Braking control device

Abstract

The present invention is such that when the vehicle speed becomes equal to or less than a prescribed replacement determination vehicle speed during execution of regenerative cooperative control, a control device executes replacement control for replacing the load of the regenerative braking force portion, of requested braking force, with friction braking force. The control device then executes front rear ratio adjustment control for adjusting a front ratio f and a rear ratio r such that a post-replacement pitch angle θps, which is the pitch angle θp of a vehicle after completion of the replacement control, approaches 0° until the replacement control is completed. As a result of this configuration, sudden changes in the pitch angle θp after stoppage of the vehicle can be suppressed by adjusting the front ratio f and the rear ratio r in advance before the replacement control is completed, even when the the vehicle after completion of the replacement control is in a nose-dive orientation or a squatting orientation.

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 relating to a regenerative cooperative control that applies a regenerative braking force and a friction braking force to a wheel of a vehicle using a regenerative braking device and a friction braking device. For example, Patent Document 1 describes a braking control device that increases the friction braking force applied to the wheel so that the friction braking force applied to the wheel becomes greater than the regenerative braking force applied to the wheel when a target vehicle braking force increases. In this braking control device, when the target vehicle braking force increases, a switching process (switching control) is performed to switch at least a portion of the friction braking force applied to the wheel to a regenerative braking force.

[0003] Japanese Patent Application Laid-Open No. 2021-115926

[0004] In a vehicle that performs regenerative cooperative control, the regenerative braking force may be replaced with friction braking force to shift the torque output from the traction motor to the driving side in advance just before the vehicle is stopped, in order to quickly output torque on the driving side when the vehicle is restarted. After completion of this replacement control, the pitch angle of the vehicle fluctuates depending on the magnitude of the braking force applied to the front and rear wheels. When the vehicle stops, the braking force applied to each wheel is eliminated, causing the pitching motion of the vehicle to stop and the pitch angle to become 0 degrees. In particular, if the pitch angle changes after the vehicle has stopped while the vehicle is changing its attitude on the nose dive side, the vehicle occupants will feel a significant change in attitude, which will affect the ride comfort of the vehicle.

[0005] The present invention has been made in consideration of these problems, and its purpose is to provide a braking control device that can suppress pitching motion that occurs after a vehicle that performs regenerative cooperative control and switching control has stopped, thereby improving ride comfort.

[0006] In order to achieve the above object, the braking control device of the present invention is a braking control device that 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, to perform regenerative cooperative control that outputs the required braking force required for braking the vehicle in coordination with the regenerative braking force and the frictional braking force, and replacement control that replaces the regenerative braking force share of the required braking force with the frictional braking force when the vehicle speed falls below a predetermined replacement judgment vehicle speed while the regenerative cooperative control is being performed, and performs front-rear ratio adjustment control that adjusts the front ratio and rear ratio, which are the distribution ratio of the braking force applied to the front wheels and the braking force applied to the rear wheels, so that the post-replacement pitch angle, which is the pitch angle of the vehicle after the replacement control is completed, changes at least tending to change the posture of the vehicle from a state on the nose dive side toward a state on the squat side until the replacement control is completed.

[0007] With this configuration, by adjusting the front and rear ratios before the completion of the switching control, the vehicle's posture after the switching control is completed can be made to tend from a nose-dive state toward a squat state. As a result, it is possible to prevent the pitch angle from suddenly changing from the nose-dive side to 0 degrees after the vehicle has stopped. Therefore, with the braking control device of the present invention, it is possible to prevent pitching motion that occurs after a vehicle that is performing regenerative cooperative control and switching control has stopped, thereby improving ride comfort.

[0008] Furthermore, it is preferable to acquire the post-switchover pitch angle when the front ratio and the rear ratio are adjusted, assuming that the required braking force at the start of the front-rear ratio adjustment control has been entirely converted to the friction braking force by the switching control. With this configuration, the post-switchover pitch angle can be easily acquired.

[0009] Furthermore, it is preferable to set the intersection of an extension of the front friction anti-angle, which is the anti-nose dive angle of the vehicle, and an extension of the rear friction anti-angle, which is the anti-tail lift angle, as an instantaneous rotation center, and to obtain the post-replacement pitch angle based on the sum of the load movement amounts due to the inertial force and anti-force acting on a spring located above a suspension of the vehicle due to the friction braking force at the instantaneous rotation center. With this configuration, the post-replacement pitch angle can be obtained with high accuracy.

