JPS62143720A - Driving force distribution control device for 4-wheel drive car - Google Patents

Abstract

PURPOSE:To enable execution of control responding to a driving force and a road surface friction factor, by a method wherein a device is constituted such that a clutch fastening force is increased depending upon a difference in a rotation speed between rear and front wheels, a fastening force is controlled in a manner that the more a driving force is increased and a road surface friction factor is decreased, the more a control constant is increased. CONSTITUTION:A controller unit 45 inputs front and rear wheel rotation speeds nf and nr, an accel opening (a), and a car speed (v). From plural control characteristics maps having different set proportional constants, a control characteristics map responding to the accel opening (a) is selected, and a control signal (c) based on the selected control characteristics map and a front and rear wheel rotation speed difference DELTAN is outputted to a valve solenoid 46 for controlling a clutch 15. In this case, a control constant is selected in a manner that the more a driving force is increased and a road surface friction factor is decreased, the more the control factor is increased. This constitution enables a clutch fastening force to be controlled depending upon the driving force and the road surface friction factor.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a driving force distribution control device for a four-wheel drive vehicle that controls the distribution of driving force to front and rear wheels according to predetermined control conditions.

(Prior Art) As a conventional driving force distribution control device for a four-wheel drive vehicle, a device as described in, for example, Japanese Unexamined Patent Publication No. 56-26636 is known.

This conventional device is configured to transmit power directly to one of the front and rear wheels in a transmission, and also to the other of the front and rear wheels via a hydraulic transfer clutch, and the clutch is usually slidable by a spring. The clutch is in a half-engaged state, and when slippage occurs between the front and rear wheels, a two-stage control is performed to bring the clutch into a fully integrated state by pressing a piston. Therefore, in the conventional device, when the slip between the front and rear wheels is below a predetermined value, the transfer clutch is in a half-clutch engaged state, and the drive force distribution state (2 (almost wheel drive), and if the slip between the front and rear wheels exceeds a predetermined value,
The transfer clutch was fully engaged and the vehicle was in full four-wheel drive.

(Problems to be Solved by the Invention) However, in such a conventional driving force distribution control device, it is difficult to switch from a two-wheel drive state to a four-wheel drive state after a predetermined slip ratio.
Because the drive force distribution was switched in an 0N-OFF manner to the wheel drive state, in the direct four-wheel drive state, the turning characteristics tended to have strong understeer, and in the two-wheel drive state, the wheels slipped when starting suddenly. Furthermore, there was a problem in that it could lead to a spin when turning.

On the other hand, with the aim of solving the above-mentioned problems, the applicant previously filed an application with the content that the best driving force distribution can be obtained according to the difference in rotational speed between the front and rear wheels. (Japanese Patent Application No. 59-276048) However, although a proportional constant setting means for setting a proportional constant of the control characteristic for controlling the clutch engagement force of the variable torque clutch is provided, it is difficult to determine the driving force state of the vehicle or the road surface friction coefficient. Because the proportional constant was set unrelated to the control characteristic, if the control characteristic was set to a small proportional constant that indicates a drive force distribution similar to that of two-wheel drive, sudden starts would easily cause wheel slip.
Rapidly accelerating turns tend to cause spin, and the slip and spin limits are reached early, especially on roads with a low friction coefficient.Also, the vehicle has a large proportionality constant that indicates a driving force distribution similar to that of four-wheel drive. When the control characteristics are set to , if a slow acceleration turn is performed, the turning characteristics tend to have a strong understeer tendency, and the problem remains that the vehicle exhibits a strong understeer tendency especially on roads with a high friction coefficient.

(Means for Solving the Problems) The present invention has been made for the purpose of solving the above-mentioned problems, and in order to achieve this purpose, the present invention employs the following solving means. did.

