JP2017087786A - Control device of four-wheel drive vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine a friction coefficient of a road surface at an earlier stage while suppressing deterioration of fuel consumption performance.SOLUTION: A four-wheel drive vehicle 1 includes: driving force distribution means 8 for distributing driving force generated in a driving source 10 to rear wheels 102 and 102 to be main driving wheels and front wheels 101 and 101 to be auxiliary driving wheels; and control means 200 including driving force distribution control means 202 for controlling the driving force distribution means. The control means further includes friction coefficient determination means 207 for determining a friction coefficient μ of a road surface on the basis of the driving force of the front wheels 101 when a prescribed condition is established. When the prescribed condition is established, forward traveling in which a steering angle is less than a prescribed steering angle is performed and the driving force distributed to the front wheels 101 is less than prescribed driving force, the driving force distribution means 8 is controlled so that driving force of the prescribed driving force or more is distributed to the front wheels 101 by the driving force distribution control means 202, and the friction coefficient μ of the road surface is determined on the basis of the driving force of the prescribed driving force or more distributed to the front wheels 101 by the friction coefficient determination means 207.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a driving force distribution unit that distributes a driving force generated by a driving source to a rear wheel that is a main driving wheel and a front wheel that is an auxiliary driving wheel, and a driving force distribution control unit that controls the driving force distribution unit. And a control device for a four-wheel drive vehicle.

  Conventionally, in a four-wheel drive vehicle in which driving force is applied to the front wheels and the rear wheels, it is possible to determine the friction coefficient of the road surface and change the driving force applied to the front wheels and the rear wheels according to the determination value. Has been done.

  For example, in Patent Document 1, in a vehicle in which one of the front wheels and the rear wheels is driven by an engine and the other is assisted by a motor, the friction coefficient of the road surface is determined, and the output of the motor at the start of the vehicle is used as the determination result. A control device that changes accordingly is disclosed. Further, the control device is configured to determine the friction coefficient of the road surface based on the slip ratio of the wheel driven by the engine and the driving force of the wheel.

JP-A-8-300964

  In order to further improve the running performance of the four-wheel drive vehicle, it is desirable to determine the friction coefficient of the road surface earlier and change the driving force applied to the front wheels and the rear wheels earlier according to this. When the road surface friction coefficient is determined with the rear wheels during forward travel, a delay corresponding to the wheel base is generated as compared with the case with the front wheels. Therefore, it is desired to determine the road surface friction coefficient with the front wheels. However, in a four-wheel drive vehicle in which the rear wheels are the main drive wheels and the front wheels are the auxiliary drive wheels, when no driving force is applied to the front wheels, the determination of the friction coefficient of the road surface based on the driving force of the front wheels is performed. The problem that cannot be done. On the other hand, for example, it is conceivable to always apply a predetermined driving force to the front wheels, but in this case, an excessive driving force is applied to the front wheels that are auxiliary driving wheels. Fuel consumption performance deteriorates.

  The present invention has been made in view of the above circumstances, and provides a control device for a four-wheel drive vehicle capable of determining a friction coefficient of a road surface at an earlier stage while suppressing deterioration in fuel efficiency. For the purpose.

  In order to solve the above-described problems, the present invention provides a driving force distribution unit that distributes a driving force generated by a driving source to a rear wheel that is a main driving wheel and a front wheel that is an auxiliary driving wheel, and the driving force distribution unit. And a control unit having a driving force distribution control unit for controlling the driving force. The control unit includes a friction coefficient of the road surface based on the driving force of the front wheel when a predetermined condition is satisfied. A friction coefficient determination means for determining whether the vehicle is traveling forward in a state where the predetermined condition is satisfied and the specific condition that the steering angle is less than the predetermined steering angle is satisfied; and When the driving force distributed to the front wheels is less than a predetermined driving force, the driving force distribution control means controls the driving force distribution means so as to distribute a driving force greater than the predetermined driving force to the front wheels. The friction coefficient determining means is Serial based on the predetermined driving force or the driving force distributed to the front wheels to provide a control apparatus for a four wheel drive vehicle, characterized in that to determine the friction coefficient of the road surface (claim 1).

  According to the present invention, since the friction coefficient of the road surface can be determined based on the driving force applied to the front wheel, that is, based on the state of the front wheel, compared to the case where the friction coefficient is determined on the rear wheel, The friction coefficient of the road surface for the wheel base can be determined at an early stage, and the running stability of the vehicle can be improved. In addition, when the steering angle is less than the predetermined steering angle and the vehicle is traveling forward, when the driving force of the front wheels is less than the predetermined driving force, the driving force of the front wheels is increased and the driving force of the front wheels is increased. More than a predetermined driving force. Therefore, the opportunity to increase the driving force of the front wheels for the determination of the friction coefficient can be reduced, and deterioration of fuel consumption performance can be suppressed.

  In the present invention, determining the friction coefficient of the road surface includes estimating the friction coefficient of the road surface, and the same applies to the following.

