JP2502520B2 - Drive force distribution controller for four-wheel drive vehicle - Google Patents

Description

The present invention relates to a drive force distribution control device for a four-wheel drive vehicle, which is used in a transfer device for a four-wheel drive vehicle and controls a drive force distribution ratio of front and rear wheels. .

(Prior Art) As a driving force distribution control device for a conventional four-wheel drive vehicle, a device described in, for example, Japanese Patent Laid-Open No. 58-93526 is known.

This conventional device is configured to transmit power directly to one of the front and rear wheels, and to transmit power to the other of the front and rear wheels by engaging a transfer clutch as necessary.
With a control system that operates the solenoid valve by manual operation of the 4-wheel drive changeover switch to engage the transfer clutch, only when the automatic changeover switch and accelerator pedal are released from the switch It was characterized in that a circuit having an accelerator switch to be turned on was connected in parallel, and it was possible to automatically switch to four-wheel drive during deceleration traveling in which the accelerator pedal was released.

(Problems to be Solved by the Invention) However, in such a conventional drive force distribution control device, the clutch control for switching to the four-wheel drive state at the time of deceleration traveling by the accelerator off operation for releasing the depression of the accelerator pedal is performed. However, when the vehicle is turning at a high lateral acceleration and the accelerator is off, the four-wheel drive mode is set, and as shown in FIG. 14, the front side control is performed by moving the load to the front wheels. When the powers Qf ₁ and Qf ₂ increase and the rear braking forces Qr ₁ and Qr ₂ decrease and a rear wheel is provided with a differential limiting means, the difference in braking force between the inner and outer wheels ΔQr (= Qr
_2- Qr ₁ ) and the wheel width tred reduce the yaw moment M _{LSD in the} direction that suppresses the tack-in, which causes the problem of allowing the occurrence of the tack-in phenomenon in which the vehicle turns in the turning direction. .

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

The solution means of the present invention will be described with reference to the conceptual diagram of the claims shown in FIG. Difference between the rear clutch and the transfer clutch means 3 capable of shifting the driving force distribution to the four-wheel drive state, the clutch control means 5 outputting a control signal for changing the driving force distribution based on the input signal from the detecting means 4. In a four-wheel drive vehicle including a differential limiting means 6 which is provided in a dynamic device and generates a differential limiting torque when a rotational speed difference occurs between the left and right wheels, the detection means 4 serves as the detecting means 4 and turns in a four-wheel drive state. A rear wheel drive state including a tack-in detection means 401 for predicting the occurrence of a tack-in phenomenon that occurs during traveling, and the clutch control means 5 based on a tack-in detection signal from the tack-in detection means 401. And a means for controlling to shift the driving force distribution.

As the tack-in detection means 401, for example, a throttle opening sensor and a vehicle lateral acceleration sensor, the vehicle lateral acceleration is higher than a set value, and the throttle opening is lower than the set value, and the throttle opening A means for outputting a tack-in detection signal when the time differential value is larger than the set value is used.

(Operation) For example, while turning while receiving a high vehicle lateral acceleration,
When the accelerator off operation is suddenly performed, the condition that the tuck-in phenomenon occurs is satisfied, and the tuck-in detection unit 401 outputs the tuck-in detection signal.

Then, in the clutch control means 5, when the tack-in detection signal is input from the tack-in detection means 401, the clutch engagement force control for the transfer clutch means 3 controls to shift the driving force distribution to the rear wheel drive state.

Therefore, the braking force from the engine is transmitted to the left and right rear wheels 2 as the driving force is distributed to the rear wheels. Then, the differential limiting means 6 provided in the differential device for the rear wheels is provided with the left and right rear wheels 2.
Of the braking force transmitted to the left and right rear wheels 2 due to the differential limiting action, the braking force is distributed to the inner wheel side having a high rotation speed. The amount is transmitted in a small amount, and the braking force distribution amount is transmitted in large amounts to the outer wheel side, which has a low rotation speed.

That is, by performing a driving force distribution control that transmits more braking force from the engine to the left and right rear wheels 2, a large braking force difference is generated between the inner wheels of the left and right rear wheels 2, and the inner and outer wheels of the left and right rear wheels 2. A large yaw moment is obtained in the direction in which the tack-in is suppressed by the braking force difference and the wheel width, and the occurrence of the tack-in phenomenon is prevented in advance.

