Transmission ratio variable mechanism

A transmission ratio variable mechanism (100) varies a transmission ratio between a steering amount of a steering wheel (2) and a turning amount of wheels (7). The transmission ratio variable mechanism (100) includes an input shaft (3) transmitted with a rotational force of the steering wheel (2), a housing (102, 103) unitarily rotating with the input shaft (3), an output shaft (4) connected to wheels side, a motor (160) fixed in the housing for transmitting the rotation to the output shaft (4) via a speed reduction device (150), and a reverse input blocking device (180) for always transmitting a rotational output from the motor (160) to the output shaft (4) and for always blocking a rotational input from the output shaft (4) to the motor (160).

FIELD OF THE INVENTION

The present invention relates to a transmission ratio variable mechanism. More particularly, the present invention pertains to a transmission ratio variable mechanism which varies a transmission ratio between a steering amount of a steering wheel and a turning amount of vehicle wheels.

BACKGROUND OF THE INVENTION

A known transmission ratio variable mechanism disposed between a steering wheel and gear device such as rack and pinion mechanism for varying a transmission ratio between a steering amount of the steering wheel and a turning amount of vehicle wheels is disclosed in Japanese Patent Laid-Open Publication No. H10-324263.

The known transmission ratio variable mechanism includes a direct connection means. The direct connection means restrict a relative rotation between an input shaft and output shaft when reverse input or an abnormality of a motor. Accordingly the transmission ratio variable mechanism prevent a deviation between the steering amount of the steering wheel and turning amount of the wheels in case a torque is applied from an output shaft of the transmission ratio variable mechanism due to the reverse input or in case of the stop of motor rotation due to the abnormality.

Notwithstanding, with the construction of the known transmission ratio variable mechanism, assembling of the direct connection means is complex. In addition, a detection means for detecting the abnormality of the motor and the reverse input and a control means for commanding the operation of the direct connection means are additionally required for operating the connection means.

This increases the number of parts and manufacturing costs. Further, the known transmission ratio variable mechanism with the foregoing construction has a drawback that it requires a response time from the detection of the abnormality of the motor or the reverse input by the detection means until the operation of the direct connection means is completed by commanding the operation of the direct connection portion by the control means.

A need thus exists for a transmission ratio variable mechanism which can maintain a relation between a steering amount of a steering wheel and a turning amount of wheels even when a reverse input from the turning wheels side is input or an abnormality of the motor are generated without providing a direct connection means which requires an additional detection means and a control means.

SUMMARY OF THE INVENTION

In light of the foregoing, the present invention provides a transmission ratio variable mechanism for varying a transmission ratio between a steering amount of a steering wheel and a turning amount of wheels, which includes an input shaft transmitted with a rotational force of the steering wheel, a housing unitarily rotating with the input shaft, an output shaft connected to wheels side, a motor fixed in the housing for transmitting the rotation to the output shaft via a speed reduction device, and a reverse input blocking device for always transmitting a rotational output from the motor to the output shaft and for always blocking a rotational input from the output shaft to the motor.

According to another aspect to of the invention, a steering device including a transmission ratio variable mechanism for varying a transmission ratio between a steering amount of a steering wheel and a turning amount of wheels includes the steering wheel operated for providing a rotational force, the wheels turned in accordance with the rotational force from the steering wheel, a rack and pinion mechanism including a rack shaft, and a transfer mechanism provided between the rack shaft and the wheels. The transmission ratio variable mechanism includes an input shaft transmitted with the rotational force of the steering wheel, a housing unitarily rotating with the input shaft, an output shaft connected to the rack and pinion mechanism, a motor fixed in the housing for transmitting the rotation to the output shaft via a speed reduction device, and a reverse input blocking device for always transmitting a rotational output from the motor to the output shaft and for always blocking a rotational input from the output shaft to the motor.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of a transmission ratio variable mechanism will be explained with reference to the illustrations of the drawing figures.FIG. 1shows a construction of a steering device1for a vehicle applied with the transmission ratio variable mechanism according to the embodiments of the present invention.

