JP2019104400A - Control device of four-wheel-drive vehicle and four-wheel-drive vehicle - Google Patents

Abstract

To relax an understeer tendency of a vehicle attitude over a wide range of a vehicle speed range.SOLUTION: A controller 100 sets first distribution torque, which is distribution torque to a rear wheel 12R, based on a target yaw rate, and sets second distribution torque, which is distribution torque to the rear wheel 12R, based on a target lateral G. The controller 100 sets the first distribution torque, which is distribution torque to the rear wheel 12R, based on a first gain in a low speed region where a vehicle speed sensor value detected by a vehicle speed sensor 43 is less than a predetermined vehicle speed, and controls a coupling 28 based on the first distribution torque. On the other hand, the controller 100 sets the second distribution torque, which is distribution torque to the rear wheel 12R, based on a second gain in a high speed region where the vehicle speed sensor value is equal to or higher than the predetermined vehicle speed, and controls the coupling 28 based the second distribution torque.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a technology for distributing a torque generated by a drive source to a main drive wheel and an auxiliary drive wheel.

  Conventionally, in four-wheel drive vehicles, the distributed torque to the rear wheels at the time of turning is determined to increase as the steering angle and the vehicle speed increase. That is, by increasing the distribution torque to the rear wheels as the steering angle and the vehicle speed increase, control is performed to increase the cornering force of the front wheels more than the cornering force of the rear wheels and alleviate the vehicle attitude from understeer. It was

  However, in this method, only the steering angle and the vehicle speed are taken into consideration, and other parameters which change depending on the traveling scene such as the engine torque are not taken into consideration. There was a problem that the vehicle attitude became understeer.

  Then, patent document 1 is known as a technique which performs suitable turning control in consideration of a run scene, for example. In this patent document 1, when performing feedback control to match the actual yaw rate actually generated in the vehicle with the target yaw rate, the feedback gain is decreased in a scene where the lateral vehicle acceleration at the initial stage of turning is small. Therefore, turning control is performed to sharpen the response. On the other hand, in a scene where the lateral vehicle acceleration at the late stage of turning is large, turning control is performed to increase the feedback gain to slow the response, and the stability of the turning vehicle is secured.

Japanese Patent Application Laid-Open No. 7-117510

  Here, the target yaw rate is set to increase with the vehicle speed to improve turning responsiveness in the low speed region, but is set to decrease as the vehicle speed increases in order to achieve stability of the vehicle posture in the high speed region. Ru.

  However, in Patent Document 1, turning control in which only the target yaw rate is taken into consideration as a target value is performed, so the actual yaw rate is reduced due to the reduction of the target yaw rate in the high speed region. The problem of becoming

  The present invention has been made to solve such problems, and it is an object of the present invention to provide a technique for alleviating the tendency of the vehicle to understeer over a wide speed range.

A control device for a four-wheel drive vehicle according to an aspect of the present invention includes a control device for a four-wheel drive vehicle having a distribution device for distributing a part of torque generated by a drive source to a rear wheel which is an auxiliary drive wheel. And
At the time of turning of the four-wheel drive vehicle, the distribution device is controlled based on a first torque distribution value which is a torque distribution value to the rear wheel set based on a target yaw rate when the vehicle speed is less than a predetermined vehicle speed.
When the vehicle speed is equal to or higher than the predetermined vehicle speed, the distribution device is controlled based on a second torque distribution value which is a torque distribution value to the rear wheels set based on a target lateral vehicle acceleration.

  Since the first torque distribution value based on the target yaw rate tends to be set smaller than the second torque distribution value based on the target lateral vehicle acceleration in the vehicle speed region above the predetermined vehicle speed, only the first torque distribution value based on the target yaw rate is used When the torque distribution value is set, there is a possibility that the torque to the rear wheels may be insufficient in the vehicle speed range above a predetermined vehicle speed, and the vehicle attitude may be understeer. On the other hand, since the first torque distribution value based on the target yaw rate tends to be set larger than the second torque distribution value based on the target lateral vehicle acceleration in the vehicle speed region below the predetermined vehicle speed, the second torque distribution based on the target lateral vehicle acceleration When the torque distribution value is set using only the value, the torque to the rear wheels may be insufficient in a vehicle speed range lower than a predetermined vehicle speed, and the vehicle attitude may be understeer.

  According to this configuration, the distribution device is controlled based on the second torque distribution value, which tends to be set larger than the first torque distribution value in the vehicle speed range above the predetermined vehicle speed. It is relieved that it becomes a tendency.

  On the other hand, in the vehicle speed region below the predetermined vehicle speed, the distribution device is controlled based on the first torque distribution value having a tendency to be set larger than the second torque distribution value, so the vehicle attitude becomes understeer in this vehicle speed region. It is relieved.

  Therefore, according to this configuration, it is possible to alleviate the tendency of the vehicle posture to understeer over a wide vehicle speed range.

  In the above aspect, the distribution device is controlled based on the maximum distribution torque and the set first torque distribution value or the second torque distribution value within a range not exceeding the maximum distribution torque to the rear wheel It is preferable to do.

  According to this configuration, since the torque applied to the rear wheels is limited to the maximum distributed torque or less, it is possible to prevent the torque applied to the rear wheels from becoming excessive and causing the vehicle posture to have an oversteer tendency.

In the above aspect, when the turning degree of the four-wheel drive vehicle is less than the first threshold value, the driving loss of the front wheel is compared with the driving loss of the rear wheel,
Preferably, the torque distribution value to the rear wheels is increased when the front wheel drive loss is large, while the torque distribution value to the rear wheels is decreased when the rear wheel drive loss is large.

