Variable ratio transmission mechanism

A variable ratio transmission mechanism is used in an automobile. The automobile includes first and second steering shafts extending along a first direction. The variable ratio transmission mechanism includes a securing unit connected to the first steering shaft, a connecting unit connected to the second steering shaft, a motor connected to the securing unit and including a revolving shaft that extends rotatably along a second direction different from the first direction, and a transmitting unit including a worm gear that is provided on the connecting unit and a worm that is provided on the revolving shaft and that engages and is angularly-slidable relative to the worm gear.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a transmission mechanism, more particularly to a variable ratio transmission mechanism for an automobile steering system.

2. Description of the Related Art

A conventional variable ratio transmission mechanism, as disclosed in U.S. Pat. No. 7,278,512, is used in an automobile steering system. The automobile steering system includes a first steering shaft coupled to a steering wheel, and a second steering shaft coaxial to the first steering shaft and coupled to a pinion shaft that is connected to a wheel unit of the automobile. The conventional variable ratio transmission mechanism includes a first unit coupled to the first steering shaft, and a second unit that is driven by the first unit and that is coupled to the second steering shaft. The first unit includes a first housing connected co-rotatably to the first steering shaft, a rotor disposed in the first housing and coaxial to the first steering shaft, and a lock mechanism for locking the rotor. The second unit includes a connector connected to the rotor, and a second housing coupled to the connector and the second steering shaft.

When the lock mechanism is operated to lock the rotor from rotating relative to the first housing, the first steering shaft is rotatable with the first housing, the rotor, the connector, the second housing and the second steering shaft, so that the second steering shaft rotates in the same rotational velocity of the first steering shaft.

When the lock mechanism is operated to unlock the rotor from the first housing, the second steering shaft would be driven rotatably by the rotor and has a rotational velocity different from that of the first steering shaft. Consequently, under the same rotational velocity of the steering wheel, the rotational velocity of the second steering shaft can be adjusted to be suitable for high-speed or low-speed motion of the automobile, thereby ensuring safety of the steering action of the automobile.

However, since the rotor does not have a self-locking function, the lock mechanism is required to control the second steering shaft to rotate synchronously or non-synchronously relative to the first steering shaft, thereby resulting in a relatively complex structure and a relatively high manufacturing cost.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to provide a variable ratio transmission mechanism with a function of self-locking and with a relatively simple structure.

Accordingly, a variable ratio transmission mechanism is adapted for use in an automobile steering system. The automobile steering system includes coaxially-disposed first and second steering shafts that extend along a first direction. The variable ratio transmission mechanism comprises a securing unit adapted to be connected co-rotatably to the first steering shaft about a first axis that extends in the first direction, a connecting unit adapted to be connected co-rotatably to the second steering shaft about the first axis, a motor, and a transmitting unit. The motor includes a main body connected to one of the securing unit and the connecting unit and co-rotatable with the one of the securing unit and the connecting unit about the first axis and a revolving shaft extending along a second axis that extends in a second direction different from the first direction and revolvable relative to the main body. The transmitting unit includes a first transmitting component that is provided on the other one of the securing unit and the connecting unit, and a second transmitting component that is provided on the revolving shaft of the motor and that engages and is angularly-slidable relative to the first transmitting component.

When the first steering shaft rotates about the first axis for a selected rotational angle without the revolving movement of the revolving shaft, the first and second transmitting components are angularly positioned relative to each other, and the second steering shaft is rotated about the first axis for the selected rotational angle.

When the first steering shaft rotates about the first axis for a selected rotational angle with the revolving movement of the revolving shaft about the second axis, the second steering shaft is rotated about the first axis for a different rotational angle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown inFIGS. 1,2and3, the preferred embodiment of a variable ratio transmission mechanism of this invention is adapted for use in a steering system21of an automobile (not shown). The automobile steering system21includes coaxially-disposed first steering shaft211and second steering shaft212that extend along a first direction (X), and a steering wheel213coupled to the first steering shaft211. The variable ratio transmission mechanism comprises a securing unit3adapted to be connected co-rotatably to the first steering shaft211about a first axis (D1) that extends in the first direction (X), a connecting unit5adapted to be connected co-rotatably to the second steering shaft212about the first axis (D1), a motor4, and a transmitting unit6.

In this embodiment, the motor4includes a main body41connected to the securing unit3and is co-rotatable with the securing unit3about the first axis (D1) and a revolving shaft42that extends along a second axis (D2) extending in a second direction (Y) perpendicular to the first direction (X) and that is revolvable relative to the main body41about the second axis (D2). The transmitting unit6includes a first transmitting component61that is configured as a worm gear and that is provided on the connecting unit5, and a second transmitting component62that is configured as a worm, that is provided on the revolving shaft42of the motor4, and that engages and is angularly-slidable relative to the first transmitting component61.

The securing unit3includes a hollow securing member31that has an end adapted to be connected co-rotatably to the first steering shaft211, and an opposite end along the first axis (D1) formed with a connecting hole32that receives rotatably the first transmitting component61of the transmitting unit6. The securing member31further has an opening33that corresponds in position to the first transmitting component61so as to permit the engagement between the first transmitting component61and the second transmitting component62. The securing member31further has an extension segment formed with a through hole34. The main body41of the motor4is connected to the extension segment of the securing member31at one side opposite to the connecting unit5along the second axis (D2), and the revolving shaft42extends from the main body41through the extension segment via the through hole34toward the first transmitting component61(i.e., the extension segment is disposed between the main body41and the second transmitting component62).

The connecting unit5includes a rotating shaft51that extends into the securing member31through the connecting hole32and that is rotatable about the first axis (D1); and the first transmitting component61is sleeved on the rotating shaft51and meshes rotatably with the second transmitting component62.

The connecting unit5further includes a connecting shaft53extending from the rotating shaft51along the first axis (D1) and adapted to be connected co-rotatably to the second steering shaft212, and a pair of bearings54sleeved on the rotating shaft51, disposed between the rotating shaft51and the securing member31, and flanking the first transmitting component61along the first axis (D1).

When the first steering shaft211rotates about the first axis (D1) for a selected rotational angle without the revolving movement of the revolving shaft42, the first transmitting component61and the second transmitting component62are angularly positioned relative to each other because of their self-locking characteristic, and the second steering shaft212is consequently and synchronously rotated about the first axis (D1) for the selected rotational angle.

When the first steering shaft211rotates about the first axis (D1) for a selected rotational angle with the revolving shaft42revolving about the second axis (D2), the second steering shaft212is rotated about the first axis (D1) for a different rotational angle which is the sum of the selected rotational angle of the first steering shaft211and an adjusting rotational angle of the connecting unit5driven by the revolving shaft42relative to the securing unit3. Therefore, under the same rotational angle of the steering wheel213, the rotational angle of the second steering shaft212can be adjusted to be suitable for high-speed or low-speed motion of an automobile by controlling the motor4, thereby ensuring safety of the steering action of an automobile.

To sum up, the preferred embodiment of the variable ratio transmission mechanism of this invention has a self-locking feature and a relatively simple structure by means of the transmitting unit6to thereby achieve the object of this invention.