JP2502735B2 - Drive force distribution controller for four-wheel drive vehicle - Google Patents

Description

TECHNICAL FIELD The present invention relates to a drive force distribution control device for a four-wheel drive vehicle in which front and rear wheel drive force distribution can be changed.

(Prior Art) Conventionally, as a drive force distribution control device for a four-wheel drive vehicle, for example, as described in Japanese Patent Laid-Open No. 63-13331, the rotational speeds from front and rear wheel rotational speed difference detection means are described. There is known a device that increases / decreases the clutch engagement force based on the difference signal to change the distribution of the driving force from the engine to the front and rear wheels.

When applying this device to vehicles, in order to suppress excessive drive wheel slip while taking advantage of maneuverability, which is an advantage of rear-wheel drive vehicles, front and rear wheel rotational speed difference (rear wheel-front wheel) and clutch engagement force (front wheel drive). As shown in Fig. 11, the relationship between torque and) is such that the front wheel drive torque is reduced when the front and rear wheel rotation speed difference is small, and the front wheel drive torque is increased as the front and rear wheel rotation speed difference is increased. It is necessary to set it as possible.

(Problems to be Solved by the Invention) However, in such a conventional drive force distribution control device, for example, when acceleration is performed while the steering angle is constant during turning, the front wheel drive torque relative to the front and rear wheel rotation speed difference is The smaller the rate of increase, the more the vehicle follows the course without going off the course even if the speed increases. Therefore, the maneuverability is improved, but the amount of decrease in lateral acceleration during acceleration operation is large, which impairs driving feeling.

On the other hand, as the increase rate of the front-wheel drive torque with respect to the front-rear wheel rotation speed difference is larger, the lateral acceleration decrease amount is smaller during the acceleration operation and the driving feeling is better, but the vehicle is off course as the speed increases after the acceleration operation. As a result, maneuverability deteriorates.

That is, the front wheel drive torque / rear wheel rotation speed difference in the area before and after the wheel rotation speed difference is smaller as the front wheel drive torque coefficient k _f, turning locus by the front wheel drive torque coefficient k _f (12
(Fig. 13) and the relationship of the lateral acceleration due to the front wheel drive torque coefficient k _f (Fig. 13), the front wheel drive torque coefficient k _f is small k _f
When = 0.1, the ability to follow the course is good, but the amount of decrease in lateral acceleration during acceleration operation is large.

This is because the lateral force generated in the tire decreases due to the increase of the driving force that exceeds the tire capacity of the rear wheels where the distribution of the driving force is large.

When the front wheel drive torque coefficient k _f is large and k _f = 2.0,
Although the amount of decrease in lateral acceleration at the time of accelerating operation is small, the vehicle goes off course as the speed increases.

This is because the driving force distribution to the front wheels is large and the understeer characteristic is exhibited as the turning characteristic as in the case of the rigid 4WD.

(Object of the Invention) The present invention has been made by paying attention to the problems as described above, and one of the front and rear wheels directly transmits the engine driving force,
On the other hand, in a torque split type four-wheel drive vehicle that transmits via a torque distribution clutch, a driving force that can improve drivability during acceleration operation while ensuring good maneuverability during subsequent vehicle acceleration. An object is to provide a distribution control device.

(Means for Solving the Problem) In order to achieve the above object, in the drive force distribution control device for a four-wheel drive vehicle according to the present invention, the final drive force distribution target value is accelerated to the target value due to the front and rear wheel rotation speed difference. The means for obtaining the sum of the target values by the operation was used.

That is, as shown in the claim correspondence diagram of FIG. 1, the engine driving force is transmitted to one of the front and rear wheels by direct coupling, and is transmitted to the other of the front and rear wheels via a torque distribution clutch a that is engaged by an external control force. A four-wheel drive vehicle having a drive system, which has front and rear wheel rotation speed difference detection means b, and sets a front and rear wheel drive force distribution target value based on front and rear wheel rotation speed difference information. A second drive force distribution target value setting means e for setting a front and rear wheel drive force distribution target value based on the acceleration operation information, which has a target value setting means c and a driver's acceleration operation detecting means d, and a first drive. A final driving force distribution target value setting means f for setting a final driving force distribution target value by adding the target value from the force distribution target value setting means c and the target value from the second driving force distribution target value setting means e; It is characterized by having ,.