  According to this configuration, when the turning degree is less than the first threshold, the distribution device is controlled so that the front wheel drive loss and the rear wheel drive loss become equal, so the front wheel drive loss and the rear wheel are lost. Can be minimized.

  In the above aspect, preferably, the target yaw rate and the target lateral vehicle acceleration are set to values according to the vehicle speed sensor value and the steering angle sensor value.

  According to this configuration, since the target yaw rate and the target lateral vehicle acceleration are set to values according to the vehicle speed sensor value and the steering angle sensor value, the first torque distribution value and the second torque are set according to the above-described vehicle speed range. When the method of setting the torque distribution value by switching to the distribution value is adopted, it is possible to alleviate the tendency of the vehicle attitude to understeer over a wide vehicle speed range.

  In the above aspect, the first torque distribution value is set larger than the second torque distribution value when the vehicle speed is lower than the predetermined vehicle speed, and the first torque distribution value is higher than the second torque distribution value when the vehicle speed is higher than the predetermined vehicle speed. It is preferable to be set small.

  According to this configuration, the larger torque distribution value among the first torque distribution value and the second torque distribution value is set in both the vehicle speed range below the predetermined vehicle speed and the vehicle speed range above the predetermined vehicle speed. It is possible to alleviate the tendency of the vehicle to understeer over a wide speed range.

A four-wheel drive vehicle according to another aspect of the present invention is
Driving source,
The front wheel, which is the main driving wheel,
Rear wheels that are auxiliary drive wheels,
A vehicle speed sensor,
Steering angle sensor,
A distribution device for distributing a part of the torque generated by the drive source to the rear wheel;
Equipped with a processor,
The processor is
It is determined whether or not the four-wheel drive vehicle is turning.
When it is determined that the vehicle is turning, it is determined whether the four-wheel drive vehicle is less than a predetermined vehicle speed.
A target yaw rate is set based on the vehicle speed sensor value detected by the vehicle speed sensor and the steering angle sensor value detected by the steering angle sensor when it is determined that the vehicle speed is less than the predetermined vehicle speed, and the target yaw rate is determined based on the target yaw rate Set the first torque distribution value, which is the torque distribution value to the rear wheels,
When it is determined that the vehicle speed is equal to or higher than the predetermined vehicle speed, target lateral vehicle acceleration is set based on the vehicle speed sensor value and the steering angle sensor value, and torque distribution value to the rear wheel is based on the target lateral vehicle acceleration. Set a second torque distribution value,
The distribution device is controlled based on the set first torque distribution value or the set second torque distribution value.

  According to this configuration, the distribution device is controlled based on the second torque distribution value, which tends to be set larger than the first torque distribution value in the vehicle speed range above the predetermined vehicle speed. It is relieved that it becomes a tendency.

  On the other hand, in the vehicle speed region below the predetermined vehicle speed, the distribution device is controlled based on the first torque distribution value having a tendency to be set larger than the second torque distribution value, so the vehicle attitude becomes understeer in this vehicle speed region. It is relieved.

  Therefore, according to this configuration, it is possible to alleviate the tendency of the vehicle posture to understeer over a wide vehicle speed range.

  According to the present invention, it is possible to alleviate the tendency of the vehicle to understeer over a wide range of vehicle speed range.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows roughly the structure of the four-wheel drive vehicle to which the control apparatus of the four-wheel drive vehicle which concerns on embodiment of this invention is applied. FIG. 1 is a block diagram showing an electrical configuration of a control device for a four-wheel drive vehicle according to an embodiment of the present invention. FIG. 6 is a diagram showing an example of a target value setting map used when the controller sets a target yaw rate and a target lateral G. It is a graph which shows an example of a 1st gain map and a 2nd gain map. It is a graph which shows an example of the applied current map which shows the correspondence of the applied current to coupling, and target rear wheel torque. It is a graph which shows the relationship between the torque distribution ratio with respect to a front wheel and a rear wheel, energy loss E1, energy loss E2, and energy loss E3. It is a flow chart which shows processing of a control device of a four-wheel drive car concerning an embodiment of the invention. It is a flow chart which shows processing of a control device of a four-wheel drive car concerning a modification of an embodiment of the invention.

  Hereinafter, embodiments of the present invention will be described with reference to the attached drawings.

  FIG. 1 is a view schematically showing a configuration of a four-wheel drive vehicle 1 to which a control device for a four-wheel drive vehicle according to an embodiment of the present invention is applied. As shown in FIG. 1, the four-wheel drive vehicle 1 according to the embodiment of the present invention includes a pair of front wheels 12F, a pair of rear wheels 12R, an engine 14 as a drive source, and driving forces of the engine 14 as front wheels. 12F and a transmission 16 for transmitting to the rear wheel 12R, a front wheel differential 20 for transmitting the driving force from the transmission 16 to the front wheel 12F via the axle 18, a transfer 22 for taking out the driving force for transmitting to the rear wheel 12R And a rear wheel differential 26 for transmitting the driving force from the transfer 22 to the left and right rear wheels 12R via an axle 24.

