JP5086602B2 - Driving force distribution control device for four-wheel drive vehicle - Google Patents

Description

  The present invention relates to a driving force distribution control device capable of distributing driving force to front and rear wheels.

Conventionally, in the driving force distribution control device described in Patent Document 1, the engagement torque of the clutch that changes the distribution ratio of the driving force is calculated based on the rotational speed difference between the front wheels and the rear wheels, and the target yaw rate is calculated. The fastening torque calculated by multiplying the correction coefficient so as to reduce the deviation of the actual yaw rate is corrected.
JP-A-5-278490

  However, there is a possibility that an appropriate fastening torque that stabilizes the behavior of the vehicle cannot be obtained due to a difference in the state of the road surface μ of the traveling road, the vehicle speed, or the like while the vehicle is traveling.

  The present invention has been made paying attention to the above problems, and an object of the present invention is to provide a driving force distribution control device for a four-wheel drive vehicle capable of applying a fastening torque that achieves an appropriate distribution ratio according to a traveling state. It is to provide.

In order to achieve the above object, according to the present invention, in a driving force distribution control device for a four-wheel drive vehicle having a clutch capable of changing the distribution of the driving force to the front wheel and the rear wheel according to the fastening torque, the front wheel and the rear wheel A reference engagement torque calculation means for calculating a reference engagement torque based on a difference in rotational speed of the vehicle, a yaw rate detection means for detecting a yaw rate generated in the vehicle, a target yaw rate calculation means for calculating a target yaw rate of the vehicle, and the detected A yaw rate deviation calculating means for calculating a deviation between the yaw rate and the calculated target yaw rate, a road surface friction coefficient detecting means for detecting or estimating a road surface friction coefficient during traveling, a correction coefficient corresponding to the yaw rate deviation and the road surface friction coefficient Friction coefficient type correction coefficient calculating means for calculating the reference fastening torque, the correction coefficient multiplied by the correction coefficient, and the detected yaw rate A correction engaging torque calculating means and serial target yaw rate calculating a fastening torque of the clutch to match, determines the oversteer or understeer of the vehicle, the calculated fastening torque by the correction fastening torque calculation means, Intervenes in oversteer control or understeer control when a predetermined oversteer intervention condition or a predetermined understeer intervention condition is satisfied, and terminates the understeer control when a predetermined understeer control end condition is satisfied. And delaying means for ending the oversteer control after delaying it for a predetermined time .

  Therefore, the correction coefficient can be changed according to the road surface friction coefficient, and the vehicle behavior can be stabilized.

  Hereinafter, the best embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a system configuration diagram of a vehicle to which a driving force distribution control device for a four-wheel drive vehicle according to the present invention is applied. The vehicle of the first embodiment is premised on a four-wheel drive vehicle that drives only the front wheels in normal times and drives the rear wheels when necessary.

  A transmission 2 composed of a torque converter and a plurality of planetary gears is connected to the engine 1. The driving force transmitted to the transmission 2 drives the drive shafts of the front wheels FL and FR via the front differential gear DF1. Further, the transmission 2 has a built-in transfer, and is provided with a first propeller shaft PS1 that transmits a driving force to the rear wheel side via the transfer.

  A second propeller shaft PS2 is connected to the first propeller shaft PS1 via a driving force distribution actuator 3. The second propeller shaft PS2 drives the drive shafts of the rear wheels RL and RR via the rear differential gear DF2.

  The driving force distribution actuator 3 incorporates an electromagnetic multi-plate clutch, and controls the fastening torque of the multi-plate clutch by the electromagnetic force, so that the driving force from the engine 1 can be distributed to the rear wheel side. The clutch engagement torque is controlled by forward / reverse rotation speed difference control and yaw rate feedback 4WD control, and the clutch engagement torque is selected as necessary.

  The front / rear rotation speed difference control is to monitor the slip condition of the front wheels (drive wheels) based on the rotation speed difference between the wheel speeds of the front wheels FL and FR and the wheel speeds of the rear wheels RL and RR. This represents control for suppressing slip by applying clutch engagement torque and distributing excessive driving force supplied to the front wheels FL and FR to the rear wheels.

  Further, the yaw rate feedback 4WD control controls the clutch engagement torque so that the actual yaw rate matches the target yaw rate, and is performed as part of VDC control described later. Details will be described later.

  The front wheels FL and FR and the rear wheels RL and RR are provided with friction brakes B1 to B4 that press and brake a brake rotor that rotates integrally with the wheels with a brake pad. In these friction brakes B1 to B4, a wheel cylinder for pressing the brake pad with the brake fluid is incorporated.

  Each of the friction brakes B1 to B4 is connected to the brake actuator 4. In the brake actuator 4, anti-skid control (hereinafter referred to as ABS control) for transmitting the brake hydraulic pressure supplied from a master cylinder (not shown) to each wheel and avoiding locking of the wheels is performed. In order to achieve a desirable vehicle behavior, a pump, a gate valve, and the like capable of applying a braking force to each wheel are provided in order to achieve a desirable vehicle behavior regardless of the necessary pressure increase / reduction valve and the driver's brake pedal operation state.

  In addition, the 4WD controller 5 that controls the engagement torque of the clutch of the driving force distribution actuator 3 and the wheel cylinder pressure of each of the friction brakes B1 to B4 are controlled by the brake actuator 4 and the engagement torque necessary for the yaw rate feedback 4WD control is controlled. A VDC controller 6 is provided. The 4WD controller 5 and the VDC controller 6 are connected by a CAN communication line so that both information can be exchanged.

