JPH04154437A - Drive force control device for four-wheel drive vehicle - Google Patents

Abstract

PURPOSE:To maintain actual yaw rate nearly the same as target yaw rate to obtain favorable turning performance in the case of judging the coupling force of a clutch to be in critical value by reducing engine torque when the actual yaw rate is deviated from the target yaw rate. CONSTITUTION:Rotation difference between front and rear wheels is controlled by coupling force of a clutch with a rotation difference control clutch 100. Meanwhile, actual yaw rate is detected by an actual yaw rate detecting means 101, and target yaw rate is computed by a target yaw rate computing means 102. The coupling force is controlled by a coupling force control means 103, so as to conform the actual vat rate to the target yaw rate. Further, whether the coupling force reaches a critical value or not is judged by a judging means 104. When the coupling force is judged to reach the critical value and the actual yaw rate is deviated from the target yaw rate, engine torque is controlled to be lowered by an engine torque control means 105.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a driving force control device for a four-wheel drive vehicle.

[Conventional technology]

Equipped with a multi-disc clutch to control the difference in rotation between the front and rear wheels by the engagement force of the clutch, the engagement force of the multi-disc clutch is controlled by the hydraulic pressure supplied to the multi-disc clutch, and the actual yaw rate is equal to the target yaw rate. A four-wheel drive vehicle has been disclosed which controls the oil pressure so that the
(See Publication No. 198522).

[Problem to be solved by the invention]

However, in this four-wheel drive vehicle, there is a limit to the engagement force of the multi-disc clutch, and when this engagement force reaches the limit, the actual yaw rate cannot be controlled by the multi-disc clutch. Therefore, if the actual yaw rate deviates from the target yaw rate when the engagement force of the multi-disc clutch reaches its limit, the actual yaw rate cannot be made to match the target yaw rate, and as a result, the vehicle's turning performance is improved. The problem is that it cannot be obtained.

[Means to solve the problem]

In order to solve the above problems, according to the present invention, as shown in the configuration diagram of the invention in FIG. an actual yaw rate detection means 101 for detecting the yaw rate); a target yaw rate calculation means 102 for calculating the target yaw rate; This is a case where the fastening force control means 103, the judging means 104 that determines whether the fastening force has reached the limit value, and the judging means 104 determine that the fastening force has reached the limit value.

The engine torque control means 105 reduces the engine torque when the actual yaw rate deviates from the target yaw rate.

[For production]

When it is determined that the clutch engagement force has reached the limit value and the actual yaw rate deviates from the target yaw rate, the engine torque is reduced to a low level. This allows the actual yaw rate to be brought closer to the target yaw rate.

〔Example〕

Referring to FIG. 2, the output of the engine 1 is transmitted to a center differential 3 via an output shaft 2. The center differential 3 has the function of equally distributing the driving force of the engine 1 to the front wheel drive shaft 4 and the rear wheel drive shaft 5, and the function of absorbing the rotation difference between the front wheel drive shaft and the rear wheel drive shaft that occurs when the vehicle turns. ing. The driving force transmitted to the center differential 3 is transmitted to the rear propeller shaft 6.
The signal is then transmitted to the rear wheel drive shaft 5 via the rear differential 7, thereby driving the left and right rear wheels 8, 9. Further, the driving force transmitted to the center differential 3 is transmitted to the front wheel drive shaft 4 via the front propeller shaft 10 and the front differential 11, thereby driving the left and right front wheels 12 and 13. A multi-plate clutch 14 is provided between the rear propeller shaft 6 and the front propeller shaft 10 in parallel with the center differential 3. The multi-disc clutch 14 has an oil passage 1
Hydraulic pressure P0 is supplied from an oil pump 16 via 5. Drain passage 1 branched from the middle of oil passage 15
A solenoid valve 18 is disposed in the middle of the valve 7, and can control the amount of drain oil to the oil tank 19 according to the current value. Therefore, by controlling the solenoid valve 18, the oil pressure P0 supplied to the multi-disc clutch 14 can be controlled. The engagement force of the multi-disc clutch 14 increases as the oil pressure Pc increases. The engagement force of the multi-disc clutch 14 acts as a force that limits the rotational difference between the front drive shaft 4 and the rear drive shaft 50, and the engagement force increases as the oil pressure Pc increases. Therefore, the allowable value of the rotational difference between the front wheel drive shaft 4 and the rear wheel drive shaft 50 becomes small.

A throttle valve 21 is disposed in an intake passage 20 of the engine 1, and the throttle valve 21 is driven and controlled by a control motor 22.

