Motor vehicles – Having four wheels driven – Including pump and fluid motor – or generator and electric...
Reexamination Certificate
2000-06-01
2001-12-18
Lerner, Avraham H. (Department: 3618)
Motor vehicles
Having four wheels driven
Including pump and fluid motor, or generator and electric...
C180S249000, C180S197000, C192S1030FA
Reexamination Certificate
active
06330928
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to four-wheel drive vehicles comprising a pair of front or rear driven wheels which are driven directly by a prime mover and another pair of front or rear driven wheels which are driven via a hydraulic clutch. A first hydraulic pump is driven by being operatively connected to the pair of driven wheels and a second hydraulic pump is driven by being operatively connected to the other driven wheels. The engagement force of the hydraulic clutch is controllable according to the difference in rotation between the first and the second hydraulic pumps.
2. Description of the Prior Art
The use of a two-wheel drive state using only one pair of front or rear driven wheels during normal travel is known in the art, and when a difference in rotation between the front and the rear wheels occurs both pairs of front and rear driven wheels are driven together so as to enhance the travel stability. If the difference in rotation between the front and the rear wheels is maintained so as to be small all the time, a tight brake phenomenon is caused when turning at a low speed causing the driver to feel uncomfortable and, moreover, it is necessary to increase the strength of the components used for transmitting the driving force between the front and the rear wheels, thus increasing the weight of the vehicle. It is disclosed in Japanese Patent Application Laid-open No. 3-224830 that the front wheels are always driven. When the difference in rotation between the front and the rear wheels is small, the torque transmitted to the rear wheels is made small, and the torque transmitted to the rear wheels is increased according to increases in the difference in rotation, and thus the above-mentioned problems are solved.
However, on a road surface having a low coefficient of friction such as a snow-covered road it is desirable to increase the amount of torque transmitted to the rear wheels even when the difference in rotation between the front and the rear wheels is small, but in the above-mentioned system the amount of torque transmitted to the rear wheels remains small when the difference in rotation between the front and the rear wheels is small, and thus the objective cannot be obtained.
SUMMARY OF THE INVENTION
The present invention has been conducted in view of the above-mentioned circumstances, and it is an object of the present invention, with regard to a four-wheel drive vehicle wherein one pair of front or rear driven wheels are always driven and the driving force of the other pair of front or rear driven wheels is controllable, to provide a driving force control device for a four-wheel drive vehicle in which the torque transmitted to the other pair of the front or rear driven wheels can be controlled according to the driving conditions of the vehicle.
In order to achieve this object, the invention is characterized in that a driving force control device is provided for a four-wheel drive vehicle which comprises one pair of front or rear driven wheels which are driven directly by a prime mover, and another pair of front or rear driven wheels which are driven via a hydraulic clutch. A first hydraulic pump which is driven is operatively connected to the one pair of driven wheels, and a second hydraulic pump which is driven, is operatively connected to the other pair of driven wheels. The engagement force of the hydraulic clutch is controllable based on the difference between the discharge and intake amounts of the first and second hydraulic pumps due to the difference in rotation of the two hydraulic pumps, such that the engagement force increases according to an increase in the difference between the discharge and intake amounts. The driving force control device includes an engagement force control means for controlling the engagement force of the hydraulic clutch by selecting from multiple engagement characteristics in which the responsiveness of the torque transmission by the hydraulic clutch is varied according to the driving conditions of the vehicle.
In accordance with this arrangement, since the engagement force of the hydraulic clutch is controlled by the engagement force control means by selecting an engagement characteristic according to the driving conditions of the vehicle, the responsiveness of the torque transmission by the hydraulic clutch can be controlled according to the driving conditions of the vehicle.
The invention is further characterized in that a hydraulic oil supply passage which carries the hydraulic oil produced according to the difference between the discharge and intake amounts of the first and second hydraulic pumps, is connected to a hydraulic oil pressure chamber in the hydraulic clutch. The engagement force control means includes an orifice provided through a drain oil passage for draining the hydraulic oil in the hydraulic oil pressure chamber and a switching valve provided between the orifice and the hydraulic oil pressure chamber.
In accordance with this arrangement of the invention, when the switching valve is open, since the engagement force of the hydraulic clutch relative to the difference in rotation between the first and second hydraulic pumps is determined by the reduction in the amount of oil drained by the orifice, the responsiveness of the torque transmission is low, whereas when the switching valve is closed, since the hydraulic oil is prevented from draining from the hydraulic oil pressure chamber, the engagement force of the hydraulic clutch relative to the difference in rotation between the first and second hydraulic pumps, increases thus enhancing the responsiveness of the torque transmission, and the arrangement of the engagement force control means can therefore be simplified.
In addition, the engagement force control means includes a bypass connecting the orifice and the hydraulic oil pressure chamber when bypassing the switching valve, and a relief valve is provided in the bypass so that it opens in the event that the oil pressure at the side of the hydraulic oil pressure chamber, is at or above a predetermined level. In accordance with this arrangement, an upper limit for the oil pressure of the hydraulic oil pressure chamber in a state in which the responsiveness of the torque transmission by the hydraulic clutch is enhanced by closure of the switching valve, that is, an upper limit for the torque transmitted by the hydraulic clutch, is determined by the valve opening pressure for the relief valve and thus excess torque transmission by the hydraulic clutch in a state where there is enhanced responsiveness, can be prevented by a simple arrangement.
The invention, in addition to the arrangement above is characterized in that a control unit for controlling the motion of the engagement force control means comprises a slip detecting means for detecting the slip of the one pair of front or rear driven wheels, a starting status detecting means for detecting the starting status of the vehicle, a counter for counting the number of times that the starting status is detected by the starting status detecting means, and an engagement characteristic selecting means for selecting an engagement characteristic in which the responsiveness of the torque transmission by the hydraulic clutch is enhanced until the count number of the counter reaches a predetermined number after the slip is detected by the slip detecting means.
In accordance with this arrangement of the invention, when the slip detecting means detects the slip in one pair of the front or rear driven wheels, the responsiveness of the torque transmission by the hydraulic clutch is enhanced until the number of times that the starting status is detected by the starting status detecting means reaches a predetermined number. That is, when slip is caused in one pair of the front or rear driven wheels on a road surface having a low coefficient of friction such as a snow-covered road, the responsiveness of the torque transmission is enhanced until the number of times that the vehicle is started reaches a predetermined number by
Arai Yasunori
Matsuo Hiroyuki
Sekiya Shigenobu
Takahashi Keiichi
Arent Fox Kintner & Plotkin & Kahn, PLLC
Honda Giken Kogyo Kabushiki Kaisha
Lerner Avraham H.
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