JP2019177739A - Control device of four-wheel drive car - Google Patents

Abstract

To properly control the longitudinal torque distribution ratio so as to become minimum in the sum total of loss energy in response to engine torque.SOLUTION: A controller 20 as a control device of a four-wheel drive car executes control for distributing driving torque to a front wheel 9 and a rear wheel 10 in response to the longitudinal torque distribution ratio by determining the longitudinal torque distribution ratio of showing the ratio of driving torque distributed to the front wheel 9 and driving torque distributed to the rear wheel 10 on the basis of the sum total of loss energy of the total of tire loss energy generated in the front wheel 9 and the rear wheel 10 and mechanical mecha-loss energy generated in response to driving of the rear wheel 10 by acquiring engine torque outputted by an engine 2. Particularly, the controller 20 determines the longitudinal torque distribution ratio of becoming minimum in the sum total of loss energy corresponding to present engine torque on the basis of the sum total of loss energy of changing in response to a size of the engine torque.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a control device for a four-wheel drive vehicle that controls drive torque distributed to front wheels and rear wheels.

  Conventionally, various techniques for controlling drive torque distributed to auxiliary drive wheels (typically rear wheels) have been proposed. For example, Patent Document 1 discloses a drive that is distributed to the front wheels based on the lateral acceleration, the engine torque, and the turning radius so that the total loss energy of the tire loss energy and the mechanical mechanical loss energy generated in the wheels is minimized. A technique for determining the front-rear torque distribution ratio between the torque and the drive torque distributed to the rear wheels is disclosed. A similar technique is also disclosed in Patent Document 2.

Japanese Patent No. 6217931 Japanese Patent No. 5793877

  By the way, the inventors of the present invention have the magnitude of the engine torque (engine driving force / drive torque) such that the total loss energy of the tire loss energy and the mechanical loss energy described above is minimized. It has been found that it varies in various ways. That is, since the relationship between the front-rear torque distribution ratio and the loss energy changes according to the magnitude of the engine torque, the front-rear torque distribution ratio at which the total loss energy is minimized changes according to the engine torque. None of the techniques described in Patent Documents 1 and 2 described above determines the front-rear torque distribution ratio in consideration of the loss energy that changes according to the engine torque.

  The present invention has been made to solve the above-described problems of the prior art, and can appropriately control the front-rear torque distribution ratio so that the total loss energy is minimized according to the engine torque. An object is to provide a control device for a wheel drive vehicle.

In order to achieve the above object, the present invention is a control device for a four-wheel drive vehicle that controls a drive torque distributed to a front wheel and a rear wheel, and obtains an engine torque output by an engine; Drive torque distributed to the front wheels at the drive torque corresponding to the engine torque based on the sum of the loss energy of the tire loss energy generated at the front wheels and the rear wheels and the mechanical energy loss energy generated by driving the rear wheels And a torque distribution ratio determining means for determining a front / rear torque distribution ratio indicating a ratio of the drive torque distributed to the rear wheels, and a drive torque corresponding to the engine torque according to the front / rear torque distribution ratio determined by the torque distribution ratio determining means. Torque distribution control means for performing control for distribution to the front wheels and the rear wheels, and the torque distribution ratio determination means Based on the sum of the loss energy that varies according to of come, the sum of the loss energy determines the longitudinal torque distribution ratio becomes minimum in accordance with the current engine torque obtained by the obtaining means, characterized in that.
According to the present invention configured as described above, the front-rear torque distribution that minimizes the total loss energy according to the current engine torque, taking into account the total loss energy that varies according to the magnitude of the engine torque. Determine the ratio. Thereby, the front-rear torque distribution ratio can be appropriately controlled so that the total loss energy is minimized according to the engine torque.

