Patent Publication Number: US-6659428-B2

Title: Jack for automobile

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a screw-type jack mounted mainly on a vehicle such as an automobile, a truck, and so on and used when the vehicle is jacked up for repair and tire change. 
     2. Description of Related Art 
     Conventionally, a screw-type jack for high lifting of a mid-load vehicle, a well-known jack called a potbellied jack is used. The potbellied jack has a hollow housing disposed to stand on a base. A cylindrical ram guide and ram are combined in the housing in a telescope style. Two screw shafts are screwed to each other in an axial direction inside the housing to be extendable/contractible in a vertical direction. Such a potbellied jack is described, for example, in Japanese Patent Laid-open Hei 7-196290. 
     A ram nut attached to a lower end portion of the ram is screwed onto the upper one of the two screw shafts. A bevel gear is fixed to a lower end portion of a lower screw shaft. A drive gear is engaged with the bevel gear. The drive gear is rotated from the outside by an operation handle to extend/contract the ram guide and the ram, whereby a vehicle mounting table disposed on an upper end of the ram is lifted or lowered, depending on the direction of rotation. 
     The housing of this conventional jack for automobile is formed in such a manner that one portion of a steel pipe expanded to a substantially conical pipe shape using a press. A portion adjacent to the expanded portion in the substantially conic pipe shape is drawn in a rectangular pipe shape. Consequently, forming these shapes using a press is complicated, difficult, and requires a lot of time and labor. Moreover, a forced strength is given to the housing at the time of forming. This method of forming often results in unacceptable shape errors and cracks in the material, which require rejection. Such rejection results in low productivity. 
     Also, in the above-described conventional jack for automobile, a cylindrical shaft portion for fitting the drive gear therein is welded to a fitting hole disposed in a lower part of a side surface of the housing, and a lower end portion of the housing is welded to a base. This welding consumes a lot of time and labor, and thus increases the production cost. Besides the cost disadvantage, the possibility of insufficient strength resulting from poor welding remains a concern. 
     In the conventional jack for automobile, an outer circumferential surface of the housing is painted after assembly is finished, with the ram and the ram guide accommodated therein. This painting is complicated and requires a lot of time and labor. In addition, only the outer surface of the housing can be painted. The inside of the housing, other parts, and so on are left unpainted, and therefore, there exists concern about rust prevention. 
     Poor painting easily happens since grease coated on the bevel gear melts out due to the exposure of the jack to a high-temperature condition before or during painting. 
     The welding angle of the cylindrical shaft portion relative to the housing is not fixed. A shaft portion of the drive gear directly contacts an inner circumference of the cylindrical shaft portion. Consequently, the drive gear and the periphery of the cylindrical shaft portion in which the drive gear is disposed are given a forced strength to generate heat due to friction heat when the jack is repeatedly lifted and lowered in load tests of the jack. Therefore, there are problems that the life of peripheral parts is shortened, a handle operation requires increased labor, and so on. 
     The ram and the ram nut of the conventional jack for automobile are separate members fixed to each other by some means such as welding in order to lower production cost. However, since this welding work requires a lot of time and labor, elimination of this operation is considered as one item to be improved. 
     In order to use the conventional jack for automobile and put its components in their accommodated state, an operation handle having a long grip is used. But there exists a problem that a lot of time is required for lifting and lowering the ram and the ram guide by this operation handle. Therefore, it has been demanded that some method be devised which can lift the ram and the ram guide quickly in a short time to an intended height when they are used and which can also return the ram and the ram guide to their original positions in a short time when they are accommodated after being used. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a screw-type jack for automobile which can solve the various problems described above. 
     It is a further object of the invention to provide a screw-type jack housing that can be efficiently formed and assembled of a housing and in which streamlined production of the housing at low cost is achieved by eliminating complicated forming work and troublesome welding operations, for the housing, can realize easy and precise surface treatment such as rust prevention to lengthen life and enhance strength, and can realize smooth and easy operation by an operation handle. 
     It is another object of the present invention to provide a jack for automobile in which a method is devised for a fixing means of a ram and a ram nut to enable its production cost to be further lowered. 
     It is yet another object of the present invention to provide a jack for automobile in which a method is devised to increase the lifting/lowering speed of a ram when necessary. 
