Vehicle control method and vehicle

Abstract

To improve a brake feeling in a plurality of deceleration areas.SOLUTION: A vehicle includes a brake device, and an electronic control unit. The brake device can change a fore-and-aft distribution ratio of brake forces related to front wheels and rear wheels. The electronic control unit controls the brake device. The electronic control unit controls the brake device so as to attain a fore-and-aft distribution ratio following a fixed distribution characteristic with a constant fore-and-aft distribution ratio regardless of deceleration, in at least a part of a first area that is a request deceleration area where deceleration is lower than a lower limit value of deceleration perceivable by an occupant. Further, the electronic control unit controls the brake device so as to attain a fore-and-aft distribution ratio that is more on a rear wheel side than in the fixed distribution characteristic, in a second area where deceleration is higher than that in the first area.SELECTED DRAWING: Figure 10

Description

[Technical field]

[0001] The present disclosure relates to a vehicle control method and a vehicle. [Background technology]

[0002] Patent Document 1 discloses a braking force control device that generates a braking force command value by filtering a required braking force based on a braking operation amount in order to improve the brake feeling, and changes the damping ratio of the filtering in response to changes in the required braking force. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-203751 A Summary of the Invention [Problem to be solved by the invention]

[0004] The inventors of the present invention have diligently studied and obtained the following knowledge. That is, a vehicle occupant feels a braking sensation not only from the occurrence of vehicle body deceleration but also from a combination of the occurrence of the deceleration and a change in the vehicle posture. In order to improve the braking sensation (more specifically, for example, the sense of deceleration and the sense of security regarding braking), it is effective to make the occupant perceive a change in the vehicle braking posture (the vehicle posture during braking) that brings about a visual or physical change to the occupant that leads to an improvement in the braking sensation. The change in the vehicle braking posture that leads to an improvement in the braking sensation differs depending on the deceleration range during braking. The technology described in Patent Document 1 does not pay attention to such knowledge, and there is still room for improvement in this respect.

[0005] The present disclosure has been made in consideration of the above-mentioned problems, and has an object to provide a vehicle control method and a vehicle that are capable of improving the braking feel in a plurality of deceleration regions. [Means for solving the problem]

[0006] A vehicle control method according to the present disclosure is a method for controlling a vehicle equipped with a braking device configured to be able to change a front / rear distribution ratio of braking force for front and rear wheels. This vehicle control method includes controlling the braking device so that the front / rear distribution ratio conforms to a fixed distribution characteristic that keeps the front / rear distribution ratio constant regardless of deceleration in at least a part of a first region, which is a required deceleration region below a lower limit value of deceleration perceptible by a passenger, and controlling the braking device so that the front / rear distribution ratio is more rear-wheel-biased than the fixed distribution characteristic in a second region where deceleration is higher than in the first region.

[0007] A vehicle according to the present disclosure includes a braking device and an electronic control unit. The braking device is configured to be able to change a front / rear distribution ratio of braking force for the front and rear wheels. The electronic control unit controls the braking device. The electronic control unit controls the braking device so that, in at least a part of a first region, which is a required deceleration region below a lower limit value of deceleration perceptible by a passenger, the front / rear distribution ratio is in accordance with a fixed distribution characteristic in which the front / rear distribution ratio is constant regardless of deceleration. The electronic control unit also controls the braking device so that, in a second region in which deceleration is higher than in the first region, the front / rear distribution ratio is closer to the rear wheels than the fixed distribution characteristic. Effect of the Invention

[0008] According to the present disclosure, in the first region of the required deceleration, a front-rear distribution ratio suitable for actively generating a pitch change is selected compared to the second region. This makes it possible to make a passenger, such as a driver, feel a sense of deceleration before the deceleration is perceived by utilizing the perception due to a visual change accompanying the movement of the head caused by the pitch change. As a result, the sense of deceleration in the first region can be improved. Also, in the second region, a front-rear distribution ratio suitable for actively generating an increase in the amount of heave (sinking of the vehicle body) compared to the first region is selected. This makes it possible to improve the passenger's sense of security regarding braking.

[0009] As described above, according to the braking force distribution characteristic obtained by changing the front / rear distribution ratio in accordance with the vehicle body deceleration according to the present disclosure, it is possible to satisfactorily improve the braking feel in a plurality of deceleration ranges. [Brief description of the drawings]

[0010] [Figure 1] 1 is a diagram illustrating an example of a configuration of a vehicle according to a first embodiment. [Diagram 2] 11 is a diagram for explaining the displacement amounts ΔXf and ΔXr of the front and rear suspensions relative to the braking force. FIG. [Diagram 3] FIG. 2 is a diagram showing a vehicle attitude during braking (vehicle braking attitude). [Figure 4] FIG. 4 is a diagram showing a fixed distribution characteristic and an ideal distribution characteristic used for comparing braking force distribution characteristics. [Diagram 5] 11 is a diagram showing a comparison of the characteristics of the pitch angle θ with respect to the deceleration Gx between a fixed distribution characteristic and an ideal distribution characteristic. FIG. [Figure 6] 1 is a diagram showing a comparison of the characteristics of the heave amount H at the center of gravity position with respect to the deceleration Gx between a fixed distribution characteristic and an ideal distribution characteristic. [Figure 7] FIG. 13 is a diagram for explaining the influence of the front-rear distribution ratio α on the change in head position caused by changes in pitch and heave accompanying braking, with the head position of a vehicle occupant being the subject. [Figure 8] FIG. 2 is a diagram for explaining the time process that elapses from when a driver depresses the brake pedal until the driver feels a braking sensation. [Figure 9] FIG. 1 is a diagram for explaining perception thresholds of pitch motion and heave motion. [Figure 10] FIG. 4 is a diagram for explaining a braking force distribution characteristic A used in the first embodiment. [Figure 11] 4 is a flowchart showing a process related to braking force distribution control according to the first embodiment. [Figure 12] 13 is a flowchart showing a modified example of the process of step S104. [Figure 13]4 is a diagram showing a comparison of the relationship between the pitch angle θ and the deceleration Gx between braking force distribution characteristics according to the first embodiment. FIG. [Figure 14] 4 is a diagram showing a comparison of the relationship between the amount of heave H and the deceleration Gx between braking force distribution characteristics according to the first embodiment. FIG. [Figure 15] FIG. 11 is a diagram showing an example of the relationship between the required deceleration Gxr and the ratio β related to the front wheels according to the second embodiment. [Figure 16] FIG. 11 is a diagram showing a comparison of the relationship between the pitch angle θ and the deceleration Gx between braking force distribution characteristics according to the second embodiment. [Figure 17] FIG. 11 is a diagram showing a comparison of the relationship between the amount of heave H and the deceleration Gx between braking force distribution characteristics according to the second embodiment. [Figure 18] 11 is a block diagram showing an example of the configuration of a vehicle control system provided in a vehicle according to a third embodiment. FIG. [Figure 19] 11 is a flowchart showing a process related to braking force distribution control according to the third embodiment. [Figure 20] 13 is a diagram showing braking force distribution characteristics A and B used in the third embodiment. FIG. [Figure 21] FIG. 11 is a diagram showing a comparison of the relationship between the pitch angle θ and the deceleration Gx between braking force distribution characteristics according to the third embodiment. [Figure 22] FIG. 11 is a diagram showing a comparison of the relationship between the amount of heave H and the deceleration Gx between braking force distribution characteristics according to the third embodiment. [Figure 23] 13 is a flowchart showing a process related to braking force distribution control according to the fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] In the embodiments described below, when reference is made to the number, quantity, amount, range, etc. of each element, the technical idea of ​​this disclosure is not limited to the mentioned numbers, unless otherwise specified or clearly specified in principle to that number.

[0012] 1. First embodiment 1-1.Vehicle configuration examples 1 is a diagram illustrating an example of a configuration of a vehicle 1 according to a first embodiment. The vehicle 1 has four wheels 2. In the following description, the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel are referred to as 2FL, 2FR, 2RL, and 2RR, respectively. There are also cases where the front wheels are collectively referred to as 2F, and the rear wheels are collectively referred to as 2R.

[0013] The vehicle 1 includes a front wheel electric motor 10F that drives the front wheels 2F via a front wheel drive shaft 3F, and a rear wheel electric motor 10R that drives the rear wheels 2R via a rear wheel drive shaft 3R. More specifically, the vehicle 1 is, as an example, a battery electric vehicle (BEV) that is driven by electric motors 10F and 10R that operate with power supplied from a battery 12. However, the "vehicle" according to the present disclosure may also be, for example, a hybrid electric vehicle (HEV) that includes an internal combustion engine together with an electric motor as a power source.

