each friction braking device 30 to the front wheels 2f, and the friction braking forces Fmr to be applied to the rear wheels 2r.

[0019] Specifically, the control device 16 sets the regeneration ratio k, friction ratio m, front ratio f, and rear ratio r, which are expressed by the following equations (1) to (4), so that the sum of the regenerative braking forces Fkf, Fkr and the friction braking forces Fmf, Fmr satisfies the required braking force Fb. The regeneration ratio k and friction ratio m are distribution ratios between the regenerative braking forces Fkf, Fkr and the friction braking forces Fmf, Fmr, and are set between 0 and 1 so that their sum is 1. The front ratio f and rear ratio r are distribution ratios between the braking forces (Fkf, Fmf) applied to the front wheels 2f and the braking forces (Fkr, Fmr) applied to the rear wheels 2r, and are set between 0 and 1 so that their sum is 1. A specific method for setting the distribution ratios will be described later. However, the regenerative braking forces Fkf, Fkr are set at least within the upper limit of the amount of regenerative power generation, which is set depending on the state of charge (SOC) and temperature of the battery 14. In the example shown in Figure 2, when the driver depresses the brake pedal (time t1), regenerative braking forces Fkf, Fkr are output within the upper limit of the regenerative power generation amount in accordance with the change in the required braking force Fb, and the shortfall of the regenerative braking forces Fkf, Fkr relative to the required braking force Fb is output as friction braking forces Fmf, Fmr.

[0020] k=(Fkf+Fkr) / (Fkf+Fkr+Fmf+Fmr)...(1) m=(Fmf+Fmr) / (Fkf+Fkr+Fmf+Fmr)...(2) f=(Fkf+Fmf) / (Fkf+Fkr+Fmf+Fmr)...(3) r=(Fkr+Fmr) / (Fkf+Fkr+Fmf+Fmr)...(4)

[0021] (Replacement Control) Furthermore, when the vehicle speed of the vehicle 1 falls below a predetermined replacement determination vehicle speed during execution of the regenerative cooperative control (time t2), the control device 16 executes replacement control to replace the regenerative braking forces Fkf and Fkr of the required braking force Fb with frictional braking forces Fmf and Fmr. The predetermined replacement determination vehicle speed can be set to a vehicle speed at which it can be determined that the vehicle is approaching a stop and at which the replacement from the regenerative braking forces Fkf and Fkr to the frictional braking forces Fmf and Fmr can be completed before the vehicle comes to a stop. However, it is preferable to perform the replacement from the regenerative braking forces Fkf and Fkr to the frictional braking forces Fmf and Fmr over a period of time that does not cause slippage in braking. When the replacement control is completed at time t3, the portion of the required braking force Fb that was previously borne by the regenerative braking forces Fkf and Fkr is completely replaced by the frictional braking forces Fmf and Fmr. This enables creep torque to be output from the front motor 10f and rear motor 10r, and after the vehicle 1 stops at time t4, driving force can be quickly output from the front motor 10f and rear motor 10r when the vehicle starts moving again.

[0022] (Vehicle Pitching Movement) Next, the pitching movement of the vehicle 1 will be described. Fig. 3 is an explanatory diagram that schematically shows the pitching movement of the vehicle 1 when it is being driven, and Fig. 4 is an explanatory diagram that schematically shows the pitching movement of the vehicle 1 when it is being braked. Here, in order to explain the general concept of the change in attitude of the vehicle 1 in the pitch direction when it is being driven and when it is being braked, and the accompanying load movement, Fig. 4 shows an example in which only frictional braking forces Fmf and Fmr are applied to the vehicle 1.

[0023] As shown in FIG. 3 , when driving forces Fdf and Fdr are applied to the front wheels 2f and the rear wheels 2r, an inertial force Fi acts on the rear side of the vehicle 1. As a result, a pitch moment Mp acts on the center of gravity G of the vehicle 1, causing the front side to tilt upward, resulting in a posture change known as a squat. Furthermore, as shown in FIG. 4 , when frictional braking forces Fmf and Fmr are applied, an inertial force Fi acts on the front side of the vehicle 1. As a result, a pitch moment Mp acts on the center of gravity G of the vehicle 1, causing the front side to tilt downward, resulting in a posture change known as a nose dive. At this time, the inclination of a line L1 extending in the fore-and-aft direction and passing through the center of gravity G of the vehicle 1 before and after the posture change is the pitch angle θp. In this embodiment, the pitch angle θp increases in the positive direction as the posture of the vehicle 1 changes toward the nose dive side, and decreases in the positive direction (increases in the negative direction) as the posture of the vehicle 1 changes toward the squat side.

