Patent Application
20090263206
The present invention relates to a method and structure for preventing the loosening of a male screw which is engaged with a female screw, and a method for manufacturing this male screw.
In a rack and pinion type steering apparatus equipped with a rack mating with a pinion which is rotated by steering operation, a female screw is formed on the inner circumference of a hole formed in a housing which covers the rack, the opening of the hole is closed by engaging a male screw formed on the outer circumference of a closing member with the female screw, and an elastic member which presses a rack supporting member inserted into the hole against the rack is sandwiched between the rack supporting member and the closing member. The gap between the rack supporting member and the closing member is adjusted by adjusting the amount by which the male screw is engaged with the female screw, so that fluctuation in the amount of mating between the rack and the pinion caused by bending of the rack and others is prevented, thus making it possible to achieve smoother mating.
Conventionally, in order to prevent loosening of the male screw formed on the abovementioned closing member, a lock nut is engaged with this male screw (Patent Document 1).
In the prior art, since the lock nut is necessary, the number of parts is increased. Furthermore, the male screw rotates with respect to the female screw when the lock nut is engaged, so that the gap between the rack supporting member and closing member fluctuates. As a result, since it is necessary to readjust this gap, the productivity drops. Furthermore, since a temporary assembly process in which the lock nut is provisionally engaged with the male screw is required prior to the process in which the male screw is engaged with the female screw, the working efficiency is poor. It is an object of the present invention to provide a method and structure for preventing screw loosening and a method for manufacturing a male screw that can solve such problems.
In the method of the present invention for preventing screw loosening, prior to engaging a male screw formed on the outer circumference of a second member with a female screw formed on the inner circumference of a hole in a first member, protruding parts which protrude outward in the radial direction and are positioned at one end side of the male screw in the axial direction are formed in a plurality of regions which are separated from each other in the circumferential direction on the outer circumference of the second member on which the male screw is formed, the male screw is then engaged with the female screw from the other end side of the male screw in the axial direction, and the torque required to rotate the male screw engaged with the female screw in the loosening direction is set so as to be greater in a state where the protruding parts are interposed between the male screw and the female screw than in a state where the protruding parts are not interposed between the male screw and the female screw.
The structure of the present invention for preventing screw loosening comprises a first member which has a hole, a female screw which is formed on the inner circumference of the hole, a second member which has an outer circumference, a male screw which is formed on the outer circumference of the second member, and a recessed part which is formed in the second member so as to be positioned to the inside of the male screw in the radial direction, wherein plastic deformation parts which are plastically deformed outward in the radial direction are formed in a plurality of regions which are separated from each other in the circumferential direction on the inner circumference of the recessed part, protruding parts which are protruded outward in the radial direction by the formation of the plastic deformation parts are formed in a plurality of regions which are separated from each other in the circumferential direction on the outer circumference of the second member on which the male screw is formed, the protruding parts are positioned at one end side of the male screw in the axial direction, and the torque required to rotate the male screw engaged with the female screw in the loosening direction is set so as to be greater in a state where the protruding parts are interposed between the male screw and the female screw than in a state where the protruding parts are not interposed between the male screw and the female screw.
According to the method of the present invention, no protruding parts are interposed between the male screw and the female screw in the initial stage of the operation for engaging the male screw with the female screw, so that this operation can be easily initiated. Since protruding parts are subsequently interposed between the male screw and the female screw, the friction between the male screw and the female screw can be increased so that loosening of the male screw with respect to the female screw is restricted. Furthermore, since loosening of the male screw with respect to the female screw can be restricted without using a lock nut, the number of parts can be reduced, so that the productivity and working efficiency can be improved. In addition, the male screw can be loosened with respect to the female screw if necessary by applying torque exceeding the set value on the male screw. Inadvertent loosening of the male screw with respect to the female screw can be prevented by controlling the torque required to loosen the male screw with respect to the female screw. The method of the present invention can be realized using the structure of the present invention.