[0010] It is also preferable to complete the front-rear ratio adjustment control before the start of the switching control. This configuration prevents adjustment of the front and rear ratios while switching from regenerative braking force to frictional braking force, ensuring stable braking of the vehicle during switching control.

[0011] It is also preferable to adjust the front ratio and the rear ratio so that the post-switching pitch angle approaches 0 degrees. This configuration makes it possible to suppress a sudden change in the pitch angle after the vehicle stops, regardless of whether the vehicle's posture after switching control is nose-dive or squat. Therefore, it is possible to more effectively suppress pitching motion that occurs after the vehicle stops.

[0012] Furthermore, when the anti-tail lift angle of the vehicle is greater than the anti-nose dive angle, it is preferable to increase the rear ratio when the post-switching pitch angle is greater on the nose dive side than 0 degrees, and decrease the rear ratio when the post-switching pitch angle is greater on the squat side than 0 degrees. With this configuration, the magnitude of the antiforce due to the friction braking force on the rear side can be adjusted to bring the post-switching pitch angle closer to 0 degrees.

[0013] Furthermore, when the anti-nose-dive angle of the vehicle is greater than the anti-tail-lift angle, it is preferable to increase the front ratio when the post-switching pitch angle is greater on the nose-dive side than 0 degrees, and decrease the front ratio when the post-switching pitch angle is greater on the squat side than 0 degrees. With this configuration, the magnitude of the antiforce due to the frictional braking force on the front side can be adjusted to bring the post-switching pitch angle closer to 0 degrees.

[0014] According to the braking control device of the present invention, it is possible to suppress pitching motion that occurs after a vehicle that is performing regenerative cooperative control and switching control has stopped, thereby improving ride comfort.

[0015] FIG. 1 is a schematic configuration diagram showing a vehicle equipped with a brake control device according to an embodiment. FIG. 2 is an explanatory diagram showing an example of time variations in required braking force, regenerative braking force, and friction braking force in regenerative cooperative control. FIG. 3 is an explanatory diagram showing a schematic view of pitching motion when the vehicle is driven. FIG. 4 is an explanatory diagram showing a schematic view of pitching motion when the vehicle is braking. FIG. 5 is an explanatory diagram showing a schematic view of the instantaneous center of rotation of the vehicle. FIG. 6 is a schematic diagram for explaining the amount of load movement due to reaction torque. FIG. 7 is an explanatory diagram plotting an example of pitch angle when the regenerative ratio, friction ratio, front ratio, and rear ratio are changed. FIG. 8 is an explanatory diagram showing an example of time variations in pitch angle when regenerative cooperative control is performed. FIG. 9 is an explanatory diagram showing an example of time variations in pitch angle when regenerative cooperative control is performed in a vehicle having other specifications.

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0017] (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).

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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)

[0024] (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.

[0025] (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.

[0026] 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.

[0027] (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.

[0028] 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.

[0029] 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.

[0030] (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."

[0031] (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.

[0032] (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.

[0033] (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.

[0034] ΔWA1=MGx(hg-ha) / L...(5)

[0035] (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.

[0036] ΔWA2=MGx・Rt / L…(6)

[0037] (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.

[0038] Fkfa=Fkf・tan(θkfa)…(7) Fkra=Fkr・tan(θkra)…(8)

[0039] (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.

[0040] ΔWB1=MGx(hg-hb) / L...(9)

[0041] (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.

[0042] Fmfa=Fmf・tan(θmfa)…(10) Fmra=Fmr・tan(θmra)…(11)

[0043] (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.

[0044] 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)

[0045] (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).

[0046] θp=ΔW / (2(Kpf+Kpr)・L)...(13)

[0047] (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.

[0048]

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] (Front-rear ratio adjustment control) Next, the main parts of the control device 16 of this embodiment will be described with reference to Figures 8 and 9. Figure 9 is an explanatory diagram showing an example of how the pitch angle θp changes over time when regenerative cooperative control is performed in a vehicle 1 having other specifications. The pitch angle θp shown in Figure 9 is an analysis result of the behavior of the regenerative braking forces Fkf, Fkr and the friction braking forces Fmf, Fmr when the front ratio f and rear ratio r are changed between values ​​0 and 1 in the example shown in Figure 2, with the friction rear-side anti-angle θmra of the vehicle 1 set to approximately 10 degrees (the other anti-angles θa are the same as in Table 1).

