JPH03189241A - Four-wheel drive device - Google Patents

Abstract

PURPOSE:To have good turning performance and maneuvering compatibly stability, in an arrangement of rear-wheel drive type equipped with wheel clutches in which the transmitted torques to the left and right wheels are changed, by performing proper control of the wheel clutches in accordance with the result from sensing of the change in steering angle at the time of cornering. CONSTITUTION:In a rear wheel drive system 20 in which the torque given from a power plant 3 is transmitted to the left and right rear axles 24, 25 through a rear wheel drive shaft 21 and bevel gears 22, 23, a left and a right wheel clutch 26, 27 are mounted on the left and right axles 24, 25. The clutches 26, 27 are of multi-plate type oil-hydraulically controlled, and are connected with oil pressure supply passages 31, 32 fitted with oil pressure control valves 33, 34. These oil pressure supply passages 31, 32 are controlled by a controller 35, into which the output signal from a steering angle sensor 41 is entered, so that the power distribution share to the rear wheel drive system is enlarged in the initial period of cornering where for ex. the change rate of steering angle exceeds a certain level and also that the torque share to the outer rear wheel about cornering is made greater than that to the inner rear wheel about cornering.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a four-wheel drive system installed in a vehicle that drives front wheels and rear wheels using the output of a power plant.

(Prior Art) For example, as shown in Japanese Unexamined Patent Publication No. 181916/1983, in a vehicle that transmits driving force from a power plant to the rear wheels, the driving force is transmitted to the drive system of the left and right rear wheels. By installing variable-torque hydraulic clutches and controlling the transmission torque of these clutches, the torque distribution between the left and right wheels can be variably controlled according to the vehicle's driving conditions, improving driving performance when turning, etc. It is known what has been done.

By the way, the configuration in which the torque distribution between the left and right wheels is variably controlled using a clutch that controls the transmission torque for each wheel (hereinafter referred to as a wheel clutch) as described above is applicable to the rear wheel drive system of a four-wheel drive vehicle. In this case, the output of the power plant would directly drive the front wheels, and the left and right rear wheels would each be driven via wheel clutches.

According to this, it is possible to variable control the torque distribution between the left and right rear wheels equipped with wheel clutches, and by controlling the total torque transmission amount of both wheel clutches, the torque distribution between the front and rear wheels can be controlled. Variable control, switching control from a four-wheel drive state to a two-wheel drive state, etc. are possible, and there is a hope that good running performance can be obtained in various running conditions.

(Problem to be Solved by the Invention) However, when left and right wheel clutches are provided in the rear wheel drive system of a four-wheel drive vehicle as described above, torque is distributed between the left and right rear wheels in relation to the front wheels that are constantly driven. The problem to be solved is how to control this, especially when trying to further improve turning performance.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to realize a four-wheel drive device that can further improve cornering performance when a wheel clutch as described above is applied to a four-wheel drive vehicle.

(Means for Solving the Problem) That is, a four-wheel drive device according to the present invention includes a power plant that generates driving force, and a front wheel drive that transmits the output of the power plant to left and right front wheels and left and right rear wheels, respectively. In a configuration having a rear wheel drive system, and left and right wheel clutches that are provided in the power transmission section to the left and right wheels in the rear wheel drive system and respectively control the transmission of power to these wheels, a steering angle detection means for detecting a steering angle; and at the beginning of a turn when a change rate of the steering angle detected by the detection means is equal to or greater than a predetermined value, increasing the distribution ratio of the power plant output to the rear wheel drive system; If the two wheel clutches are controlled so that the torque distribution of the outer wheel in the turning direction among the left and right rear wheels is larger than the torque distribution of the inner wheel, and the steering angle shifts to a stable turning state where the steering angle is approximately constant, A control means for controlling the wheel clutches so that the distribution ratio to the rear wheel drive system gradually decreases (Function) According to the above structure, the engagement/disengagement control of the left and right wheel clutches Alternatively, variable control of transmission torque can be used to control switching between a 4-wheel drive state in which the front and rear wheels are driven and a 2-wheel drive state in which only the front wheels are driven, and torque distribution between the front and rear wheels in the 4-wheel drive state. It also becomes possible to control the torque distribution between the left and right rear wheels.

