Patent Publication Number: US-2004045429-A1

Title: Pneumatic motor assembly for a lubricant pump

Description:
[0001] The present invention relates to a pneumatic motor assembly for a lubricant pump, which is used particularly in the field of maintenance and repair of vehicles such as cars, vans, trucks, tractors, et cetera.  
       [0002] The background art is constituted by a pneumatic motor assembly, for lubricant pumps, comprising a body that forms a cavity supplied with compressed air. A first hole and a second hole are formed axially in the side wall of the cavity. The holes slidingly accommodate a stem. The stem supports, at one end, a piston that moves in a cylinder that is associated with the body and cooperates, at the other end, with the riser of the pump An exchanger means is accommodated inside the cavity and is provided with an axial through hole, which slidingly accommodates a narrow intermediate portion of the stem. The exchanger means cooperates frontally with a means for diverting the air, which is associated with a front opening of the cavity and is laterally associated with an elastic means. In particular, the cooperation between the exchanger means and the elastic means is provided by two levers, which are pivoted between the side walls of the body and the front faces of two bushes slidingly inserted in holes provided laterally in the body. The elastic means acts on the rear faces of the bushes and is constituted by two spiral springs. The springs are accommodated in two caps, which are screwed by virtue of one end to the holes formed laterally in the body.  
       [0003] The operation of such motor assembly is as follows. Assume, for example, that the piston is performing its forward stroke inside the cylinder. Initially, the exchanger means is in a retracted position. The air is introduced in the cylinder so as to move the piston through a hole provided to the rear in the cavity, the diverting means and a passage that runs within the body and leads to the bottom of the cylinder. Correspondingly, the air contained in the chamber, whose volume is gradually reduced by the piston, is discharged externally through the diverting means. The exchanger means moved by the stem reaches the inversion position from the retracted position, and from that position it is moved to the forward position by the intervention of the elastic means. In this transfer, the exchanger means acts on the diverting means so as to block the intake and outlet, preparing them for the return stroke of the piston. In this case, the air is introduced through the usual hole, the diverting means and the pipe for connection to the top of the cylinder. Correspondingly, the air contained in the chamber, whose volume is gradually reduced by the piston, is discharged externally through the passage and the diverting means. The exchanger means, entrained by the stem, again reaches the inversion position from the forward position. From the inversion position it is moved to the retracted position by the intervention of the elastic means. During this transfer, the exchanger means acts on the diverting means so as to block the intake and the outlet, preparing them for the new forward stroke of the piston, and so forth. The reciprocating movement of the stem aspirates the lubricant, which by rising up the riser becomes available for dosage.  
       [0004] The main drawback of the above described motor assembly is its performance, which is highly impaired by the fact that the stroke available inside the cylinder is not utilized completely by the piston. In fact, during the return stroke, the piston stops before it reaches the bottom of the cylinder. This is due to the fact that the narrow portion of the stem is necessarily longer than the exchanger means. Therefore, during the forward stroke of the piston, the narrow portion of the stem protrudes partially with respect to the bottom of the cylinder. Accordingly, it is necessary to prevent the variation in diameter that occurs between the narrow portion and the rest of the stem that lies outside the bottom from interfering with the annular gasket arranged so as to wrap around the stem on a guiding and sealing bush associated with the first hole of the cavity that is directed toward the cylinder. For this reason, a bush of considerable height is currently used and in turn prevents the piston from reaching the bottom at the end of its return stroke. Furthermore, within the scope of this main drawback it is noted that this actuation of the cooperation between the exchanger means and the elastic means is particularly complicated and therefore expensive. Moreover, the lateral protrusions formed by the caps worsen the overall aesthetic appearance of the assembly.  
       [0005] A second drawback of conventional devices is that they comprise a means, for guiding and sealing the stem toward the riser, constituted by a guiding bush, an annular gasket and a closure flange, packed and inserted in a compartment formed axially in the body, just below the cavity, and retained by an elastic end ring engaged in the compartment. Accordingly, the lubricant delivery hole is provided just below the compartment. This entails that the axial dimension of the body is particularly large. Since the body is normally made of aluminum, a material that is notoriously valuable and therefore expensive, the purchase costs of the raw material are rather onerous and have a considerable effect on selling prices of the end products.  
       [0006] Furthermore, the number of machine-tool treatments required to obtain the finished assembly is particularly large, thus increasing production costs. The body of the assembly is in fact obtained from a solid cylindrical block, which is initially provided with an axial bore having different diameters and so forth, accordingly also entailing considerable machining waste.  
       [0007] The aim of the present invention is to overcome the drawbacks noted in the prior art, by providing an improved pneumatic motor assembly for a lubricant pump that in particular improves appreciably the operating efficiency and reduces its manufacturing costs in relation to the material used and to the number of machining treatments required, so as to contain the final cost.  
       [0008] Within this aim, an object of the invention is to provide a motor assembly that is highly compact.  
       [0009] This aim, this object and others that will become better apparent hereinafter are achieved by a pneumatic motor assembly for a lubricant pump as claimed in the accompanying claims. 
     