[0014] The vehicle 1 is equipped with a braking device 20. The braking device 20 includes a brake pedal 22, a master cylinder 24, a brake actuator 26, a brake mechanism 28, and hydraulic piping 30. The master cylinder 24 generates hydraulic pressure according to the depression force of the brake pedal 22, and supplies the generated hydraulic pressure (brake hydraulic pressure) to the brake actuator 26.

[0015] The brake actuator 26 includes a hydraulic circuit (not shown) that is interposed between the master cylinder 24 and the brake mechanism 28. The hydraulic circuit includes a pump for increasing the brake hydraulic pressure without relying on the master cylinder pressure, a reservoir for storing brake fluid, and a plurality of electromagnetic valves.

[0016] The brake actuator 26 is connected to a brake mechanism 28 via hydraulic piping 30. The brake mechanism 28 is disposed on each wheel 2. The brake actuator 26 distributes brake hydraulic pressure to the brake mechanism 28 of each wheel 2. More specifically, the brake actuator 26 can supply brake hydraulic pressure to the brake mechanism 28 of each wheel 2 using the master cylinder 24 or the pump as a pressure source. The brake mechanism 28 has a wheel cylinder 28a that operates in response to the supplied brake hydraulic pressure. By operating the wheel cylinder 28a by the brake hydraulic pressure, the brake pads are pressed against the brake discs. As a result, a frictional braking force is applied to the wheel 2.

[0017] Furthermore, the brake actuator 26 can independently adjust the brake hydraulic pressure applied to each wheel 2 by controlling various electromagnetic valves provided in the hydraulic circuit. More specifically, the brake actuator 26 has a pressure increase mode for increasing the pressure, a pressure holding mode for holding the pressure, and a pressure reduction mode for decreasing the pressure as control modes of the brake hydraulic pressure. The brake actuator 26 can vary the control mode of the brake hydraulic pressure for each wheel 2 by controlling ON / OFF of various electromagnetic valves. The friction braking force applied to each wheel 2 is determined according to the brake hydraulic pressure supplied to the respective wheel cylinders 28a. By changing the control mode in this way, the brake actuator 26 can independently control the braking force of each wheel 2.

[0018] The braking device 20 also includes a regenerative braking device 34. Specifically, the vehicle 1 includes an inverter 32 for driving the electric motors 10F and 10R. The inverter 32 is controlled based on commands from an ECU 40, which will be described later. Under the control of the inverter 32, the electric motors 10F and 10R function as electric motors that generate vehicle drive torque. The electric motors 10F and 10R also function as generators that generate regenerative torque (negative torque) by being driven by the rotation of the wheels 2F and 2R during vehicle deceleration. The magnitude of the regenerative torque is controlled by the inverter 32.

[0019] The regenerative braking device 34 includes electric motors 10F and 10R and an inverter. 32 In this way, the regenerative braking device 34 can control a front wheel regenerative braking force applied to the front wheels 2F using the front wheel electric motor 10F, and a rear wheel regenerative braking force applied to the rear wheels 2R using the rear wheel electric motor 10R.

[0020] Furthermore, the vehicle 1 includes an electronic control unit (ECU) 40. The ECU 40 includes a processor, a storage device, and an input / output interface. The input / output interface takes in sensor signals from various sensors attached to the vehicle 1, and outputs operation signals to the electric motors 10F and 10R, various actuators such as the brake actuator 26, and the inverter 32. The storage device stores various control programs for controlling the various actuators and the inverter 32. The processor reads out and executes the control programs from the storage device, thereby realizing various controls using the various actuators and the inverter 32. Note that there may be multiple ECUs 40.

[0021] The various sensors described above include, for example, a wheel speed sensor 42, a longitudinal acceleration sensor 44, and a brake position sensor 46. The wheel speed sensors 42 are disposed corresponding to each wheel 2, and output a wheel speed signal corresponding to the rotational speed of the wheel 2. The longitudinal acceleration sensor 44 outputs an acceleration signal corresponding to the longitudinal acceleration (longitudinal G) of the vehicle 1. The brake position sensor 46 outputs a signal corresponding to the amount of depression of the brake pedal 22.

[0022] 1-2.Braking control The braking device 20 having the above-mentioned configuration can change the front / rear distribution ratio α of the braking force for the front wheels 2F and the rear wheels 2R. When braking force is generated on the front wheels 2F and the rear wheels 2R, reaction forces are generated in the suspensions 4F and 4R (see FIG. 2 described later) according to the generated braking force. When the generated suspension reaction force changes, the vehicle posture during braking (hereinafter also referred to as "vehicle braking posture") changes. The suspension reaction force can be controlled by adjusting the front / rear distribution ratio of the braking force.

[0023] In this embodiment, therefore, in order to realize a vehicle braking posture that provides a passenger with a high braking feeling (more specifically, for example, a feeling of deceleration and a sense of security regarding braking) by utilizing the suspension reaction force, braking force distribution control is executed in consideration of the vehicle posture. In this braking force distribution control, the front / rear distribution ratio α of the braking force is changed according to the region of the required deceleration Gxr.

[0024] 1-2-1. Changes in vehicle dynamic posture due to changes in front-rear distribution ratio Figure 2 shows the displacement ΔX of the front and rear suspensions 4F and 4R relative to the braking force. f and ΔX r The front / rear distribution ratio α of the braking force is the ratio of the front wheel braking force to the sum of the braking force applied to the front wheels 2F (front wheel braking force) and the braking force applied to the rear wheels 2R (rear wheel braking force) (i.e., the total braking force F). Therefore, the front wheel braking force is αF, and the rear wheel braking force is (1-α)F.

[0025] More specifically, in the example of the vehicle 1 equipped with the braking device 20 including the regenerative braking device 34, each of the front wheel braking force and the rear wheel braking force is the sum of the friction braking force and the regenerative braking force. Here, the ratio of the front wheel regenerative braking force to the front wheel braking force (front wheel regenerative distribution ratio) is referred to as β, and the ratio of the rear wheel regenerative braking force to the rear wheel braking force (rear wheel regenerative distribution ratio) is referred to as γ. In this case, each braking force is expressed as follows: Front wheel regenerative braking force: αβF Front wheel friction braking force: α(1-β)F Rear wheel regenerative braking force: (1-α)γF Rear wheel Friction braking force: (1-α)(1-γ)F

[0026] FIG. 2 shows the suspension displacement ΔX when a braking force is applied to the vehicle 1. f and ΔX r That is, as shown in FIG. 2, when braking, the posture of the vehicle body (sprung structure) 5 changes so that the front wheel side sinks and the rear wheel side rises. Therefore, the front wheel side suspension 4F strokes toward the compression side, and the rear wheel side suspension 4R strokes toward the extension side. The amount of suspension displacement ΔX during such braking is f and ΔX r is expressed by the following equations (1) and (2).

[0027]

number

[0028] In the above formulas (1) and (2), W B is the wheelbase, which is known. h is the height of the center of gravity when the vehicle is stationary, which is known. k f and k r are the spring constants of the springs of the suspensions 4F and 4R, respectively, and are known.

[0029] Moreover, AntiDive is the anti-dive rate. AntiLift_f and AntiLift_r are the anti-lift rates of the front and rear wheels, respectively. AntiSquat is the anti-squat rate. More specifically, the suspension 4F has a suspension geometry that generates an anti-dive force and an anti-lift force, which are suspension reaction forces, in association with the generation of a braking force. Moreover, the suspension 4R has a suspension geometry that generates an anti-lift force and an anti-squat force, which are suspension reaction forces, in association with the generation of a braking force. The anti-dive rate, the anti-lift rate, and the anti-squat rate in the formulas (1) and (2) are values ​​that indicate the vertical reaction force ratio, and are known values ​​determined by the specifications of the suspensions 4F and 4R.

[0030] In equation (1), h / WB and the total braking force F is related to the amount of load transfer of the vehicle body 5, and corresponds to the force that sinks the front wheel side of the vehicle body 5 downward due to the load transfer. The product of the front wheel friction braking force α(1-β)F and AntiDive corresponds to the force that lifts the front wheel side of the vehicle body 5 upward due to the anti-dive force that acts in conjunction with the generation of the front wheel friction braking force α(1-β)F. The product of the front wheel regenerative braking forces αβF and AntiLift_f corresponds to the force that lifts the front wheel side of the vehicle body 5 upward due to the anti-lift force that acts in conjunction with the generation of the front wheel regenerative braking force αβF.

[0031] In equation (2), h / W B and the total braking force F corresponds to a force that lifts the rear wheel side of the vehicle body 5 upward due to load transfer. The product of the rear wheel friction braking force (1-α)(1-γ)F and AntiLift_r corresponds to a force that sinks the rear wheel side of the vehicle body 5 downward due to an anti-lift force that acts in conjunction with the generation of the rear wheel friction braking force (1-α)(1-γ)F. The product of the rear wheel regenerative braking force (1-α)γF and AntiSquat corresponds to a force that sinks the rear wheel side of the vehicle body 5 downward due to an anti-squat force that acts in conjunction with the generation of the rear wheel regenerative braking force (1-α)γF.