[0024] (Anti-angles and anti-forces) Furthermore, anti-forces act on the vehicle 1 according to anti-angles θa that are predetermined as vehicle specifications. The anti-angles θa include an anti-nose-up angle θaU, an anti-squat angle θaS, an anti-nose-dive angle θaD, and an anti-tail-lift angle θaL. Each anti-angle θa is determined by the geometry of the suspensions 18 (front suspensions 18f and rear suspensions 18r) connected to the front wheels 2f and rear wheels 2r of the vehicle 1.

[0025] When the vehicle 1 is driven, an anti-nose-up force FaU, which is a vertical component of the driving force Fdf, acts on the front side of the vehicle 1 in accordance with the anti-nose-up angle θaU, and an anti-squat force FaS, which is a vertical component of the driving force Fdr, acts on the rear side of the vehicle 1 in accordance with the anti-squat angle θaS. Because the anti-nose-up force FaU is a downward force and the anti-squat force FaS is an upward force, changes in the squat posture of the vehicle 1 are suppressed.

[0026] On the other hand, when the vehicle 1 is braking, an anti-nose-dive force FaD, which is a vertical component of the frictional braking force Fmf, acts on the front side of the vehicle 1 in accordance with the anti-nose-dive angle θaD, and an anti-tail-lift force FaL, which is a vertical component of the frictional braking force Fmr, acts on the rear side of the vehicle 1 in accordance with the anti-tail-lift angle θaL. Because the anti-nose-dive force FaD is an upward force and the anti-tail-lift force FaL is a downward force, changes in the nose-up attitude of the vehicle 1 are suppressed.

[0027] (Weight Transfer) When a squat posture change occurs as described above, the front suspension 18f of the vehicle 1 extends and the rear suspension 18r contracts. On the other hand, when a nose dive posture change occurs, the front suspension 18f of the vehicle 1 contracts and the rear suspension 18r extends. A force corresponding to this amount of expansion and contraction becomes the load transfer amount ΔW acting on the inboard portion of the vehicle 1 located above the suspension 18 when a pitching motion occurs. In this embodiment, the load transfer amount ΔW during regenerative cooperative control is calculated using the method described below, and the regenerative braking forces Fkf, Fkr and friction braking forces Fmf, Fmr during regenerative cooperative control are set based on the relationship between the load transfer amount ΔW and the pitch angle θp. In the following description, the inboard portion of the vehicle 1 above the suspension 18 is referred to as the "sprung portion," and the outboard portion of the vehicle 1 located below the suspension 18 is referred to as the "unsprung portion."

[0028] (Instantaneous Rotation Center) Here, the pitching motion of the vehicle 1 on the springs during regenerative cooperative control can be considered to be behavior caused by a pitch moment acting on the center of gravity G, with the instantaneous rotation center (pitching instantaneous center) of each force acting on the vehicle 1 as a fulcrum. FIG. 5 is an explanatory diagram schematically showing the instantaneous rotation center of the vehicle 1. As shown in the figure, the regenerative braking forces Fkf and Fkr are forces output from the front motor 10f and the rear motor 10r, which are provided on the springs. Therefore, in this embodiment, the intersection of an extension line L2 extending along the anti-nose-up angle θaU and an extension line L3 extending along the anti-squat angle θaS is set as the first instantaneous rotation center A of the pitching motion when the regenerative braking forces Fkf and Fkr are acting. On the other hand, the frictional braking forces Fmf and Fmr are forces output from the frictional braking device 30 provided under the springs. Therefore, in this embodiment, the intersection of an extension line L4 extending along the anti-nose dive angle θaD and an extension line L5 extending along the anti-tail lift angle θaL is set as the second instantaneous center of rotation B of the pitching motion when the frictional braking forces Fmf and Fmr act.

[0029] (Calculation of Load Movement Amount) Next, a method for calculating the load movement amount ΔW on the springs of the vehicle 1 based on the first instantaneous center of rotation A and the second instantaneous center of rotation B will be described. During regenerative braking of the vehicle 1, the following load movements occur on the springs of the vehicle 1 with the first instantaneous center of rotation A as the fulcrum: a load movement amount ΔWA1 due to inertial force, a load movement amount ΔWA2 due to reaction torque (see FIG. 6 ), and a load movement amount ΔWA3 due to antiforce. Furthermore, during frictional braking of the vehicle 1, the following load movements occur on the springs of the vehicle 1 with the second instantaneous center of rotation B as the fulcrum: a load movement amount ΔWB1 due to inertial force, and a load movement amount ΔWB2 due to antiforce.

[0030] (Load movement amount due to inertial force during regenerative braking) The load movement amount ΔWA1 due to inertial force generated when regenerative braking forces Fkf and Fkr are applied to vehicle 1 is calculated according to the following equation (5). In equation (5), "M" is the weight of vehicle 1, and "Gx" is the longitudinal deceleration acting on vehicle 1 (longitudinal acceleration with the deceleration side being positive). Also, "L" is the wheelbase, which is the distance between front wheel 2f and rear wheel 2r, "hg" is the height of center of gravity G, and "ha" is the height of first instantaneous center of rotation A.