  The VDC controller 6 includes a steering angle sensor 10 that detects the steering angle of the driver, a wheel speed sensor 11 that detects the wheel speed of each wheel, a yaw rate sensor 12 that detects the yaw rate generated in the vehicle, A longitudinal acceleration sensor 13 for detecting longitudinal acceleration generated in the vehicle is connected to detect each sensor signal.

  Here, the ABS control estimates the vehicle body speed based on the wheel speed, and the wheel cylinder pressure is adjusted so that the wheel speed of each wheel coincides with the vehicle body speed (or a decompression threshold value obtained by subtracting a predetermined value from the vehicle body speed). Increase / decrease control is performed.

  In the VDC control, a target yaw rate that is an ideal vehicle behavior is set based on the vehicle speed and the steering angle of the driver, and the clutch of the driving force distribution actuator 3 is set so that the actual yaw rate sensor signal matches the target yaw rate. In addition to controlling the engagement torque, only the wheel cylinder pressure of the necessary friction brake is increased (or only the wheel cylinder pressure of the necessary friction brake is reduced).

  More specifically, the deviation from the actual yaw rate is calculated with respect to the target yaw rate, and in the case of the deviation due to the fact that the actual yaw rate is larger (hereinafter referred to as the yaw rate deviation signal for OS), there is an oversteer tendency. It is judged that there is. At this time, the fastening torque is controlled so as to eliminate oversteer, that is, the vehicle tends to be understeered, and if necessary, the wheel cylinder pressure is controlled.

  On the other hand, when the deviation from the actual yaw rate is calculated with respect to the target yaw rate, and the deviation is due to the fact that the actual yaw rate is smaller (hereinafter, referred to as the US yaw rate deviation signal), it is determined that there is an understeer tendency. . At this time, the clutch engagement torque is controlled so as to eliminate the understeer tendency, that is, the vehicle tends to oversteer, and the wheel cylinder pressure is controlled if necessary. Hereinafter, oversteer related signals are denoted by OS, and understeer related signals are denoted by US.

  Note that VDC control includes TCS control. TCS control means that when the driving force is excessive from the engine 1 and the driving wheel slips, the slip is suppressed by the friction brake of the slipped wheel, and the engine output torque is suppressed by suppressing the throttle opening degree of the engine 1 and the like. To suppress slip.

  In VDC control (including ABS control and TCS control), a road surface friction coefficient estimating unit (corresponding to road surface friction coefficient detecting means) that estimates a road surface friction coefficient (hereinafter referred to as road surface μ) based on longitudinal acceleration and the like. The vehicle behavior control and anti-skid control corresponding to the road surface μ are performed.

  FIG. 2 is a block diagram showing a part of the VDC controller 6 and a control configuration in the 4WD controller 5. Various controls are performed in the VDC control. In the first embodiment, only the portions directly related are extracted. A 4WD controller 5 a is provided in the 4WD controller 5. The VDC controller 6 is provided with a VDC existing signal unit 6a that constantly monitors the behavior of the vehicle and outputs various signals, and a yaw rate feedback 4WD control unit 6b that performs yaw rate feedback 4WD control.

[About the VDC control unit]
As described above, the vehicle speed and the target yaw rate and actual yaw rate deviation signal (OS yaw rate deviation signal, US yaw rate deviation signal), steering angle signal, and estimated road surface μ signal exist (VDC existing signal). . Using these various signals output from the VDC existing signal unit 6a, the yaw rate feedback 4WD control unit 6b outputs a required torque gain and a control active flag, which will be described later, to the 4WD controller 5.

  The yaw rate feedback 4WD control unit 6b is provided with a control intervention determination unit 100 and a required torque gain value calculation / selection unit 200. The control intervention determination unit 100 is further provided with an intervention threshold value creation unit 101 that creates an intervention threshold value (OS threshold value, US threshold value) based on the vehicle speed. Further, an intervention permission determination unit 102 is provided for determining whether to permit control intervention based on the OS yaw rate deviation signal and the US yaw rate deviation signal.

  In addition, in this control intervention permission determination, as another signal, a fail determination that indicates whether or not an abnormality has occurred in the system, a VDC switch determination that selects whether or not to perform VDC control by the driver's selection (ON, 4WD switch discriminating to select whether or not to perform 4WD control according to the driver's selection (selecting appropriately from ON, AUTO, OFF), reverse judgment to judge whether to reverse (inhibitor) Switch signal, etc.), vehicle speed determination for determining whether or not the control execution vehicle speed, split determination for determining whether or not it is a split μ road, straight line determination for detecting whether or not the vehicle is traveling straight (detected by steering angle, etc.), etc. It has been broken.

  Further, the OS intervention determination unit 103 determines whether or not to interpose oversteer suppression control (hereinafter referred to as OS control) based on the OS threshold and the OS yaw rate deviation, and outputs the determination result as an OS determination flag. A US intervention determination unit 104 that determines whether or not to intervene understeer suppression control (hereinafter referred to as US control) based on the US threshold and the US yaw rate deviation, and outputs the determination result as a US determination flag; Is provided. In addition, a control active flag creation unit 105 that creates a control active flag based on the results of the OS judgment flag and the US judgment flag is provided.

  The required torque gain value calculation / selection unit 200 is provided with an OS required torque gain map 201, a US required torque gain map 202, a fixed value 203, and a selection unit 204.

  The OS required torque gain map 201 outputs the OS required torque gain shown in FIGS. 13 and 14 based on the vehicle body speed, the OS yaw rate deviation, and the estimated road surface μ. Details will be described later. The US required torque gain map 202 shown in FIGS. 13 and 14 is output to the US required torque gain map 202 based on the vehicle body speed, the US yaw rate deviation, and the estimated road surface μ. Details will be described later. In the fixed value 203, a preset fixed value is output as the required torque gain. The selection unit 204 selects any one of the OS torque gain, the US torque gain, and a fixed value based on the values of the OS determination flag and the US determination flag.