     In order to achieve the above-described objects, in a screw-type jack for automobile comprising: a base; a hollow and integrated housing provided to stand on this base; a ram mounted in the center portion inside this housing in an axial direction to be extendable/contractible in a vertical direction; and a drive mechanism mounted in the housing, for extending/contracting this ram in the vertical direction, and in which the housing includes a cylindrical shaft portion protrudingly disposed on a lower part of a side surface of the housing, and a drive gear is pivotally and rotatably supported in this cylindrical shaft portion, the present invention defines the housing as constituted of a plurality of housing pieces, namely, vertically divided portions of the housing, wherein the housing pieces are mechanically joined to each other to form the housing. This structure makes it possible to realize easy and uniform forming of the housing by eliminating complicated and difficult forming; furthermore, to realize efficient forming and assembly and streamlined production of the housing at low cost by eliminating troublesome and high-cost welding; and moreover, to enable easy and precise surface treatment such as painting and plating of the housing pieces and so on, thereby lengthening their life and enhancing their strength. 
     The present invention provides a jack in which the housing is divided in the vertical direction along the axis position of the cylindrical shaft portion, so that forming of the housing pieces is facilitated. 
     The present invention also provides two-divided portions of the cylindrical shaft portion integrally formed with the housing pieces, so that inefficiency of disposing the cylindrical shaft portion separately as in the conventional art is eliminated and streamlined production is realized. 
     The present invention provides a housing that is divided into two pieces in the vertical direction. A pair of these housing pieces are formed symmetrically, so that the structure thereof is simplified and the production thereof is facilitated. 
     The present invention also provides a jack in which each of the housing pieces includes joining pieces along edge portions of the housing piece to extend from these edge portions. When the housing pieces are mechanically joined with each other to form one housing, the joining pieces of the housing pieces are fixed with each other by a rivet, so that welding of the housing pieces is eliminated to realize cost reduction of the housing. 
     The present invention provides a jack in which the housing piece includes: joining pieces along edge portions of each of the housing portions extend from these edge portions. A connecting piece extends from one or both of the joining pieces. When the housing pieces are mechanically joined with each other to form the housing, the connecting piece is folded to overlappingly fix the joining pieces with each other. In this structure, the housing pieces are fixed to each other by one press work without requiring welding, to further reduce cost. 
     The present invention provides a jack in which the housing includes a leg piece protruding from a lower end portion of the housing. The leg piece is fixed to the base by a rivet to eliminate welding, so that cost reduction is also realized here. 
     The present invention also provides a jack in which a bush or a bearing layer is interposed between an inner circumferential surface of the two-divided portions of the cylindrical shaft portion and a shaft portion of the drive gear, so that the drive gear can be rotated smoothly, labor necessary for driving operation is reduced, and heat generation in the periphery of the cylindrical shaft portion is prevented. 
     In a screw-type jack for automobile comprising: a base; a hollow and integrated housing provided to stand on this base; a ram guide mounted in a center portion inside this housing in an axial direction to be extendable/contractible in a vertical direction; a ram mounted in the ram guide to be extendable/contractible; and a screw shaft for extending/contracting the ram guide and the ram in the vertical direction, and in which the housing includes a cylindrical shaft portion provided protrudingly on a lower part of a side surface of the housing, and a drive gear is pivotally and rotatably supported in this cylindrical shaft portion, the present invention a housing that is constituted of a plurality of housing pieces, namely, vertically divided portions of the housing and both side portions of these housing pieces are mechanically joined with each other to form the housing. This structure makes it possible to realize easy and uniform forming of the housing by eliminating complicated and difficult forming work; and furthermore, to realize efficient forming and assembly and streamlined production of the housing at low cost by eliminating troublesome and high-cost welding. Moreover, easy and precise surface treatment such as painting and plating of the housing pieces and so on is enabled, thereby lengthening their life and enhancing their strength. 
     The present invention provides a jack in which the ram is constituted of a cylindrical portion and a rum nut. A circumferential groove is formed around an outer circumference of an inserting portion of the ram nut which is to be inserted to the cylindrical portion. After the inserting portion is inserted into the cylindrical portion, an inner surface of the cylindrical portion is bulged out and fixed to the circumferential groove by caulking an outer circumferential portion of the cylindrical portion. Thereby, the ram nut is fixed to the cylindrical portion without welding to realize cost reduction. 
     The present invention provides a jack in which a quick moving lever is added in order to move a ram quickly in a vertical direction. The quick moving lever is caught in a handle joint of a drive gear and rotates a handle joint with a small rotation radius. 
     The present invention provides a jack in which a spacer ring is attached between a handle joint of an operation handle and an end portion of an outer surface of the cylindrical shaft portion. The handle joint is attached to the shaft portion of the drive gear to swing freely via a pin, so that backlash of the shaft portion in an axial direction is prevented and the handle joint is free to swing easily. 
     The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross sectional view of an embodiment of the present invention, showing its extended state in use. 
     FIG. 2 is a cross sectional view taken along the line A—A in FIG.  1 . 
