Motor vehicles – Having four wheels driven – With differential means for driving two wheel sets at...
Reexamination Certificate
1999-11-12
2002-05-07
Swann, J. J. (Department: 3611)
Motor vehicles
Having four wheels driven
With differential means for driving two wheel sets at...
C180S242000, C180S252000
Reexamination Certificate
active
06382339
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a driving apparatus for use in four-wheel drive vehicles for transmitting power from a drive source to steerable wheels and nonsteerable wheels via a main HST (hydraustatic transmission).
2. Prior Art
When four-wheel drive vehicles having steerable wheels and nonsteerable wheels respectively at a front position and a rear position of the vehicle are turned, a difference occurs in turning radius between the steerable wheel and the nonsteerable wheel. For example, when the vehicle shown in FIG.
1
and having rear wheels serving for steering is turned, the rear wheel turns along a path of a greater radius than the front wheel. If the front and rear wheels are rotated at the same speed, therefore, the rear wheel skids on the terrain. Such a skid of the rear wheel roughs the terrain or causes wear on the rear wheel. Especially with vehicles adapted to travel on lawns like lawn mowers, roughing the terrain is undesirable.
Already proposed to preclude this drawback are (1) a driving apparatus having a one-way clutch provided in the path of power transmission to the steerable wheels for transmitting a driving power to the steerable wheel and also permitting the steerable wheel to rotate at a higher speed than the nonsteerable wheel when the vehicle is turned, and (2) a driving apparatus wherein the path of power transmission to the steerable wheels is provided with a gear transmission unit for giving an increased speed. The gear transmission unit is brought out of operation when the vehicle is advanced straight, or is operated to rotate the steerable wheel at a higher speed than the nonsteerable wheel when the vehicle is turned.
However, the driving apparatus (1) has the drawback the vehicle fails to fully exhibit the performance of four-wheel drive since the nonsteerable wheels only are driven as in a two-wheel drive vehicle when the vehicle is turned. This entails another drawback that the vehicle is impaired in running performance when turning with a small radius since the nonsteerable wheels only are driven for turning.
Further with the driving apparatus (2), the steerable wheel is rotatable only at two speeds, i.e., a high speed and the same speed as the nonsteerable wheel. On the other hand, the difference between the steerable wheel and the nonsteerable wheel in turning radius is proportional to the steering angle of the steering wheel to be handled by a driver. Thus, in order to effectively prevent the steerable wheels from skidding during turning of the vehicle, there is a need to vary the rotational speed difference between the steerable wheel and the nonsteerable wheel. Accordingly the driving apparatus (2) which affords only two different rotational speeds to the steerable wheels fails to fully preclude the steerable wheels from skidding. Further although the driving apparatus is capable of providing two different speeds, i.e., a high speed and the same speed, for the steerable wheel, it is impossible to increase the rotational speed difference between the steerable wheel and the nonsteerable wheel because the rotational speed of the nonsteerable wheel is constant. If the vehicle is turned with a small radius, i.e., if the difference between the steerable wheel and the non and the nonsteerable wheel in turning radius is great, it is difficult to obtain such a speed difference as to offset the radius difference.
Also known is a driving apparatus similar to the apparatus
1
and having a transmission unit for giving an increased speed which unit comprises a pair of pulleys and a belt reeved around the pulleys, the pulleys being variable in effective diameter according to the rotation angle of the steering wheel at the driver's seat. However, although adapted to vary the rotational speed of the steerable wheel, the apparatus also encounters difficulty in increasing the rotational speed difference between the steerable wheel and the nonsteerable wheel since the rotational speed of the nonsteerable wheel is constant.
Further, in a vehicle with a four-wheels steering system, the resembling problem occurs. That is, the turning radius of front ground wheel and rear ground wheel is usually different to each other. Therefore, the adjustment between the rotational speed of the front wheels and the rear wheels is necessary.
SUMMARY OF THE INVENTION
An object of the present invention, which has been accomplished to overcome the foregoing problems, is to provide a driving apparatus for use in four-wheel drive vehicles, the apparatus being adapted to effectively prevent the steerable wheels from skidding while transmitting power to the steerable wheels when turning the vehicle.
To fulfill the foregoing object, the present invention provides a driving apparatus for a vehicle for transmitting power from a drive source installed in a body of the vehicle to steerable wheels and nonsteerable wheels via a main HST, the driving apparatus comprises: a transmission unit for receiving a rotational output from the main HST, a steerable wheel drive shaft and a nonsteerable wheel drive shaft for receiving a rotational output from the transmission unit and transmitting the rotational output respectively to an axle for driving the steerable wheels and an axle for driving the nonsteerable wheels, and a differential unit for rotating the steerable wheel drive shaft at an increased speed and rotating the nonsteerable wheel drive shaft at a decreased speed according to the steering angle of the steering wheel.
Preferably, the driving apparatus can be so constructed that the steerable wheel drive shaft and the nonsteerable wheel drive shaft are arranged on approximately the same axis and spaced apart from each other at opposed ends thereof, the transmission unit comprising: a main drive shaft disposed between the opposed ends of the steerable wheel drive shaft and the nonsteerable wheel drive shaft on the same axis as the two shafts, a driving power transmission mechanism for transmitting the rotational output of the main HST to the main drive shaft, and a steerable wheel planetary gear unit and a nonsteerable wheel planetary gear unit for transmitting the rotation of the main drive shaft respectively to the steerable wheel drive shaft and the nonsteerable wheel drive shaft so as to rotate the wheel drive shafts in the same direction, the steerable wheel planetary gear unit having a first sun gear mounted on the main drive shaft, a first outer wheel surrounding the first sun gear, a first inner gear provided on an inner periphery of the first outer wheel, first planetary gears arranged between the first sun gear and the first inner gear, and a first carrier supported on the steerable wheel drive shaft nonrotatably relative thereto and rotatable with the revolution of the planetary gears, the nonsteerable wheel planetary gear unit having a second sun gear mounted on the main drive shaft, a second outer wheel surrounding the second sun gear, a second inner gear provided on an inner periphery of the second outer wheel, second planetary gears arranged between the second sun gear and the second inner gear, and a second carrier supported on the nonsteerable wheel drive shaft nonrotatably relative thereto and rotatable with the revolution of the second planetary gears.
The driving apparatus can be so constructed that the differential unit comprises: a differential HST for receiving the power from the drive source and outputting a differential rotational drive force, and a second differential power transmission mechanism for receiving the rotational output from the differential HST and giving the first outer wheel and the second outer wheel respective additional rotations in opposite directions to each other, the differential HST being adapted not to output the rotational drive force when the vehicle is advanced straight and to output the rotational drive force with a number of revolutions in accordance with the steering angle of the steering wheel when the vehicle is turned, the differential power tran
Kanzaki Kokyukoki Mfg. Co. Ltd.
Lum L.
Swann J. J.
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