[4WD control unit]
Next, the configuration of the 4WD control unit 5a will be described. The 4WD control unit 5a includes a driving force distribution control unit 301 that outputs the engagement torque of the clutch based on the driving force distribution control, and an initial torque output unit that outputs the initial torque necessary to loosen the clutch plate. 302 and a front-rear rotation speed difference control unit 303 that outputs clutch engagement torque based on front-rear rotation speed difference control.

  In the driving force distribution control unit 301, when the driver's accelerator pedal operation is excessive, it is highly possible that slip will occur on the front wheels, and accelerator-sensitive control that preliminarily applies clutch engagement torque (when starting or accelerating), Interlocked with steering angle sensitive control and yaw rate feedback 4WD control that apply or reduce the clutch engagement torque in advance as the driver steers suddenly and there is a high possibility that the cornering force of the front wheels will be insufficient or the cornering force of the rear wheels will decrease. Then, yaw rate feedback 4WD control interlocking F / F control, etc., for applying a fastening torque by feedforward control is executed, and a fastening torque command value corresponding to them is output.

  Further, the 4WD control unit 5a outputs the fastening torque command value output from the driving force distribution control unit 301, the fastening torque command value output from the initial torque output unit 302, and the output from the front / rear rotation speed difference control unit 303. A select high section 304 is provided for selecting the highest fastening torque among the fastening torque command values. The fastening torque command value selected by the select high unit 304 is formed as the reference torque (corresponding to the reference fastening torque calculation means).

  Further, the 4WD control unit 5a multiplies the reference torque selected by the select high unit 304 by the request torque gain selected by the calculation / selection unit 200 of the request torque gain value to calculate a final torque command value. A final output torque calculator 305 (corresponding to a corrected fastening torque calculator) is provided. This final output torque command value is output to the driving force distribution actuator 3 to achieve a desired vehicle behavior.

[Yaw rate feedback 4WD control processing]
Next, the yaw rate feedback 4WD control process will be described with reference to FIGS. FIG. 3 is a flowchart showing the main flow.

  In step S1, the select high unit 304 selects a reference torque.

  In step S2, the intervention threshold creation unit 101 creates an intervention threshold.

  In step S3, intervention determination is performed by the intervention permission determination unit 102, the OS intervention determination unit 103, and the US intervention determination unit 104.

  In step S4, the required torque gain value is calculated from the OS required torque gain map 201, the US required torque gain map 202, and the fixed value 203.

  In step S5, the selection unit 204 selects a required torque gain value based on the OS determination flag and the US determination flag.

  In step S6, the control active flag creation unit 105 creates a control active flag based on the OS determination flag and the US determination flag.

  In step S7, the final output torque is calculated based on the reference torque selected by the final output torque calculator 305 and the required torque gain.

  FIG. 4 is a flowchart showing the reference torque selection process in step S1.

  In step S101, it is determined whether or not only the front-rear rotational speed difference torque is output in the reference torque selection. If only the front-rear rotational speed difference torque is output, the process proceeds to step S102 and the reference torque is changed to the front-rear rotational speed difference torque. Set to. Otherwise, the process proceeds to step S103.

  In step S103, it is determined whether or not only the driving force distribution control torque is output in the reference torque selection. If only the driving force distribution control torque is output, the process proceeds to step S104 and the reference torque is converted into the driving force distribution control torque. Set to. Otherwise, the process proceeds to step S105.

  In step S105, a torque indicating a high value is set as the reference torque among the front-rear rotational speed difference torque and the driving force distribution control torque. By setting the selection high in this way, the safe side can be controlled.

FIG. 5 is a flowchart showing the intervention threshold value creation process in step S2. In this flowchart, (* n) (n: 1 to 6) represents a point on a two-dimensional plane determined by the relationship between the threshold value and the vehicle body speed as shown in FIG. Therefore, in the vehicle speed, V1: the boundary between the low speed prohibited area and the low speed area, V2: the boundary between the low speed area and the medium speed area, V3: the boundary between the medium speed area and the high speed area, and V4: the boundary between the high speed area and the high speed prohibited area. Represent each. When the set threshold is P1, P2, P3 (P1>P2> P3),
(* 1) = (V1, P3)
(* 2) = (V1, P2)
(* 3) = (V1, P1)
(* 4) = (V2, P3)
(* 5) = (V3, P3)
(* 6) = (V4, P1)
It is expressed.

  In step S201, it is determined whether or not the vehicle body speed is in the low speed prohibited region. If the vehicle speed is in the low speed prohibited region, the process proceeds to step S202, and the threshold is set to P1. Otherwise, the process proceeds to step S203.

  In step S203, it is determined whether or not the vehicle body speed is in the low speed range. If the vehicle speed is in the low speed range, the process proceeds to step S204. Otherwise, the process proceeds to step S209.

  In step S204, it is determined whether or not the estimated road surface μ is equal to or smaller than a predetermined value. If the estimated road surface μ is equal to or smaller than the predetermined value, the process proceeds to step S206. Otherwise, the process proceeds to step S205 and the threshold values are interpolated (* 3) and (* 4). Set to value.

  In step S206, it is determined whether or not TCS control is in operation. If TCS control is in operation, the process proceeds to step S208. Otherwise, the process proceeds to step S207 and the thresholds are set to (* 2) and (* 4). Set to the interpolation value.

  In step S208, the threshold value is set to the interpolated values (* 1) and (* 4).