  The transfer 22 and the rear wheel differential 26 are connected via a drive force transmission shaft 30 extending in the front-rear direction of the vehicle body and a coupling 28 for changing the torque transmitted to the rear wheel 12R. Specifically, the output shaft of the transfer 22 is connected to one end of the driving force transmission shaft 30, the other end of the driving force transmission shaft 30 is connected to the input shaft of the coupling 28, and the output shaft of the coupling 28 is a rear wheel It is connected to the input shaft of the differential 26. The coupling 28 is an example of a dispensing device. Further, in the four-wheel drive vehicle 1 according to the present embodiment, the front wheel 12F is a main drive wheel, and the rear wheel 12R is an auxiliary drive wheel.

  The coupling 28 adjusts the distribution torque to the rear wheel 12R out of the torque generated by the engine 14 under the control of the controller 100. Here, the coupling 28 is formed of, for example, an electromagnetic clutch including a plurality of clutch plates, and adjusts the fastening force between the clutch plates according to the applied current output from the controller 100, thereby to the rear wheel 12R. Adjust the distributed torque.

  Furthermore, the four-wheel drive vehicle 1 includes a front wheel speed sensor 36 for detecting the wheel speed of the front wheel 12F, a rear wheel speed sensor 38 for detecting the wheel speed of the rear wheel 12R, and a controller 100 for controlling the operation of the coupling 28. Is equipped. The wheel speed of the front wheel 12F detected by the front wheel speed sensor 36 and the wheel speed of the rear wheel 12R detected by the rear wheel speed sensor 38 are input to the controller 100, respectively. When the front wheel speed sensor 36 and the rear wheel speed sensor 38 are not distinguished from one another, the vehicle speed sensor 43 is described. Further, a sensor value detected by the vehicle speed sensor 43 is described as a vehicle speed sensor value. In the following description, as the vehicle speed sensor value, a sensor value detected by the front wheel speed sensor 36 may be adopted, or a sensor value detected by the rear wheel speed sensor 38 may be adopted, or an average of both sensor values May be employed.

  Furthermore, the four-wheel drive vehicle 1 is provided with a steering 40 which is rotated when the rider steers the four-wheel drive vehicle 1, and a steering angle sensor 41 which detects a steering angle of the steering 40. The steering angle sensor value detected by the steering angle sensor 41 is input to the controller 100.

  FIG. 2 is a block diagram showing the electrical configuration of the control device 10 of the four-wheel drive vehicle 1 according to the embodiment of the present invention. In addition to the steering angle sensor 41, the vehicle speed sensor 43, the coupling 28, and the controller 100 shown in FIG. 1, the control device 10 includes an accelerator opening sensor 42, a throttle valve 44, an ignition plug 45, a variable valve mechanism 46, and fuel. An injector 47 is provided.

  The controller 100 receives various information such as the torque of the engine 14, the shift speed, and the rotational speed of the output shaft of the transmission 16. In the present embodiment, the controller 100 controls the operation of the coupling 28 based on the various information as described later.

  The steering angle sensor 41 is attached to, for example, a steering shaft, and outputs a signal corresponding to the steering direction, the neutral position, and the steering angle to the controller 100. The steering angle sensor 41 is configured of, for example, a disk-like slit plate that rotates in conjunction with a steering wheel, and a photo interrupter disposed so as to sandwich the slit plate.

  The accelerator opening degree sensor 42 is, for example, a potentio type angle sensor in which a contact slides on a resistor, detects a displacement amount of an accelerator pedal, converts it into an electric signal, and outputs the electric signal to the controller 100.

  The vehicle speed sensor 43 includes, for example, a gear-shaped rotor provided on a rotating portion such as a brake drum, and a sensing unit provided with a fixed gap with respect to the rotor and configured of a coil, a magnetic pole, and the like. The rotational speed of the wheel is detected based on the AC voltage generated in the coil by the rotation of the rotor.

  The throttle valve 44 adjusts the amount of intake air to the engine 14. The spark plug 45 blows a spark in the cylinder of the engine 14 to ignite the fuel. The variable valve mechanism 46 is, for example, a hydraulic variable valve mechanism or an electric variable valve mechanism, and is a mechanism that adjusts the opening and closing timings of the intake valve and the exhaust valve. The fuel injection device 47 is configured of a direct injection type fuel injection device that injects fuel directly into the cylinder of the engine 14.

  The controller 100 is configured by one or more computers including a processor such as a CPU and a memory. Then, the controller 100 determines whether the four-wheel drive vehicle 1 is turning or not, and when it is determined that the vehicle is turning, the vehicle speed sensor value detected by the vehicle speed sensor 43 and the steering angle sensor value detected by the steering angle sensor 41 And set a target yaw rate based on Further, the controller 100 sets a target lateral vehicle acceleration (hereinafter, described as “target lateral G”) based on the vehicle speed sensor value and the steering angle sensor value.

  FIG. 3 is a diagram showing an example of a target value setting map used when the controller 100 sets the target yaw rate and the target lateral G. Here, the target yaw rate is a target value of the yaw rate generated in the four-wheel drive vehicle 1. The target lateral G is a target value of lateral vehicle acceleration (hereinafter referred to as “lateral G”) generated in the four-wheel drive vehicle 1. The target value setting map is stored in advance in the memory of the controller 100.

  In recent years, equipped with vehicle attitude control that stabilizes the vehicle attitude by decreasing the torque of the engine 14 at the time of turning of the vehicle and causing the vehicle to generate deceleration to lean forward and improve the responsiveness of the steering operation. No. 6,112,304, for example. In this vehicle, vehicle posture control is completed, and predetermined braking control is performed to stabilize the vehicle posture for a certain period of time after the torque of the engine 14 is restored to the normal torque. Although the target yaw rate and the target lateral G are inherently used for the braking control, in the present embodiment, the target yaw rate and the target lateral G are set to the distribution torque to the rear wheel 12R. It is used as a parameter.