  The present invention also provides a driving force distribution means for distributing the driving force generated by the driving source to the rear wheels as the main driving wheels and the front wheels as the auxiliary driving wheels, and the driving force distribution for controlling the driving force distribution means. In the control device for a four-wheel drive vehicle comprising a control means having a control means, the control means determines a friction coefficient of the road surface based on the driving force of the front wheels when a predetermined condition is satisfied. The vehicle is traveling forward in a state where the specific condition that the predetermined condition is satisfied and the turning amount of the vehicle is less than the predetermined turning amount is satisfied, and the front wheel When the driving force distributed to the vehicle is less than the predetermined driving force, the driving force distribution control unit controls the driving force distribution unit to distribute the driving force equal to or higher than the predetermined driving force to the front wheels, and The friction coefficient determining means is provided on the front wheel. Arranged a based on the predetermined driving force or the driving force to provide a control apparatus for a four wheel drive vehicle and judging the friction coefficient of the road surface (claim 2).

  Also in the present invention, the road surface friction coefficient can be determined in the state of the front wheel, so that it is possible to determine the road surface friction coefficient earlier than the case of determining the friction coefficient at the rear wheel by the amount of the wheel base. When the turning amount of the vehicle is less than the predetermined turning amount and the vehicle is traveling forward, when the driving force of the front wheels is less than the predetermined driving force, the driving force of the front wheels is increased and the driving force of the front wheels is increased. By setting the value to be equal to or greater than the predetermined driving force, the opportunity for excessively applying the driving force to the front wheels for the determination of the friction coefficient can be reduced, and deterioration of fuel consumption performance can be suppressed.

  The present invention also provides a driving force distribution means for distributing the driving force generated by the driving source to the rear wheels as the main driving wheels and the front wheels as the auxiliary driving wheels, and the driving force distribution for controlling the driving force distribution means. In the control device for a four-wheel drive vehicle comprising a control means having a control means, the control means determines a friction coefficient of the road surface based on the driving force of the front wheels when a predetermined condition is satisfied. And the vehicle is traveling forward in a state where the specific condition that the predetermined condition is satisfied and the lateral G applied to the vehicle is less than a predetermined value is satisfied, and the front wheel When the driving force distributed to the vehicle is less than the predetermined driving force, the driving force distribution control unit controls the driving force distribution unit to distribute the driving force equal to or higher than the predetermined driving force to the front wheels, and The friction coefficient determining means is provided on the front wheel. Arranged a based on the predetermined driving force or the driving force to provide a control apparatus for a four wheel drive vehicle and judging the friction coefficient of the road surface (claim 3).

  Also in the present invention, the road surface friction coefficient can be determined in the state of the front wheel, so that it is possible to determine the road surface friction coefficient earlier than the case of determining the friction coefficient at the rear wheel by the amount of the wheel base. When the lateral G of the vehicle is less than a predetermined value and the vehicle is traveling forward, when the driving force of the front wheels is less than the predetermined driving force, the driving force of the front wheels is increased and the driving force of the front wheels is increased. By setting the value to be equal to or greater than the predetermined driving force, the opportunity for excessively applying the driving force to the front wheels for the determination of the friction coefficient can be reduced, and deterioration of fuel consumption performance can be suppressed.

  In the present invention, the control means further includes driving support control means for performing driving support control for reducing the driving force generated by the driving source so as to reduce the deceleration of the vehicle when the steering angle changes. When the steering angle changes, the driving support control means generates the driving source when the predetermined condition is satisfied and the vehicle is traveling forward with the specific condition being satisfied. Preferably, the driving force distribution means is controlled so that the driving force distributed to the front wheels by the driving force distribution control means is equal to or greater than the predetermined driving force while reducing the driving force to be applied. .

  In this way, it is possible to determine the friction coefficient of the road surface earlier while enhancing the operability when the vehicle turns by implementing the vehicle support control.

  Further, in the present invention, the control means is configured such that the friction coefficient of the road surface is based on a steering reaction force applied to the steering for operating the front wheels or a lateral force applied to the front wheels when a predetermined condition is satisfied. It is preferable that the second friction coefficient determination means further determines a friction coefficient of the road surface during forward traveling in a state where the specific condition is not satisfied ( Claim 5).

  By doing so, the friction coefficient of the road surface can be determined earlier by the front wheels even when the specific condition is not satisfied.

  Here, there is a correlation between the friction coefficient of the road surface, the driving force applied to the wheels, and the slip ratio. Therefore, it is preferable that the friction coefficient determination means determines the friction coefficient of the road surface based on the driving force applied to the front wheel and the slip ratio of the front wheel.

  In this way, the friction coefficient of the road surface can be determined with a simple configuration.

  As described above, according to the control device for a four-wheel drive vehicle of the present invention, it is possible to determine the friction coefficient of the road surface at an earlier stage while suppressing deterioration in cost performance.

1 is a schematic configuration diagram of a drive system for a vehicle according to an embodiment of the present invention. It is a control block diagram concerning one embodiment of the present invention. It is the figure which showed the change of each parameter at the time of GVC control implementation. It is the flowchart which showed the detection procedure of the road surface (mu) by the 1st detection part. It is the figure which showed the relationship between the slip ratio, the driving force provided to the wheel, and the friction coefficient. It is the flowchart which showed the detection procedure of road surface (mu) by the 2nd detection part. It is the figure which showed the relationship between a slip angle, the lateral force of a wheel, and a friction coefficient. It is the flowchart which showed the control procedure which concerns on road surface micro detection. It is the figure which showed the change of the front-wheel drive force at the time of implementing the detection in a 1st micro | micron | mud detection part at the time of GVC control implementation.