[0032] In addition, as shown in Fig. 2, the points of application of the frictional braking force and the regenerative braking force are different for the front wheels 2F and the rear wheels 2R. That is, the frictional braking force acts on the contact surface of the wheels 2. On the other hand, the regenerative torque generated by the electric motor 10F is input to the front wheels 2F via the front drive shaft 3F, so the regenerative braking force acts on the center position of the front wheels 2F. Similarly, the regenerative torque generated by the electric motor 10R is input to the rear wheels 2R via the rear drive shaft 3R, so the regenerative braking force acts on the center position of the rear wheels 2R.

[0033] The suspension displacement ΔX calculated by the above formulas (1) and (2) f and ΔX r By utilizing the above, the pitch angle θ of the vehicle 1 that changes due to braking, the heave amount H at the center of gravity of the vehicle 1, and the pitch center position P are expressed by the following equations (3) to (5), respectively. fis the distance between the front wheel drive shaft 3F and the center of gravity, and is known.

[0034]

number

[0035] FIG. 3 is a diagram showing the vehicle posture during braking (vehicle braking posture). During braking, an inertial force equal to the total braking force F acts toward the front of the vehicle. As a result, as shown in FIG. 3, a pitch change occurs in the vehicle 1 such that the front wheels sink, and a heave change occurs (vertical displacement of the vehicle body 5). The manner in which the pitch angle θ and the heave amount H change with braking changes by changing the front-rear distribution ratio α. This is because, when the front-rear distribution ratio α changes, the suspension displacement amount ΔX expressed by the above formulas (1) and (2) changes. f and ΔX r This is because changes.

[0036] The manner in which the pitch angle θ and the heave amount H change with braking can also be changed by changing the ratios (regeneration distribution ratios) β and γ. In the first embodiment, however, as an example, the ratios β and γ are constant regardless of the deceleration Gx (see FIG. 15, described later). Changing the pitch angle θ and the heave amount H by changing the ratios β and γ will be described in the second embodiment, described later.

[0037] Next, changes in the pitch angle θ and the heave amount H accompanying changes in the front / rear distribution ratio α will be described with reference to Fig. 4 to Fig. 6. Fig. 4 is a diagram showing fixed distribution characteristics and ideal distribution characteristics used for comparing braking force distribution characteristics.

[0038] The "fixed distribution characteristic" here refers to a braking force distribution characteristic that realizes a front / rear distribution ratio α that is constant regardless of the deceleration Gx of the vehicle 1. This fixed distribution characteristic is realized, for example, by applying equal hydraulic pressure to the wheel cylinders 28a of the front wheels 2F and the rear wheels 2R. Generally, due to differences in brake specifications between the front and rear wheels, the fixed distribution characteristic results in a braking force distribution characteristic that is biased toward the front wheels, for example, a front / rear distribution ratio α of 0.7.

[0039] The "ideal distribution characteristic" here refers to a braking force distribution characteristic that realizes a front / rear distribution ratio α such that the front wheels 2F and rear wheels 2R lock simultaneously when braking. As shown in Fig. 4, when compared at the same deceleration Gx, the ideal distribution characteristic is a braking force distribution characteristic that is generally biased toward the rear wheels compared to the fixed distribution characteristic.

[0040] 5 is a graph showing the characteristics of the pitch angle θ with respect to the deceleration Gx, comparing the fixed distribution characteristics with the ideal distribution characteristics. According to equation (3), the pitch angle θ is calculated by the suspension displacement amount ΔX according to equations (1) and (2). f and ΔX r As a result, the pitch angle θ in the fixed distribution characteristic increases monotonically as the deceleration Gx increases. In contrast, as shown in FIG. 5, in the ideal distribution characteristic, the pitch angle θ is smaller overall than in the fixed distribution characteristic. More specifically, in a comparison at the same deceleration Gx, the difference in the pitch angle θ basically increases as the difference in the front / rear distribution ratio α increases. In this way, in the ideal distribution characteristic, the increase in the pitch angle θ is suppressed due to the braking force distribution being biased toward the rear wheels compared to the fixed distribution characteristic.

[0041] FIG. 6 is a graph showing the characteristics of the heave amount H at the center of gravity position against the deceleration Gx, comparing the fixed distribution characteristics with the ideal distribution characteristics. According to the formula (4), the heave amount H is calculated by multiplying the suspension displacement amount ΔX by the formulas (1) and (2). f and ΔX r of Calculation result and pitch angle according to formula (3) θ As a result, the heave amount H in the fixed distribution characteristic increases monotonically with an increase in the deceleration Gx. In the example shown in FIG. 6, the heave amount H takes a negative value with braking, that is, the vehicle body 5 is displaced downward.

[0042] On the other hand, as shown in Fig. 6, in the ideal distribution characteristic, the heave amount H is larger overall than in the fixed distribution characteristic. More specifically, when comparing at the same deceleration Gx, the difference in the heave amount H basically increases as the difference in the front / rear distribution ratio α increases. In this way, in the ideal distribution characteristic, the braking force distribution is biased toward the rear wheels compared to the fixed distribution characteristic, which promotes an increase in the heave amount H (sinking of the vehicle body 5).

[0043] As can be seen from the description with reference to Figs. 4 to 6, by changing the front / rear distribution ratio α, it is possible to control the pitch angle θ and the heave amount H during braking.

[0044] Next, Fig. 7 is a diagram for explaining the influence of the front-rear distribution ratio α on the change in head position caused by changes in pitch and heave due to braking, with the head position of an occupant of the vehicle 1 as the subject. Note that in this explanation as well, the fixed distribution characteristic and the ideal distribution characteristic shown in Fig. 4 are used for comparison of braking force distribution characteristics.

[0045] 7(A) is a diagram for explaining the influence of the front / rear distribution ratio α on the relationship between the pitch center position P and the deceleration Gx. In a fixed distribution characteristic in which the front / rear distribution ratio α is constant regardless of the deceleration Gx, the pitch center position P1 is constant regardless of the deceleration Gx. In contrast, the pitch center position P in the ideal distribution characteristic changes according to the deceleration Gx. More specifically, the pitch center position P in the ideal distribution characteristic is generally located toward the rear of the vehicle compared to the fixed distribution characteristic, and approaches the pitch center position P1 of the fixed distribution characteristic as the deceleration Gx increases.

[0046] FIG. 7(A) shows a reference line L0 connecting the rotational axis of the front wheel 2F and the rotational axis of the rear wheel 2R when the vehicle is stationary, a reference line L1 when the fixed distribution characteristic is selected, and a reference line L2 when the ideal distribution characteristic is selected. The reference line L1 shows a change in the reference line when a pitch change occurs under a certain deceleration Gx. The reference line L2 shows, as an example, a change in the reference line when a pitch change occurs around the pitch center position P2 when the pitch center position P is on the rotational center axis of the rear wheel 2R. FIG. 7(A) also shows the head 7F of the passenger in the front seat 6F and the head 7R of the passenger in the rear seat 6R. The positions of these heads 7F and 7R are shown corresponding to the three reference lines L0, L1, and L2, respectively.

[0047] As described with reference to Fig. 7(A), by changing the front-rear distribution ratio α, the pitch center position P during braking changes. In association with the change in the pitch center position P, the pitch attitude of the vehicle body (sprung structure) 5 including the heave change (i.e., the vehicle braking attitude) changes. As a result, as shown in the following Figs. 7(B) and 7(C), it becomes possible to change the amount of movement of the head position of the passenger in the front-rear and up-down directions associated with braking.

[0048] Fig. 7(B) is a diagram for explaining the effect of the front-to-rear distribution ratio α on the amount of movement in the front-to-rear and up-to-down directions of the head 7F of the passenger in the front seat 6F. An example will be explained using a plot point where the deceleration Gx is 0.1G. With the fixed distribution characteristic, the amount of movement in the up-to-down direction of the head 7F is small, but the amount of movement in the front-to-rear direction is large. On the other hand, with the ideal distribution characteristic that distributes the braking force toward the rear wheels, the amount of movement in the front-to-rear direction of the head 7F is kept small compared to the fixed distribution characteristic.

[0049] Fig. 7(C) is a diagram for explaining the influence of the front-rear distribution ratio α on the amount of movement of the head 7R of the passenger in the rear seat 6R in the front-rear and up-down directions. This figure will also be explained using the plot point where the deceleration Gx is 0.1G as an example. With the fixed distribution characteristic, the head 7R moves forward and is lifted upward as a result of braking. In contrast, with the ideal distribution characteristic, the amount of movement in the up-down direction is suppressed compared to the fixed distribution characteristic, and the amount of movement in the front-rear direction is also kept small.