In particular, according to the above configuration, at the beginning of a turn when the rate of change in the steering angle detected by the steering angle detection means is equal to or higher than a predetermined value, the distribution ratio of the power plant output to the rear wheel drive system is large; The wheel clutches are controlled so that the torque distribution of the wheels on the outside in the turning direction of the left and right rear wheels is larger than the torque distribution of the wheels on the inside. Orality is obtained.

On the other hand, when the above state shifts to a stable turning state where the steering angle is approximately constant, the wheel clutches are controlled so that the torque distribution to the rear wheel drive system gradually decreases, so that the vehicle gradually shifts to a stable turning state where the steering angle is approximately constant. Shifts to two-wheel drive mode,
As a result, the driving condition changes to a tendency toward understeer, thereby improving steering stability.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the general configuration and control system of a four-wheel drive vehicle according to this embodiment. This four-wheel drive vehicle includes a power plant 3 consisting of an engine 1 and a transmission 2, The driving force generated in 3 is transferred to a pair of transmission gears 4.
5, and has a front wheel drive system 10 and a rear wheel drive system 20 that drive left and right front wheels 6.7 and left and right rear wheels 8.9, respectively.

The front wheel drive system 10 includes a front wheel drive shaft 11 that is disposed in the longitudinal direction of the vehicle body and is driven by the driving force from the power plant 3 via the gear 4.5, and a front wheel drive shaft 11 that transmits power input from the shaft 11 to the left and right sides. a differential device 12 that divides the device 12 into
The left and right axles 13 and 14 transmit the power divided by the left and right front wheels 6.7, respectively, so that the left and right front wheels 6.7 are constantly driven by the driving force from the power plant 3. It has become.

On the other hand, the rear wheel drive system 20 includes a rear wheel drive shaft 21 which is also arranged in the longitudinal direction of the vehicle body and is driven by the driving force from the power plan 1-3 via the gear 4.5, and the drive shaft. 21 through a pair of bevel gears 22, 23, and left and right axles 24, 25 that transmit power to left and right rear wheels 8, 9, respectively.

In this rear wheel drive system 20, left and right axles 2
4.25, from the rear wheel drive shaft 21 side to the left and right rear wheels 8.9
Left and right wheel clutches 26 and 27 are provided, respectively, for connecting and disconnecting power transmission to the sides and changing the transmitted torque. These wheel clutches 26 and 27 are all multi-plate hydraulic clutches, and hydraulic pressure supply passages 31 and 32 led from a hydraulic power source (not shown) are connected to these passages 31 and 32. 26.27
Hydraulic control valves 33 and 34 are provided for controlling the supply and discharge of hydraulic pressure to and from the cylinders, respectively.

Furthermore, the control system includes the hydraulic control valves 33 and 34.
A controller 35 is provided to control the operation of the hydraulic control valves 33 and 34, and the hydraulic control valves 33 and 34 are controlled to open and close according to control signals a and b output from the controller 35, thereby supplying and discharging hydraulic pressure to and from the left and right wheel clutches 26 and 27. This controls the connection and disconnection of both wheel clutches 26 and 27 or the transmission torque thereof.

The controller 35 receives signals c, d, and e from each wheel speed sensor 36 to 39 that detects the rotational speed of the front, rear, left, and right wheels 6 to 9, respectively, for each of the above-mentioned controls.
, f, a signal g from a steering angle sensor 41 that detects the amount of operation of a steering wheel 40 provided at the driver's seat of the vehicle, that is, the amount of steering angle, and a lateral acceleration sensor that detects lateral acceleration acting on the vehicle body when turning. 42, and a signal i indicating whether or not ABS control is in progress from an ABS controller 43 that controls the operation of an ABS (anti-lock braking system) provided in the vehicle.
The controller 35 controls the left and right wheel clutches 26 and 27 based on these input signals C to i.

Next, the operation of this embodiment will be explained according to a flowchart showing the control operation of the controller 35.

FIG. 2 shows the main routine of the control operation of the controller 35. First, in step S1, the controller 35
initializes various variables, flags, and others used in the following control, and then in step S2 determines the degree of engagement of the left and right wheel clutches 26, 27, in other words, the torque distribution ratio for the left and right rear wheels 8.9. do. Then, in step S3, control signals a and b are output to the hydraulic control valves 33, 34 shown in FIG. 1 so that the degree of engagement of both wheel clutches 26, 27 becomes the value determined in step S2.