[0055] 8 and 9, when the execution of the switching control is started at time t2, the friction ratio m increases and the pitch angle θp decreases. Thereafter, the switching control is completed at time t3, and when the vehicle 1 stops at time t4, the required braking force Fb (i.e., the frictional braking forces Fmf, Fmr) becomes zero. Then, the load shift amount ΔW acting on the vehicle 1 by the frictional braking forces Fmf, Fmr also becomes zero, so the pitching motion of the vehicle 1 stops and the pitch angle θp becomes zero degrees. In particular, if the pitch angle θp becomes zero degrees after the vehicle 1 has stopped while changing its attitude to the nose dive side, the occupants of the vehicle 1 will feel a significant change in attitude, which will affect the ride comfort.

[0056] Therefore, during execution of regenerative cooperative control, before the switching control is completed, the control device 16 of this embodiment executes front-rear ratio adjustment control to adjust the front ratio f and the rear ratio r so that the pitch angle θp after the switching control is completed (hereinafter referred to as the "post-switching pitch angle θps") tends to approach 0 degrees. In this embodiment, the control device 16 completes the front-rear ratio adjustment control before the start of the switching control (time t2). As described above, the front-rear ratio adjustment control only needs to be completed at least before the completion of the switching control (time t3).

[0057] Furthermore, the front-rear ratio adjustment control may be initiated when the vehicle speed of the vehicle 1 reaches a predetermined vehicle speed. The predetermined vehicle speed is at least equal to or greater than a predetermined switching determination vehicle speed. The predetermined vehicle speed is preferably set as the lowest vehicle speed that ensures sufficient time to complete adjustment of the front ratio f and the rear ratio r without destabilizing the braking of the vehicle 1 before the switching control begins (or until the switching control is completed, if this control is performed before the switching control is completed). The front-rear ratio adjustment control is preferably performed when the pitch angle θp of the vehicle 1 remains constant (e.g., between time t10 and time t2 in FIGS. 8 and 9 ), that is, when the required braking force Fb remains constant for a predetermined period of time or longer. The switching control is performed within a deceleration range that does not lock the rotation of the front wheels 2f and the rear wheels 2r due to braking. Therefore, the time between time t2 and t3 when the vehicle 1 is decelerated at the limit deceleration at which the locking does not occur is the shortest time for which the switching control can be executed. Therefore, considering that front-rear ratio adjustment control must be completed at least by the time switching control is completed, the execution time of front-rear ratio adjustment control may be set to a time equivalent to the aforementioned shortest time. In other words, front-rear ratio adjustment control may be initiated at a time prior to time t2 or t3 that corresponds to the aforementioned shortest time. Note that the aforementioned shortest time may be obtained through experimentation or analysis based on vehicle specifications, and the time equivalent to the aforementioned shortest time may include a margin. In this example, it is assumed that front-rear ratio adjustment control is initiated at time t11 in FIGS. 8 and 9 .

[0058] (Post-Replacement Pitch Angle) The post-replacement pitch angle θps can be calculated according to equations (12) and (13) when the required braking force Fb is entirely set to the friction braking forces Fmf and Fmr. After the replacement control is completed, the load shift amounts ΔWA1, ΔWA2, and ΔWA3 based on the regenerative braking forces Fkf and Fkr can be considered to have a value of 0, and therefore equation (12) can be expressed by the following equation (14). If the load shift amount ΔW calculated by equation (14) has a value of 0, the post-replacement pitch angle θps calculated by equation (13) will be 0 degrees.

[0059] ΔW=mΔWB1+ΔWB2=mMGx(hg-hb) / L-Fmf・tan(θmfa)−Fmr・tan(θmra)...(14)

[0060] Therefore, assuming that the required braking force Fb at the start of front-rear ratio adjustment control (time t11) has been entirely replaced by frictional braking forces Fmf and Fmr, control device 16 calculates and obtains the post-replacement pitch angle θps when the front ratio f and rear ratio r are adjusted according to equations (13) and (14). This makes it possible to adjust the front ratio f and rear ratio r so that the post-replacement pitch angle θps approaches zero as closely as possible. Note that if the required braking force Fb fluctuates significantly after the start of front-rear ratio adjustment control, it is assumed that the driver has suddenly applied the brakes. In this case, the occupants of vehicle 1 are aware that sudden braking has occurred, and therefore, even if the post-replacement pitch angle θps deviates from the target and the vehicle 1 changes position after stopping, the discomfort felt by the occupants is likely to be minimal. Therefore, if the required braking force Fb fluctuates by more than a predetermined value after the start of front-rear ratio adjustment control, the front-rear ratio adjustment control may be continued or may be discontinued.