  A plurality of target setting value maps are present according to the steering angle, and in the example of FIG. 3, six target value setting maps of (A) to (F) are shown. FIG. 3 (A) shows a target value setting map at a certain steering angle θ (for example, 30 degrees), and (B), (C), (D), (E) and (F) in FIG. The target value setting map when the steering angle is 2θ, 3θ, 4θ, 5θ, 6θ is shown. That is, in FIG. 3, in the target value setting maps shown in (A) to (F), the steering angles increase toward (A) to (F).

  In each target value setting map, the vertical axis on the left indicates the yaw rate (rad / s), the vertical axis on the right indicates the horizontal G, and the horizontal axis indicates the vehicle speed (km / h).

  As shown in FIGS. 3A to 3F, as the steering angle increases, both the target yaw rate and the target lateral G have a tendency to increase the slope at the time of start-up with respect to the vehicle speed. Further, in each target value setting map, the target yaw rate is transitioned at a larger value than the target lateral G in the region where the vehicle speed is lower than the intersection point P (hereinafter referred to as "low speed region"). . This is because when the vehicle speed is low, a large lateral G does not occur in the four-wheel drive vehicle 1, so even if a large target lateral G is set, it can not be achieved. Further, in the low speed region, the target yaw rate and the target lateral G both increase at a steeper slope than the high speed region (the region where the vehicle speed is higher than the intersection point P) as the vehicle speed increases.

  On the other hand, in the high-speed range, the target lateral G is generally larger than the target yaw rate, and in detail, the target lateral G gradually increases as the vehicle speed increases. The yaw rate gradually decreases as the vehicle speed increases. This is because it takes into consideration that the vehicle attitude becomes unstable if the target yaw rate is set large at the time of high speed traveling.

  The target yaw rate and the target lateral G shown in the target value setting map are determined by performing an experiment for determining the yaw rate and the lateral G required to stabilize the vehicle posture.

  Here, six target value setting maps shown in (A) to (F) are illustrated, but this is an example, and the number of target value setting maps may be five or less, or seven. It may be more than.

  When the steering angle sensor value and the vehicle speed sensor value are input from the steering angle sensor 41 and the vehicle speed sensor 43, the controller 100 determines the steering angle indicated by the input steering angle sensor value from the target value setting map shown in FIG. The target yaw rate and the target lateral G corresponding to the input vehicle speed sensor value may be determined with reference to the target value setting map corresponding to. When there is no target value setting map corresponding to the input steering angle sensor value, for example, the controller 100 sets two target values for which the steering angle goes back and forth with respect to the steering angle indicated by the input steering angle sensor value. The target yaw rate and the target lateral G may be determined by linearly interpolating the target yaw rate and the target lateral G shown in these target value setting maps with reference to the setting map.

  Refer back to FIG. The controller 100 sets a first distribution torque that is a distribution torque to the rear wheel 12R based on the target yaw rate, and sets a second distribution torque that is a distribution torque to the rear wheel 12R based on the target lateral G. . Here, the controller 100 sets a first gain corresponding to the set target yaw rate with reference to a first gain map shown in FIG. 4A, and a second gain map shown in FIG. 4B. And set the second gain corresponding to the set target lateral G. The first gain map and the second gain map are stored in advance by the memory of the controller 100.

  FIGS. 4A and 4B are graphs showing an example of the first gain map and the second gain map. In FIG. 4A, the vertical axis and the horizontal axis indicate the first gain and the target yaw rate, respectively, and in FIG. 4B, the vertical axis and the horizontal axis indicate the second gain and the target horizontal G, respectively. ing.

  As shown in FIGS. 4A and 4B, as the target yaw rate increases, the first gain and the second gain respectively increase from 0 toward a maximum gain value of 1. ing. In addition, when the first gain map and the second gain map are compared, it can be seen that the slope of the rising edge of the first gain is slightly steeper than that of the second gain. This is because in the low speed region, it is considered that the lateral G occurs relatively lower than the yaw rate.

  Refer back to FIG. The controller 100 sets a first distribution torque, which is a distribution torque to the rear wheel 12R, based on the first gain, in a low speed region where the vehicle speed sensor value detected by the vehicle speed sensor 43 is less than a predetermined vehicle speed. The coupling 28 is controlled based on (an example of the first torque distribution value). On the other hand, the controller 100 sets a second distribution torque (an example of a second torque distribution value) which is a distribution torque to the rear wheel 12R based on the second gain in a high speed region where the vehicle speed sensor value is a predetermined vehicle speed or more. The coupling 28 is controlled based on the second distribution torque.

  Referring to FIG. 3, the vehicle speed at an intersection point P at which the magnitude relationship between the target yaw rate and the target lateral G switches is set to have the same value regardless of the steering angle if the same vehicle. Therefore, in the present embodiment, the vehicle speed at the intersection point P is adopted as the predetermined vehicle speed. Here, for example, a value such as 40 km / h can be adopted as the vehicle speed of the intersection point P, but this is an example.

  The target yaw rate is set larger than the target lateral G in the low speed region where the vehicle speed is lower than the intersection point P, but the target yaw rate is set smaller than the target lateral G in the high speed region where the vehicle speed is higher than the intersection point P . Therefore, in the low speed region, the first gain tends to be set higher than the second gain, and in the high speed region, the second gain tends to be set higher than the first gain.