(Examples) Hereinafter, examples of the present invention will be described in detail with reference to the drawings. In describing this embodiment, a driving force distribution control device for a four-wheel drive vehicle based on rear wheel drive will be described as an example.

 First, the configuration of the embodiment will be described.

As shown in FIG. 2, a four-wheel drive vehicle to which the driving force distribution control device D of the embodiment is applied includes a transfer device 10, an engine 11, a transmission 12, a transfer input shaft 13,
A rear wheel side drive shaft 14, a multi-plate friction clutch (friction clutch means) 15, a rear differential 16, a rear wheel 17, a front differential 18, a front wheel 19, a gear train 20, and a front wheel side drive shaft 21 are provided.

The transmission 12 shifts the rotational driving force from the engine 11 according to the gear position selected by the shift operation, and in the embodiment, a type in which two parallel shafts are provided with a gear set having different gear ratios. I use the one.

The transfer input shaft 13 is a shaft that inputs the rotational driving force from the transmission 12 to the multi-plate friction clutch 15 in the transfer device 10.

The rear wheel side drive shaft 14 is directly connected concentrically with the transfer input shaft 13, and the rotational driving force from the transfer input shaft 13 is transmitted as it is.

The multi-plate friction clutch 15 is a clutch whose transmission torque can be changed to the front wheel side by the clutch hydraulic pressure, and includes a clutch drum 15a fixed to the transfer input shaft 13 and the rear wheel side drive shaft 14, and the clutch drum 15a. Friction plates 15b rotationally engaged with each other, a clutch hub 15c rotatably supported on the outer peripheral portion of the input shaft 13, and friction discs 15d rotationally engaged with the clutch hub 15c are alternately arranged. Friction plate 15b
A clutch piston 15e provided at one end of the friction disk 15d, and a cylinder chamber 15f formed between the clutch piston 15e and the clutch drum 15a.
It has.

The above rear differential 16 has 17 and 17 rear wheels.
A differential device that distributes and transmits the driving force to the rear differential 16. Inside the rear differential 16, there are built-in differential limiting clutches (differential limiting means) 16a, 16a, and the rotational speed difference between the left and right rear wheels 17, 17 is reduced. When it occurs, the differential limiting torque is generated in the direction of limiting the differential by engaging the clutch. Note that the limited differential clutch 16a, 16a is a well-known technique, and for details, refer to pages 321 to 324 of “Automotive Engineering Complete Book 9 Volume Power Transmission Device” (published by Sankaido Co., Ltd. in 1980). See.

As the front differential 18, an ordinary differential device having no differential limiting means is used.

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.
And means for transmitting the driving force to the front wheels by the engagement of the multi-plate friction clutch 15.

The front wheel-side drive shaft 21 is a shaft that transmits rotational driving force to the front wheels 19 of the vehicle.

FIG. 4 shows a specific example of the transfer device 10, in which the multi-plate friction clutch 15, gears and shafts are housed in a transfer case 22.

In FIG. 4, 15g is a dish plate, 15h is a return spring, 24 is a clutch pressure oil input port, 25 is a clutch pressure oil passage, 26 is a rear wheel output shaft, 27 is a lubrication oil passage, and 28 is a pinion for a speedometer. , 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.

Next, the driving force distribution control device D of the embodiment, as shown in FIG. 3, is a hydraulic pressure generation device 50 as an external device that generates hydraulic pressure for engaging the multi-plate friction clutch 15.
And a hydraulic control device 40 for controlling the hydraulic pressure from the hydraulic pressure generation device 50 to a predetermined clutch hydraulic pressure P.

The oil pressure generating device 50 includes an oil pump 51, a pump pressure oil passage 52, a clutch pressure oil passage 53, a branch drain oil passage 54, a reserve tank 55, and a suction oil passage 56.
An electromagnetic proportional relief valve 58 that is opened and closed by the hydraulic pressure from the check oil passage 57 and the electromagnetic force from the valve solenoid 58a is provided in the middle of 54.

