1. Field of the Invention
This invention relates to a power switching device, and more particularly to vehicle power switching device.
2. Description of the Related Art
Referring to FIG. 1, a transmission system disclosed in U.S. Pat. No. 7,018,317 is used in a vehicle, such as an all-terrain vehicle (ATV), and includes a controller 100, a first-coupler pushing member 102 driven by the controller 100, an input shaft (or driving shaft) 11, an output shaft 12 (or driven shaft) 12, a first sliding block 13 (or coupler), and a differential 14 driven by the output shaft 12 to interconnect a left axle 15 and a right axle 16 so as to allow for co-rotation of the left and right axles 15, 16. The first sliding block 13 is sleeved movably on the output shaft 12. When the first sliding block 13 is moved to a four-wheel drive position, a portion of the first sliding block 13 is moved onto the input shaft 11, so that the vehicle is in a four-wheel drive mode. When the portion of the first sliding block 13 is not moved onto the input shaft 11, the first sliding block 13 is at a two-wheel drive position whereat the vehicle is in a two-wheel drive mode. As such, through operation of the controller 100, the vehicle is convertible between the four-wheel drive mode and the two-wheel drive mode.
Due to the function of the differential 14, the left and right axles 15, 16 can rotate at different speeds to facilitate turn of the vehicle. However, if one of the left and right axles 15, 16 drops into a sandy or muddy road surface, different speeds of the left and right axles 15, 16 will result in difficulties in removing the one of the left and right axles 15, 16 from the road surface. At this time, to remove the one of the left and right axles 15, 16 from the road surface, it is necessary to lock the differential 14 to allow for co-rotation of the left and right axles 15, 16.
To lock the differential 14, an actuator (not shown) is operated to pull a cable 144 to thereby move a shaft 141 downwardly. Hence, a second-coupler pushing member 142 on the shaft 141 moves a portion of a second sliding block 143 from the left axle 15 onto the right axle 16, thereby allowing for co-rotation of the left and right axles 15, 16.
The aforesaid conventional transmission system suffers from the following disadvantages:
1. Difficult Control:
The differential 14 is locked by pulling the cable 144 to move the shaft 141, the second-coupler pushing member 142, and the second sliding block 143. The vehicle can be changed between the four-wheel drive mode and the two-wheel drive mode through operation of the controller 100. That is, the differential locking operation and the vehicle mode changing operation are performed by operating two different members, thereby resulting in difficult control on the transmission system.
2. Unsteady Locking:
Although the shaft 141 and the second-coupler pushing member 142 can be moved by pulling the cable 144, typically, they are not moved during an initial small-distance pulling movement of the cable 144. As a result, the displacement amount of the second sliding block 143 is insufficient to lock the differential 14 effectively. To compensate for such insufficiency, a sensor 143 can be provided to detect the position of the second sliding block 143, thereby increasing the manufacturing costs of the transmission system.