[0061] Furthermore, the control device 16 may use equations (13) and (14), or may obtain the relationship between the required braking force Fb, the front ratio f, the rear ratio r, and the post-segmentation pitch angle θps through prior analysis or experimentation, and store the obtained map. The control device 16 may then obtain from the map the post-segmentation pitch angle θps when the front ratio f and the rear ratio r are adjusted according to the required braking force Fb at the start of the front-rear ratio adjustment control. Depending on the attitude of the vehicle 1, the values ​​of "hg" and "hb" in equation (14) may fluctuate. Therefore, by creating the map in advance through analysis or experimentation, the post-segmentation pitch angle θps can be adjusted with greater precision.

[0062] (Example of Front-Rear Ratio Adjustment Control) In the example shown in FIG. 8 , when regenerative cooperative control is being executed with the front ratio f between 0.8 and 1, it can be seen that the post-switching pitch angle θps is larger toward the nose-dive side than 0 degrees. Therefore, the control device 16 increases the rear ratio r before time t2 when the switching control is started, as indicated by the white arrow in FIG. 8 . This allows the post-switching pitch angle θps to approach 0 degrees. On the other hand, when regenerative cooperative control is being executed with the front ratio f between 0 and 0.6, it can be seen that the post-switching pitch angle θps is larger toward the squat side than 0 degrees. Therefore, the control device 16 increases the front ratio f before time t2 when the switching control is started, as indicated by the black arrow in FIG. 8 . This allows the post-switching pitch angle θps to approach 0 degrees. In either case, it is preferable to adjust the front ratio f and the rear ratio r so that the post-switching pitch angle θps approaches 0 degrees as close as possible.

[0063] Furthermore, in the example shown in Figure 9, the friction rear anti-angle θmra is smaller than in the example shown in Table 1, and the friction rear anti-force Fmra is smaller, so all of the post-switching pitch angles θps are larger toward the nose dive side than 0 degrees. Therefore, as shown by the white arrow in Figure 9, the control device 16 increases the rear ratio r before time t2 when switching control is started. This makes it possible to bring the post-switching pitch angle θps closer to 0 degrees. In the example shown in Figure 9, it is preferable to increase the rear ratio r to a value of 1 so that the post-switching pitch angle θps approaches 0 degrees as much as possible.

[0064] As described above, the control device 16 of the embodiment executes front-rear ratio adjustment control to adjust the front ratio f and the rear ratio r before the switching control is completed so that the post-switching pitch angle θps, which is the pitch angle θp of the vehicle 1 after the switching control is completed, approaches 0 degrees. With this configuration, by adjusting the front ratio f and the rear ratio r before the switching control is completed, it is possible to suppress a sudden change in the pitch angle θp after the vehicle stops even when the posture of the vehicle 1 after the switching control is completed is on the nose dive or squat side. Therefore, the control device 16 can more effectively suppress pitching motion that occurs after the vehicle 1 stops when the regenerative cooperative control and the switching control are performed, thereby improving ride comfort.

[0065] In addition, the control device 16 assumes that the required braking force Fb at the start of the front-rear ratio adjustment control has been entirely converted to friction braking forces Fmf, Fmr through the switching control, and obtains the post-switching pitch angle θps when the front ratio f and rear ratio r are adjusted. This configuration makes it possible to easily obtain the post-switching pitch angle θps.

[0066] The control device 16 also sets the intersection of an extension line L4 of the friction front anti-angle θmfa, which is the anti-nose dive angle θaD of the vehicle 1, and an extension line L5 of the friction rear anti-angle θmra, which is the anti-tail lift angle θaL, as a second instantaneous center of rotation B (instantaneous center of rotation), and obtains the post-replacement pitch angle θps based on the sum of the load shift amounts ΔWB1 and ΔWB2 due to the inertial force and antiforce acting on the springs due to the friction braking forces Fmf and Fmr at the second instantaneous center of rotation B. With this configuration, the post-replacement pitch angle θps can be obtained with high accuracy, taking the second instantaneous center of rotation B into consideration.

[0067] Furthermore, the control device 16 completes the front-rear ratio adjustment control before the start of the switching control. With this configuration, the front ratio f and rear ratio r are not adjusted while the regenerative braking forces Fkf, Fkr are being switched to the friction braking forces Fmf, Fmr, and stable braking of the vehicle can be performed during the switching control.

[0068] Furthermore, the control device 16 increases the rear ratio r when the post-switching pitch angle θps is greater than 0 degrees toward the nose dive side, and decreases the rear ratio r when the post-switching pitch angle θps is greater than 0 degrees toward the squat side. With this configuration, the magnitude of the antiforce due to the rear friction braking forces Fmf and Fmr can be adjusted to bring the post-switching pitch angle θps closer to 0 degrees.

