The present invention relates to a throttle valve operating device for use with an engine for a vehicle, and more particularly to a throttle valve operating device with traction control function such that when a slip condition of driving wheels of the vehicle is detected, a throttle valve is forcibly closed irrespective of accelerator pedal operation to reduce an output of the engine.
Conventionally, such a throttle valve operating device with traction control function is disclosed in Japanese Patent Laid-open Publication No. 61-75024, for example. A construction of the conventional throttle valve operating device is schematically shown in FIGS. 11A to 11C.
Referring to FIGS. 11A to 11C, reference numeral 200 designates a throttle shaft adapted to be rotated with a throttle valve (not shown). An arm 201 extends radially outwardly from the throttle shaft 200. A throttle lever 202 is connected to an end of an accelerator cable 204. The other end of the accelerator cable 204 is connected to an accelerator pedal (not shown). When the accelerator pedal is depressed, the throttle lever 202 is rotated clockwise through the accelerator cable 204. The throttle lever 202 is mounted on the throttle shaft 200 so as to be rotatable relative to the throttle shaft 200. Both the arm 201 of the throttle shaft 200 and the throttle lever 202 are biased by a torsion spring 206 so as to maintain a given positional relationship. That is, an end portion of the torsion spring 206 normally biases the throttle lever 202 in a counterclockwise direction, and the other end portion of the torsion spring 206 normally biases the arm 201 of the throttle shaft 200 in a clockwise direction.
FIG. 11A shows a condition where the accelerator pedal is not depressed. Under the condition, the throttle valve is in a full closed condition.
FIG. 11B shows a condition where the accelerator pedal is depressed from the condition of FIG. 11A. When the accelerator pedal is depressed, the accelerator cable 204 is drawn in a direction of arrow P, and the throttle lever 202 is accordingly rotated clockwise from the condition of FIG. 11A. At the same time, the arm 202 and the throttle shaft 200 are rotated clockwise by the torsion spring 206 from the condition of FIG. 11A. As a result, the throttle valve is opened.
FIG. 11C shows a condition where a traction control motor (not shown) is driven upon detection of the slip condition to forcibly rotate the throttle shaft 200 in the closing direction of the throttle valve. Under the condition, the accelerator cable 204 is maintained in the drawn condition by the depression of the acclerator pedal, and the throttle lever 202 is maintained in abutment against the one end portion of the torsion spring 206. On the other hand, the other end portion of the torsion spring 206 is urged by the arm 201 due to the forced rotation of the throttle shaft 200 in the counterclockwise direction from the condition of FIG. 11B by the operation of the traction control motor. As a result, the torsion spring 206 is elastically deformed as shown in FIG. 11C.
According to the above construction utilizing the torsion spring 206, when the traction control motor is in an inoperative condition, the throttle shaft 200 is rotated by the operation of the accelerator pedal through the torsion spring 206, while when the traction control motor is operated, the throttle shaft 200 is rotated in the closing direction of the throttle valve by the operation of the motor owing to the elastic deformation of the torsion spring 206 irrespective of the depression of the accelerator pedal.
However, the above interconnection between the throttle lever 202 and the throttle shaft 200 is provided by the single torsion spring 206. Accordingly, if the torsion spring 206 is broken for any reason, the throttle shaft 200 cannot be rotated by the throttle lever 202. That is, the throttle valve cannot be operated by the operation of the accelerator pedal. In the circumstances that recent improvement of engine performance has permitted high-speed rotation of the engine, the throttle valve and its peripheral region tend to be vibrated at a high frequency, causing a risk of breakage of the torsion spring 206.