JP2006149086A - Braking force controller for electric vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a braking force controller for en electric vehicle capable of preventing the generation of an overcurrent in an electrical unit in advance by inhibiting the occurrence of a re-slipping of drive wheels in which braking force is added when braking traction control is released. <P>SOLUTION: The braking force controller for the electric vehicle includes at least one motor set with a power source of the drive wheels, the electrical unit connected to the motor, and a braking traction controller for recovering a tire grip by adding the braking force to slipping wheels in occurring the driving slip. A road surface friction factor equivalent value detector (step S2) is provided for detecting an amount of road surface friction factor equivalent value, and the braking traction controller is made into means (step S3) of changing a release speed of the braking force in accordance with the amount of road surface friction factor equivalent value when the braking traction control is released. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is applied to an electric vehicle such as a hybrid vehicle or an electric vehicle, and relates to a braking force control device for an electric vehicle in which at least one motor is provided as a power source of driving wheels.

  In a hybrid vehicle equipped with a motor as the power source, when the drive wheel slips, the motor over-rotates in accordance with the drive slip and an overcurrent is generated in the motor drive circuit. Needs to converge the driving slip with good response. The motor traction control device for converging the drive slip for the purpose of protecting the components is configured to predict that the drive slip will occur when the change rate (angular acceleration) of the rotational angular velocity of the drive wheel is equal to or greater than a predetermined value, and to reduce the motor torque. And driving slip that occurs with an increase in motor torque is prevented (see, for example, Patent Document 1).

A motor traction control device for converging drive slip for the purpose of protecting other components has a drive slip when the current value applied to the electric motor is equal to or greater than a predetermined value and the change amount of the current value is equal to or greater than the predetermined change amount. It is predicted that the motor torque is generated, and the motor torque is reduced to prevent the drive slip caused by the increase of the motor torque (see, for example, Patent Document 2).
JP-A-10-304514 JP 2004-96824 A

  However, in the motor traction control device using the conventional motor torque reduction, the motor torque reduction control is performed when a drive slip occurs only on one wheel while traveling on a split μ road having different road surface friction coefficients between the left and right wheels. As a result, the torque to the drive wheels on the high μ road side also decreases. Therefore, as used in existing engine vehicles, when brake traction control that can apply braking force only to slip wheels while running on split μ roads is performed, When the brake fluid pressure on the road-side drive wheels is suddenly removed, traction is restored and slip occurs again, and in hybrid and electric vehicles equipped with a motor as the power source, a high-power unit with a motor drive circuit is used. There is a problem that overcurrent occurs.

  The present invention has been made paying attention to the above problem, and when releasing the brake traction control, it suppresses the occurrence of re-slip of the driving wheel to which the braking force is applied, and prevents the overcurrent generation in the high voltage unit in advance. An object of the present invention is to provide a braking force control device for an electric vehicle that can be prevented.

In order to achieve the above object, in the braking force control apparatus for an electric vehicle according to the present invention, at least one motor provided in the power source of the drive wheels, a high-power unit connected to the motor, and a slip when a drive slip occurs In a braking force control device for an electric vehicle comprising: brake traction control means for restoring tire grip by applying a braking force to the wheel;
A road surface friction coefficient equivalent value detecting means for detecting a road surface friction coefficient equivalent value is provided,
The brake traction control means is characterized in that, when releasing the brake traction control, the braking force releasing speed is changed according to a road surface friction coefficient equivalent value.

  Therefore, in the braking force control device for an electric vehicle according to the present invention, when releasing the brake traction control, the release speed of the braking force is changed according to the road surface friction coefficient equivalent value according to the brake traction control means. . That is, the lower the friction coefficient corresponding to the road surface friction coefficient, the slower the braking force release speed, and gradually releasing the braking force. Recovery is delayed and the occurrence of re-slip due to the release of the braking force is suppressed. As described above, when releasing the brake traction control, it is possible to suppress the occurrence of re-slip of the drive wheel to which the braking force is applied, and to prevent the overcurrent generation in the high-power unit in advance.

  Hereinafter, the best mode for realizing a braking force control apparatus for an electric vehicle according to the present invention will be described based on a first embodiment shown in the drawings.

First, the drive system configuration of the hybrid vehicle will be described.
FIG. 1 is an overall system diagram showing a drive system of a hybrid vehicle to which the motor traction control device of Embodiment 1 is applied. As shown in FIG. 1, the drive system of the hybrid vehicle in the first embodiment includes an engine E, a first motor generator MG1, a second motor generator MG2 (motor), an output sprocket OS, and a power split mechanism TM. Have.

