Abstract:
The present invention provides a garage jack provided with a dual cylinder mechanism for rapid traversing in which there is no fear that damage will be caused by an accidental load during rapid traverse and working of a hydraulic circuit is simple. The garage jack comprises, a movable frame provided with wheels, an arm pivotably supported at the frame and having a support plate at an end thereof, a hydraulic cylinder ( 9 ) for operating the arm up-and-down, the hydraulic cylinder ( 9 ) comprising a dual cylinder mechanism comprising a low pressure chamber ( 15 ) of a small effective cross-sectional area relative to a piston ( 8 ) and a high pressure chamber ( 16 ) of a large effective cross-sectional area, a pump cylinder ( 10 ) for supplying hydraulic fluid to the hydraulic cylinder and a handle ( 13 ) for operating the pump cylinder wherein, a hydraulic fluid channel ( 27 ) provided with a sequence valve ( 19 ) is provided connected in-line with the low pressure chamber ( 15 ) and the high pressure chamber ( 16 ) and in a case where a pressure of hydraulic fluid in the low pressure chamber is greater than a predetermined pressure of the sequence valve, the hydraulic fluid in the low pressure chamber is fed to the high pressure chamber.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    (a) Field of the Invention  
           [0002]    The present invention relates to a garage jack used for raising or lowering automotive vehicles such as passenger cars and trucks when performing maintenance or repair, and, in particular to a garage jack including a movable frame equipped with wheels, an arm pivotably supported at the frame and having a support plate at an end thereof and a hydraulic cylinder for operating the arm up-and-down, a pump cylinder for supplying hydraulic fluid to the hydraulic cylinder and a handle for operating the pump cylinder.  
           [0003]    (b) Description of the Related Art  
           [0004]    As shown in FIG. 4, a conventional garage jack such as above includes a movable frame  1  equipped with wheels  2 , an arm  5  supported at the frame by means of a pivot  3  and having a support plate  4  at an end thereof, a link rod  6  for assisting actuation of the arm  5  pivotably attached to the frame  1 , a hydraulic cylinder  9  provided with a piston rod  8  of which a tip is connected to a base  7  of the arm  5 , a pump cylinder  10  for supplying hydraulic fluid to the hydraulic cylinder  9  and a handle  13  for operating the pump cylinder  10  via links  11 ,  12 .  
           [0005]    The handle  13  is operated by human power to operate the pump cylinder  10  via the links  11 ,  12 , and the hydraulic cylinder  9  is operated by hydraulic fluid from the pump cylinder  10 . The arm  5  is raised to raise the support plate  4  and an object to be lifted, an automotive vehicle, is lifted. Also, the raised vehicle can be lowered by evacuating hydraulic fluid from the relief valve of the hydraulic circuit (see Japanese Patent Laid-open No. Hei 10-33090).  
           [0006]    Incidentally, when raising or lowering an object to be lifted, an automotive vehicle, with this type of garage jack, the support plate must be properly set to a jack point (for example, a differential, axle, etc.) located at the underside of an automotive vehicle in order to safely support the vehicle. Moreover, in order for a support plate to be properly set, it is necessary to slide the frame of the garage jack beneath the vehicle and position the support plate directly underneath the jack point.  
           [0007]    Accordingly, the height of this type of garage jack is limited by the height from the ground to the lowest part of a vehicle, that is, by the ground clearance of the automotive vehicle, and the garage jack should be constructed to be as low as possible. For example, in the garage jack disclosed in the above Japanese Patent Application Laid-open No. Hei 10-33090, the arm  5 , link rod  6  and hydraulic cylinder  9  are arranged in-line horizontally so that it may be used even on cars that are very low to the ground. Also, as shown in FIG. 5, a compact structure is also already known from Japanese Patent Application Laid-open No. Hei 10-33090 in which it is possible to dispose the hydraulic cylinder  9  below the arm  5  and operate the arm  5  provided with the support plate  4  at an end thereof through a link  14 .  
