Abstract:
A pneumatically operated hydraulic pump includes a cylinder housing accommodating a main piston to subdivide the housing interior in two working chambers. The main piston is connected to a hydraulic piston for joint reciprocation so that the hydraulic piston can carry out a suction stroke when the main piston moves to one end position and a pressure stroke when the main piston moves to the other end position. Arranged laterally to the cylinder housing is a control mechanism for regulating a flow of working fluid alternately to the working chambers. The control mechanism includes a plastic valve casing for accommodating a control piston having opposite end faces of different size to define different effective areas and thereby realize reciprocation of the control piston by the working fluid. A slide shoe is guided in the valve casing for conjoint movement with the control piston. A displacement of the main piston into the two end positions actuates respective pilot valves which regulate the reciprocation of the control piston and the slide shoe to thereby move the main piston between the end positions which discharging working fluid via the deflection zone in the slide shoe to the atmosphere.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the priority of German Patent Application Serial No. 198 60 466.1, filed Dec. 28, 1998. 
     BACKGROUND OF THE INVENTION 
     The present invention relates, in general, to pneumatically operated hydraulic pumps. 
     German Pat. No. DE 26 26 954 C2 describes a pneumatically operated hydraulic pump which includes a cylinder housing for accommodating a main piston which reciprocates in response to admission of air under pressure and has attached thereto a hydraulic piston connected via a suction valve with a suction conduit and via a pressure valve with a pressure conduit. Thus, the hydraulic piston alternately executes, in response to the reciprocating motion of the main piston, a suction stroke by which hydraulic medium is aspirated, and a pump stroke by which the hydraulic medium is pumped under pressure. The reciprocating movement of the main piston is realized by a partially hollow piston-type slide valve and at least one pilot valve which is actuated by the main piston and effects a movement of the slide valve from one end position into the other end position. The slide valve has opposite end faces which are different in size to thereby provide different effective areas. The smaller end face is continuously acted upon by a working fluid under pressure, such as compressed air, while the greater end face is acted upon by working fluid via the pilot valve when the slide valve is moved in the other direction. Supply of working fluid into the working chambers on either side of the main piston and discharge of outgoing air is realized by providing a complicated, stepped sleeve in which the slide valve is guided and which has formed therein transverse bores and circumferential grooves and includes several sealing rings in spaced-apart disposition. Apart from the complexity of the sleeve, a further shortcoming of this conventional hydraulic pump is the substantial wear to which the sealing rings are subject during their continuous passage of the ports of the bores in the sleeve. In addition, the sleeve must be sealingly supported in the receiving bore of the hydraulic valve casing. 
     SUMMARY OF THE INVENTION 
     It is thus an object of the present invention to provide an improved pneumatically operated hydraulic pump, obviating the afore-stated drawbacks. 
     In particular, it is an object of the present invention to provide an improved pneumatically operated hydraulic pump which is simple in structure and can easily be manufactured on a large scale and as a modular system. 
     These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention by providing a cylinder housing of plastic having formed thereon a plastic valve bottom at one end and detachably connected thereto a plastic end cap at the other end thereof; a main piston subdividing the housing in two working chambers and movable between two end positions in response to admission of a working fluid, with the main piston having attached thereon a hydraulic piston, guidingly received in the end cap, for joint reciprocation with the main piston so that the hydraulic piston can carry out a suction stroke when the main piston moves to one end position, and a pressure stroke when the main piston moves to the other end position; a control mechanism for regulating a flow of working fluid alternately to the working chambers, with the control mechanism including a plastic valve casing which is mounted laterally to the valve bottom and has a chamber which contains working fluid under pressure, a control piston accommodated in the valve casing and having axial end faces which are different in size so as to define different effective areas and thereby permit reciprocation of the control piston by the working fluid, and a slide shoe guided in the chamber of the valve casing for conjoint movement with the control piston and having formed interiorly therein a deflection zone; and a valve arrangement which includes a first pilot valve disposed in a stepped bore of the valve bottom, and a second pilot valve disposed in a stepped bore of the end cap, and which is actuated by the main piston during displacement thereof into the two end positions, for regulating a flow of working fluid to the control mechanism to effect reciprocation of the control piston and the slide shoe so that the main piston moves between the end positions while working fluid is discharged via the deflection zone in the slide shoe to the atmosphere. 