(Operation) During acceleration operation, second driving force distribution target setting means e for setting front and rear wheel driving force distribution target values based on the acceleration operation information.
Then, the second driving force distribution target value is set, and in the final driving force distribution target value setting means f, the value obtained by adding the second driving force distribution target value and the first driving force distribution target value is the final value. It is set as a driving force distribution target value.

Therefore, during the acceleration operation, the driving force distribution to the non-direct drive wheels is temporarily increased and the driving force to the direct drive wheels is prevented from increasing, and the drivability is improved.

Then, the first drive force distribution target value setting means for setting the front and rear wheel drive force distribution target values based on the front and rear wheel rotation speed difference information by not accompanied by the acceleration operation during vehicle acceleration that occurs after the acceleration operation. A value that is almost the same as the driving force distribution target value from c is set as the final driving force distribution target value.

Therefore, by optimally setting the driving force distribution characteristic with respect to the front-rear wheel rotation speed difference, good maneuverability is secured.

(Example) Hereinafter, the Example of this invention is described based on drawing.

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

 First, the configuration will be described.

As shown in FIG. 2, the drive system of a four-wheel drive vehicle to which the drive force distribution control device of the embodiment is applied has an engine 1, a transmission 2, a transfer input shaft 3, a transfer clutch device C, a rear propeller shaft 4 as shown in FIG. The rear differential 5, the rear wheel 6, the transfer output shaft 7, the front propeller shaft 8, the front differential 9, and the front wheel 10 are provided, and the engine driving force that has passed through the transmission 2 is directly transmitted to the rear wheel and the front wheel 10 To the transfer input / output shafts 3 and 7 via a transfer clutch device C provided between the transfer input / output shafts 3 and 7.

Further, outside the transfer clutch device C, a hydraulic pressure control device 20 is provided as a driving force distribution control means for generating a control hydraulic pressure Pc which is a clutch engagement force based on predetermined input information and control content.

The hydraulic control device 20 includes a motor 22 driven or stopped by a relief switch 21, a hydraulic pump 24 which is operated by the motor 22 to suck up from a reservoir tank 23, and a pump discharge pressure (primary pressure) from the hydraulic pump 24. An accumulator 26 that stores via a check valve 25, and an electromagnetic proportional pressure valve 28 that adjusts a line pressure (secondary pressure) from the accumulator 26 to a predetermined control hydraulic pressure Pc by a command control current value i ^* from a control unit 27. And is supplied to the control hydraulic boat 30 through the control hydraulic pipe 29.

The control unit 27 has an electronic control circuit configuration and includes a front wheel rotation speed sensor 31, a rear wheel rotation speed sensor 32, an accelerator operation amount sensor 33, and the like as information input sensors.

Then, in the control unit 27, there is provided a first target value setting circuit 27a (FIG. 5) for setting a first torque coefficient target value k ₀ ′ based on the front and rear wheel rotational speed difference information, and an accelerator as acceleration operation information. A second target value setting circuit 27b (FIG. 6) that sets a second torque coefficient target value k ₁ ′ based on the operation speed, and a first torque coefficient target value k ₀ ′ from the first target value setting circuit 27a. The final torque coefficient target value k _f ′ is obtained by adding the second torque coefficient target value k ₁ ′ from the second target value setting circuit 27b.
And a driver circuit for outputting to the solenoid proportional pressure valve 28 a command control current value i ^* for obtaining a front wheel drive torque target value ΔT _F obtained from the final torque coefficient target value k _f ′.
27d and.

As shown in FIG. 3, the transfer clutch device C includes a multi-plate friction clutch 60 that is engaged by a pressing mechanism 40 that is operated by a control hydraulic pressure Pc from an external hydraulic control device 20,
A lubrication pump (70) that sucks up the lubricating oil (15) for cooling the clutch in the transfer case (11) and the case cover (12) and guides the lubricating oil (15) to an inner position of the multi-plate friction clutch (60) is provided.

The pressing mechanism 40 of the multi-plate friction clutch 60 includes a cylinder block 41, a piston chamber 42, a piston 43, a piston rod 44, a swing plate 45, a swing pin 46, a fixed pressure plate 47, a bearing 48, and a rotary pressure plate.
It is equipped with 49, pressure block 50, and return spring 51.

The multi-plate friction clutch 60 includes a clutch drum 61 that is spline-coupled to the transfer input shaft 3, a drive plate 62 that is spline-fitted to the clutch drum 61,
The driven plate 63 sandwiched between the drive plates 62 and the driven plate 63 are spline-fitted,
Needle bearing 64 for transfer input shaft 3
And a clutch hub 65 rotatably supported by the clutch hub 65.