The hydraulic control device 40 includes a front wheel side rotation sensor 41, a rear wheel side rotation sensor 42, and a throttle opening degree sensor 4 as detection means.
3. A vehicle lateral acceleration sensor 44 is provided, a control unit 45 is provided as a control circuit, and the electromagnetic proportional relief valve 58 (provided in the branch drain oil passage 48) having a valve solenoid 58a is provided as a control actuator. There is.

The front wheel side rotation sensor 41 and the rear wheel side rotation sensor 42 are provided in the middle of the front wheel side drive shaft 21 and the rear wheel side drive shaft 14, respectively, and are located at the rotary plate fixed to the shaft and the hole position of the rotary plate. A rotation sensor or the like formed by the arranged photoelectric tube and photoelectric element is used, and rotation signals (nf) and (nr) are output from these rotation sensors 41 and 42 by pulse signals according to shaft rotation.

The throttle opening sensor 43 is a sensor that detects a throttle opening θ (also called an accelerator opening) of the engine 11 and outputs a throttle opening signal (θ) corresponding to the throttle opening θ.

The vehicle lateral acceleration sensor 44 is a sensor that detects a vehicle lateral acceleration Y _G applied in the vehicle width direction during turning or the like and outputs a lateral acceleration signal (g) corresponding to the vehicle lateral acceleration Y _G.

The throttle opening sensor 43 and the vehicle lateral acceleration sensor 44 are used as a tuck-in detection means for predicting the occurrence of a tuck-in phenomenon that occurs during turning traveling in a four-wheel drive state.

The control unit 45 uses a control circuit centered on a vehicle-mounted microcomputer, inputs rotation signals (nf) and (nr) from the rotation sensors 41 and 42, and basically drives the front and rear wheels. 21,14 Rotation speed difference ΔN (Nr-N
f) is calculated, and the command current signal (i) for increasing the clutch hydraulic pressure P as the rotational speed difference ΔN increases to bring the driving force distribution closer to the four-wheel drive state is given to the electromagnetic proportional relief valve.
As shown in FIG. 5, the internal circuit includes an input circuit 451, a clock circuit 453, a RAM 454, and a ROM 45.
5, CPU456, output circuit 457 is provided.

The ROM 455 (read only memory) is a read-only memory, and a control characteristic map M of the rotational speed difference ΔN and the command current value i ^* is shown in this ROM 455 as shown by the solid line in FIG. It is pre-stored in the form of a table)
After the rotation speed difference ΔN (ΔN = Nr−Nf) is calculated at 56,
A table lookup is done.

This control characteristic map M is set to an initial command current value i ₀ ^* with a constant value when the rotational speed difference ΔN is zero,
The command current value i ^* increases as the rotational speed difference ΔN increases, and when the rotational speed difference ΔN exceeds a predetermined value ΔN ₁ , the command current value i ^* is rapidly increased.

CPU456 above (Central Processing Unit)
Is a central processing unit that performs arithmetic processing. In this CPU 456, the rotational speed difference ΔN between the front and rear wheels is calculated, and RAM 454 and ROM 4
Read circuit from 55 and output the resulting signal
Output to 457.

When the output of the command current signal (i) to the electromagnetic proportional relief valve 58 is the command current value i ^* = 0, the relief valve 58 is opened by the hydraulic pressure from the check oil passage 57, and the clutch is released. When the output of the command current signal (i) is the command current value i ^* > 0, the relief valve 58 moves in the closing direction, and the pump pressure from the oil pump 51 is changed according to the magnitude of the control current value i ^*. And the clutch hydraulic pressure P (see FIG. 7).

The clutch hydraulic pressure P is expressed by the following equation (see FIG. 8).

P = ΔT / (μ · S · 2n · Rm) μ; Friction coefficient of clutch plate S; Pressure acting area on piston n; Number of friction discs Rm; Torque transmission effective radius of friction disc Next, action of the embodiment Will be explained.

First, the flow of the front and rear wheel drive force distribution control operation in the control unit 45 will be described with reference to the flowchart of the main routine shown in FIG.