As shown inFIG. 1, the steering device1for the vehicle includes a steering wheel2. The steering wheel2is connected to a top end of a top steering shaft3serving as an input shaft. A bottom end of the top steering shaft3is connected to an input portion of a transmission ratio variable mechanism100. An output portion of the transmission ratio variable mechanism100is connected to a top end of a bottom steering shaft4serving as an output shaft.

A bottom end of the bottom steering shaft4is assembled to a pinion (not shown) of a rack and pinion mechanism5. Wheels7are provided on both ends of a rack shaft5aof the rack and pinion mechanism5via a transfer mechanism6.

As shown inFIG. 2, the transmission ratio variable mechanisms100according to the first embodiment of the present invention includes a first housing102, a second housing103, a spiral cable case170, a motor160, a speed reduction device150, and a reverse input blocking device180.

An input shaft fitting portion102ahaving a small cylindrical shape formed on a top portion of the housing102is secured to the top steering shaft3so that the housing102is unitarily rotatable with the top steering shaft103. An external peripheral portion of the input shaft fitting portion102ais provided with the spiral cable case170made of synthetic resin.

The spiral cable case170includes a convex portion170bat a contact surface with the housing102and stores a spiral cable171therein. One end of the spiral cable171is pulled out to the outside of the contact surface between the spiral cable case170and the housing102via a spiral cable bus bar172to be extended in the housing102through a through hole102cprovided on the housing102. On the other hand, the other end of the spiral cable171is pulled out to the outside of the spiral cable case170via a cable173to be connected to a connector174as shown in FIG.3. The connector174is connected to a control device (not shown).

The convex portion170bis inserted into a through hole102bformed on the housing102to determine a position of the spiral cable case170and the housing102in a rotational direction. By inserting a bush104into a bush inserting portion102dprovided on the housing102, the spiral cable case170is pushed in the axial direction to be fixed to the housing102by a flange portion104aof the bush104.

The housing103is unitarily connected to the housing102. The housing103includes the motor160, the reverse input blocking device180, and the speed reduction device150which are arranged in this order from the input shaft side.

The motor160includes a motor housing162, a stator163, a motor rotational shaft164, a rotor165, and a motor end plate161.

The stator163is fixed to an internal periphery of the approximate cylindrical shaped motor housing162. The motor end plate161is provided for covering an opening portion of the motor housing162.

The motor rotational shaft164is supported by a first bearing167and a second bearing168coaxially rotatably relative to the motor housing162and the motor end plate161. An external periphery of the motor rotational shaft164is unitarily equipped with the rotor165.

The motor160is unitarily fixed to the housing103by fitting the motor housing162to an internal periphery of the housing103. A key groove is formed on the motor housing162and the motor end plate161. By gearing a key106between the key formed on the motor housing162and the motor end plate161and a key groove formed on the housing102, the position of the motor160relative to the housing102in the rotational direction is determined.

A motor bus bar166for supplying electric power to the stator163is pulled out from the motor end plate161. The motor bus bar166is connected to the spiral cable bus bar172.

The reverse input blocking device180includes a stationary member181, a drive shaft182, an intermediate member183, and a driven shaft184. The known reverse input blocking device is disclosed in Japanese Patent Laid-Open Published No. 2000-199532.

The stationary member181is unitarily fixed to the housing103to serve as a part of the housing. The cylindrical stationary member181includes lid portions181b,181con both sides thereof. The driven shaft184is penetrated through the lid portion181cto be rotatably supported by a bearing186and not to be moved in the axial direction. One end of the drive shaft184is formed with a small diameter portion184a. The intermediate member183is provided on an external periphery of the small diameter portion184anot to be rotated and to be movable in the axial direction. A disc shaped flange portion183cis formed on the intermediate member183. A coil spring185serving as a spring means is provided between the flange portion183cand the driven shaft184to bias the flange portion183cof the intermediate member183towards the lid portion181b. Contacting surfaces of the flange portion183cand the lid portion181bare formed with clutch teeth181aand clutch teeth183aserving as clutch means respectively. A frictional clutch may be applied as the clutch means.

