Vehicle control system

Abstract

The present invention provides a vehicle control device that can suppress vibrations and shocks that occur when the parking lock mechanism is released while the drive shaft is twisted. [Solution] When the parking lock mechanism is locked and the braking torque acting on the wheels is greater than or equal to a predetermined torque, an estimated torsional acceleration is calculated by subtracting the acceleration in the longitudinal direction of the vehicle corresponding to the vehicle's tilt angle from the acceleration at the time the braking torque exceeds the predetermined torque. When switching the parking lock mechanism from the locked state to the unlocked state, if the braking torque is greater than or equal to the predetermined torque (Yes in step S34), a torque based on the estimated torsional acceleration is output from the motor, and if the braking torque is less than the predetermined torque (No in step S34), a torque based on the acceleration in the longitudinal direction of the vehicle corresponding to the vehicle's tilt angle is output from the motor.

Description

Technical Field

[0001] This invention relates to a vehicle control device capable of locking a drive shaft by a parking lock mechanism.

Background Art

[0002] Patent Document 1 describes a parking mechanism composed of a parking gear interlocked with a wheel and a parking pole that operates according to a driver's shift operation and meshes with the parking gear to lock the parking gear, a foot brake device that applies a braking force to the wheel by operating according to a depression operation of a brake pedal by the driver, and an electric parking brake that applies a braking force to the wheel continuously by operating in conjunction with the parking lock mechanism. This control device is configured such that, when the road surface gradient angle is greater than or equal to a predetermined angle, even if the depression operation of the brake pedal by the driver is released after a shift operation for selecting the parking position is performed until the electric parking brake applies a braking force to the wheel, the foot brake device continues to apply a braking force to the wheel.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The control device described in Patent Document 1 is configured to prevent the drive shaft from twisting by applying braking torque to the wheels via the foot brake device until the braking torque from the electric parking brake acts on the wheels. In other words, when the parking lock is engaged, the device is configured to constantly apply braking torque to the wheels. However, if the electric parking brake cannot be activated, or if there is no electric parking brake, or if the control device does not have a function to apply braking torque to the wheels via the foot brake device until the braking torque from the electric parking brake acts on the wheels, the drive shaft may twist. Since the control device described in Patent Document 1 does not anticipate such twisting of the drive shaft, it may not be able to suppress the vibrations and shocks that occur when the drive shaft twist is released after the parking lock mechanism is released.

[0005] This invention was made in view of the above-mentioned technical problems, and the object of this invention is to provide a vehicle control device that can suppress the occurrence of vibrations and shocks when the parking lock mechanism is released while the drive shaft is twisted. [Means for solving the problem]

[0006] To achieve the above objective, this invention provides a vehicle control device comprising: a drive shaft with one end connected to a wheel; a motor capable of transmitting torque to the drive shaft; a parking lock mechanism capable of selectively switching between a locked state in which the rotation of a predetermined rotating member between the motor and the drive shaft is prohibited and an unlocked state in which the predetermined rotating member is rotatable; and a braking device that applies braking torque to the wheel, wherein the device includes a controller for controlling the motor, the controller comprising: a parking determination unit for determining whether the parking lock mechanism is in the locked state; a brake determination unit for determining the braking torque being applied to the wheel by the braking device; an acceleration acquisition unit for acquiring the longitudinal acceleration of the vehicle; and a control device for determining whether the parking lock mechanism is in the locked state. The invention is characterized by comprising: a torsional acceleration calculation unit that calculates an estimated torsional acceleration by subtracting the acceleration in the longitudinal direction of the vehicle corresponding to the vehicle's tilt angle from the acceleration acquired by the acceleration acquisition unit at the time the braking torque becomes equal to or equal to the predetermined torque, and a motor control unit that, when switching the parking lock mechanism from the locked state to the unlocked state, outputs a torque from the motor based on the estimated torsional acceleration if the braking torque is equal to or equal to the predetermined torque, and outputs a torque from the motor based on the acceleration in the longitudinal direction of the vehicle corresponding to the vehicle's tilt angle if the braking torque is less than the predetermined torque.

[0007] Furthermore, in this invention, the torsional amount estimation acceleration calculation unit may perform a low-pass filter process to extract accelerations of a predetermined frequency or lower from the accelerations acquired by the acceleration acquisition unit, thereby determining the acceleration of the vehicle in the longitudinal direction corresponding to the vehicle's tilt angle.

[0008] Furthermore, in this invention, the predetermined frequency may include the natural frequency of the drive shaft.