(1) Drive system FIG. 1 is a schematic diagram showing a drive system of a vehicle 1 on which a control device for a four-wheel drive vehicle according to an embodiment of the present invention is mounted.

  The vehicle 1 according to the present embodiment is a four-wheel drive vehicle, and has an engine 2 as a drive source, and the output of the engine 2, that is, the driving force generated by the engine is applied to the front wheels 101 and 101 and the rear wheels 102 and 102, respectively. It is to be transmitted. The vehicle 1 is a vehicle having rear wheels 102 and 102 as main driving wheels and front wheels 101 and 101 as driven wheels.

  The vehicle 1 includes a transmission 4 that is connected to the engine 2 and transmits engine output to wheels. A propeller shaft 10 extends from the transmission 4 and is connected to the rear wheels 102. More specifically, the propeller shaft 10 is connected to the wheels 102 and 102 via a differential gear 11 on the rear wheel side and a drive shaft 12 on the rear wheel side. Hereinafter, the total driving force that is the output of the engine 2 transmitted to the propeller shaft 10 via the transmission 4 and is transmitted to the wheels 101, 101, 102, 101 will be referred to as vehicle driving force.

  On the other hand, the front wheels 101 are connected to the propeller shaft 10 via the transfer 6 and 4WD coupling (driving force distribution means) 8. More specifically, the front wheels 101 and 101 and the propeller shaft 10 are connected via a drive transmission shaft 14 and a differential gear 15 on the front wheel side in addition to the transfer 6 and the 4WD coupling 8.

  The transfer 6 is a device for branching the driving force of the propeller shaft 10, that is, the vehicle driving force, to the drive transmission shaft 14.

  The 4WD coupling 8 is a device that changes the driving force transmitted from the propeller shaft 10 to the drive transmission shaft 14 in a state where the drive transmission shaft 14 and the propeller shaft 10 are coupled. In this embodiment, the 4WD coupling 8 is an electromagnetic type and includes a multi-plate clutch and an electromagnet that controls the multi-plate clutch, and the contact state of the multi-plate clutch is changed by changing the current flowing through the electromagnet. Accordingly, the driving force transmitted from the propeller shaft 10 to the drive transmission shaft 14 and applied to the front wheels 101 and 101 is changed.

  The vehicle 1 is provided with a power steering device 24 that assists the operation of the steering 20. Specifically, the vehicle 1 is provided with a steering wheel 20 for operating the wheels, and a column shaft 22 that extends forward from the steering wheel 20 in the vehicle front-rear direction and rotates integrally with the steering wheel 20. The power steering device 24 assists the rotation of the column shaft 22. In the present embodiment, the power steering device 24 is electrically operated, and assists the rotation of the column shaft 22 by a motor.

(2) Control system The vehicle 1 configured as described above includes a control unit 200 for controlling the engine 2 (in detail, a spark plug, a throttle valve, and the like provided in the engine 2), the 4WD coupling 8, and the like. Is provided. The control unit 200 performs calculations based on information from various sensors and issues commands to the engine 2 and the like.

  For example, as shown in FIG. 2, the vehicle 1 includes a steering angle sensor 302, a wheel speed sensor 304, a column torque sensor 306, a power steering torque sensor 308, a coupling current sensor 310, a lateral G sensor 312, a yaw rate sensor 314, an accelerator. An opening sensor 316, an intake air amount sensor 318, an outside air temperature sensor 320, a vehicle speed sensor 322, and the like are provided.

  The steering angle sensor 302 is a sensor that detects the steering angle of the steering 20. The wheel speed sensor 304 is a sensor that detects the rotational speed of each wheel 101, 101, 102, 102. The column torque sensor 306 is a sensor that detects the torque applied to the column shaft 22. The power steering torque sensor 308 is a sensor that detects the torque generated by the motor of the power steering device 24. The coupling current sensor 310 is a sensor that detects a current that is energized to the 4WD coupling 8. The lateral G sensor 312 is a sensor that detects lateral G applied to the vehicle 1, that is, acceleration in the lateral direction (vehicle width direction). The yaw rate sensor 314 is a sensor that detects the yaw rate of the vehicle 1, that is, the angular velocity in the turning direction of the vehicle 1. The accelerator opening sensor 316 is a sensor that detects the amount of depression of an accelerator pedal provided in the vehicle 1. The intake air amount sensor 318 is a sensor that detects the amount of intake air flowing into the engine 2. The outside air temperature sensor 320 is a sensor that detects outside air, that is, a temperature outside the engine 2. The vehicle speed sensor 322 is a sensor that detects the vehicle speed.

  The control unit 200 functionally includes a coupling control unit (driving force distribution control unit) 202, a GVC control unit (driving support control unit) 204, and a μ detection unit 206. Further, the μ detection unit 206 functionally includes a first μ detection unit (friction coefficient determination unit) 207 and a second μ detection unit (second friction coefficient determination unit) 208.