A first thrust cam183bis provided at an internal periphery side of the clutch teeth183aof the flange portion183c. A second thrust cam182bcorresponding to the first thrust cam183bis provided on an end surface periphery surface of the drive shaft182. The thrust cams183b,182bserve as cam means. The other end of the drive shaft182is connected to the motor rotational shaft164.

The intermediate member183is biased towards the drive shaft182side by the force of the coil spring185provided between the driven shaft184and the intermediate member183so that the first thrust cam183bis fitted into the second thrust cam182bof the drive shaft182and the clutch teeth183ais geared with the clutch teeth181aof the stationary member181.

By forming an internal diameter small portion corresponding to the lid portions181b,181cof the stationary member181on the housing103, and by providing the clutch teeth geared with the clutch teeth183aof the intermediate member183at the internal diameter small portion on the side corresponding to the lid portion181b, the housing103may include the function as the stationary member.

Known speed reduction device such as planetary gear mechanism or harmonic drive mechanism are applied as the speed reduction device150. The speed reduction device150includes a fixed portion150a, an input portion150b, and an output portion150c. The fixed portion150ais provided not to be rotated relative to the housing103, the driven shaft184of the reverse input blocking device180is connected to the input portion150b, and the bottom steering shaft4is connected to the output portion150c. The speed reduction device150decelerate the rotation of the input portion150binput from the driven shaft184by predetermined speed ratio, and the speed reduction device150transmit this decelerated rotation to the output portion150cso that fixed portion150aand output portion150brotate relatively. Thus, when both the housing103and the driven shaft184of the reverse input blocking device180rotate, the decelerated rotational amount of the input portion150bis added to the rotational amount of the fixed portion150ato be transmitted to the output portion150c.

The operation of the transmission ratio variable mechanism100under the condition that the rotational force is input from the steering wheel2side and the motor160normally functions will be explained.

By applying the rotational force from the steering wheel2, the control device (not shown) outputs the rotational command to the motor160in accordance with the steering amount of the steering wheel2and so on. The rotational command is transmitted to the motor160through the spiral cable171. The motor160is operated by the rotational command to rotate the motor rotational shaft164relative to the motor housing162. The rotation of the motor rotational shaft164is transmitted to the unitarily connected drive shaft182of the reverse input blocking device180.

At the initial stage when the drive shaft182is rotated, the intermediate member183and the stationary member181cannot be relatively rotated because the clutch teeth183aof the intermediate member183is geared with the clutch teeth181aof the stationary member181. When the rotational force affects the drive shaft182under this condition, the intermediate member183moves in the axial direction by the function of the thrust cams182b,183bagainst the biasing force of the coil spring185. By the movement of the intermediate member183in the axial direction, the geared connection between the clutch teeth183aof the intermediate member183and the clutch teeth181aof the stationary member181is eventually released. Thus, the intermediate member183is rotated relative to the stationary member181to be unitarily rotated with the driven shaft184. Accordingly, the rotation of the drive shaft182is transmitted to the drive shaft184and thus to the input portion150bof the speed reduction device150. The rotation transmitted to the input portion150bis decelerated to be transmitted to the output portion150c. Thus, (he output portion150crotates relative to the fixed portion150a.

The rotational force from the steering wheel2is also transmitted to the fixed portion150aof the speed reduction device150via the top steering shaft3, the housing102, and the housing103.

Accordingly, the output portion150cis transmitted with the addition of the rotation directly transmitted to the fixed portion150aof the speed reduction device150via the steering wheel2and the housing103and the relative rotational element from the motor160to be output to the bottom steering shaft4. Thus, the transmission ratio between the steering wheel2and the wheels7is varied.

