JPS61275031A - Drive selection controller for four-wheel drive car - Google Patents

Abstract

PURPOSE:To reduce the operating frequency of a clutch and make improvements in durability of the clutch, by installing a device which alters a slip criterion for selection to a four-wheel drive with detection of a frozen state, at the time of driving on a surfaced road and a frozen road surface. CONSTITUTION:A slip standard reference value which grows large when a road surface is not yet frozen but becomes small when frozen on the basis of an output signal out of a road state detecting device 16 is outputted out of a reference value setting device 17. On the other hand, a slip of one side wheel of front wheels or rear wheels is detected by a slip detecting device 15. When this slip exceeds the standard reference value, a selection signal to a four-wheel drive is outputted to a driving device 19 from a comparing device 18, driving a clutch 14. Therefore, the slip generated at the time of driving on a frozen road comes to a slight something, whereby running stability in a car is well improved, and at the time of driving on a surfaced road, it is selectable to the four-wheel drive only at a time when an undue slip occurs, thus operating frequency in the clutch 14 is reduced and its durability is improvable.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention relates to a drive switching control device for a four-wheel drive vehicle that automatically switches between two-wheel drive that drives one of the front and rear wheels and four-wheel drive that drives both. In particular, when driving on a good road, the system shifts to four-wheel drive only when the drive wheels experience a large slip (rotation relative to the road surface), but when driving on an icy road, the drive wheels shift to four-wheel drive only when a slight slip occurs. The present invention also relates to a drive switching control device for shifting to four-wheel drive.

(Prior Art) As a conventional drive switching control device for a four-wheel drive vehicle, for example, one described in Japanese Patent Application Laid-Open No. 58-56924 is known. This drive switching control device controls the rotational angular acceleration of the two-wheel drive system in a four-wheel drive vehicle, which transmits power directly to one of the front and rear wheels and, if necessary, transmits power to the other front and rear wheels by engaging a clutch. The vehicle is configured to automatically switch to four-wheel drive if it is in two-wheel drive immediately upon occurrence of slip, and to return to two-wheel drive again in response to a predetermined release signal.

(Problem to be solved by this invention) However,
Such a conventional drive switching control device for a four-wheel drive vehicle is configured to switch to four-wheel drive when a slip occurs where the rotational angular acceleration is greater than a predetermined reference value.
If the above reference value is set to a small value with the aim of eliminating slips on roads with low friction coefficients such as frozen roads, switching to 4-wheel drive will occur even if there is a slight slip on stable roads such as asphalt pavements. Therefore, there was a problem in that the frequency of clutch operation increased, which adversely affected durability.

(Means for Solving the Problems) The drive switching control device for a four-wheel drive vehicle according to the present invention has been made for the purpose of solving the conventional problems as described above, and is shown in FIG. In a four-wheel drive vehicle in which one of the front wheels 11 or the rear wheels 12 is directly connected to the engine 13 and the other wheel of the front wheels 11 or the rear wheels 12 is connected to the engine 13 via the clutch 14, slip detection means 15 for detecting wheel slip;
Road surface condition detection means 16 for detecting whether the road surface is a frozen road surface
and a reference value setting means 17 for outputting a comparison reference value which is large when the road surface is not a frozen road surface and small when the road surface is a frozen road surface based on the output signal of the road surface condition detection means 16; a comparison means 18 that compares a comparison reference value with the slip detected by the slip detection means 15 and outputs a drive signal when the slip exceeds the comparison reference value; and a comparison means 18 that outputs a drive signal when the comparison means 18 outputs a drive signal; 14 and connects the other wheel to the engine 13 by means of the clutch 14.

(Function) According to the drive switching control device for a four-wheel drive vehicle according to the present invention, when driving on a frozen road surface, wheel slip is compared with a relatively small reference value, and when the slip is larger than the reference value, If the vehicle is driving on a stable road such as an asphalt paved road, the vehicle will switch to four-wheel drive when the slip exceeds a relatively large reference value. Therefore, when driving on a frozen road, the slip generated by the wheels is small, improving the running stability of the vehicle, and when driving on a good road, if the wheels spin excessively, Now you can switch to four-wheel drive only.
The frequency of operation of the clutch 14 is also reduced, and durability can be improved.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIGS. 2 and 3 are diagrams showing an embodiment of a drive switching control device for a four-wheel drive vehicle according to the present invention. Note that this example is a 4-wheel drive vehicle based on a front-engine rear-wheel drive vehicle.
Shows what is applied to wheel drive vehicles.