The solution of the present invention will be explained with reference to the conceptual diagram of the claim shown in FIG. 1. A variable torque clutch 3 provided in the middle of the drive power transmission system to the front and rear wheels 1 and 2, and an actuator that operates the variable torque clutch 3 4, and state detection means 5
In a driving force distribution control device for a four-wheel drive vehicle, the control means 6 outputs a control signal for controlling the clutch engagement force of the variable torque clutch 3 to the actuator 4 based on an input signal from the variable torque clutch 3. , the state detection means 5 includes a front and rear wheel rotational speed difference detection means 501, a driving force state detection means 502, and a road surface friction coefficient detection means 503, and the control means 6 includes a clutch engagement function according to the front and rear wheel rotational speed difference. The clutch is based on a control characteristic in which a control characteristic is set such that the force increases, and the control constant is large as the driving force state detected by the driving force state sensor 502 indicates a large driving force and the road surface friction coefficient indicates a low road surface friction coefficient. The fastening force was controlled.

(Function) Therefore, in the driving force distribution control device for a four-wheel drive vehicle of the present invention, the driving force distribution changes smoothly according to the difference in rotational speed between the front and rear wheels, and the steering characteristics are improved by using the means described above. There is no sudden change, and during sudden acceleration on a road with a low road friction coefficient, the clutch engagement force is controlled based on control characteristics with a large control constant, resulting in drive force distribution control similar to that of four-wheel drive, reducing wheel slip during sudden starts. During slow acceleration on roads with high road friction coefficients, clutch engagement force is controlled based on control characteristics with small control constants, resulting in drive force distribution control similar to that of two-wheel drive. Therefore, the understeer tendency during slow acceleration turns is reduced, and driving force distribution control can be performed in accordance with the driving force state and the road surface friction coefficient.

(Example) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

In describing this embodiment, a driving force distribution control system for a four-wheel drive vehicle based on rear wheel drive will be taken as an example.

First, the configuration of the embodiment shown in FIGS. 2 to 7 will be explained.

10 is a driving force distribution device, as shown in FIG.
Drive input shaft 11. Transmission 12, input shaft 13
．． Rear wheel side drive shaft 14. Multi-plate friction clutch 15. Oil pump 16. Pressure oil discharge pipe 17, oil suction pipe 18. Reserve tank 19. Gear train 20. A front wheel side drive shaft 21 is provided.

The drive input shaft 11 is a shaft to which the driving force that has passed through the engine and the clutch is input.

The transmission 12 changes the speed of the rotational driving force from the drive input shaft 11 according to a gear position selected by a shift operation, and in the embodiment, gear sets with different gear ratios are provided on two parallel shafts. I am using a similar type.

The input shaft 13 is a shaft for inputting the rotational driving force from the transmission 12 to the multi-disc friction clutch 15 as a transfer.

The rear wheel drive shaft 14 is coaxially and directly connected to the input shaft 13, and the rotational driving force from the input shaft 13 is directly transmitted thereto.

The multi-disc friction clutch 15 can change the driving force transmitted to the front wheels by means of clutch engagement pressure. 15a and a friction plate 15b that is rotationally engaged with the input shaft 13.
A clutch hub 15c rotatably supported on the outer periphery of the clutch hub 15c, a friction disk 15d rotationally engaged with the clutch hub 15c, and a friction plate 15b and a friction disk 15d arranged alternately. It includes a clutch piston 15e and a cylinder chamber 15f formed between the clutch piston 15e and the clutch drum 15a.

The oil pump 16 is a pump that sucks oil in the reserve tank 19 through an oil suction pipe 18, pressurizes it, and supplies it to a pressure oil discharge pipe 17, which is communicated with the cylinder chamber 15f. When pressurized oil is supplied from the oil pump 16, a clutch engagement pressure P is applied to the clutch piston 15e to press the friction plate 15b and the friction disc 15d into contact with each other, thereby transmitting the driving force from the input shaft 13 to the front wheels. let

The gear train 20 includes a first gear 20a provided on the clutch hub 15C, a second gear 20c provided on the intermediate shaft 20b, and a third gear 20d provided on the front wheel drive shaft 21. , is means for transmitting the driving force to the front wheels by engaging the multi-disc friction clutch 15.

The front wheel drive shaft 21 is a shaft that transmits rotational driving force to the front wheels of the vehicle.

Incidentally, FIG. 3 shows a specific example of the transfer, in which the multi-disc friction clutch 15 is installed in the transfer case 22.
It houses gears, shafts, etc.

In Figure 3, 15g is a dish plate, 23 is a return spring, and 24 is a control pressure oil input boat.