  The engine E is a gasoline engine or a diesel engine, and the opening degree of a throttle valve and the like are controlled based on a control command from an engine controller 1 described later.

The first motor generator MG1 and the second motor generator MG2 are synchronous motor generators in which a permanent magnet is embedded in a rotor and a stator coil is wound around a stator. Based on a control command from the motor controller 2 described later, Each is controlled independently by applying a three-phase alternating current generated by the control unit 3.
Both of the motor generators MG1 and MG2 can operate as electric motors that are rotated by receiving power supplied from the battery 4 (hereinafter, this state is referred to as “powering”), and the rotor is rotated by an external force. If it is, the battery 4 can be charged by functioning as a generator that generates electromotive force at both ends of the stator coil (hereinafter, this state is referred to as “regeneration”).

  The power split mechanism TM is configured by a simple planetary gear having a sun gear S, a pinion P, a ring gear R, and a pinion carrier PC. And the connection relationship of the input / output member with respect to the three rotating elements (sun gear S, ring gear R, and pinion carrier PC) of the simple planetary gear will be described. A first motor generator MG1 is connected to the sun gear S. A second motor generator MG2 and an output sprocket OS are connected to the ring gear R. An engine E is connected to the pinion carrier PC via an engine damper ED. The output sprocket OS is connected to the left and right front wheels via a chain belt CB, a differential and a drive shaft (not shown).

Due to the above connection relationship, the first motor generator MG1 (sun gear S), the engine E (planet carrier PC), the second motor generator MG2 and the output sprocket OS (ring gear R) are arranged in this order on the alignment chart shown in FIG. It is possible to introduce a rigid lever model (a relationship in which three rotational speeds are always connected by a straight line) that can simply express the dynamic operation of a simple planetary gear.
Here, the “collinear diagram” is a velocity diagram used in a simple and easy-to-understand method of drawing instead of the method of obtaining by equation when considering the gear ratio of the differential gear, Take the number of rotations (rotation speed) of the rotating elements, take each rotating element on the horizontal axis, and based on the gear ratio λ of sun gear S and ring gear R, the interval between each rotating element (S ~ PC): (PC ~ R ) Length ratio is 1: λ.

Next, the control system of the hybrid vehicle will be described.
As shown in FIG. 1, the hybrid vehicle control system in the first embodiment includes an engine controller 1, a motor controller 2, a power control unit 3 (high power unit), a battery 4 (secondary battery), and a brake controller 5. And an integrated controller 6.

  The integrated controller 6 receives input information from an accelerator opening sensor 7, a vehicle speed sensor 8, an engine speed sensor 9, a first motor generator speed sensor 10, and a second motor generator speed sensor 11. Brought about. Note that the vehicle speed sensor 8 and the second motor generator rotation speed sensor 11 are for detecting the output rotation speed of the same power split mechanism TM, so the vehicle speed sensor 8 is omitted and the second motor generator rotation speed sensor 11 The sensor signal may be used as a vehicle speed signal. Further, the motor controller 2 provides information on the battery S.O.C representing the state of charge of the battery 4.

  The brake controller 5 includes a front left wheel speed sensor 12, a front right wheel speed sensor 13, a rear left wheel speed sensor 14, a rear right wheel speed sensor 15, a steering angle sensor 16, and a master cylinder pressure sensor 17. The brake stroke sensor 18 and the yaw rate sensor 27 provide input information.

  The engine controller 1 responds to an engine operating point (Ne) according to a target engine torque command or the like from an integrated controller 6 that inputs an accelerator opening AP from an accelerator opening sensor 7 and an engine speed Ne from an engine speed sensor 9. , Te), for example, is output to a throttle valve actuator (not shown).

  The motor controller 2 receives the motor of the first motor generator MG1 in response to a target motor generator torque command or the like from the integrated controller 6 that inputs the motor generator rotational speeds N1 and N2 from the motor generator rotational speed sensors 10 and 11 by the resolver. A command for independently controlling the operating point (N1, T1) and the motor operating point (N2, T2) of the second motor generator MG2 is output to the power control unit 3.