[0050] As shown in FIG. 7(B) and FIG. 7(C), it is understood that the forward and backward movement amount of the heads 7F and 7R (more specifically, the forward movement amount of the heads 7F and 7R) can be suppressed by changing the front-rear distribution ratio α. That is, a vehicle braking posture that is more comfortable and reassuring for the passenger in the front seat 6F can be obtained. Also, as shown in FIG. 7(C), it is understood that for the rear seat 6R, the vertical movement amount of the head 7R can be suppressed by changing the front-rear distribution ratio α. This also leads to a vehicle braking posture that is more comfortable and reassuring for the passenger in the rear seat 6R. Also, it is understood that for the front seat 6F, the downward movement amount of the head 7F can be increased by changing the front-rear distribution ratio α. In this way, the downward sinking movement of the head 7F and the body can give the passenger a sense of security that the vehicle 1 is stuck to the road surface during braking. This also leads to a vehicle braking posture that is more comfortable and reassuring. Also, it is understood that for the rear seat 6R, the upward movement amount of the head 7R can be suppressed by changing the front-rear distribution ratio α. Such a movement that suppresses the upward movement of the head 7R and the body also gives the occupant a sense of security during braking, as if the vehicle 1 is stuck to the road surface.

[0051] 1-2-2. Braking sensation perception Next, FIG. 8 is a diagram for explaining the time process that passes from when the driver depresses the brake pedal 22 until the driver feels braking.

[0052] First, at time t0, when the driver starts to depress the brake pedal 22, braking begins. Specifically, the brake pedal 22 strokes due to the driver's depressing force, and as a result, hydraulic pressure is generated in the master cylinder 24. Next, brake hydraulic pressure corresponding to the hydraulic pressure generated in the master cylinder 24 acts on the wheel cylinder 28a. As a result, the brake pads are pressed against the brake discs, generating a braking torque, and a braking force is applied to the wheels 2. As a result, a suspension reaction force such as the anti-dive force described above is generated, and deceleration Gx occurs in the vehicle body 5 (time t1). The process up to this point is called the "absolute performance" of the vehicle 1 realized by the braking function of the vehicle 1, and is distinguished from the "sensible performance" that follows. This sensible performance is the performance that a passenger such as a driver perceives through the five senses.

[0053] When deceleration Gx occurs, a load transfer occurs in the vehicle body (sprung structure) 5. The load transfer causes a change in the sprung posture (vehicle posture). The change in the sprung posture at this time occurs due to the influence of not only the load transfer but also the suspension reaction force described above. The time t2 at which a passenger such as a driver actually feels the deceleration Gx as a braking sensation (deceleration sensation) is delayed from the time t1 at which the deceleration Gx occurs in the vehicle body 5. In other words, it is considered that the passenger feels the braking sensation due to a combination of the occurrence of the deceleration Gx in the vehicle body 5 and the change in the sprung posture.

[0054] More specifically, it is considered that the driver or other passengers may feel a sense of security in braking or may feel less deceleration depending on how the sprung posture is changed. In other words, controlling the vehicle braking posture by changing the front / rear distribution ratio α means that the sensation that the passengers receive from braking can be changed.

[0055] Next, Fig. 9 is a diagram for explaining the perception threshold of pitch motion and heave motion. As already explained, the vehicle motion related to the change in the vehicle braking attitude includes pitch motion and heave motion. The perception threshold here corresponds to the amount of change in each motion (more specifically, the rate of change or the acceleration of change) required for a person to perceive the pitch change and the heave change, and is evaluated by a prior test or the like.

[0056] FIG. 9 shows the perception thresholds for each type of motion, both for visual perception and for bodily perception (e.g., perception using changes in acceleration). The smaller the perception threshold, the easier it is for a person to perceive vehicle motion. Therefore, FIG. 9 shows that pitch changes are more easily perceived visually than bodily. In other words, it is clear that passengers such as the driver can easily sense pitch changes through visual changes. On the other hand, it is clear that heave changes are more easily perceived bodily than visually. In other words, it is clear that passengers such as the driver can easily sense heave changes through bodily sensations such as changes in the vehicle's vertical acceleration.

[0057] 1-2-3. Brake force distribution control considering vehicle posture Fig. 10 is a diagram for explaining the braking force distribution characteristic A used in the embodiment 1. For comparison with the braking force distribution characteristic A, Fig. 10 also shows the same fixed distribution characteristic and ideal distribution characteristic as shown in Fig. 4.

[0058] As described above, the passenger of the vehicle 1 feels the braking sensation not only from the occurrence of the deceleration Gx but also from a combination of the occurrence of the deceleration Gx and a change in the vehicle posture. Therefore, in order to improve the braking sensation (more specifically, for example, the sense of deceleration and the sense of security regarding braking), it is effective to make the passenger perceive a change in the vehicle braking posture that brings about a visual or physical change to the passenger that leads to an improvement in the braking sensation.

[0059] Furthermore, the change in vehicle braking posture that leads to an improvement in the braking feeling differs depending on the region of the deceleration Gx. Specifically, attention is paid here to a reduced speed region R1 and a medium deceleration region R2 related to the deceleration Gxr requested by the driver. The reduced speed region R1 and the medium deceleration region R2 correspond to examples of the "first region" and the "second region" according to the present disclosure, respectively.

[0060] The reduced speed region R1 is the lower limit Gx of the deceleration Gx that can be perceived by a driver or other passenger. LMT The required deceleration is below the lower limit Gx LMT is a value that can be known in advance by testing or the like, for example, 0.1 G. Alternatively, the lower limit Gx LMT For example, the deceleration Gx may be 0.15 G. In such a reduced speed region R1, the driver does not feel the deceleration Gx, or at least it is difficult for the driver to feel the deceleration Gx. However, if the driver can be made to perceive that a pitch change is occurring during braking using the reduced speed region R1, the following effects can be obtained.

[0061] That is, the driver knows from experience that the body, including the head 7F, tends to move forward when the driver depresses the brake pedal 22. Furthermore, the pitch change is easily perceived by utilizing visual changes due to the perception threshold shown in Fig. 9. Therefore, if a pitch change is actively generated as a change in the vehicle braking posture that allows the driver to quickly perceive the occurrence of the pitch change even if the driver does not feel the deceleration Gx, the visual changes accompanying the pitch change can be utilized to give the driver a sense of deceleration before the driver perceives the degree of deceleration.

[0062] Therefore, according to the braking force distribution characteristic A, in the reduced speed region R1, the braking device 20 is controlled so that the front / rear distribution ratio α is in line with the fixed distribution ratio, as shown in Fig. 10. In other words, in the reduced speed region R1, the braking device 20 is controlled so that the front / rear distribution ratio α is closer to the front wheels than the ideal distribution characteristic.

[0063] Moreover, the medium deceleration region R2 is, for example, a required deceleration region of 0.3 G to 0.5 G. Alternatively, the medium deceleration region R2 may be, for example, a required deceleration region of 0.3 G to 0.6 G. According to the braking force distribution characteristic A, in the medium deceleration region R2, as shown in Fig. 10, the braking device 20 is controlled so that the front / rear distribution ratio α is closer to the rear wheels than the fixed distribution characteristic.

[0064] According to the braking force distribution characteristic A, in the medium deceleration region R2, the front / rear distribution ratio α is controlled to a value located between the ideal distribution characteristic and the fixed distribution characteristic, as shown in Fig. 10. Also, according to the braking force distribution characteristic A, in a required deceleration region located between the reduced speed region R1 and the medium deceleration region R2, the front / rear distribution ratio α is gradually changed to a value closer to the rear wheels as the required deceleration Gxr increases, from the value of the front / rear distribution ratio α in region R1 to the value of the front / rear distribution ratio α in region R2.

[0065] Furthermore, a high deceleration region R3 exists on the high deceleration side of the medium deceleration region R2. The high deceleration region R3 is a required deceleration region equal to or greater than the deceleration Gx at which the distribution line of the braking force distribution characteristic A and the distribution line of the fixed distribution characteristic intersect on the high deceleration side. For this reason, in the example shown in FIG. 10, the high deceleration region R3 is a required deceleration region of 0.8G or more. Alternatively, the high deceleration region R3 may be, for example, a required deceleration region of 0.7G or more. The upper limit of the high deceleration region R3 is, for example, 1.0G. According to the braking force distribution characteristic A, in the high deceleration region R3, as shown in FIG. 10, the braking device 20 is controlled so that the front / rear distribution ratio α is in line with the fixed distribution characteristic. The high deceleration region R3 corresponds to an example of the "third region" according to the present disclosure.

[0066] According to the braking force distribution characteristic A, in a required deceleration region located between the medium deceleration region R2 and the high deceleration region R3, the front / rear distribution ratio α is gradually changed to a value closer to the front wheels as the required deceleration Gxr increases, from the value of the front / rear distribution ratio α in region R2 to the value of the front / rear distribution ratio α in region R3.