     FIG. 3 is a cross sectional view taken along the line B—B in FIG.  1 . 
     FIG. 4 is a cross sectional view taken along the line C—C in FIG.  1 . 
     FIG. 5 is a fragmentary cross sectional view of the embodiment of the present invention, showing its contracted state when it is not in use. 
     FIG. 6 is a plan view of FIG.  5 . 
     FIG. 7 is a plan view showing the state while the present invention is being assembled, in which a ram and a ram guide are omitted. 
     FIG. 8 is a plan view showing one of housing pieces applied to the present invention. 
     FIG. 9 is a front view showing an inner surface of one of the housing pieces applied to the present invention. 
     FIG. 10 is a perspective view showing a pair of the housing pieces applied to the present invention. 
     FIG. 11 is a cross sectional view taken along the line D—D in FIG.  8 . 
     FIG. 12 is a cross sectional view taken along the line E—E in FIG.  9 . 
     FIG. 13 is a perspective view showing another embodiment of the housing. 
     FIG. 14 is an exploded perspective view before the housing pieces of a housing shown in FIG. 13 are joined with each other. 
     FIG. 15 is a perspective view showing a quick moving lever as one embodiment of a quick moving means. 
     FIG. 16 is a vertical sectional view of the quick moving lever shown in FIG.  15 . 
     FIG. 17 is an enlarged horizontal sectional view of the quick moving lever shown in FIG. 15 taken along portions of resilient catching pieces. 
     FIG. 18 is an explanatory view for explaining how the quick lever shown in FIG. 15 is accommodated when it is not in use. 
     FIG. 19 is an explanatory view for explaining how the quick moving lever shown in FIG. 15 is used. 
     FIG. 20 is a fragmentary cross sectional view showing a fixing means of the ram and the ram nut. 
     FIG. 21 is an enlarged cross sectional view showing a portion of a in FIG.  20 . 
     FIG. 22 is a plan view showing another embodiment of a reinforcing means of a leg piece of the housing piece. 
     FIG. 23 is an enlarged cross sectional view showing another embodiment of a portion where a handle joint is provided. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring FIG. 1 a substantially rectangular base  1  made of a steel plate can be placed on a grounding surface  2 . A hollow, cylindrical housing  3  extends upward from the base  1 . 
     The housing  3  has a substantially rectangular pipe-shaped upper half portion. The housing  3  also includes a substantially conic pipe-shaped lower half portion which widens toward its lower part. A cylindrical shaft portion  4  on a lower portion of a side circumferential surface supports a later-described drive gear. The cylindrical shaft portion  4  protrudes slightly upward. A plurality of leg pieces  5  extend outward from a lower end portion of the housing  3 . 
     The housing  3  is formed by joining a pair of right and left housing pieces  6 ,  7  along a joining line L (see FIGS. 7 and 8) passing an axis of the cylindrical shaft portion  4 . The right and left housing pieces  6 ,  7  are formed in substantially the same shape by symmetrically press-forming a medium-thickness steel plate. In this case, the housing  3  can be structured by two or more housing pieces by vertically dividing the housing  3 . Thereby, press-forming of the housing pieces is facilitated. 
     As shown in FIG. 10, the housing pieces  6 ,  7  are formed in a substantially bucket shape widening toward their lower ends. Upper pieces  6   a,    7   a  corresponding to upper halves thereof have cross sections substantially in a V-shape. Lower pieces  6   b,    7   b  corresponding to lower halves thereof have substantially semicircular cross sections. The upper pieces  6   a ,  7   a  are formed substantially in the same shape, with convex beads  8 ,  9  (FIGS. 7 and 10) having substantially outwardly protruding V-shaped or U-shaped cross sections along an axial direction on center portions of circumferential surfaces having substantially semicircular cross sections, as shown in the drawing. 
     Catching portions  10 ,  11  (FIGS. 6 and 7) protrude from upper inner surfaces of the beads  8 ,  9 . Projections protruding from a later-described ram guide can be fitted in the catching portions  10 ,  11 . Joining pieces  12 ,  13  which can be joined with each other are provided along both edges of the upper pieces  6   a ,  7   a  respectively. The joining pieces  12 ,  13  have a plurality of through holes  15 ,  16  to receive rivets  14 . 