(A) When the two-wheel drive command signal is not output When the vehicle is traveling straight ahead or is turning due to low lateral acceleration, and the tuck-in detection means does not output the two-wheel drive command signal as the tuck-in detection signal, step 100 → Step 101 →
The flow proceeds from step 102 to step 103 to step 104, and this flow is repeated each time the control is activated.

Incidentally, step 100 is a step of reading the rotational speeds Nf and Nr of the front and rear wheels, and step 101 is a difference in the front and rear wheel rotational speeds ΔN.
(= Nr−Nf) is a calculation step, step 102 is a search step for table lookup of the command current value i ^* from ΔN obtained by the calculation, and step 103 is a tenth step.
It is a determination step for determining whether or not a two-wheel drive command signal is being output by the tuck-in detection operation shown in the figure.
Step 104 is the command current value i ^* obtained in step 102 ^.
Is an output step for outputting the command current signal (i) according to.

The above-described control operation allows the vehicle to travel with driving force distribution as described below.

The initial command current value i ₀ ^* moves to the front wheel side even when the speed difference ΔN between the front and rear wheels is near zero, such as during high-speed straight running on dry asphalt or straight running with the foot off the accelerator pedal. The initial transmission torque ΔT ₀ is generated as the transmission torque ΔT, and the four-wheel drive state is reached in which the driving force is slightly distributed to the front wheels.

Therefore, even if the vehicle receives a disturbance such as a side wind, the road surface grip force by the front wheels is increased, and the straight running stability of the vehicle is secured.

The rotational speed difference ΔN between the front and rear wheels is generated due to the drive wheel slip. At the time of starting, acceleration, braking, traveling on a low friction coefficient road, etc., the degree of occurrence of the rotational speed difference ΔN between the front and rear wheels is determined from the control characteristic map M of FIG. A command current signal (i) having a command current value i ^* that gradually increases in response to is output.

Then, as the command current value i ^* increases, the transmission torque ΔT to the front wheels also increases, and the distribution of the driving force gradually changes from a four-wheel drive state close to rear-wheel drive to a complete four-wheel drive state. To be done.

Therefore, instability of the vehicle behavior due to a sudden change in the driving force distribution, such as when the two-wheel drive state and the four-wheel drive state are switched ON-0FF, does not occur, and the drive loss is reduced.

In addition, the rotation speed difference ΔN exceeding the predetermined rotation speed difference ΔN ₁
In the case of occurrence of, the command current value i ^* suddenly rises to bring the multi-plate friction clutch 15 into a completely engaged state without slip, so that transmission torque loss due to slip friction can also be prevented.

(B) When outputting a two-wheel drive command signal When the accelerator is suddenly turned off while turning while receiving a high vehicle lateral acceleration Y _G , the tuck-in detection means detects the tuck-in based on the prediction of the occurrence of the tuck-in phenomenon. A two-wheel drive command signal as a signal is output.

At this time, the flow of the front and rear wheel driving force distribution control operation proceeds in the order of step 100 → step 101 → step 102 → step 103 → step 105, and in step 105 which is an output step, the command current value i ^* = 0 The current signal (i) is output, the multi-plate friction clutch 15 is engaged and released, the transmission torque ΔT to the front wheels becomes zero, and the driving force distribution is changed to the rear wheel driving state.

Further, the tuck-in detection operation for obtaining the two-wheel drive command signal is performed by the flow shown in the flowchart of the subroutine in FIG. 10, and proceeds to step 200 → step 201 → step 202 → step 203 → step 204 → step 205. At that time, that is, when the tuck-in generation conditions in steps 202, 203, and 204 are all satisfied, the two-wheel drive command signal is output.

In step 200, throttle opening θ and vehicle lateral acceleration Y
_G reading step, step 201 is throttle opening θ
Of time differential value (= (θt-θ) / Δt; θt is the throttle opening read by the previous control start), step 202 is the time differential value of throttle opening θ (throttle opening change rate) Is over the set value a, step 203 is a step for determining whether the throttle opening θ is smaller than the set value θo and is close to full closing, and step 204 is for setting the vehicle lateral acceleration Y _G. This is a step of determining whether or not the lateral acceleration exceeds the value Y _Ga .