  The first distribution torque is calculated by multiplying a first distribution by a maximum distribution torque described later, and the second distribution torque is calculated by multiplying a second distribution with a maximum distribution torque described later. Therefore, in the low speed region, the first distributed torque tends to be set higher than the second distributed torque, and in the high speed region, the second distributed torque tends to be set higher than the first distributed torque.

  Therefore, in the present embodiment, the controller 100 controls the coupling 28 using the first distribution torque in the low speed region, and controls the coupling 28 using the second distribution torque in the high speed region. As a result, it is possible to control the coupling 28 using the larger distribution torque of the first distribution torque and the second distribution torque as the final distribution torque in either the low speed region or the high speed region.

  Here, as in Patent Document 1, a case where an aspect in which only the target yaw rate is set is adopted is considered. In this case, as shown in FIG. 3, in the high speed region, the target yaw rate is generally lower than the target lateral G and gradually decreases. Therefore, using the first gain corresponding to the target yaw rate If the distribution torque to the rear wheel 12R is set, the distribution torque to the rear wheel 12R may be insufficient, and the vehicle attitude may tend to understeer.

  On the other hand, when adopting a mode in which only the target lateral G is set, the target lateral G is set lower than the target yaw rate in the low speed region, so the distributed torque to the rear wheel 12R is insufficient, and the vehicle attitude understeer It could be

  On the other hand, in the present embodiment, as described above, the larger one of the first distribution torque and the second distribution torque is used as the final distribution torque in either the low speed region or the high speed region. Since the coupling 28 is controlled to be used, it is possible to alleviate the tendency of the vehicle to understeer in a wide speed range.

  If the final distributed torque is excessive, the vehicle attitude may be oversteer. Therefore, the controller 100 sets the maximum distribution torque according to the current state of the four-wheel drive vehicle 1 (for example, the target G obtained from the vehicle speed and the accelerator opening), and does not exceed the maximum distribution torque. The final distribution torque is set to alleviate the tendency of the vehicle to oversteer. Here, the maximum distribution torque indicates the maximum value of the distribution torque to the rear wheel 12R that can be set for the current state of the four-wheel drive vehicle 1.

  Thus, when the final distribution torque is determined, the controller 100 sets an applied current for driving the rear wheel 12R with the final distribution torque, and outputs the same to the coupling 28.

  FIG. 5 is a graph showing an example of an applied current map showing the correspondence between the applied current ID to the coupling 28 and the target rear wheel torque (torque transfer capacity), and the vertical axis represents the target rear wheel of the coupling 28. The torque (torque transfer capacity) is shown, and the horizontal axis shows the applied current ID. As shown in FIG. 5, the coupling 28 has a characteristic that the target rear wheel torque increases as the applied current ID increases. The target rear wheel torque is a target value of distributed torque to the rear wheel 12R. Therefore, the controller 100 can adjust the distribution torque to the rear wheel 12R to a target value by increasing or decreasing the applied current ID. The applied current map is stored in advance in the memory of the controller 100.

  Refer back to FIG. When the controller 100 determines that the four-wheel drive vehicle 1 is not turning, for example, control for minimizing the sum of the energy loss of the front wheel 12F and the energy loss of the rear wheel 12R (hereinafter referred to as "minimum loss control" To set the final distributed torque. As a method of minimum loss control, for example, the method described in Japanese Patent No. 5793877 can be adopted.

  Here, the energy loss of the front wheel 12F includes the energy loss E1 due to the slip of the front wheel 12F. Further, the energy loss of the rear wheel 12R includes an energy loss E2 due to the slip of the rear wheel 12R and an energy loss E3 based on a mechanical loss of a torque transmission mechanism that transmits the torque of the engine 14 to the rear wheel 12R. As the torque transmission mechanism, for example, the transfer 22, the driving force transmission shaft 30, the coupling 28, the rear wheel differential 26 and the like in FIG. 1 are applicable.

  FIG. 6 is a graph showing the relationship between the torque distribution ratio for the front wheel 12F and the rear wheel 12R, the energy loss E1, the energy loss E2, and the energy loss E3. In FIG. 6, the vertical axis represents energy loss, and the horizontal axis represents torque distribution ratio. In the horizontal axis, the torque distribution ratio between the front wheel and the rear wheel is shown by front wheel: rear wheel. The left end of the horizontal axis indicates that the torque distribution ratio between the front wheel 12F and the rear wheel 12R is 100: 0, and all the torque is distributed to the front wheel 12F. The right end of the horizontal axis indicates that the torque distribution ratio between the front wheel 12F and the rear wheel 12R is 50:50, and the torque distribution ratios for the front wheel 12F and the rear wheel 12R are equal. That is, in the horizontal axis, the torque distribution ratio to the rear wheel 12R increases from 0 to 50 as it goes from the left end to the right end.

  Further, in FIG. 6, the solid line graph indicates the energy loss E1, the dashed line graph indicates the energy loss E2, and the dashed line graph indicates the energy loss E3.

  As shown in FIG. 6, the energy loss E1 gradually decreases as the torque distribution ratio to the rear wheel 12R increases. This is because the amount of slip of the front wheel 12F decreases as the torque distribution ratio to the rear wheel 12R increases. Also, the energy loss E2 gradually increases as the torque distribution ratio increases. This is because the slip amount of the rear wheel 12R increases as the torque distribution ratio to the rear wheel 12R increases. Also, the energy loss E3 gradually increases as the torque distribution ratio increases. This is because the mechanical loss of the mechanism transmitting torque to the rear wheel 12R increases as the torque distribution ratio to the rear wheel 12R increases.