In the present invention, preferably, the four-wheel drive vehicle transmits a part of the engine torque to the rear wheel via the coupling, and changes the coupling torque of the coupling to the rear wheel of the engine torque. The driving torque to be transmitted is variably configured, and the torque distribution ratio determining means uses the coupling loss energy generated in the coupling, which changes in a linear function according to the engine torque, as the mechanical loss energy, and the front-rear torque distribution ratio. To decide.
According to the present invention configured as described above, the coupling loss energy that changes in a linear function according to the engine torque is used as the mechanical loss energy, so that the total loss energy including such coupling loss energy can be obtained. The front-rear torque distribution ratio that is minimized can be appropriately determined.

  In the present invention, preferably, the torque distribution control means obtains a coupling fastening torque according to the front-rear torque distribution ratio determined by the torque distribution ratio determination means, and performs control to apply the fastening torque to the coupling. It is good.

In the present invention, preferably, the four-wheel drive vehicle has a power take-off for transmitting engine torque from the transmission to the propeller shaft, and the torque distribution ratio determining means is a quadratic function according to the engine torque as mechanical loss energy. The front-rear torque distribution ratio is determined using at least the gear unit loss energy generated in the gear unit included in the power take-off.
According to the present invention configured as described above, by using the gear unit loss energy that changes in a quadratic function according to the engine torque as the mechanical loss energy, the sum of the loss energy including such gear unit loss energy can be obtained. The front-rear torque distribution ratio that is minimized can be appropriately determined.

In the present invention, preferably, the torque distribution ratio determining means determines the front-rear torque distribution ratio based on a sum of tire loss energy that changes in a quadratic function according to the engine torque.
According to the present invention thus configured, the front-rear torque that minimizes the sum of the loss energy including such tire loss energy by using the tire loss energy that changes in a quadratic function according to the engine torque. The distribution ratio can be determined appropriately.

In the present invention, preferably, the torque distribution ratio determining means uses a calculation expression representing a total sum of loss energies determined based on at least the engine torque and the wheel speeds of the front wheels and the rear wheels, to calculate the current engine torque and the front wheels and Based on the current wheel speed of the rear wheel, the front-rear torque distribution ratio that minimizes the total loss energy is determined.
According to the present invention configured as described above, it is possible to accurately determine the front-rear torque distribution ratio at which the total loss energy is minimized.

  According to the control device for a four-wheel drive vehicle of the present invention, the front-rear torque distribution ratio can be appropriately controlled so that the total loss energy is minimized according to the engine torque.

1 is an overall configuration diagram schematically showing a vehicle to which a control device for a four-wheel drive vehicle according to an embodiment of the present invention is applied. The functional block diagram of the controller by embodiment of this invention is shown. It is explanatory drawing about the relationship between an engine torque and various loss energy. It is explanatory drawing about the change of the sum total of the loss energy according to the magnitude | size of an engine torque. It is further explanatory drawing about the change of the sum total of loss energy according to the magnitude | size of engine torque.

  Hereinafter, a control apparatus for a four-wheel drive vehicle according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[Device configuration]
First, an overall configuration of a vehicle to which a control device for a four-wheel drive vehicle according to an embodiment of the present invention is applied will be described with reference to FIG. FIG. 1 is an overall configuration diagram schematically showing a vehicle 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 vehicle 1 mainly includes an engine 2, a transmission 3, a PTO (Power Take Off) 5, front drive shafts 7R and 7L, and a pair of left and right front wheels 9 (right Front wheel 9R and left front wheel 9L), a pair of left and right rear wheels 10 (right rear wheel 10R and left rear wheel 10L), propeller shaft 12, electromagnetic coupling 13, rear differential gear 15, rear drive shaft 17R, 17L, controller 20, accelerator opening sensor 31, front wheel speed sensors 32R and 32L, and rear wheel speed sensors 33R and 33L.