The operation under the condition that the reverse input is applied from the wheels7side to the transmission ratio variable mechanism100will be explained as follows.

When the reverse input is applied to the bottom steering shaft4from the wheels7side, the rotational force is transmitted to the output portion150cof the speed reduction device150to try to transmit the rotational force to the input portion150bof the speed reduction device150. In this case, because the clutch teeth183aof the intermediate member183is geared with the clutch teeth181aof the stationary member181by biasing force of the coil spring185, the driven shaft184is not rotatable relative to the stationary member181. Because the stationary member181is provided unitarily with the fixing portion150aof the speed reduction device150and the housing103, the input portion150bis unrotatable relative to the fixed portion150ato lock the speed reduction device150. Thus, the rotation is directly transmitted from the output portion150cto the fixed portion150aat the speed reduction device150and the rotation of the bottom steering shaft4is transmitted to the steering wheel2via the housings102,103, and the top steering shaft3.

In case the motor160is failed to stop, the rotational force from the top steering shaft3is transmitted to the fixed portion150aof the speed reduction device150via the housings102,103. Because the input from the speed reduction device150to the motor160is blocked by the reverse input blocking device180likewise the case of the reverse input, the fixed portion150aand the input portion150bare not relatively rotatable to lock the speed reduction device150. Thus, because of the direct transmission of the rotation from the fixed portion150ato the output portion150cat the speed reduction device150, the rotation of the top steering shaft3is transmitted to the bottom steering shaft4to turn the wheels7.

As forgoing, the transmission ratio variable mechanism100does not cause the division between the steering amount of the steering wheel2and the turning amount of the wheels7without applying the electronic controlled direct connection means even when the reverse input from wheels7or the motor abnormality are generated. Accordingly, with the transmission ratio variable mechanism100, the steering can be performed with a constant transmission ratio.

In addition, by arranging the reverse input blocking device180between the motor160and the speed reduction device150, the rotational force applied to the clutch teeth181a,183aof the reverse input blocking device180can be reduced compared to the rotational force applied to the bottom steering shaft4. And thus, the reverse input blocking device which endures smaller loads is applicable.

Although the stationary member181of the reverse input blocking device180is fixed to the housing103not to be rotatable, the stationary member181may be fixed not to be rotatable via other parts fixed to the housing103not to be rotatable. For example, the stationary member181may be fixed to motor housing162.

A second embodiment of the present invention will be explained referring to FIG.4. The constructions of the second embodiment which are the same with the first embodiment are indicated with the common numerals and the explanations thereof are not repeated.

A transmission ratio variable mechanism110includes a first housing102, a second housing, a spiral cable case170, a motor160, a speed reduction device150, and a reverse input blocking device180′.

The housing102and the spiral cable case170are arranged likewise the transmission ratio variable mechanism100of the first embodiment. The housing105is unitarily connected to the housing102. The housing105is provided with the motor160and the speed reduction device150in this order from the input shaft side therein. A reverse input blocking device180′ is provided at the bottom end of the housing105.

A fixed portion150aof the speed reduction device150is provided not to be rotatable relative to the housing105. An input portion150bis connected to a motor rotational shaft164of the motor160. An output portion150cis connected to a drive shaft182of the reverse input blocking device180′.

With the reverse input blocking device180′, the stationary member181of the reverse input blocking device180is replaced by a stationary member181′ having a large diameter portion. The large diameter portion of the stationary member181′ is unitarily connected to the housing105to serve as a part of the housing. The bottom steering shaft4is unitarily connected to the driven shaft184.

The operation of the transmission ratio variable mechanism110when the rotational force from the steering wheel2side is input and the motor160normally functions will be explained.

When the rotational force is applied from the steering wheel2, a control device (not shown) outputs a rotational command to the motor160in accordance with the steering amount of the steering wheel2and so on, and the rotational command is transmitted to the motor160via a spiral cable171. The command operates the motor160to rotate the motor rotational shaft164relative to the motor housing162. The rotation of the motor rotational shaft164is transmitted to the unitarily connected input portion150bof the speed reduction device150.