[0009] Furthermore, in this invention, the torsional acceleration estimation unit may determine the acceleration in the longitudinal direction of the vehicle based on the average value of the acceleration acquired by the acceleration acquisition unit over a predetermined period. [Effects of the Invention]

[0010] The vehicle control device in this invention calculates an estimated torsional acceleration by subtracting the acceleration corresponding to the vehicle's tilt angle from the acceleration at the point when the braking torque exceeds a predetermined torque, provided that the parking lock mechanism is locked and the braking torque acting on the wheels is greater than or equal to a predetermined torque. Then, when switching the parking lock mechanism from the locked state to the unlocked state, if the braking torque is greater than or equal to the predetermined torque, the motor outputs torque based on the estimated torsional acceleration. If the braking torque is less than the predetermined torque, the motor outputs torque based on the acceleration in the longitudinal direction of the vehicle corresponding to the vehicle's tilt angle. In other words, the motor torque is determined based on the acceleration at the point when the braking torque acts on the wheels and the acceleration corresponding to the vehicle's tilt angle. Therefore, it is possible to suppress the discrepancy between the torsional torque released when the parking lock mechanism is released and the torque output from the motor, and to suppress the occurrence of vibrations and shocks when the parking lock mechanism is released. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a schematic diagram showing an example of a vehicle according to an embodiment of this invention. [Figure 2] Figure 2 is a block diagram illustrating the functional configuration of the controller. [Figure 3] Figure 3 is a flowchart illustrating an example of control for setting the non-braking and braking states of the EPB (Electronic Packing Bearing). [Figure 4] Figure 4 is a flowchart illustrating an example of control for setting the twist detection flag. [Figure 5] Figure 5 is a flowchart illustrating an example of control for determining the estimated torsional acceleration. [Figure 6]Figure 6 is a time chart illustrating the changes in drive shaft torque (torsional torque), vehicle longitudinal acceleration, torsional detection flag, and EPB state when the EPB switches from a non-braking state to a braking state during the process of drive shaft twisting. [Figure 7] Figure 7 is a flowchart illustrating an example of control for determining the motor's assist torque. [Figure 8] Figure 8 shows an example of a map for determining the target value of assist torque based on the estimated torsional acceleration. [Modes for carrying out the invention]

[0012] This invention will be described based on the embodiments shown in the figures. The embodiments described below are merely examples of how this invention can be implemented and do not limit it.

[0013] An example of a vehicle in this embodiment of the present invention is schematically shown in Figure 1. The vehicle Ve shown in Figure 1 is an electric vehicle equipped with a motor (MG) 1 as a driving force source. The motor 1 can be configured in the same way as motors provided as driving force sources in conventional electric vehicles and hybrid vehicles. That is, in addition to functioning as a motor that generates driving torque by being supplied with power from an energy storage device (not shown), it also functions as a generator that converts at least a portion of the power of the output shaft 2 into electricity by being rotated along with the output shaft 2. Specifically, it is configured as a permanent magnet synchronous motor or an induction motor, etc.

[0014] A first drive gear 3 is attached to the output shaft 2 of motor 1. A first driven gear 4, which meshes with the first drive gear 3 and is formed to be larger in diameter than the first drive gear 3, is attached to an intermediate shaft 5 that is positioned parallel to the output shaft 2 of motor 1. In other words, the first drive gear 3 and the first driven gear 4 constitute a reduction gear pair.

[0015] A second drive gear 6 is further attached to the intermediate shaft 5. A second driven gear 7, which meshes with the second drive gear 6 and is formed to be larger in diameter than the second drive gear 6, is attached to the output shaft 8 of the motor 1, which is arranged parallel to the output shaft 2 and the intermediate shaft 5. In other words, the second drive gear 6 and the second driven gear 7 constitute a reduction gear pair. One end of a drive shaft 9 is connected to the output shaft 8 so as to be able to rotate as a whole, and a wheel 10 is connected to the other end of the drive shaft 9.

[0016] Furthermore, a parking lock mechanism 11 is provided that can selectively switch between a locked state in which the rotation of the intermediate shaft 5 is prohibited and an unlocked state in which the intermediate shaft 5 is rotatable. This parking lock mechanism 11 can be configured in the same way as parking lock mechanisms provided in conventional vehicles. Specifically, the parking lock mechanism 11 consists of a parking lock gear 12 attached to the intermediate shaft 5, a parking pawl 13 that can selectively engage with the parking lock gear 12, and an actuator (not shown) that operates the parking pawl 13. When a parking range is selected by the shift device 24 described later, the parking pawl 13 is rotated by an actuator (not shown) or the like to engage with the parking lock gear 12. By engaging the parking pawl 13 with the parking lock gear 12 in this way, the rotation of the parking lock gear 12 is prohibited. Therefore, the rotation of the drive shaft 9, which is connected to the parking lock gear 12 via the intermediate shaft 5 or the like in a way that allows torque transmission, is prohibited.