25 is a control pressure oil passage, 26 is a rear wheel side output shaft, 27 is a lubricating oil passage, and 28 is a speedometer pinion.

29 is an oil seal, 30 is a bearing, 31 is a needle bearing, 32 is a thrust bearing, and 33 is a joint flange.

Reference numeral 40 denotes a driving force distribution control device, which includes a front wheel rotation sensor 41 as an input sensor. Rear wheel side rotation sensor 42. Accelerator opening sensor 43. A vehicle speed sensor 44 is provided, a control unit 45 is provided as a control means, and an electromagnetic proportional control relief valve 47 (provided in a branch drain pipe 48) having a valve solenoid 46 is provided as an actuator.

The front wheel rotation sensor 41 and the rear wheel rotation sensor 42 are provided in the middle of the front wheel drive shaft 21 and the rear wheel drive shaft 14, respectively, and include, for example, a rotary plate fixed to the shaft,
This re-rotation sensor 41, 42 is performed using a rotation sensor or the like based on a phototube and a photoelectric element arranged in the hole position of the rotary plate.
From there, rotation signals (nf) and (nr) corresponding to the shaft rotation are outputted to the front and rear wheel rotational speed difference detection means 45a in the control unit 45.

The accelerator opening sensor (driving force state detection means) 43 is a sensor that detects the degree of depression of the accelerator and outputs an accelerator opening signal (a) according to the degree of depression.

The vehicle speed sensor 44 generates a vehicle speed signal (V) according to the speed V of the vehicle.
This outputs the following.

Reference numeral 45b denotes road surface friction coefficient detection means provided in the control unit 45, which indirectly detects the road surface friction coefficient based on the occurrence of the rotational speed difference ΔN between the front and rear wheels with respect to the vehicle speed V detected by the vehicle speed sensor 44. It is.

The control unit 45 includes the rotation sensor 41
．． 42, the accelerator opening signal (a) from the accelerator opening sensor 43, and the vehicle speed signal (V) from the vehicle speed sensor 44. Each time the control is activated, a control characteristic map corresponding to the vehicle speed V and accelerator opening A at that time is selected from among a plurality of control characteristic maps with different control constants), and the control characteristic map is selected based on the control characteristic map and the front and rear wheel rotational speed difference ΔN. outputs a control signal (c) to the valve solenoid 46,
As shown in FIG. 4, an input circuit 451, a clock circuit 4
52, RAM 453, ROM 454, CPU 455, and output circuit 456.

The input circuit 451 includes input sensors 41, 42, 43 .
This circuit converts an input signal inputted from 44 into a signal that can be processed by CPU 455.

The clock circuit 452 gives time instructions and the CPU 45
This is a circuit for performing the arithmetic processing in step 5 at predetermined time intervals.

The RAM 453 (random access memory) is a memory that can be written to and read from.
This is a circuit that temporarily stores input signals input while the PU 455 is performing calculation processing and information necessary for the calculation processing.

The ROM 454 (read-only memory) is a read-only memory, and a control characteristic map shown in FIG. 5 is stored in advance in the form of a table. One control characteristic is selected, and the rotation speed difference Δ calculated by the CPU 455 is
Based on N, a table lookup is performed.

Note that the clutch engagement pressure P (transmission torque ΔT to the front wheel side) is expressed as a function of the rotational speed difference ΔN (ΔN=N r - N f ) c7) as shown in the following equation.

P = −func (ΔN) K, constant of proportionality, that is,
A plurality of control characteristics can be set by changing the proportionality constant, and in the embodiment, as shown in FIG.
≦V<V+) control characteristic map Ml, at medium speed (V+≦
Control characteristic map M2 for V<V2), at high speed (V2≦V
) control characteristic map M3 is set, and each map M1.

M2. In M3, control characteristics of +, 2, 3, and Ka are set to proportional constants that vary depending on the magnitude of the accelerator opening A.

This proportionality constant is made larger as the accelerator opening A indicates a large accelerator opening, and increases as the vehicle speed ■ indicates a low vehicle speed.

The CPU 455 (central processing unit) is a central processing unit that performs arithmetic processing.
55 calculates the rotational speed difference ΔN between the front and rear wheels, and
53 and the ROM 454, and outputs the resultant signal to the output circuit 456.

