GB2221739A

GB2221739A - Method for controlling a change-over between two and four wheel drive modes for a vehicle

Info

Publication number: GB2221739A
Application number: GB8913330A
Authority: GB
Inventors: Shohei Matsuda; Tadatoshi Haga; Kougyoku Go; Hiroshi Ikegami
Original assignee: Honda Motor Co Ltd
Current assignee: Honda Motor Co Ltd
Priority date: 1988-06-10
Filing date: 1989-06-09
Publication date: 1990-02-14
Anticipated expiration: 2009-06-09
Also published as: SE8902056L; DE3918612A1; JPH01311923A; JP2719926B2; SE466342B; GB8913330D0; CA1332574C; SE8902056D0; GB2221739B; DE3918612C2

Description

1 54309.503 Iú1 -_j 2"2 1 r17-9 METHOD FOR CONTROLLING A CHANGE-OVER

BETWEEN TWO AND FOUR-WHEEL DRIVE MODES FOR A VEHICLE The present invention relates to a method for controlling the change-over between two and four-wheel drive modes of a vehicle. The four-wheel drive mode is changed to the two-wheel drive mode when at least one wheel produces a locking tendency during braking.

In a control of change-over from a two to a fourwheel drive mode, conventional practice is to restore the drive mode from the two-wheel drive mode to the four-wheel drive mode when there is no tendency for all the wheels to be locked, after the drive mode has been changed from the four-wheel drive mode to the two-wheel drive mode.

Some of the operators or drivers may be accelerating while effecting a braking operation in vehicles equipped with an automatic transmission. In such a case, in spite of a desire to restore the drive mode from the two-wheel drive mode to the four-wheel mode, the restoration cannot be achieved when there is a locking tendency produced in the wheels which are driven wheels in the two-wheel drive mode.

The present invention has been accomplished with the circumstances of the prior art in view, and it is an object of the present invention to provide a method for controlling the change-over between two and four-wheel drive modes of a vehicle, wherein the two-wheel drive mode can be smoothly changed to the four-wheel drive mode during acceleration in the two-wheel drive mode.

Viewed from a first aspect the present invention provides a method for controlling the change-over between two-wheel and four-wheel drive modes of a vehicle comprising the steps of:

2 changing a four-wheel drive mode to a two-wheel drive mode when at least one wheel produces a locking tendency during braking; and changing the two-wheel drive mode to the four-wheel drive mode when the driving wheels have no locking tendency produced in the two-wheel drive mode.

With the feature that two-wheel drive mode is changed to the four-wheel drive mode when the driving wheels have no locking tendency produced in the two- wheel drive mode, it is possible to smoothly change over the drive mode to the four-wheel drive mode, when a driver is accelerating while conducting a braking operation in the two-wheel drive mode, by changing over to the four-wheel drive mode, even if the driven wheels in the two-wheel drive mode are in a locking tendency.

A second feature of the present invention is that when the driven wheels tend to be locked, the two-wheel drive mode is maintained until a predetermined time has elapsed after changing over from the four-wheel drive mode to the two-wheel drive mode. With the second feature, two-wheel drive mode is not changed back to the four-wheel drive mode during an initial stage of changing over from the four wheel drive mode to the twowheel drive mode, when the driven wheels are in a locking tendency and the driving wheels are not in a locking tendency.

A third feature of the present invention is that even if a locking tendency is produced in the driven wheels in the two-wheel drive mode, the four-wheel drive mode is maintained until a predetermined time has elapsed after changing over from the two-wheel drive mode to the four-wheel drive mode. With the third feature, the four-wheel drive mode is not changed back to the two- wheel drive node during an initial stage of changing over from the two-wheel drive mode to the fourwheel drive mode, when the driven wheels are in a locking tendency and the driving wheels are not in a 3 locking tendency.

The drawings illustrate one embodiment of the present invention, wherein Fig. 1 is a schematic illustration of a driving 5 system; Fig. 2 is a circuit diagram illustrating the arrangement of an essential portion of a control means; and Fig. 3 is a timing chart.

The present invention will now be described with reference to the accompanying drawings, by way of one embodiment applied in a vehicle in which the front wheels are driving wheels and the rear wheels are driven wheels in a two-wheel drive mode. Referring first to is Fig.1, a pair of front wheels Wfl and Wfr and a pair of rear wheels WrI amd Wrr are suspended respectively on a front portion and a rear portion of a vehicle body (which is not shown). Brakes Bft and Bfr; BrI and Brr are provided on the front and rear wheels Wfl and Wfr; WrI and Wrr, respectively. Anti-lock control means 2 is added to a hydraulic pressure control circuit 1. The hydraulic pressure control circuit 1 includes a brake device, together with the brakes BfI, Brf, Brt and Brr, for controlling the brakes BfI and Bfr on the front wheels Wfl and Wfr and the brakes BrI and Brr on the rear wheels WrI and Wrr with different operation modes. The anti-lock control means 2 is, for example, to separately control the hydraulic braking pressures for the brake Bft on the left front wheels Wft, the brake Bfr on the right front wheel Wfr and the brakes BrI and Brr on the rear wheels WrI and Wrr. The hydraulic braking pressure is reduced during anti- lock control.

