JPH04372428A - Two-wheel/four-wheel drive change control device for vehicle - Google Patents

Abstract

PURPOSE:To reduce a clutch changing shock by counting a time from a change timing at which four-wheel drive is changed to two-wheel drive to a next change to four-wheel drive estimating that a road surface mu is small when a counted value is a set value or less, and setting a clutch fastening speed faster than normal. CONSTITUTION:During operation of a vehicle, a control unit 10 determines if a current operating condition is a 4WD changing condition or not by determining if a rotation difference between front wheel 3 and rear wheels 7 is a predetermined value or more based on each wheel velocity obtained by wheel velocity sensors 8a-8d. A time from a timing of a change from a four-wheel drive into a two-wheel drive till a timing which is determined to be that for a change into the next four-wheel drive is counted based on a result of determination. When it is determined that a counted value exceeds a set value, a clutch fastening speed is set as that for normal run, while the counted value is determined to be the set value or less, the clutch fastening speed is controlled to be increased.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention can control two-wheel drive (2WD) and four-wheel drive (4WD) by controlling clutch engagement and disengagement.
The present invention relates to a two-wheel to four-wheel switching control device for a vehicle that performs switching from two-wheel drive to four-wheel drive, and particularly to one that controls the clutch engagement speed when switching from two-wheel drive to four-wheel drive.

0002

2. Description of the Related Art Conventionally, in a vehicle, a clutch mechanism is provided at the rear stage of a transmission, and the clutch is disconnected or connected based on the difference in rotational speed between the front and rear wheels.
There are devices that allow switching between wheel drive and four-wheel drive (see Utility Model Application No. 1-146462, etc.).

By the way, such a conventional vehicle normally runs in two-wheel drive, and when four-wheel drive driving conditions are reached, the clutch is connected to switch to four-wheel drive. And 4
After switching to wheel drive, the clutch is disengaged and the system returns to two-wheel drive after a set period of time has elapsed, regardless of the state of the vehicle.

0004

[Problem to be Solved by the Invention] By the way, switching between 2 wheels and 4 wheels is performed using, for example, an electromagnetic clutch, but when driving on a normal road, turning the clutch on and off instantaneously causes a large shock, so it is difficult to switch between 2 wheels and 4 wheels. Gradually turn O from clutch state
N. Turned off. On the other hand, for example, when driving on a low μ road, when the 4-wheel drive setting time expires and the 4-wheel drive switches to 2-wheel drive, it is desirable to switch back to 4-wheel drive as soon as possible. When switching to four-wheel drive due to a rotational difference occurring again, if the clutch is gradually turned on from the half-clutch state, the time spent in the half-clutch state becomes loss time.

The present invention has been made in view of the above circumstances, and it is possible to change the engagement speed of the clutch variably depending on the road surface condition when switching from two-wheel drive to four-wheel drive.
An object of the present invention is to provide a two-wheel to four-wheel switching control device for a vehicle that appropriately switches from one wheel to four wheels.

[0006]

[Means for Solving the Problems] Therefore, the present invention has the following features:
As shown in the figure, the clutch is controlled to engage and disengage based on the rotational difference between the front and rear wheels of the vehicle to switch between two-wheel drive and four-wheel drive, and the point at which the switch is made from two-wheel drive to four-wheel drive. 2 of the vehicle that switches to two-wheel drive after a set time has elapsed.
In the wheel-to-four wheel switching control device, a time counting means for counting the time from the time when switching from four-wheel drive to two-wheel drive to the time when it is determined to switch back to four-wheel drive, and a count value of the time counting means. Clutch control means for increasing the clutch engagement speed during normal driving when it is determined that the count value exceeds the set value, and increasing the clutch engagement speed when the count value is determined to be below the set value. Configured.