  The vehicle 1 is a four-wheel drive vehicle based on a front engine / front drive system (FF system). Specifically, the vehicle 1 does not perform full-time four-wheel drive, but has a two-wheel drive state (a state in which only the front wheels 9 are driven) and a four-wheel drive state (both the front wheels 9 and the rear wheels 10). The state in which the motor is driven) can be switched as appropriate. The vehicle 1 is configured to steer the front wheels 9 in response to a steering operation (not shown). Note that. The present invention is not limited to application to the drive type of a four-wheel drive vehicle as shown in FIG. 1, and is applicable to various drive types of a four-wheel drive vehicle (for example, a front engine / rear drive method (FR method)). It is applicable to.

  The engine 2 burns a mixture of fuel and air to generate a driving torque (engine torque) as a driving force of the vehicle 1, and transmits this driving torque to the transmission 3. The transmission 3 is a transmission capable of changing a gear ratio in a plurality of stages, and transmits a driving torque from the engine 2 at a set gear ratio. In this case, the transmission 3 transmits the driving torque from the engine 2 to the front wheels 9 via the front drive shafts 7R and 7L and also to the PTO 5 corresponding to the transfer. The PTO 5 transmits drive torque from the transmission 3 to the propeller shaft 12, and the propeller shaft 12 transmits drive torque from the PTO 5 to the electromagnetic coupling 13. The electromagnetic coupling 13 transmits the driving torque from the propeller shaft 12 to the rear differential gear 15, and the rear differential gear 15 transmits the driving torque transmitted from the electromagnetic coupling 13 via the rear drive shafts 17R and 17L. To the right rear wheel 10R and the left rear wheel 10L.

  Specifically, the electromagnetic coupling 13 is a coupling that connects the propeller shaft 12 and a shaft connected to the rear differential gear 15, and includes an electromagnetic coil, a cam mechanism, a clutch, and the like (not shown). The electromagnetic coupling 13 is configured to vary the fastening torque in the electromagnetic coupling 13 according to the current supplied to the internal electromagnetic coil under the control of the controller 20. By changing the fastening torque in this way, the electromagnetic coupling 13 is the maximum value of the driving torque transmitted from the propeller shaft 12 to the rear differential gear 15 (that is, the driving torque transmitted to the rear wheel 10). A certain maximum transmission torque can be changed. In this case, the electromagnetic coupling 13 functions to set a maximum transmission torque under the control of the controller 20 and to transmit a driving torque corresponding to the maximum transmission torque to the rear differential gear 15.

  Specifically, the electromagnetic coupling 13 transmits the driving torque transmitted from the propeller shaft 12 to the rear differential gear 15 as it is, with respect to the driving torque equal to or less than the maximum transmission torque. On the other hand, the electromagnetic coupling 13 does not transmit all of the transmitted driving torque to the rear differential gear 15 for the driving torque that is transmitted from the propeller shaft 12 and exceeds the maximum transmitting torque, and corresponds to the maximum transmitting torque. Only the drive torque is transmitted to the rear differential gear 15. Note that the electromagnetic coupling 13 can be configured as described in, for example, Japanese Patent Application Laid-Open No. 2013-3260.

  On the other hand, the accelerator opening sensor 31 detects an accelerator opening corresponding to an operation amount of an accelerator pedal (not shown) by the driver. The front wheel speed sensor 32R detects the wheel speed of the right front wheel 9R, and the front wheel speed sensor 32L detects the wheel speed of the left front wheel 9L. The rear wheel speed sensor 33R detects the wheel speed of the right rear wheel 10R, and the rear wheel speed sensor 33L detects the wheel speed of the left rear wheel 10L. The accelerator opening sensor 31, front wheel speed sensors 32R and 32L, and rear wheel speed sensors 33R and 33L respectively detect the detected accelerator opening, front wheel speed (the wheel speeds of the right front wheel 9R and the left front wheel 9L), and the rear wheel. Detection signals corresponding to the speeds (the wheel speeds of the right rear wheel 10R and the left rear wheel 10L) are output to the controller 20.

  Next, FIG. 2 shows a functional block diagram of the controller 20 according to the embodiment of the present invention. As shown in FIG. 2, the controller 20 functionally includes an acquisition unit 21, a torque distribution ratio determination unit 22, and a torque distribution control unit 23.

