JP2518444B2 - Driving force distribution switchable four-wheel drive vehicle - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a four-wheel drive vehicle, and more particularly, to a drive force distribution switching type 4 capable of switching drive force distribution based on a yaw angular acceleration and a steering angular velocity of the vehicle. It relates to a wheel drive vehicle.

[Prior Art] In a four-wheel drive vehicle, conventionally, a driving force transmission device configured to adjust a ratio of a torque transmitted to a front wheel side and a torque transmitted to a rear wheel side according to a driving state. Have been developed.

As such a device, for example, a VCU is installed in the center differential.
(Viscous coupling unit) and other differential limiting devices are installed to properly control the center differential speed difference, and a hydraulic multi-plate clutch is used to respond to control hydraulic pressure. It is known that the power transmission state can be adjusted.

It is conceivable to perform various controls by such a driving force transmission device according to the running state of the vehicle and the like.

[Problems to be Solved by the Invention] By the way, as one of the controls by the driving force transmission device described above, control for suppressing the spin of the vehicle (spin suppression control)
Can be considered.

This spin means that when the vehicle makes a turning acceleration motion,
While losing steerability and accompanied by a sudden change in vehicle attitude,
This is a phenomenon in which the vehicle greatly bulges outward with respect to the target trajectory. For example, as shown in FIG. 9, when acceleration is started while the vehicle is making a steady circular turn, the vehicle is accompanied by rotation of the vehicle itself. On the other hand, a traveling locus h2 that bulges outward with respect to the target locus h1 is taken. Such a phenomenon is likely to occur in rear-wheel drive vehicles (generally FR vehicles). In other words, the driving force transmitted to the road surface by the driving wheels increases at the time of acceleration, so the lateral force of the driving wheels decreases by the amount of this driving force increase, and it becomes easier to slip laterally. The wheels are slippery and tend to oversteer and spin easily.

In order to suppress such a spin, front-wheel drive or four-wheel drive with the front wheels as the main component is more advantageous, but in order to travel while enjoying the steerability called so-called sports running, the rear-wheel drive is used. Is more suitable.

So, for example, when driving normally, drive with rear wheel drive,
If a spin is about to occur, only at this time, it is desirable to switch to front-wheel drive (or four-wheel drive with the front wheels as the main component).

The present invention was devised in view of the above problems, and when traveling normally, the vehicle is driven mainly by the rear wheels, and when spin occurs or is about to occur, the front wheel drive (front wheel distribution) is surely performed. It is an object of the present invention to provide a four-wheel drive vehicle for switching driving force distribution, which is adapted to switch to a four-wheel drive including increased four-wheel drive.

[Means for Solving the Problems] Therefore, the four-wheel drive vehicle with a drive force distribution switchover according to claim (1) of the present invention drives the vehicle by transmitting the output torque of the engine to the front wheels and the rear wheels. In a four-wheel drive vehicle, a driving force distribution control unit that can control the distribution of the output torque between the front wheels and the rear wheels, and a front lateral acceleration detection unit that detects a lateral acceleration applied to the front part of the vehicle, Rear lateral acceleration detecting means for detecting a lateral acceleration applied to the rear portion of the vehicle, steering angular velocity detecting means for detecting a steering angular velocity of the vehicle, and the front wheel and the rear wheel based on the information from these detecting means. The yaw angular acceleration of the vehicle is calculated based on the lateral acceleration detected by each of the lateral acceleration detecting means, the controlling means outputting a control signal for controlling the distribution state of the driving force. Yaw angular acceleration calculator , The state where the current vehicle state should prevent excessive driving force from being transmitted to the rear wheels, or the state where the rear wheels should be driven mainly, based on the calculated yaw angular acceleration value and the detected steering angular velocity value And a control signal output unit that outputs a control signal in a predetermined driving state to the driving force distribution control unit based on the determination result of the determination unit. I am trying.