[0007]

[Operation] In this configuration, the time counting means counts the time from when four-wheel drive is switched to two-wheel drive until it is determined to switch back to four-wheel drive. When this counted value is less than a preset value, it means that the frictional resistance coefficient of the road surface is small and a rotation difference will occur again even if you return to two-wheel drive. It would be better to switch to four-wheel drive. Therefore, when the count value exceeds the set value, the clutch is operated during normal driving, but when the count value is below the set value, the clutch engagement speed is increased to prevent loss time.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 2 showing the configuration of this embodiment, the driving force of the engine 1 is divided into two parts via a transfer (not shown), one part is transmitted to the front differential 2 to drive the front wheels 3, and the other part is transmitted to the propeller shaft 4.
The signal is transmitted to a rear differential 6 via an electromagnetic clutch 5 interposed therein to drive the rear wheels 7. Further, near the left and right front wheels 3 and rear wheels 7, wheel speed sensors 8a to 8d are provided to detect wheel speeds, respectively. 2 wheel drive-4
Control unit 10 that controls wheel drive switching
has a built-in microcomputer, inputs detection signals from the wheel speed sensors 8a to 8d, and determines when to switch between two-wheel drive and four-wheel drive based on the detection signals as shown in the flowchart of FIG. The electromagnetic clutch 5 is controlled to be disconnected and connected. Therefore, the control unit 10 corresponds to a time counting means and a clutch control means, and in this embodiment, these functions are provided in the control unit 10 in the form of software as shown in each flowchart described later.

Further, the signals from the wheel speed sensors 8a to 8d are used for ABS (anti-lock brake system) control, and are sent to the ABS control control unit 1.
5 is also entered. and control unit 1
0 constantly monitors the operation of the ABS control control unit 15, and when the ABS is activated and an activation signal is input, the electromagnetic clutch 5 is immediately disconnected and the system switches to two-wheel drive.

Next, according to the flowchart shown in FIG.
The switching control operation between two-wheel drive and four-wheel drive in the control unit 10 will be explained. In step 1 (denoted as "S" in the figure, the same applies hereinafter), each wheel speed is input from the wheel speed sensors 8a to 8d. Step 2
Then, the 4WD flag value is determined, and if the current driving is two-wheel drive (4WD flag value=0), the process proceeds to step 3.

[0011] In step 3, the current driving state is 4WD.
It is determined whether the switching condition is met. This determination is made by checking whether the rotational difference between the front wheels 3 and the rear wheels 7 based on the respective wheel speeds is greater than or equal to a predetermined value. If the wheel rotation difference is less than a predetermined value, it is determined that the 2WD driving condition is met, and the process proceeds to step 4. In step 4, the count value of the 2WD timer is incremented. The 2WD timer will switch to 2WD and then switch to 4WD.
This is a timer that counts the time until it is determined that the switch should be made. This step 4 corresponds to a time counting means. In this state, when it is determined in step 3 that the difference in rotation between the front wheels 3 and the rear wheels 7 exceeds a predetermined value and the 4WD switching condition is met, the process proceeds to step 5.

In step 5, the 4WD flag value is set to 1. In step 6, a hold time, which is a 4WD setting time, is set. In step 7, the count value of the 2WD timer counted in step 4 is compared with a preset count setting value. This count setting value is a value set in advance assuming that the road is a low μ (frictional resistance coefficient) road. For example, when driving on a low μ road such as a snowy road, even if you switch to 2WD after the set time has passed after switching to 4WD, a rotation difference will occur again and the condition for switching to 4WD will be met immediately, so the count value will be less than this count setting value. When necessary, increase the clutch engagement speed. When it is determined that the count value of the 2WD timer exceeds the count setting value, it is determined that normal driving is being performed, and the high speed ON flag is set to 0 in step 9, and the process proceeds to step 10. Then, in step 10, it is determined that the 4WD flag value = 1, and in step 12
Proceed to.

[0013] In step 12, the high-speed ON flag value = 0.
is determined and the process proceeds to step 13. In step 13,
Normal clutch engagement control is performed. That is, when switching from 2WD to 4WD, the ON speed of the 4WD clutch is made gentle as shown in the schedule in the graph in step 13 to avoid shock caused by the clutch switching operation. Then return to step 1.

[0014] When switching from 2WD to 4WD is performed in this manner, it is determined in step 2 that the 4WD flag value=1, and the process proceeds to step 15. In step 15, the hold time is counted down. In step 16, it is determined whether the hold time has exceeded the time limit, and when it is determined that the hold time has exceeded the time limit,
In step 17, the 4WD flag is set to 0, and in step 18, the count value of the 2WD timer is cleared to 0, and the process proceeds to step 10.