  The acquisition unit 21 of the controller 20 acquires the engine torque output by the engine 2. The controller 20 is a target acceleration to be generated from the vehicle 1 based on the driving state of the vehicle 1 (typically, the accelerator opening detected by the accelerator opening sensor 31. In addition, the vehicle speed, the gear stage of the transmission 3, etc.). Is set, a target engine torque of the engine 2 for realizing the target acceleration is set, and the engine 2 is controlled. In one example, the acquisition unit 21 acquires the engine torque set as such. The acquisition unit 21 is not limited to acquiring the engine torque in this way, and the engine torque may be obtained using a predetermined sensor.

  The torque distribution ratio determination unit 22 of the controller 20 includes a front-rear torque distribution ratio that indicates a ratio between the drive torque distributed to the front wheels 9 and the drive torque distributed to the rear wheels 10 in the drive torque corresponding to the engine torque output by the engine 2. To decide. In particular, the torque distribution ratio determining unit 22 is based on the engine torque acquired by the acquiring unit 21, the wheel speeds detected by the front wheel speed sensors 32R and 32L, and the rear wheel speed sensors 33R and 33L, and the like. The front / rear torque distribution ratio is determined according to the sum of the loss energy of the tire loss energy generated at 10 and the mechanical energy loss energy generated when the rear wheel 10 is driven.

  The torque distribution control unit 23 of the controller 20 performs control for distributing the drive torque to the front wheels 9 and the rear wheels 10 according to the front-rear torque distribution ratio determined by the torque distribution ratio determination unit 22. Specifically, the torque distribution control unit 23 obtains the maximum transmission drive torque to be set for the electromagnetic coupling 13 based on the front-rear torque distribution ratio, and sets the maximum transmission drive torque for the electromagnetic coupling 13. Thus, a desired drive torque is transmitted to the rear wheel 10. More specifically, the torque distribution control unit 23 obtains a fastening torque to be applied to the electromagnetic coupling 13 and performs control to apply the fastening torque to the electromagnetic coupling 13. In this case, the torque distribution control unit 23 calculates the amount of current that flows through the electromagnetic coupling 13.

  Thus, the controller 20 corresponds to the “control device for a four-wheel drive vehicle” in the present invention. The controller 20 includes at least one processor (CPU) and various programs interpreted and executed on the processor (including a basic control program such as an OS and an application program that is activated on the OS and realizes a specific function). And a computer having an internal memory such as a ROM or RAM for storing programs and various data. For example, the controller 20 is configured by an ECU (Electronic Control Unit).

[Control method]
Next, the control method performed by the controller 20 in the present embodiment will be specifically described.

  As described above, the controller 20 determines the front-rear torque according to the sum of the loss energy of the tire loss energy generated at the front wheels 9 and the rear wheels 10 and the mechanical energy loss energy generated when the rear wheels 10 are driven. A distribution ratio is determined, and control is performed to distribute the driving torque to the front wheels 9 and the rear wheels 10 according to the front-rear torque distribution ratio. In particular, in the present embodiment, the controller 20 determines the front-rear torque distribution ratio that minimizes the total loss energy according to the current engine torque, based on the total loss energy according to the magnitude of the engine torque. This is because the front-rear torque distribution ratio that minimizes the sum of the loss energy of tire loss energy and mechanical loss energy varies depending on the magnitude of the engine torque. That is, since the relationship between the front-rear torque distribution ratio and the loss energy changes according to the magnitude of the engine torque, the front-rear torque distribution ratio that minimizes the total loss energy changes according to the engine torque.

  Here, with reference to FIG. 3 thru | or FIG. 5, the basic concept of the control method which concerns on this embodiment is demonstrated concretely.