[0017] In the vehicle Ve shown in FIG. 1, a braking device 14 is provided that applies a braking torque corresponding to the operation amount of a brake pedal (not shown) operated by a driver to the wheel 10. This braking device 14 can be configured in the same manner as the braking devices provided in conventional vehicles. That is, by sandwiching a brake rotor that rotates integrally with the wheel 10 with brake pads, a disc brake that applies a braking torque to the wheel 10, or by pressing a brake shoe from the inside of a drum that rotates integrally with the wheel 10, a drum brake that applies a braking torque to the wheel 10, etc. can be configured. Further, the clamping force of these brake pads and the pressing force of the brake shoes can be controlled by an actuator (not shown) that generates hydraulic pressure or electromagnetic force according to the operation amount of the brake pedal.

[0018] Furthermore, an electric parking brake (hereinafter referred to as EPB) 15 is provided in the vehicle Ve shown in FIG. 1. This EPB 15 is configured in the same manner as the EPBs provided in conventional vehicles. When a shift operation for selecting the parking range is performed, the motor 16 operates, causing a caliper or brake shoe (not shown) to be driven to apply a braking torque to the wheel 10. When a driving range other than the parking range is selected, it is configured to reduce the braking torque. From the perspective of the mounting property of the motor 16, etc., the motor 16 is provided on the vehicle body, and wires or the like for connecting the motor 16 to the caliper or brake shoe are provided, and by rotating the motor 16, the wires can be wound up or the like to drive the caliper or brake shoe. The above-described braking device 14 and EPB 15 correspond to the "braking device" in the embodiment of this invention.

[0019] In the example shown in FIG. 1, the motor 1, the gear train that transmits torque from the motor 1 to the output shaft 8, and the output shaft 8 are housed in one case 17, and the case 17 is connected to the vehicle body 19 via the mount 18. Also, the wheel 10 is held by the vehicle body 19 via the suspension 20.

[0020] In the vehicle Ve shown in Figure 1, when the brake pedal is operated and the driver performs a shift operation to select the parking range, the vehicle is permitted to switch the driving range to the parking range. When switching to the parking range in this manner, the rotation of the intermediate shaft 5 is prohibited by the parking lock mechanism 11, and braking torque is applied to the wheels 10 by the EPB 15.

[0021] As described above, the time from when the shift operation is performed until the rotation of the intermediate shaft 5 is prohibited by the parking lock mechanism 11 may be shorter than the time until braking torque is applied to the wheels 10 by the EPB 15. Therefore, for example, when parking the vehicle Ve on a slope or when the wheels 10 are parked on top of some object, if the driver reduces the amount of brake pedal operation before braking torque is applied to the wheels 10 by the EPB 15, the wheels 10 will rotate (turn) even though the rotation on the input side of the drive shaft 9 is prohibited. Also, if the EPB 15 cannot be activated for some reason, the wheels 10 will rotate (turn) even though the rotation on the input side of the drive shaft 9 is prohibited after the driver reduces the amount of brake pedal operation. As a result, the drive shaft 9 twists. In other words, torque (hereinafter referred to as torsional torque) corresponding to its elastic modulus and the amount of twist accumulates in the drive shaft 9.

[0022] When the drive shaft 9 is twisted in this manner, and the shift is operated to select a driving range other than the parking range, the twist of the drive shaft 9 is released at the same time that the lock on the intermediate shaft 5 by the parking lock mechanism 11 is released. In other words, the torsional torque accumulated in the drive shaft 9 is transmitted to the motor 1, which is the driving force source. When this twist of the drive shaft 9 is released, the torque pulsates according to the elastic modulus of the drive shaft 9. As a result, the transmission of the pulsating torque to the motor 1 may cause the vehicle Ve to vibrate.

[0023] Furthermore, the pulsation of torque in the drive shaft 9 can cause the suspension 20 to vibrate vertically, and this vibration can be transmitted to the vehicle body 19, potentially causing the vehicle Ve to vibrate.

[0024] Therefore, if the drive shaft 9 is twisted, the motor 1 outputs an assist torque to counteract the torsional torque accumulated in the drive shaft 9, thereby suppressing vibration when the parking lock mechanism 11 is released.

[0025] On the other hand, the parking lock mechanism 11 prevents rotation of one end, and the small braking torque acting on the wheel 10 allows the wheel 10 to rotate, which in turn allows rotation of the other end, causing the drive shaft 9 to twist. At this time, a torsional torque accumulates in the drive shaft 9, corresponding to the rotation angle of the other end relative to the one end and the elastic modulus of the drive shaft 9. In this process of the drive shaft 9 twisting, a reaction torque is generated in the direction that eliminates the twist of the drive shaft 9. This reaction torque increases or decreases in magnitude according to the elastic modulus of the drive shaft 9. Therefore, the amount of twist in the drive shaft 9 gradually increases while fluctuating.