  In step S209, it is determined whether or not the vehicle body speed is in the middle speed range. If the vehicle speed is in the middle speed range, the process proceeds to step S210, and the threshold value is set to the interpolation values of (* 4) and (* 5). Otherwise, the process proceeds to step S211.

  In step S211, it is determined whether the vehicle body speed is in the high speed range. If the vehicle speed is in the high speed range, the process proceeds to step S212 and the threshold is set to (* 5). In other cases, the process proceeds to step S213 and the threshold value is set to (* 6).

  In other words, in the extremely low speed prohibition region, the vehicle behavior that requires yaw rate feedback does not occur, and the effect is not expected so much. In this case, control is basically not performed.

  When the speed is high in the low speed range, excessive control intervention is suppressed by setting the interpolation values of (* 3) and (* 4). On the other hand, when the speed is low in the low speed range, the interpolation values (* 2) and (* 4) are set to make it easier to intervene in the control. In addition, even in the low speed range, when it is low μ and TCS control is activated, it is judged that the steering state is on an icy road, and the interpolation value of (* 1) and (* 4) is set so that control intervention can be performed immediately. To do.

  In the middle and high speed range, the effect cost of yaw rate feedback 4WD control is large. In the high-speed prohibited area, even if control is performed, the limit of each tire force is exceeded, so yaw rate feedback 4WD control is prohibited, and control is simply performed to decelerate.

  FIG. 7 is a flowchart showing the intervention determination process in step S3.

  In step S301, it is determined whether an abnormality has occurred in any of the driving force distribution actuator 3, the brake actuator 4, the 4WD controller 5, and the VDC controller 6. If abnormal, the process proceeds to steps S302 to S304, which will be described later. The OS delay counter, OS active flag, US active flag, etc. to be reset are all reset to 0 and control is immediately withdrawn from control. If there is no abnormality, the process proceeds to step S305.

  In step S305, it is determined whether or not the VDC switch and the 4WD switch are OFF. When the VDC switch and the 4WD switch are OFF, the VDC control is not performed as the driver's intention, so the process proceeds to step S302 and the control is immediately released.

  In step S306, it is determined whether or not the engine has just been started (whether or not a predetermined time has elapsed since the ignition was turned on). If there is a possibility that various sensors have not been initialized immediately after the engine is started, the process proceeds to step S302. When the process proceeds to leave the control and a predetermined time has elapsed, the process proceeds to step S307.

  In step S307, it is determined whether the vehicle is moving backward. If the vehicle is moving backward, the process proceeds to step S302. Otherwise, the process proceeds to step S308.

  In step S308, it is determined whether or not the vehicle is traveling straight. If the vehicle is traveling straight, the process proceeds to step S309. Otherwise, the process proceeds to step S312.

  In step S309, it is determined that the control is no longer necessary, processing B (OS delay counter subtraction) is performed, processing proceeds to step S310, processing C (OS active flag setting) is performed, processing proceeds to step S311 and the US active flag is set to 0. Set to. Processing B and processing C will be described later.

  In step S312, it is determined whether the vehicle body speed is in the high speed prohibition region or the low speed prohibition region. If the vehicle speed is in the high speed or low speed prohibition region, the process proceeds to step S309, and the control end process is performed otherwise.

  In step S313, during TCS control by the friction brake and when the actual yaw rate is less than the predetermined value, it is determined that the vehicle is traveling on a split μ road (the road surface μ is different between the right side and the left side), and the process proceeds to step S309. Control end processing is performed, otherwise the process proceeds to step S314.

  In step S314, process A (OS intervention determination, OS delay counter addition / subtraction) is performed as an intervention determination for OS control or US control, the process proceeds to step S315, process C (OS active flag is set), and the process proceeds to step S316. D (US intervention judgment, US active flag setting).

  In other words, the yaw rate feedback 4WD control has no abnormality in the system, the VDC switch and 4WD switch are ON (or AUTO), the predetermined time has passed since the ignition was turned on, the vehicle is not moving backward, it is not going straight, It is executed when the speed is the control intervention area and not the split μ road, and is otherwise prohibited. Each determination can be omitted from the viewpoint of vehicle behavior characteristics and safety.

  FIG. 8 is a flowchart showing process A in step S314.

  In step A1, it is determined whether or not the vehicle is turning right. If the vehicle is turning right, the process proceeds to step A2. Otherwise, the process proceeds to step A4.

  In step A2, when the OS yaw rate deviation signal is equal to or less than the negative OS intervention threshold (intervention conditions are satisfied), the process proceeds to step A3, and the OS delay counter is set to a predetermined value. The OS delay counter is a counter for ending the yaw rate feedback 4WD control after a predetermined time has elapsed. Otherwise, go to step A5.

  In step A4, when the OS yaw rate deviation signal is equal to or greater than the OS intervention threshold (intervening conditions are satisfied), the process proceeds to step A3, and the OS delay counter is set to a predetermined value. Otherwise, go to step A5.

  In step A5, it is determined whether or not the OS delay counter is 0. If it is 0, the process A is terminated, otherwise the process proceeds to step A6 and the OS delay counter is subtracted.

  Here, for the convenience of explanation, the explanation shifts to the explanation of FIG. FIG. 10 is a flowchart showing process C in step S315.

  In step C1, it is determined whether the OS delay counter is 0. If it is 0, the process proceeds to step C2 and the OS active flag is set to 0. Otherwise, the process proceeds to step C3 and the OS active flag is set to 1. To do.