  The power control unit 3 constitutes a high-power unit with a high voltage of the power supply system that can supply power to both motor generators MG1 and MG2 with a smaller current. As shown in FIG. It has a converter 3b, a drive motor inverter 3c, a generator generator inverter 3d, and a capacitor 3e. A drive motor inverter 3c is connected to the stator coil of the second motor generator MG2. A generator generator inverter 3d is connected to the stator coil of the first motor generator MG1. The joint box 3a is connected to a battery 4 that is discharged during power running and charged during regeneration.

  The brake controller 5 is adapted to control a brake fluid pressure unit 19 that independently controls the brake fluid pressures of the four wheels during low μ road braking or sudden braking. In the control, the ABS control for preventing the braking lock and the VDC control for ensuring the stability of the turning behavior of the vehicle are performed, and the control command to the integrated controller 6 and the brake hydraulic pressure unit 19 are applied when braking by the engine brake or the foot brake. Regenerative brake cooperative control is performed by issuing a control command.

  The brake controller 5 includes wheel speed information from the wheel speed sensors 12, 13, 14, 15, steering angle information from the steering angle sensor 16, braking operation from the master cylinder pressure sensor 17 and the brake stroke sensor 18. Quantity information, actual yaw rate information from the yaw rate sensor 27, and lateral acceleration information from the lateral acceleration sensor 28 are input. And based on these input information, a predetermined calculation process is performed and the control command by the process result is output to the integrated controller 6 and the brake hydraulic pressure unit 19. A front left wheel wheel cylinder 20, a front right wheel wheel cylinder 21, a rear left wheel wheel cylinder 22, and a rear right wheel wheel cylinder 23 are connected to the brake fluid pressure unit 19.

  The integrated controller 6 manages the energy consumption of the entire vehicle and has a function for running the vehicle with the highest efficiency. The integrated controller 6 performs engine operating point control by a control command to the engine controller 1 during acceleration running or the like. In addition, the motor generator operating point control is performed by a control command to the motor controller 2 at the time of stopping, running, braking, or the like. The integrated controller 6 includes the accelerator opening AP, the vehicle speed VSP, the engine speed Ne, the first motor generator speed N1, and the second motor generator speed N2 from the sensors 7, 8, 9, 10, and 11. Entered. And based on these input information, a predetermined calculation process is performed and the control command by the process result is output to the engine controller 1 and the motor controller 2. FIG. The integrated controller 6 and the engine controller 1, the integrated controller 6 and the motor controller 2, and the integrated controller 6 and the brake controller 5 are connected by bidirectional communication lines 24, 25, and 26, respectively, for information exchange.

Next, driving force performance will be described.
As shown in FIG. 2 (b), the driving force of the hybrid vehicle of the first embodiment includes the engine direct driving force (the driving force obtained by subtracting the generator driving amount from the total engine driving force) and the motor driving force (both motor generators MG1). , Driving force by the sum of MG2). As shown in FIG. 2A, the maximum driving force is configured such that the lower the vehicle speed, the greater the motor driving force. In this way, since the vehicle does not have a transmission and travels by adding the direct driving force of the engine E and the motor driving force that is electrically converted, the full power of the accelerator pedal is fully opened from low speed to high speed from the state of low steady driving power. Until now, it is possible to control the driving force seamlessly with good response to the driver's required driving force (torque on demand).
In the hybrid vehicle of the first embodiment, the engine E, the motor generators MG1, MG2, and the left and right front wheels (wheels) are connected without a clutch via the power split mechanism TM. Further, as described above, most of the engine power is converted into electric energy by a generator, and the vehicle is driven by a motor with high output and high response. For this reason, for example, when driving on a slippery road such as an ice burn, when the driving force of the vehicle changes suddenly due to wheel slip or wheel lock during braking, the parts of the power control unit 3 are protected from excessive current. Alternatively, it is necessary to protect the parts from over-rotation of the pinion of the power split mechanism TM. On the other hand, taking advantage of the characteristics of high-output and high-response motors, it has been developed from a component protection function to detect the drive slip of the drive wheel instantly, recover its grip, and drive the vehicle safely Adopts traction control. In addition to the motor traction control, the brake traction control that applies the braking force by the TCS brake hydraulic pressure only to the driving wheel in the driving slip state when only one wheel enters the driving slip state on the split μ road or the like is adopted. ing.