Further, the four-wheel drive vehicle of the driving force distribution switching type according to claim (2) of the present invention is a four-wheel drive vehicle capable of driving the vehicle by transmitting the output torque of the engine to the front wheels and the rear wheels. To the front wheels and the rear wheels, drive force distribution control means, front lateral acceleration detection means for detecting lateral acceleration applied to the front part of the vehicle, and lateral acceleration applied to the rear part of the vehicle. Rear lateral acceleration detecting means, a steering angular velocity detecting means for detecting a steering angular velocity of the vehicle, and a control means for controlling a distribution state of the driving force to the front wheels and the rear wheels based on information from these detecting means. A yaw angular acceleration calculating section for calculating a yaw angular acceleration of the vehicle based on the lateral acceleration detected by each of the lateral acceleration detecting means. Value of the yaw angular acceleration and A determination unit that determines whether the value of the yaw angular acceleration is at a value corresponding to or greater than the value of the steering angular velocity based on the detected value of the steering angular velocity, and a determination by the determination unit If the value of the yaw angular acceleration is appropriate based on the result, a control signal for the rear wheel drive mode or the drive mode mainly for the rear wheels is output to the driving force distribution control means, and the value of the yaw angular acceleration is appropriate. With the above size, the driving force distribution control means is provided with a control signal output section for outputting a control signal in the front wheel drive mode or the four-wheel drive mode in which the rear wheels are not the main components.

[Operation] In the four-wheel drive vehicle with drive force distribution switching according to claim (1) of the present invention described above, the yaw angular acceleration calculation unit of the control unit detects the front lateral acceleration detection unit and the rear lateral acceleration detection unit. The yaw angular acceleration of the vehicle is calculated based on the lateral acceleration, and the determination unit determines that the current vehicle state is excessive driving force on the rear wheels based on the calculated yaw angular acceleration value and the detected steering angular velocity value. Is determined to be not transmitted or is driven mainly by the rear wheels, and the control signal output unit determines the driving force distribution control means based on the determination result of the determination unit. The control signal of a predetermined driving state is output to. As a result, if a vehicle running in the drive mode mainly for the rear wheels tries to generate spin, an excessive driving force will not be transmitted to the rear wheels, and the steer characteristics of the vehicle will change from the oversteer tendency to the understeer side. To make it difficult for the vehicle to spin.

In the four-wheel drive vehicle for switching driving force distribution according to claim (2) of the present invention described above, the determination unit of the control means determines the yaw angle based on the calculated value of the yaw angular acceleration and the detected value of the steering angular velocity. It is determined whether the value of the acceleration has a value corresponding to or larger than the value of the steering angular velocity,
In the control signal output unit, if the value of the yaw angular acceleration has an appropriate value based on the determination result of the determination unit, the drive force distribution control unit controls the front wheel drive mode or the drive mode mainly including the rear wheels. When a signal is output and the value of the yaw angular acceleration is more than a suitable value, a control signal for the front wheel drive mode or the four-wheel drive mode not mainly for the rear wheels is output to the drive force distribution control means. As a result, when a vehicle running in the rear wheel drive mode or the drive mode mainly composed of the rear wheels tries to generate spin, the vehicle will travel in the front wheel drive mode or the four-wheel drive mode not composed mainly of the rear wheels. The steer characteristic of the vehicle changes from oversteer tendency to understeer tendency or neutral steer tendency, which makes it difficult for the vehicle to spin.

[Embodiment] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIGS. 1 to 6 show a four-wheel drive vehicle with a drive power distribution switching as a first embodiment of the present invention. FIG. 2 is a schematic configuration diagram of the drive system, FIG. 2 is a flowchart showing the control content, FIG. 3 is a diagram showing a map used for the control, and FIG. 4 is a frequency response of the yaw angular acceleration with respect to the steering angular velocity. FIGS. 5, 5 and 6 are diagrams showing simulation results relating to vehicle spin, and FIGS. 7 and 8 show a driving force distribution switching type four-wheel drive vehicle as a second embodiment of the present invention. FIG. 7 is a schematic configuration diagram of the drive system, and FIG. 8 is a flowchart showing the control contents.

