Cylinder device

A cylinder device such as a power cylinder of a power steering system includes a slidable shaft slidably disposed inside a housing. A joint member is connected to the end section of the slidable shaft. A stopper member is disposed between the slidable shaft and the joint member. Here, the end section of the slidable shaft is cutout to form an axial engagement surface. The slidable shaft and the joint member are connected in a condition where the end face of the slidable shaft is in contact with the end face of the joint member so as to from a groove between the axial engagement surface and the joint member. The stopper member is formed annular and has an engagement section formed along its inner periphery. The engagement section is fitted in the groove so that the stopper member is prevented from at least an axial movement.

BACKGROUND OF THE INVENTION

This invention relates to improvements in a cylinder device of the type including a stopper section for stopping a relative sliding movement between a housing and a shaft (rack bar) extending through and slidably movable in the housing at a position where the sliding movement terminates, for example, a power cylinder of a power steering system, and more particularly to the improvements in technique of the stopper section.

Hitherto a variety of such cylinder devices have been proposed and put into practical use. One of them is disclosed in Japanese Utility Model Publication No. 62-3368 relating to a rack-and-pinion steering gear. In this rack-and-pinion steering gear, a socket for a tie rod is connected to an end section of a rack bar (slidable shaft) under being screwed in, in which a stopper member is incorporated to buffer contact between the socket and the end section of a housing. The stopper member is constituted of a metal ring having an opening to be mounted on the threaded section of the socket, and an annular elastomeric member fixed to the metal ring at an outer peripheral side facing the rack bar. This stopper member is incorporated and fixed in a state where the inner peripheral section of the metal ring is put between the end face of the rack bar and the end face of the socket at a screw-in joint. The metal ring is provided with projections which are to be engaged with radial cutouts formed at the end face of the rack bar so that the metal ring is prevented from its rotation.

However, in the above conventional cylinder device, the stopper member is incorporated and fixed in the state where the inner peripheral section of the metal ring is put between the end face of the rack bar and the end face of the socket at the screw-in joint as discussed above, and therefore the length of the cylinder device is unavoidably increased by an amount corresponding to the thickness of the metal ring. This enlarges the size of the cylinder device while providing considerable restriction in designing the cylinder device.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide an improved cylinder device which can effectively overcome drawbacks encountered in conventional cylinder devices such as a power cylinder of a power steering system.

Another object of the present invention is to provide an improved cylinder device which can be prevented from being large-sized without receiving restriction relating to its axial length in design.

A further object of the present invention is to provide an improved cylinder device including a stopper member having a buffering function, which can be installed without changing the axial length of the cylinder device.

An aspect of the present invention resides in a cylinder device comprising a housing. A slidable shaft is slidably movably disposed inside the housing and projectable out of the housing. A joint member is connected to the end section of the slidable shaft. A stopper member is disposed at a joint section between the slidable shaft and the joint member so as to be brought into contact with an end section of the housing to stop a relative slidable movement between the slidable shaft and the housing and to provide a buffering function during contact of the slidable shaft to the housing. In the above cylinder device, the end section of the slidable shaft is partially cutout to form an axial engagement surface exposed at an tip end of the slidable shaft including an end face whose surface area is smaller than a cross-sectional area of the end section. The slidable shaft and the joint member are connected to each other in a condition where the end face of the slidable shaft is in contact with an end face of the joint member so that a groove is formed between the axial engagement surface of the slidable shaft and the end face of the joint member. Additionally, the stopper member is formed annular to have an opening so as to be mountable on an outer peripheral surface of the slidable shaft and has an engagement section formed along an inner periphery of the stopper member, the engagement section of the stopper member being fitted in the groove so that the stopper member is prevented from at least an axial movement.