Next, the braking force performance will be described.
In the hybrid vehicle of the first embodiment, the kinetic energy of the vehicle is converted into electric energy by operating the second motor generator MG2 operating as a motor as a generator (generator) during braking by an engine brake or a foot brake. Then, a regenerative braking system that recovers and reuses the battery 4 is adopted.
As shown in Fig. 3 (a), the general regenerative brake cooperative control in this regenerative brake system calculates the required braking force with respect to the brake pedal depression amount, regardless of the magnitude of the required braking force. The required braking force is shared by the regenerative component and the hydraulic component.
In contrast, the regenerative brake cooperative control employed in the hybrid vehicle of the first embodiment calculates the required braking force with respect to the brake pedal depression amount as shown in FIG. 3 (b), and calculates the calculated required braking force. On the other hand, the regenerative brake is given priority, and as long as the regenerative portion can cover it, the regenerative portion is expanded to the maximum without using the hydraulic component. Thereby, especially in a traveling pattern in which acceleration / deceleration is repeated, energy recovery efficiency is high, and energy recovery by regenerative braking is realized up to a lower vehicle speed.

Next, the vehicle mode will be described.
As the vehicle mode in the hybrid vehicle of the first embodiment, as shown in the collinear diagram of FIG. 4, “stop mode”, “start mode”, “engine start mode”, “steady travel mode”, “acceleration mode” Have
In the “stop mode”, as shown in FIG. 4A, the engine E, the generator MG1, and the motor MG2 are stopped. In the “start mode”, as shown in FIG. 4 (2), the vehicle starts by driving only the motor MG2. In the “engine start mode”, as shown in FIG. 4 (3), the sun gear S rotates to start the engine E by the generator MG1 having a function as an engine starter. In the “steady travel mode”, as shown in FIG. 4 (4), the vehicle travels mainly by the engine E, and power generation is minimized in order to increase efficiency. In the “acceleration mode”, as shown in FIG. 4 (5), the engine E is rotated and the generator MG1 starts generating power. The electric power of the battery 4 is used to increase the driving force of the motor MG2. In addition, it accelerates.
In reverse running, in the “steady running mode” shown in FIG. 4 (4), if the rotation speed of the generator MG1 is increased while the increase in the rotation speed of the engine E is suppressed, the rotation speed of the motor MG2 becomes negative. Transition and reverse travel can be achieved.

  At the time of start-up, when the ignition key is turned, the engine E starts, and after the engine E is warmed up, the engine E stops immediately. When starting or at a light load, when starting or when going down a gentle hill that runs at a very low speed, the fuel is cut in areas where engine efficiency is low, and the engine stops and the motor MG2 runs. During normal travel, the driving force of the engine E is driven directly by one of the wheels by the power split mechanism TM, while the other drives the generator MG1 and assists the motor MG2. At the time of full open acceleration, power is supplied from the battery 4 and further driving force is added. When decelerating or braking, the wheel drives the motor MG2 and acts as a generator to perform regenerative power generation. The collected electrical energy is stored in the battery 4. When the charge amount of the battery 4 decreases, the generator MG1 is driven by the engine E and charging is started. When the vehicle is stopped, the engine E is automatically stopped except when the air conditioner is used or when the battery is charged.

Next, the operation will be described.
[Braking force control processing]
FIG. 6 is a flowchart showing the flow of the braking force control process executed by the integrated controller 6 of the first embodiment. Each step will be described below (braking force control means).

In step S1, it is determined whether or not it is time to release the TCS brake fluid pressure. If YES, the process proceeds to step S2. If NO, the TCS brake fluid pressure release determination in step S1 is repeated.
Here, “when the TCS brake fluid pressure is released” is, for example,
・ When the drive slip converges and the brake traction control ends,
-A VDC control system (vehicle behavior control) that applies braking force to each wheel independently to stabilize the turning behavior of the vehicle when running while executing brake traction control that applies braking force to only one of the left and right front wheels In the case of (means), when the start determination of the VDC control is made,
Etc.

In step S2, following the determination of releasing the TCS brake hydraulic pressure in step S1, a road surface friction coefficient is estimated based on the traveling torque at that time, and the process proceeds to step S3 (road surface friction coefficient equivalent value detecting means).
Here, the “estimation of the road surface friction coefficient” is estimated to be a low friction coefficient road as the cruise torque at the time of release determination of the TCS brake hydraulic pressure is small, and to be a high friction coefficient road as the cruise torque is large. .