First of all, the first embodiment will be described. The drive system of this four-wheel drive vehicle for switching driving force distribution is constructed as shown in FIG.

In FIG. 1, reference numeral 2 is an engine, and the output of the engine 2 is a torque converter 4 and an automatic transmission 6.
Is transmitted to the output shaft 8 via. The output of the output shaft 8 is transmitted to the front wheel side and the rear wheel side via the intermediate gear 10.

Wet multi-plate clutches 11 and 13 as driving force distribution control means are provided between the intermediate gear 10 and the front wheels and between the intermediate gear 10 and the rear wheels, respectively. The output torque of the engine 2 is, on the other hand, the wet multi-plate clutch 11
Transmitted from the axles 17L, 17R to the left and right front wheels 16, 18 via the reduction gear mechanism 19, the front wheel differential gear device 14, and, on the other hand,
Hydraulic multi-plate clutch 13 to bevel gear mechanism 15, propeller shaft 20 and bevel gear mechanism 21, differential gear unit 2 for rear wheels
It is adapted to be transmitted from the axles 25L, 25R to the left and right rear wheels 24, 26 via 2.

In other words, the hydraulic multi-plate clutches 11 and 13 can adjust the amount of transmission of the output torque of the engine 2 by changing the frictional force depending on the pressure supplied to the hydraulic chamber (not shown).

That is, the hydraulic multi-plate clutches 11 and 13 can be continuously adjusted from the completely free state to the completely locked state, and should be in an appropriate intermediate engagement state from the completely free state to the completely locked state. Thus, the amount of transmission torque can be controlled.

The hydraulic multi-plate clutches 11 and 13 can be individually controlled, but by controlling the hydraulic multi-plate clutches 11 and 13 in combination, the ratio of the torque distributed to the front wheel side and the rear wheel side can be controlled. can do.

Specifically, when the pressure in the hydraulic chamber of the hydraulic multi-plate clutch 11 is raised to a predetermined pressure and is completely locked, and the pressure in the hydraulic chamber of the hydraulic multi-plate clutch 13 is zero and completely free, The engine torque is effectively transmitted only to the front wheels, and the front wheels are driven. When the pressure in the hydraulic chamber of the hydraulic multi-plate clutch 11 is zero and completely free, and when the pressure in the hydraulic chamber of the hydraulic multi-plate clutch 13 is raised to a predetermined pressure and completely locked, the engine torque is It is effectively transmitted only to the side, and the rear wheel drive state is set. When the pressure in the hydraulic chambers of the hydraulic multi-plate clutches 11 and 13 is equal to or higher than a certain level, power is transmitted according to the pressure,
The four-wheel drive state is set.

Therefore, the front wheel drive mode (FF mode), the direct four wheel drive mode (direct drive 4WD mode), the distribution control four wheel drive mode (distribution control 4WD mode), the rear In addition to the wheel drive mode (FR mode), both hydraulic multi-plate clutches 11 and 13 can be set to free drive force cutoff mode.

Further, reference numeral 30 is a steering sensor and a steering angular velocity sensor (steering angle detecting means) for detecting a rotation angle from the neutral position of the steering wheel 32, that is, a steering angle θ and a steering angular velocity (hereinafter referred to as δ ′), and 34a is a vehicle body. A front lateral acceleration sensor (front lateral acceleration means) that detects a lateral acceleration G ₁ that acts on the front of the vehicle, and a rear lateral acceleration detection sensor 34b that detects a lateral acceleration G ₂ that acts on the rear of the vehicle body. (Rear lateral acceleration detecting means), 36 is a longitudinal acceleration sensor that detects the longitudinal acceleration G _X acting on the vehicle body, and 38 is the engine 2
Throttle sensor for detecting the throttle opening θ _T of
Is the engine key switch for engine 2, 40, 42, 44, 46
Are wheel speed sensors that detect the rotational speeds of the left front wheel 16, the right front wheel 18, the left rear wheel 26, and the right rear wheel 28, respectively, and also serve as vehicle speed detection means. Reference numeral 41 is an engine speed sensor.