In step 10, it is determined that the 4WD flag value is 0, and the process proceeds to step 11. In step 11, switching control to 2WD is performed at a normal clutch speed. That is, when switching from 4WD to 2WD, the OFF speed of the 4WD clutch is made gentle as shown in the schedule in the graph in step 11, so that there is no shock caused by the clutch switching operation. Then return to step 1.

[0016] The vehicle is running in 2WD and time is counted. Then, when the 4WD driving condition is reached, the determination in step 7 is performed. In step 7, the count value of the 2WD timer and the count setting value are compared, and if the road is low μ, it is determined to switch to 4WD in a short time, and it is determined that the count value is less than the count setting value. In this case, proceed to step 8.

In step 8, the high speed ON flag is set to 1 and the process proceeds to step 10. and in step 10 4
It is determined that the WD flag value is 1, and the process proceeds to step 12. In step 12, the high-speed ON flag value is determined to be 1, and the process proceeds to step 14. In step 14, 4W when driving on a low μ road
D clutch engagement control is performed. That is, from 2WD to 4W
When switching to D, increase the ON speed of the 4WD clutch as shown in the schedule in the graph in step 14,
To prevent time loss due to a half-clutch state when switching to 4WD. Then return to step 1.

Here, steps 10 to 14 correspond to clutch control means. The graphs in steps 11, 13, and 14 show the relationship between the switching time between two wheels and four wheels and the amount of current applied to the 4WD electromagnetic clutch, which is proportional to the engagement speed of the 4WD clutch. According to this configuration, 2WD
When switching from 2WD to 4WD, if the count value of the timer in 2WD is less than the count setting value, the system assumes that the road is low and controls the 4WD clutch engagement speed to be faster. , if the count exceeds the set value, it is assumed that the road is not low μ and the engagement speed is controlled slowly. For example, when driving on a low μ road, when it is determined to switch from 2WD to 4WD, It is possible to eliminate time loss due to a half-clutch state when switching to 4WD, and during normal driving, the shock caused by the 4WD clutch switching operation is reduced, and appropriate clutch control can be performed depending on the road surface condition.

[0019]

[Effects of the Invention] As explained above, according to the present invention, 4
Counts the time from the time when switching from wheel drive to two-wheel drive until the time when it is determined to switch back to four-wheel drive, and if the count value of the timer during two-wheel drive is less than the set value, the frictional resistance of the road surface is measured. By estimating that the coefficient is small and engaging the clutch faster than usual, there is no time loss when switching to four-wheel drive on roads with a small coefficient of frictional resistance, and the shock caused by clutch switching during normal driving is reduced. Therefore, appropriate clutch control can be performed depending on the road surface condition, and the performance of the 2-wheel to 4-wheel switching control device can be improved.

[Brief explanation of drawings]

[Fig. 1] Block diagram explaining the configuration of the present invention

[Fig. 2] A configuration diagram showing an embodiment of the present invention.

[Fig. 3] Flowchart showing the switching control operation of the embodiment same as above.

[Explanation of symbols]

1 Engine 3 Front wheel 5 Electromagnetic clutch 7 Rear wheel 8a Wheel speed sensor 8b Wheel speed sensor 8c Wheel speed sensor 8d Wheel speed sensor 10 Control unit (for 2WD-4WD switching control)

Claims (1)

[Claims] Claim 1: Switching between two-wheel drive and four-wheel drive is performed by controlling clutch engagement and disengagement based on the rotational difference between the front and rear wheels of the vehicle, and the point at which the switch is made from two-wheel drive to four-wheel drive. Switches to 2-wheel drive after a set time elapses In the 2-4 wheel switching control device of a vehicle, it counts the time from the time it switches from 4-wheel drive to 2-wheel drive until the time it decides to switch back to 4-wheel drive. When the count value of the time count means is determined to exceed the set value, the clutch engagement speed is set to normal driving, and when the count value is determined to be below the set value, the clutch engagement speed is set to A two-wheel-to-four-wheel switching control device for a vehicle, comprising: a clutch control means for increasing the engagement speed of the vehicle.