  The GVC control unit 204 performs driving support control (hereinafter referred to as GVC control), which is control for increasing deceleration during vehicle turning, that is, cornering, in order to improve traveling performance. Specifically, as shown in FIG. 3, when the change amount of the steering angle of the steering wheel 30 detected by the steering angle sensor 302 becomes equal to or greater than a preset reference change amount, the GVC control unit 204 causes the cornering of the vehicle 1. Slowly increase deceleration as if it were in the middle. In the present embodiment, the engine torque is reduced by retarding the ignition timing of the engine 2, thereby reducing the vehicle driving force and increasing the deceleration.

  Specifically, the GVC control unit 204 determines the engine torque with respect to the engine torque that is required engine torque during normal operation and is determined based on the accelerator pedal opening detected by the accelerator opening sensor 316. Reduce. In addition, the GVC control unit 204 gradually decreases the deceleration when a predetermined time has elapsed after starting the increase in the deceleration. If it does in this way, the cornering force in front wheels 101 and 101 can be raised at the time of cornering, and vehicle 1 can be turned smoothly.

  The first μ detection unit 207 and the second μ detection unit 208 respectively detect a road surface friction coefficient μ (hereinafter referred to as a road surface friction coefficient in the claims, and hereinafter simply referred to as a road surface μ). That is, the road surface friction coefficient μ is determined. The detection and determination here include estimation. However, the first μ detection unit 207 and the second μ detection unit 208 have different detection procedures.

  The first μ detection unit 207 detects the road surface μ based on the slip ratio of the front wheel 101 (the ratio between the vehicle speed and the wheel speed and the vehicle speed) and the driving force applied to the front wheel 101.

  This will be specifically described with reference to FIG.

  The first μ detection unit 207 reads signals from various sensors in step S1. Next, in step S <b> 2, the slip ratio of the front wheel 101 is calculated based on the vehicle speed detected by the vehicle speed sensor 332 and the wheel speed of the front wheel 101 detected by the wheel speed sensor 304 provided on the front wheel 101. In the present embodiment, the slip ratio of the left and right front wheels 101 is calculated, and the larger slip ratio is used as the slip ratio of the front wheel 101. Next, in step S3, the driving force applied to the front wheels 101 is calculated. In the present embodiment, the driving force of the front wheels 101 is calculated based on the amount of current energized in the 4WD coupling 8 detected by the coupling current sensor 310. In step S4, the friction coefficient μ of the road surface on which the front wheel 101 is grounded is calculated and detected based on the slip ratio of the front wheel 101 calculated in step S2 and the driving force of the front wheel 101 calculated in step S3.

  That is, there is a correlation as shown in FIG. 5 among the wheel slip ratio, the wheel driving force, and the road surface μ. Specifically, in FIG. 5, each line Lμ1 to Lμ3 indicates the relationship between the wheel slip ratio and the wheel driving force on a predetermined road surface μ, and the road surface μ in the order of Lμ1, Lμ2, and Lμ3. Is getting higher. Thus, even if the slip ratio is the same, the driving force of the wheel increases as the road surface μ increases. Further, as the road surface μ is higher when the slip ratio is less than or equal to a predetermined value, the amount of change in the driving force with respect to the change in the slip ratio (the slope of each line in FIG. 5) increases. The first μ detection unit 207 detects the road surface μ based on this correlation. In this embodiment, the relationship between the slip ratio of the wheel, the driving force of the wheel, and the road surface μ is stored in a map, the slip ratio and the driving force of the front wheel are detected, and the road surface μ corresponding to these detected values is determined. Extract from the map.

  On the other hand, the second μ detection unit 208 detects the road surface μ based on the slip angle of the front wheel 101 and the lateral force applied to the front wheel 101 (force in the vehicle width direction).

  This will be specifically described with reference to FIG.

  The second μ detection unit 208 reads signals from various sensors in step S11. Next, in step S12, the lateral force applied to the vehicle 1 is calculated based on the lateral G of the vehicle 1 detected by the lateral G sensor 312 and the vehicle weight stored in advance. Next, in step S <b> 13, the lateral force related to the front wheel 101 is calculated based on the calculated lateral force applied to the vehicle 1. Specifically, the second μ detection unit 208 calculates the ratio of the separation distance in the vehicle front-rear direction between the center of gravity position of the vehicle 1 and the rear wheel 102 with respect to the wheel base in the lateral force related to the vehicle 1 calculated in step S12. And calculated as a lateral force related to the front wheel 101.

  Further, in step S14, the second μ detection unit 208 detects the vehicle speed detected by the vehicle speed sensor 322, the lateral G of the vehicle 1 detected by the lateral G sensor 312, and the yaw rate of the vehicle 1 detected by the yaw rate sensor 314. Based on the above, the slip angle of the front wheel 101 (the inclination angle of the front wheel 101 with respect to the traveling direction of the vehicle 1) is calculated.