     The lower pieces  6   b,    7   b  have substantially the same shape, each formed in a shape obtained by dividing a substantially truncated cone in two in a vertical direction as shown in the drawings. The convex beads  8 ,  9  extend from the centers of upper circumferential surfaces of the lower pieces  6   b,    7   b.  Short pipe pieces  17 ,  18  which constitute the cylindrical shaft portion  4 , are formed on a middle bulged portion of its circumferential surface to extend in an upper direction. The short pipe pieces  17 ,  18  have semicircular cross sections which are obtained by vertically dividing the cylindrical shaft portion  4  into two pieces along the joining line L. Inside the short pipe pieces  17 ,  18  are fitting stepped portions  19 ,  20  whose diameters are larger than those of the short pipe pieces  17 ,  18 . A shaft portion of a later-described drive gear is rotatably accommodated inside the joined short pipe pieces  17 ,  18 . Catching projections  21 ,  22  protrude from inner circumferential surfaces of the lower pieces  6   b,    7   b  opposite the short pipe pieces  17 ,  18 . The catching projections  21 ,  22  are disposed directly above a later-described bevel gear to permit fitting the catching projections  21 ,  22  in the lower pieces  6   b,    7   b.    
     Connecting pieces  23 ,  24 , having substantially the same shape as the joining pieces  12 ,  13 , are disposed along both edges of the lower pieces  6   b,    7   b.  connecting pieces  23 ,  24  can be joined to each other. A plurality of through holes  15 ,  16  in the connecting pieces  23 ,  24  permit insertion of the rivets  14 . 
     Through holes  25  in the leg portions  5  permit the insertion of rivets  37  therethrough. This enables the leg portions  5  to be fixed to the base  1  using the rivets  37 . Reinforcing beads  26  are formed on folded portions of the leg pieces  5 . A concave portion  27  is formed on the center part of an inner surface of the base  1 . A thrust bearing  28  is accommodated in the concave portion  27 . A lower end portion of a first screw shaft  29  is rotatably supported in the thrust bearing  28 . A substantially bowl-shaped bevel gear  30  is fixed to a small-diameter shaft portion  29   a  at the lower end portion of the first screw shaft  29 . The bevel gear  30  rotates with the first screw shaft  29 . A bottom surface of the bevel gear is seated on an inner race of the thrust bearing  28 . 
     A connecting pin  31  (FIG. 5) is attached to the small-diameter shaft portion  29   a  to retain the bevel gear  30  on the small-diameter shaft  29   a.  The catching projections  21 ,  22  are disposed directly above a rotation area of the bevel gear  30  so that they can be fitted in the bevel gear  30 , whereby the bevel gear  30  and the first screw shaft  29  are prevented from moving upward and coming off: 
     A drive gear  32  is affixed to an inner end of a shaft portion  33 . The drive gear  32  engages the bevel gear  30 . A boss of the drive gear  32  is fitted in the fitting stepped portions  19 ,  20 . The drive gear  32  is integrally formed with a shaft portion  33 . The shaft portion  33  is supported rotatably inside the short pipe pieces  17 ,  18  via a bush  34 . An end portion of the shaft portion  33  projects outward from the short pipe pieces  17 ,  18 . A handle joint  35  is connected to this projecting portion via a pin  36  to permit the handle joint to swing freely. An end portion of an outer surface of the handle joint  35  includes a fitting groove  38  (FIG. 6) into which an end portion of an operation handle (not shown) can be inserted. The fitting groove  38  is shown with a rectangular cross section for mating with a rectangular end of the operation handle. Other shapes may be adopted for the fitting groove  38  and the mating operation handle. 
     The first screw shaft  29  is a steel rod a little shorter than the height of the housing  3 . The first screw shaft  29  has a male screw portion on its entire outer circumferential surface. A stopper pin  39  (FIG. 1) protrudes from an upper end portion of the male screw portion. The stopper pin  39  is positioned on a surface substantially equal in height with an outer diameter of the male screw portion of the first screw shaft  29  so that it can engage a female potion  41  on a lower end of an inner surface of a second screw shaft  40  to restrict the lifting position of the second screw shaft  40  when they are caught by each other. 
     The second screw shaft  40 , which is substantially equal in length to the first screw shaft  29 , is made of a steel pipe with a relatively large diameter. The second screw shaft  40  has a male screw portion over its entire outer circumferential surface. The female screw portion  41 , which can be screwed to the male screw portion of the first screw shaft  29 , is formed on a lower end portion of an inner surface thereof. A ram nut  42  is screwed to the male screw portion of the second screw shaft  40 , so that the ram nut  42  can vertically move along the male screw portion. When the ram nut  42  reaches its highest position, it is stopped by a stopper pin  43  which is attached in an upper end portion of the second screw shaft  40 . This limits the upward movement of the ram nut  42 . In this case, the stopper pin  43  is positioned in a surface substantially equal in height to the outer diameter of the male screw portion of the second screw shaft  40 . The ram nut  42 , which has a female screw portion, which can be screwed to the male screw portion of the second screw shaft  40 , has an external shape of a substantially truncated cone. The ram nut  42  has a plurality of convex beads  44  (FIG. 3) formed on a tapered outer circumferential surface thereof in an axial direction, so that the ram nut  42  can be caught by a ram guide  45  when the ram nut  42  reaches its highest position. 