           [0008]    As can be seen from the above, in this type of garage jack, the height is limited by the ground clearance of the automotive vehicle because, especially when lifting, the frame must be slid underneath the object to be lifted, the automotive vehicle. And when the diameter of the hydraulic cylinder is increased to increase the output of the garage jack, the number of automotive vehicles on which the jack can be used is severely limited.  
           [0009]    Accordingly, in this type of garage jack, efforts have been made to increase the pressure in the hydraulic cylinder in order to obtain a large output. However, the operating force of the pump cylinder is generally limited because its operation is performed by human power, and since it is necessary to prevent the diameter of the pump cylinder from being small compared to the diameter of the hydraulic cylinder, the operating frequency of the pump piston increases remarkably when creating a high pressure in the hydraulic cylinder.  
           [0010]    Incidentally, since only the arm is lifted in the operation of contacting the support plate of the garage jack to the vehicle jack point, and this load may be substantially ignored, the output of the hydraulic cylinder may be very low. That is, since the operation of raising the arm from the lowest height of the support plate to the jack point is not the originally intended use of the garage jack, that is, lifting an automotive vehicle, but is preliminary work which is supplementary thereto, decreasing the frequency of operation of the handle for operating the pump cylinder to operate the arm greatly enhances the convenience of the garage jack.  
           [0011]    A garage jack provided with, as a means for eliminating the increased frequency of operation of the handle, a dual cylinder mechanism, that is, a dual cylinder mechanism including a low pressure chamber for rapid traversing having a small effective cross-sectional area relative to a piston and a high pressure chamber for normal operation having a large effective cross-sectional area for reducing the operating frequency of the handle during the substantially no-load operation of raising the support plate from its lowest position to the jack point has already been disclosed in U.S. Pat. No. 5,755,099.  
           [0012]    Namely, as shown in FIG. 6, a hydraulic cylinder  9  is a dual cylinder mechanism including an inner cylinder being a low pressure chamber  15  of a small effective cross-sectional area relative to a piston  8  and an outer cylinder being a high pressure chamber  16  of a large effective cross-sectional area, hydraulic fluid pumped by means of the pump cylinder  10  is divided into two channels  17 ,  18  toward the low pressure chamber  15  and high pressure chamber  16 , respectively, and a check valve  25  for preventing reverse flow is provided in the hydraulic fluid channel  17  leading to the low pressure chamber  15  and a sequence valve  19  is provided in the hydraulic fluid channel  18  leading to the high pressure chamber  16 . Hydraulic fluid is allowed to flow to the high pressure chamber  16  in a case where the pressure in the hydraulic fluid channel  18  is greater than a predetermined pressure of the sequence valve  19 .  
           [0013]    Accordingly, during the substantially no-load operation of raising the arm from the lowest position of the support plate to the jack point, hydraulic fluid is first pumped to the low pressure chamber  15  of a small effective cross-sectional area via the hydraulic fluid channel  17  to rapidly operate the piston  8  of the hydraulic cylinder  9  and quickly raise the arm provided with the support plate. The arm rises and when the support plate of the arm reaches jack point, operation becomes a load condition of lifting the object to be lifted, the automotive vehicle. That is, the pressure of the hydraulic fluid in the low pressure chamber  15  increases and the pressure of hydraulic fluid pumped by the pump cylinder  10  exceeds a preset pressure of the sequence valve  19 , and the sequence valve  19  opens and hydraulic fluid is pumped to the high pressure chamber  16 . Thus, the piston  8  operates slowly, but the output thereof is very large and it is possible to lift the object to be lifted, the automotive vehicle.  