  FIG. 3 is an explanatory diagram regarding the relationship between engine torque and various types of loss energy. FIG. 3 (a) shows the relationship between engine torque and gear unit loss energy, FIG. 3 (b) shows the relationship between engine torque and coupling loss energy, and FIG. The relationship with tire loss energy is shown. FIGS. 3A to 3C show examples of loss energy at a certain longitudinal torque distribution ratio. That is, an example of loss energy when the engine torque is changed while fixing the front-rear torque distribution ratio is shown.

  The gear unit loss energy in FIG. 3A is a loss energy generated in a gear unit such as PTO5, and the coupling loss energy in FIG. 3B is a loss energy generated in the electromagnetic coupling 13, which is the present embodiment. Then, at least the sum of the gear unit loss energy and the coupling loss energy is used as the mechanical loss energy. The gear unit loss energy mainly corresponds to a loss generated in the PTO 5, and includes a loss caused when the gear tooth surface slips in the PTO 5 and a loss associated with oil agitation in the PTO 5. The coupling loss energy is typically a loss energy generated when the electromagnetic coupling 13 is slipping. Other mechanical loss energy is due to rear differential, which has the same tendency as the loss of PTO5. Strictly speaking, the mechanical loss energy includes not only mechanical loss energy related to driving of the rear wheels 10 but also mechanical loss energy related to driving of the front wheels 9. On the other hand, the tire loss energy in FIG. 3C is the sum of the tire loss energy generated at the front wheels 9 and the tire loss energy generated at the rear wheels 10.

  As shown in FIG. 3A, the gear unit loss energy tends to change in a quadratic function depending on the engine torque. However, as shown in FIG. 3B, the coupling loss energy is There is a tendency to change in a linear function according to the engine torque, and as shown in FIG. 3C, the tire loss energy tends to change in a quadratic function according to the engine torque. As described above, the gear unit loss energy, the coupling loss energy, and the tire loss energy change separately according to the engine torque. Note that “change in a quadratic function” here is not only a change in accordance with a complete quadratic function, but is not actually a change in accordance with a quadratic function. It also includes changing like a function. The same applies to “change in a linear function”.

  Next, with reference to FIG. 4, the change of the total loss energy according to the magnitude of the engine torque will be described. FIG. 4A shows an example of the relationship between the front-rear torque distribution ratio and the loss energy when the engine torque is relatively large, and FIG. 4B shows the front-rear torque distribution ratio when the engine torque is relatively small. An example of the relationship with loss energy is shown. FIGS. 4A and 4B show the loss energy when the engine torque is fixed and the front-rear torque distribution ratio is changed in a state where the four wheels are on a uniform road surface.

  Specifically, in FIGS. 4 (a) and 4 (b), graphs G11 and G21 indicate tire loss energy generated at the front wheels 9, and graphs G12 and G22 indicate tire loss energy generated at the rear wheels 10, respectively. G13 and G23 indicate mechanical loss energy (mainly the sum of gear unit loss energy and coupling loss energy), and graphs G14 and G24 indicate tire loss energy of the front wheel 9, tire loss energy and mechanical loss energy of the rear wheel 10, respectively. And the sum.

  From the graph G14 in FIG. 4A, when the engine torque is relatively large, the total loss energy is minimized in the front-rear torque distribution ratio R1. On the other hand, from the graph G24 in FIG. 4B, when the engine torque is relatively small, the sum of the loss energy is minimized at the front / rear torque distribution ratio R2 different from the front / rear torque distribution ratio R1. Therefore, the front-rear torque distribution ratio that minimizes the total loss energy changes according to the magnitude of the engine torque. This is because the relationship between the tire loss energy of the front wheels 9, the tire loss energy of the rear wheels 10, and the mechanical loss energy with respect to the front-rear torque distribution ratio changes separately according to the magnitude of the engine torque. The reason is that, as described with reference to FIGS. 3A to 3C, the gear unit loss energy, the coupling loss energy, and the tire loss energy change separately according to the engine torque. .