The output circuit 456 is a circuit that outputs a control signal (C) according to a result signal from the CPU 455 to the valve solenoid 46, which is an actuator.

The valve solenoid 46 is an actuator that drives an electromagnetic proportional control relief valve 47 provided in the middle of a branch drain pipe 48 that branches from the pressure oil discharge pipe 17 to the reserve tank 19, and is connected to the hydraulic pressure from the signal pressure oil path 49. By opening and closing the relief valve 47 in balance with the electromagnetic force, a clutch engagement pressure P corresponding to the control signal (C) is achieved.

Note that the clutch engagement pressure P is expressed by the following formula.

P=ΔT/ (JL-S ・2n-Rm) Le; Coefficient of friction of clutch plate S; Area of pressure action on piston n
: Number of friction disks Rm; Effective radius of torque transmission of the friction disks Therefore, when the clutch engagement pressure P is increased, the transmission torque ΔT also increases in proportion.

Next, the operation of the embodiment will be explained.

First, factors influencing the rotational speed difference ΔN will be described.

The rotational speed difference ΔN is expressed by the following equation.

AN=f1 (R, V) + f2 (Q, JL) R; Turning radius V; Vehicle speed Q; For driving force; Road friction coefficient. As shown in Figure 6(a), the influence of turning radius R will be high rotational speed difference ΔN at low vehicle speeds if the road friction coefficient is low, and the influence of turning radius R will be as shown in Figure 6(b).
As shown in Fig. 6 (
As shown in e), the larger the driving force, the higher the rotational speed difference ΔN at lower vehicle speeds.

Therefore, it is most preferable to satisfy all of these relationships and then perform driving force distribution control that gradually shifts from the two-wheel drive state to the four-wheel drive state in proportion to the rotational speed difference ΔN.

Among these influencing factors, vehicle speed ■ and turning radius R are fundamental factors that cause the rotational speed difference ΔN, so
Changes in vehicle speed V and turning radius H remain as rotational speed difference ΔN
However, since the driving force Q and the road friction coefficient are fluctuation factors of the rotational speed difference ΔN, the driving force Q and the road friction coefficient are different from the detected value or the calculated value of the rotational speed difference ΔN. We need to monitor how much of an impact it is having.

Therefore, in the embodiment, information on the driving force Q is incorporated based on the accelerator opening degree A, and the rotational speed difference Δ with respect to the vehicle speed V is
Information on the road surface friction coefficient is incorporated depending on the N generation situation.

Next, the flow of the driving force distribution control operation in the embodiment will be explained with reference to the flowchart shown in FIG.

(a) When the rotational speed difference ΔN between the front and rear wheels is positive When the rotational speed difference ΔN between the front and rear wheels is positive, that is, when the rear wheels are slipping, the flow of control operation is as follows: Step 200 → Step 201 → Step 202 → Step 203 → Step 204 → Step 205 → Step 206, and this operation is repeated.

Note that step 200 is a step of reading the front and rear wheel rotational speeds Nf and Nr, and step 201 is a calculation step of the front and rear wheel rotational speed difference ΔN (ΔN=Nr−Nf).
Step 202 is a step for determining whether ΔN is positive or negative, step 203 is a step for reading vehicle speed V and accelerator opening A, and step 204 is a control characteristic group shown in FIG. 5 based on vehicle speed V and accelerator opening A. Step 205 is a search step of looking up the clutch engagement pressure P from the selected control characteristic based on the front and rear wheel rotation speed difference ΔN, and Step 206 is a search step of looking up the clutch engagement pressure P from the selected control characteristic based on the front and rear wheel rotational speed difference ΔN. This is a step of outputting a control signal (C) from which the table-lookup clutch engagement pressure P is obtained.

As a specific example, when the accelerator pedal is depressed and the accelerator pedal is pressed down on a road with a low friction coefficient for sudden acceleration, when the front and rear wheel rotational speed difference ΔN is ΔN1, the accelerator opening degree A increases, but the vehicle speed V increases. Therefore, as shown in Fig. 5(a), when the accelerator opening A reaches approximately %, the clutch engagement pressure P changes from P1 → P2 → P3 → P4, and almost all four wheels are pressed in a short time. It becomes a driving state.