[0026] Therefore, for example, if no braking torque from the brake device 14 or EPB 15 is acting on the wheel 10, the drive shaft 9 will twist until the torsional torque of the drive shaft 9 balances out with the torque that rotates the wheel 10 according to the tilt angle of the vehicle Ve and the vehicle weight, and a torsional torque corresponding to the amount of twist at that point will accumulate in the drive shaft 9. In other words, the torsional torque of the drive shaft 9 will gradually decrease toward an magnitude corresponding to the tilt angle of the vehicle Ve.

[0027] Furthermore, if braking torque is applied to the wheel 10 by the brake device 14 or EPB 15 while the drive shaft 9 is twisting, the amount of twist in the drive shaft 9 becomes the amount of twist at the time the braking torque is applied. In other words, the amount of twist in the drive shaft 9 is maintained while the amount of twist in the drive shaft 9 is increasing or decreasing. That is, depending on the timing of when the braking torque is applied to the wheel 10, the amount of twist in the drive shaft 9 may be greater or less than the amount of twist in the drive shaft 9 when no braking torque is applied to the wheel 10. In other words, the torsional torque of the drive shaft 9 may differ from the torque corresponding to the inclination angle of the vehicle Ve.

[0028] Therefore, the vehicle Ve shown in Figure 1 is equipped with an electronic control unit (hereinafter referred to as ECU) 21 that controls the motor 1 to output an assist torque corresponding to the torsional torque of the drive shaft 9 when the parking lock mechanism 11 is released. This ECU 21 is mainly composed of a microcomputer and is configured to control the output torque of the motor 1 based on the input signal and pre-stored calculation formulas. This ECU 21 corresponds to the "controller" in this embodiment of the invention.

[0029] In the example shown in Figure 1, the ECU 21 is connected to an acceleration sensor 22 that detects the longitudinal acceleration of the vehicle Ve, a resolver 23 that detects the rotational speed (rotation angle) of the motor 1, and a shift sensor 25 that detects the driving range selected by the shift device 24, and signals are input from these sensors 22, 23, and 25. In addition, the ECU 21 is connected to an EPB-ECU 26 that controls the EPB 15 and a B-ECU 27 that controls the brake device 14, and signals are input from these ECUs 26 and 27.

[0030] The above-described shift device 24 may be a so-called momentary type shift device in which, for example, operating the shift lever 28 to a shift position corresponding to the driving range turns on a shift sensor 25 corresponding to that shift position, a signal is input to the ECU 21, and releasing the operation of the shift lever 28 returns the shift lever 28 to a predetermined standby position. The shift device 24 may also be provided with a parking button for selecting a parking range, and the shift sensor 25 may include a sensor that is turned on when the parking button is pressed.

[0031] Furthermore, the EPB-ECU26 is connected to, for example, the shift sensor 25, and based on the signal input from the shift sensor 25, it determines whether or not the EPB 15 is operating, and based on the result of that determination, it outputs a command signal to the ECU21 and the motor 16. In addition, the B-ECU27 receives signals such as the amount of brake pedal depression or pedal force or master cylinder pressure, or signals that detect hydraulic pressure or electromagnetic force to generate braking torque for the brake device 14, and based on these signals, it determines the braking torque to be applied to the brake device 14 or the braking torque that is currently applied to the brake device 14. Then it outputs a signal representing the magnitude of that braking torque to the ECU21.

[0032] Figure 2 shows a block diagram illustrating the functional configuration of the ECU 21. The ECU 21 shown in Figure 2 comprises a parking determination unit 29, a brake determination unit 30, an acceleration acquisition unit 31, a torsion amount estimation acceleration calculation unit 32, and a motor control unit 33.

[0033] The parking determination unit 29 determines whether the vehicle is in a parking range where the rotation of the intermediate shaft 5 is prohibited by the parking lock mechanism 11, or in other words, whether it is in a locked state where the rotation of the intermediate shaft 5 is prohibited. Specifically, it determines whether the vehicle is in a parking range based on whether a predetermined time has elapsed since the parking range was selected by a shift operation, or based on a command signal to the actuator that operates the parking pole 13.

[0034] The brake determination unit 30 determines the braking torque acting on the wheel 10. Specifically, it determines the braking torque acting on the wheel 10 based on signals input to the ECU 21 from the EPB-ECU 26 and B-ECU 27.

[0035] The acceleration acquisition unit 31 acquires the acceleration acting on the vehicle Ve in the longitudinal direction based on the signal detected by the acceleration sensor 22.

[0036] The torsional acceleration calculation unit 32 estimates the torsional amount of the drive shaft 9 from the acceleration acquired by the acceleration acquisition unit 31. Specifically, when the parking lock mechanism 11 is locked and braking torque is applied by the brake device 14 or EPB 15 to suppress the rotation of the wheel 10, the acceleration at the moment when the braking torque is first applied to the wheel 10 by the brake device 14 or EPB 15 is acquired, and the torsional acceleration is calculated by subtracting the acceleration corresponding to the inclination angle of the vehicle Ve from the acquired acceleration.