It is desirable that the torque required to rotate the male screw engaged with the female screw in the loosening direction is set so as to be equal to or greater than 10 Newton-meter in a state where the protruding parts are interposed between the male screw and the female screw, and is set so as to be equal to or less than 1 Newton-meter in a state where the protruding parts are not interposed between the male screw and the female screw. As a result, the male screw can be easily engaged with the female screw, and inadvertent loosening of the male screw with respect to the female screw can be securely prevented.
It is desirable that the second member is pressed against a pressure receiving part which is to be fixed to the first member, at the other end of the male screw engaged with the female screw via the protruding parts, and that the torque required to rotate the male screw engaged with the female screw in the loosening direction is set so as to be equal to or greater than 3 Newton-meter in a state where the protruding parts are interposed between the male screw and the female screw, and is set so as to be equal to or less than 1 Newton-meter in a state where the protruding parts are not interposed between the male screw and the female screw. As a result, the male screw can be easily engaged with the female screw, and the friction between the male screw and the female screw can be increased by the reaction force that acts on the other end of the male screw, so that inadvertent loosening of the male screw with respect to the female screw can be securely prevented.
It is desirable that the first member is constituted by a housing which covers a rack mating with a pinion, which is caused to rotate by steering operation, that an elastic member is provided so as to apply elastic force for pressing a rack supporting member inserted into the hole against the rack, that the second member is constituted by a closing member which closes the opening of the hole, and that the elastic member is sandwiched between the rack supporting member and the closing member. As a result, the present invention can be applied to a rack and pinion type steering apparatus, the male screw can be loosened with respect to the female screw if necessary by applying torque which exceeds a set torque on the male screw, and the adjustment of the gap between the rack supporting member and the closing member can be performed with good efficiency.
In the method of the present invention for manufacturing the male screw in the structure for preventing screw loosening, three pressing parts are integrally disposed so as to be inclined with respect to the axis of the male screw and separated from each other in the circumferential direction of the male screw with facing the circumferential edge of the opening of the recessed part, these three pressing parts as an integral unit are then moved integrally in the axial direction of the male screw relatively to the second member, and the plastic deformation parts are formed by pressing the respective pressing parts against the circumferential edge of the opening of the recessed part. In the present invention, since the number of pressing parts which are pressed against the circumferential edge of the opening in the second member is three, the respective pressing parts can be uniformly pressed against the circumferential edge of the opening of the recessed part. As a result, the amounts of plastic deformation in the respective plastic deformation parts can be made uniform, so that the amounts of protrusion of the respective protruding parts can be made uniform; therefore, the torque required to loosen the male screw can be accurately set, so that inadvertent loosening of the male screw with respect to the female screw can be securely prevented.
The present invention makes it possible to provide a method and structure for preventing screw loosening in which the number of parts can be reduced, the productivity can be improved, and the working efficiency can be improved.
The rack and pinion type steering apparatus 1 shown in
The housing 5 has a retaining part 5″ extending from the position at which the pinion 3 mates with the rack 4 to a direction perpendicular to the longitudinal direction of the rack 4. A hole 15 is formed in the retaining part 5″. A rack supporting member 16 is inserted into the hole 15 so as to be capable of reciprocating in a direction perpendicular to the longitudinal direction of the rack 4. The opening of the hole 15 is closed by a closing member 18. The second member of the present invention is constituted by the closing member 18. A male screw 18A is formed on the outer circumference of the closing member 18, and the male screw 18A is engaged with a female screw 15A formed on the inner circumference of the hole 15, so that the opening of the hole 15 is closed by the closing member 18. A recessed part 18a is formed in one end of the closing member 18 so as to be positioned to the inside of the male screw 18A in the radial direction, so that the closing member 18 has the shape of a tube having a bottom. The opening side of the inner circumference of the recessed part 18a is formed as a tool engaging part 18b conforming to the shape of a polygonal column, the bottom side 18c of the recessed part 18a is formed with a shape conforming to a circular conical surface. The male screw 18A can be engaged with the female screw 15A or loosened with respect to the female screw 15A by inserting a tool (not shown in the figures) such as a wrench or the like which has an outer circumference conforming to the tool engaging part 18b, and rotating the closing member 18. Furthermore, a sealing ring 19a is disposed between the closing member 18 and the housing 5.