The front and rear wheels M, Wfr, WrI and Wrr are connected through a driving system A to a power unit P.

The driving system A comprises a front differential Df connecting the front wheels Wfl and Wfr with the power unit P, a rear differential Dr connecting the rear 4 wheels WrI and Wrr, and a propeller shaft 3 connecting the power unit P with the rear differential Dr. At the middle of the propeller shaft, there is a dog clutch 4 which permits changing over between the connection and disconnection between the front and rear wheels Wfl, Wfr and WrI, Wrr. An actuator 5, such as a cylinder for driving the dog clutch 4, is controlled by a control means 6.

Fig. 2 illustrates the arrangement of an essential portion of the control means 6. A signal indicative of an anti-lock control state is input from the anti-lock control means 2 to input terminals 7, 8 and 9. Specifically, when the brake Bfl of the left front wheel Wfl is being anti-lock controlled, a higher level signal than normal is input to the input terminal 7, and when the brake Bfr of the right front wheel Wfr is being anti-lock controlled, a higher level signal is input to the input terminal 8. When the brakes Brf and Brr of both rear wheels Wrt and Wrr are being anti-lock controlled, the higher level signal is input to the input terminal 9. The input terminals 7 and 8 are connected in parallel to an OR circuit 10, and the input terminal 9 is connected to an AND circuit 11.

The OR circuit 10 is connected to an AND circuit 12 which is, in turn, connected to an output terminal 13 to deliver a higher level signal when the dog clutch 4 is disengaged to change over the four- wheel drive mode into the two-wheel drive mode. The AND circuit 12 is also connected to an invertor circuit 14 which is connected, in an inverted manner, to an input terminal of a timer circuit 15. The timer circuit 15 produces a higher level signal sustained for a given time TA from the change-over when the output from the invertor circuit 14 has been changed from a higher level into a lower level, i.e., when the output from the AND circuit 11 has been changed from a higher level into a lower level to change over the two-wheel drive mode into the four-wheel drive mode. The output from the timer circuit 15 is input, in an inverted manner, to the AND circuit 11.

A detector 16 (see Fig. 1) is added to the dog clutch 4 for detecting the operated state thereof and produces a higher level signal when the dog clutch 4 is in a disengaged state. The detector 16 is connected to a delay circuit 17 which produces a signal rising with a delay of a given time TB from the rising of a signal produced from the detector 16. The delay circuit 17 is invertedly connected to the AND circuit 11. Thus, output from the AND circuit 11 becomes a higher level, when the rear wheels WrI and Wrr are in a locking tendency, and within a period from a point when the given time T. has elapsed after changing over of the two- wheel drive mode into the four-wheel drive mode to a point when the given time TB has elapsed after the change-over into the two-wheel drive mode has been achieved.

A brake switch 18 is also connected to the AND circuit 12 and produces a higher level signal when a braking operation has been provided. Therefore, in order that the output from the AND circuit 12 goes to the higher level, the braking operation is a necessary condition.

The operation of this embodiment will be described below with reference to Figs. 3(a) to 3(c). Fig. 3(a) illustrates the output from the AND circuit 12. Fig.

3(b) illustrates the output from the timer circuit 15.

Fig. 3(c) illustrates the output from the delay circuit 17. Until the given time TA elapses after changing over from the two- wheel drive mode into the four-wheel drive mode, the output from the AND circuit 11 is at the lower level. After the given time TB has elapsed after changing over from the four-wheel drive mode into the two-wheel drive mode, the output from the AND circuit 11 becomes the lower level. Therefore, the output from the AND circuit 11 becomes the higher level, only when 6 the rear wheels WrI and Wrr show a tendency to be locked, and between a point A, after a lapse of the given time TA from changing over from the two-wheel drive mode into the four-wheel drive mode, and a point B, after a lapse of the given time T after changing over from the four-wheel drive mode into the twowheel drive mode.

If the braking occurs when the dog clutch 4 is in an engaged state to provide the four-wheel drive mode in which the front wheels Wfl and Wfr are connected to the rear wheels WrZ and Wrr, the output from the AND circuit 12 becomes the higher level in response to the output from the OR circuit 10 becoming the higher level, so that the dog clutch 4 is disengaged to permit changing is over from the four-wheel drive mode into the two-wheel drive mode. In other words, the dog clutch 4 is disengaged to provide the two-wheel drive mode, either in a condition where either one of the front wheels Wfl and Wfr tends to be locked and is anti-lock controlled, or in a condition where the rear wheels WrZ and Wrr are being anti-lock controlled.