Therefore, when the accelerator is suddenly turned off while turning while receiving a high vehicle lateral acceleration Y _G , the two-wheel drive command signal is output immediately because the condition for generating the tuck-in phenomenon is satisfied, and immediately after 4 The driving force distribution is changed from the wheel drive state to the rear wheel drive state.

In this rear wheel drive state, as shown in FIG. 11, all the braking force Q from the engine 11 is transmitted to the rear wheels 17, 17, and the differential limiting clutch 16a,
16a is fastened due to the difference in rotational speed between the two rear wheels 17,17.
With 7 connected directly, braking force Q _r1 on the inner wheel side and braking force Q _r2 on the outer wheel side
Generate.

At this time, the yaw moment M _{LSD in the} direction that suppresses the tuck-in that occurs between the inner and outer wheel braking force difference ΔQr (= Q _r2 −Q _r1 ) and the wheel width tred by the differential limiting clutches 16a and 16a is M _LSD = ΔQr × tred, and the magnitude of the yaw moment M _LSD is larger than when the inner / outer wheel braking force difference ΔQr is four-wheel drive,
It is obtained as a large moment, and the tack-in phenomenon is prevented in advance.

On the other hand, the rear wheel braking forces Q _r1 and Q _r2 increase the slip ratio of the rear wheels 17 and 17, which may cause a decrease in lateral force.However, in the case of a high friction coefficient road, the braking force by engine braking (about 0.2 G (Deceleration) does not matter.

Further, in the case of a low friction coefficient road, the two-wheel drive command signal is not output because the vehicle lateral acceleration Y _G does not increase.

As described above, in the driving force distribution control device D of the embodiment, the tack-in detection means is composed of the throttle opening sensor 43 and the vehicle lateral acceleration sensor 44, and the vehicle lateral acceleration Y _G is the set value. Higher than Y _Ga and throttle opening θ
Is lower than the set value θo and the time differential value of the throttle opening θ is larger than the set value a, the device outputs the two-wheel drive command signal as the tack-in detection signal. Therefore, the drive is performed based on the prediction of the tack-in phenomenon. The force distribution is switched from four-wheel drive to rear-wheel drive, and it is possible to prevent the occurrence of the tuck-in phenomenon.

The embodiment of the present invention has been described in detail above with reference to the drawings.
The specific configuration is not limited to this embodiment, and even if there are design changes and the like within the scope of the present invention, they are included in the present invention.

For example, in the embodiment, the example in which the driving force distribution between the four-wheel drive state and the rear-wheel drive state can be gradually changed is shown. However, the four-wheel drive state and the rear-wheel drive state are switched ON / OFF. Also applicable to a four-wheel drive vehicle or a four-wheel drive vehicle in which a planetary gear set is provided in the drive force distribution control device and the drive force distribution ratio of the front and rear wheels can be changed by a combination of fastening and releasing predetermined elements of the planetary gear set. .

Further, in the embodiment, the driving force distribution control based on the rotational speed difference ΔN of the front and rear wheels is shown as the basic control content of the driving force distribution, but the control content is not limited to the example, and the rotational speed difference ΔN. Other conditions, or conditions other than the rotational speed difference ΔN, and when the tuck-in phenomenon occurs or at other predetermined times, the rear-wheel drive is used, and normally the four-wheel drive is performed in the four-wheel drive state. It may be applied to a driving vehicle.

In the embodiment, the condition shown in FIG. 10 is used as the tuck-in generation condition. However, as shown in FIG. 12, the set value a of the time differential value of the throttle opening θ and the vehicle lateral acceleration are set.
The relationship with Y _G is set in the map in advance, and as shown in FIG. 13, the set value a is set to the vehicle lateral acceleration Y _{G in} step 206.
It may be an example in which the setting value a calculated in step 207 is compared with the actual time differential value to make a determination, and the condition for occurrence of tuck-in is set to the conditions in steps 207 and 204.

In this case, the map shown in FIG. 12 defines a set value a that allows tuck-in from the vehicle lateral acceleration Y _G. That is, when the vehicle lateral acceleration Y _G is high, the tuck-in occurs with a slight change in the throttle opening in a short time. Therefore, the set value a is set small to deal with it.