     The ram guide  45  is made of a steel pipe substantially equal in length to the first screw shaft  29 . The ram guide  45  has a substantially square cross section as shown in FIG.  3  and FIG. 4, with a shape similar to the external appearance of the ram nut  42  or the shape of an inner surfaces of the joined housing pieces  6 ,  7 . The ram guide  45  has a plurality of fitting grooves  46  on its inner surface into which the convex beads  44  can be fitted. 
     A tapered diameter-reducing portion  45   a  is disposed in an upper end portion of the ram guide  45 . The ram nut  42  can be caught by an inner surface of the diameter-reducing portion  45   a  to permit the ram guide  45  to move with the ram nut  42 . Projections (not shown) which can be fitted in the aforesaid catching portions  10 ,  11  are formed on a circumferential surface of a lower end portion of the ram guide  45 , to limit the upward motion of the ram guide  45 . 
     A lower end portion of a ram  47  is welded to the ram nut  42 . The ram  47  is made of a steel pipe which can be accommodated in the ram guide  45 . The ram  47  is shorter than the ram guide  45  by the length of the ram nut  42 . 
     A top plate  48  is connected to an upper end portion of the ram  47  by caulking. A vehicle mounting table  50  is connected by caulking to a fitting shaft  49  protruding upward from the top plate  48 . The top plate  48  may alternatively be connected using a bolt or a screw instead of being connected by caulking. 
     The mechanical joining means described above for joining the housing pieces  6 ,  7  with each other and fixing the housing  3  to the base  1  can be substituted for by other joining means without departing from the spirit and scope of the invention. For example both of the members maybe fitted to each other and connected by pressure or by fixing them to each other by a screw, and so on. 
     In producing thus-structured jack for automobile, an iron plate is press-formed to produce a pair of the housing pieces  6 ,  7 , the housing  3  is formed in a cylindrical shape by joining the housing pieces  6 ,  7 . Thereafter, the base  1 , the ram  47 , the ram guide  45 , and so on are assembled together. Surface treatment such as painting and plating of the components is performed as described later before the assembly of the base  1 , the ram  47 , the ram guide  45 , and so on is combined in the housing  3 . That is, the surface treatment is performed when the parts can be handled easily. In other words, the surface treatment of each of the components is separately or synchronously performed before being assembled in the housing  3 , and this assembly is combined in the housing  3  after each of the components undergo the surface treatment. 
     This makes it possible to perform the surface treatment for both of the outer and inner surfaces of each of the components and take precautionary means to prevent oil and fat content from adhering to the treated surfaces. This permits realization of easy, sure, and precise surface treatment compared with a conventional producing method in which the surface treatment is performed after the components is combined in the cylindrical housing  3 . In this manner, an anti-corrosive property thereof is improved and the life of the jack is lengthened. 
     The housing pieces  6 ,  7  are formed symmetrically by press-forming a steel plate. This can be done easily, quickly, and uniformly compared with a conventional press-forming in which one portion of a cylindrical steel pipe is formed in a rectangular pipe shape and this portion in a rectangular pipe shape is formed to bulge to a substantially conic pipe. 
     The housing pieces  6 ,  7  are portions of the housing divided in the vertical direction along the joining line L passing the axis of the cylindrical shaft portion  4 . Thus the housing pieces  6 ,  7  are easily and uniformly formed compared with a device that is divided in the vertical direction along another line and the cylindrical shaft portion  4  is formed separately. 
     The housing pieces  6 ,  7  after being press-formed, which are shown in FIG. 10, are formed to be in a bucket shape, with the upper half portion thereof having a substantially V-shaped cross section and a substantially semicircular shaped lower half portion. 
     In addition, the short pipe pieces  17 ,  18 , which constitute the cylindrical shaft portion  4 , are integrally formed with the housing pieces  6 ,  7 , so that the time/labor and the number of parts is reduced and the cylindrical shaft portion  4  is produced easily and at low cost, compared with a conventional production method in which the cylindrical shaft portion  4  is produced separately and welded to a forming hole of the housing. 
     The aforesaid assembly is combined in the housing  3  after each of the components undergoes surface treatment, and the actual processes will be described as follows. 