[0067] In addition, "controlling the braking device 20 so that the front / rear distribution ratio α conforms to the fixed distribution characteristics" in each of the reduced speed region R1 and the high deceleration region R3 does not necessarily require that the front / rear distribution ratio α be controlled to completely match the fixed distribution characteristics, and also includes controlling the braking device 20 so that the front / rear distribution ratio α is substantially in line with the fixed distribution characteristics.

[0068] 11 is a flowchart showing a process related to braking force distribution control according to the embodiment 1. The process of this flowchart is repeatedly executed while the vehicle 1 is traveling.

[0069] 11, in step S100, the ECU 40 determines whether or not the vehicle 1 is being braked. This determination can be made based on, for example, whether or not the depression amount of the brake pedal 22 detected by the brake position sensor 46 is equal to or greater than a predetermined threshold value.

[0070] As a result, if the vehicle 1 is not braking in step S100, the process proceeds to return. On the other hand, if the vehicle 1 is braking, the process proceeds to step S102. In step S102, the ECU 40 calculates a required deceleration Gxr. The required deceleration Gxr is calculated based on, for example, the depression amount of the brake pedal 22. Alternatively, the required deceleration Gxr may be calculated based on, for example, the master cylinder pressure.

[0071] Next, in step S104, the ECU 40 executes braking force distribution control that takes into account the vehicle attitude. The storage device of the ECU 40 stores, as a map, a braking force distribution characteristic A (see FIG. 10) that is specified based on the relationship between the front wheel braking force, the rear wheel braking force, and the required deceleration Gxr. The ECU 40 calculates the target front wheel braking force and the target rear wheel braking force according to the current required deceleration Gxr from such a map.

[0072] Then, the ECU 40 controls the braking device 20 to generate the calculated target front wheel braking force and target rear wheel braking force. More specifically, as described above, in this embodiment, the ratios (regenerative distribution ratios) β and γ are constant, for example. The target front wheel braking force is distributed to the target front wheel friction braking force and the target front wheel regenerative braking force according to the ratio β. The target rear wheel braking force is distributed to the target rear wheel friction braking force and the target rear wheel regenerative braking force according to the ratio γ. The ECU 40 controls the braking device 20 including the regenerative braking device 34 to generate these target friction braking forces and target regenerative braking forces, respectively.

[0073] In other words, the braking force distribution characteristic A determines the front / rear distribution ratio α according to the required deceleration Gxr. Therefore, controlling the front wheel braking force αF and the rear wheel braking force (1-α)F using the above map means controlling the front / rear distribution ratio α according to the required deceleration Gxr.

[0074] In addition, in step S104, instead of the above map, for example, a map that directly defines the relationship between the required deceleration Gxr specified by the braking force distribution characteristic A (see FIG. 10) and the front / rear distribution ratio α may be used. Then, the ECU 40 may calculate the target braking force Ft, which is a target value of the total braking force F, based on, for example, the depression amount of the brake pedal 22 or the master cylinder pressure. Then, the ECU 40 may calculate the target front wheel braking force and the target rear wheel braking force from the calculated target braking force Ft and the front / rear distribution ratio α calculated from the map according to the required deceleration Gxr.

[0075] Moreover, the process of step S104 relating to the braking force distribution control may be executed, for example, as follows: Fig. 12 is a flowchart showing a modified example of the process of step S104.

[0076] 12, in step S200, the ECU 40 determines whether the required deceleration Gxr is within the high deceleration region R3. If the result of this determination is Yes, the ECU 40 selects the fixed distribution characteristic (for example, see FIG. 10) in step S202.

[0077] On the other hand, when the determination result of step S200 is No, the ECU 40 determines in step S204 whether the required deceleration Gxr is within the medium deceleration region R2'. The medium deceleration region R2' (see FIG. 10) here includes not only the medium deceleration region R2 but also a required deceleration region located between the medium deceleration region R2 and the reduced deceleration region R1, and a required deceleration region located between the medium deceleration region R2 and the high deceleration region R3. The medium deceleration region R2' corresponds to another example of the "second region" according to the present disclosure. That is, the "second region" may include the medium deceleration region R2 specified as a required deceleration region of, for example, 0.3G to 0.5G or 0.3G to 0.6G. For this reason, the second region may be regarded as a region continuous with both the reduced deceleration region R1 and the high deceleration region R3, like the medium deceleration region R2', or may be regarded as a region continuous with only one of the regions R1 and R3.

[0078] If the determination result in step S204 is Yes, the ECU 40 selects a heave-priority distribution characteristic in step S206. This heave-priority distribution characteristic prioritizes promotion of heave change in the vehicle downward direction over suppression of pitch change, and is realized by a front-rear distribution ratio α that is closer to the rear wheels than the fixed distribution characteristic, as shown in Fig. 10.

[0079] On the other hand, if the determination result in step S204 is No, that is, if the required deceleration Gxr is within the reduced speed region R1, the ECU 40 selects a pitch priority distribution characteristic in step S208. This pitch priority distribution characteristic prioritizes promotion of pitch change over promotion of heave change in the vehicle downward direction, and is realized by a front / rear distribution ratio α according to a fixed distribution characteristic as shown in Fig. 10.

[0080] As described above, the process of step S104 may be executed so that the braking force distribution characteristic is switched depending on the result of determination of the region of the required deceleration Gxr, as in the process shown in FIG.

[0081] 1-3.Effects As described above, according to the braking force distribution characteristic A (see FIG. 10) according to the first embodiment, in the reduced speed region R1, the braking device 20 is controlled so that the front / rear distribution ratio α conforms to the fixed distribution characteristic.

[0082] FIG. 13 is a diagram showing a comparison of the relationship between the pitch angle θ and the deceleration Gx according to the first embodiment between braking force distribution characteristics. According to the braking force distribution characteristic A, as shown in FIG. 13, the pitch angle θ in the reduced speed region R1 is equivalent to the value obtained by the fixed distribution characteristic. That is, the pitch angle θ can be made larger than the value obtained by the ideal distribution characteristic. By actively generating a pitch change compared to the ideal distribution characteristic in this way, the pitch change can be quickly conveyed to passengers such as the driver through their vision. Therefore, in the reduced speed region R1 where the deceleration Gx during braking is low, it is possible to give a sense of deceleration to passengers such as the driver early. More specifically, it is possible to give the driver a good sense of deceleration that the responsiveness of the vehicle 1 to the operation of the brake pedal 22 is good before the driver perceives the deceleration Gx by utilizing the perception due to the visual change accompanying the movement of the head 7F caused by the pitch change. This leads to an improvement in the driver's sense of security regarding the braking performance.

[0083] Moreover, according to the braking force distribution characteristic A, in the medium deceleration region R2, the braking device 20 is controlled so as to obtain a front / rear distribution ratio α that is closer to the rear wheels than the fixed distribution characteristic.

[0084] FIG. 14 is a diagram showing a comparison of the relationship between the heave amount H and the deceleration Gx between braking force distribution characteristics according to the first embodiment. According to the braking force distribution characteristic A, as shown in FIG. 14, the heave amount H in the medium deceleration region R2 can be made larger than the value obtained by the fixed distribution characteristic. The heave change is conveyed to the passengers such as the driver as a change in acceleration in the vertical direction of the vehicle. As described with reference to FIG. 9, the heave change is easily perceived by the passengers' bodily sensation. Therefore, by actively increasing the heave amount H (sinking of the vehicle body 5) in the medium deceleration region R2 compared to the fixed distribution characteristic, it is possible to provide the passengers with a sense of security that each wheel 2 of the vehicle 1 is stuck to the road surface (i.e., a sense of security regarding braking).

[0085] In addition, as can be seen from FIG. 14, the ideal distribution characteristic also allows the heave change in the medium deceleration region R2 to be large. However, according to the ideal distribution characteristic, the front / rear distribution ratio α is biased toward the rear wheels even in the reduced speed region R1 compared to the fixed distribution characteristic. For this reason, the ideal distribution characteristic does not provide the effect of giving the driver an early deceleration sensation by actively generating pitch changes in the reduced speed region R1 (see FIG. 13). Therefore, in the braking force distribution characteristic A, the front / rear distribution ratio α is changed between the reduced speed region R1 and the medium deceleration region R2. This realizes a good braking force distribution characteristic that can improve the deceleration sensation in the reduced speed region R1 and improve the sense of security regarding braking in the medium deceleration region R2. In this way, according to the first embodiment, the braking sensation can be improved in a plurality of deceleration regions (R1 and R2).

[0086] In addition, according to the braking force distribution characteristic A, in the medium deceleration region R2 where the driver is more likely to feel the deceleration Gx because it is on the high deceleration side compared to the reduced speed region R1, the pitch angle θ is suppressed to be smaller than when the fixed distribution characteristic is selected (see Figure 13).