In changing over into the two-wheel drive mode, the output from the AND circuit 11 remains at the higher level to maintain the two-wheel drive mode, until the given time TB has elapsed from the point of change-over, when the rear wheels WrI and Wrr, which are now driven wheels, tend to be locked. Thus, the drive mode is not immediately returned to the fourwheel drive mode when it has been changed over into the two-wheel drive mode in a condition where the rear wheels WrI and Wrr are in a locking tendency and the front wheels Wfl and Wfr are not in a locking tendency in the four-wheel drive mode.

When the front wheels WfZ and Wfr, which are at least driving wheels, have no locking tendency produced in the two-wheel drive mode, the output from the AND circuit 11 is at the lower level after the given time TB has elapsed after changing over, so that the output from 4 7 the OR circuit 10 goes to the lower level. In response to this, the output from the AND circuit 12 goes to the lower level, thereby permitting the dog clutch 4 to be engaged, resulting in the four-wheel drive mode. When the vehicle is accelerating while the operator of the vehicle is braking, the drive mode can be rapidly restored from the two-wheel drive mode to the four-wheel drive mode.

With this change-over from the two-wheel drive mode to the four-wheel drive mode, the output from the AND circuit 11 remains at the lower level until the given time TA has elapsed from the change- over. Accordingly, the drive mode is not immediately returned to the twowheel drive mode when it has been changed over into the is four-wheel drive mode in a condition where the rear wheels WrI and Wrr are in a locking tendency and the front wheels Wfl and Wfr are not in a locking tendency in the two-wheel drive mode.

As discussed above, according to the first aspect of the present invention, the two-wheel drive mode is changed to the four- wheel drive mode when the driving wheels have no locking tendency produced in the twowheel drive mode. Therefore, it is possible to smoothly change over the drive mode to the four-wheel drive mode when the vehicle is accelerating while the operator of the vehicle is braking during the two-wheel drive mode.

According to the second feature of the present invention, when the driven wheels tend to be locked, the two-wheel drive mode is maintained until a predetermined time has elapsed after changing over from the four-wheel drive mode to the two-wheel drive mode. Therefore, the two-wheel drive mode is not changed back to the fourwheel drive mode during an initial stage of changing over from the four-wheel drive mode to the two-wheel drive mode, when the driven wheels are in a locking tendency and the driving wheels are not in a locking tendency.

8 According to the third feature of the present invention, even if a locking tendency is produced in the driven wheels in the two-wheel drive mode, the fourwheel drive mode is maintained until a predetermined time has elapsed after changing over from the two-wheel drive mode to the four-wheel drive mode. Therefore, the four-wheel drive mode is not changed back to two-wheel drive mode during an initial stage of changing over from the two-wheel drive mode to the four-wheel drive mode, when the driven wheels are in a locking tendency, and the driving wheels are not in a locking tendency.

From the foregoing description of the preferred embodiment of the invention, it will be apparent that many modifications may be made therein. It should be understood that these embodiments are intended as one example of the invention only, and that the invention is not limited thereto.

It is to be clearly understood that there are no particular features of the foregoing specification, or of any claims appended hereto, which are at present regarded as being essential to the performance of the present invention, and that any one or more of such features or combinations thereof may therefore be included in, added to, omitted from or deleted from any of such claims if and when amended during the prosecution of this application or in the filing or prosecution of any divisional application based thereon. Furthermore the manner in which any of such features of the specification or claims are described or defined may be amended, broadened or otherwise modified in any manner which falls within the knowledge of a person skilled in the relevant art, for example so as to encompass, either implicitly or explicitly, equivalents or generalisations thereof.

9

Claims

CLAIMS:

1. A method for controlling the change-over between two-wheel and fourwheel drive modes of a vehicle comprising the steps of: changing a fourwheel drive mode to a two-wheel drive mode when at least one wheel produces a locking tendency during braking; and changing the two-wheel drive mode to the four-wheel drive mode when the driving wheels have no locking tendency produced in the two-wheel drive mode.

2. A method for controlling the change-over between two and four-wheel drive modes of a vehicle according to claim 1, further comprising the step of maintaining the two-wheel drive mode until a predetermined time has elapsed after change-over from the four-wheel drive mode to the two-wheel drive mode when driven wheels tend to be locked.

3. A method for controlling the change-over between two and four-wheel drive modes of a vehicle according to claim 1 or 2, further comprising the step of maintaining the four-wheel drive mode until a predetermined time has elapsed after change-over from the two-wheel drive mode to the four-wheel drive mode even if a locking tendency is produced in driven wheels in the two-wheel drive mode.

4. A method for controlling the change-over between two-wheel and fourwheel drive modes of a vehicle, substantially as hereinbefore described with reference to the accompanying drawings.

PubWied 1990 at The Patent Office, State House, 86 71 High Holborn, London WC1R 4TP. Further copiesmaybe obtained from The Patent OfficeSales Branch. St Mary Cray. Orpingtor. Kei.t BR5 3RD. Primed by Muldplex techniques ltd, St Mary Cray, Kent. Con. 1187