From the clutch hub 65, the first sprocket 66
→ Chain 67 → Drive torque is transmitted to the transfer output shaft 7 through the second sprocket 68.

The lubrication pump 70 is of a trochoid pump type provided in a pump housing 71 and a pump cover 72 at the inlet of the transfer input shaft 3, and has a suction port 73.
Communicates with a suction tube 75 having a suction port 74, and its discharge port 76 is connected to a radial oil passage 77, an axial oil passage 78, a radial oil passage 79 and a clutch hub 65 formed in the transfer input shaft 3. It communicates with the formed oil holes 80, 81, sucks up the lubricating oil 15 for cooling the clutch in the transfer case 11, guides the lubricating oil 15 to the multi-plate friction clutch 60, and discharges it through the oil hole 82. The clutch cooling lubricant 15 stored in the lower portion of the transfer case 11 is provided with a front wheel 10 offset from the transfer input shaft 3.
The transfer output shaft 7 and the chain 67 are immersed, and the suction port 74 of the lubrication pump 70 is arranged. In FIG. 3, 90 is a joint flange, 91, 92, 93
Are seals, and 94,95,96,97,98 are bearings.

 Next, the operation will be described.

First, the flow of the clutch engagement force control processing operation performed by the control unit 27 of the embodiment will be described with reference to the flowchart of FIG.

In step 101, the front wheel rotation speed N _f , the rear wheel rotation speed N _r, and the accelerator operation amount 1 are read from both the rotation speed sensors 31, 32 and the accelerator operation amount sensor 33.

In step 102, the front wheel rotation speed N _f and the rear wheel rotation speed N _r
Based on and, the front-rear wheel rotation speed difference ΔN (= N _r −N _f ) is calculated.

In step 103, the accelerator operation speed (= dl / dt) is calculated from the accelerator operation amount l.

In step 104, the first torque coefficient target value k ₀ ′ is calculated based on the front and rear wheel rotation speed difference ΔN.

The first torque coefficient target value k ₀ ′ is a constant value in a region where the front and rear wheel rotation speed difference ΔN is small, as shown in FIG.

In step 105, the second torque coefficient target value k ₁ ′ is calculated based on the accelerator operation speed. As shown in FIG. 6, the second torque coefficient target value K ₁ is obtained as a value that increases in proportion to an increase in accelerator operating speed due to a predetermined proportional constant A.

In step 106, the first torque coefficient target value k ₀ ′ and the second torque coefficient target value k ₀ ′
The final torque coefficient target value k _f ′ is calculated by addition with the torque coefficient target value k ₁ ′.

In step 107, the front wheel drive torque target value ΔT _F is calculated from the final torque coefficient target value k _f ′ and the front and rear wheel rotation speed difference ΔN (FIG. 4).

In step 108, the command control current value i ^{* with} which the front wheel drive torque target value ΔT _F is obtained is output to the electromagnetic proportional pressure valve 28.

Next, the driving force distribution control operation in the embodiment in the case where the steering angle is kept constant and the vehicle is accelerated during turning will be described.

When the driver depresses the accelerator pedal, the accelerator operation amount changes as shown in the accelerator operation amount characteristic of FIG.
l varies from ₀ to l _1, as shown in the accelerator operating speed characteristic of Figure 8, the accelerator operating speed ₁ in pedal depression time Delta] t. Therefore, this accelerator operation speed l ₁
The second 'will be given, as shown in final torque coefficient target value characteristic of Figure 8, during the Δt time final torque coefficient target value k _f' torque coefficient target value k ₁ based on the high characteristics However, in reality, it is not possible to immediately respond to this torque coefficient target value command. Therefore, if this transfer function is a first-order lag, the actual front wheel drive torque coefficient k _f is the front wheel drive torque coefficient of FIG. It is possible to increase only the shaded portion of the characteristic.

As described above, at the time of the acceleration operation, the increase in the driving force to the rear wheels is suppressed as the distribution of the driving force to the front wheels temporarily increases based on the acceleration operation information.

Therefore, as shown in the comparative lateral acceleration and characteristic diagram of the comparison between the case of the present embodiment of FIG. 9 and the case where the front wheel drive torque is determined only by the rotational speed difference, conventionally, as shown in the characteristic curve, the tire capacity at the rear wheel with a large drive force distribution is large. By increasing the driving force to exceed
The reduction amount of the lateral acceleration caused by the reduction of the lateral force generated in the tire is suppressed to be small, and the drivability is improved.