The outputs of these switches and each sensor are input to a controller (control means) 48. In the controller 48, each hydraulic multi-disc clutch 1 is based on the detection values of these sensors.
It is designed to control the combined state of 1,13.

Reference numeral 50 is an antilock brake device, and this antilock brake device 50 operates in conjunction with a brake switch (not shown). That is, when the brake switch is turned on when the brake pedal is stepped on, an antilock brake operation signal is output in conjunction with this, and the antilock brake device 50 is operated. Then, when the operation signal of the antilock brake is output, at the same time, a signal indicating that state is input to the controller 48. Further, reference numeral 52 is a warning lamp which is turned on based on a control signal from the controller 48.

The controller 48 is a computer including a CPU, a ROM, a RAM, an interface and the like, which are necessary for control described later, although not shown.

Reference numeral 54 is a hydraulic power source, 56 is the hydraulic power source 54 and a hydraulic multi-plate clutch.
It is a pressure control valve interposed between 28 hydraulic chambers, and the pressure control valve 56 is controlled by a control signal from the controller 48.

By the way, the controller 48 has a control signal output unit 48c that outputs a control signal to the pressure control valve 56 as described above in order to control the distribution state of the driving force to the front wheels 16 and 18 and the rear wheels 24 and 26. In addition to this, the controller 48 has a lateral acceleration detected by each sensor 34a, 34b.
Yaw angular acceleration of the vehicle from G ₁ and G ₂ (hereinafter referred to as γ ′)
Based on the calculated yaw angular acceleration γ ′ and the steering angular velocity δ ′, the yaw angular acceleration calculation unit 48a that calculates In addition to the determination unit 48b for determining whether or not the state is present, a drive mode detection unit (not shown) for detecting the current drive mode is provided.

In the yaw angular acceleration calculation unit 48a, the distance between the sensors 34a and 34b
Let L ₁ and calculate the yaw angular acceleration γ ′ by the calculation formula γ ′ = (G ₁ −G ₂ ) / L ₁ .

The determination made by the determination unit 48b is to determine whether or not the vehicle is likely to spin, and it is determined that the vehicle should be in the front-wheel drive state when the vehicle is in the easily-spinning state and the rear-wheel drive is performed. It is judged that it is in a state to run,
This is when the vehicle is in a state where there is no risk of spinning.

Therefore, when the vehicle normally travels without the risk of spinning, the determination unit 48b determines that rear-wheel drive traveling should be performed,
When the control signal output unit 48c outputs a control signal to drive the vehicle in the rear-wheel drive mode and the pressure control valve 56 is adjusted to spin the vehicle during rear-wheel drive traveling, the determination unit 48
Since it is determined in b that the vehicle should travel in front-wheel drive, at this time, the control signal is output from the control signal output unit 48c so that the vehicle travels in the front-wheel drive mode, and the pressure control valve 56 is adjusted.

Here, a method of determining whether the vehicle is likely to spin will be described.

Since the vehicle spin is a vertical rotation of the vehicle, it can be detected using yaw rate γ or yaw angular acceleration γ ′. Also, it seems advantageous to use the yaw angular acceleration γ '. Therefore, here, the spin is detected using the yaw angular acceleration γ ′.

The yaw angular acceleration γ'increases during a spin, but also changes during normal steering of the steering wheel in accordance with the steering angular acceleration δ '. Therefore, the spin is judged from the relationship between the yaw angular acceleration γ'and the steering angular velocity δ '.

By the way, the transfer function G (S) of the response of the yaw rate γ with respect to the steering angle δ _H is expressed by the following equation.

However, Yaw angular acceleration gain constant, ωn: Natural frequency of vehicle, ζ: Damping ratio Tr: Delay time On the other hand, the transfer function G ′ (S) of the response of the yaw angular acceleration γ ′ to the steering angular velocity δ ′ is And agrees with the above equation (1).

Therefore, the yaw angular acceleration γ ′ that appears during normal steering of the steering wheel is expressed by the equation (1), and when there is an unusually large response of the yaw angular acceleration γ ′, it can be said that the vehicle is in the spin state.