Further, the clutch hydraulic pressure control means is not limited to the electromagnetic proportional relief valve of the embodiment, but may be other means, for example, a solenoid on-off valve structure or the like when a duty control signal is used.

Further, in the embodiment, the multi-plate friction clutch by hydraulic engagement is shown as the transfer clutch means, but other clutches such as an electromagnetic clutch, a viscous clutch and a dog clutch may be used.

Further, in the embodiment, an example in which a complete transition to the two-wheel drive state of only the rear wheels is shown when the tuck-in detection signal is generated. It is also possible to shift to the ratio of 90 wheels.
That is, the ratio of the driving force distribution to the rear wheels having the differential limiting device may be changed so as to increase.

(Effects of the Invention) As described above, in the driving force distribution control device for a four-wheel drive vehicle of the present invention, as a detection means, occurrence of a tuck-in phenomenon that occurs during turning traveling in a four-wheel drive state. Since the clutch control means includes the tack-in detection means that predicts the occurrence of the tuck-in phenomenon, the clutch control means is a means for controlling the driving force distribution to the rear wheel drive state by the tack-in detection signal from the tack-in detection means. Force distribution is switched from four-wheel drive to rear-wheel drive,
The effect that the occurrence of the tuck-in phenomenon can be prevented by the yaw moment generated in the tack-in suppressing direction by the differential limiting device can be obtained.

[Brief description of drawings]

FIG. 1 is a conceptual view of a driving force distribution control device for a four-wheel drive vehicle according to the present invention. FIG. 2 is a diagram showing a four-wheel drive vehicle to which the driving force distribution control device according to the embodiment is applied. Is an overall view showing a driving force distribution control device of the embodiment, FIG. 4 is a sectional view showing a transfer device of the embodiment device, FIG. 5 is a block diagram showing a control unit of the embodiment device, and FIG. 8 is a control characteristic map diagram showing the relationship between the rotational speed difference and the command current value preset in the control unit of the example device; FIG. 7 is a relationship characteristic diagram between the command current value and the clutch hydraulic pressure in the example device; FIG. 9 is a characteristic diagram of the relationship between the clutch hydraulic pressure and the transmission torque to the front wheels in the embodiment apparatus, and FIG. 9 is a flow chart diagram showing the flow of the driving force distribution control operation in the control unit of the embodiment apparatus.
FIG. 10 is a flow chart showing the flow of the tuck-in detection operation, FIG. 11 is an explanatory view of the tuck-in prevention action in the embodiment apparatus, FIG. 12 is a map showing the set value characteristic of the throttle opening differential value, and FIG. FIG. 14 is a flowchart showing another example of the tuck-in detection operation, and FIG. 14 is an explanatory view of the tuck-in prevention action in the prior art. 1 ... front wheel 2 ... rear wheel 3 ... transfer clutch means 4 ... detection means 401 ... tuck-in detection means 5 ... clutch control means 6 ... differential limiting means

Claims (2)

(57) [Claims] 1. A transfer clutch provided in the middle of an engine drive system for transmitting engine drive force to front and rear wheels and capable of shifting drive force distribution from a rear wheel drive state to a four wheel drive state by an external clutch engagement force. Means, a clutch control means for outputting a control signal for changing the driving force distribution based on an input signal from the detection means, and a differential limiting torque when a rotational speed difference occurs between the left and right wheels provided in the differential device of the rear wheels. In a four-wheel drive vehicle including a differential limiting unit that generates, a clutch-in detecting unit that predicts an occurrence of a tack-in phenomenon that occurs during turning traveling in a four-wheel drive state as the detecting unit, The means is a means for performing control for shifting the driving force distribution to a rear wheel drive state in response to a tack-in detection signal from the tack-in detection means. Drive force distribution control device for moving vehicles. 2. The drive force distribution control device for a four-wheel drive vehicle according to claim 1, wherein the tuck-in detection means is composed of a throttle opening sensor and a vehicle lateral acceleration sensor, and the vehicle lateral acceleration is A four-wheel drive vehicle characterized in that it is a means for outputting a tack-in detection signal when the throttle opening is higher than a set value, the throttle opening is lower than the set value, and the time differential value of the throttle opening is larger than the set value. Driving force distribution control device.