  Energy losses E1 to E3 It is known that the total energy loss (E1 + E2 + E3) is minimized when the energy loss E1 is equal to the energy loss (E2 + E3). Thus, the controller 100 minimizes the total energy loss (E1 + E2 + E3) by controlling the coupling 28 so that the energy loss E1 equals the energy loss (E2 + E3).

  Specifically, the controller 100 calculates the slip amount of the front wheel 12F based on the wheel speed of the front wheel 12F detected by the front wheel speed sensor 36, and the energy loss E1 due to the slip of the front wheel 12F based on the calculated slip amount. calculate. Further, the controller 100 calculates the slip amount of the rear wheel 12R based on the wheel speed of the rear wheel 12R detected by the rear wheel speed sensor 38, and calculates the energy loss E2 of the rear wheel 12R based on the calculated slip amount. Do. The controller 100 also calculates an energy loss E3 based on the mechanical loss of the torque transmission mechanism that transmits the torque of the engine 14 to the rear wheel 12R.

  Then, if the energy loss E1 is larger than the energy loss (E2 + E3) which is the sum of the energy loss E2 and the energy loss E3, the controller 100 increases the torque distribution ratio to the rear wheel 12R. On the other hand, controller 100 increases the torque distribution ratio to front wheel 12F when energy loss E1 is equal to or less than energy loss (E2 + E3). The controller 100 thereby determines the torque distribution ratio of the engine 14 such that the energy loss E1 is equal to the energy loss (E2 + E3). Then, the controller 100 multiplies the target torque by the determined torque distribution ratio to the rear wheel 12R to obtain a distribution torque to the rear wheel 12R, and generates an applied current for driving the coupling 28 with the calculated distribution torque. , Output to the coupling 28.

  FIG. 7 is a flowchart showing processing of the control device 10 of the four-wheel drive vehicle 1 according to the embodiment of the present invention. The flowchart of FIG. 7 is repeatedly executed at a predetermined calculation cycle. At S1, the controller 100 reads various sensor signals. Here, for example, the steering angle sensor value detected by the steering angle sensor 41, the accelerator opening degree sensor value detected by the accelerator opening degree sensor 42, and the vehicle speed sensor value detected by the vehicle speed sensor 43 are read as sensor signals.

  At S2, the controller 100 sets a target G from the vehicle speed sensor value and the accelerator opening sensor value read at S1. The target G is a concept including acceleration and deceleration, and indicates acceleration and deceleration to be applied to the four-wheel drive vehicle 1 in the traveling direction.

  Here, the controller 100 stores in memory a target G map in which a target G corresponding to the vehicle speed and the accelerator opening degree is registered in advance, and by referring to the target G map, the current vehicle speed and the accelerator opening degree It is sufficient to set a target G corresponding to.

  In S3, the controller 100 sets the target torque of the engine 14 from the target G. Here, the controller 100 may calculate the target torque by performing a predetermined calculation taking into consideration the currently set gear position and the like with respect to the target G set in S2.

  In S4, the controller 100 determines whether the four-wheel drive vehicle 1 (vehicle) is turning. Here, the controller 100 calculates the yaw rate (an example of the degree of turning) by substituting the vehicle speed sensor value and the steering angle sensor value acquired in S1 into a predetermined arithmetic expression, and the calculated yaw rate is the threshold Th1 (first threshold) For example, if it is determined that the four-wheel drive vehicle 1 is turning, it may be determined that the four-wheel drive vehicle 1 is not turning if the calculated yaw rate is less than the threshold Th1. As the threshold value Th1, for example, a lower limit value of a predetermined yaw rate at which the four-wheel drive vehicle 1 can be regarded as substantially turning can be adopted. As a result, although the four-wheel drive vehicle 1 is turning, the degree of turning is small to such an extent that it can be regarded as going straight and there is no need to alleviate the tendency of the vehicle posture to undershoot. The processing load on the controller 100 can be alleviated because it is not implemented.

  Then, if the four-wheel drive vehicle 1 is turning (YES at S4), the process proceeds to S5, and if the four-wheel drive vehicle 1 is not turning (NO at S4), the process proceeds to S18.

  In S5, if the target torque set in S3 is equal to or greater than the threshold Th2 (YES in S5), the controller 100 proceeds to S6, and if the target torque set in S3 is less than the threshold Th2 (NO in S5) The process proceeds to step S18. Here, as the threshold value Th2, it is possible to adopt a predetermined value that is expected to cause the vehicle attitude to understeer when the target torque becomes larger than this. As a result, in a scene where the four-wheel drive vehicle 1 is turning but there is no need to mitigate that the target torque is small and the vehicle attitude tends to be under, processing after S6 is not performed, and the processing load on the controller 100 Can be reduced.

  In S6, the controller 100 obtains the ground contact load of each of the front wheel 12F and the rear wheel 12R according to the target G set in S2, and the distributed torque that can be applied to the rear wheel 12R from the obtained ground load. Set the maximum distribution torque, which is the maximum value.