In this embodiment, the determination control of the degree of engagement of the wheel clutches 26, 27 in step S2 is performed as follows by the subroutine shown in FIG.

That is, in this control, first in step S11, each wheel of the left front wheel 6, the right front wheel 7, the left rear wheel 8, and the right rear wheel 9 is Input the steering angle amount θ of the steering wheel 40, its rate of change, vehicle speed ■, and lateral acceleration G, and also input a signal i from the ABS controller 43 to determine whether ABS control is being performed. Input the ABS activation signal F ABS indicating Here, the change rate S is calculated based on the change in the steering angle amount θ, and the vehicle speed (2) is the slowest of the wheel speeds ωFL, ωFR1ωRL, and ωRλ.

Next, the controller 35 performs the above A in step SI2.
The value of the BS operation signal FABfi is determined, and if it is 1, that is, if the ABS control is currently being performed by the ABS controller 43, the torque distribution ratios TRL and TRR of the left and right rear wheels 8.9 are determined in step S13. Set both to O. Therefore, in this case, the left and right wheel clutches 26.
Hydraulic pressure is not supplied to any of the wheels 27, the axles 24.25 are cut off, and no driving force is transmitted to the left and right rear wheels 8.9. This is to ensure that the left and right rear wheels 8.9 can freely rotate and perform ABS control accurately.

On the other hand, when ABS control is not performed, F^85=
0, the controller 35 executes steps S12 to S14, and the absolute value of the steering angle amount θ is the predetermined value θ. Determine whether it is smaller. This predetermined value θ0 is an extremely small value indicating the width of the dead zone, and is 1θ1×θ. In this case, it is determined that the steering wheel 40 is not being operated and the vehicle is traveling straight.

Then, when the controller 35 is in the straight-ahead state,
First, in step S+5, both the turning flag FC and the timer flag FTM used for control during turning, which will be described later, are reset to 0, and then in step S16, the rotational speed difference Δω1 between the front and rear wheels is calculated according to the following equation.

Δω1 =(ωPL+ωPc)−(ωRL+ωI) Furthermore, in step SI7, the controller 35 applies the above speed difference Δωl to the preset map shown in FIG. 4, and determines the final torque distribution ratio TRL of the rear wheels 8.9. , find the first rear wheel distribution ratio T1 used for determining TRR. In that case, the map in FIG. Since the wheel distribution ratio T1 is set to be large, for example, if the driving force applied to the front wheels 6.7 is excessive and slip occurs, the I for the rear wheels 8.9 will be adjusted according to the degree of slippage. - The torque distribution ratio is increased and the slip of the front wheels 6.7 is suppressed.

Further, in step SI8, the controller 35 calculates the rotational speed difference Δω2 between the left and right wheels according to the following equation.

Δω2: (ωFL+ωR,)-(ωFR+ωRR)
Then, in step SI9, the absolute value of this speed difference Δω2 is applied to the map shown in FIG. 5 to determine the second wheel distribution ratio T2, which is also used to determine the final torque distribution ratios TILL and 'r''RR. In that case, the map in Figure 5 is 1
Since the second rear wheel distribution ratio T2 is set to be larger as Δω21 is larger, for example, if the el friction coefficient of the road surface to the left and right wheels is different and a speed difference occurs between the left and right wheels, the rear wheel distribution ratio T2 is set to be larger. By increasing the torque distribution ratio with respect to 8.9, the running stability of the vehicle when running on such a road surface is ensured.

Further, in step S20, the controller 35 applies the vehicle speed ■ to the map shown in FIG. 6 to determine the third rear wheel distribution ratio T3, which is also used to determine the final torque distribution ratios TRL and TRR. In that case, since the map in FIG. 6 is set so that the third torque distribution ratio T3 increases as the vehicle speed V increases in the high vehicle speed range, the rear wheels 8.
The torque distribution ratio relative to 9 is increased, resulting in increased straight-line stability.