[0087] Furthermore, according to the braking force distribution characteristic A, in the high deceleration region R3, the braking device 20 is controlled so that the front / rear distribution ratio α conforms to the fixed distribution characteristic. If the braking force distribution characteristic A had a characteristic like the dashed line L3 in FIG. 10, in the high deceleration region R3, the front / rear distribution ratio α would be biased toward the front wheels compared to the fixed distribution characteristic. As a result, the braking load on the front wheels 2F would be high. In contrast, according to the braking force distribution characteristic A, in such a high deceleration region R3, the burden on the front wheels braking force can be reduced compared to the characteristic of the dashed line L3, so that it is possible to effectively suppress brake fade on the front wheels and ensure understeer characteristics during braking.

[0088] In the example of braking force distribution characteristic A shown in Fig. 10, the braking device 20 is controlled so that the front / rear distribution ratio α is in line with the fixed distribution characteristic throughout the entire reduced speed region R1 (first region). Instead of this example, the braking device 20 may be controlled so that the front / rear distribution ratio α is in line with the fixed distribution characteristic by actively generating a pitch change in only a part of the reduced speed region R1 (first region) to give the passenger an early sense of deceleration.

[0089] 2. Second embodiment In the above-described first embodiment, the ratios (regenerative distribution ratios) β and γ are constant. The second embodiment differs from the first embodiment in that the ratios β and γ are changed according to the deceleration Gx.

[0090] Specifically, first, in the braking force distribution control that takes into account the vehicle attitude according to the second embodiment, the braking force distribution characteristic A (see FIG. 10) is used to change the front / rear distribution ratio α according to the required deceleration Gxr. In addition, in the vehicle 1 in which the regenerative torques of the electric motors 10F and 10R are applied to the front wheels 2F and the rear wheels 2R via the drive shafts 3F and 3R, respectively, the vehicle braking attitude can also be changed by changing the ratios β and γ.

[0091] Here, as a result of considering the anti-lift ratio and the anti-squat ratio of a general vehicle with respect to the above formulas (1) to (5), the rear wheel 2R is 16 and17 As shown in the above, it has been found that the variable range of the pitch angle θ and the heave amount H is improved by lowering the ratio γ and generating the braking force by hydraulic pressure.

[0092] Therefore, in the second embodiment, in a required deceleration region on the higher deceleration side than the reduced speed region R1, the braking device 20 is controlled so that the ratio β (i.e., the ratio of the front wheel regenerative braking force to the front wheel braking force) is larger and the ratio γ (i.e., the ratio of the rear wheel regenerative braking force to the rear wheel braking force) is smaller than in the reduced speed region R1. Note that the ratios β and γ correspond to examples of the "first ratio" and "second ratio" according to the present disclosure, respectively.

[0093] Fig. 15 is a diagram showing an example of the relationship between the required deceleration Gxr and the ratio β for the front wheels 2F according to the second embodiment. The thin line in Fig. 15 corresponds to the first embodiment in which a constant ratio β is used regardless of the required deceleration Gxr. The value of the ratio β of 75% is just an example.

[0094] In the second embodiment, the ratio β is varied as shown by the thick line in FIG. 15. That is, in the reduced speed region R1, the ratio β is constant at, for example, 75%. Then, when the required deceleration Gxr becomes 0.1 G or more (that is, when it exceeds the reduced speed region R1), as the required deceleration Gxr increases, the ratio β increases from 75% and reaches 100% at 0.6 G. In the required deceleration region of 0.6 G or more, the ratio β is constant at 100%. Unlike the example shown in FIG. 15, the ratio β may be changed to reach 100% at any required deceleration Gxr value other than 0.6 G (including 1.0 G). Also, the maximum value of the ratio β due to the variation is not necessarily limited to 100%.

[0095] Furthermore, in the second embodiment, the ratio γ is determined to be equal to the value (γ=1-β) obtained by subtracting the ratio β from 1. Therefore, according to the example shown in Fig. 15, the ratio γ is changed within the range of 0.25 (25%) to 0 (0%) in conjunction with the change in the ratio β within the above-mentioned range of 0.75 (75%) to 1.0 (100%).

[0096] In essence, the rate γ for the rear wheels 2R can be changed independently of the rate β. Therefore, unlike the above example, the rate γ for the rear wheels 2R can be changed independently of the rate β. Gamma The increase in the rate β and the decrease in the rate β may be performed independently of each other. Gamma By performing the reduction in the ratios β and γ in conjunction with the reduction in the ratios β and γ, the following effect can be obtained: It is possible to increase the variable range of the vehicle braking posture while ensuring the amount of regenerative power equivalent to the amount of regenerative power obtained at each deceleration Gx in an example in which the ratios β and γ are constant regardless of the deceleration Gx.

[0098] fruit Compared with embodiment 1 (constant regenerative distribution), according to embodiment 2 (variable regenerative distribution), in the region on the high deceleration side of reduced speed region R1, the front wheel regenerative braking force is increased and the rear wheel friction braking force is increased.

[0099] As explained above, according to the braking force distribution control of the second embodiment, the front / rear distribution ratio α is controlled in response to the required deceleration Gxr so as to follow the braking force distribution characteristic A (see FIG. 10) in the same manner as in the first embodiment. In the second embodiment, the front wheel braking force is distributed to the friction braking force and the regenerative braking force in accordance with the setting of the ratio β shown in FIG. 15. Also, the rear wheel braking force is distributed to the friction braking force and the regenerative braking force in accordance with the ratio γ (=1-β) determined in accordance with the ratio β. As a result, as shown in the following figure, 16 and Figure 17 The vehicle braking attitude is obtained, which is expressed with reference to

[0100] figure 16 FIG. 11 is a diagram showing a comparison of the relationship between the pitch angle θ and the deceleration Gx according to the second embodiment between braking force distribution characteristics. 17 13 is a diagram showing a comparison of the relationship between the amount of heave H and the deceleration Gx according to the second embodiment between braking force distribution characteristics. FIG.

[0101] figure 16As shown in Fig. 1, when compared with the constant regenerative distribution (Embodiment 1), the variable regenerative distribution (Embodiment 2) can suppress the change in pitch angle θ to a small value in the high deceleration region from the reduced speed region R1 (reducing nose dive of the vehicle 1). This makes it possible to more effectively suppress the amount of movement of the heads 7F and 7R of the occupants toward the front of the vehicle in the high deceleration region. In other words, a more comfortable and secure vehicle braking posture can be obtained.

[0102] Also, Fig. 17 As shown in Fig. 1, compared to the constant regeneration allocation (Embodiment 1), the amount of heave change in the downward direction of the vehicle (the amount of sinking of the vehicle body 5) can be increased in the high deceleration region from the reduced speed region R1. This makes it possible to more effectively give the passengers a sense of security that the vehicle 1 is sticking to the road surface in the high deceleration region. In other words, a more comfortable and secure vehicle braking posture can be obtained.

[0103] 15, the rate β is increased and the rate γ is decreased in the entire region on the high deceleration side of the reduced speed region R1, compared to the reduced speed region R1. Instead of this example, the rate β may be increased and the rate γ may be decreased in only a part of the region on the high deceleration side, such as only the medium deceleration region R2, compared to the reduced speed region R1.

[0104] 3. Third embodiment 3-1.Vehicle configuration examples figure 18 is a block diagram showing an example of the configuration of a vehicle control system 50 provided in a vehicle 8 according to an embodiment 3. The vehicle 8 is configured to be switchable between a manual driving mode in which the vehicle is driven by a driver, and an automatic driving mode.

[0105] Specifically, the vehicle 8 includes a configuration similar to that of the vehicle 1 shown in Fig. 1 (including suspensions 4F and 4R shown in Fig. 2), as well as a vehicle control system 50. An ECU 40 that controls the vehicle control system 50 can perform automatic driving of the vehicle 8. The vehicle control system 50 includes, in addition to the ECU 40, a vehicle state sensor 52, a recognition sensor 54, a position sensor 56, and a driving device 58.

[0106] The vehicle state sensor 52 detects the state of the vehicle 8. The vehicle state sensor 52 includes, in addition to the wheel speed sensor 42 and the longitudinal acceleration sensor 44 described above, a yaw rate sensor and a steering angle sensor, for example.

[0107] The recognition sensor 54 recognizes (detects) the surroundings of the vehicle 8. 54 Examples of such devices include cameras, LIDAR (Laser Imaging Detection and Ranging), and radar.

[0108] The position sensor 56 detects the position and orientation of the vehicle 8. For example, the position sensor 56 includes a Global Navigation Satellite System (GNSS) receiver.

[0109] The traveling device 58 includes the above-mentioned braking device 20 and the electric motors 10F and 10R, as well as a steering device 60. The steering device 60 steers the wheels 2. For example, the steering device 60 includes an electric power steering (EPS) device.