  That is, when the OS yaw rate deviation exceeds each threshold shown in FIG. 6, it is determined that the OS is in progress, and the OS active flag is set to 1. In order to stabilize the vehicle behavior, the OS control is terminated after a delay of a certain time from the time when the OS yaw rate deviation falls below the OS threshold. OS control represents oversteer suppression control of yaw rate feedback 4WD control. As a result, the control can be stably terminated without suddenly terminating the control.

  FIG. 11 is a flowchart showing process D in step 316.

  In step D1, it is determined whether or not the OS active flag is 0. If it is 0, the process proceeds to step D3. Otherwise, the process proceeds to step D2 and the US active flag is set to 0.

  In step D3, it is determined whether or not the vehicle is turning right. If the vehicle is turning right, the process proceeds to step D4. Otherwise, the process proceeds to step D6.

  In step D4, if the US yaw rate deviation is greater than or equal to the US intervention threshold (intervention conditions are met), proceed to step D5 and set the US active flag to 1, otherwise proceed to step D7 and enter the US active flag. Is set to 0.

  In step D6, if the US yaw rate deviation is less than or equal to the negative US intervention threshold (intervention conditions are met), proceed to step D5 and set the US active flag to 1, otherwise proceed to step D7 and proceed to US Set the active flag to 0.

  That is, when the US yaw rate deviation exceeds each threshold shown in FIG. 6, it is determined that the US state is set, and the US active flag is set to 1. US control is basically control for generating yaw in a vehicle. On the other hand, since the vehicle is set as an understeer tendency as a conventional state, the vehicle is immediately terminated without performing a delay or the like after the end of US control.

  FIG. 9 is a flowchart showing process B of step S309.

  In step B1, it is determined whether or not the OS delay counter is 0. If it is 0, the process B is terminated, otherwise the process proceeds to step B2 and the OS delay counter is subtracted.

  In other words, in addition to the time when normal OS control ends, even when other permission conditions are not satisfied, the OS control is ended after a certain time delay using an OS delay counter to stabilize the vehicle behavior. It is.

FIG. 12 is a flowchart showing the calculation process of the required torque gain value in step S4.
In step S401, the OS required torque gain (for low, medium, and high speed) is created.
In step S402, a required torque gain for US (for low, medium and high speed) is created.
In step S403, the OS required torque gain (for low, medium and high μ) is created.
In step S404, the required torque gain for US (for low, medium and high μ) is created.

  13 shows an image of the required torque gain (hereinafter referred to as OS / US gain (μ) considering the road surface μ component, and FIG. 14 shows an image of the required torque gain including the vehicle body speed component (hereinafter referred to as OS / US gain (V)). As shown in the image in consideration of the road surface μ component shown in Fig. 13, when the vehicle is low, the vehicle behavior tends to be unstable, and behavior control that emphasizes stability is necessary. At this time, the OS / US gain (μ) for the yaw rate deviation must be set so that the drive torque is distributed from the front wheels, so that a small required torque is output as a whole (friction coefficient type). (This corresponds to the correction coefficient calculation means.) It goes without saying that when the driving torque is distributed from the front wheels, the cornering force of the rear wheels is secured and the vehicle behavior is stabilized.

  On the other hand, when the value is high, the vehicle behavior tends to be stable, and behavior control that emphasizes turning performance is required. At this time, the OS / US gain (μ) with respect to the yaw rate deviation needs to be set so that the drive torque is distributed from the rear wheels, so that a large required torque is output as a whole (friction coefficient). Equivalent to mold correction coefficient calculation means). Needless to say, when the driving torque is distributed from the rear wheel, the cornering force of the front wheel is secured and the turning performance is improved.

  Further, as shown in the image including the vehicle body speed component shown in FIG. 14, at low speed, the vehicle behavior tends to change gradually, and high response behavior control is required. At this time, the OS / US gain (V) with respect to the yaw rate deviation needs to be set to such a value that the change in the drive torque becomes rapid, so the gradient with respect to the deviation is made steep (corresponding to the vehicle speed type correction coefficient calculation means). ).

  On the other hand, at high speeds, vehicle behavior tends to change suddenly, and low response behavior control is required. At this time, the OS / US gain (V) with respect to the yaw rate deviation must be set to such a value that the change in the driving torque becomes gentle, so that the gradient with respect to the deviation is made gentle (corresponding to the vehicle speed type correction coefficient calculation means). ).

  FIG. 15 is a flowchart showing the required torque gain value selection process in step S5.

In step S501, it is determined whether or not the vehicle body speed is within the low speed prohibited area. If it is within the low speed prohibited area, the process proceeds to step S502. Otherwise, the process proceeds to step S503.
In step S502, the OS / US gain (V) is set to an interpolation value between the base gain (= 1) and the low speed gain.

In step S503, it is determined whether or not the vehicle body speed is within the low speed range. If it is within the low speed range, the process proceeds to step S504. Otherwise, the process proceeds to step S505.
In step S504, the OS / US gain (V) is set to an interpolation value between the low speed gain and the medium speed gain.

In step S505, it is determined whether or not the vehicle body speed is in the middle speed range. If the vehicle speed is in the middle speed range, the process proceeds to step S506. Otherwise, the process proceeds to step S507.
In step S506, the OS / US gain (V) is set to an interpolated value between the medium speed gain and the high speed gain.

In step S507, it is determined whether or not the vehicle body speed is within the high speed range. If the vehicle speed is within the high speed range, the process proceeds to step S508. Otherwise, the process proceeds to step S509 and the OS / US gain is set to 1.
In step S508, the OS / US gain (V) is set to a high-speed gain value.

In step S511, it is determined whether or not the estimated road surface μ is in the extremely low μ region. If it is an extremely low μ road, the process proceeds to step S512. Otherwise, the process proceeds to step S513.
In step S512, the OS / US gain (μ) is set to a low μ gain.