     First, when the housing  3  is to be assembled, a pair of the right and left housing pieces  6 ,  7  are disposed facing each other as shown in FIG. 10 with the through holes  15 ,  16  in the joining pieces  12 ,  13 ,  23 ,  24  aligned with each other. The rivets  14  are inserted through the through holes  15 ,  16 . The rivets  14  are struck, so that the housing pieces  6 ,  7  are riveted to each other. The upper half portion of thus assembled housing  3  has a cross section in a substantially square shape as shown in FIG.  3 . Catching grooves in a substantially similar shape to the convex beads  8 ,  9  are formed in four corners of its inner circumferential surface. A cylindrical space is formed opposite the short pipe pieces  17 ,  18  on the lower part of the housing  3 . A short cylindrical space is formed opposite the fitting stepped portions  19 ,  20 . 
     Then, the bush  34  is inserted from the inside of the housing  3  into the cylindrical space. Next, the drive gear  32  is inserted into the cylindrical space from the inside of the housing  3 . The shaft portion  33  of the drive gear  32  is inserted into the bush  34 . The handle joint  35  is fitted to the projecting portion of the shaft portion  33 , where they are connected with each other via the pin  36  free to swing freely. 
     The ram nut  42  is welded to the lower end portion of the ram  47  before the top plate  48  is attached thereto. An assembly of the second screw shaft  40  and the first screw shaft  29  is inserted from an upper opening portion of the ram  47 . The ram guide  45  is inserted from the top of the ram  47 , and the ram guide  45  is caught by the ram nut  42 . 
     To specifically explain the assembly of the first and second screw shafts  29 ,  40 , the pin  43  is inserted into the upper end portion of the second screw shaft  40 . The first screw shaft  29  is screwed onto the screw portion  41  in the lower end portion of the second screw shaft  40 . The first and second screw shafts are caught with each other via the pin  39 . 
     Then, the bevel gear  30  is attached to the small-diameter shaft portion  29   a  in the lower end of the first screw shaft  29 , and the connecting pin  31  is inserted directly under the bevel gear  30  to connect and integrate them. 
     In this way, the ram  47  to which the top plate  48  is not yet attached, the ram guide  45 , the first and second screw shafts  29 ,  40 , the bevel gear  30 , and so on are integrally assembled, and this assembly is combined in the housing  3 . 
     Specifically, the base  1  is placed on a work table. The bearing  28  is inserted into its concave portion  27 . The small-diameter shaft portion  29   a  of the aforesaid assembly is inserted into a center hole of the bearing  28 , so that this assembly remains in a standing state. 
     Next, the housing  3  is placed from above over this assembly with the through holes  25  of the leg pieces  5  matched with predetermined positions of the base  1 . The rivets  37  are inserted into the through holes  25 , these rivets  37  are struck, so that the leg pieces  5  are riveted to the base  1 . In this way, conventional welding is not used for fixing the housing  3  to the base  1 , so that they can be surely and easily connected at low cost. Thereafter, after the top plate  48  is attached to the upper end portion of the ram  47  by caulking and the vehicle mounting table  50  is attached to its fitting shaft  49  by caulking, the assembly work is finished. 
     Thus assembled jack for automobile contracts to a small size as shown in FIG. 5 when it is not in use. At this time, the second screw shaft  40 , the ram  47 , and the ram guide  45  are contracted to the minimum length and accommodated in the housing  3  in a triple cylinder state. The ram nut  42  is placed at the lowest position and the vehicle mounting table  50  is positioned directly above the upper end portion of the housing  3 . 
     In this state, when the jack for automobile is to be used for jacking up a vehicle, the jack for automobile is positioned directly under a jack point of the vehicle, for example, a jack point around a tire housing, the end portion of the operation handle (not shown) is inserted in the fitting groove  38  thereof and the handle is rotated around an axis of a shaft. This operation rotates the drive gear  32  and, as a result, rotates the bevel bear  30  engaged with the drive gear  32 . The first screw shaft  29 , integral with the bevel gear  30 , is also rotated. 
     This causes the second screw shaft  40  to move upward along the first screw shaft  29  via the female screw portion  41 . When the upper end potion of the female screw portion  41  contacts the pin  39  of the first screw shaft  29 , in other words, when the second screw shaft  40  is extended to its full stroke, the upward movement of the second screw shaft  40  is stopped so that it rotates idly in this position. 
     In accordance with the idle rotation of the second screw shaft  40 , the ram nut  42  moves upward along the male screw portion of the second screw shaft  40  without rotating and the diameter-reducing portion  45   a  is caught by the rain nut  42  to move the ram guide  45  upward. The upward movement of the ram nut  42  causes the ram  47  fixed to the ram nut  42  to move upward. 