     One aspect of the present invention is the fact that the cylinder housing with the integral valve bottom, the detachably secured end cap, the valve casing for the control piston and the slide shoe can all be made of plastic material, e.g. polyoxymethylene. Suitably, these components are manufactured as injection molded parts, thereby assuring a cost-efficient, large scale production of all sizes and types. Another aspect of the present invention is the operation of the slide shoe as a slide valve which can also be manufactured as an injection molded part of plastic material. Depending on its position in the valve casing, the slide shoe ensures a fluid communication of the working fluid into one or the other working chamber on both sides of the main piston and, as a consequence of the formed deflection zone, realizes a discharge of outgoing air from the working chambers into the atmosphere, suitably via a sound absorber. 
     The displacement of the slide shoe is implemented by a control piston which is accommodated in the valve casing and has opposite end faces of different sizes to thereby establish different effective areas. The smaller end face is always disposed in the chamber of the valve casing in which the slide shoe is also located and which is permanently acted upon by the working fluid. The control piston can be made from a light metal alloy and is sealingly guided in the valve casing. Unlike in conventional hydraulic pumps, the seals in accordance with the present invention do not move past ports and thus are not exposed to wear. The slide shoe is at all times constrained to move in the chamber but slides along the outer sidewall of the valve bottom. As the valve casing is flange-mounted to the side of the valve bottom, the operational position of the slide shoe is ensured. The slide shoe passes ports of a total of three channels which are positioned in sequence and extend transverse to the travel direction of the main piston. Both outer channels are directly connected to the working chambers of the cylinder housing, whereas the central channel communicates with the atmosphere, suitably via a sound absorber. 
     According to another feature of the present invention, the control piston has an elongate piston section which terminates in the smaller end face of the control piston and projects into the chamber of the valve casing, with the piston section having a recess which complements the length of the slide shoe and envelopes the slide shoe, thereby enhancing an interaction of the control piston with the slide shoe in a force-fitting and form-fitting manner. Suitably, the recess is made by suitably grooving the control piston. 
     According to another feature of the present invention, the chamber is in permanent fluid communication with the stepped bore, receiving the first pilot valve, via a branch duct. This ensures that in each position of the main piston the working fluid acts upon either the greater end face of the control piston via the first pilot valve as well as upon the channels in the valve bottom and in the valve casing, or the valve stem of the first pilot valve is pushed into the working chamber between the main piston and the valve bottom. 
     According to another feature of the present invention, the stepped bore in the valve bottom is connected to a space in the valve casing adjacent the greater end face of the control piston via channels in the valve bottom and in the valve casing and connected with the stepped bore, receiving the second pilot valve, in the end cap via channels in the wall of the cylinder housing and in the end cap. The greater end face is always located in a space of the valve casing, separated and sealed from the chamber. This space is acted upon by working fluid via the first pilot valve, which is disposed in the valve bottom, and relieved to the ambient atmosphere via the second pilot valve, disposed in the end cap. As the control piston and the slide shoe are not fixedly connected to one another, manufacture and assembly are further simplified. 
     In order to assure a discharge of air from the space, the stepped bore with the second pilot valve and the channels between the first pilot valve, space and second pilot valve, the stepped bore in the end cap is connected to the atmosphere via a transverse channel. 
     In a pneumatically operated hydraulic pump of the double acting type in which the main piston is connected to a second hydraulic piston in coaxial alignment with the first hydraulic piston, the incorporation of the second hydraulic piston can easily be carried out by simply providing a respective guide bore in the valve bottom. Other modifications are not necessary. 
     According to another concept of the present invention, the main piston may be interconnected with a bar linkage which transverses the valve bottom and is movable relative thereto and allows a manual displacement of the main piston in opposition to a force applied by a spring positioned between the main piston and the end cap. Thus, it is only necessary to incorporate the spring in the cylinder housing and to plug the connection between the chamber and the working chamber adjacent the end cap. Further modifications are not necessary. Thus, a hydraulic pump according to the present invention can be operated selectively with air or by hand. 