In step S3, following the estimation of the road surface friction coefficient in step S2, a time constant for determining a decrease rate in the decrease response characteristic of the TCS brake hydraulic pressure corresponding to the estimated road surface μ is set, and the process proceeds to step S4.
Here, as shown in FIG. 7, the setting of the “time constant” is set to a higher value as the estimated road surface μ is lower, and set to a lower value as the estimated road surface μ is higher. , Given in inverse proportion. Also, the higher the “time constant”, the slower the zero return rate of the TCS brake hydraulic pressure, and the lower the “time constant”, the faster the zero return rate of the TCS brake hydraulic pressure.

  In step S4, following the setting of the time constant in step S3, a zero return hydraulic pressure command for gradually decreasing the TCS brake hydraulic pressure at the time of release determination is output based on the reduction response characteristic by the set time constant, and the process proceeds to the end. To do.

[Background of traction control]
For example, Japanese Patent Application Laid-Open No. 10-304514 discloses a technique (angular acceleration control) for improving torque down response in the initial stage of slip. This technique is often applied to a vehicle using a motor as a unit for generating a driving force, such as a hybrid vehicle, an electric vehicle, and a fuel cell vehicle. The basis of this technology is a configuration that predicts that drive slip will occur when the rate of change (angular acceleration) of the rotational angular velocity of the drive wheels is greater than or equal to a predetermined value, and reduces the motor torque. With this configuration, it is possible to prevent a drive slip that occurs with an increase in motor torque.

Here, the reason why “angular acceleration control” that suppresses slip with high responsiveness in the early stage of generation of drive slip in a hybrid vehicle using a motor as a unit for generating drive force will be described.
If there is no motor traction control device and the drive slips, the power generation of the engine cannot catch up and the motor draws more current from the battery. Therefore, an overcurrent is generated in the motor drive circuit, and the elements on the circuit are damaged. For example, in the power control unit 3 according to the first embodiment, as shown by the arrow in FIG. 5, when an overcurrent flows through the capacitor 3e, the fuse of the joint box 3a and the switching circuit of the boost converter 3b are damaged. There is a case. Moreover, in a hybrid vehicle or a fuel cell vehicle, overcurrent tends to flow as the motor output (motor output ratio) is larger than that of the secondary battery. Further, there is a relationship that overvoltage and overcurrent flow more easily as the output of the engine and fuel cell (engine output ratio) is larger than the secondary battery. Therefore, in order to reliably protect the parts, it is necessary to perform motor traction control that converges the drive slip with good response by "angular acceleration control" in which torque is limited when slipping.

  However, when driving slip occurs only on one wheel while traveling on split μ roads with different road surface friction coefficients, the torque to the driving wheel on the high μ road side also decreases when motor traction control is performed by reducing the motor torque. It will be. Therefore, as used in existing engine cars, for example, when there is a difference in the slip amount between the left and right drive wheels while traveling on a split μ road, braking force is applied only to the drive wheels that have slipped first. Brake traction control is possible.

  In this brake traction control, although slip suppression can be performed with good response to driving slip of one wheel, for example, the TCS brake hydraulic pressure remains by intervening VDC control during TCS brake control on the split μ road. When releasing the brake traction control without removing the TCS brake fluid pressure of the driving wheel on the low μ road side, the traction recovers and a slip occurs again. The hybrid vehicle is equipped with a motor as the power source. And in an electric vehicle, a motor is rotated by a drive wheel in a slip state, and an overcurrent is generated in a high-power unit having a drive circuit. In particular, when the motor is a three-phase AC motor, an overcurrent flows in a single phase.

That is, in the case of a three-phase AC motor, as shown in FIG. 8 (a), PWM control is performed when the motor speed is low (see FIG. 8 (b)), and when the motor speed is high, Rectangular wave control is performed (see FIG. 8 (c)), and modulation control is performed when the motor rotational speed is in the intermediate rotational speed region.
In this case, when the three-phase AC motor is rotated by the drive slip and the motor rotation speed enters the high rotation speed region, rectangular wave control is performed as shown in FIG. In the rectangular wave control region surrounded by, an overcurrent flows in a single phase among the three-phase power cables connected to the motor.

[About VDC control]
The VDC control system is a system that ensures the stability of the turning behavior of the vehicle. Normally, the vehicle turns stably according to the steering operation. However, depending on unexpected conditions such as road surface conditions, vehicle speed, emergency avoidance of obstacles, or external factors, it tends to cause strong rear-wheel skidding or front-wheel skidding. . In such a case, the VDC control system automatically controls engine / motor output control and brake control of each wheel in order to ensure the stability of the vehicle behavior, and relieves strong front wheel skidding or rear wheel skidding. System.