Then, the controller 35 executes step S2□ to obtain the first to third rear wheel distribution ratios T obtained as described above.
1. Select the largest one from T2 and T3 and use it as the total torque distribution ratio T for the left and right rear wheels, 8.9.
R, and in step S22, this total rear wheel distribution ratio T. Divide into two and connect these to the left and right rear wheels8.
The final torque distribution ratios TRL and TRR for 9 are assumed to be the final torque distribution ratios TRL and TRR.

In this way, the torque distribution ratios TRL and TRR for the left and right rear wheels 8.9 when traveling straight are determined, but in that case, as is clear from the maps in Figs. During normal driving, such as when there is no rotational speed difference between the left and right wheels and the vehicle speed is not particularly high, the first
~ Since the third rear wheel distribution ratios T, , T2, and T3 are all 0, it becomes a two-wheel drive state in which the driving force from the power plant 3 is transmitted only to the front wheels 6.7, and each of the above distribution ratios If at least one of T1, T2, and T3 is not 0, a four-wheel drive state is established in which driving force is also transmitted to the rear wheels 8.9. In this four-wheel drive state when traveling straight, the torque distribution ratio between the left and right rear wheels 8.9 is always set equally. In addition, each of the above rear wheel distribution ratios T r , T2
, Ts is the maximum value (0, 5>),
Drive power is distributed evenly between the front and rear wheels, resulting in a quarter of the powerplant's output being transmitted to all wheels.

On the other hand, during a turn when the steering angle amount θ of the steering wheel 40 is equal to or greater than the predetermined value 60, the controller 35 executes steps S14 to S23 described above and determines the value of the turning flag Fc. This flag Fc becomes 1 in a stable turning state where the steering angle amount θ stops increasing during the O1 turn while the steering angle amount θ is increasing when traveling straight and at the beginning of a turn. Therefore, at the time of transition from the straight-ahead state to the turning state, since F c = 0, the controller 35 performs step S2S.
Step S24 is then executed to determine whether the absolute value of the steering angle amount change rate θ is greater than 0. Since this value is greater than O at the start of a turn, step S25 is further executed to determine whether the steering angle amount change rate θ is greater than 0. Maximum value of change rate up to the present moment max
Let (θ) be the rate of change at that point (at the start of a turn, the rate of change at this point is the maximum value ma
x (6)).

Then, in step S26, base distribution ratios T RLB and T RRII of the left and right rear wheels 8.9 corresponding to the change rate 6 are set based on the map shown in FIG. In that case, if the change rate skew becomes a positive value when the steering angle amount θ increases when the steering wheel is operated to the left, then the seventh
As shown in the figure, when the steering wheel is operated in that direction, the base distribution ratio TRRB of the right rear wheel 9 is set to a larger value than the base distribution ratio TRLB of the left rear wheel 8, and conversely, when the steering wheel is operated to the right, The base distribution ratio TRLB of the left rear wheel 8 is set to a larger value than the base distribution ratio TRRB of the right rear wheel 9, and these base distribution ratios TRLB, TRR
B is set to a larger value as the steering angle amount change rate θ becomes larger.

Then, in step S27, the base distribution ratios TRLB, TRRB set in this way are replaced as they are with the final torque distribution ratios TRL, TRR for the left and right rear wheels 8.9.

As a result, as shown in Fig. 9, during the period (A) in which the rate of change in the amount of steering angle at the beginning of a turn is increasing, the final torque distribution ratios TRL and TRR also increase in accordance with the increase, and this distribution With the ratio TRL and TR8, the left and right rear wheels are driven 8.9, and after the rate of change reaches the maximum value 6 MAX, 0
During the period (b) during which the steering angle amount θ stops increasing and stabilizes at a constant steering angle θl, the maximum distribution ratio (b) corresponding to the maximum value b MAX of the steering angle amount change rate B T.R.L.
) MAX, (T RR) will be held at MAX. In this way, until the transition to a stable turning state where the amount of steering angle is constant, a large distribution ratio is given to the rear wheels 8.9, and moreover, the rear wheels on the outside of the turning direction have a larger distribution ratio than the rear wheels on the inside. By giving the distribution, the vehicle exhibits a tendency to oversteer, and good turning performance at the beginning of a turn can be obtained.