  Then, the second μ detection unit 208 calculates the friction coefficient μ of the road surface on which the front wheel 101 is in contact with the ground based on the slip angle of the front wheel 101 calculated in step S14 and the lateral force of the front wheel 101 calculated in step S13. ,To detect.

  That is, there is a correlation as shown in FIG. 7 between the slip angle of the wheel, the lateral force applied to the wheel, and the road surface μ. Specifically, in FIG. 7, each of the lines Lμ12 to Lμ13 indicates the relationship between the slip angle of the wheel on the predetermined road surface μ and the lateral force applied to the wheel, and the road surface in the order of Lμ11, Lμ12, and Lμ13. μ is higher. Thus, even if the slip angle is the same, the higher the road surface μ, the higher the lateral force applied to the wheels. Further, as the road surface μ is higher when the slip angle is equal to or less than a predetermined value, the amount of change in the lateral force applied to the wheel with respect to the change in the slip angle (the inclination of each line in FIG. 7) increases. Therefore, the second μ detection unit 208 detects the road surface μ based on this correlation. In the present embodiment, the relationship between the slip angle of the wheel, the lateral force applied to the wheel, and the road surface μ is stored as a map, and corresponds to the slip angle calculated in step S14 and the lateral force applied to the front wheel calculated in step S13. The road surface μ to be extracted is extracted from the map.

  As described above, in this embodiment, the road surface μ is detected based on the state of the front wheel 101 in both the first μ detection unit 207 and the second μ detection unit 208. Then, depending on the driving conditions, switching between the first μ detection unit 207 and the second μ detection unit 208 for detecting the road surface μ is switched.

  The coupling control unit 202 calculates the driving force to be applied to the front wheels 101, and controls the amount of current supplied to the 4WD coupling 8 so that this driving force is realized.

  In the present embodiment, the coupling control unit 202 calculates a basic value of driving force of the front wheels 101 (hereinafter referred to as basic front wheel driving force) as follows.

  First, the coupling control unit 202 is given to the wheels 101 and 102 calculated based on the wheel speed detected by the wheel speed sensor 304, the vehicle speed detected by the vehicle speed sensor 322, and the coupling current sensor 310. Distribution based on the driving force and the like, in which the loss of the driving force due to the slip of the wheels 101 and 102 and the mechanical loss at the transfer 6 and the like due to the distribution of the driving force to the front wheels 101 is minimized. The ratio (distribution ratio of the vehicle driving force to the front wheels 101 and the rear wheels 102) is determined. Next, the coupling control unit 202 corrects this distribution ratio according to the road surface μ to determine the basic distribution ratio. For example, when a sudden change in the road surface μ is detected when the vehicle 1 moves forward, the coupling control unit 202 changes the distribution ratio according to the road surface μ so that the slip of the vehicle 1 is suppressed. Then, the coupling control unit 202 calculates the basic front wheel driving force based on the current vehicle driving force and the basic distribution ratio.

  Here, the vehicle driving force is calculated based on the output of the engine 2 and the gear ratio in the transmission 4. The output of the engine 2 is calculated based on the accelerator pedal opening detected by the accelerator opening sensor 316 and the intake air amount of the engine 2 detected by the intake air sensor 318.

  However, during the execution of the GVC control, the engine output is automatically reduced with respect to the engine output based on the opening degree of the accelerator pedal as described above. Therefore, during the execution of the GVC control, the current vehicle driving force and the basic front wheel driving force are calculated based on the engine output that has been reduced along with this execution. Hereinafter, the basic front wheel driving force at the time of driving support control is referred to as GVC basic front wheel driving force.

  The coupling control unit 202 controls the energization amount of the 4WD coupling 8 so that the basic front wheel driving force calculated in this way is realized under normal driving conditions. On the other hand, as described below, when the road surface μ is detected by the first μ detection unit 207 under a predetermined condition, the basic front wheel driving force is corrected to be increased.

  Next, switching between the first μ detection unit 207 and the second μ detection unit 208 and the control procedure of the front wheel driving force will be described with reference to the flowchart of FIG.

  First, in step S101, the control unit 200 determines whether or not there is a request to detect the road surface μ based on the state of the front wheel 101. In the present embodiment, it is determined that there is this requirement in the case of an operating condition where the road surface μ is likely to change suddenly. That is, when the road surface μ changes suddenly, it is preferable to set the driving force of the front wheel 101 and the rear wheel 102 to an appropriate value earlier according to the road surface μ in order to suppress the slip of the vehicle 1 and so on. The road surface μ is detected earlier by the front wheel 101. For example, when the outside air temperature detected by the outside air temperature sensor 320 is low, or when the wiper is operated, the road surface μ changes suddenly due to freezing of the road surface or rainwater accumulating on the road surface. Probability is high. Therefore, in this embodiment, in these cases, it is determined that there is a request for detecting the road surface μ at the front wheel 101 (that is, a predetermined condition in the claims is satisfied).

  Next, in step S102, each sensor signal, the current road surface μ detected previously (detected μ), and the basic front wheel driving force calculated as described above by the coupling control unit 202 are read.