Another aspect of the present invention resides in a method of assembling a cylinder device including a housing, a slidable shaft which is slidably movably disposed inside the housing and projectable out of the housing, a joint member connected to the end section of the slidable shaft, and a stopper member disposed at a joint section between the slidable shaft and the joint member so as to be brought into contact with an end section of the housing to stop a relative slidable movement between the slidable shaft and the housing and to provide a buffering function during contact of the slidable shaft to the housing. The assembling method comprises the following steps of: (a) providing the slidable shaft whose end section is partially cutout to form an axial engagement surface exposed at an tip end of the slidable shaft including an end face whose surface area is smaller than a cross-sectional area of the end section; (b) providing the stopper member formed annular to have an opening so as to be mountable on an outer peripheral surface of the slidable shaft and having an engagement section formed along an inner periphery of the stopper member; and (c) connecting the slidable shaft and the joint member to each other in a condition where the end face of the slidable shaft is in contact with an end face of the joint member so that a groove is formed between the axial engagement surface of the slidable shaft and the end face of the joint member, and the engagement section of the stopper member is fitted in the groove so that the stopper member is prevented from at least an axial movement.

DETAILED DESCRIPTION OF THE INVENTION

Referring now toFIGS. 1to9, more specifically toFIG. 1, a power cylinder (cylinder device) of a power steering system is illustrated. The power cylinder comprises a cylinder (housing)1inside which a rack bar or slidable shaft2is axially slidably movably disposed. Rack bar2has opposite end sections which are extendable out of cylinder1and connected respectively to tie rods3,3through sockets (joint members)4,4and stopper members5,5. Each tie rod3is to be connected to a road wheel (not shown).

Each of the opposite end sections of rack bar2is formed cylindrical and formed at its inner peripheral surface with an internal thread21as shown inFIGS. 2 and 3. A tip end portion of each end section of rack bar2is formed with two cutouts (axial engagement sections)22,22which are located diametrically opposite to each other. Two cutouts22,22extend along a first diametrically extending plane (not shown) in the end section of the rack bar2, so that each cutout22diametrically extends from the inner peripheral surface to the outer peripheral surface of the tip end portion of the end section of the rack bar2, and axially extends to the end face of rack bar2. Additionally, the tip end portion of each end section of the rack bar2is formed with two long flat surfaces23,23extends parallel with the first diametrically extending plane in the end section of rack bar2. Two long flat surfaces23,23are located on the opposite sides of the first diametrical extending plane. Each of two long flat surfaces23,23extends perpendicular to a second diametrically extending plane perpendicular to the first diametrically extending plane, and have two sections (not identified) which extend from the second diametrically extending plane by equal distances. Each flat surface axially extends to the end face of the rack bar2.

Further, an extreme end portion (including the end face of rack bar2) of each end section of rack bar2is annularly cutout to form an annular cutout (no numeral) which radially outwardly extends to the outer peripheral surface of the end section of rack bar2and axially extends to the end face of rack bar2, thereby forming a small-diametrical cylindrical surface24and an annular flat surface (axial engagement section or surface)25. The annular flat surface25is exposed at a tip end of rack bar2which tip end includes the end face of rack bar2and forms part of the extreme end portion. Small-diametrical cylindrical surface24is an outer peripheral surface of a small-diameter section of rack bar2. Cylindrical surface24is coaxial with the end section of rack bar2and axially extends to the end face of rack bar2. Annular flat surface25is coaxial with the end section of the rack bar2and radially outwardly extends to the outer peripheral surface the end section of rack bar2.

As shown inFIGS. 4 and 5, each of sockets4,4is bendably connected at its one end with the tie rod3through a spherical or ball joint. Socket4forms a large diameter section4A of a one-piece body (no numeral). A shaft section4B forming a small diameter section of the one-piece body formed at and axially extends from the end face of the socket4so as to be coaxial with the socket4. The shaft section4B is formed at its outer peripheral surface with an external thread41which is to be engaged with the internal thread21of each end section of rack bar2so that socket4is connected to rack bar2in a condition where the end face of socket4is in contact with the end face of rack bar2.