The rotational force from the steering wheel2is also transmitted to a fixed portion150aof the speed reduction device150via a top steering shaft3, the housing102, and the housing105. Relative rotational element from the motor160is added to the rotation directly transmitted from the steering wheel2to be transmitted to the drive shaft182of the reverse input blocking device180from the output portion150c.

At the initial stage when the drive shaft182is rotated, because the clutch teeth183aof the intermediate member183is geared with the clutch181aof the stationary member181′, the intermediate member183cannot be rotated. When the rotational force affects the drive shaft182, the intermediate member183is moved in the axial direction against the biasing force of a coil spring185by the function of thrust cams182b,183b. When the intermediate member183is moved in the axial direction, the geared connection between the clutch teeth183aof the intermediate member183and the clutch teeth181aof the stationary member181′ are eventually released. Thus, the intermediate member183is rotatable relative to the stationary member181′ to be unitarily rotated with the driven shaft184. Accordingly, the rotation of the drive shaft182is transmitted to the driven shaft184and the bottom steering shaft4.

In the foregoing manner, the rotation directly transmitted from the steering wheel2and the relative rotational element transmitted by the motor160is added at the speed reduction device150to be output to the bottom steering shaft4via the reverse input blocking device. Thus, the transmission ratio between the steering wheel2and the wheels7are varied.

The operation under the condition that the reverse input is applied from the wheels7side to the transmission ratio variable mechanism110will be explained as follows.

When the input is applied from the wheels7to the bottom steering shaft4side, the rotational force affects the driven shaft184of the reverse input blocking device180′. However, because the clutch teeth183aof the intermediate member183is geared with the clutch teeth181aof the fixed stationary member181′, the driven shaft184is unrotatable relative to the stationary member181′. Thus, the rotational force applied to the driven shaft184is transmitted to the stationary member181′ via the clutch teeth183a,181ato be transmitted to the steering wheel2via the housings105,102, and the top steering shaft3.

In case the motor160is failed to stop, because the input from the motor160is not applied to the input portion150bof the speed reduction device150, the output portion150cis not rotated not to apply the rotation to the drive shaft182of the reverse input blocking device180′. Thus, the clutch teeth181aof the stationary member181′ is remained to be geared with the clutch teeth183aof the intermediate member183. Thus, the rotation of the housing103is transmitted to the stationary member181′ of the reverse input blocking device180′, the intermediate member183, and the driven shaft184. Accordingly, the rotation of the steering wheel2is transmitted to the bottom steering shaft4via the housings102,105, and the reverse input blocking device180′ to turn the wheels7.

Accordingly, with the transmission ratio variable mechanism110, the steering can be achieved with a constant transmission ratio without generating the deviation between the turning amount of the wheels7and the steering amount of the steering wheel2without applying the electronic controlled type direct connection means even when the reverse input from the wheels7or the motor abnormality is generated.

Although the housing is separated into two portions with the embodiments of the present invention, the housing may be constructed in one unit in case ignoring the assembling performance.

According to the embodiments of the present invention, the transmission ratio variable mechanism can maintain the relation between the steering amount of the steering wheel and the turning amount of the wheels without providing the direct connection means which requires the additional detection means and the control means even when the reverse input from the wheels side or the abnormality of the motor is generated.

According to the embodiments of the transmission ratio variable mechanism of the present invention, the rotational force from the motor is always transmitted and the input of the rotation from other portions to the motor is blocked. Thus, the transmission ratio between the steering wheel and the wheels are varied by transmitting the motor rotation at the normal operation of the motor. The generation of the deviation between the steering amount of the steering wheel and the steering amount of the turning amount of the vehicle wheels can be prevented by not transmitting the rotational force to the motor under the condition that the reverse input is generated from the wheels or under the abnormality of the motor stop.