[0031] ΔWA1=MGx(hg-ha) / L...(5)

[0032] (Load Transfer Due to Reaction Torque During Regenerative Braking) FIG. 6 is a schematic diagram illustrating a load transfer amount ΔWA2 due to reaction torque. When regenerative braking forces Fkf and Fkr are applied to the vehicle 1, a reaction torque Fc is generated that tends to rotate the differential case 5 of the differential gear, which is mounted on the sprung body frame 1a, in the opposite direction without passing through the suspension 18. The vehicle 1 is configured so that this reaction torque Fc is transmitted from the differential case 5 to the body frame 1a as a braking torque without passing through the suspension 18. As a result, a load transfer amount ΔWA2 is generated on the sprung body of the vehicle 1 due to the reaction torque Fc in a direction that lifts the front side and pushes down the rear side. The load transfer amount ΔWA2 is calculated according to the following equation (6). In equation (6), "Rt" is the radius of the front wheels 2f and the rear wheels 2r.

[0033] ΔWA2=MGx・Rt / L…(6)

[0034] (Antiforce During Regenerative Braking) During regenerative braking of the vehicle 1, as shown in FIG. 5, an antiforce is generated in accordance with the regenerative braking forces Fkf and Fkr. The antiforce generated during regenerative braking is a force on the front side opposite to the anti-nose-up force FaU (FIG. 3) during driving, and a force on the rear side opposite to the anti-squat force FaS (FIG. 3). Therefore, in the following description of regenerative braking, the anti-nose-up angle θaU will be referred to as the "regenerative front-side anti-angle θkfa," and the antiforce generated by the regenerative braking force Fkf will be referred to as the "regenerative front-side anti-force Fkfa." Furthermore, the anti-squat angle θaS will be referred to as the "regenerative rear-side anti-angle θkra," and the antiforce generated by the regenerative braking force Fkr will be referred to as the "regenerative rear-side anti-force Fkra." The regenerative front antiforce Fkfa and the regenerative rear antiforce Fkra are calculated by the following equations (7) and (8): The sum of the regenerative front antiforce Fkfa and the regenerative rear antiforce Fkra is the load shift amount ΔWA3.

[0035] Fkfa=Fkf・tan(θkfa)…(7) Fkra=Fkr・tan(θkra)…(8)

[0036] (Load Movement Due to Inertial Force Caused by Frictional Braking) The load movement amount ΔWB1 due to inertial force generated when frictional braking forces Fmf and Fmr are applied to the vehicle 1 can be calculated according to the following equation (9): "hb" in equation (9) is the height of the second instantaneous center of rotation B.

[0037] ΔWB1=MGx(hg-hb) / L...(9)

[0038] (Antiforce Due to Frictional Braking Force) Furthermore, as shown in FIG. 5, during frictional braking of the vehicle 1, antiforces corresponding to the frictional braking forces Fmf and Fmr are generated. The antiforces generated during frictional braking are an anti-nose dive force FaD and an anti-tail lift force FaL ( FIG. 4 ). In the following description of frictional braking, the anti-nose dive angle θaD will be referred to as the "friction front-side anti-angle θmfa," and the antiforce generated by the frictional braking force Fmf will be referred to as the "friction front-side antiforce Fmfa." Furthermore, the anti-tail lift angle θaL will be referred to as the "friction rear-side anti-angle θmra," and the antiforce generated by the frictional braking force Fmr will be referred to as the "friction rear-side antiforce Fmra." The friction front-side antiforce Fmfa and the friction rear-side antiforce Fmra are calculated using the following equations (10) and (11). The sum of the front friction antiforce Fmfa and the rear friction antiforce Fmra is the load movement amount ΔWB2.

[0039] Fmfa=Fmf・tan(θmfa)…(10) Fmra=Fmr・tan(θmra)…(11)

[0040] (Sum of Load Transfer Amounts on the Springs) By adding up the first load transfer amount, which is the sum of the above load transfer amounts ΔWA1, ΔWA2, and ΔWA3, and the second load transfer amount, which is the sum of the load transfer amounts ΔWB1 and ΔWB2, while taking into account the regeneration ratio k and the friction ratio m, the load transfer amount ΔW on the springs is calculated as shown in the following equation (12). Note that "MGx," which is the longitudinal force acting on the vehicle 1 in equation (12), can be calculated as the sum of the regenerative braking forces Fkf and Fkr and the friction braking forces Fmf and Fmr. Furthermore, for "tan(θ)" in equation (12), if the absolute value of the pitch angle θp is sufficiently small, each anti-angle θa may be used as an approximate value.