Also, on a road with a high friction coefficient, during slow acceleration with a small amount of depression on the accelerator pedal, the difference in rotational speed of the front and rear wheels Δ
When N is ΔN1, the change in accelerator opening A is small, but the increase in vehicle speed V is large;
b) As shown in (c), for example, when the accelerator opening A is 1
/16 → 1/8 → 1/4, whereas if the vehicle speed V increases from low speed → medium speed → high speed, clutch engagement pressure P remains unchanged at P2. , the distribution of driving force to the front wheels is close to that of a rear wheel drive state where the distribution of driving force to the front wheels is small.

(b) When the rotational speed difference ΔN between the front and rear wheels is zero or negative If the rotational speed difference ΔN between the front and rear wheels is zero or negative, that is, when driving straight on a dry road where the tires do not slip, etc. The flow is as follows: step 200→step 201→step 202→step 2.7, the control signal (C) is output as zero, and the rear wheel drive state is maintained.

As described above, in the embodiment, the accelerator opening degree A is used as the input information for the driving force, the generation status of the rotational speed difference ΔN with respect to the vehicle speed ■ is used as the input information for the road surface friction coefficient, and as the accelerator opening degree A increases, Since the device is designed to select a control characteristic in which the proportionality constant K increases as the road surface friction coefficient W decreases, when the accelerator pedal is depressed on a road with a low friction coefficient and the vehicle enters a sudden acceleration state, the proportionality constant The clutch engagement force is controlled based on a large control characteristic, that is, the driving force distribution control is similar to that of a four-wheel drive, and it is possible to prevent wheel slip during a sudden start and spin during a sudden acceleration turn.

In addition, when accelerating slowly on a road with a high friction coefficient and the amount of depression on the accelerator pedal is small, the clutch engagement force is controlled based on a small control characteristic of the proportional constant, that is, the drive force distribution control is similar to rear wheel drive. This makes it possible to reduce the tendency for understeer when turning at slow acceleration.

In this way, driving force distribution control is performed that does not cause sudden changes in steering characteristics by smoothly changing the driving force distribution according to the difference in rotational speed between the front and rear wheels, and driving force distribution control is performed according to the driving force condition and the road surface friction coefficient. can be done.

Although the embodiments of the present invention have been described above in detail with reference to the drawings, the specific configuration is not limited to these embodiments, and the present invention may be modified without departing from the gist of the present invention. included.

For example, although the embodiment shows a four-wheel drive vehicle based on a rear-wheel drive vehicle, it may also be a four-wheel drive vehicle based on a front-wheel drive vehicle. In that case, the rotational speed difference ΔN is Nf-N
It may be calculated as r.

In addition, in the embodiment, the clutch engagement pressure P and the rotational speed difference ΔN
Although an example of control characteristics based on the proportional relationship has been shown, the relationship is not necessarily limited to the relationship shown in the embodiment, and other control characteristics such as those showing viscous clutch characteristics may be used.

Furthermore, although an accelerator opening sensor is shown in the embodiment as an acceleration state sensor, a negative pressure sensor provided in the engine intake pipe, a sensor that detects the operation of an accelerator pedal, or the like may be used.

Furthermore, in the embodiment, a vehicle speed sensor that indirectly detects the road surface friction coefficient in relation to the rotational speed difference ΔN is used as the road surface friction coefficient sensor, but a sensor that directly detects the road surface friction coefficient may also be used. .

In addition, in the embodiment, an example was shown in which a plurality of control characteristics are stored in advance in the form of a table and the clutch engagement pressure P is determined by table lookup, but the control characteristics are stored in the form of an arithmetic expression. Alternatively, the clutch engagement pressure P may be calculated by substituting the proportionality constant and the front and rear wheel rotational speed difference into this calculation equation, or by setting one control characteristic map, for example, as shown in Fig. 5 (C )), when the vehicle speed V is lower than the set vehicle speed, the proportionality constant may be varied depending on the correction value.

At this time, the proportionality constant is not limited to the four types of proportionality constants as in the embodiment, but the value of the accelerator opening may be directly used as the proportionality constant, or the proportionality constant may be calculated from the accelerator opening by a predetermined calculation. good.