[0037] The motor control unit 33 controls the motor 1 to output an assist torque that counteracts the torsional torque of the drive shaft 9 when switching the parking lock mechanism 11 from the locked state to the unlocked state. Specifically, when switching the parking lock mechanism 11 to the unlocked state, if braking torque is being applied to the wheels 10 by the brake device 14 or EPB 15, the torque of the motor 1 is set based on the estimated torsional acceleration. If no braking torque is being applied to the wheels 10 by the brake device 14 or EPB 15, the torque of the motor 1 is set based on the acceleration corresponding to the tilt angle of the vehicle Ve.

[0038] As described above, the drive shaft 9 twists when one end is locked and the other end is rotatable. In other words, the drive shaft 9 twists when the parking lock mechanism 11 is locked and no braking torque is applied to the wheel 10 by the brake device 14 or EPB 15. Therefore, it is first determined whether or not braking torque is being applied to the wheel 10. A flowchart illustrating an example of this control is shown in Figure 3. This control example shown in Figure 3 is executed by the brake determination unit 30.

[0039] In the example shown in Figure 3, first, it is determined whether the EPB 15 has switched from a release state, where it is not braking and the motor 16 is not energized, to a transition state, where the motor 16 is energized in order to apply braking torque to the wheel 10 (step S1). This step S1 is a step to determine whether the EPB 15 has been activated in order to apply braking torque to the wheel 10. Therefore, the determination can be made based on whether or not the motor 16 has been energized in order to begin applying braking torque to the wheel 10.

[0040] If step S1 is positively determined because the EPB15 has switched from the released state to the transition state, in other words, because power has started to be supplied to the motor 16, the EPB holding force determination counter is set to "0" (step S2). On the other hand, if step S1 is negatively determined because the EPB15 is in the released state, or in the transition state, or in the locked state with the wheel 10 locked, and it is not the timing when it has switched from the released state to the transition state, the EPB holding force determination counter is increased (step S3). In other words, the EPB holding force determination counter is reset at the timing when the EPB15 switches from the released state to the transition state, and in all other states, the EPB holding force determination counter is increased. Note that it is sufficient to measure the time from when the EPB15 starts to operate until braking torque begins to act on the wheel 10, and the EPB holding force determination counter may have an upper limit that is longer than the measured time.

[0041] Following steps S2 and S3, it is determined whether at least one of the following conditions is met: a first condition that the EPB 15 is in a released state, and a second condition that the EPB 15 is in a transition state and the EPB holding force determination counter is less than or equal to a predetermined value. Step S4 is a step to determine whether the EPB 15 is in a non-braking state. Therefore, the time from when the motor 16 is energized to apply braking torque to the wheel 10 by the EPB 15 until the EPB 15 begins to apply braking torque to the wheel 10 can be determined in advance through experiments or simulations, and this time can be set as the predetermined value in step S4.

[0042] If step S4 is positively determined because EPB15 is in a released state, or EPB15 is in a transition state and the EPB holding force determination counter is below a predetermined value, then it is determined that EPB15 is in a non-braking state (step S5), and this routine is terminated. Conversely, if step S4 is negatively determined because neither the first nor the second condition in step S4 is met, then it is determined that EPB15 is in a braking state (step S6), and this routine is terminated.

[0043] Based on the state of the EPB15 determined as described above, it is determined whether or not the drive shaft 9 has twisted. A flowchart illustrating an example of this control is shown in Figure 4. In the control example shown in Figure 4, it is first determined whether or not the parking range is set and whether or not the abnormality determination flag is off (step S11). Whether or not the parking range is set in step S11 can be determined by the parking determination unit 29. Specifically, this can be determined based on whether or not a predetermined time has elapsed since the parking range was selected by a shift operation, or based on a command signal to the actuator that operates the parking pole 13.

[0044] Furthermore, the abnormality determination flag in step S11 is a flag that is set to ON when the braking torque applied to the wheel 10 by the brake device 14 or EPB 15 cannot be controlled, or when the ECU 21 cannot receive a signal related to that braking torque. This determination can be made based on the signals input to the ECU 21 from the EPB-ECU 26 or B-ECU 27. In other words, it determines whether the brake device 14 or EPB 15 is operating normally and whether the ECU 21 can receive a signal indicating that it has operated.

[0045] If the parking range is not set or the abnormality detection flag is turned on, and a negative result is determined in step S11, the flag indicating that the drive shaft 9 is twisted (hereinafter referred to as the twist detection flag) is set to off (step S12), that is, it is determined that the drive shaft 9 is not twisted, and this routine is terminated. If the twist detection flag is set to off, the twist detection counter, which will be described later, is set to "0".