[0041] ΔW=kΔWA1+kΔWA2+ΔWA3+mΔWB1+ΔWB2=kMGx(hg-ha) / L+kMGx・Rt / L-Fkf・tan (θkfa)-Fkr・tan(θkra)+mMGx(hg-hb) / L-Fmf・tan(θmfa)-Fmr・tan(θmra) ...(12)

[0042] (Calculation of Pitch Angle) The pitch angle θp is calculated by the following equation (13). In equation (13), "Kpf" is the spring constant of the front suspension 18f, and "Kpr" is the spring constant of the rear suspension 18r. Since "Kpf", "Kpr", and "L" in equation (13) are constants determined by the vehicle specifications, the pitch angle θp changes depending on the load movement amount ΔW calculated by equation (12).

[0043] θp=ΔW / (2(Kpf+Kpr)・L)...(13)

[0044] (Example of Calculation Results of Pitch Angle θp) Next, an example of the calculation results of the pitch angle θp calculated using the above equations (12) and (13) will be described. Table 1 shows an example of the anti angle θa of the vehicle 1. In the vehicle 1 of this embodiment, the regenerative rear-side anti angle θkra is larger than the regenerative front-side anti angle θkfa, and the friction rear-side anti angle θmra is larger than the friction front-side anti angle θmfa. Furthermore, the friction front-side anti angle θmfa is larger than the regenerative front-side anti angle θkfa, and the friction rear-side anti angle θmra is larger than the regenerative rear-side anti angle θkra. Furthermore, the friction rear-side anti angle θmra is the largest of all the anti angles θa, and the difference between the friction rear-side anti angle θmra and the remaining anti angles θa is set to be larger than the difference between the remaining anti angles θa. In other words, in the vehicle 1, the friction rear-side anti force Fmra acts greatest.

[0045]

[0046] FIG. 7 is an explanatory diagram plotting an example of pitch angle θp when the regeneration ratio k, friction ratio m, front ratio f, and rear ratio r are changed. The values ​​of pitch angle θp shown in the shaded area in FIG. 7 are calculated based on equations (12) and (13) using the vehicle specifications shown in Table 1, assuming that the deceleration and required braking force Fb (= Fkf + Fkr + Fmf + Fmr) are constant. FIG. 7 assumes that the height hg of the center of gravity G, the height ha of the first instantaneous center of rotation A, and the height hg of the second instantaneous center of rotation B do not change during braking of the vehicle 1. In this case, the variables in equation (12) are only the regenerative braking forces Fkf, Fkr, and the frictional braking forces Fmf, Fmr, and the pitch angle θp can be treated as a value that changes depending on the regenerative braking forces Fkf, Fkr, and the frictional braking forces Fmf, Fmr. If the heights hg, ha, and hb vary depending on the attitude of the vehicle 1, these values ​​may be obtained by a sensor (not shown) that detects the vehicle body position.

[0047] As shown in the figure, in vehicle 1, the pitch angle θp increases as the regeneration ratio k increases, and the pitch angle θp decreases as the friction ratio m increases. This is because the friction front anti-angle θmfa is greater than the regeneration front anti-angle θkfa, and the friction rear anti-angle θmra is greater than the regeneration rear anti-angle θkra. In other words, when the friction ratio m increases, the friction side anti-forces (Fmfa, Fmra) tend to become relatively large, and the pitch angle θp tends to become small. On the other hand, even when the regeneration ratio k increases, the regeneration side anti-forces (Fkfa, Fkra) do not tend to become relatively large, and the pitch angle θp tends to become small.

[0048] Furthermore, in vehicle 1, the pitch angle θp increases as the front ratio f increases, and the pitch angle θp decreases as the rear ratio r increases. This is because the regenerative rear-side anti-angle θkra is greater than the regenerative front-side anti-angle θkfa, and the friction rear-side anti-angle θmra is greater than the friction front-side anti-angle θmfa. In other words, when the rear ratio r increases, the rear-side anti-forces (Fkra, Fmra) tend to become relatively large, and the pitch angle θp tends to become small. On the other hand, even when the front ratio f increases, the front-side anti-forces (Fkfa, Fmfa) tend not to become relatively large, and the pitch angle θp tends not to become small.

[0049] FIG. 8 is an explanatory diagram showing an example of how the pitch angle θp changes over time when regenerative cooperative control is performed. The pitch angle θp shown in FIG. 8 is an analysis result obtained by using the example shown in FIG. 2 for the behavior of the regenerative braking forces Fkf, Fkr and the friction braking forces Fmf, Fmr in vehicle 1, and varying the front ratio f and rear ratio r between 0 and 1. As shown in the figure, although the pitch angle θp changes in response to changes in the required braking force Fb shown in FIG. 2, the tendency remains that the pitch angle θp increases as the front ratio f increases and decreases as the rear ratio r increases. Furthermore, as shown in the change in the pitch angle θp between time t2 and time t3, for example, when the switching control is started and the friction ratio m increases, the pitch angle θp tends to decrease.