By the way, the simulation result regarding the spin of the vehicle running in the FR mode will be described with reference to FIGS.

FIG. 5 shows a traveling locus during simulation, a curve f1 is a steady turning locus without acceleration, and a curve f2 is an acceleration start point P1.
Is a running locus when acceleration is started at, and the rectangular rows drawn with solid lines or broken lines along the respective loci f1 and f2 are used to identify the running direction of the vehicle at the corresponding running position. It is shown.

FIG. 6 shows the time variation of the yaw angular acceleration A, which is the curve g1.
Indicates that there is no acceleration, and the curve g2 indicates that when acceleration starts at time t ₁ . It should be noted that the curve g2 steeply descending at the right end indicates that the vehicle has stopped.

From these FIGS. 5 and 6, it can be seen that the yaw angular acceleration γ ′ rises after the start of acceleration, and when the yaw angular acceleration γ ′ rises to some extent, the vehicle begins to spin.

FIG. 4 is a graph showing the frequency response of the yaw angular acceleration γ ′ with respect to the steering angular velocity δ ′, where the curve a is 10 [m / s] and the curve b is 20 [m / s]. ]in the case of,
Curve c is for a vehicle speed of 30 [m / s], and curve d is for a vehicle speed of 40 [m
/ s], respectively. As shown in the figure, the response gain becomes substantially constant as a whole, although the gain partially increases near 0.3 to 0.5 cpm during high-speed traveling.

Therefore, as shown in FIG. 3, for example, the steering angular velocity δ '
A determination diagram based on the relationship between the acceleration and the yaw angular acceleration γ ′ can be considered. In FIG. 3, the region described as FF mode is a region where spin is likely to occur (spin region), and the region described as FR mode is a region not susceptible to spin (stable region), A hatched area α is an area for preventing control chattering. Although FIG. 3 shows the case where the steering angular velocity δ ′ and the yaw angular acceleration γ ′ are positive (for example, to the right), the steering angular velocity δ ′ and the yaw angular acceleration γ ′ are negative (for example, the right direction). (Left direction)
Will be the same.

The determination line a1 for switching from the FR mode (stable region) to the FF mode (spin region) is that the yaw angular acceleration γ'is constant (this value is set in the region where the steering angular velocity δ'is small (that is, δ '<ε)). A straight line (γ ′ = E) such that
And a region where the steering angular velocity δ ′ is large (that is, δ ′ ≧
In ε), the yaw angular acceleration γ'is a straight line (γ '= mδ', where m is a proportional constant; m = E / ε), which has a proportional relationship with the steering angular velocity δ '.

The determination line a2 for switching from the FR mode (stable region) to the FF mode (spin region) is a straight line whose yaw angular acceleration γ'is smaller than the determination line a1 by a fixed amount (for example, d), and the steering angular velocity δ ' In the region where δ is small (δ ′ <ε), the straight line: γ ′ = E−d, the region where the steering angular velocity δ ′ is large (δ ′
≧ ε), it is a straight line (γ ′ = mδ′−d, m is a proportional constant).

By the way, a region where the steering angular velocity δ ′ is small (δ ′ <ε)
, The yaw angular acceleration γ'is based on a constant value (E, E-d) that is larger than the corresponding value with the steering angular velocity δ '. This is because the stability of is more important, and unnecessary switching of drive modes is omitted.

The determination unit 48b in the controller 48 is traveling in the FR mode based on the value of the steering angular velocity δ ′ detected by the steering angular velocity sensor 30 and the value of the yaw angular acceleration γ ′ calculated by the yaw angular acceleration calculation unit 48a. When the relationship between the steering angular velocity δ'and the yaw angular acceleration γ'is in the region above the judgment line a1, the mode is changed to the FF mode, and the steering angular velocity δ'and the yaw angular acceleration γ'during traveling in the FF mode. When the relation of is in the region below the determination line a2, it is determined to return to the FR mode.