     Suitably, a hand lever is connected to the bar linkage and lockable in place during pneumatic operation of the hydraulic pump so that uncontrolled movements by the hand lever that may result in injury are prevented. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The above and other objects, features and advantages of the present invention will be more readily apparent upon reading the following description of preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which: 
     FIG. 1 is a schematic vertical longitudinal section of a single acting hydraulic pump according to the present invention in one end position; 
     FIG. 2 is a schematic side view of the hydraulic pump in the direction of arrow II in FIG. 1; 
     FIG. 3 is a horizontal cutaway view of the hydraulic pump, taken along the line III—III and showing in detail a control valve mechanism in one control position; 
     FIG. 4 is a sectional view of the control valve mechanism, taken along the line IV—IV in FIG. 3; 
     FIG. 5 is a schematic vertical longitudinal section of the single acting hydraulic pump of FIG. 1 in an intermediate position; 
     FIG. 6 is a sectional view of the control valve mechanism of FIG. 3 in another control position; 
     FIG. 7 is a sectional view of the control valve mechanism, taken along the line VII—VII in FIG. 6; 
     FIG. 8 is a schematic vertical longitudinal section of a double acting hydraulic pump according to the present invention in one end position; 
     FIG. 9 is a schematic vertical longitudinal section of another embodiment of a single acting hydraulic pump according to the present invention in one operational position; and 
     FIG. 10 is a schematic vertical longitudinal section of the hydraulic pump of FIG. 9 in another operational position. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. 
     Turning now to the drawing, and in particular to FIG. 1, there is shown a schematic vertical longitudinal section of a single acting pneumatically operated hydraulic pump according to the present invention, generally designated by reference numeral  1 . The hydraulic pump  1  includes a cylinder housing  2  which is made of plastic material, e.g. polyoxymethylene, and is formed in one piece with a valve bottom  3 . Accommodated in the cylinder housing  2  is a main piston  6  which subdivides the housing  2  in two working chambers  34 ,  36  and has a circumferential groove  8  for receiving a sealing ring  9  which sealingly rests against an inside wall surface  10  of the housing  2 . The main piston  6  reciprocates in the housing  2  between two end positions in response to admission of a working fluid, e.g. air under pressure, and actuates a pilot valve  4 , when moving to the end position shown in FIG. 1, and actuates a pilot valve  5 , when moving to the other end position. Each of the pilot valves  4  and  5  includes a head portion  15  and a valve stem  14  which extends from the head portion  15  and includes a central portion with a sealing ring  16  secured thereto. A further sealing ring  17  is confined between the valve stem  14  and the head portion  15 . 
     The valve stem  14  and the head portion  15  of the pilot valve  4  are mounted in a stepped bore  12  which is formed in the valve bottom  3  and defines two bore sections  37 ,  38 . The pilot valve  4  is loaded in the direction of the main piston  6  by a helical compression spring  18  which is disposed in a spring compartment  20  of the stepped bore  12  and rests with one end against the head portion  15  and with the other end against a confronting surface of a screw bolt  19  which can be screwed into the spring compartment  20 . In like manner, the valve stem  14  and the head portion  15  of the pilot valve  5  are mounted in a stepped bore  13 , which defines also two bore sections  37 ,  38  and is formed in an end cap  11  detachably mounted to the valve bottom distal end of the cylinder housing  2  and made of plastic material, e.g. polyoxymethylene. The pilot valve  5  is loaded by another helical compression spring  18  in the direction of the main piston  6 , whereby the compression spring  18  is disposed in a spring compartment  20  and rests with one end against the head portion  15  and with the other end against a confronting surface of another screw bolt  19  which is rotated into the spring compartment  20 . 