First, to explain the configuration, in FIG. 2, 21 is an engine, 22 is a transmission (transmission) assembled integrally with the engine 21, and the output shaft of the transmission 22 is connected to the rear wheel propeller shaft 24 via a transfer 23. and is connected to the front wheel propeller shaft 25. The transfer 23 has a motor 26 connected to a drive circuit to be described later and a dog clutch 27 that is switched and driven by the motor 26, and directly connects the output shaft of the transmission 22 and the rear propeller shaft 24, and also connects the output shaft of the transmission 22. The shaft and the front wheel propeller shaft 25 are connected via a dog clutch 27. In this transfer 23, for example, when the motor 26 rotates forward, the dog clutch 27 is connected to the transmission 22.
The output shaft of the transmission 22 and the front propeller shaft 25 are connected to switch to four-wheel drive, and conversely, when the motor 26 reverses, the dog clutch 27 disconnects the output shaft of the transmission 22 and the front propeller shaft 25 to switch to two-wheel drive. The rear wheel propeller shaft 24 connects rear wheels 30L, 30 via a rear wheel differential 28 and left and right axles 29L, 29R.
Similarly, the front wheel propeller shaft 25 is connected to
Front wheel differential 31 and left and right axles 32L, 32R
It is connected to the front wheels 33L and 33R via. In addition,
The motor 26 of the transfer 23 can also be replaced with a fluid cylinder or the like.

34 is a rotational speed sensor that detects the rotational speed of the rear wheels 30L and 30R; 35 is a road surface condition detector that detects the road surface condition using ultrasonic waves; Detects the strength and amplitude of the reflected waves from the The rotational speed sensor 34 outputs a signal indicating the rotational speed to the differentiator 36, and the road surface condition detector 35 outputs a signal indicating the amplitude of the reflected wave to the judgment signal generation circuit 37. The differentiator 3°6 differentiates the output signal of the rotational speed sensor 34 and converts the output signal of the rotational angular acceleration into a comparison circuit 38.
Output to. The judgment signal generation circuit 37 is the road surface condition detector 3
The road surface condition is determined based on the signal input from the road surface condition detector 35 and the signal stored in the memory circuit.

When the judgment signal generation circuit 37 receives a signal indicating that the amplitude of the reflected wave is less than a predetermined value, it judges that the road surface is a low friction coefficient road surface such as a snowy road, and issues a four-wheel drive command signal. In addition, when a signal indicating that the amplitude of the reflected wave exceeds a predetermined value is input, a signal indicating that the amplitude of the reflected wave is less than the predetermined value has been input to the storage circuit within the previous predetermined time. is not memorized, it is determined that the road surface is a good road such as an asphalt paved road, and the first reference signal (
A first reference value) is output to the comparison circuit 38, and when a signal indicating that the amplitude of the reflected wave exceeds a predetermined value is input, a signal indicating that the amplitude of the reflected wave is less than or equal to a predetermined value is input to the storage circuit. If it is stored that the input signal is input within a predetermined time, it is determined that the road surface is a frozen road surface, and a second reference signal (second reference value) smaller than the first reference signal is output to the comparison circuit 38.

The comparison circuit 38 outputs a two-wheel drive or four-wheel drive drive signal to the drive circuit 39 based on the output signals of the differentiator 36 and the signal judgment circuit 37. This comparison memory circuit 38 is
4 when the signal judgment circuit 37 outputs a four-wheel drive command signal
When the signal judgment circuit 37 outputs the first reference signal and the output signal of the differentiator 36 is equal to or higher than the first reference signal, it outputs the four-wheel drive drive signal. If the first reference signal is less than the first reference signal, a two-wheel drive drive signal is output, and when the signal judgment circuit 37 outputs the second reference signal, if the output signal of the differentiator 36 is greater than or equal to the second reference signal, the four-wheel drive signal is output. A drive signal for driving is output, and if the second reference signal is not satisfied, a drive signal for two-wheel drive is output. The drive circuit 39 is
When a four-wheel drive drive signal is input from the comparison memory circuit 38, the motor 26 of the transfer 23 is energized to rotate forward and the dog clutch 27 is connected, and when a two-wheel drive drive signal is input, the motor 26 is turned on. The dog clutch 27 is disconnected by applying electricity so as to reverse the rotation.

The rotational speed sensor 34 and the differentiator 36 described above correspond to the threshold detection means, the road surface condition detector 35 and the signal judgment circuit 37 correspond to the road surface condition detection means, and the signal judgment circuit 37 corresponds to the reference value setting means. , furthermore, the comparison circuit 38 corresponds to comparison means, and furthermore, the above-mentioned motor 26
and the drive circuit 39 correspond to the drive means.

In addition, in the above-mentioned embodiment, the slip, that is, the relative rotation of the wheel with respect to the road surface is estimated based on the rotational angular acceleration of the wheel.
It is also possible to estimate based on the rotational speed difference between the front and rear wheels.

Next, the effect will be explained.

This drive switching control device for a four-wheel drive vehicle sets a reference limit according to road surface conditions, and switches from two-wheel drive to four-wheel drive when the slip of the rear wheels 30L, 30R exceeds the reference limit.