In step S513, it is determined whether or not the estimated road surface μ is in the low μ region. If it is in the low μ region, the process proceeds to step S514. Otherwise, the process proceeds to step S515.
In step S514, the OS / US gain (μ) is set to an interpolation value between a low μ gain and a medium μ gain.

In step S515, it is determined whether or not the estimated road surface μ is in the middle μ region. If the estimated road surface μ is in the middle μ region, the process proceeds to step S516. Otherwise, the process proceeds to step S517.
In step S516, the OS / US gain (μ) is set to an interpolated value between the medium μ gain and the high μ gain.

In step S517, the OS / US gain (μ) is set to a high μ gain value.
In step S518, the OS / US gain (Vμ) taking into account both the speed component and the road surface μ component is calculated from the following equation.
OS / US gain (Vμ)
= (OS / US gain (V) x speed component weighting coefficient + OS / US gain (μ) x road surface μ component weighting coefficient) / 2

  In step S519, it is determined whether or not only the speed component is added. When only the speed component is added, the process proceeds to step S520, and the OS / US gain (V) is selected.

  In step S521, it is determined whether or not only the road surface μ component is added. When only the road surface μ component is added, the process proceeds to step S522 to select the OS / US gain (μ). In other cases, the process proceeds to step S522, and the OS / US gain (Vμ) taking into consideration both the speed component and the road surface μ component is selected.

When the OS / US gain is selected in steps S520, S522, and S523, the process proceeds to process X. FIG. 16 is a flowchart showing the process X.
In step X1, it is determined whether or not the OS active flag is set to 1. If it is set to 1, the process proceeds to step X2, otherwise the process proceeds to step X3.
In step X2, the required torque gain is set to the OS gain.
In step X3, it is determined whether or not the US active flag is set to 1. If it is set to 1, the process proceeds to step X4. Otherwise, the process proceeds to step X5.
In step X4, the required torque gain is set to the US gain.
In step X5, the required torque gain is set to the base gain (= 1).
Through the above processing, a required torque gain corresponding to the vehicle behavior is set.

FIG. 17 is a flowchart showing the process of creating a control active flag in step S6.
In step S601, it is determined whether the OS active flag is 0 and the US active flag is 0. If the OS active flag = 0 and the US active flag = 0, the process proceeds to step S602 and the control active flag is set to 0. . Otherwise, the process proceeds to step S603, and the control active flag is set to 1.

  That is, when either the OS active flag or the US active flag is set to 1, since the yaw rate feedback 4WD control is being executed, the control active flag is set to 1, and both the OS active flag and the US active flag are set. When it is set to 0, the control active flag is set to 0 because yaw rate feedback 4WD control is not executed.

FIG. 18 is a flowchart showing the final output torque calculation process in step S7.
In step S701, the selected reference torque is multiplied by the selected required torque gain and output as the final output torque.

  The operation based on the control flow will be described based on the time chart of FIG. FIG. 19 is a time chart when the yaw rate feedback 4WD control of the first embodiment is activated when a lane change is performed during straight traveling.

  At time t1 when the vehicle is traveling straight ahead, the driver starts steering to the right side in order to start a lane change. At this time, the OS yaw rate deviation does not exceed the OS intervention threshold, but the US yaw rate deviation exceeds the US intervention threshold, so US control is started. Note that the US active flag is turned ON, and at the same time, the control active flag is turned ON. At this time, as shown in the image diagrams of FIGS. 13 and 14 and the flowchart of FIG. 15, the required torque gain corresponding to the estimated road surface μ and the vehicle body speed is calculated, and the final output torque multiplied by the reference torque is calculated.

  When it is in the US trend, the required torque gain at the time of US with respect to the US yaw rate deviation is set to be large, so that a final output torque larger than the required torque by the normal 4WD control can be obtained. As a result, the front wheel cornering force is secured by distributing the driving force of the front wheels to the rear wheels, and the actual yaw rate follows the target yaw rate for US by improving the turning ability.

  At time t2, when the yaw is generated in the vehicle by the US control, and the OS yaw rate deviation exceeds the absolute value of the OS intervention threshold, the US control is canceled and the OS control is started. In the OS control, the required torque gain is calculated as in the US control, and the final output torque obtained by multiplying the reference torque by the required torque gain is calculated. The OS control reduces the clutch engagement torque, reduces the distribution of driving force to the rear wheels, secures the cornering force of the rear wheels, and improves the stability so that the actual yaw rate follows the target yaw rate for the OS. .

  The target yaw rate during OS control is a target yaw rate obtained from the absolute value of the lateral G with respect to the target yaw rate obtained from the steering angle and the vehicle body speed. Basically, the yaw movement of the vehicle is performed by the difference between the cornering force generated at the front wheels and the cornering force generated at the rear wheels. The lateral G is generated as a value balanced with the cornering force acting on both the front wheel and the rear wheel. Therefore, even if the difference in cornering force is small, in the scene where the lateral G is excessive, most of the tire friction circle is used for the lateral G other than the yaw rate, and the turning ability and stability cannot be secured. . Therefore, limiter processing is performed with the yaw rate obtained from the absolute value of the lateral G to avoid the deterioration of the turning performance and the stability due to excessive lateral G generation.

  At time t3, if the US yaw rate deviation falls below the absolute value of the US control intervention threshold, it is determined that the OS behavior has ended, but immediately to prevent hunting between the OS control and the US control and stabilize the vehicle behavior, Without ending OS control, a delay of a certain time is provided and OS control continuation processing is performed.