When the vehicle accelerates after the acceleration operation, the final torque coefficient target value is
Since k _f ′ becomes the first torque coefficient target value k ₀ ′, the first torque coefficient target value k ₀ ′ is set to a small value in advance (for example, k ₀ ′ = 0.1).
If set to, the trackability of the course will be high and the 10th
As shown in the figure, good maneuverability without course out is secured. As a result, it is possible to improve the drivability during the acceleration operation and ensure good maneuverability during the subsequent vehicle acceleration.

If the vehicle acceleration is monitored and a large amount of drive torque is distributed to the front wheels during acceleration, the driving feeling deteriorates during an acceleration operation in which vehicle acceleration does not occur, and four wheels are used during subsequent vehicle acceleration. Become the driving side and go off the course.

Although the embodiment has been described with reference to the drawings, the specific configuration and control contents are not limited to this embodiment.

For example, in the embodiment, an example of application to the drive force distribution control device of a rear wheel-based four-wheel drive vehicle in which the rear wheel side is directly connected to the engine is shown. It can also be applied to a drive force distribution control device for a wheel drive vehicle.

Further, in the embodiment, the operation at the time of turning traveling is described, but when the acceleration operation is performed by depressing the pedal at the time of traveling straight, the four-wheel drive distribution direction is temporarily set and the increase of the driving force to the driving wheels is suppressed. Therefore, the drive wheel slip that occurs when the drive force exceeds the tire capacity of the drive wheels is effectively prevented, and as with the case of turning acceleration, the drivability during acceleration operation is improved and the vehicle after that is improved. Good maneuverability during acceleration can be secured.

Further, the acceleration operation can be detected not only by the accelerator operation amount but also by the throttle valve opening degree, the engine intake negative pressure and the like.

(Effects of the Invention) As described above, in the drive force distribution control device for a four-wheel drive vehicle of the present invention, the final drive force distribution target value is the target value due to the front-rear wheel rotation speed difference and the target due to the acceleration operation. Since it is a means to obtain the sum of the values, one of the front and rear wheels directly transmits the engine drive force, and the other one transmits it via the torque distribution clutch. It is possible to obtain the effect that good maneuverability can be ensured during the subsequent vehicle acceleration while improving the driving performance.

[Brief description of drawings]

FIG. 1 is a diagram showing a drive force distribution control device for a four-wheel drive vehicle according to the present invention, and FIG. 2 shows a drive system and a control system for a four-wheel drive vehicle to which the drive force distribution control device of the embodiment is applied. Figure,
FIG. 3 is a sectional view showing a transfer clutch device used in the embodiment apparatus, FIG. 4 is a front wheel drive torque target value characteristic diagram with respect to front and rear wheel rotation speed difference, and FIG. 5 is a first torque coefficient target value characteristic diagram, FIG. 6 is a second torque coefficient target value characteristic diagram,
FIG. 7 is a flow chart showing the flow of driving force distribution control operation in the control unit of the embodiment, FIG. 8 is a time chart during acceleration operation, and FIG. 9 is the case of this embodiment during acceleration turn and the conventional case. FIG. 10 is a lateral acceleration characteristic comparison diagram, FIG. 10 is a comparison diagram of turning trajectories in the case of the present embodiment and a conventional case at the time of accelerated turning, and FIG. The figure shows the turning locus comparison diagram when the front wheel drive torque coefficient is set variously.
FIG. 13 is a lateral acceleration characteristic comparison diagram when various front wheel drive torque coefficients are set. a ... Torque distribution clutch b ... Front / rear wheel rotational speed difference detection means c ... First driving force distribution target value setting means d ... Acceleration operation detection means e ... Second driving force distribution target value setting means f ... Final driving force distribution target Value setting means

Claims (1)

(57) [Claims] 1. A four-wheel drive vehicle having a drive system in which an engine driving force is transmitted to one of the front and rear wheels by direct coupling and is transmitted to the other of the front and rear wheels via a torque distribution clutch that is engaged by an external control force. And a first driving force distribution target value setting means for setting front and rear wheel driving force distribution target values based on the front and rear wheel rotation speed difference information, and a driver's acceleration operation. Second drive force distribution target value setting means for setting front and rear wheel drive force distribution target values based on acceleration operation information, and target values from the first drive force distribution target value setting means and second drive A driving force of a four-wheel drive vehicle, comprising: a final driving force distribution target value setting means for adding a target value from the force distribution target value setting means to set a final driving force distribution target value. Distribution control device.