  With reference additionally to FIG. 5, the change of the sum total of the loss energy according to the magnitude | size of an engine torque is further demonstrated. FIG. 5 three-dimensionally shows a change in the relationship between the front-rear torque distribution ratio and the loss energy according to the engine torque. In FIG. 5, the graph G14 shows the sum of the tire loss energy of the front wheels 9, the tire loss energy of the rear wheels 10 and the mechanical loss energy when the engine torque is relatively large, similar to FIG. The graph G24 shows the sum of the tire loss energy of the front wheels 9, the tire loss energy of the rear wheels 10, and the mechanical loss energy when the engine torque is relatively small, as in FIG. 4B. The front-rear torque distribution ratios R1 and R2 are also the same as those shown in FIGS. 4 (a) and 4 (b). As shown by the arrow A1 in FIG. 5, it can be easily understood that the front-rear torque distribution ratio at which the total sum of the loss energy is minimized changes according to the magnitude of the engine torque.

  As described above, in the present embodiment, the controller 20 takes into account the total loss energy that changes in accordance with the magnitude of the engine torque, and the total loss energy in accordance with the current engine torque is minimized. Determine the front-rear torque distribution ratio. In particular, the controller 20 uses the arithmetic expression representing the sum of the loss energy determined based on at least the engine torque and the wheel speeds of the front wheels 9 and the rear wheels 10 to determine the current engine torque and the current values of the front wheels 9 and the rear wheels 10. The front-rear torque distribution ratio that minimizes the total loss energy is determined based on the wheel speed. Below, the arithmetic expression for determining the front-rear torque distribution ratio will be specifically described.

First, main symbols used in this specification are defined as follows.
F _fl , F _fr , F _rl , F _rr : Left front wheel drive torque, right front wheel drive torque, left rear wheel drive torque, right rear wheel drive torque F: Drive torque (engine torque)
V _fl , V _fr , V _rl , V _rr : Left front wheel speed, right front wheel speed, left rear wheel speed, right rear wheel speed V _f , V _r : front wheel speed, rear wheel speed V _V : vehicle body speed x: longitudinal torque distribution ratio L _tire: the sum of the tire loss energy L _U: gear unit loss energy L _C: coupling loss energy L _UC: mechanical loss energy L _total: total loss energy

  In general, in a predetermined region, the relationship between the driving torque and the slip ratio in the wheel is a linear function according to the driving stiffness. Therefore, the drive torque Fw generated by each wheel can be obtained by the product of the detected slip ratio of each wheel and the driving stiffness.

  The driving torque of each wheel can be expressed by a mathematical formula including the engine torque F and the front / rear torque distribution ratio x (the ratio of distribution of the engine torque to the rear wheels, which is a variable of 1 or less). In this case, the driving torque corresponding to the expression expressed using x is applied to the rear wheels, and the driving torque corresponding to the expression expressed using (1-x) is applied to the front wheels. Become.

Here, the product of the driving torque generated by each wheel and the slip ratio of each wheel is tire loss energy. Since the slip ratio of each wheel is estimated by the difference between the vehicle speed and the wheel speed of each wheel, the tire loss energy is a value obtained by multiplying the difference between the driving force, the vehicle speed, and the wheel speed for each wheel by four wheels. It is expressed as the sum of Since each wheel driving force includes the front-rear torque distribution ratio x as described above, the tire loss energy is expressed by the following equation when arranged.
L _tire = F ² {(P _f + P _r ) x ² −2P _f x + P _f } Equation (1)

In Expression (1), “P _f ” and “P _r ” are processes in which the tire loss energy is expressed so that the square of the engine driving force and the square of the front / rear torque distribution ratio x are represented as representative variables. Each coefficient generated in is divided into a front wheel side and a rear wheel side. In particular, “P _f ” is represented by front wheel speeds V _fl and V _fr and front wheel driving stiffness, and “P _r ” is represented by rear wheel speeds V _rl and V _rr and rear wheel driving stiffness.