[0069] Although the description of the embodiment has been completed, aspects of the present invention are not limited to this embodiment. For example, the front-rear ratio adjustment control may adjust the front ratio f and the rear ratio r so that the post-switching pitch angle θps changes at least to a tendency for the posture of the vehicle 1 to move from a nose-dive to a squat. That is, when the front ratio f is between 0.8 and 1 in FIG. 8 , the rear ratio r may be increased until the post-switching pitch angle θps falls below 0 degrees and moves to the negative side, i.e., the squat. In this case, an attitude change occurs after the vehicle 1 stops, from a squat posture to a pitch angle θp of 0 degrees. However, this behavior is an attitude change in the same direction as the attitude change that occurs when the vehicle 1 decelerates, in which the pitch angle moves toward a nose-dive. On the other hand, when an attitude change occurs after the vehicle 1 stops, from a nose-dive posture to a pitch angle θp of 0 degrees, the behavior is opposite to the attitude change during deceleration, and the occupant is likely to feel the attitude change. In other words, even if a posture change occurs in which the pitch angle θp changes from a squat posture to 0 degrees, it is thought that the passenger will feel relatively little discomfort. Therefore, if it is possible to at least prevent the phenomenon in which the pitch angle θp changes from nose dive to 0 degrees after the vehicle 1 has stopped, it will be possible to improve the riding comfort of the passenger.

[0070] Furthermore, in this embodiment, the anti-tail lift angle θaL of the vehicle 1 is larger than the anti-nose dive angle θaD, but the control device 16 of the embodiment may be applied to a vehicle in which the anti-nose dive angle θaD is larger than the anti-tail lift angle θaL. In that case, the front ratio f may be increased when the post-replacement pitch angle θps is larger than 0 degrees toward the nose dive side, and the front ratio f may be decreased when the post-replacement pitch angle θps is larger than 0 degrees toward the squat side. With this configuration, the magnitude of the antiforces (Fmfa, Fmra) due to the front friction braking forces Fmf, Fmr can be adjusted to bring the post-replacement pitch angle θps closer to 0 degrees.

[0071] 1 Vehicle 1a Body frame 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 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 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) θps: Pitch angle after switching

Claims

1. A braking control device that executes: a regenerative cooperative control that uses 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; and a switching control that switches the regenerative braking force share of the required braking force to the frictional braking force when the vehicle speed falls below a predetermined switching judgment vehicle speed while the regenerative cooperative control is being executed; and a front-rear ratio adjustment control that adjusts the front ratio and rear ratio, which are the distribution ratio of the braking force applied to the front wheels and the braking force applied to the rear wheels, so that the post-switching pitch angle, which is the pitch angle of the vehicle after the switching control is completed, at least changes the attitude of the vehicle from a state on the nose dive side to a state tending toward the squat side until the switching control is completed.

2. A braking control device as described in claim 1, which acquires the post-switching pitch angle when the front ratio and the rear ratio are adjusted, assuming that the required braking force at the start of the front-rear ratio adjustment control has been entirely converted to the frictional braking force by the switching control.

3. A braking control device as described in claim 2, wherein the intersection point of an extension line of a friction front side anti-angle, which is the anti-nose dive angle of the vehicle, and an extension line of a friction rear side anti-angle, which is the anti-tail lift angle, is set as the instantaneous center of rotation, and the post-switching pitch angle is obtained based on the sum of the load movement due to the inertial force and anti-force acting on a spring located above the suspension of the vehicle due to the friction braking force at the instantaneous center of rotation.

4. A brake control device as set forth in claim 1, wherein the front-rear ratio adjustment control is completed before the switching control is started.

5. A brake control device according to any one of claims 1 to 4, which adjusts the front ratio and the rear ratio so that the post-switching pitch angle approaches 0 degrees.

6. A brake control device as described in claim 5, wherein, when the anti-tail lift angle of the vehicle is greater than the anti-nose dive angle, the rear ratio is increased when the post-switching pitch angle is greater than 0 degrees on the nose dive side, and the rear ratio is decreased when the post-switching pitch angle is greater than 0 degrees on the squat side.

7. A brake control device as described in claim 5, wherein, when the anti-nose dive angle of the vehicle is greater than the anti-tail lift angle, the front ratio is increased when the post-switching pitch angle is greater than 0 degrees on the nose dive side, and the front ratio is decreased when the post-switching pitch angle is greater than 0 degrees on the squat side.

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