The electronic control unit 30 consists of a digital combicoater with ROMs interconnected by a bidirectional bus 31.
(read only memory) 32, RAM (random access memory) 33, CPU (microprocessor) 34
, an input port 35 and an output port 36.

The throttle opening sensor 50 detects the opening of the throttle valve 210, and this detection signal is input to the manual port 35 via the AD converter 37. Front wheels12.13 and rear wheels8.
9 is provided with wheel speed sensors 51, 52, 53, and 54 for detecting the rotational speed of each wheel, and these detection signals are input to the input port 35. Vehicle speed sensor 55 detects vehicle speed, and its detection signal is input to input port 35 . The steering angle sensor 56 detects the steering angle of the front wheels, and this detection signal is input to the input port 35 via the AD converter 38. Yaw rate sensor 57 detects the actual yaw rate, and this detection signal is input to input port 35 via AD converter 39.

On the other hand, the output port 36 has corresponding drive circuits 40 and 41
.

42, the engine 10 is connected to a spark plug (not shown), a control motor 22, and a solenoid valve 18, respectively.

When the vehicle is turning, the engagement force of the multi-disc clutch 14 is controlled so that the actual yaw rate detected by the yaw rate sensor 57 is equal to the target yaw rate calculated based on the vehicle speed and steering angle. For example, when the actual yaw rate is smaller than the target yaw rate, that is, in the case of understeer, the hydraulic pressure Pc supplied to the multi-disc clutch 14 is reduced, thereby reducing the engagement force of the multi-disc clutch 14. For this reason, front wheel 1
Since the difference in rotation between 2.13 and the rear wheel 8.9 can be increased, the actual yaw rate can be increased and brought closer to the target yaw rate. On the other hand, when the actual yaw rate is greater than the target yaw rate, that is, in the case of oversteer, the operation is opposite to the above.

In this way, good turning performance can be obtained.

However, in the case of understeer, for example, the oil pressure Pc supplied to the multi-disc clutch 14 is set to the minimum oil pressure PXI).
Even if the engagement force of the multi-disc clutch 14 is set to the minimum value as I, if the actual yaw rate is smaller than the target yaw rate,
There is a problem in that the actual yaw rate cannot be made equal to the target yaw rate, and good turning performance cannot be obtained.

On the other hand, in the case of oversteer, even if the hydraulic pressure Pc is set to the maximum hydraulic pressure PXAX and the engagement force of the multi-disc clutch 14 is set to the maximum value, if the actual yaw rate is larger than the target yaw rate, the actual yaw rate cannot be made equal to the target yaw rate. However, there is a problem in that good turning performance cannot be obtained.

Therefore, in this embodiment, the oil pressure P supplied to the multi-disc clutch 14.

is the minimum oil pressure P! If the actual yaw rate does not match the target yaw rate even when the maximum oil pressure P MAX is set, the engine torque is reduced to make the actual yaw rate match the target yaw rate.

The reason why the actual yaw rate can be made equal to the target yaw rate by reducing the engine torque is as follows.

First, let's consider the case of understeer.

Figure 3 is a model showing only the two wheels turning to the right.

When the vehicle is turning, lateral force FFL'FI is applied to the front and rear wheels.
LL is acting, the lateral force FFL acting on the front wheels 13 is acting in the direction of the yaw motion of the vehicle, and the lateral force F acting on the rear wheels 9 is
IIL acts in a direction opposite to the direction of vehicle yaw motion. In the case of understeer, the lateral force FFL acting on the front wheels is insufficient relative to the lateral force FILL acting on the rear wheels. In this case, the driving force Q of the front wheels and the lateral force F
The relationship between FL and FL is shown in FIG. 4 using the concept of a friction circle. The radius of the friction circle indicates the maximum grip force of the tire, and the resultant force of the driving force and lateral force cannot exceed the friction circle.

In this case, the resultant force of the driving force Q and the lateral force FFL has almost reached its maximum value, and the lateral force FFL cannot be increased. Therefore, by reducing the engine torque, the driving force Q,
The lateral force FFL can be increased by decreasing (
(indicated by dotted line). Furthermore, when the engine torque is reduced, negative acceleration is generated, which causes the center of gravity to move forward, thereby relatively increasing the ground load on the front wheels. Therefore, the maximum grip force of the tire, that is, the radius of the friction circle increases, so that the lateral force FPL can further increase. - On the other hand, the relationship between the rear wheel driving force (b) and the lateral force FIL is as shown in Fig. 5.The resultant force of the driving force Qi and the lateral force FIL has not reached its maximum value, so the engine torque Even if the driving force Ql is decreased, the lateral force FIL hardly changes.As a result of the above, when the engine torque is reduced during understeer, the lateral force FFL of the front wheels increases relative to the lateral force FIL of the rear wheels. In order to do so, the actual yaw rate is increased to be equal to the target yaw rate, and good turning performance can be obtained.