The driving force distribution switching type four-wheel drive vehicle as the first embodiment of the present invention is configured as described above, and the operation of the drive system will be described with reference to the flowchart of FIG.

First, the lateral accelerations G ₁ and G ₂ and the steering angular velocity δ ′ are read through the respective sensors (step S1), and the yaw angular acceleration calculator 48a uses the lateral acceleration values G ₁ and G ₂ to determine the yaw angular acceleration γ ′. Is calculated (step S2).

Then, when it is determined that the current traveling state is the FR mode in the determination in step 3 by the traveling mode determination unit,
In step S4, it is determined whether or not the magnitude of the steering angular velocity | δ '| is smaller than a predetermined value ε.

If │δ'│ <ε, the process proceeds to step S5, and it is determined whether the magnitude of the yaw angular acceleration │γ'│ is larger than the predetermined value E or not.

The drive mode cannot be switched unless │γ'│> E. However, if │γ'│> E, it is determined that the motor is in the spin region, the process proceeds to step S6, and the control signal output unit 48c transfers to the pressure control valve 56. A control signal corresponding to the FF mode is output.
As a result, the drive mode is switched from the FR mode to the FF mode.

On the other hand, if │δ'│ <ε, the process proceeds to step S7 to determine whether or not │γ'│ is larger than m | δ '| (where m = E / ε).

The drive mode cannot be switched unless | γ ′ |> m | δ ′ |, but if | γ ′ |> m | δ ′ |, it is determined that the spin region is in effect and the process proceeds to step S6 to output the control signal. Department
A control signal corresponding to the FF mode is output from the 48c to the pressure control valve 56. This will change the drive mode from the FR mode.
Switch to FF mode.

In addition, in the determination of step 3 by the traveling mode determination unit,
If it is determined that the current traveling state is the FF mode, the process proceeds to step S8, and it is determined whether or not the magnitude | δ '| of the steering angular velocity is smaller than a predetermined value ε.

If │δ'│ <ε, the routine proceeds to step S9, where it is determined whether or not the magnitude of the yaw angular acceleration │γ'│ is larger than a predetermined value E-d.

If | γ '|> E-d, the drive mode cannot be switched because it is in the spin region or a region close to it, but if it is not | γ'|> E-d, it is in the stable region. In step S11, the control signal output unit 48c outputs the control signal corresponding to the FR mode to the pressure control valve 56. As a result, the drive mode is switched from the FF mode to the FR mode.

On the other hand, if │δ'│ <ε is not established, the process proceeds to step S10 to determine whether │γ'│ is larger than m | δ'│-d (where m = E / ε).

If | γ '|> m | δ' | -d, it is assumed that the drive mode is in the spin region or a region close to this, but the drive mode cannot be switched, but if it is not | γ '|> m | δ' | -d. Assuming that it is in the stable region, the process proceeds to step S11, and the control signal output unit 48c outputs the control signal corresponding to the FF mode to the pressure control valve 56. As a result, the drive mode is switched from the FR mode to the FF mode.

In this way, by controlling the drive state of the vehicle in accordance with the response (gain γ '/ δ') of the yaw angular acceleration γ'to the steering angular velocity δ ', the oversteer tendency with good steering response during normal running can be obtained. In the FR mode (rear wheel drive mode) that is exhibited, you can run while enjoying the so-called vertical running that is called sports running, and if spin is about to occur during FR mode driving, FF mode (front wheel drive mode) Then, the vehicle tends to understeer and the occurrence of spin is avoided.

As a result, the driving limit of the vehicle will be greatly improved, and even unskilled drivers will be able to safely enjoy sports driving in the FR mode.

Further, since the chattering prevention area (see FIG. 3) is provided between the switching condition from the FR mode to the FF mode and the return condition from the FF mode to the FR mode, stable drive mode control is performed. There are also advantages.

Next, the second embodiment will be described. This embodiment is constructed as shown in FIG.