[0050] As described above, in vehicle 1, the pitch angle θp increases as either the front ratio f or the regeneration ratio k increases, and the pitch angle θp decreases as either the rear ratio r or the friction ratio m increases. Furthermore, the tendency of change in the pitch angle θp in vehicle 1 remains the same even when the required braking force Fb changes, as shown in Figure 8. In other words, vehicle 1 has vehicle specifications such that the contribution of the antiforce load shift amounts ΔWA3 and ΔWB2 to the tendency of change in the pitch angle θp is greater than the contribution of the other load shift amounts ΔWA1, ΔWA2, and ΔWB1 to the tendency of change in the pitch angle θp, regardless of the magnitude of the required braking force Fb.

[0051] (Change in Center of Gravity Position During Braking) Next, a change in the position of the center of gravity G due to a change in posture during braking of the vehicle 1 will be described. FIG. 9 is an explanatory diagram showing an example of pitching motion of the vehicle body when frictional braking forces Fmf and Fmr are applied only to the front wheels 2f in the vehicle 1 of this embodiment. FIG. 10 is an explanatory diagram showing an example of pitching motion of the vehicle body when frictional braking forces Fmf and Fmr are applied only to the rear wheels 2r in the vehicle 1 of this embodiment. In the example shown in FIG. 9, a frictional front antiforce Fmfa acts on the vehicle 1. However, as described above, because the frictional front antiforce Fmfa is relatively small, the vehicle 1 is prone to a nose dive posture change in which the front side sinks downward and the rear side rises upward. At this time, the position of the center of gravity G tends to remain almost constant in the up-down direction. On the other hand, in the example shown in FIG. 10, the center of gravity G of the vehicle 1 moves downward from the position before braking indicated by the dashed line, while the pitch angle θp is closer to 0 degrees than in the example shown in FIG. 9. This is because the rear friction antiforce Fmra is larger than the front friction antiforce Fmfa, and the rear side of the vehicle body sinks further downward than in the example shown in FIG.

[0052] (Track Patch Load Shift) When the pitching motion described above occurs, the track patch load shift amount ΔWG, which is the shift amount of the load acting on the track patches of the front wheels 2f and rear wheels 2r, is calculated using the following equation (14). The track patch load shift amount ΔWG calculated using equation (14) corresponds to the load shift amount of the entire vehicle 1, which is the sum of the sprung load shift amount ΔW calculated using equation (12) and the unsprung load shift amount. In the example shown in FIG. 10, the position of the center of gravity G moves downward compared to the example shown in FIG. 9, so the height hg of the center of gravity G (see FIG. 5) in equation (14) is smaller. Therefore, the track patch load shift amount ΔWG2 in the example shown in FIG. 10 is smaller than the track patch load shift amount ΔWG1 in the example shown in FIG. 9. In this way, when the height of the center of gravity G changes, the value of the track patch load shift amount ΔWG changes.

[0053] ΔWG=MGx・hg / L…(14)

[0054] (Regenerative Cooperative Control During Turning Braking) Next, a description will be given of regenerative cooperative control during turning braking of the vehicle 1, which utilizes the change in the position of the center of gravity G and the change in the contact patch load shift amount ΔWG. In regenerative cooperative control during turning braking of the vehicle 1, the control device 16 performs either a first distribution adjustment or a second distribution adjustment of the braking force shown in Table 2 depending on the driving mode, in order to improve the maneuverability and ride comfort of the vehicle 1. Regardless of whether the first distribution adjustment or the second distribution adjustment is performed, control is performed so that at least the required braking force Fb is satisfied by the sum of the braking forces (Fkf+Fkr+Fmf+Fmr).

[0055]

[0056] First, as shown in Table 2, the vehicle 1 is configured to be able to select a driving mode including a sport mode and a comfort mode. In this embodiment, the sport mode is a driving mode that prioritizes improved maneuverability over ride comfort of the vehicle 1, and the comfort mode is a driving mode that prioritizes ride comfort over maneuverability of the vehicle 1. The driving mode may be changed by the driver operating a selector switch provided in the driver's seat (not shown). Then, the control device 16 performs either the first distribution adjustment or the second distribution adjustment when the driving mode is set to the sport mode, depending on an index value that indicates the degree of turning of the vehicle 1, and performs the second distribution adjustment when the driving mode is set to the comfort mode.