Next, the gear unit loss energy L _U is expressed by Expression (2) using the front-rear torque distribution ratio x. “A”, “b”, and “c” in Equation (2) are coefficients determined in the gear unit. As shown in Expression (2), the gear unit loss energy L _U is expressed as a quadratic function of the front-rear torque distribution ratio x.
L _U = ax ² + bx + c Formula (2)

Further, the coupling loss energy L _C is expressed as a linear function of the driving torque (engine torque) F, depending on the rotational speed difference between the front and rear wheels and the driving torque transmitted by the coupling to the rear wheels. It is expressed as a linear function of the front-rear torque distribution ratio x.
L _C = (DV _f −EV _r ) × αFx Equation (3)

  In Equation (3), D, E, and α are the coefficients generated in the process of organizing the equations so that the engine driving force F and the front-rear torque distribution ratio x are represented as representative variables. It is divided and divided.

When the formula (2) and the formula (3) are integrated, the mechanical loss energy L _UC is expressed as the formula (4).
L _UC = L _U + L _C
= Ax ² + Bx + C Formula (4)

  “A”, “B”, and “C” in Expression (4) are obtained by summarizing coefficients generated in the process of organizing the expression so that the front-rear torque distribution ratio x is represented as a representative variable. .

Next, the total loss energy L _total is expressed by the equation (5) from the total tire loss energy L _tire and the mechanical loss energy L _UC . As shown in Expression (5), the total loss energy L _total is expressed as a quadratic function of the front-rear torque distribution ratio x and is expressed as a quadratic function of the drive torque (engine torque) F.
L _total = L _tire + L _{UC
^{= F 2 {(P f +}} P r) x 2 -2P f x + P f}
+ Ax ² + Bx + C
_{= {A + (P f +} P r) F 2} x 2
^{_{+ (B-2P f F 2}} ) x + C + P f F 2 Equation (5)

Here, regarding the expression “d / dx (L _total )” obtained by differentiating the expression (5) by x, the loss energy of the front-rear torque distribution ratio x when “d / dx (L _total ) = 0” is satisfied. The total L _total is minimized. The front-rear torque distribution ratio x _min that minimizes the _total loss energy L _total is expressed by equation (6).
^{_{x min = (2P f F 2}} -B) / 2 {A + (P f + P r) F 2} Equation (6)

According to the equation (6), the total loss energy L _total is minimized by the driving torque (engine torque) F, “P _f ”, “P _r ”, “A”, “B”. The front-rear torque distribution ratio x _min can be obtained. In this case, "P _f", "P _r" is obtained in decreasing wheel speed, "B" obtained from the wheel speed and the driving torque (engine torque). Therefore, the front-rear torque distribution ratio x _min in equation (6) can be obtained from the drive torque (engine torque) F and the wheel speeds V _fl , V _fr , V _rl , V _rr .

Therefore, the controller 20 (torque distribution ratio determination unit 22) described above stores the arithmetic expression (6) (may be the expression (5)) in a predetermined internal memory or the like, and the acquisition unit 21 acquires the current And the current wheel speeds V _fl , V _fr , V _rl , V _rr detected by the front wheel speed sensors 32R, 32L and the rear wheel speed sensors 33R, 33L are substituted into equation (6). Thus, the front-rear torque distribution ratio x _min to be applied is obtained.

[Function and effect]
Next, operational effects of the control device for a four-wheel drive vehicle according to the embodiment of the present invention will be described.

  According to the present embodiment, the controller 20 takes into account the total loss energy that changes according to the magnitude of the engine torque, and the front-rear torque distribution ratio that minimizes the total loss energy according to the current engine torque. To decide. Thus, the front-rear torque distribution ratio can be appropriately controlled so that the total loss energy is minimized according to the engine torque.

  Further, according to the present embodiment, the controller 20 uses the coupling loss energy that changes in a linear function according to the engine torque as the mechanical loss energy, so that the total of the loss energy including such coupling loss energy is obtained. It is possible to appropriately determine the front-rear torque distribution ratio that minimizes.