  Next, in step S103, a μ-detectable driving force (predetermined driving force in claims) is set. The μ-detectable driving force is the driving force of the front wheel 101 that enables the first μ detection unit 207 to detect the road surface μ. That is, when the driving force applied to the front wheel 101 is small, there is a possibility that the road surface μ cannot be detected appropriately because the difference in the slip ratio due to the difference in the road surface μ is small, and the μ detectable driving force is the first μ This is a driving force that allows the detection unit 207 to accurately detect the road surface μ based on the slip ratio and the driving force of the front wheel 101.

  In the present embodiment, this μ-detectable driving force is set based on the detected μ. Specifically, the μ detection drive force is set to a smaller value as the detected μ is lower. That is, as shown in FIG. 5, the lower the road surface μ, the smaller the driving force of the wheel. When the road surface μ is low, even if the driving force applied to the wheel is relatively low, the road surface μ is accompanied by a difference. Since the difference in the slip ratio becomes large, the driving force necessary to detect the change in the slip ratio and thus the road surface μ can be small. Therefore, in the present embodiment, when the detected μ is low and the road surface μ is traveling on a road surface with a low road surface μ, the μ detectable driving force is set to a small value, and when the detected μ is high, the μ detectable driving is performed. Increase force.

  Next, in step S104, it is determined whether or not the vehicle 1 is moving forward.

  If the determination in step S104 is NO, the subsequent process, that is, the road surface μ on the front wheel 101 is not detected, and the process ends.

  On the other hand, if the determination in step S104 is YES, whether or not a specific condition is satisfied that the steering angle detected by the steering angle sensor 302 in step S105 is less than the reference steering angle (predetermined steering angle in the claims). Determine. The reference steering angle is a steering angle of the steering 20 that can accurately detect the road surface μ by the second μ detection unit 208, that is, the road surface μ based on the slip angle of the wheel and the lateral force applied to the wheel. That is, in order to detect the road surface μ by the second μ detection unit 208 based on the slip angle of the front wheel 101 and the lateral force applied to the front wheel 101, the slip angle generated on the front wheel 101 needs to be large to some extent, and the reference steering angle Is a steering angle at which this detection can be performed with high accuracy, and is preset and stored.

  If the determination in step S105 is no and the steering angle is less than the reference steering angle, the process proceeds to step S106. In step S <b> 106, the front wheel basic driving force set by the coupling control unit 202 is applied to the front wheel 101. Specifically, the energization amount of the 4WD coupling 8 is set to a current corresponding to this driving force.

  After step S106, the process proceeds to step S107. In step S107, the road surface μ is detected by the second μ detector 208, and the road surface μ is detected based on the lateral force applied to the front wheel 101. Specifically, as described above, the road surface μ is detected based on the slip angle and lateral force of the front wheel 101. After step S107, the process ends.

  On the other hand, if the determination in step S105 is yes and the steering angle is less than the reference steering angle, the process proceeds to step S108. In step S108, it is determined whether GVC control is stopped. If this determination is YES and GVC control is not performed, the process proceeds to step S109.

  In step S109, it is determined whether the driving force of the front wheels 101 is less than the μ detectable driving force set in step S103. In the present embodiment, the driving force applied to the front wheel 101 is calculated based on the amount of current that is supplied to the 4WD coupling detected by the coupling current sensor 310, and this calculated value and the μ detectable driving force Compare

  If the determination in step S109 is YES and the driving force of the front wheels 101 is less than the μ detectable driving force, the process proceeds to step S110. In step S2110, a μ-detectable driving force is applied to the front wheel 101. Specifically, a current corresponding to the μ-detectable driving force is supplied to the 4WD coupling 8. After step S110, the process proceeds to step S111.

  In step S111, the road surface μ is detected by the first μ detector 207, and the road surface μ is detected based on the driving force applied to the front wheels 101. Specifically, as described above, the road surface μ is detected based on the slip ratio and the driving force of the front wheels 101. After step S111, the process ends.

  On the other hand, if the determination in step S109 is NO and the driving force of the front wheels 101 is greater than or equal to the μ detectable driving force, the process proceeds to step S111 as it is, the road surface μ is detected by the first μ detection unit 207, and the process is terminated. .

  Further, when the determination in step S108 is NO and the GVC control is being performed, the process proceeds to step S112. In step S112, it is determined whether or not the GVC basic front wheel driving force is less than μ detectable driving force. If this determination is YES, the process proceeds to step S110. Then, a μ-detectable driving force is applied to the front wheel 101, and the road surface μ is detected by the first μ detection unit 207.

  On the other hand, if the determination in step S22 is YES and the GVC basic front wheel driving force is greater than or equal to the μ detectable driving force, the process proceeds to step S113, and the GVC basic front wheel driving force is applied to the front wheels.

(3) Operation etc. As described above, in this embodiment, the road surface μ can be detected on the front wheel 101, and the road surface μ can be detected earlier. That is, when the road surface μ can be detected only by the rear wheel 102, the road surface μ cannot be detected until the rear wheel 102 reaches the portion where the friction coefficient μ changes, and the front wheel 101 and the rear wheel 102 are detected. Therefore, there is a risk that the vehicle 1 slips due to the slow application of the appropriate driving force. On the other hand, in the present embodiment, since the road surface μ can be detected by the front wheels 101, the traveling stability of the vehicle 1 can be improved by detecting the road surface μ earlier.