  When the yaw rate deviation for OS again exceeds the absolute value of the US control intervention threshold at time t4, the above-described delay is initialized and OS control is continued.

  Even when the OS yaw rate deviation exceeds the absolute value of the threshold value at time t5, if the direction of the actual yaw rate is reversed, it is determined that the OS behavior has ended, and the OS control continuation process is performed by delay as at time t4. Do.

  When the OS yaw rate deviation again exceeds the absolute value of the US control intervention threshold at time t6, the delay described above is initialized and OS control is continued.

  At time t7, when the OS yaw rate deviation falls below the absolute value of the OS control intervention threshold, it is determined that the OS behavior has ended, but immediately to prevent hunting between the OS control and the US control and to stabilize the vehicle behavior, Without ending OS control, a delay of a certain time is provided and OS control continuation processing is performed. When the delay time elapses at time t8, the OS control process ends.

  The above is the basic operation of yaw rate feedback 4WD control. Next, the operation of the required torque gain according to the estimated road surface μ and the vehicle body speed according to the first embodiment will be described. FIG. 20 shows a case where the required torque gain is changed according to the road surface μ (hereinafter referred to as road surface μ sensitive), a case where the required torque gain is changed according to the vehicle body speed (hereinafter referred to as speed sensitive), and both the road surface μ and the vehicle body speed. 5 is a table summarizing the vehicle behavior tendency, the required behavior control, the drive torque control, and the required torque gain setting when the required torque gain is changed according to the above.

(Road surface μ sensitivity only)
The vehicle behavior in the low μ range tends to be unstable, and behavior control that emphasizes stability is necessary, so the required torque gain for yaw rate deviation must be set so that the drive torque is distributed more than the front wheels. is there.

  On the other hand, the vehicle behavior in the high μ range tends to be stable, and behavior control that emphasizes turning performance is necessary, so the required torque gain for yaw rate deviation must be set so that the drive torque is distributed from the rear wheels. There is.

  Therefore, the required torque gain is set for each road surface μ. Specifically, at low μ, the driving force is more distributed to the front wheel side than at high μ, and at high μ, the driving force is distributed to the rear wheel side more than at low μ. Set the required torque gain to. Thereby, both the turning ability on the high μ road and the stability on the low μ road can be achieved.

(Vehicle speed only)
The vehicle behavior in the low-speed range tends to change gradually, and high-response behavior control is required. Therefore, the required torque gain for the yaw rate deviation needs to be set so that the change in the drive torque is quick.

  On the other hand, vehicle behavior at high speeds tends to change suddenly, and behavior control with low response is required, so the required torque gain for yaw rate deviation must be set so that the change in drive torque becomes gradual. .

  Therefore, the required torque gain is set for each vehicle speed range. Specifically, the required torque gain is set so that the change rate of the fastening torque is increased during low speed running compared to that during high speed running, and the change rate of fastening torque is reduced during high speed running compared to during low speed running. . As a result, it is possible to prevent sudden changes in vehicle behavior in the high speed range, and to achieve both quick vehicle behavior control in the low speed range.

(Sensitive to speed and road surface μ)
The vehicle behavior at low μ and low speed ranges is unstable and tends to change slowly, and high-response behavior control that emphasizes stability is required, so the required torque gain for yaw rate deviation is the front wheel for the distribution of drive torque. Therefore, it is necessary to set so that the change is rapid.

  The vehicle behavior in the low μ and high speed range is unstable and tends to change suddenly, and low response behavior control that emphasizes stability is necessary, so the required torque gain for yaw rate deviation is about the distribution of drive torque It is necessary to set so that the change is gentler than the front wheels.

  The vehicle behavior at high μ and low speeds tends to be stable and change quickly, and high-response behavior control with an emphasis on turning performance is required.Therefore, the required torque gain for yaw rate deviation depends on the distribution of drive torque. It is necessary to set so that the change is quicker than the wheel.

  The vehicle behavior in the high μ and high speed range tends to be stable and suddenly changed, and low response behavior control with emphasis on turning performance is required. Therefore, the required torque gain for yaw rate deviation depends on the drive torque distribution. It is necessary to set the value so that the change is gentler than the circle.

  Therefore, by setting for each vehicle speed range and for each road surface μ, it is possible to achieve both prevention of sudden changes in vehicle behavior in the high speed range and quick vehicle behavior control in the low speed range. Further, it is possible to achieve both the turning ability on the high μ road and the stability on the low μ road.

The technical idea that can be grasped based on the first embodiment will be described based on the claims.
(A) In the driving force distribution control device for a four-wheel drive vehicle according to claim 1 or 2,
The driving force distribution control device for a four-wheel drive vehicle, wherein the reference fastening torque calculation means is calculated according to the engine output and / or the steering angle.

  Therefore, no matter what idea the reference torque is calculated based on, the desired vehicle behavior can be achieved simply by applying a correction coefficient to the calculated value. It can also be applied to a force distribution control device.