           [0014]    A hydraulic circuit provided with a check valve  20  for preventing reverse flow is provided between the high pressure chamber  16  and an oil tank  21 . When hydraulic fluid is pumped to the low pressure chamber  15  only to operate the piston  8 , hydraulic fluid may be sucked into the high pressure chamber  16  from the oil tank  21  via the check valve  20  so that a vacuum is not caused in the high pressure chamber  16 . Also, a safety valve  22  prevents an overpressure in the hydraulic circuit and a relief valve  23  returns oil in the hydraulic cylinder  9  and each hydraulic circuit to the oil tank  21 . Moreover, a check valve  24  operates to pump up hydraulic fluid from the oil tank  21 .  
           [0015]    The garage jack provided with the above dual cylinder mechanism in which, hydraulic fluid pumped by means of the pump cylinder is divided into two channels leading toward the low pressure chamber and high pressure chamber, respectively, and the check valve for preventing reverse flow is provided in the hydraulic fluid channel leading to the low pressure chamber  15 , is designed to positively feed hydraulic fluid to the low pressure chamber. Thus, when an accidental load occurs on the arm provided with the support plate during rapid traverse, that is, when hydraulic fluid is supplied to the low pressure chamber, high pressure develops in the hydraulic fluid in the low pressure chamber and there is a concern that components of the low pressure chamber or the hydraulic fluid channel leading to the low pressure chamber may become damaged. Also, because the sequence valve provided in the hydraulic fluid channel leading to the high pressure chamber is provided in a bed of the garage jack and the sequence valve, check valves and the like are concentrated in the bed of the garage jack, the hydraulic circuit becomes very complicated and fabrication of the hydraulic circuit in the bed is very difficult.  
         SUMMARY OF THE INVENTION  
         [0016]    The present invention aims to solve the above problems with the conventional art and an object of the present invention is to provide a garage jack in which a hydraulic circuit may be simply fabricated and in which there is no concern that damage will be caused due to an accidental load during rapid traverse.  
           [0017]    In order to achieve the above mentioned object, according to one aspect of the present invention there is provided a garage jack including, a movable frame provided with wheels, an arm pivotably supported at the frame and having a support plate at an end thereof, a hydraulic cylinder for operating the arm up-and-down, the hydraulic cylinder including a dual cylinder mechanism including a low pressure chamber of a small effective cross-sectional area relative to a piston and a high pressure chamber of a large effective cross-sectional area, a pump cylinder for supplying hydraulic fluid to the hydraulic cylinder and a handle for operating the pump cylinder wherein, a hydraulic fluid channel provided with a sequence valve is provided connected in-line with the low pressure chamber and the high pressure chamber and in a case where a pressure of hydraulic fluid in the low pressure chamber is greater than a predetermined pressure of the sequence valve, the hydraulic fluid in the low pressure chamber is fed to the high pressure chamber.  
           [0018]    According to another aspect of the present invention the hydraulic fluid channel provided with the sequence valve provided connected in-line with the low pressure chamber and the high pressure chamber may be preferably disposed in the piston of the hydraulic cylinder. In this case, the sequence valve may preferably include a stepped opening formed in the piston of the hydraulic cylinder, packing for sealing between the stepped opening and a hydraulic fluid supply pipe, and a spring for pressing the packing to a step portion of the stepped opening. Also, a hydraulic circuit provided with a check valve may be preferably provided between the high pressure chamber and an oil tank for preventing a vacuum in the high pressure chamber. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 is circuit diagram of a hydraulic circuit of a garage jack according to the present invention.  
         [0020]    [0020]FIG. 2 is a cross-sectional drawing of an essential portion of an example of a sequence valve of a garage jack according to the present invention.  
         [0021]    [0021]FIG. 3(A) is a plan view of packing of the sequence valve of FIG. 2; FIG. 3(B) is a plan view of the presser bar  32  of the sequence valve of FIG. 2.  
         [0022]    [0022]FIG. 4 is an explanatory drawing of a conventional garage jack.  
         [0023]    [0023]FIG. 5 is an explanatory drawing of another conventional garage jack.  