One end of the rack supporting member 16 faces the other end of the closing member 18. The other end of the rack supporting member 16 supports the back surface of the rack 4 via a sheet 17. An elastic member 20 constituted by a compression coil spring is inserted into a hole 16a formed in one end of the rack supporting member 16. The elastic member 20 is compressed by being sandwiched between the rack supporting member 16 and the closing member 18, so that elastic force is applied so as to press the rack supporting member 16 against the rack 4. As a result, smooth engagement between the rack 4 and the pinion 3 is ensured by the movement of the rack supporting member 16. The amount of movement of the rack supporting member 16 due to the bending of the rack 4 and others is corrected by the adjustment of the gap S between one end of the rack supporting member 16 and the other end of the closing member 18, so that the engagement between the rack 4 and pinion 3 is ensured. This adjustment of the gap S is performed by adjusting the amount by which the male screw 18A is engaged with the female screw 15A. Furthermore, a sealing ring 19b is disposed between the rack supporting member 16 and the housing 5.
As is shown in
In the present embodiment, the male screw 18A is formed by, for example, rolling, and then the plastic deformation parts 30 are formed by the pressing tool 50 shown in
For example, one of the pressing tool 50 and the closing member 18 is attached to the ram of a pressing device, and the other is fastened to a table or the like. As a result, as shown in
In the present embodiment, it is desirable that the torque required to rotate the male screw 18A engaged with the female screw 15A in the loosening direction is set equal to or greater than 10 Newton-meter, preferably equal to or greater than 25 Newton-meter and equal to or less than 50 Newton-meter, in a state where the protruding parts 40 are interposed between the male screw 18A and the female screw 15A, and that this torque is set equal to or less than 1 Newton-meter in a state where the protruding parts 40 are not interposed between the male screw 18A and the female screw 15A. Since the protruding parts 40 are formed by the formation of the plastic deformation parts 30 which are formed by pressing the pressing parts 52a against the circumferential edge 18a′ of the opening of the recessed part 18a in the axial direction, the protruding parts 40 can be formed, after determining the value of pressing force or the amount of pressing in the axial direction by preliminary experiment so that the torque required to rotate the male screw 18A engaged with the female screw 15A in the loosening direction becomes a set torque. It is desirable to reduce the manufacturing tolerance of the male screw 18A and the female screw 15A prior to forming the protruding parts 40 for accurately setting this set torque at a desired value. For example, the precision of the male screw 18A is set at a precision higher than 4 h (ISO), and the precision of the female screw 15A is set at a precision higher than 4 H (ISO). Furthermore, in the initial stage of the operation for engaging the male screw 18A with the female screw 15A, torque exceeding 50 Newton-meter, e.g., approximately 75 Newton-meter, is applied in the tightening direction, so that the rack 4 is pressed against the pinion 3 by the closing member 18 via the rack supporting member 16. In this state, the pinion 3 is rotated so that members, which contact with each other, such as the rack 4 and pinion 3, and the rack 4 and rack supporting member 16 work in with each other in a good fit condition. It is desirable that torque oriented in the loosening direction of the male screw 18A subsequently applied in order to adjust the gap S.
In the abovementioned construction, prior to engaging the male screw 18A with the female screw 15A, respective protruding parts 40 positioned at one end side of the male screw in the axial direction are formed on the outer circumference of the closing member 18 on which the male screw 18A is formed, and then the male screw 18A is engaged with the female screw 15A from the other end side of the male screw 18A in the axial direction. The torque required to rotate the male screw 18A engaged with the female screw 15A in the loosening direction is set so as to be greater in a state where the protruding parts 40 are interposed between the male screw 18A and female screw 15A than in a state where the protruding parts 40 are not so interposed. As a result, as shown in
Instead of the snap ring 9 for fastening the outer race 6b in the abovementioned embodiment, an annular member 70 illustrated in
The present invention is not limited to the abovementioned embodiments. For example, the present invention is not limited to application to rack and pinion type steering apparatuses, but can be applied to any structure in which a male screw formed on the outer circumference of a second member is engaged with a female screw formed on the inner circumference of a hole in a first member.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2005/013968 | 7/29/2005 | WO | 00 | 1/24/2008 |