In addition, in the embodiment, an example was shown in which the accelerator opening degree A, which allows the accelerator opening degree to be known over time, is used as input information of the driving force state that determines the proportionality constant K, but the accelerator opening degree A can be changed over time. The differentiated accelerator opening degree differential value A may be used as input information for the driving force state, or the value obtained by adding the accelerator opening degree A and the accelerator opening degree differential value A (αA+β
A) may be used as input information.

In addition, in the case of the accelerator opening differential value A, the rate of change of the accelerator opening can be known, and in the case of αA + β, the most accurate driving force state can be known by setting the constants α and β. It is possible.

Further, the clutch engagement pressure control means is not limited to the electromagnetic proportional relief valve of the embodiment, and other means may be used.

Further, the mounting position of the rotation sensor is not limited to the mounting position of the embodiment as long as it is provided in the drive transmission system of the front wheel side and the rear wheel side.

(Effects of the Invention) As explained above, in the driving force distribution control device for a four-wheel drive vehicle of the present invention, a control characteristic is set in which the clutch engagement force increases in response to the difference in rotational speed between the front and rear wheels. , the greater the driving force state determined by the driving force state sensor, the greater the driving force is.
In addition, since the clutch engagement force is controlled based on a control characteristic in which the control constant is larger as the road friction coefficient indicates a lower road surface friction coefficient, the driving force distribution changes smoothly according to the difference in rotational speed between the front and rear wheels, resulting in steering characteristics. In addition to preventing sudden changes in driving force, wheel slips during sudden starts and spins during sudden acceleration turns are prevented, especially on roads with a low friction coefficient, and the tendency for understeer during slow acceleration turns is reduced, especially on high friction coefficient roads. The effect is that driving force distribution control can be performed according to the state and the road surface friction coefficient.

[Brief explanation of drawings]

Fig. 1 is a conceptual diagram of a claim showing a driving force distribution control device for a four-wheel drive vehicle according to the present invention, Fig. 2 is an overall view showing a driving force distribution control device of an embodiment, and Fig. 3 is a transfer diagram of the embodiment device. 4 is a block diagram showing the control unit of the embodiment device, and FIG. 5 (a), (b), and (c).
6(a) and 6(b) are maps showing control characteristics stored in advance in the control unit of the embodiment device.
(C) is an influence characteristic diagram of each influencing factor on the rotation speed difference,
FIG. 7 is a flowchart showing the flow of operations in the control unit in the embodiment device. l...Front wheel 2...Rear wheel 3...Variable torque clutch 4...Actuator 5...State detection means 501...Front and rear wheel rotational speed difference detection means 502...Driving force state detection means 503 Road surface friction coefficient detection means 6 Control means Patent application Nissan Motor Co., Ltd. Figure 5 (a) O%v<v. (I6, Rainbow!,) (b) Vl ≦ v < Vl (4'L!-) (C) Vl ≦V (breathing)

Claims (1)

[Claims] 1) A variable torque clutch provided in the middle of the drive power transmission system to the front and rear wheels, an actuator that operates the variable torque clutch, and a variable torque control based on input signals from the state detection means. A driving force distribution control device for a four-wheel drive vehicle, comprising: control means for outputting a control signal for controlling a clutch engagement force of a clutch to the actuator, wherein the state detection means includes front and rear wheel rotational speed difference detection means. , a driving force state detecting means, and a road surface friction coefficient detecting means, the control means is configured to set a control characteristic in which the clutch engagement force increases in accordance with a difference in front and rear wheel rotational speeds, and the driving force by the driving force state detecting means is set. A four-wheel drive vehicle characterized in that the clutch engagement force is controlled based on a control characteristic having a larger control constant as the state indicates a larger driving force and as the road surface friction coefficient indicates a lower road surface friction coefficient. Driving force distribution control device. 2) The road surface friction coefficient detection means includes a vehicle speed sensor that detects vehicle speed, and determines the road surface friction coefficient based on a value of a difference in rotational speed of the front and rear wheels with respect to the vehicle speed. The driving force distribution control device for the four-wheel drive vehicle described above.