  Moreover, in the present embodiment, when the vehicle 1 is moving forward and the steering angle of the steering wheel 20 is less than the reference steering angle, the road surface μ is detected by the first μ detection unit 207 based on the driving force of the front wheels 101, When the vehicle 1 is moving forward and the steering angle of the steering 20 is greater than or equal to the reference steering angle, the road surface μ is detected by the second μ detection unit 208 based on the lateral force of the front wheel 101. That is, when it is difficult to detect the road surface μ based on the steering angle of the steering wheel 20, the first μ detection unit 207 detects the road surface μ based on the driving force of the front wheels 101. Further, when the road surface μ is detected by the first μ detection unit 207, the driving force of the front wheels is increased when the driving force of the front wheels is less than the driving force capable of detecting μ. Therefore, the opportunity to increase the driving force of the front wheels 101 for detecting the road surface μ can be reduced, and deterioration of fuel consumption performance can be suppressed.

  In addition, a condition that there is a request to detect the road surface μ at the front wheel 101, a condition that the vehicle 1 is moving forward, a condition that the steering angle is less than the reference steering angle, and further, during the execution of GVC control, Even when the GVC basic front wheel driving force is less than the μ-detectable driving force, the driving force applied to the front wheel 101 is the μ-detectable driving force. Specifically, as shown by the broken line in FIG. 9, the driving force of the front wheel 101 is gradually reduced with the execution of the GVC control, but when the driving force decreases to the μ detectable driving force, the further decrease is regulated. μ is maintained at a detectable driving force. Therefore, while the vehicle 1 is appropriately turned by performing the GVC control, the road surface μ can be detected at an early stage by the first μ detection unit 207 to improve the running stability.

(4) Other Embodiments In the above embodiment, the case where the road surface μ is detected based on the lateral force of the front wheel 101 when the steering angle is equal to or larger than the reference steering angle has been described, but instead of this lateral force, the steering 20 Alternatively, the road surface μ may be detected based on a reaction force applied to the so-called steering reaction force. Specifically, since the lateral force applied to the front wheels 101 is substantially proportional to the steering reaction force, the steering reaction force may be used instead of the lateral force in step S107. That is, the road surface μ may be detected by the second μ detection unit 208 based on the steering reaction force and the slip angle. Here, the relationship among the steering reaction force, the slip angle, and the road surface μ is substantially the same as that in FIG. 7 in which the vertical axis is changed from the lateral force to the steering reaction force. Note that the steering reaction force is, for example, torque applied to the column shaft 22 detected by the column torque sensor 306, and torque applied to the column shaft 22 from the power steering device 24 detected by the power steering torque sensor 308. Can be calculated based on

  Further, the steering angle and the turning amount of the vehicle 1 or the lateral G applied to the vehicle 1 are substantially proportional. Therefore, in step S105, it is determined whether the steering angle is less than the reference steering angle, whether the turning amount of the vehicle 1 is less than a preset reference turning amount (predetermined turning amount in the claims), or You may replace with the determination whether the horizontal G is less than the reference | standard G (predetermined value in a claim) set beforehand. For example, the detected value of the yaw rate sensor 314 may be used as the turning amount of the vehicle 1. For the lateral G related to the vehicle 1, the detection value of the lateral G sensor 312 may be used.

  Moreover, although the said embodiment demonstrated the case where the drive source was the engine 2, a drive source is not restricted to this. Further, the mechanism for transmitting the drive amount of the drive source to the front wheels 101, 101 and the rear wheels 102, 102 is not limited to the above.

  In the above-described embodiment, the case where the road surface μ is likely to change suddenly is described as the case where the outside air temperature detected by the outside air temperature sensor 320 is low, or the case where the wiper is operated. . Furthermore, in the above-described embodiment, the case where it is determined that there is a request for detecting the road surface μ on the front wheel 101 when there is a high possibility that the road surface μ is suddenly changed. The standard is not limited to this. For example, even when the possibility that the road surface μ changes suddenly is low, it may be determined that there is a request to detect the road surface μ on the front wheel 101. Further, there may be a request to detect the road surface μ at the front wheel 101 every several milliseconds.

  Further, in the above embodiment, when GVC control is performed when there is a request for detecting the road surface μ on the front wheel 101, the driving force of the front wheel 101 is maintained to be greater than or equal to the μ detectable driving force, that is, the road surface μ Although the case where the detection is prioritized over the GVC control has been described, the GVC control is prioritized over the detection of the road surface μ, and when the GVC control is performed, the front wheel 101 is driven even if there is a request to detect the road surface μ on the front wheel 101. The force may be allowed to be less than the μ-detectable driving force.

