Differential device for 4WD-vehicles

Details Differential device for 4WD-vehicles Differential device for 4WD-vehicles

2002-03-26

2003-10-21

Wright, Dirk (Department: 3681)

Planetary gear transmission systems or components

Differential planetary gearing

With universal joint in drive train

C180S247000, C475S223000

Reexamination Certificate

active

06634978

ABSTRACT:

The present application is based on and claims priority under 35 U.S.C §119 with respect to Japanese Patent Application No. 2001-088873 filed on Mar. 26, 2001, the entire content of which is incorporated herein by reference.
FIELD OF THE INVENTION
The present invention generally relates to four wheel drive vehicles (4WD-vehicles). More particularly, the present invention pertains to a differential device for 4WD-vehicles which is capable of selecting any one of a two wheel drive (2WD) state, a differential-free 4WD state, and a differential-locked 4WD state.
BACKGROUND OF THE INVENTION
A known differential device for 4WD-vehicles is disclosed in Japanese Patent Laid-Open Publication No. Hei.8-85355. This differential device for 4WD-vehicles is capable of selecting any one of a 2WD state, a differential-free 4WD state, and a differential-locked 4WD state. This differential device includes a differential case to which a driving force is transmitted from a driving shaft to rotate, a differential accommodated in the differential case and having a pair of side gears, with the pair of side gears being adapted to deliver the driving force transmitted to the differential case to a pair of wheel axles, a driving shaft adapted to rotate together with one of the road-wheels, and a first sleeve establishing and interrupting a connection between one of the side gears associated with one of the road-wheels and the driving shaft. The first sleeve is operated upon being shifted in position to switch from the 2WD state to the differential-free 4WD state and vice versa. A second shaft is connected to the outer surface of the first sleeve in a spline connection manner, with the second sleeve establishing and interrupting a connection between the driving shaft and the differential case. The second sleeve is operated upon being position shifted to switch from the differential-free 4WD state to the differential-locked 4WD state and vice versa.
However, the above-described known differential device requires a pair of actuators for shifting the positions of the respective first and second sleeves. The need for these two actuators increases the mass and production costs associated with the differential device.
A need thus exists to provide a differential device which is free from the aforementioned drawbacks.
SUMMARY OF THE INVENTION
A differential device for 4WD vehicles includes a differential case which receives a driving force from a driving shaft to rotate the differential case, first and second side gears accommodated in the differential case to deliver the driving force transmitted to the differential case at a ratio to first and second wheels, a rotation member rotatable together with the first wheel, a sole actuator, a switching mechanism operably driven in a wheel-axis direction by the sole actuator, and a relative movement inhibiting mechanism. The switching mechanism selectively establishes one of a 2WD state in which the rotation member is out of connection with the first side gear, a differential-free 4WD state in which a connection is established only between the rotation member and the first side gear, and a differential-locked 4WD state in which the first side gear is connected to both the differential case and the rotation member. The switching mechanism includes a movable first member continually connected to the rotation member, with the first member being connected to the first side gear when the first member is moved in one direction along the wheel-axis relative to the rotation member, and with the first member being disconnected from the first side gear when the first member is moved in an opposite direction relative to the rotation member. The switching mechanism also includes a movable second member continually connected to the first member, with the second member being connected to the differential case when the second member is moved in one direction along the wheel-axis relative to the first member, and with the second member being disconnected from the differential case when the second member is moved in an opposite direction along the wheel-axis relative to the first member. The second member is positionable in a first position corresponding to the 2WD state, a second position corresponding to the differential-free 4WD state, and a third position corresponding to the differential-locked 4WD state. The relative movement inhibiting mechanism inhibits on demand movement of the first member relative to the rotation member, and inhibits on demand movement of the second member relative to the first member. The relative movement inhibiting mechanism is constructed so that while the second member is positioned within a range from the first position to the second position, the relative movement inhibiting mechanism inhibits the movement of the second member relative to the first member while the first member and the second member are concurrently moved relative to the rotation member. The relative movement inhibiting mechanism is also constructed so that while the second member is positioned within a range from the second position to the third position, the relative movement inhibiting mechanism inhibits the movement of only the first member relative to the rotation member, while the second member is brought into movement relative to the first member under an immovable condition of the first member along the wheel-axis.
The sole actuator drives the second member to move to the first position, resulting in the 2WD state in which the connection is released between the rotation member and one of the side gears. When the second member is moved to the second position, the first member moves together with the second member resulting in the differential-free 4WD state in which the first member connects the rotation member to only one of the side gears. Moreover, when the second member is further moved to the third position, only the second member is moved, with the first member remaining unchanged in position, thus causing both the second and first members to connect the differential case to the rotation member while also causing the first member to connect the rotation member to one of the side gears. This produces the differential-locked 4WD state in which the rotation member, one of the side gears and the differential case are connected. Thus, a differential is provided in which any one of the 2WD state, the differential-free 4WD state, and the differential-locked state can be selected when the second member is moved to respective positions by driving only the sole actuator, resulting in that the differential device can be down-sized and produced at a lower cost.
It might be possible to integrate the first and second members and drive the resulting member to move to the first, second and third positions to establish the aforementioned driving states. However, when such an integrated member is at its second position at which the rotation member and the side gear are connected by the integrated member, the three members receive a driving torque. Thus, to move the three members to the third position would require movement against the friction force asserted between two adjacent members. Thus, a higher output force is required. In contrast, with the differential here, the second member is moved from the second position to the third position and the second position establishes the connection between the rotation member and the side gear via the first member. Thus, only the second member is moved without having to also move the first member whose sliding friction is relatively large. By making the first member and the second member separate from each other, an excessively high output force of the actuator is not necessary.
The rotation member, the first member, the second member, the first side gear and the differential case are preferably in coaxial alignment with each other, and the second member is preferably a substantially cylindrical member in spline connection with the outer surface of the first member which is also preferably a substantially cylindrical member. In addition, the fi

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