         [0024]    [0024]FIG. 6 is circuit diagram of a hydraulic circuit of yet another conventional garage jack. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    Preferred embodiments of the garage jack of the present invention will be described below with reference to the drawings. Moreover, similar or corresponding portions are denoted by the same reference numerals.  
         [0026]    As shown in FIG. 1, a hydraulic cylinder  9  is constructed as a dual cylinder mechanism including a low pressure chamber  15  of a small effective cross-sectional area relative to a piston  8  in an inner cylinder and a high pressure chamber  16  of a large effective cross-sectional area in an outer cylinder. A hydraulic fluid channel  27  is provided connected with the low pressure chamber  15  and the high pressure chamber  16  and a sequence valve  19  is provided before the high pressure chamber  16  of the hydraulic fluid channel  27 . Thus, the sequence valve  19  opens and hydraulic fluid is pumped from the low pressure chamber  15  to the high pressure chamber  16  through the sequence valve  19  when an internal pressure generated in the low pressure chamber  15  is greater than a predetermined pressure of the sequence valve  19 .  
         [0027]    In this hydraulic circuit, first, hydraulic fluid pumped from a pump cylinder  10  by operating an handle  13  via a link  11  is delivered to the low pressure chamber  15 . Hydraulic fluid pumped to the low pressure chamber  15  of a small effective cross-sectional area relative to the piston  8  operates the piston  8  of the hydraulic cylinder  9 , which is in a substantially no-load condition, at a high speed to raise the arm  5  provided with the support plate  4  and it is possible to quickly contact the support plate  4  to the vehicle jack point.  
         [0028]    After contacting the support plate  4  of the arm  5  to the jack point, a load for lifting the automotive vehicle is applied to the piston when further operating the handle  13  and the pressure of hydraulic fluid in the low pressure chamber  15  increases. When the pressure in the low pressure chamber  15  exceeds a predetermined pressure of the sequence valve  19  provided in the hydraulic fluid channel  27  connected in-line with the low pressure chamber  15  and the high pressure chamber  16 , the sequence valve  19  opens and hydraulic fluid is fed from the low pressure chamber  15  to the high pressure chamber  16  and the piston  8  is operated at a slow speed. Nevertheless, the pressure of the hydraulic fluid does not just merely increase, but an output of the piston increases because an aggregate effective cross-sectional area of the low pressure chamber  15  and high pressure chamber  16  is increased, and it is possible to raise an object to be lifted, an automotive vehicle. Moreover, a hydraulic fluid channel for intake provided with a check valve  20  is provided between the high pressure chamber  16  and an oil tank  21 , and even when the piston  8  is moved by the hydraulic fluid delivered to the low pressure chamber  15  to increase the volume of the high pressure chamber  16 , a vacuum is not caused in the high pressure chamber  16  because hydraulic fluid may be drawn into the high pressure chamber  16  from the oil tank  21  via the hydraulic fluid channel for intake.  
         [0029]    In the garage jack according to the present invention, the hydraulic cylinder employs the dual cylinder mechanism and because the substantially no-load operation of raising the arm from the lowest height of the support plate to the jack point is performed by the inner cylinder comprising the low pressure chamber  15 , the operating convenience is increased by decreasing the operating frequency of the handle. Also, since the hydraulic fluid channel  27  is provided connected in-line with the low pressure chamber  15  and the high pressure chamber  16  and the sequence valve  19  is provided in the hydraulic fluid channel  27 , by continuing to operate the handle  13  after the support plate  4  contacts the vehicle jack point, the pressures in the low pressure chamber  15  comprising the inner cylinder and the high pressure chamber  16  comprising the outer cylinder are raised together and the automotive vehicle may be raised.  