[0046] Conversely, if a positive determination is made in step S11 because the parking range is set and the abnormality determination flag is off, then it is determined whether the EPB 15 and the brake device 14 are in a non-braking state (step S13). This step S13 is for determining whether the conditions for twisting of the drive shaft 9 are met. That is, it is determined whether the rotation on the input side of the drive shaft 9 is prohibited, while the wheel 10 is able to rotate, or in other words, whether sufficient braking torque is not acting on the wheel 10. This step S13 can be determined by referring to the results of the braking state and non-braking state set by the control example shown in Figure 3.

[0047] If a positive determination is made in step S13 because the EPB15 and brake device 14 are not braking, the amount of torsion of the drive shaft 9 may increase. Therefore, if a positive determination is made in step S13, the torsion determination counter for determining whether or not the drive shaft 9 has torn is incremented (step S14). Conversely, if a negative determination is made in step S13 because at least one of the EPB15 and brake device 14 is applying braking torque to the wheel 10, the torsion determination counter is maintained (step S15).

[0048] Following steps S14 and S15, it is determined whether the tilt angle (absolute value) of the vehicle Ve in the pitching direction is greater than or equal to a predetermined first predetermined angle, and whether the torsion judgment counter is greater than or equal to a predetermined value (step S16). In this step S16, the tilt angle of the vehicle Ve is measured based on the longitudinal acceleration of the vehicle Ve detected by the acceleration sensor 22, and it is determined whether the tilt angle is greater than or equal to the first predetermined angle at which the wheels 10 rotate. Note that if the vehicle Ve vibrates, vibration components and noise may be included in the acceleration signal detected by the acceleration sensor 22. In such cases, a low-pass filter may be used to extract signals below a predetermined frequency to determine the tilt angle of the vehicle Ve, or the tilt angle of the vehicle Ve may be determined based on the average value of the detected signal over a predetermined period.

[0049] Furthermore, the predetermined value in step S16 is the time required for the drive shaft 9 to twist to the point where the motor 1 needs to output assist torque when releasing the parking lock mechanism 11, and is determined by conducting experiments or simulations. Since the rate of change of the drive shaft 9's twist amount is thought to differ depending on the vehicle Ve's tilt angle, the predetermined value in step S16 may be a variable number set to decrease as the vehicle Ve's tilt angle increases.

[0050] If the tilt angle of vehicle Ve is greater than or equal to a first predetermined angle, and the twist detection counter is greater than or equal to a predetermined value, and the result is positive in step S16, the twist detection flag is set to ON (step S17), and this routine is terminated. Conversely, if the tilt angle (absolute value) of vehicle Ve is less than the first predetermined angle, or the twist detection counter is less than a predetermined value, and the result is negative in step S16, the twist detection flag is maintained (step S18), and this routine is terminated.

[0051] Next, the estimated torsional acceleration is calculated. Figure 5 shows a flowchart illustrating an example of this control. In the control example shown in Figure 5, it is first determined whether the torsional judgment flag is on and whether the EPB15 has switched from a non-braking state to a braking state (step S21). This step S21 can be determined based on whether step S6 in Figure 3 was executed first and whether the torsional judgment flag was set to on by step 17 in Figure 4.

[0052] If the torsion detection flag is on and the EPB15 has switched from a non-braking state to a braking state, and a positive determination is made in step S21, the estimated torsion acceleration is calculated (step S22), and this routine is terminated. Specifically, the estimated torsion acceleration is calculated by subtracting the acceleration corresponding to the tilt angle of the vehicle Ve from the acceleration detected by the acceleration sensor 22 at the time step S22 is executed. The acceleration corresponding to the tilt angle of the vehicle Ve may be determined by performing a low-pass filter process to extract signals below a predetermined frequency, such as the natural frequency of the drive shaft 9, from the acceleration signals detected by the acceleration sensor 22 as described above, or by determining the tilt angle of the vehicle Ve based on the average value of the detected signals over a predetermined period.

[0053] Conversely, if the torsion detection flag is off, or if the EPB15 remains in an unbraked or braked state, and a negative determination is made in step S21, the estimated torsional acceleration is maintained (step S23), and this routine is terminated. In other words, the estimated torsional acceleration is calculated only when the torsion detection flag is on and the EPB15 switches from an unbraked state to a braked state. The initial value of the estimated torsional acceleration may be, for example, "0".

[0054] Figure 6 shows a time chart illustrating the torque (torsional torque) of the drive shaft 9, the longitudinal acceleration of the vehicle Ve, the torsional judgment flag, and the changes in the state of the EPB15 when the EPB15 switches from an unbraked state to a braking state during the process of the drive shaft 9 twisting. The changes in torsional torque and the longitudinal acceleration of the vehicle Ve when the EPB15 maintains an unbraked state are shown by dashed lines.

[0055] In the example shown in Figure 6, the drive shaft 9 is not twisted because the parking lock mechanism 11 is released at time t0. The EPB 15 is not braking. As a result, the torsional torque of the drive shaft 9 is almost "0". In addition, the longitudinal acceleration of the vehicle Ve detected by the acceleration sensor 22 is maintained at a predetermined acceleration corresponding to the tilt angle of the vehicle Ve.