This VDC control system senses the state of the vehicle by signals from various sensors such as the yaw rate sensor 27 and the lateral acceleration sensor 28, and outputs a control signal to the brake actuator, and outputs the engine and motor. And torque control. For example, the following two examples are given as situations in which the tire exceeds the lateral grip limit.
(1) The rear wheel is losing grip relative to the front wheel (strong rear wheel skidding).
(2) When the front wheel is losing grip relative to the rear wheel (strong front skid).
The VDC control system operates in the situation shown in FIG. 9 to alleviate the strong rear wheel skid or front wheel skid tendency of the vehicle.

  The turning state of the vehicle is determined by calculating by the brake controller 5 based on detected values such as a steering angle, a vehicle speed, a yaw rate, and a lateral acceleration. Judgment of the strong rear wheel skid tendency of the vehicle is made based on the values of the slip angle of the vehicle body and the slip angular velocity of the vehicle body. When the slip angle of the vehicle body is large and the slip angular velocity is also large, it is calculated that the vehicle body tends to skid on the rear wheels (see FIG. 10 (a)). The determination of the strong front wheel skid tendency of the vehicle is made based on the values of the target yaw rate and the actual yaw rate. This means that when the driver steers, if the actual yaw rate is less than the target yaw rate that should be generated (determined from the steering angle and vehicle speed), the car and others will not bend. When it is larger, the calculation is performed (see FIG. 10B).

  As an operation method of the VDC control, for example, when it is determined by the brake controller 5 that the vehicle is in a strong rear-wheel skid or a strong front-wheel skid, the engine / motor output is reduced and the front or rear wheel A braking force is applied to the vehicle and the yawing moment of the vehicle is controlled to alleviate the side slip condition of the vehicle. In order to mitigate the strong rear-wheel skidding tendency of the vehicle, when it is determined that the rear-wheel skidding tendency is large, the front and rear wheels on the outside of the turn are braked according to the degree of the tendency, A moment is generated to suppress the rear wheel skid tendency (see FIG. 11 (a)). In addition, a reduction in vehicle speed due to braking force also contributes to ensuring vehicle behavior stability. In order to mitigate the strong front skidding tendency of the vehicle, when it is judged that the front skidding tendency is large, the engine / motor output is controlled according to the degree of the tendency, and the front and rear wheels are braked to By reducing the force, the tendency of skidding on the front wheels is suppressed (see FIG. 11 (b)).

[Brake force control action]
In the first embodiment, when releasing the brake traction control, by changing the release speed of the TCS brake hydraulic pressure according to the estimated road surface μ, the occurrence of re-slip of the driving wheel to which the braking force has been applied is suppressed. In addition, the overcurrent generation in the high power unit was prevented.

  That is, in the flowchart of FIG. 6 in which the determination of release of the TCS brake hydraulic pressure is made, the flow proceeds from step S1, step S2, step S3, and step S4. In step S2, the road surface friction coefficient is estimated based on the cruise torque. In step S3, a time constant for determining the rate of decrease in the TCS brake hydraulic pressure decrease response characteristic according to the estimated road surface μ is set. In step S4, the TCS at the time of release determination is determined by the decrease response characteristic based on the set time constant. A zero return hydraulic pressure command for gradually decreasing the brake hydraulic pressure is output.

  For example, on a split μ road, VDC brake control that suppresses the tendency of skidding on the rear wheels when the vehicle starts turning during running while performing brake TCS control that applies braking force only to the right front wheel of the left and right front wheels intervenes The braking force control action when the TCS brake hydraulic pressure is released by the intervention of the VDC brake control will be described with reference to FIGS.

  For example, as shown in FIG. 12, on a split μ road where μ = 0.3 and μ = 0.1, the brake traction control that applies the braking force by the TCS brake hydraulic pressure only to the right front wheel among the left and right front wheels Driving slip of the front wheels is suppressed. When the split μ road is over and at the same time the vehicle enters a right curve road, the vehicle has a tendency to skid on the rear wheels at the time when the vehicle starts turning. The TCS brake fluid pressure is released, and on the VDC control side, a braking force based on the VDC brake fluid pressure is applied to the front and rear wheels (left front wheel and left rear wheel) on the turning outer wheel side, thereby generating a counterclockwise moment. The rear wheel skid tendency is suppressed.