         [0030]    Moreover, the sequence valve  19  opens in a case where, during operation of the inner cylinder comprising the low pressure chamber  15  only, some sort of load occurs on the arm  5  and pressure of the hydraulic fluid in the low pressure chamber  15  suddenly surges beyond the predetermined pressure limit of the sequence valve  19 . And, since hydraulic fluid may be automatically fed from the low pressure chamber  15  to the high pressure chamber  16 , the inner cylinder of the garage jack, that is the components of the low pressure chamber  15 , may be prevented from being damaged. For example, in the hydraulic cylinder shown in FIG. 2, even if the load of an automotive vehicle is applied to the support plate  4  when hydraulic fluid is being supplied to the low pressure chamber  15  only, localized pressure in the low pressure chamber  15  of the inner cylinder and in/on components thereof such as a supply pipe  29 , a packing  30 , a spring  31  and a presser bar  31  does not increase because the pressure in the low pressure chamber  15  and the high pressure chamber  16  increase simultaneously. Accordingly, these components are not damaged.  
         [0031]    Also, in the garage jack according to the present invention, it is possible to provide the sequence valve  19  in the piston, and since the sequence valve  19  is not provided in a bed of the garage jack, a fabrication of the garage jack bed, in particular, a fabrication for forming a hydraulic circuit to the bed is facilitated. Accordingly, it is possible to provide a simple garage jack in which the fabrication of the hydraulic circuit is facilitated; the garage jack is equipped with a rapid traverse function from the lowest height of the support plate to the jack point, and, in the operation of lifting an automotive vehicle by means of the garage jack, the low pressure chamber  15  and components thereof are not damaged even when an external load is applied to the support plate while hydraulic fluid is being supplied to the low pressure chamber.  
         [0032]    As shown in FIG. 2, in a preferred example of a sequence valve of the present invention, a stepped opening  28  of an appropriate diameter is formed in the piston  8  of the hydraulic cylinder  9 , and a supply pipe  29  fixed to the jack bed (not shown) is inserted in the stepped opening in order to supply hydraulic fluid. The low pressure chamber  15  is formed between ends of the stepped opening  28  and the supply pipe  29 , and a hydraulic fluid channel from the low pressure chamber  15  to the high pressure chamber  16  is formed by a gap between an inner circumferential surface of the stepped opening  28  and an outer circumferential surface of the supply pipe  29 .  
         [0033]    Switching between the low pressure chamber  15  and the high pressure chamber  16  is performed by a step portion  28   b  and the annular packing  30  or gasket fitted to an outer circumference of the supply pipe  29  at the position of an expanded portion  28   a  of the stepped opening  28 . As shown in FIG. 3(A), the annular packing  30  includes a central opening  30   a  capable of being slidingly fitted to an outer circumference of the supply pipe  29 . An outer diameter D of the annular packing  30  is smaller than an inner diameter of the expanded portion  28   a  of the stepped opening  28  and a passage for hydraulic fluid is formed between an outer circumferential surface of the annular packing  30  and an inner circumferential surface of the expanded portion  28   a  of the stepped opening  28 . A circumferential groove  8   a  is formed at an end of the expanded portion  28   a  of the stepped opening  28  formed in the piston  8 , and the annular packing  30  is pressed by means of a compression spring  31  inserted between an annular presser bar  32  fixed thereat to the step portion  28   b  formed at a boundary of the expanded portion  28   a  of the stepped opening  28  to seal the hydraulic fluid channel. Moreover, as shown in FIG. 3(B), a diameter of a central opening  32   a  formed in the annular presser bar  32  is smaller than an inner diameter of the compression spring  31  and larger than an outer diameter of the supply pipe  29 . Accordingly, the presser bar supports the compression spring  31  and forms a hydraulic fluid channel from the low pressure chamber  15  to the high pressure chamber  16  between the central opening  32   a  thereof and an outer circumferential surface of the supply pipe  29 .  