     At this time, the ram nut  42  is fitted in the inner surface of the ram guide  45  and the outer surface of the ram guide  45  is fitted in the inner surface of the housing  3  so that the moving posture thereof is stabilized. This state is shown in FIG.  3  and FIG.  4 . 
     When the ram  47  moves upward, the vehicle mounting table  50  fits in the jack point around the tire housing of the vehicle to jack up the vehicle. 
     In this way, when the ram nut  42  is moved to the highest position of the second screw shaft  40 , the upper end portion of the ram nut  42  is caught by the pin  43  so that its upward movement is restricted. 
     At this time, the projections (not shown) on the lower end portion of the ram guide  45  are caught by the catching portions  10 ,  11  so that the upward moving position of the ram guide  45  is restricted. 
     Then, the ram  47  is extended to its full stroke to cause the vehicle mounting table  50  on the upper end portion of the ram  47  to reach its highest position so that the periphery of the tire housing of the vehicle is jacked up to a predetermined height to enable a tire to be changed. This, extended state is shown in FIG.  1 . 
     After the jack for automobile is used, the operation handle is rotated n the reverse direction to cause the drive gear  32  and the bevel gear  30  to reversely rotate so that the first screw shaft  29  is reversely rotated. 
     This causes the second screw shaft  40  to rotate reversely and to move downward along the first screw shaft  29  so that the ram nut  42  and the ram guide  45  move with it until the second screw shaft  40  and the ram guide  45  are accommodated in the housing  3 . 
     As described above, in this embodiment, a drive means  51  mounted in the housing  3  for vertically moving the ram  47  is composed of the drive gear  32 , the bevel gear  30  engaged with the drive gear  32 , the first screw shaft  29  fixed to the bevel gear  30 , the second screw shaft  40  screwed to the first screw shaft  29  in an axial direction, and the ram guide  45 . However, the drive means  51  is not limited to this embodiment. Only one screw shaft may be used. When only one screw shaft is used, the ram guide  45  may sometimes be omitted. What is important is that any drive means may be used as long as it causes the ram to move vertically by rotating the drive gear  37  which is pivotally and rotatably supported in the cylindrical shaft portion  4 . 
     After being accommodated, the ram nut  42  is positioned at the upper end portion of the second screw shaft  40  which corresponds to the upper end portion of the housing  3 . 
     Thereafter, when rotation of the operation handle is reversed, the second screw shaft  40  rotates idly in its accommodated position to cause the ram nut  42  to move downward along the second screw shaft  40  without rotating and the ram  47  and the ram guide  45  rotate with it. 
     At this time, the ram nut  42  is fitted in the inner surface of the ram guide  45  and the outer surface of the ram guide  45  is fitted in the inner surface of the housing  3  so that the moving posture thereof is stabilized. 
     When the vehicle mounting table  50  is moved away from the jack-up point of the vehicle and the ram  47  and the ram guide  45  are returned to their original positions, the jack for automobile can be taken out from under the vehicle. 
     The rotation of the drive gear  32 , when the jack for automobile is used, causes the periphery of the shaft portion  33  to generate heat due to contact friction between the shaft portion  33  and the bush  34 . However, a flat and smooth contact surface of the bush  34  reduces the contact friction to reduce the heat generation, so that a normal usage state is maintained, and thereby, the life of the shaft portion  33  is lengthened compared with a case when the shaft portion  33  directly contacts the inner surfaces of the short pipe pieces  17 ,  18 . 
     The bush  34  can be omitted when thin bearing layers made of metal or synthetic resin is coated on the respective inner surfaces of the short pipe pieces  17 ,  18  in which the bush  34  is attached and on the respective inner surfaces of the fitting stepped portions  19 ,  20 , in the above-described embodiment. In this case, the bearing layers may overlap the aforesaid surface treatment layers, or the beating layers may be directly coated without the surface treatment layers. The former case facilitates the forming of the bearing layers. The latter case enhances the fixability of the bearing layers, so that detachment and abrasion of the bearing layers due to the elapse of time can be prevented. 
     The housing pieces  6 ,  7 , which are made of metal plates in the above-described embodiment, may be made of cast iron, by die-casting, or of synthetic resin. This makes it possible to form the housing pieces  6 ,  7  easily and at low cost. 