On the other hand, in the case of oversteer, the lateral force FI acting on the rear wheels
L is relatively insufficient compared to the lateral force FFL acting on the front wheels. In this case, at the rear wheels, the resultant force of the driving force Qi and the lateral force FIL has almost reached its maximum value, and the lateral force FI
L is in a state where it cannot be increased. Therefore, by reducing the engine torque and reducing the driving force Q11, the lateral force FIL can be increased. In the front wheel,
The resultant force of the driving force QF and the lateral force FFL has not reached the maximum value, so the engine torque is reduced and the driving force Q,
Even if the lateral force FFL is decreased, the lateral force FFL hardly changes. As a result of the above, when engine torque is reduced during oversteer, the lateral force FIL on the rear wheels increases relative to the lateral force FFL on the front wheels, so the actual yaw rate is decreased and made equal to the target yaw rate, resulting in a good result. It is possible to obtain excellent turning performance.

FIG. 6 shows a routine for executing this embodiment.

This routine is executed by interrupts at regular intervals. Referring to FIG. 6, first, in step 60, the rotational speeds W and L of the left front wheel 12, right front wheel 13, left rear wheel 8, rear right wheel 9, and the rear right wheel 9 are determined.

W, , W, L, W□, front wheel steering angle δ, vehicle speed V1
The actual yawlay) T and throttle valve opening θ are read. Next, in step 61, the rotation difference ΔN between the front and rear wheels is calculated.

is calculated by the following formula.

Next, in step 62, the vehicle starting oil pressure PST is calculated from the following equation.

PST: KI - Kl ・ PST0 Here, Kl
and 2 are coefficients, and PST0 is the standard oil pressure.

As shown in Fig. 7, 1 is a function of the absolute value 1δ1 of the steering angle, and while 1δ1 is smaller than a certain value δ,i, 1 is 1, and when 1δ1 becomes larger than δ,1, gradually decreases. The reason why 1 is decreased as 1δ1 increases is that as the absolute value of the steering angle increases, that is, as the turning radius decreases, KI is decreased to reduce the oil pressure supplied to the multi-disc clutch 14. This is to make it smaller. Kl is the throttle opening θ as shown in Figure 8.
2 is 1 when θ is less than θ1, and as θ increases from θ1 to θ2, 2 also increases,
When θ is 02 or more, it becomes a constant value. 2 as θ increases
The reason for increasing this is to increase the hydraulic pressure as the load increases, making it difficult to turn.

Next, in step 63, the oil pressure P when one wheel slips.

is calculated. Ps is the rotational difference Δ as shown in FIG.
It is a function of N□ and vehicle speed V. Ps increases as ΔNFR increases, and decreases as ■ increases.

In step 64, the vehicle high-speed operation oil pressure PIIS is calculated. As shown in FIG. 10, Fils is a function of the vehicle speed ■ and the absolute value iδ1 of the front wheel steering angle. Fils increases as V increases and decreases as 1δI increases.

In step 65, the maximum of P, A, Ps and Fils is set as the basic oil pressure P. Set to 0. In step 66, the target yawlay (To) is calculated based on the following equation.

As shown in FIG. 11, K is a function of vehicle speed.

S is a Laplace operator and T is a time constant.

In step 67, the difference between the actual yaw rate T and the target yaw rate T0 is calculated based on the following equation.

Δr=r·(To T) Here, for r is multiplied by T in order to unify the sign of ΔT to be negative in the case of oversteer and to be positive in the case of understeer. That is, the 1211th! As shown in I, if turning right is taken as negative and turning left as positive,
During oversteer, ΔT becomes negative both when turning to the right and when turning to the left. Although not shown, similarly, during understeer, Δ
γ is positive.

Next, in step 68, □ is calculated as a correction coefficient. K
Yll is a function of Δγ as shown in FIG.

When Δγ is 0, that is, when the actual yaw rate T matches the target yaw rate (To), KYl is 1, and Δ
As γ increases from 0 to α, □ decreases, when Δγ is greater than or equal to α, MA becomes a constant value, as ΔT decreases from 0 to 1 α, Kyl increases, and when ΔT is less than 1 α, □ decreases. □
is a constant value.

Next, in step 69, the multi-disc clutch 1 is calculated based on the following equation.
4 is calculated.

Pc = Pea-Kvm In other words, the oil pressure Pc is reduced as the difference between the actual yaw rate T and the target yaw rate To increases during understeer, and the difference between the actual yaw rate T and the target yaw rate T during oversteer.