         [0034]    Hydraulic fluid pumped by the pump cylinder  10  by operating the handle  13  travels through the supply pipe  29  fixed to the garage jack bed and is delivered to the low pressure chamber  15 . The pressure in the low pressure chamber is low in a condition where there is substantially no-load on the piston  8  of the hydraulic cylinder  9 , and the hydraulic fluid channel connecting the low pressure chamber  15  and the high pressure chamber  16  is sealed by the force of the spring  31  pressing the packing  30  against the step portion(s)  28   b  of the stepped opening, and the hydraulic fluid moves the piston  8  at a high speed and low output.  
         [0035]    When the support plate contacts the jack point and a load is applied to the piston  8  of the hydraulic cylinder  9 , the pressure in the low pressure chamber  15  increases, and the packing  30  retreats when a force acting on the packing  30  due to this pressure exceeds a force of the compression spring  31  pressing the packing  30  against the step portion  28   b . The hydraulic fluid passes around an outer circumference of the supply pipe  29 , between the step portion  28   b  and the packing  30 , between an outer circumferential surface of the packing and an inner circumferential surface of expanded portion  28   a  and between the central opening  32   a  of the presser plate  32  and an outer circumferential surface of the pipe, and is fed into the high pressure chamber  16  and the piston  8  moves at a low speed and a high output.  
         [0036]    Moreover, a force F of the compression spring  31  is selected to be greater than a force F 1  which acts on the packing  30  due to a pressure P 1  in the low pressure chamber  15  in the condition where substantially no-load acts on the arm. Namely, when F 1 &lt;F, the hydraulic fluid channel is sealed by the packing  30  and since hydraulic fluid from the pump cylinder  10  is fed to the small volume low pressure chamber  15  only, the piston  8  may be moved at a high speed and a low output. In a condition where there is a load on the piston  8 , the pressure P 1  of the hydraulic fluid in the low pressure chamber  15  increases. The force Fl due to this pressure P 1  increases and F 1 &gt;F, and the packing is forced to retreat back and hydraulic fluid is pumped to the high pressure chamber  16 .  
         [0037]    When a pressure P 2  in the high pressure chamber  16  roughly equals the pressure P 1  in the low pressure chamber  15 , a resultant force F 2 +F of the force F of the compression spring  31  and a force F 2  acting on the packing  30  due to the pressure P 2  in the high pressure chamber  16  exceeds the force F 1  acting on the packing  30  due to the pressure P 1  in the low pressure chamber  15 , and the resultant force F 2 +F causes the packing  30  to seal the hydraulic fluid channel once again. Furthermore, when the pressure P 1  of the hydraulic fluid in the low pressure chamber  15  increases and F 1 &gt;F 2 +F, the packing  30  retreats and hydraulic fluid is delivered to the high pressure chamber  16 . The pressure P 2  of hydraulic fluid in the high pressure chamber  16  is sequentially increased by repeating this operation, and when a force acting on the piston due to the pressure P 2  in the high pressure chamber  16  becomes greater than the load, the piston moves at a slow speed and a high output and it is possible to lift the load, an automotive vehicle.  
         [0038]    In the garage jack according to the present invention in which the hydraulic cylinder includes a dual cylinder mechanism and the operating frequency is not increased when operating the handle to raise the support plate from its lowest position to the jack point in a no-load condition, the hydraulic fluid channel provided with the sequence valve is provided in connection with the low pressure chamber and high pressure chamber of the hydraulic cylinder, and when the pressure of hydraulic fluid is greater than a predetermined value of the sequence valve, the hydraulic fluid is fed from the low pressure chamber to the high pressure chamber. Thus, there is no concern that the garage jack will be damaged even if a large load occurs on the arm provided with the support plate while hydraulic fluid is being supplied to the low pressure chamber, and the working of a hydraulic circuit to the bed of the garage jack may be simplified.  
         [0039]    Many changes and modifications in the above embodiment of the invention can be carried out without departing from the scope thereof. Accordingly, the invention is intended to be limited only by the scope of the appended claims.