     FIG.  13  and FIG. 14 show another embodiment of the housing, in which a housing  55  is made up of housing pieces  56 ,  57 . The housing pieces  56 ,  57  consist of two vertically divided portions of the housing  55  as in the aforesaid embodiment. However, this embodiment is different from the aforesaid embodiment in that the forming method of the housing  55  in which the housing pieces  56 ,  57  are not joined to each other by rivets. Instead, joining pieces  58  of one housing piece  56  overlap joining pieces  60  of the other housing piece  57 . A plurality of connecting pieces  59  provided to further protrude from the joining pieces  58  are folded to catch the joining pieces  60  of the other housing piece  57 . Thereby the housing pieces  56 ,  57  are joined to each other, 
     This structure makes it possible to join the housing pieces  56 ,  57  with each other in one operation using a pressing machine, which offers the advantage of reduced cost, compared with a case when the housing pieces  56 ,  57  are joined with each other by riveting using a plurality of rivets. 
     The connecting pieces  59  maybe provided to all of the joining pieces  58 , or they may be provided only to portions joined by the rivets as described in he aforesaid embodiment. The connecting pieces  59  may be provided to the other connecting pieces  60  or may be provided alternately to the joining pieces  58 ,  60 . Moreover, joining by rivets may also be employed together with the use of joining pieces  58 ,  60 . 
     FIG. 15 to FIG. 19 show a quick moving means of the ram. In the drawings, the quick moving means consists of a flexible synthetic resin quick moving lever  61  made of, for example, PE. The quick moving lever  61  is composed of a grip portion  62  having a U-shaped cross section and resilient catching pieces  63 ,  63  protruding from the substantially central portion of the grip portion  62 . As shown in FIG. 19, the resilient catching pieces  63 ,  63  are inserted in a fitting groove  38  in the handle joint  35 . The resilient catching pieces  63 ,  63  are resiliently urged outward to catch in the fitting groove  38 . The handle joint  35  is attached to the shaft portion of the drive gear. The grip portion  62  is gripped by a hand to rotate the handle joint  35 , which results in quick rotation of the not-shown drive gear. 
     This operation rotates the drive gear more quickly than in a case when it is rotated using an operation handle since the rotation radius is small and is easily operated. Consequently, the ram guide and the ram can be lifted/lowered more quickly. After the vehicle mounting table contacts the jack point of the vehicle, it is necessary to use the operation handle to apply the increased torque needed to raise the vehicle. The quick moving lever  61  working as a quick moving means is also effective while returning the components to their original stowed positions after usage. A pair of catching projections  64 ,  64  are provided on the inner surface of portions where the resilient catching pieces  63 ,  63  are formed. As shown in FIG. 18, these catching projections  64 ,  64  are fitted in not-shown catching holes in the joining pieces or the connecting pieces of the housing. The quick moving lever  61  is kept in this state when it is not used. Note that bulging portions  62   a,    62   b  formed on one side deviated from the center portion of the grip portion  62  make the grip portion easy to grip during use. 
     FIG.  20  and FIG. 21 show a fixing means for the ram and the ram nut. A circumferential groove  67  is formed in a fitting portion  65   a,  which is inserted in the ram  66 , of the ram nut  65 . An outer circumferential portion of the ram  66  corresponding to this circumferential groove  67  is caulked by pressure to cause an inner circumference of the ram  66  to bulge inwardly and to be pushed into the circumferential groove  67  of the ram nut  65 . This fixedly connects together the ram  66  and the ram nut  65 . This structure brings about the advantage of reducing production cost compared with a case when the ram  66  and the ram nut  65  are welded to be fixed with each other. 
     FIG. 22 shows another embodiment of the reinforcing means of the leg pieces of each of the housing pieces. The reinforcing beads, which are provided in the aforesaid embodiment, are not included on leg pieces  71   a,    71   a,    72   a,    72   a  of the housing pieces  71 ,  72  constituting the housing  70 . Instead, a flange portion  71   b  connect the leg pieces  71   a,    71   a  of the housing piece  72 , and a flange portion  72   b  connect the leg pieces  72   a,    72   a  of the housing piece  72 . The reference numeral  73  denotes a base. 
     This structure brings about an advantage that the reinforcing means can be formed more easily than in a case when the reinforcing beads are formed even though they are formed by press work in both cases. 
     FIG. 23 shows another embodiment of attaching a drive gear to a cylindrical shaft portion. A circumferential groove  76   a  is formed in a portion of a shaft portion  76  of the drive gear  75 . This portion matches the position of an end portion of an outer surface of the cylindrical shaft portion  77 . A spacer ring  78  is fitted in this circumferential groove  76   a  to contact the end portion of the outer surface of the cylindrical shaft portion  77 . 
     This structure eliminates backlash of the shaft portion  76  in an axial direction and enables a handle joint  80 , which is attached to the shaft portion  76  via a pin  79  to swing freely, to swing more smoothly so that an advantage of improving operability of the operation handle is brought about. 
     Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.