[0110] The vehicle control program 70 is a computer program for controlling the vehicle 8, and is executed by the processor 41 of the ECU 40. The vehicle control program 70 is stored in the storage device 43 of the ECU 40. Alternatively, the vehicle control program 70 may be recorded in a computer-readable recording medium. The processor 41 executes the vehicle control program 70, thereby realizing the functions of the ECU 40.

[0111] The driving environment information 80 is information indicating the driving environment of the vehicle 8, and is stored in the storage device 43. The driving environment information 80 includes map information, vehicle state information, surrounding situation information, and position information. More specifically, the vehicle state information is information indicating the state of the vehicle 8, such as the vehicle speed, longitudinal acceleration, and steering angle. The surrounding situation information is information indicating the situation around the vehicle 8, and is acquired using the recognition sensor 54. The position information is information indicating the position and orientation (vehicle traveling direction) of the vehicle 8, and is acquired from the measurement results by the position sensor 56.

[0112] The vehicle 8 is also equipped with an HMI (Human Machine Interface) device 90 such as a switch or a touch panel. The HMI device 90 allows the vehicle driving mode to be switched between a manual driving mode and an automatic driving mode. The HMI device 90 is operated by the driver.

[0113] 3-2.Braking control Brake force distribution control that takes into account the vehicle attitude is also performed in the third embodiment. However, in the third embodiment, the brake force distribution characteristic is switched depending on whether the vehicle 8 is in the manual driving mode or the automatic driving mode.

[0114] Specifically, as described above, according to the braking force distribution characteristic A (see FIG. 10), in the reduced speed region R1, the driver or other passenger visually perceives a pitch change before the driver perceives the deceleration Gx, thereby providing the passenger with a sense of deceleration at an early stage. On the other hand, in the automatic driving mode in which the driver is not driving the vehicle, it can be said that there is no need to provide the passenger with a sense of deceleration at an early stage.

[0115] Therefore, the braking force distribution control according to the third embodiment is executed as follows. 19 10 is a flowchart showing a process related to braking force distribution control according to the third embodiment. The process of this flowchart is repeatedly executed while the vehicle 8 is traveling. 20 13 is a diagram showing braking force distribution characteristics A and B used in the third embodiment.

[0116] figure 19 In step S300, the ECU 40 determines whether the current vehicle driving mode is the automatic driving mode or the manual driving mode. The ECU 40 can make this determination based on a signal received from the HMI device 90, for example.

[0117] If the determination result in step S300 is No, that is, if the vehicle is in the manual driving mode, the process proceeds to step S302. In step S302, the ECU 40 selects the braking force distribution characteristic A, which is a characteristic for the manual driving mode. 20 As shown in FIG. 10, the selected braking force distribution characteristic A is the same as that used in the first embodiment (see FIG. 10).

[0118] On the other hand, if the determination result in step S300 is Yes, that is, if the vehicle is in the autonomous driving mode, the process proceeds to step S304. In step S304, the ECU 40 selects the braking force distribution characteristic B, which is a characteristic for the autonomous driving mode.

[0119] figure 20 1, the braking force distribution characteristic B differs from the braking force distribution characteristic A in the characteristics of the reduced speed region R1. That is, the braking force distribution characteristic B is set so as to obtain a front / rear distribution ratio α closer to the rear wheels than the fixed distribution characteristic equivalent to the braking force distribution characteristic A in the reduced speed region R1. Note that, for the required deceleration region located between the reduced speed region R1 and the medium deceleration region R2, the front / rear distribution ratio α is gradually changed to a value closer to the rear wheels as the required deceleration Gxr increases, from the value of the front / rear distribution ratio α in region R1 to the value of the front / rear distribution ratio α in region R2.

[0120] In addition, the control of the braking device 20 to realize the braking force distribution characteristic B can be performed by, for example, causing the ECU 40 to execute the same process as the flowchart shown in Fig. 11. However, since the autonomous driving mode is being executed, the required deceleration Gxr is calculated according to a request from the vehicle control system 50, not from the driver.

[0121] Effects figure 21 FIG. 11 is a diagram showing a comparison of the relationship between the pitch angle θ and the deceleration Gx according to the third embodiment between braking force distribution characteristics. 22 13 is a diagram showing a comparison of the relationship between the amount of heave H and the deceleration Gx between braking force distribution characteristics according to the third embodiment. FIG.

[0122] figure 21 As shown in Fig. 1, according to the braking force distribution characteristic B, the pitch change caused by braking can be suppressed to a smaller value in the reduced speed region R1 compared to the braking force distribution characteristic A (=fixed distribution characteristic). As a result, the amount of movement of the heads 7F and 7R of the passengers toward the front of the vehicle can be suppressed, making it possible to make the passengers less likely to feel a sense of deceleration. This improves the comfort of the passengers when braking while the autonomous driving mode is being executed.

[0123] As described above, according to the third embodiment, in the reduced speed region R1, when the manual driving mode is selected, it is possible to give a sense of deceleration to passengers such as the driver early on, while when the automatic driving mode is selected, the pitch change is suppressed to make it difficult to give a sense of deceleration.

[0124] In addition, Fig. 22 As shown in Fig. 1, according to the braking force distribution characteristic B, in the reduced speed region R1, the heave in the downward direction of the vehicle (sinking of the vehicle body 5) caused by braking can be made larger than that in the braking force distribution characteristic A (=fixed distribution characteristic). Therefore, in the reduced speed region R1 while the autonomous driving mode is being executed, the sense of security regarding braking can be improved.

[0125] In the braking force distribution control according to the above-mentioned third embodiment, the rates β and γ may also be changed as described in the second embodiment.

[0126] 4. Fourth embodiment The fourth embodiment is the same as the third embodiment in that the braking force distribution characteristic is switched between braking force distribution characteristic A and braking force distribution characteristic B while the vehicle 8 is traveling. However, in the fourth embodiment, the switching (selection) of the braking force distribution characteristic is performed as follows. Note that the vehicle to which the fourth embodiment is applied is not limited to an autonomously driven vehicle.

[0127] Vehicles may be driven by professional drivers such as chauffeurs or taxi drivers. When a professional driver drives a vehicle with passengers or other specific passengers in the back seat 6R, the comfort of the passengers in the back seat 6R must be given priority.

[0128] Therefore, the braking force distribution control according to the fourth embodiment is executed as follows. 23 10 is a flowchart showing a process related to braking force distribution control according to embodiment 4. The process of this flowchart is repeatedly executed while the vehicle 8 is traveling.

[0129] figure 23 In step S400, the ECU 40 determines whether or not the situation requires a priority to be given to the comfort of the passenger in the rear seat 6R. This determination can be made, for example, based on a signal from the HMI device 90 operated by the driver (professional driver). Specifically, the determination can be made based on whether or not the ECU 40 has received a request from the driver via the HMI device 90 to prioritize the comfort of the passenger in the rear seat 6R. Instead of this example, the ECU 40 may make the determination based on whether or not it has been recognized that a passenger has sat in the rear seat 6R, using, for example, an in-vehicle camera or a seat belt fastening detection sensor.

[0130] If the determination result in step S400 is No, that is, if priority is not given to the comfort of the passenger in the rear seat 6R (for example, if there is no passenger in the rear seat 6R), the ECU 40 selects the braking force distribution characteristic A in step S302.

[0131] On the other hand, if the determination result in step S400 is Yes, that is, if priority is given to the comfort of the passenger in the rear seat 6R, the ECU 40 selects the braking force distribution characteristic B in step S304.

[0132] According to the braking force distribution control of the fourth embodiment described above, when priority is given to the comfort of the passenger in the rear seat 6R, the braking force distribution characteristic B is selected. According to the braking force distribution characteristic B, in the reduced speed region R1, the effect of giving the driver an early deceleration sensation cannot be obtained, but the comfort of the passenger in the rear seat 6R can be improved by suppressing the pitch change (FIG. 21 In other words, the comfort of the rear passengers in the 6R seats is given priority over the driver's early perception of deceleration.

[0133] In the braking force distribution control according to the above-described fourth embodiment, the rates β and γ may also be changed as described in the second embodiment.

[0134] 5. Other embodiments The above-mentioned braking force distribution characteristic A (FIG. 10 and FIG. 20 Change in the front / rear distribution ratio α according to the brake force distribution characteristic B (see Fig. 20 The change in the front / rear distribution ratio α according to (see) may be performed for a vehicle that does not have a regenerative braking force (i.e., a vehicle that uses only a friction braking force). In this case, the suspension displacement ΔX f and ΔX r is expressed by the following equations (6) and (7).