  Further, according to the present embodiment, the controller 20 uses the gear unit loss energy that changes in a quadratic function according to the engine torque as the mechanical loss energy, so that the total loss energy including such gear unit loss energy is obtained. It is possible to appropriately determine the front-rear torque distribution ratio that minimizes.

  Further, according to the present embodiment, the controller 20 uses tire loss energy that changes in a quadratic function according to the engine torque, so that the sum of loss energy including such tire loss energy is minimized. The torque distribution ratio can be determined appropriately.

  Further, according to the present embodiment, the controller 20 uses the arithmetic expression that represents the sum of the loss energy determined based on the engine torque and the wheel speeds of the front wheels 9 and the rear wheels 10 to determine the current engine torque and the front wheels 9. Based on the current wheel speed of the rear wheel 10, the front-rear torque distribution ratio that minimizes the total loss energy can be determined with high accuracy.

1 Vehicle 2 Engine 3 Transmission 5 PTO (Power Take Off)
9 Front wheel 10 Rear wheel 12 Propeller shaft 13 Electromagnetic coupling 15 Rear differential gear 20 Controller 31 Accelerator opening sensor 32R, 32L Front wheel speed sensor 33R, 33L Rear wheel speed sensor

Claims (6)

A control device for a four-wheel drive vehicle that controls drive torque distributed to front wheels and rear wheels,
Obtaining means for obtaining engine torque output by the engine;
Drive distributed to the front wheels at the drive torque corresponding to the engine torque based on the sum of the loss energy of the tire loss energy generated at the front wheels and the rear wheels and the mechanical energy loss energy generated by driving the rear wheels Torque distribution ratio determining means for determining a front-rear torque distribution ratio indicating a ratio of torque and driving torque distributed to the rear wheels;
Torque distribution control means for performing control for distributing drive torque corresponding to the engine torque to front wheels and rear wheels in accordance with the front-rear torque distribution ratio determined by the torque distribution ratio determination means;
Have
The torque distribution ratio determining means minimizes the total loss energy according to the current engine torque acquired by the acquisition means based on the total loss energy that changes according to the magnitude of the engine torque. A control device for a four-wheel drive vehicle, wherein the front-rear torque distribution ratio is determined. The four-wheel drive vehicle transmits a part of the engine torque to the rear wheel via a coupling, and changes the coupling torque of the coupling to change the driving torque transmitted to the rear wheel out of the engine torque. The variable is configured,
The torque distribution ratio determining means determines the front-rear torque distribution ratio using a coupling loss energy generated in the coupling, which varies in a linear function according to the engine torque, as the mechanical loss energy. Item 4. A control device for a four-wheel drive vehicle according to Item 1.   The torque distribution control means obtains the coupling torque of the coupling according to the front-rear torque distribution ratio determined by the torque distribution ratio determination means, and performs control to apply the fastening torque to the coupling. Item 4. The control device for a four-wheel drive vehicle according to Item 2. The four-wheel drive vehicle has a power take-off that transmits engine torque from a transmission to a propeller shaft.
The torque distribution ratio determining means uses, as the mechanical loss energy, the front-rear torque distribution using at least gear unit loss energy generated in a gear unit included in the power take-off, which changes in a quadratic function according to the engine torque. The control device for a four-wheel drive vehicle according to any one of claims 1 to 3, wherein the ratio is determined.   The torque distribution ratio determining means determines the front / rear torque distribution ratio based on a sum of the tire loss energy that changes in a quadratic function according to the engine torque. The four-wheel drive vehicle control device described.   The torque distribution ratio determining means uses an arithmetic expression representing the sum of the loss energy determined based on at least the engine torque and the wheel speeds of the front wheels and the rear wheels, and calculates the current engine torque and the current values of the front wheels and the rear wheels. The control device for a four-wheel drive vehicle according to any one of claims 1 to 5, wherein the front-rear torque distribution ratio that minimizes the sum of the loss energy is determined based on a wheel speed.

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