1. Field of the Invention
The present invention relates to an improvement in a V-pulley control mechanism for a variable-speed drive of belt type used as a transmission of a vehicle such as a motor vehicle.
2. Related Background Art
In recent years, in place of a conventional automatic transmission (AT), a variable-speed drive of belt type in which a speed can be changed in a stageless fashion has been used as a transmission of a vehicle such as a motor vehicle. The reason is that the variable-speed drive of belt type does almost not have speed change shock and has higher transmission efficiency than that of the AT and can achieve lower fuel consumption.
As an example of the variable-speed drive of belt type, there is a variable-speed drive of V-belt type comprising two pulleys each having variable V-shaped groove, and an endless metallic belt extending between the pulleys, in which any speed change ratio can be obtained in a stageless fashion by varying widths of the grooves of the pulleys.
As such a conventional variable-speed drive of belt type, for example, there is a V-belt control mechanism for a variable-speed drive of V-belt type as shown in FIG. 10. In FIG. 10, torque from a drive motor 100 such as an electric motor is converted into a thrust force by a screw mechanism 101 through a plurality of gears. The converted torque shifts a movable sheave 103 of a V-pulley 102 comprised of a movable sheave 103 which can be shifted in an axial direction and a fixed sheave 104 in a thrust direction, with the result that desired speed change ratio can be obtained by increasing or decreasing the width of the V-pulley 102.
Further, in a conventional V-belt control mechanism for a variable-speed drive of V-belt type as shown in FIG. 11, the screw mechanism of FIG. 10 is replaced by a ball screw mechanism 106, and a worm gear portion 107 is provided between the ball screw mechanism and a drive motor 105, thereby providing a reverse rotation preventing mechanism.
The movable sheave (primary sheave) of the V-pulley is always biased toward a direction for widening the V-pulley by a tension force of the V-belt and a spring force of a secondary pulley. In order to prevent the returning of the movable sheave upon stoppage of the drive motor, a lead angle of the screw portion is set to be smaller. In such a case, however, there is a danger of reducing efficiency for converting the rotational torque into the thrust force. Further, if the ball screw is used in the screw mechanism of the drive portion for the movable sheave of the V-pulley, although the converting efficiency for converting the rotational torque into the thrust force or vice versa is increased, a worm gear (for preventing reverse rotation) must be interposed between the V-pulley and the drive motor to prevent the returning of the movable sheave of the V-pulley, with the result that the converting efficiency for converting the rotational torque of the drive motor into the thrust force of the movable sheave or vice versa will be decreased.
Accordingly, an object of the present invention is to provide a V-pulley control mechanism for a variable-speed drive of belt type in which returning of a movable sheave (reverse rotation of a drive motor) can be prevented without reducing converting efficiency for converting rotational torque of the drive motor into a thrust force of the movable sheave and vice versa.
To achieve the above object, according to the present invention, there is provided a V-pulley control mechanism for a variable-speed drive of belt type in which driving of a V-pulley of the variable-speed drive of belt type is controlled by a motor, wherein the V-pulley control mechanism is disposed between the motor and the V-pulley and comprises a clutch tightening portion, a clutch mechanism which can be tightened by the clutch tightening portion, and a one-way clutch portion.
When it is assumed that a rotational direction of the drive motor for decreasing a width of the primary V-pulley is a normal (forward) direction, as the drive motor is rotated in the normal direction, the clutch tightening portion tightens the clutch mechanism. In this case, since the rotational direction is a direction that the one-way clutch is rotated idly, the clutch mechanism and the one-way clutch portion are rotated integrally, with the result that the torque is transmitted to the V-pulley to shift the movable sheave toward the fixed sheave. As the drive motor is rotated in a reverse direction, the clutch tightening portion releases the clutch mechanism, with the result that the movable sheave is shifted away from the fixed sheave. When the drive motor is stopped, the rotation from the movable sheave is transmitted to the clutch tightening portion to tighten the clutch mechanism, with the result that the clutch mechanism and the one-way clutch portion try to be rotated integrally. However, since the rotational direction only results in engagement of the one-way clutch, the rotation from the movable sheave is stopped to prevent the returning of the movable sheave. Further, the reverse rotation of the drive motor can be prevented.
Further, the present invention provides a V-pulley control mechanism in which driving of a V-pulley of the variable-speed drive of belt type is controlled by a motor, wherein the V-pulley control mechanism is disposed between the motor and the V-pulley and comprises a clutch tightening portion, a clutch mechanism which can be tightened by the clutch tightening portion, and a one-way clutch portion.
Further, the clutch tightening portion may include a screw mechanism.
Further, the clutch tightening portion may include a ball screw mechanism.
Further, the clutch tightening portion may include a cam mechanism.
Furthermore, the movable sheave of the V-pulley can be urged in an axial direction by a second ball screw mechanism.