[0135]

number

[0136] Furthermore, when using regenerative braking force, an in-wheel motor may be used instead of the front wheel motor 10F and the rear wheel motor 10R which drive the front wheels 2F and the rear wheels 2R via the front wheel drive shaft 3F and the rear wheel drive shaft 3R, respectively. However, the point of application of the regenerative braking force when an in-wheel motor is used is different from the center position of the wheel 2, which is the point of application when the motors 10F and 10R are used, and is the contact surface of the wheel 2, which is the same as the point of application of the friction braking force. Therefore, the suspension displacement amount ΔX in the example where an in-wheel motor is used f and ΔX r The equations become (6) and (7).

[0137] In addition, when the front / rear distribution ratio α is changed by utilizing regenerative braking force, except for the braking force distribution control according to embodiment 2 (see FIG. 15) in which the ratios β and γ are made variable according to the required deceleration Gxr, the electric motor (including an in-wheel motor) may be configured to drive only either the front wheels or the rear wheels. [Explanation of symbols]

[0138] 1, 8 cars 2F Front wheel 2R rear wheel 3F Front wheel drive shaft 3R rear wheel drive shaft 4F, 4R Suspension 5. Body 6F front seats 6R Rear seat 7F Head of a front seat passenger 7R Rear seat passenger's head 10F Front wheel electric motor 10R rear wheel electric motor 20 Braking device 22 Brake pedal 24 Master cylinder 26 Brake Actuator 28a Wheel cylinder 32 Inverter 34 Regenerative braking device 40 Electronic Control Unit (ECU) 44 Front and rear acceleration sensor 46 Brake position sensor 50 Vehicle Control System 70 Vehicle control program 80 Driving Environment Information 90 HMI (Human Machine Interface) equipment

Claims

1. A vehicle control method for controlling a vehicle equipped with a braking device configured to be able to change a front / rear distribution ratio of a braking force for front wheels and a rear wheel, comprising: controlling the braking device so that the front / rear distribution ratio is in accordance with a fixed distribution characteristic in which the front / rear distribution ratio is constant regardless of deceleration in at least a part of a first region, which is a required deceleration region that is less than a lower limit value of deceleration that can be perceived by a passenger; controlling the braking device so that the front / rear distribution ratio is biased toward the rear wheels more than the fixed distribution characteristic in a second region in which the deceleration is higher than that in the first region; Including, The vehicle further includes a front wheel electric motor that drives the front wheels via a front wheel drive shaft, and a rear wheel electric motor that drives the rear wheels via a rear wheel drive shaft, the braking device includes a regenerative braking device capable of controlling a front wheel regenerative braking force applied to the front wheels by using the front wheel electric motor and a rear wheel regenerative braking force applied to the rear wheels by using the rear wheel electric motor, The vehicle control method includes controlling the braking device such that, in at least a part of a required deceleration region that is on a higher deceleration side than the first region, a first proportion of the front wheel regenerative braking force in the braking force of the front wheels is larger and a second proportion of the rear wheel regenerative braking force in the braking force of the rear wheels is smaller than in the first region. A vehicle control method.

2. The second percentage is determined to be equal to one minus the first percentage. The vehicle control method according to claim 1 .

3. A vehicle control method for controlling a vehicle equipped with a braking device configured to be able to change a front / rear distribution ratio of braking force for front wheels and rear wheels, comprising: controlling the braking device so that the front / rear distribution ratio is in accordance with a fixed distribution characteristic in which the front / rear distribution ratio is constant regardless of deceleration in at least a part of a first region, which is a required deceleration region that is less than a lower limit value of deceleration that can be perceived by a passenger; controlling the braking device so that the front / rear distribution ratio is biased toward the rear wheels more than the fixed distribution characteristic in a second region in which the deceleration is higher than that in the first region; Including, The vehicle is configured to be switchable between a manual driving mode and an automatic driving mode, The vehicle control method includes: In the manual driving mode, the braking device is controlled so that a front / rear distribution ratio conforms to the fixed distribution characteristic in at least the portion of the first region; In the automatic driving mode, the braking device is controlled so that the front / rear distribution ratio is closer to the rear wheels than the fixed distribution characteristic in at least the part of the first region. Includes A vehicle control method.

4. A vehicle control method for controlling a vehicle equipped with a braking device configured to be able to change a front / rear distribution ratio of braking force for front wheels and rear wheels, comprising: controlling the braking device so that the front / rear distribution ratio is in accordance with a fixed distribution characteristic in which the front / rear distribution ratio is constant regardless of deceleration in at least a part of a first region, which is a required deceleration region that is less than a lower limit value of deceleration that can be perceived by a passenger; controlling the braking device so that the front / rear distribution ratio is biased toward the rear wheels more than the fixed distribution characteristic in a second region in which the deceleration is higher than that in the first region; Including, The vehicle control method includes: When comfort of a passenger in a rear seat of the vehicle is not a priority, the braking device is controlled so that a front-rear distribution ratio conforms to the fixed distribution characteristic in at least the portion of the first region. When priority is given to comfort of passengers in the rear seats of the vehicle, the braking device is controlled so that the front / rear distribution ratio is closer to the rear wheels than the fixed distribution characteristic in at least the part of the first region; Includes A vehicle control method.

5. The vehicle control method includes controlling the braking device so that a front / rear distribution ratio conforms to the fixed distribution characteristic in a third region in which deceleration is higher than in the second region. A vehicle control method according to any one of claims 1 to 4.

6. A braking device configured to be able to change a front / rear distribution ratio of braking force for front wheels and rear wheels; an electronic control unit for controlling the braking device; A vehicle comprising: The electronic control unit includes: The brake device is controlled so that the front / rear distribution ratio is in accordance with a fixed distribution characteristic in which the front / rear distribution ratio is constant regardless of the deceleration in at least a part of a first region, which is a required deceleration region that is less than a lower limit value of the deceleration that can be perceived by a passenger, and In a second region in which the deceleration is higher than that in the first region, the braking device is controlled so that the front / rear distribution ratio is more rear-wheel-biased than the fixed distribution characteristic. The vehicle further includes a front wheel electric motor that drives the front wheels via a front wheel drive shaft, and a rear wheel electric motor that drives the rear wheels via a rear wheel drive shaft, the braking device includes a regenerative braking device capable of controlling a front wheel regenerative braking force applied to the front wheels by using the front wheel electric motor and a rear wheel regenerative braking force applied to the rear wheels by using the rear wheel electric motor, The electronic control unit controls the braking device such that, in at least a part of a required deceleration region on a higher deceleration side than the first region, a first proportion of the front wheel regenerative braking force in the braking force of the front wheels is larger and a second proportion of the rear wheel regenerative braking force in the braking force of the rear wheels is smaller than in the first region. vehicle.

7. The second percentage is determined to be equal to one minus the first percentage.

7. A vehicle as claimed in claim 6.

8. A braking device configured to be able to change the front / rear wheel braking force distribution ratio; an electronic control unit for controlling the braking device; A vehicle comprising: The electronic control unit includes: The brake device is controlled so that the front / rear distribution ratio is in accordance with a fixed distribution characteristic in which the front / rear distribution ratio is constant regardless of the deceleration in at least a part of a first region, which is a required deceleration region that is less than a lower limit value of the deceleration that can be perceived by a passenger, and In a second region in which the deceleration is higher than that in the first region, the braking device is controlled so that the front / rear distribution ratio is more rear-wheel-biased than the fixed distribution characteristic. The vehicle is configured to be switchable between a manual driving mode and an automatic driving mode, The electronic control unit includes: In the manual driving mode, the braking device is controlled so that the front / rear distribution ratio is in accordance with the fixed distribution characteristic in at least the portion of the first region. In the automatic driving mode, the braking device is controlled so that the front / rear distribution ratio is more rear-wheel-biased than the fixed distribution characteristic in at least the part of the first region. vehicle.

9. A braking device configured to be able to change the front / rear wheel braking force distribution ratio; an electronic control unit for controlling the braking device; A vehicle comprising: The electronic control unit includes: The brake device is controlled so that the front / rear distribution ratio is in accordance with a fixed distribution characteristic in which the front / rear distribution ratio is constant regardless of the deceleration in at least a part of a first region, which is a required deceleration region that is less than a lower limit value of the deceleration that can be perceived by a passenger, and In a second region in which the deceleration is higher than that in the first region, the braking device is controlled so that the front / rear distribution ratio is more rear-wheel-biased than the fixed distribution characteristic. The electronic control unit includes: When comfort of a passenger in a rear seat of the vehicle is not a priority, the braking device is controlled so that a front-rear distribution ratio conforms to the fixed distribution characteristic in at least the portion of the first region. When priority is given to the comfort of passengers in the rear seats of the vehicle, the braking device is controlled so that the front / rear distribution ratio is more rear-wheel-biased than the fixed distribution characteristic in at least the part of the first region. vehicle.

10. The electronic control unit controls the braking device so that the front / rear distribution ratio conforms to the fixed distribution characteristic in a third region where the deceleration is higher than that in the second region. A vehicle according to any one of claims 6 to 9.

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