The larger the difference, the greater the oil pressure.

Next, in step 70, the relaynoid valve 18 is controlled based on the oil pressure Pc to be supplied to the multi-disc clutch 14.

In step 71, it is determined whether the oil pressure Pc is below the minimum oil pressure PxrNJ2J or whether the oil pressure Pc is greater than or equal to the maximum oil pressure PXAX. When it is determined that P, , I, Pc, pxAx, this routine ends. If Pc≦pxrN or Pc≧P is determined to be □, proceed to step 72;
It is determined whether 1Δrl>ε1. ε is a sufficiently smaller value than α (see FIG. 13), and in this step it is determined whether the actual yaw rate γ substantially matches the target yaw rate To. If 1ΔT1≦ε, it is determined that the actual yaw rate T substantially matches the target yaw rate T0, and this routine ends. If 1Δγ〉ε,
That is, the actual yaw rate T is the target yaw rate γ. If it is determined that there is a deviation, the process advances to step 73. In step 73, an ignition timing retard amount Ti is calculated based on Δγ. As shown in FIG. 14, Tt is Δr=
When Δγ is 0, T1 is 0, and as ΔT increases from O to β, Ti also increases linearly, and becomes a constant value when Δγ is equal to or larger than β. Further, as ΔT decreases from 0 to −β, TI increases linearly, and becomes a constant value H when ΔT is −β or less. Here H is larger than L. This is to prevent spin since there is a risk of spin when Δγ is negative, that is, on the oversteer side.

Next, in step 74, the target throttle opening degree θ is determined.

is calculated based on the following formula.

θS=θ−Ke Here, θ is the current throttle opening, and Ke is the opening reduction value. Ke is calculated based on ΔT, and as shown in FIG. 15, Ke is 0 when Δr=0, and as ΔT increases from 0 to a, Ke also increases linearly, and ΔT
is a constant value above a. Further, as Δγ decreases from 0 to 10, KO increases linearly, and becomes a constant value d when Δγ is −C or less. Here d is greater than b and a is C
bigger.

Next, in step 75, the ignition timing is retarded based on Tt, and in step 76, the throttle valve opening is controlled based on θ. Engine torque can be reduced by retarding the ignition timing and reducing the throttle valve opening.

As described above, according to this embodiment, the oil pressure Pc supplied to the multi-disc clutch 14 is either the minimum oil pressure pxrw or the maximum oil pressure PM.
If the actual yaw rate does not match the target yaw rate even when AX is set, the engine torque is reduced so that the actual yaw rate matches the target yaw rate. Therefore, good turning performance can be obtained.

〔Effect of the invention〕

Even when the clutch engagement force reaches a limit value, the actual yaw rate can be controlled, and therefore the actual yaw rate can be made approximately equal to the target yaw rate, and good turning performance can be obtained.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the invention, Fig. 2 is a schematic overall view of a four-wheel drive vehicle, Fig. 3 is a model diagram showing only two wheels during a right turn, and Fig. 4 is the force acting on the front wheels during understeer. Figure 5 is a diagram showing the force acting on the rear wheels during understeer, Figure 6 is a flowchart for controlling oil pressure and engine torque, and Figure 7 is 1δj and K.
Figure 8 is a diagram showing the relationship between θ and 2, Figure 9 is a diagram showing the relationship between ΔNFII and V and P, and Figure 10 is a diagram showing the relationship between A diagram showing the relationship between PIIIs, Figure 11 is a diagram showing the relationship between V and K, Figure 12 is a diagram explaining the sign of Δr, and Figure 13 is a diagram showing the relationship between Δγ and □. 14 is a diagram showing the relationship between ΔT and T1, and FIG. 15 is a diagram showing the relationship between ΔT and Ke. 8.9...Rear wheel, 12.13...Front wheel, 1
4...Multi-disc clutch, 18...Solenoid valve, 57
...Yaw rate sensor. Figure Figure Figure Figure Figure Figure 2 Figure PC. Figure 10 Figure 10 Figure 10

Claims (1)

[Claims] a rotation difference control clutch for controlling the rotation difference between the front and rear wheels by a clutch engagement force; an actual yaw rate detection means for detecting an actual yaw rate; a target yaw rate calculation means for calculating a target yaw rate; a fastening force control means for controlling the fastening force so that the yaw rate of the fastening force becomes the target yaw rate; a determining means for determining whether the fastening force has reached a limit value; A driving force control device for a four-wheel drive vehicle, comprising: engine torque control means for reducing engine torque when it is determined that a limit value has been reached and the actual yaw rate deviates from the target yaw rate.