     The main piston  6  is connected in force fit engagement with a hydraulic pumping piston  7  which is received for sliding in the end cap  11  and projects outwardly for interaction with a valve arrangement, generally designated by reference numeral  65 , and including a suction valve  64  and a pressure valve  67 . The hydraulic piston  7  is slidingly received in a T-shaped conduit  63  of a high-pressure valve casing  65 ′ and draws hydraulic fluid from a suction conduit  66  via the suction valve  64  and pumps hydraulic fluid via the pressure valve  67  through a pressure conduit  68 , in response to the reciprocating motion of the main piston  6 . Persons skilled in the art will appreciate that structure and operation of suction and pressure valves are generally known and thus are not described in detail here for the sake of simplicity. 
     The valve bottom  3  is formed with three transverse channels  21 ,  22 ,  23  which are arranged in succession behind one another and terminate at an outer sidewall  24  of the valve bottom  3 , as best seen in particular in FIG.  3 . As shown in FIG. 2, a control valve assembly, generally designated by reference numeral  25  and including a valve casing  25 ′ made of plastic material, such as polyoxymethylene, is flange-mounted laterally to the outer sidewall  24  of the valve bottom  3 . The central transverse channel  22  is fluidly connected via a channel  28  to a connection port  27  which extends inwardly from an end face  26  of the valve bottom  3 . Optionally, a sound absorber may be attached to the port  27 . The transverse channel  23  adjoins the pilot valve  4  and is fluidly connected via a channel  72 , formed in the valve bottom  3 , via a longitudinal channel  30 , formed in a wall  29  of the cylinder housing  2 , and via channels  31 ,  33 , formed in the end cap  11 , to the working chamber  34  adjacent the end cap  11 . The transverse channel  21  is fluidly connected via a channel  35  with the working chamber  36  adjacent the valve bottom  3 . 
     Referring again to FIG. 1, it can be seen that the bore section  37  of the stepped bore  12  in the valve bottom  3  guides the valve stem  14  of the pilot valve  4  and communicates via channels  39 ,  40 , formed in the valve bottom  3 , via channel  41 , formed in the wall  29  of the cylinder housing  2 , and via channel  42 , formed in the end cap  11 , with the spring compartment  20  of the stepped bore  13  in the end cap  11 . The channel  39  is further fluidly connected via a channel  43 , formed in the valve bottom  3 , and via a channel  44 , formed in the valve casing  25 ′, with a space  45  (FIG. 3) in the valve casing  25 ′. The control valve assembly  25  includes a control piston  48  which is accommodated in the valve casing  25 ′ for reciprocation between two control positions in response to admitted working fluid and includes an end portion  47  which is received in the space  45 . A sealing ring  46  is secured to the end portion  47  of the control piston  48  to seal the end portion  47  against the valve casing  25 ′. The bore section  38  of the stepped bore  13 , located between the bore section  37  and the spring compartment  20  is connected with the ambient atmosphere A via a transverse channel  48  formed in the end cap  11 . 
     Turning again to FIG. 3, it can be seen that the control piston  48  is sealingly guided in the valve casing  25 ′ in the space  45  via the sealing ring  46 , on the one hand, and in a bore  50  of the valve casing  25 ′ via a sealing ring  51  which is embedded in a circumferential groove  52  of the control piston  48 . At its end distant to the sealing ring  46 , the control piston  48  is provided with an elongate piston section  54  which projects into a chamber  55  of the valve casing  25 ′ and is formed with a recess  53 . The chamber  55  is in continuous communication via a port  56  with a source of working fluid AL, such as air under pressure, and, as indicated, e.g. in FIGS. 1 and 4, is in fluid communication with the spring compartment  20  of the stepped bore  12  in the valve bottom  3  via a branch duct  62 . The piston section  54  terminates in an end face  57  which exhibits an effective area  58  that is smaller than an effective area  59  at the end of the piston section  47  of the control piston  48  in the space  45 . 
     Received in the recess  53  of the piston section  54  of the control piston  48  is a slide shoe  60  which has a rectangular configuration and is made of plastic material, e.g. polyoxymethylene, with the slide shoe  60  having a length that corresponds to the length of the recess  53 . The slide shoe  60  is formed interiorly with a deflection zone  61  and is capable of sliding along the outer sidewall  24  of the valve bottom  3 , thereby regulating a flow of working fluid through the transverse channels  21 ,  22 ,  23 . 