  Specifically, the controller 100 performs a predetermined operation using a predetermined ground contact load of the front wheel 12F and the rear wheel 12R at the time of stop, and the target G set at S2. The amount of increase in the contact load of the rear wheel 12R with respect to the contact load of the rear wheel 12R is determined. Then, the controller 100 obtains the ratio of the ground contact load between the front wheel 12F and the rear wheel 12R from the calculated increase amount, and multiplies the target torque set in S3 by the ratio of the ground load of the rear wheel 12R to obtain the rear wheel 12R. Calculate the maximum distribution torque of This calculation is based on the idea that, as the target G increases, the contact load on the rear wheel 12R increases, and the maximum distribution torque that can be applied to the rear wheel 12R increases with the increase in the contact load. There is. By providing S6, the distribution torque applied to the rear wheel 12R is limited to the maximum distribution torque or less, and it is possible to alleviate the tendency of the vehicle to oversteer.

  In S7, the controller 100 sets a target yaw rate based on the steering angle sensor value and the vehicle speed sensor value acquired in S1. Here, the controller 100 determines a target yaw rate corresponding to the steering angle sensor value and the vehicle speed sensor value with reference to the target value setting map shown in FIG.

  At S8, the controller 100 sets the first gain based on the target yaw rate set at S7. Here, the controller 100 determines a first gain corresponding to the target yaw rate with reference to the first gain map shown in FIG.

  In S9, the controller 100 sets the target lateral G based on the steering angle sensor value and the vehicle speed sensor value. Here, the controller 100 refers to the target value setting map shown in FIG. 3 to determine the target lateral G corresponding to the steering angle sensor value and the vehicle speed sensor value.

  In S10, the controller 100 sets a second gain based on the target lateral G set in S9. Here, the controller 100 determines the second gain corresponding to the target lateral G with reference to the second gain map shown in FIG.

  In S11, the controller 100 determines whether the vehicle speed sensor value is less than a predetermined vehicle speed (for example, 40 km / h). If the vehicle speed sensor value is less than the predetermined vehicle speed (YES in S11), the controller 100 sets the final distribution torque to the rear wheel 12R from the maximum distribution torque set in S6 and the first gain set in S8 (S12) ). Here, the controller 100 may set the final distribution torque by multiplying the maximum distribution torque by the first gain.

  On the other hand, if the vehicle speed sensor value is equal to or higher than the predetermined vehicle speed (NO in S11), the controller 100 performs the final distribution torque from the maximum distribution torque set in S6 and the second gain set in S10 to the rear wheel 12R. Is set (S13). Here, the controller 100 may set the final distribution torque by multiplying the maximum distribution torque by the second gain.

  Since the first gain and the second gain are 1 or less, the final distribution torque to the rear wheel 12R is limited to the maximum distribution torque or less, which can alleviate the vehicle attitude from being oversteered.

  In S14, the controller 100 sets an applied current corresponding to the final distribution torque set in S12 or S13. Here, the controller 100 sets the applied current corresponding to the final distribution torque with reference to the applied current map shown in FIG.

  In S15, the controller 100 sets a target intake air amount for achieving the target torque set in S3, a target fuel injection amount, and a target ignition timing. When the target torque is determined, the target intake amount, the target fuel injection amount, and the target ignition timing can be uniquely determined. Therefore, the controller 100 stores, in the memory, a determination map in which the correspondence relationship between the target intake air amount, the target fuel injection amount, the target ignition timing, and the target torque is registered in advance, and refers to this determination map. Then, the target intake amount, the target fuel injection amount, and the target ignition timing may be determined.

  In S16, the controller 100 sets the opening degree of the throttle valve 44 and the closing timing of the variable valve mechanism 46 for realizing the target intake amount set in S15. In S16, the fuel injection time for realizing the target fuel injection amount set in S15 is set.

  In S17, the controller 100 outputs, to the throttle valve 44, a command value for setting the opening degree set in S16. Further, in S17, the controller 100 outputs a command value for closing the valve at the valve closing timing set in S16 to the variable valve mechanism 46. Further, in S17, a command value for injecting the fuel in the fuel injection time set in S16 is output to the fuel injection device 47. In S17, a command value for causing ignition at the target ignition timing set in S15 is output to the spark plug 45.

  At S18, since the vehicle is not turning, the controller 100 sets the final distribution torque using the method of minimum loss control described using FIG.

  As described above, according to the present embodiment, the coupling 28 is controlled based on the second distribution torque, which tends to be set larger than the first distribution torque in the vehicle speed range equal to or higher than the predetermined vehicle speed. Can reduce the tendency of the vehicle to understeer.

  On the other hand, since the coupling 28 is controlled based on the first distribution torque which tends to be set larger than the second distribution torque in the vehicle speed range lower than the predetermined vehicle speed, the vehicle posture becomes understeer in this vehicle speed range. Is relieved.

  Therefore, according to this configuration, it is possible to alleviate the tendency of the vehicle posture to understeer over a wide vehicle speed range.

  The present invention can adopt the following modifications.

  (1) FIG. 8 is a flowchart showing processing of the control apparatus for a four-wheel drive vehicle according to a modification of the embodiment of the present invention. In the flowchart of FIG. 8, the same processing as that of FIG. 7 is denoted by the same reference numeral, and the description of the common part is omitted. In FIG. 7, the first gain and the second gain are set regardless of whether the vehicle speed sensor value is less than the predetermined vehicle speed. On the other hand, in FIG. 8, the process of setting the second gain is omitted when the vehicle speed sensor value is less than the predetermined vehicle speed, and the process of setting the first gain is omitted when the vehicle speed sensor value is equal to or higher than the predetermined vehicle speed. Are largely different from FIG.