  At this time, as shown in FIG. 13, at the time t1 when switching from the TCS brake control to the VDC brake control, the TCS brake hydraulic pressure of the right front wheel is released, and the supply of the VDC brake hydraulic pressure of the left front wheel is started. Here, if the TCS brake fluid pressure of the right front wheel is suddenly released, the braking force of the right front wheel disappears all at once, and the traction is restored, causing the right front wheel to re-slip and rotate by the right front wheel ( The rotational speed of the second motor generator MG2) rises rapidly and enters a slip-up state, as shown by the dotted line characteristics in FIG.

  However, in the first embodiment, at the time point t1 when switching from the TCS brake control to the VDC brake control, the TCS brake hydraulic pressure of the right front wheel is made slower as the road becomes lower μ according to the estimated road surface μ (cruising torque). As shown in the drive motor rotational speed characteristics shown by the solid line in FIG. 13, the slip-up that suppresses the occurrence of re-slip and flows an overcurrent to a single phase is shown. It is prevented from entering a state.

  That is, when switching from TCS brake control to VDC brake control, leaving the TCS brake hydraulic pressure may cause a slight decrease in control performance that stabilizes the vehicle behavior for VDC control. By preventing this in advance, parts protection by TCS brake control is prioritized.

Next, the effect will be described.
In the braking force control apparatus for an electric vehicle according to the first embodiment, the effects listed below can be obtained.

  (1) At least one motor mounted on the drive wheel power source, a high-power unit connected to the motor, and brake traction control for restoring tire grip by applying braking force to the slip wheel when drive slip occurs And a road surface friction coefficient equivalent value detecting means (step S2) for detecting a road surface friction coefficient equivalent value, wherein the brake traction control means cancels the brake traction control. When the brake traction control is released, the occurrence of re-slip of the driving wheel to which the braking force is applied is suppressed in advance because the release speed of the braking force is changed according to the road surface friction coefficient equivalent value (step S3). In addition, it is possible to prevent the occurrence of overcurrent in the high voltage unit.

  (2) When releasing the brake traction control, the brake traction control means slows the release speed of the braking force as the road surface friction coefficient equivalent value indicates a low friction coefficient road. Regardless of whether the road surface friction coefficient is high or low, the occurrence of re-slip can be reliably suppressed while ensuring the release responsiveness of the brake traction control.

(3) The road surface friction coefficient equivalent value detection means uses the vehicle's cruise torque when releasing the brake traction control as a road surface friction coefficient equivalent value, and detects a lower friction coefficient road as the cruise torque is smaller. Using the torque, the road surface friction coefficient can be estimated easily and accurately.
In other words, the vehicle's cruising torque when releasing the brake traction control exists in the limit region of the friction circle, which becomes a larger circle as the road surface μ becomes larger, so the magnitude of the cruising torque represents the height of the road surface μ. Therefore, it is possible to estimate the road friction coefficient with high accuracy.

  (4) The brake traction control means is configured to independently apply braking force to each wheel in order to stabilize the behavior of the vehicle during running while executing brake traction control that applies braking force to only one of the left and right drive wheels. In the VDC control system that provides the VDC control, when it is determined that the VDC control is started, it is determined that it is time to release the brake traction control. At the time of transition to, seamless control transition can be achieved with a small influence on the vehicle behavior.

  As mentioned above, although the braking force control apparatus of the electric vehicle of this invention was demonstrated based on Example 1, it is not restricted to this Example 1 about a concrete structure, Each claim of a claim is a claim. Design changes and additions are allowed without departing from the gist of the invention.

  In the first embodiment, an example is shown in which only “angular acceleration control” is executed as motor traction control. However, the present invention is also applicable to a motor that executes motor traction control combining “angular acceleration control” and “slip amount control”. it can.

  In the first embodiment, as the road surface friction coefficient equivalent value detecting means, the estimated road surface μ is detected based on the traveling torque of the vehicle. For example, the means for detecting the estimated road surface μ based on the output torque at the start of slip, infrastructure information It is also possible to use well-known road surface friction coefficient equivalent value detection means such as means for detecting road surface μ by obtaining.