The following will be explained with reference to the flowchart in Figure 3.
First, in step P1, it is determined whether the amplitude of the reflected wave incident on the road surface condition detector 35 is less than a predetermined value, that is, whether the road surface has a low coefficient of friction such as a snowy road, and the amplitude of the reflected wave is determined. When it is determined that the amplitude is less than the predetermined value (when the road surface has a low friction coefficient), the process proceeds to step P2, and the amplitude of the reflected wave exceeds the predetermined value. When it is determined that (when the road surface has a high friction coefficient such as an asphalt pavement), the process proceeds to step P3. In step P2, the drive circuit 39 applies current to the motor 26 of the transfer 23 to cause it to rotate forward, and the dog clutch 27 connects the engine 21 and the front wheels 33L, 33R, resulting in four-wheel drive that drives both the front and rear wheels. Switch. Therefore, when driving on such a low friction coefficient road surface, the rear wheels 30L,
30R no longer generates slip, and driving performance can be improved.

In step P3, it is determined whether the rotational angular acceleration of the rear wheels 30L, 30R is equal to or greater than the first reference value, and if the rotational angular acceleration is less than or equal to the first reference value, the process proceeds to step P2 described above and the four-wheel drive is activated. If the rotational angular acceleration does not meet the first reference value, the process proceeds to step P4. In step P4, it is determined whether the amplitude of the reflected wave that has entered the road surface condition detector 35 during a predetermined period of time has become equal to or less than a predetermined value. That is, in this step P4, the reflected wave of the ultrasonic wave reflected on the frozen road surface is not attenuated in the same way as on a good road, so if the amplitude of the reflected wave becomes small within a certain period of time,
The road surface is estimated to be partially covered with snow and frozen. In this step P4, if it is determined that the amplitude of the reflected wave has fallen below a predetermined value within a predetermined time (if it is estimated that the road surface is frozen), the process proceeds to step P, where the amplitude of the reflected wave is If it is determined that the amplitude has never been below a predetermined value, the process proceeds to step P. In step P, similarly to step P3, it is determined again whether the rotational angular acceleration of the rear wheels 30L, 30R is greater than or equal to the second reference value, and if the rotational angular acceleration is greater than or equal to the second reference value, step P2 described above is performed. The process proceeds to step P6 to switch to four-wheel drive, and if the rotational angular acceleration does not meet the second reference value, the process proceeds to step P6 to switch to two-wheel drive. This step P.

In this case, a current is applied to the motor 26 of the transfer 23 to reverse the rotation, and the dog clutch 27 disconnects the front wheels 33L and 33R from the engine 21.

In this way, when driving on a frozen road surface, even if a slight slip occurs, the system switches to four-wheel drive to improve driving stability, but when driving on a good road, a large slip occurs. Since the system switches to four-wheel drive only when the
7 durability can be improved.

Note that the above-mentioned embodiment is applied to a four-wheel drive vehicle equipped with the transfer 23 of the dog clutch 27, but it is also applicable to a part-time four-wheel drive vehicle having a hydraulic or electromagnetic friction clutch or a differential limiting device. Needless to say, it is also possible to apply the present invention to a full-time four-wheel drive vehicle having an attached central differential.

(Effects of the Invention) As explained above, according to the drive switching control device for a four-wheel drive vehicle according to the present invention, even if a slight slip occurs when driving on a frozen road surface, the drive switching control device for a four-wheel drive vehicle can switch to four-wheel drive. ,
Since the system switches to four-wheel drive only when a relatively large slip occurs when driving on a good road, it is possible to improve the driving performance of the vehicle and reduce the frequency of clutch operation, thereby improving clutch durability.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a drive switching control device for a four-wheel drive vehicle according to the present invention. 2 and 3 show an embodiment of a drive switching control device for a four-wheel drive vehicle according to the present invention,
FIG. 2 is a schematic overall diagram, and FIG. 3 is a flowchart. 11.33L, 33R・・・front wheel, 12.30L
, 3OR... Rear wheel, 13.21... Engine, 14.27... Clutch (dog clutch), 15... Slip detection means, 16.25...Road surface condition detection means (road surface condition detector) 17.37...Reference value setting means (signal judgment circuit), 18.38...Comparison means ( comparison circuit), 1
9... Drive means, 34... Rotational speed sensor, 36... Differentiator.

Claims (1)

[Claims] One of the front wheels or the rear wheels is directly connected to the engine, and the other front wheel or the rear wheel is connected to the engine via a clutch, and when the slip of the one wheel exceeds a reference limit, the other wheel is connected to the engine. The drive switching control device for a four-wheel drive vehicle connected to the engine by the clutch includes a road surface condition detection means for detecting whether the road surface is in a frozen state, and a road surface state detection means for detecting whether the road surface is in a frozen state based on an output signal of the road surface state detection means. 1. A drive switching control device for a four-wheel drive vehicle, comprising: reference value changing means for lowering the reference limit when the reference limit is present.