1 is a system configuration diagram of a vehicle to which a driving force distribution control device for a four-wheel drive vehicle according to a first embodiment is applied. It is a block diagram showing a part of VDC control controller of Example 1, and the control structure in a 4WD control controller. 3 is a flowchart illustrating a main flow of yaw rate feedback 4WD control according to the first embodiment. 3 is a flowchart illustrating a reference torque selection process according to the first embodiment. 3 is a flowchart illustrating an intervention threshold value creation process according to the first embodiment. It is a figure showing the relationship between the intervention threshold value and vehicle body speed of Example 1. FIG. 3 is a flowchart illustrating an intervention determination process according to the first embodiment. 3 is a flowchart illustrating a process A according to the first embodiment. 3 is a flowchart illustrating a process B of the first embodiment. 6 is a flowchart illustrating a process C of the first embodiment. 6 is a flowchart illustrating a process D of the first embodiment. 3 is a flowchart illustrating a calculation process of a required torque gain value according to the first embodiment. It is a figure showing the image of the demand torque gain which considered the road surface μ component of Example 1. It is a figure showing the image of the demand torque gain which considered the vehicle body speed component of Example 1. FIG. 3 is a flowchart illustrating a selection process of a required torque gain value according to the first embodiment. 3 is a flowchart illustrating a process X of the first embodiment. 6 is a flowchart illustrating a process for creating a control active flag according to the first embodiment. 3 is a flowchart illustrating a final output torque calculation process according to the first embodiment. It is a time chart when the yaw rate feedback 4WD control of Example 1 acts when a lane change is performed during straight traveling. 5 is a table summarizing vehicle behavior trends, required behavior control, drive torque control, and required torque gain settings when both road surface μ sensitivity, speed sensitivity, and road surface μ sensitivity and speed sensitivity are performed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Transmission 3 Driving force distribution actuator 4 Brake actuator 5 4WD controller 6 VDC controller 10 Steering angle sensor 11 Wheel speed sensor 12 Yaw rate sensor 13 Longitudinal acceleration sensor
B1-B4 Friction brake
DF1 differential gear
DF2 differential gear
FL, FR Front wheel
RL, RR rear wheel

Claims (5)

In the drive force distribution control device for a four-wheel drive vehicle provided with a clutch capable of changing the distribution of the drive force to the front wheel and the rear wheel according to the fastening torque
Reference fastening torque calculating means for calculating a reference fastening torque based on a difference in rotational speed between the front wheel and the rear wheel;
A yaw rate detecting means for detecting a yaw rate generated in the vehicle;
Target yaw rate calculating means for calculating the target yaw rate of the vehicle;
A yaw rate deviation calculating means for calculating a deviation between the detected yaw rate and the calculated target yaw rate;
Road surface friction coefficient detecting means for detecting or estimating the road surface friction coefficient during traveling;
Friction coefficient type correction coefficient calculating means for calculating a correction coefficient according to the yaw rate deviation and the road surface friction coefficient;
A correction engagement torque calculating means for multiplying the reference engagement torque by the correction coefficient and calculating the engagement torque of the clutch so that the detected yaw rate and the target yaw rate coincide with each other;
Determine oversteer tendency or understeer tendency of the vehicle, and intervene in oversteer control or understeer control when a predetermined oversteer intervention condition or a predetermined understeer intervention condition is satisfied by the engagement torque calculated by the corrected engagement torque calculation means Delay means for ending the understeer control when a predetermined understeer control end condition is satisfied, and ending the oversteer control after a predetermined time delay when the predetermined oversteer control end condition is satisfied;
A driving force distribution control device for a four-wheel drive vehicle. In the drive force distribution control device for a four-wheel drive vehicle provided with a clutch capable of changing the distribution of the drive force to the front wheel and the rear wheel according to the fastening torque,
Reference fastening torque calculating means for calculating a reference fastening torque based on a difference in rotational speed between the front wheel and the rear wheel;
Vehicle speed detection means for detecting the vehicle speed;
A yaw rate detecting means for detecting a yaw rate generated in the vehicle;
Target yaw rate calculating means for calculating the target yaw rate of the vehicle;
A yaw rate deviation calculating means for calculating a deviation between the detected yaw rate and the calculated target yaw rate;
Vehicle speed type correction coefficient calculating means for calculating a correction coefficient according to the yaw rate deviation and the vehicle speed;
A correction engagement torque calculating means for multiplying the reference engagement torque by the correction coefficient and calculating the engagement torque of the clutch so that the detected yaw rate and the target yaw rate coincide with each other;
Determine oversteer tendency or understeer tendency of the vehicle, and intervene in oversteer control or understeer control when a predetermined oversteer intervention condition or a predetermined understeer intervention condition is satisfied by the engagement torque calculated by the corrected engagement torque calculation means Delay means for ending the understeer control when a predetermined understeer control end condition is satisfied, and ending the oversteer control after a predetermined time delay when the predetermined oversteer control end condition is satisfied;
A driving force distribution control device for a four-wheel drive vehicle. The drive force distribution control device for a four-wheel drive vehicle according to claim 1,
The friction coefficient type correction coefficient calculating means distributes the driving force to the front wheel side more greatly when the road is a low friction coefficient road than when the road is a high friction coefficient road, and when the road is a low friction coefficient road. A driving force distribution control device for a four-wheel drive vehicle, wherein a coefficient for correcting the driving force to be largely distributed to the rear wheel side is calculated. The drive force distribution control device for a four-wheel drive vehicle according to claim 2,
The vehicle speed type correction coefficient calculation means corrects the change rate of the fastening torque to be greater during low speed running than during high speed running and to be smaller during high speed running than during low speed running. A driving force distribution control device for a four-wheel drive vehicle characterized by calculating a coefficient. The drive force distribution control device for a four-wheel drive vehicle according to claim 1,
Reference fastening torque calculating means for calculating a reference fastening torque based on a difference in rotational speed between the front wheel and the rear wheel;
Vehicle speed detection means for detecting the vehicle speed;
Vehicle speed type correction coefficient calculating means for calculating a correction coefficient according to the vehicle speed;
Provided,
The corrected engagement torque calculating means calculates the engagement torque of the clutch by multiplying the reference engagement torque by the friction coefficient type correction coefficient and the vehicle speed type correction coefficient, and driving force distribution of a four-wheel drive vehicle Control device.

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