As seen inFIG. 8, each stopper member5is disposed at the joint between rack bar2and socket4in order to stop a relative sliding movement between cylinder1and rack bar2upon coming into contact with an end cover11provided to the end section of cylinder1or with cylinder1itself and to exhibit a buffering or shock-absorbing function when socket4strikes against cylinder1. As shown inFIGS. 6 and 7, stopper member5is formed generally annular to form an opening51through which stopper member5is mounted on the outer peripheral surface of the tip end portion of the end section of rack bar2which tip end portion is formed with two long parallel surfaces23,23. A generally annular engagement section52extends radially inwardly from the inner peripheral surface of stopper member5defining opening51and located on the side of socket4. Annular engagement section52is loosely disposed around small-diametrical cylindrical surface24of the extreme end portion of rack bar2and loosely fitted between annular flat surface25of the extreme end portion of rack bar2and socket4. It will be understood that an annular groove is formed by small-diametrical cylindrical surface24, annular flat surface25and the end face of main body section4A of socket4, in which the stopper member5can be prevented from its axial movement in a condition where annular engagement section52is loosely fitted in the annular groove.

Additionally, engagement projections53,53are formed projecting from the inner peripheral surface (defining opening51) of stopper member5and project radially inwardly and axially toward rack bar2. Engagement projections53,53are to be respectively loosely fitted in cutouts22,22of rack bar2. An annular projection54is formed at the outer peripheral section of stopper member5and axially projects toward cylinder1. This annular projection54is to be brought into contact with end cover11or cylinder1. Annular projection54is formed of an elastomeric material such as polyurethane resin or the like, and formed as a one-piece structure. Each stopper member5is formed with two long flat surfaces (no numerals) which are parallel with each other and face to each other, and correspond respectively to the two long flat surfaces23,23of rack bar2. The two long flat surfaces of stopper member5are to be in contact with two long flat surfaces23,23of rack bar2.

Hereinafter, production and effects of the above-arranged power cylinder will be discussed.

The above power cylinder is assembled as follows: First, engagement projections53,53of stopper member5are respectively loosely fitted into cutouts22,22of the end section of rack bar2while annular engagement section52of stopper member56is mounted around cylindrical surface24of the small-diameter section of rack bar2, thereby accomplishing assembly of stopper member5to the end section of rack bar2. Thereafter, external thread41of shaft section4B of socket4is engaged with the internal thread21of the end section of rack bar2so as to establish a condition where the end face of socket4is brought into contact with the end face of rack bar2through stopper member5. This assembly operation is carried out for each of the opposite end sections of rack bar2. Thus, the assembly operation for the power cylinder is completed.

In the assembled condition of the power cylinder, as shown inFIGS. 8 and 9, annular engagement section52of stopper member5is put in a loose fit condition between annular flat surface25of rack bar2and the end face of socket4so that stopper member5can be prevented from its axial movement. Annular flat surface25faces the end face of socket4. Furthermore, engagement projections53,53of stopper member5are respectively loosely fitted into cutouts22,22so that stopper member5is prevented from its rotation, while tip end faces of engagement projections53,53are brought into axial contact with the axial end faces of cutouts22,22upon stopper member5being in contact with the end face of socket4so that stopper member5is prevented from its axial movement.

Furthermore, the end face of stopper member on the side of socket4is in contact with and supported by the end face of socket4, and therefore an axial load produced when annular projection54of stopper member5is brought into contact with stopper section11aof end cover11or the cylinder1is received through stopper member5by the end face of socket4.

In the power cylinder of this embodiment, as discussed above, the end face of rack bar2is reduced in surface area under formation of annular cutout (for stopper member5) defined by cylindrical surface24and annular flat surface25. This area-reduced end face of rack bar2and the end face of socket4are brought into contact with each other, in which rack bar2and socket4are put into a connected state. Accordingly, installation of stopper member5can be made without changing the axial length of a connected body of rack bar2and socket4. As a result, the power cylinder can be prevented from becoming large-sized while effectively exhibiting the buffer function. Additionally, the power cylinder can avoid receiving restriction in design for its axial length.

Engagement projections53,53of stopper member5are respectively loosely fitted into cutouts22,22so that stopper member5is prevented from its rotation. Simultaneously, engagement projections53,53are brought into axial contact with the axial end faces of cutouts22,22upon stopper member5being in contact with the end face of socket4so that stopper member5is prevented from its axial movement. Additionally, annular engagement section52of stopper member5is fitted between annular flat surface25of rack bar2and the end face of socket4so that stopper member5is prevented from its axial movement. As a result, the assembled state of the power cylinder can be securely maintained.