     The hydraulic pump  1  operates as follows: The chamber  55  is continuously under pressure by working fluid AL, e.g. compressed air, admitted via the port  56 , thereby urging the control piston  48  to seek the control position shown in FIG.  3 . As a consequence of the form-fitting and force-fitting engagement of the control piston  48  with the slide shoe  60  via the recess  53 , the slide shoe  60  conjointly moves with the control piston  48  into this control position which is reached when the slide shoe  60  bears against a confronting end surface  69  of the chamber  55 . In this control position, the slide shoe  60  is moved to the left, and, as shown in particular in FIG. 4, connects the transverse channels  21 ,  22 , so that working fluid AL can flow from the chamber  55  via the channels  23 ,  30 ,  31 ,  32 ,  33  into the working chamber  34  adjacent the end cap  11 , whereas the working chamber  36 , adjacent the valve bottom  3  is relieved through the connection of transverse channels  21 ,  22  by the slide shoe  60  as the working chamber  36  is connected by the deflection zone  61  of the slide shoe  60  via the channels  35  and  28  to the atmosphere. The main piston  6  thus travels in the direction toward the valve bottom  3 . Simultaneous with this displacement of the main piston  6 , working fluid AL in the chamber  55  flows also via the branch duct  62  into the spring compartment  20  of the pilot valve  4  to thereby force the valve stem  14  into the working chamber  36  into a position, shown in FIG.  5 . 
     Shortly before reaching the upper end position, shown in FIG. 1, the main piston  6  actuates the valve stem  14  of the pilot valve  4  and displaces the valve stem  14  in opposition to the spring force of the compression spring  18  until the sealing ring  17  is lifted from its seat in the stepped bore  12 . This allows working fluid AL to flow via the bore section  38  of the stepped bore  12  into the channel  39  and ultimately via the channel  43  in the valve bottom  3  and the channel  44  in the valve casing  25 ′ into the space  45  to act on the greater effective area  59  at the end of the piston section  47  of the control piston  48 . At the same time, working fluid AL can also flow via the channels  40 ,  41 ,  42  into the spring compartment  20  of the pilot valve  5  so that the valve stem  14  of the pilot valve  5  is urged into the working chamber  34 . This situation is illustrated in FIG.  1 . The displacement of the main piston  6  into the upper end position is followed by the hydraulic piston  7  which thus executes a suction stroke by which hydraulic fluid is drawn from the suction conduit  66  through the suction valve  64 . 
     As the effective area  59  at the end of the piston section  47  of the control piston  48  is greater than the effective area  58  at the opposite end of the control piston  48  in the chamber  55 , the control piston  48  is moved conjointly in the direction of the port  56  for the working fluid AL until a ring surface  70  of the control piston bears against a ring surface  71  of the valve casing  25 ′, as shown in FIG.  6 . The movement of the control piston  48  is accompanied by a displacement of the slide shoe  60  which thus clears the transverse channel  21  and fluidly connects the transverse channels  22 ,  23  (cf. FIG.  7 ). As a result, the connection between the port  56  and the working chamber  34  adjacent the end cap  11  is cut, and the working chamber  34  is now relieved through communication via the channels  31 ,  32 ,  33  in the end cap  11 , via the channel  30  in the wall  29  of the cylinder housing  2 , and via the channels  72 ,  23  in the valve bottom  3  with the deflection zone  61  in the slide shoe  60  and ultimately via the channels  22 ,  28  in the valve bottom  3  with the ambient atmosphere A. 
     The working fluid AL now flows via the channels  21 ,  35  in the valve bottom  3  into the working chamber  36  and displaces the main piston  6  in the direction toward the end cap  11 . Thus the valve stem  14  of the pilot valve  4  is released from the main piston  6  so that the compression spring  18  moves the valve stem  14  to project into the working chamber  34 , thereby forcing the sealing ring  17  into its seat in the stepped bore  12 . As a result, the communication between the branch duct  62  and the channel  39 , which connects to the bore section  38  of the stepped bore  12  in the valve bottom  3 , is cut, thereby entrapping compressed air in the channels  39 ,  40 ,  41 ,  42 ,  43 , in space  45  and in spring compartment  20  of the pilot valve  5 . This situation is shown in FIG.  5 . 