  In the first embodiment, an example of application to a hybrid vehicle including one engine, two motor generators, and a power split mechanism has been shown. However, the braking force control device of the present invention is a hybrid vehicle including another power unit structure. In short, any vehicle such as an electric vehicle, a fuel cell vehicle, a motor 4WD vehicle, or the like that is equipped with at least one motor as a power source for driving wheels can be applied.

1 is an overall system diagram illustrating a hybrid vehicle to which a braking force control device according to a first embodiment is applied. FIG. 2 is a driving force performance characteristic diagram and a driving force conceptual diagram in a hybrid vehicle to which the braking force control device of Example 1 is applied. It is a contrast characteristic figure showing the braking force performance by regenerative cooperation in the hybrid vehicle to which the braking force control device of Example 1 was applied. It is a collinear diagram which shows each vehicle mode in the hybrid vehicle to which the braking force control apparatus of Example 1 was applied. It is a block diagram which shows the high electric power unit (battery, power control unit, 1st motor generator, 2nd motor generator) of the hybrid vehicle of Example 1. FIG. 3 is a flowchart illustrating a flow of a braking force control process executed by the integrated controller according to the first embodiment. It is a figure which shows the time constant characteristic with respect to the estimated road surface (micro | micron | mu) used by the braking force control process of Example 1. FIG. It is a figure explaining the mechanism in which an overcurrent flows into the single phase by the braking force control in Example 1. FIG. It is a situation explanatory view in which VDC control operates. FIG. 6 is an explanatory diagram of a method for determining whether a vehicle body has a rear-wheel side-slip tendency or a front-wheel side-slip tendency in VDC control. It is explanatory drawing of the relaxation condition of the rear-wheel skid tendency and the mitigation condition of the front-wheel skid tendency in VDC control. FIG. 7 is an operation explanatory diagram illustrating an example of a transition from TCS brake control to VDC brake control in the braking force control according to the first embodiment. 4 is a time chart showing characteristics of a right front wheel brake fluid pressure, a left front wheel brake fluid pressure, and a drive motor rotational speed when shifting from TCS brake control to VDC brake control in the braking force control in the first embodiment.

Explanation of symbols

E engine
MG1 1st motor generator
MG2 Second motor generator (motor)
OS output sprocket
TM power split mechanism 1 engine controller 2 motor controller 3 power control unit 4 battery 5 brake controller 6 integrated controller 7 accelerator opening sensor 8 vehicle speed sensor 9 engine speed sensor 10 first motor generator speed sensor 11 second motor generator speed Sensor 12 Front left wheel speed sensor 13 Front right wheel speed sensor 14 Rear left wheel speed sensor 15 Rear right wheel speed sensor 16 Steering angle sensor 17 Master cylinder pressure sensor 18 Brake stroke sensor 19 Brake fluid pressure unit 20 Front left wheel wheel cylinder 21 Front right wheel wheel cylinder 22 Rear left wheel wheel cylinder 23 Rear right wheel wheel cylinder 27 Yaw rate sensor 28 Lateral acceleration sensor

Claims (4)

At least one motor mounted on the power source of the drive wheel, a high-power unit connected to the motor, and a brake traction control means for recovering the tire grip by applying a braking force to the slip wheel when drive slip occurs; In a braking force control device for an electric vehicle equipped with
A road surface friction coefficient equivalent value detecting means for detecting a road surface friction coefficient equivalent value is provided,
The brake traction control device for an electric vehicle, wherein the brake traction control means changes a braking force release speed according to a road surface friction coefficient equivalent value when releasing the brake traction control. In the braking force control device for an electric vehicle according to claim 1,
When the brake traction control means cancels the brake traction control, the braking force control apparatus for an electric vehicle slows the braking force release speed as the road surface friction coefficient equivalent value indicates a low friction coefficient road. In the braking force control device for an electric vehicle according to claim 1 or 2,
The road surface friction coefficient equivalent value detecting means uses the vehicle's cruising torque when releasing the brake traction control as a road surface friction coefficient equivalent value, and detects that the road surface is a lower friction coefficient road as the cruising torque is smaller. Vehicle braking force control device. In the braking force control device for an electric vehicle according to any one of claims 1 to 3,
The brake traction control means applies braking force to each wheel independently in order to stabilize the behavior of the vehicle during running while executing brake traction control that applies braking force to only one of the left and right drive wheels. A braking force control device for an electric vehicle, characterized in that, in the vehicle behavior control means, it is determined that it is time to release the brake traction control when the vehicle behavior control start determination is made.

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