In FIG. 7, the same symbols as those in FIG. 1 indicate the same things, and in this four-wheel drive vehicle, the driving force distribution control means is different. That is, the distribution switching intermediate gear 10 is directly connected to the rear wheel side, and the wet multi-plate clutch 11 as the driving force distribution control means is interposed between the intermediate gear 10 and the front wheel side. As a result, when the hydraulic multi-plate clutch 11 is completely free, the rear wheels are driven, and when the hydraulic multi-plate clutch 11 is completely locked, the direct-coupled four-wheel drive (the front wheel: rear wheel distribution ratio is
50:50), and when the hydraulic multi-plate clutch 11 is semi-engaged, the front wheel: rear wheel distribution ratio is 0: 100 (rear wheel drive) to 50:50.
It can be continuously adjusted up to 50 (four-wheel drive directly connected).

Then, when a spin is about to occur while traveling in the FR mode, the 4WD mode is selected.

Except for these portions, the configuration is almost the same as that of the first embodiment.

With the above-described configuration, as shown in FIG. 8, it is determined that spin is about to occur, and the drive mode is switched from the FR mode to the 4WD mode (step S6 '), On the contrary, it is determined that there is no possibility of spin, as in the first embodiment, and the drive mode is 4W.
Switching from D mode to FR mode (step S1
1).

As a result, in normal driving mode, you can drive in FR mode while enjoying the so-called sports running longitudinal performance, and if a spin is about to occur during FR mode driving, it will be appropriately switched to 4WD mode and the vehicle The oversteering tendency is avoided, and the generation of spin is suppressed.

In each of the above-described embodiments, the determination unit of the controller 48
Although the determination in 48b is performed by calculation, the yaw angular acceleration γ'as shown in FIG.
And a steering angular velocity δ ′ as parameters, a map divided into a spin region (a region to be driven by the front wheels or a region to be driven by four wheels), a stable region (a drive region for the rear wheels), a chattering prevention region, etc. is stored. The determination unit in the controller 48 may refer to the calculated or detected yaw angular acceleration γ'and the steering angular velocity δ'in this map to determine the drive mode switching.

Further, generally, the FR mode is a mode in which only the rear wheels are driven, and the FF mode is a mode in which only the front wheels are driven. However, in each of the above-described embodiments, the FR mode is mainly driven by the rear wheels. It may be a mode including a wheel drive mode,
The FF mode may be a mode that also includes a four-wheel drive mode in which the front wheel drive is mainly used.

Further, as shown in FIG. 4, the response gain of the yaw angular acceleration γ'to the steering angular velocity δ'is 0.3 to
Since it partially increases in the vicinity of 0.5 cps, it may be possible to control in consideration of this point at the time of high speed, which makes it possible to control the drive mode more appropriately.

[Effects of the Invention] As described in detail above, according to the four-wheel drive vehicle with drive force distribution switching according to claims (1) and (2) of the present invention, the value of yaw angular acceleration and the value of steering angular velocity are determined. By controlling the drive mode on the basis of the rear wheel drive mode, if a spin is about to occur during traveling while traveling mainly in the rear wheel drive mode, the mode is appropriately switched to the front wheel drive mode or the four-wheel drive mode with appropriate drive force distribution, The occurrence of spin due to oversteering tendency of the vehicle is avoided. As a result, the travel limit of the vehicle is significantly improved, and even a driver who is unfamiliar can safely and easily enjoy sports travel in the rear wheel drive mode.

[Brief description of drawings]