  In S81 following S6, as in S11, the controller 100 determines whether the vehicle speed sensor value is less than a predetermined vehicle speed (for example, 40 km / h). If the vehicle speed sensor value is less than the predetermined vehicle speed (YES in S81), the controller 100 sets the target yaw rate (S7), sets the first gain (S8), and advances the process to S82. On the other hand, if the vehicle speed sensor value is equal to or higher than the predetermined vehicle speed (NO in S81), controller 100 sets target lateral G (S9), sets the second gain (S10), and advances the process to S82.

  In S82, the controller 100 multiplies the maximum distributed torque set in S6 by the gain (first gain or second gain) set in S8 or S10 to set the final distributed torque, and advances the process to S14.

  In this modification, the process of setting the second gain is omitted when the vehicle speed sensor value is less than the predetermined vehicle speed, and the process of setting the first gain is omitted when the vehicle speed sensor value is equal to or greater than the predetermined vehicle speed. The processing load on the controller 100 can be reduced.

  (2) In the above embodiment, the target yaw rate and the target lateral G are determined by referring to the target value setting map shown in FIG. 3 regardless of whether the steering 40 is turning or turning back. Although the value according to is determined, the present invention is not limited thereto. For example, during turning of the steering wheel 40, the target yaw rate and the target lateral G may be set to be larger than during turning back. In this case, when the change amount of the steering angle is positive or when the derivative value of the steering angle is positive, the controller 100 determines that the steering 40 is turning, and the change amount of the steering angle is negative or When the derivative value of the steering angle is negative, it may be determined that the steering 40 is being switched back.

  (3) In the above embodiment, the engine 14 is adopted as the drive source, but the present invention is not limited to this, and a motor may be adopted, and a hybrid drive in which the motor and the engine 14 are combined. Sources may be employed.

  (4) In the flowcharts of FIGS. 7 and 8, the process of S5 for determining whether or not the target torque is the threshold value Th2 or more is provided, but this process may be omitted in the present invention.

  (5) In the above embodiment, the yaw rate is adopted as an example of the turning degree, but the present invention is not limited to this, and a steering angle sensor value may be adopted as the turning degree. Further, a yaw rate sensor may be provided, and the yaw rate sensor value detected by the yaw rate sensor may be adopted as an example of the turning degree.

1 Four-wheel drive vehicle 10 controller 12F front wheel 12R rear wheel 14 engine 40 steering 41 steering angle sensor 42 accelerator opening sensor 43 vehicle speed sensor 44 throttle valve 45 spark plug 46 variable valve mechanism 47 fuel injection device 100 controller

Claims (6)

A control device for a four-wheel drive vehicle having a distribution device for distributing a part of torque generated by a drive source to a rear wheel which is an auxiliary drive wheel,
At the time of turning of the four-wheel drive vehicle, the distribution device is controlled based on a first torque distribution value which is a torque distribution value to the rear wheel set based on a target yaw rate when the vehicle speed is less than a predetermined vehicle speed.
The distribution device is controlled based on a second torque distribution value, which is a torque distribution value to the rear wheels set based on a target lateral vehicle acceleration, when the vehicle speed is higher than the predetermined vehicle speed.
Control device for four-wheel drive vehicles. The control device for a four-wheel drive vehicle according to claim 1,
The distribution device is controlled based on the maximum distribution torque and the set first torque distribution value or the second torque distribution value within a range not exceeding the maximum distribution torque to the rear wheels.
Control device for four-wheel drive vehicles. The control device for a four-wheel drive vehicle according to claim 1 or 2,
When the turning degree of the four-wheel drive vehicle is less than a first threshold value, the driving loss of the front wheels is compared with the driving loss of the rear wheels,
The torque distribution value to the rear wheels is increased when the front wheel drive loss is large, while the torque distribution value to the rear wheels is decreased when the rear wheel drive loss is large.
Control device for four-wheel drive vehicles. A control device for a four-wheel drive vehicle according to any one of claims 1 to 3,
The target yaw rate and the target lateral vehicle acceleration are set to values according to a vehicle speed sensor value and a steering angle sensor value.
Control device for four-wheel drive vehicles. It is a control device of a four-wheel drive vehicle according to any one of claims 1 to 4,
The first torque distribution value is set larger than the second torque distribution value when the vehicle speed is lower than the predetermined vehicle speed, and the first torque distribution value is set smaller than the second torque distribution value when the vehicle speed is higher than the predetermined vehicle speed. ,
Control device for four-wheel drive vehicles. It is a four-wheel drive car,
Driving source,
The front wheel, which is the main driving wheel,
Rear wheels that are auxiliary drive wheels,
A vehicle speed sensor,
Steering angle sensor,
A distribution device for distributing a part of the torque generated by the drive source to the rear wheel;
Equipped with a processor,
The processor is
It is determined whether or not the four-wheel drive vehicle is turning.
When it is determined that the vehicle is turning, it is determined whether the four-wheel drive vehicle is less than a predetermined vehicle speed.
A target yaw rate is set based on the vehicle speed sensor value detected by the vehicle speed sensor and the steering angle sensor value detected by the steering angle sensor when it is determined that the vehicle speed is less than the predetermined vehicle speed, and the target yaw rate is determined based on the target yaw rate Set the first torque distribution value, which is the torque distribution value to the rear wheels,
When it is determined that the vehicle speed is equal to or higher than the predetermined vehicle speed, target lateral vehicle acceleration is set based on the vehicle speed sensor value and the steering angle sensor value, and torque distribution value to the rear wheel is based on the target lateral vehicle acceleration. Set a second torque distribution value,
Configured to control the distributor based on the set first torque distribution value or the second torque distribution value.
Four-wheel drive car.

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