[0057] The index values ​​representing the degree of turning of the vehicle 1 include, for example, the steering angle, lateral acceleration, yaw rate, and slip angle of the rear wheels 2r. The control device 16 calculates the steering angle based on the amount of steering operation of the vehicle 1 (not shown). The control device 16 also acquires the lateral acceleration detected by an acceleration sensor (not shown) and the yaw rate detected by a yaw rate sensor (not shown). The control device 16 also calculates the slip angle of the rear wheels 2r based on the vehicle speed detected by a vehicle speed sensor (not shown), the acceleration at the center of gravity G of the vehicle 1, the steering angle, vehicle specifications, etc.

[0058] (First distribution adjustment in sport mode) First, a case where the driving mode is set to sport mode and the first distribution adjustment is performed will be described with reference to Fig. 11. Fig. 11 is an explanatory diagram that schematically shows a state where the braking force is adjusted by the first distribution adjustment during cornering braking of the vehicle 1. The dashed arrows in the figure indicate the magnitudes of the regenerative braking forces Fkf, Fkr and the frictional braking forces Fmf, Fmr before the first distribution adjustment is performed, and the solid arrows indicate the magnitudes of the regenerative braking forces Fkf, Fkr and the frictional braking forces Fmf, Fmr after the first distribution adjustment is performed.

[0059] In this case, the control device 16 sets the index value to at least one of the steering angle and the lateral acceleration. Then, the control device 16 executes a first distribution adjustment such that, as at least one of the steering angle and the lateral acceleration increases, the control device 16 increases the regenerative braking force Fkr of the rear wheels 2r while decreasing the regenerative braking force Fkf of the front wheels 2f, and decreases the frictional braking force Fmr of the rear wheels 2r while increasing the frictional braking force Fmf of the front wheels 2f.

[0060] As a result, the rear-side frictional braking force Fmr decreases, thereby reducing the frictional rear-side anti-force Fmra. Furthermore, even if the rear-side regenerative braking force Fkr increases, the regenerative rear-side anti-force Fkra is less likely to increase compared to the frictional rear-side anti-force Fmra. As a result, the rear side of the vehicle 1 tends to be less likely to sink (more likely to float). On the other hand, on the front side, compared to the rear side, even if the frictional braking force Fmf increases, the frictional front-side anti-force Fmfa is less likely to increase. Therefore, when the first distribution adjustment is performed, the vehicle 1 is more likely to experience a nose-dive attitude change without a large change in the height of the center of gravity G as shown in FIG. 9 .

[0061] As a result, the contact patch load shift amount ΔWG (ΔWG1) increases, and the load applied to the contact patch of the front wheel 2f increases, so that the friction circle Cf of the front wheel 2f becomes larger than before the first distribution adjustment, as shown in Figure 11. The friction circle schematically indicates the grip limit of the wheel, and in the figure, the friction circle before the distribution adjustment is shown as a dashed circle, and the friction circle after the distribution adjustment is shown as a solid circle, with the lower side of the figure indicating the deceleration region. In this way, by increasing the friction circle Cf of the front wheel 2f, the grip limit of the front wheel 2f as a steered wheel increases, and the maneuverability of the vehicle 1 during cornering braking is improved.

[0062] (Second Distribution Adjustment in Sport Mode) Next, a case where the driving mode is set to sport mode and the second distribution adjustment is performed will be described with reference to FIG. 12 . FIG. 12 is an explanatory diagram that schematically shows the state when the braking force is adjusted by the second distribution adjustment during cornering braking of the vehicle 1. The definitions of the arrows and circles in the figure are the same as those in FIG. 11 . The control device 16 sets the index value to at least one of the yaw rate and the slip angle of the rear wheels 2r. Then, the control device 16 performs the second distribution adjustment such that, the larger at least one of the yaw rate and the slip angle of the rear wheels 2r is, the larger the second distribution adjustment is, and the larger the regenerative braking force Fkf is while decreasing the regenerative braking force Fkr, and the larger the frictional braking force Fmr is while decreasing the frictional braking force Fmf.

[0063] As a result, the rear-side frictional braking force Fmr increases, which further increases the frictional rear-side anti-force Fmra. Furthermore, even if the regenerative braking force Fkr decreases, the regenerative rear-side anti-force Fkra is less likely to become smaller than the frictional rear-side anti-force Fmra. Furthermore, because the regenerative rear-side anti-force Fkra is already smaller than the frictional rear-side anti-force Fmra, any change in the force has little effect. As a result, the rear side of the vehicle 1 tends to sink. Therefore, when the second distribution adjustment is performed, the height of the center of gravity G of the vehicle 1 moves downward as shown in FIG. 10 above, and an attitude change in which the pitch angle θp becomes relatively close to 0 degrees is likely to occur.