1 to 6 show a driving force distribution switching type four-wheel drive vehicle as a first embodiment of the present invention. FIG. 1 is a schematic configuration diagram of its drive system, and FIG. 2 is its control content. FIG. 3 is a flowchart showing FIG.
FIG. 4 is a diagram showing the frequency response of yaw angular acceleration with respect to steering angular velocity, FIGS. 5 and 6 are diagrams showing simulation results relating to vehicle spin, and FIGS. 7 and 8 are the second embodiment of the present invention. FIG. 7 shows an example of a driving force distribution switching type four-wheel drive vehicle. FIG. 7 is a schematic configuration diagram of its drive system, FIG. 8 is a flowchart showing its control contents, and FIG. It is a schematic diagram which shows the state of spin. 2 ... engine, 4 ... torque converter, 6 ... automatic transmission, 8 ... output shaft, 10 ... intermediate gear, 11,13 ... hydraulic multi-plate clutch as control means, 14 ... differential gear Device, 15 …… Bevel gear mechanism, 16 …… Front wheel, 17L, 17R ……
Axle, 18 …… Front wheel, 19 …… Reduction gear mechanism, 20 …… Propeller shaft, 21 …… Bevel gear mechanism, 22 …… Differential gear unit, 24 …… Rear wheel, 25L, 25R …… Axle, 28 …… Hydraulic multi-plate clutch, 30 …… Steering sensor (steering angle detection means), 32 ……
Steering wheel, 34a ... front lateral acceleration sensor (front lateral acceleration means), 34b ... rear lateral acceleration sensor (rear lateral acceleration means), 36 ... longitudinal acceleration sensor, 38 ...
… Throttle sensor, 39 …… Engine key switch, 41
...... Engine speed sensor, 40,42,44,46 …… Wheel speed sensor, 48 …… Controller, 48a …… Yaw angular acceleration calculation unit, 48b …… Determination unit, 48c …… Control signal output unit, 50 ・ ・ ・… Anti-lock brake device, 50A …… Brake switch, 5
0B …… Brake (braking means), 51 …… Brake pedal,
52 …… Warning light, 54 …… Hydraulic source, 56 …… Pressure control valve.

Claims (2)

(57) [Claims] 1. A four-wheel drive vehicle capable of transmitting an output torque of an engine to front wheels and rear wheels to drive a vehicle, and a driving force distribution control capable of distributing the output torque to the front wheels and the rear wheels. Means, front lateral acceleration detecting means for detecting a lateral acceleration applied to the front portion of the vehicle, rear lateral acceleration detecting means for detecting a lateral acceleration applied to the rear portion of the vehicle, and steering for detecting a steering angular velocity of the vehicle. An angular velocity detecting means and a control means for outputting a control signal for controlling the distribution state of the driving force to the front wheels and the rear wheels based on the information from these detecting means are provided. Of the yaw angular acceleration of the vehicle based on the lateral acceleration detected by each of the lateral acceleration detection means, based on the value of the calculated yaw angular acceleration and the value of the detected steering angular velocity Current vehicle status A determination unit that determines whether an excessive driving force should not be transmitted to the rear wheels or a state in which the rear wheels should be driven mainly, and the driving force distribution based on the determination result of the determination unit. A driving force distribution switching type four-wheel drive vehicle, comprising: a control signal output section for outputting a control signal of a predetermined driving state to the control means. 2. A four-wheel drive vehicle capable of transmitting an engine output torque to front wheels and rear wheels to drive a vehicle, and a driving force distribution control capable of distributing the output torque to the front wheels and the rear wheels. Means, front lateral acceleration detecting means for detecting a lateral acceleration applied to the front portion of the vehicle, rear lateral acceleration detecting means for detecting a lateral acceleration applied to the rear portion of the vehicle, and steering for detecting a steering angular velocity of the vehicle. An angular velocity detecting means and a control means for outputting a control signal for controlling the distribution state of the driving force to the front wheels and the rear wheels based on the information from these detecting means are provided. Of the yaw angular acceleration of the vehicle based on the lateral acceleration detected by each of the lateral acceleration detection means, based on the value of the calculated yaw angular acceleration and the value of the detected steering angular velocity Yaw angular acceleration And a yaw angular acceleration value based on the result of the judgment by the judgment unit for judging whether or not the value is equal to or larger than the value of the steering angular velocity. If there is, a control signal for the rear wheel drive mode or a drive mode mainly for the rear wheels is output to the driving force distribution control means, and if the value of the yaw angular acceleration is more than a suitable value, the driving force distribution control means outputs to the front wheels. A four-wheel drive vehicle with a drive power distribution switchover type, comprising a control signal output section for outputting a control signal for a drive mode or a four-wheel drive mode not mainly for rear wheels.