Thereafter, when the steering angle amount change rate becomes O and the state shifts to a stable turning state, the turning flag Fc is set to 1 in step 328, so the controller 35 next executes steps S23 to 329, Timer flag FT
Determine the value of M. This flag FTM is initially 0, so the controller 35 then, in step SSO,
A constant co for decreasing the torque distribution ratio to the rear wheels 8 and 9 is set. This constant CO is set based on the map shown in Fig. 8, and is a constant steering angle amount θ during stable turning.
The larger the absolute value of , the smaller the value is set.

Then, in step S3t, the timer flag FTM is set to 1.
and clear the torque distribution ratio reduction value C to O, and in step S3□, the torque distribution ratio reduction coefficient K is calculated using this reduction value C according to the following equation.

K=(1000-C)/1000 Here, the numerical value (1000) is an example value determined in relation to the control cycle period, and in this case, the constant C8 has a value of 1000 or less.

Initially, the reduction coefficient is 1, but in the next and subsequent control cycles, steps S29 to S33 are executed (FTM=1), and a constant C6 is sequentially added to the reduction value C in each cycle. As it gradually decreases from
When it is determined in step S34 that the value has decreased to 0 or less, it is fixed to O in step S35.

Then, in step S36, the controller 35 converts the reduction coefficient K, which changes from 1 to 0 as described above, into a base distribution ratio T RLB (-(T KL) MAX),
Multiply by TRRB (= (TRR) MAX),
Calculate the final torque distribution ratios T RL and T RR for the rear wheels 8.9.

In this way, the final torque distribution ratios TRL and TRR are
As shown in Figure 9, during the stable turning period (c),
Maximum allocation ratio (TRL) MAX, (
TRR) □ will be gradually decreased from X to O,
The vehicle gradually transitions from a four-wheel drive state to a two-wheel drive state where only the front wheels are driven, and the oversteer tendency at the beginning of the turn shifts to the understeer tendency, resulting in stable driving in the middle of the turn. You will gain sex. In particular, the constant C8 is set to a smaller value as the constant steering angle amount θ1 increases, so that when the constant steering angle amount θ1 is large, the rear wheel 8.9
The torque distribution ratios TRL and TFLR are reduced to 0 over a longer period of time than when the steering angle amount θ is small, so that the transition to the two-wheel drive state is always performed smoothly.

(Effects of the Invention) As described above, according to the present invention, in a four-wheel drive system in which a rear wheel drive system is provided with a wheel clutch that variably controls transmission torque to left and right wheels, the steering angle of the vehicle is detected. By providing a means and appropriately controlling the wheel clutch based on the change in steering angle during turning detected by the detecting means, both good retrospective performance and steering stability can be achieved. Therefore, the effect of further improving the turning performance in a four-wheel drive vehicle can be obtained.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, and FIG. 1 is a diagram showing the general configuration and control system of a four-wheel drive vehicle, FIG. 2 is a flowchart showing the main routine of the control operation, and FIG.
The figure is a flowchart showing the subroutine of the vehicle clutch engagement degree determination control, Figures 4 to 8 are explanatory diagrams of each map used in this control, and Figure 9 is a time chart diagram showing the specific operation of this control. . 3...Power plant, 6.7...Front wheel, 8.9.
... Rear wheel, 10... Front wheel drive system, 20... Rear wheel drive system, 26.27... Wheel clutch, 35... Control means (controller), 41... Steering angle detection means ( steering angle sensor).

Claims (1)

[Claims] (1) A power plant that generates driving force, a front wheel drive system and a rear wheel drive system that transmit the output of the power plant to the left and right front wheels and the left and right rear wheels, respectively, and the power plant that transmits the output of the power plant to the left and right front wheels and the left and right rear wheels, respectively. A four-wheel drive device having left and right wheel clutches provided in a power transmission section and controlling transmission of power to these wheels, respectively, comprising: a steering angle detection means for detecting a steering angle of the vehicle; At the beginning of a turn when the rate of change in the steering angle detected by the means is greater than or equal to a predetermined value, the distribution ratio of the power plant output to the rear wheel drive system is increased, and among the left and right rear wheels, the outer wheel in the turning direction is If the two wheel clutches are controlled so that the torque distribution of the rear wheel is larger than that of the inside wheel, and the steering angle reaches a stable turning state where the steering angle is approximately constant, the distribution ratio to the rear wheel drive system gradually decreases. A four-wheel drive device comprising: control means for controlling the wheel clutches so as to control the wheel clutches.