[0064] As a result, the contact patch load shift amount ΔWG (ΔWG2) decreases, and the load applied to the contact patch of the rear wheel 2r increases, so the friction circle Cr of the rear wheel 2r becomes larger than before the second distribution adjustment, as shown in Figure 12. Increasing the friction circle Cr of the rear wheel 2r in this way increases the grip limit of the rear wheel 2r, suppresses slippage of the rear wheel 2r, and suppresses spinning of the vehicle 1.

[0065] (Selection of First Distribution Adjustment and Second Distribution Adjustment in Sport Mode) In sport mode, whether to perform the first distribution adjustment or the second distribution adjustment may be determined by selecting which of the friction circles Cf and Cr to increase depending on the dynamic characteristics of the vehicle 1, or by other conditions. As other conditions, for example, the first distribution adjustment may be performed depending on the steering angle and lateral acceleration among the index values ​​for a predetermined time after the start of turning of the vehicle 1, and the second distribution adjustment may be performed depending on the yaw rate and slip angle of the rear wheels 2r after the predetermined time has elapsed since the start of turning. This may increase the grip limit of the front wheels 2f at the beginning of the turn to achieve smoother turning, while increasing the grip limit of the rear wheels 2r from the middle to late stages of the turn when the vehicle 1 may be prone to spinning, thereby suppressing spinning. Furthermore, for example, predetermined thresholds may be set for each index value, and the first distribution adjustment may be performed when the steering angle and lateral acceleration exceed the predetermined thresholds, and the second distribution adjustment may be performed when the yaw rate and slip angle of the rear wheels 2r exceed the predetermined thresholds. In this case, when the yaw rate and the slip angle of the rear wheels 2r exceed a predetermined threshold value while the first distribution adjustment is being performed, the adjustment may be switched to the second distribution adjustment.

[0066] (Second Distribution Adjustment in Comfort Mode) When the driving mode is the comfort mode, the control device 16 sets the index value to at least one of the steering angle and the lateral acceleration. The control device 16 then performs the second distribution adjustment such that, as at least one of the steering angle and the lateral acceleration increases, the control device 16 increases the regenerative braking force Fkf while decreasing the regenerative braking force Fkr, and decreases the frictional braking force Fmf while increasing the frictional braking force Fmr. By performing the second distribution adjustment in the comfort mode in this manner, the vehicle 1 is likely to experience an attitude change in which the height of the center of gravity G moves downward and the pitch angle θp becomes relatively close to 0 degrees, as shown in FIG. 10 above. Therefore, the greater the steering angle or the lateral acceleration, the more likely the driver is to feel a change in ride comfort. This suppresses attitude changes that tend to nose-dive the vehicle 1, improving the driver's ride comfort.

[0067] As described above, the control device 16 (brake control device) of the embodiment performs either the first distribution adjustment or the second distribution adjustment while regenerative cooperative control is being performed. With this configuration, when the first distribution adjustment is performed, the larger the index value representing the degree of turning, the higher the grip limit of the front wheels 2f, thereby improving the maneuverability of the vehicle 1. Furthermore, when the second distribution adjustment is performed, the larger the index value representing the degree of turning, the higher the grip limit of the rear wheels 2r, thereby suppressing spin of the vehicle 1 and improving the maneuverability. Furthermore, by making it easier for the rear side of the vehicle 1 to sink, it is possible to adjust the pitch angle θp of the vehicle 1 to approach 0 degrees. Therefore, the control device 16 of the embodiment makes it possible to appropriately adjust the maneuverability and ride comfort during cornering braking of the vehicle 1 that performs regenerative cooperative control.

[0068] Additionally, in both the first distribution adjustment and the second distribution adjustment, when the regenerative braking forces Fkf, Fkr or the frictional braking forces Fmf, Fmr of either the front wheels 2f or the rear wheels 2r are increased, the regenerative braking forces Fkf, Fkr or the frictional braking forces Fmf, Fmr of the other wheel are adjusted to be smaller. This reduces the impact on the front ratio f, rear ratio r, regeneration ratio k, and friction ratio m. As a result, it becomes easier to control the attitude of the vehicle 1 according to the front ratio f, rear ratio r, regeneration ratio k, and friction ratio m, and it is also possible to suppress a decrease in the amount of regenerative power generation. Note that in both the first distribution adjustment and the second distribution adjustment, it is preferable to adjust each braking force so that the front ratio f, rear ratio r, regeneration ratio k, and friction ratio m are maintained.

[0069] Furthermore, when the driving mode of the vehicle 1 is a sport mode that prioritizes improving maneuverability over ride comfort, the first distribution adjustment is performed using at least one of the steering angle and the lateral angular velocity as the index value. With this configuration, in the sport mode, it is possible to improve maneuverability during cornering braking by increasing the grip limit of the front wheels 2f while realizing distribution adjustment according to the degree of turning of the vehicle 1. Furthermore, by using the steering angle or the lateral acceleration as the index value, it is possible to realize distribution adjustment according to the degree of turning of the vehicle.