[0056] As the parking lock mechanism 11 switches to the locked state, the torsion detection flag is switched on at time t1. Also, at time t1, the EPB 15 is still not braking. Therefore, the drive shaft 9 is beginning to twist. That is, the torsional torque of the drive shaft 9 is gradually increasing. In addition, as the drive shaft 9 twists, a reaction torque is generated in a direction that reduces the amount of twist of the drive shaft 9, and as a result, the longitudinal acceleration at time t1 is beginning to increase. There is a correlation between the torsional torque of the drive shaft 9 and the longitudinal acceleration of the vehicle Ve. That is, the longitudinal acceleration of the vehicle Ve pulsates in accordance with the pulsation of the torsional torque of the drive shaft 9.

[0057] At time t2, the torsional torque reaches its maximum value and then decreases. This is because the reaction torque of the drive shaft 9 pulsates according to the elastic modulus of the drive shaft 9. Consequently, the longitudinal acceleration of the vehicle Ve reaches its maximum value and then decreases.

[0058] Then, at time t3, the EPB15 switches from a non-braking state to a braking state, and the estimated torsional acceleration is calculated. Specifically, as shown in Figure 6, the acceleration obtained by subtracting the acceleration corresponding to the vehicle Ve tilt angle from the acceleration at time t3 is calculated as the estimated torsional acceleration.

[0059] As shown by the dashed line in Figure 6, when the EPB15 remains in an unbraked state, the torsional torque and longitudinal acceleration amplitude of the drive shaft 9 pulsate while gradually decreasing, converging to predetermined torque and acceleration.

[0060] Next, the assist torque by motor 1 is determined. A flowchart illustrating an example of this control is shown in Figure 7. In the control example shown in Figure 7, first, it is determined whether the motor control execution flag is off or not (step S31). If the determination in step S31 is positive because the motor control execution flag is off, the target value of the assist torque by motor 1 (hereinafter simply referred to as target torque) is set to "0" (step S32). Conversely, if the determination in step S31 is negative because the motor control execution flag is on, it is determined whether the motor control execution flag has switched from off to on or not (step S33). This step S33 can be determined depending on whether the determination in step S31 in the previous routine was positive or negative.

[0061] If a positive determination is made in step S33 because the motor control execution flag has switched from off to on, then it is determined whether the EPB 15 is in a braking state (step S34). Step S34 is a step to determine whether the drive shaft 9 is twisted according to the tilt angle of the vehicle Ve. That is, it determines whether braking torque is acting on the wheels 10. Therefore, although the example shown in Figure 7 assumes that the brake device 14 is not operating, in addition to determining whether the EPB 15 is in a braking state, it may also be determined whether the brake device 14 is in a braking state.

[0062] If it is determined in step S34 that the EPB15 is in a braking state, the target value of the assist torque of motor 1 is set according to the estimated torsional acceleration (step S35). Specifically, at the point when it is determined in step S33 that the acceleration is positive, the acceleration corresponding to the tilt angle of the vehicle Ve is subtracted from the acceleration detected by the acceleration sensor 22. That is, the estimated torsional acceleration is calculated by subtracting the acceleration corresponding to the tilt angle of the vehicle Ve shown by the dashed line in Figure 6 from the acceleration at time t3 in Figure 6. Then, the target value of the assist torque of motor 1 is set by referring to the map shown in Figure 8 for determining the target value of the assist torque based on the estimated torsional acceleration.

[0063] The map shown in Figure 8 determines the torsional torque of the drive shaft 9 through experimentation, simulation, or calculation when the vehicle Ve is tilted at a predetermined angle, and sets the torque that can offset that torsional torque as the target value of the assist torque of the motor 1. Then, using the acceleration corresponding to the vehicle Ve's tilt angle as a reference, the target value of the assist torque of the motor 1 increases as the estimated torsional acceleration increases, and decreases as the estimated torsional acceleration decreases. Multiple maps configured in this way for each vehicle Ve tilt angle are stored in the ECU 21.

[0064] Conversely, if it is determined negatively in step S34 that the EPB15 is in a non-braking state, the target value of the assist torque of motor 1 is set according to the tilt angle of the vehicle Ve (step S36).

[0065] On the other hand, if the motor control execution flag has not yet switched from off to on, that is, if the motor control execution flag has already been switched on and a target value for the assist torque of motor 1 has been set, and therefore the result in a negative determination in step S33, the target value for the assist torque of motor 1 is maintained at the previous value (step S37). In other words, the target value for the assist torque of motor 1 is maintained after it has been set when the motor control execution flag has been switched on.