  In the above embodiment, whether or not GVC control is stopped is determined in step S108, and whether or not the GVC basic front wheel driving force is less than μ detectable driving force is determined in step S112, and the GVC control is performed. The case where the reference detected torque is distributed to the front wheels 101 when the GVC basic front wheel driving force is less than the μ detectable driving force (determination in step S112 is YES) has been described. That is, when the GVC control is performed, the driving force of the front wheel 101, that is, the basic front wheel driving force during GVC may be less than the μ detectable driving force, and the GVC basic front wheel driving force does not fall below the μ detectable driving force. Although the case of controlling has been described, instead of this, it may be configured such that the GVC basic front wheel driving force is maintained in advance at or above the μ detectable driving force during GVC control. For example, when the GVC control is started, the driving force of the front wheel 101 is increased by the difference between these so that the minimum value of the driving force of the front wheel 101 that changes with the execution of the GVC control becomes the μ detectable driving force. It may be left.

  Further, the GVC control can be omitted.

1 Vehicle 6 Transfer 8 4WD coupling (drive force distribution means)
10 Engine 20 Steering 101 Front wheel 200 Control unit (control means)
202 Coupling control unit (driving force distribution control means)
204 GVC control unit (driving support control means)
207 first μ detection unit (friction coefficient determination means)
208 second μ detection unit (second friction coefficient determination means)

Claims (6)

Control means having drive force distribution means for distributing the drive force generated by the drive source to the rear wheel as the main drive wheel and the front wheel as the auxiliary drive wheel, and drive force distribution control means for controlling the drive force distribution means In a control device for a four-wheel drive vehicle comprising:
The control means further includes a friction coefficient determination means for determining a friction coefficient of the road surface based on the driving force of the front wheels when a predetermined condition is satisfied,
The driving force distributed to the front wheels is predetermined while the predetermined condition is satisfied, the vehicle is traveling forward with the specific condition that the steering angle is less than the predetermined steering angle. When the driving force is less than the driving force, the driving force distribution control unit controls the driving force distribution unit to distribute a driving force equal to or greater than the predetermined driving force to the front wheel, and the friction coefficient determination unit applies the front wheel. A control device for a four-wheel drive vehicle, wherein a road surface friction coefficient is determined based on a distributed driving force equal to or greater than the predetermined driving force. Control means having drive force distribution means for distributing the drive force generated by the drive source to the rear wheel as the main drive wheel and the front wheel as the auxiliary drive wheel, and drive force distribution control means for controlling the drive force distribution means In a control device for a four-wheel drive vehicle comprising:
The control means further includes a friction coefficient determination means for determining a friction coefficient of the road surface based on the driving force of the front wheels when a predetermined condition is satisfied,
Drive that is traveling forward in a state where the predetermined condition is satisfied, and the specific condition that the turning amount of the vehicle is less than the predetermined turning amount is satisfied, and is distributed to the front wheels When the force is less than a predetermined driving force, the driving force distribution control unit controls the driving force distribution unit to distribute a driving force equal to or greater than the predetermined driving force to the front wheels, and the friction coefficient determination unit includes: A control device for a four-wheel drive vehicle, characterized in that a friction coefficient of a road surface is determined based on a drive force equal to or greater than the predetermined drive force distributed to the front wheels. Control means having drive force distribution means for distributing the drive force generated by the drive source to the rear wheel as the main drive wheel and the front wheel as the auxiliary drive wheel, and drive force distribution control means for controlling the drive force distribution means In a control device for a four-wheel drive vehicle comprising:
The control means further includes a friction coefficient determination means for determining a friction coefficient of the road surface based on the driving force of the front wheels when a predetermined condition is satisfied,
Drive that is traveling forward in a state where the predetermined condition is satisfied and the specific condition that the lateral G applied to the vehicle is less than a predetermined value is satisfied, and is distributed to the front wheels When the force is less than a predetermined driving force, the driving force distribution control unit controls the driving force distribution unit to distribute a driving force equal to or greater than the predetermined driving force to the front wheels, and the friction coefficient determination unit includes: A control device for a four-wheel drive vehicle, characterized in that a friction coefficient of a road surface is determined based on a drive force equal to or greater than the predetermined drive force distributed to the front wheels. A control device for a four-wheel drive vehicle according to any one of claims 1 to 3,
The control means includes
The vehicle further comprises driving support control means for performing driving support control for reducing the driving force generated by the driving source so that the deceleration of the vehicle is reduced when the steering angle changes,
When the steering angle changes, the driving support control means generates the driving source when the predetermined condition is satisfied and the vehicle is traveling forward with the specific condition being satisfied. A four-wheel drive vehicle characterized in that the driving force distribution means is controlled so that the driving force distributed to the front wheels by the driving force distribution control means is not less than the predetermined driving force while reducing the driving force. Control device. A control device for a four-wheel drive vehicle according to any one of claims 1 to 4,
The control means determines the friction coefficient of the road surface based on a steering reaction force applied to the steering for operating the front wheels or a lateral force applied to the front wheels when a predetermined condition is satisfied. A coefficient determination means;
The control device for a four-wheel drive vehicle, wherein the second friction coefficient determination means determines a friction coefficient of the road surface during forward traveling in a state where the specific condition is not satisfied. A control device for a four-wheel drive vehicle according to any one of claims 1 to 5,
The control apparatus for a four-wheel drive vehicle, wherein the friction coefficient determination means determines a friction coefficient of a road surface based on a driving force applied to the front wheel and a slip ratio of the front wheel.

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