[0070] Furthermore, when the driving mode of the vehicle 1 is a sport mode that prioritizes improved maneuverability over ride comfort, the second distribution adjustment is performed using at least one of the yaw rate and the slip angle of the rear wheels 2r as the index value. With this configuration, it is possible to increase the grip limit of the rear wheels 2r in the sport mode and suppress spin of the vehicle 1 while realizing distribution adjustment according to the degree of spin of the vehicle 1. Furthermore, by using the yaw rate or the slip angle of the rear wheels as the index value, it is possible to realize distribution adjustment according to the degree of spin of the vehicle.

[0071] Furthermore, when the driving mode of the vehicle 1 is a comfort mode that prioritizes ride comfort over improved maneuverability, the second distribution adjustment is performed using at least one of the steering angle and the lateral angular velocity as the index value. With this configuration, it is possible to bring the pitch angle of the vehicle 1 closer to 0 degrees while achieving distribution adjustment according to the turning degree of the vehicle 1, thereby suppressing changes in posture during turning, which are likely to cause changes in ride comfort. Furthermore, by using the steering angle or the lateral acceleration as the index value, it is possible to achieve distribution adjustment according to the turning degree of the vehicle.

[0072] Although the description of the embodiment is now complete, aspects of the present invention are not limited to this embodiment. For example, in this embodiment, the index value representing the degree of turning of the vehicle 1 is any one of the steering angle, lateral acceleration, yaw rate, and slip angle of the rear wheels 2r, but the index value may include other values, such as the slip angle of the front wheels 2f. Furthermore, the control device 16 may perform the first distribution adjustment and the second distribution adjustment using at least one of the above index values ​​whether the driving mode of the vehicle 1 is the sport mode or the comfort mode.

[0073] 1 vehicle 2f front wheels 2r rear wheels 10f front motor 10r rear motor 16 control device (brake control device) 18 suspension 18f front suspension 18r rear suspension 20 regenerative braking device 30 friction braking device A first instantaneous center of rotation B second instantaneous center of rotation Cf, Cr friction circle f front ratio Fb required braking force Fc reaction torque Fdf, Fdr driving force Fi inertia force Fkf, Fkr regenerative braking force Fkfa regenerative front antiforce Fkra regenerative rear antiforce Fmf, Fmr friction braking force Fmfa friction front antiforce Fmra friction rear antiforce G center of gravity k regenerative ratio L1 straight line L2, L3, L4, L5 extension line m friction ratio r rear ratio ΔW, ΔWA1, ΔWA2, ΔWA3, ΔWB1, ΔWB2: Load transfer amount ΔWG, ΔWG1, ΔWG2: Contact patch load transfer amount θa: Anti-angle θkfa: Regenerative front-side anti-angle (anti-nose-up angle) θkra: Regenerative rear-side anti-angle (anti-squat angle) θmfa: Friction front-side anti-angle (anti-nose-dive angle) θmra: Friction rear-side anti-angle (anti-tail-lift angle) θp: Pitch angle

Claims

1. A braking control device that performs regenerative cooperative control using a regenerative braking device that applies a regenerative braking force to the front and rear wheels of a vehicle, and a friction braking device that applies a frictional braking force to the front and rear wheels, to output a required braking force required for braking the vehicle in coordination with the regenerative braking force and the frictional braking force, wherein, during the execution of the regenerative cooperative control, the braking control device performs one of the following: a first distribution adjustment that, as an index value indicating the degree of turning of the vehicle becomes larger, reduces the regenerative braking force applied to the front wheels while increasing the regenerative braking force applied to the rear wheels, and increases the frictional braking force applied to the front wheels while decreasing the frictional braking force applied to the rear wheels; and a second distribution adjustment that, as the index value becomes larger, increases the regenerative braking force applied to the front wheels while decreasing the regenerative braking force applied to the rear wheels, and decreases the frictional braking force applied to the front wheels while increasing the frictional braking force applied to the rear wheels.

2. A brake control device according to claim 1, wherein the first distribution adjustment is executed when the driving mode of the vehicle is a sports mode which prioritizes improvement of driving performance over ride comfort.

3. A brake control device according to claim 1, wherein the second distribution adjustment is executed when the driving mode of the vehicle is a comfort mode which prioritizes ride comfort over improvement of driving performance.

4. A brake control device according to claim 2 or 3, wherein the index value is at least one of a steering angle and a lateral angular velocity of the vehicle.

5. A brake control device according to claim 1, wherein the second distribution adjustment is executed when the driving mode of the vehicle is a sports mode which prioritizes improvement of driving performance over ride comfort.

6. A brake control device according to claim 5, wherein the index value is at least one of the yaw rate of the vehicle and the slip angle of the rear wheels.

Images