Furthermore, the end face of stopper member5on the side of socket4is in contact with and supported by the end face of socket4, and therefore it is unnecessary to use any support member (formed of a high stiffness material such as metal) for stopper member5in order that only stopper member5endures the axial load generated upon contacting of stopper member5to the cylinder1. Thus, it becomes possible that stopper member5is formed of only the elastomeric material, which reduces the number of parts of the power cylinder thereby achieving a cost reduction for the power cylinder.

The power cylinder is arranged such that engagement projections53,53of stopper member5are respectively loosely fitted into cutouts22,22, while annular engagement section52of stopper member5is loosely fitted between annular flat surface25of rack bar2and the end face of socket4in such a manner that the annular engagement section is axially restrained in a loose fit condition. As a result, the elastomeric material forming stopper member5can be prevented from receiving stress thereby avoiding its early aging or deterioration.

FIG. 10illustrates a second embodiment of the power cylinder according to the present invention, which is similar to the first embodiment power cylinder with the following exception: The width or axial dimension of the small-diametrical cylindrical surface24of rack bar2is generally the same as the thickness of the main body section (except for annular projection54) of stopper member5. Annular engagement section52of stopper member5has the same thickness as that of the main body section of stopper member5.

Accordingly, with the second embodiment power cylinder, in addition to be able to obtaining the same effects as in the first embodiment power cylinder, the thickness (axial dimension) of annular engagement section52is increased thereby improving the durability of stopper member5.

FIG. 11illustrates a third embodiment of the power cylinder according to the present invention, which is similar to the first embodiment power cylinder with the following exception: The extreme end portion (including the end face) of rack bar2is cutout in such a manner as to form an annular tapered or frustoconical surface55whose diameter decreases in a direction toward the end face of rack bar2. Tapered surface55is exposed at the tip end (including the end face) of rack bar2and faces the end face of socket4. Additionally, stopper member5is formed along its inner periphery with annular engagement section52awhich has a generally right-triangular cross-section. In other words, stopper member5has an annular inner peripheral surface (defining opening51) which is tapered or frustoconical so that its diameter decreases in a direction toward socket4. The annular inner peripheral surface of stopper member5is in tight contact with annular tapered surface55of rack bar2so that annular tapered surface55serves as the axial engagement section or surface for stopper member5.

Accordingly, with the third embodiment power cylinder, in addition to be able to obtaining the same effects as in the first embodiment power cylinder, machining for the axial engagement section or surface in rack bar2is easily accomplished thereby making it possible to reduce the production cost of the power cylinder since the axial engagement section can be formed by cutting out the outer peripheral portion of the tip end portion of rack bar2.

While the preferred embodiments of the invention have been described with reference to the drawings, it is to be understood that changes and variations may be made without departing from the spirit of scope of the present invention. For example, although the principle of the present invention has been shown and described as being applied to the power cylinder of the power steering system, it will be understood that it may be applicable to all cylinder devices arranged such that a shaft is slidably inserted in a housing.

Although stopper member5of the embodiments of the present invention has been shown and described as being provided with engagement projections53,53which are respectively loosely fitted in cutouts22,22and annular engagement section52which is loosely fitted between annular flat surface25of rack bar2and the end face of socket4in such a manner as to be axially restrained in a loose fit condition, it will be understood that it may be sufficient that either one of the engagement projections53,53and the annular engagement section52is provided at least for the purpose of preventing stopper member5from its axial movement. In case of providing only engagement projections53,53, stopper member5may be prevented from its both axial and rotational movements.

As appreciated from the above, according to the present invention, the stopper member is installed in position in such a manner that its engagement section is fitted in the groove formed between the axially restraining surface of a slidable shaft (rack bar) and the end face of a joint member (socket), so that the shaft and the joint member are connected to each other in the condition where the end face of the shaft is in contact with an end face of the joint member which end face is smaller in surface area than the cross-sectional area of the end section of the slidable shaft. As a result, the stopper member having a buffering function can be installed without changing the axial length of a cylinder device (power cylinder), thereby preventing the cylinder device from being large-sized without receiving restriction relating to its axial length in design.

The entire contents of Japanese Patent Application No. 2002-144781, filed May 20, 2002, are incorporated herein by reference.