     Shortly before reaching the lower end position, the main piston  6  actuates the valve stem  14  of the pilot valve  5  and displaces the valve stem  14  in opposition to the spring force of the compression spring  18  until the sealing ring  17  is lifted from its seat in the stepped bore  13 . This allows a relief of the entrapped compressed air via the spring compartment  20  of the pilot valve  5  and via the bore section  38  and a transverse channel  49  into the atmosphere A. Thus, the space  45  of the control casing  25 ′ is relieved, so that working fluid AL in the chamber  55  displaces the control piston  48  and the slide shoe  60  to the left in FIG. 6 in the direction to the space  45  to commence another cycle. 
     The displacement of the main piston  6  into the lower end position is followed by the hydraulic piston  7  which now executes a pump stroke by which hydraulic fluid is forced through the pressure valve  67  into the pressure conduit  68  for use in a hydraulic fluid operated system. The oscillating movement of the main piston  6  and thus of the hydraulic piston  7  results in a substantially pulsation-free flow of hydraulic fluid in the pressure conduit  68 . 
     Turning now to FIG. 8, there is shown a schematic vertical longitudinal section of a double acting hydraulic pump according to the present invention, generally designated by reference numeral  1   a . Parts corresponding with those in FIG. 1 are denoted by identical reference numerals and not explained again. For the sake of simplicity, the hydraulic pump  1   a  will be described hereinafter only in connection with those components that are different from the embodiment of FIG.  1 . 
     The hydraulic pump  1   a  differs from the hydraulic pump  1  only in the provision of a further hydraulic piston  7   a  to realize a double action. The hydraulic piston  7   a  is securely fixed to the main piston  6  in coaxial alignment to the hydraulic piston  7  and so extends through the valve bottom  3  as to be able to slide therein. Interacting with the hydraulic piston  7   a  is a further valve arrangement, generally designated by reference numeral  65   a  and including a suction valve  64   a  and a pressure valve  67   a . The hydraulic piston  7  is slidingly received in a T-shaped duct  63   a  of a high-pressure valve casing  65 ′ a  and draws hydraulic fluid from a suction conduit  66   a  and the suction valve  64   a  and pumps hydraulic fluid via the pressure valve  67   a  through a pressure conduit  68   a , in response to the reciprocating motion of the main piston  6 . 
     Referring now to FIG. 9, there is shown a schematic vertical longitudinal section of a variation of the single acting hydraulic pump  1 , which is further equipped with a manually operated actuating mechanism. The actuating mechanism includes a bar linkage  73  which extends through the valve bottom  3  and is moveable relative thereto. The linkage  73  has one end bearing against a confronting surface of the main piston  6  and another end which is secured to a handle  75 . Disposed between the linkage distal surface of the main piston  6  and the end cap  11  is a helical compression spring  74 . A rotation of the handle  75  by hand about a longitudinal axis  76 , defined by the hydraulic pump  1 , by 180° results in a reciprocating movement of the linkage  73  commensurate with the stroke of the main piston  6  in the cylinder housing  2 , so that the hydraulic piston  7  can carry out a suction stroke via suction valve  64  and a pump stroke via pressure valve  67 . Channel  23  between the chamber  55  in the valve casing  25   a  and channels  30 ,  31 ,  32 ,  33  between the end cap  11  and the working chamber  34  are thereby closed off by a plug  77 . Both actuating positions of the handle  75  and the resultant end positions of the main piston  6  are shown in FIGS. 9 and 10, respectively. 
     The hydraulic pump of FIGS. 9 and 10 can also be operated pneumatically, in which case the handle  75  is locked in the position shown in FIG. 10, and thus is prevented from causing any injuries as a result of uncontrolled movement during pneumatic operation. Channels  30 ,  31 ,  32 ,  33  are permanently closed by the plug  77 , with the suction stroke being realized by the compression spring  74 . Relief of the working chamber  34  is realized via a channel  78  which has disposed therein in press-fit a filter  79  to prevent contamination of the working chamber  34 . 
     While the invention has been illustrated and described as embodied in a pneumatically operated hydraulic pump, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.