[0066] Following steps S32, S35, S36, and S37, the rate at which the assist torque output from motor 1 decreases is determined (step S38), and the value obtained by multiplying this decrease rate by the elapsed time is subtracted from the target torque to determine the effective value of the output torque of motor 1 (step S39), and this routine is terminated. This assist torque decrease rate may be, for example, the maximum rate determined by the structure of motor 1, or it may be a rate corresponding to the target value of the assist torque so that the assist torque becomes "0" in a predetermined time.

[0067] As described above, there is a correlation between the amount of torsion (torsional torque) of the drive shaft 9 and the longitudinal acceleration of the vehicle Ve. Therefore, the target value of the output torque of the motor 1 is set based on the acceleration at the time when braking torque is applied to the wheels 10 and the acceleration corresponding to the tilt angle of the vehicle Ve. In other words, by setting the target value of the assist torque of the motor 1 at the point when braking torque is applied to the wheels 10 and the amount of torsion of the drive shaft 9 is maintained, it is possible to suppress the discrepancy between the torsional torque released and the assist torque at the time the parking lock mechanism 11 is released. As a result, it is possible to suppress the occurrence of vibrations and shocks when the parking lock mechanism 11 is released.

[0068] Furthermore, the vehicle in this embodiment of the invention is not limited to a vehicle in which a motor is connected to each wheel, but may also be a vehicle configured to transmit torque from a single motor to a pair of front wheels or rear wheels, or to all wheels. In addition, it may be a hybrid vehicle equipped with an engine as a driving force source in addition to the motor.

[0069] Furthermore, the configuration connecting the motor 1 and the drive shaft 9, and the rotating member whose rotation is prohibited by the parking lock mechanism 11, are not limited to those shown in Figure 1. Moreover, the vehicle in this embodiment of the invention does not need to be equipped with an EPB 15. In that case, it is sufficient to determine whether to set the target value of the assist torque based on the estimated torsional acceleration or based on the inclination angle of the vehicle Ve, based on whether or not the brake device 14 is applying braking torque to the wheels 10. [Explanation of Symbols]

[0070] 1,16 motor 2.8 Output shaft 3.6 drive gear 4.7 Driven gear 5 Intermediate axis 9 Drive shaft 10 wheels 11 Parking lock mechanism 12 Parking lock gear 13 Parking poles 14 Brake system 15. Electric Parking Brake (EPB) 17 cases 18 Mount 19 car bodies 20 Suspension 21 Electronic Control Unit (ECU) 22 Accelerometer 23 resolvers 24 Shift device 25 Shift Sensor 26 EPB-ECU 27 B-ECU 28 Shift lever 29 Parking determination unit 30 Brake detection unit 31 Acceleration acquisition section 32 Torsion Amount Estimation Acceleration Calculation Unit 33 Motor control unit Vehicle

Claims

1. A vehicle control device comprising: a drive shaft with one end connected to a wheel; a motor capable of transmitting torque to the drive shaft; a parking lock mechanism capable of selectively switching between a locked state in which the rotation of a predetermined rotating member between the motor and the drive shaft is prohibited and an unlocked state in which the predetermined rotating member is rotatable; and a braking device that applies braking torque to the wheel, The motor is equipped with a controller that controls the motor, The aforementioned controller, A parking determination unit that determines whether the parking lock mechanism is in the locked state, A brake determination unit that determines the braking torque acting on the wheel by the braking device, An acceleration acquisition unit that acquires the acceleration of the vehicle in the longitudinal direction, When the parking lock mechanism is in the locked state and the braking torque acting on the wheels is greater than or equal to a predetermined torque, a torsional acceleration estimation unit calculates a torsional acceleration estimation by subtracting the acceleration in the longitudinal direction of the vehicle corresponding to the vehicle's tilt angle from the acceleration acquired by the acceleration acquisition unit at the time the braking torque becomes greater than or equal to the predetermined torque; The system is configured as follows: When switching the parking lock mechanism from the locked state to the unlocked state, if the braking torque is equal to or greater than the predetermined torque, the motor controls the motor to output a torque based on the estimated torsional acceleration, and if the braking torque is less than the predetermined torque, the motor controls the motor to output a torque based on the acceleration in the longitudinal direction of the vehicle corresponding to the vehicle's tilt angle. A vehicle control device characterized by the following features.

2. A vehicle control device according to claim 1, The torsional acceleration estimation unit performs a low-pass filter process to extract accelerations below a predetermined frequency from the accelerations acquired by the acceleration acquisition unit, thereby determining the acceleration in the longitudinal direction of the vehicle according to the vehicle's tilt angle. A vehicle control device characterized by the following features.

3. A vehicle control device according to claim 2, The predetermined frequency includes the natural frequency of the drive shaft. A vehicle control device characterized by the following features.

4. A vehicle control device according to claim 1, The torsional acceleration estimation unit determines the acceleration in the longitudinal direction of the vehicle based on the average value of the acceleration acquired by the acceleration acquisition unit over a predetermined period. A vehicle control device characterized by the following features.

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