    
    
     [0010] Further characteristics and advantages of the invention will become better apparent from the description of a preferred embodiment thereof, illustrated only by way of non-limitative example in the accompanying drawings, wherein:  
     [0011]FIG. 1 is a perspective view of a lubricant pump provided with the assembly according to the invention;  
     [0012]FIG. 2 is a partially sectional exploded view of the assembly;  
     [0013]FIG. 3 is a sectional view, taken along the line III-III of FIG. 2, of a detail of the assembly;  
     [0014]FIG. 4 is a sectional view, taken along the line IV-IV of FIG. 2, of another detail of the assembly;  
     [0015]FIG. 5 is a sectional view of the assembly, taken along a meridian plane that passes through its longitudinal axis;  
     [0016]FIG. 6 is a detail sectional view of the assembly, taken along a meridian plane that passes through its longitudinal axis;  
     [0017]FIG. 7 is a detail sectional view, taken along the line VII-VII of FIG. 6, of the assembly in the unassembled condition;  
     [0018]FIG. 8 is a detail sectional view, taken along the line VII-VII of FIG. 6, of the assembly in the assembled condition. 
    
    
     [0019] With reference to the accompanying figures, and initially to FIG. 1, the pump, generally designated by the reference numeral  6 , is applied vertically to a drum  7  containing liquid or semisolid lubricant.  
     [0020] The pump  6  is substantially axially elongated and includes, in the following order, a pneumatic cylinder  8 , a motor assembly  9 , and a riser  10 .  
     [0021] The riser is rigidly associated with the lid  11  of the drum  7 .  
     [0022] The pump  6  receives compressed air through a hose  12  and dispenses the lubricant through a hose  13 , which has, at its free end, a dosage gun  14  that can be operated manually.  
     [0023] The motor assembly  9  includes a body  15  that is predominantly axially elongated.  
     [0024] The body  15  forms a cylindrical cavity  16 , which lies approximately at right angles to the length of the body  15 . The cavity  16  is fed with compressed air through a hole provided at the rear (not shown) for connection to the hose  12 .  
     [0025] A first hole  18  and a second hole  19  are provided on the side wall  17  of the cavity  16 , along the main axis of the body  15 .  
     [0026] A stem, generally designated by the reference numeral  20 , slides within the holes and supports, at one end, a piston  21 , which moves inside the cylinder  8  and cooperates with the riser  10  at the other end.  
     [0027] The stem  20  is formed in two portions  22  and  23 , which are mutually joined by virtue of a screw coupling.  
     [0028] An exchanger means  24  is accommodated inside the cavity  16  and is provided with an axial through hole  25 , which slidingly accommodates a narrow intermediate portion  26  of the stem  20 .  
     [0029] The narrow intermediate portion  26  is formed in the end part of the portion  22  that lies opposite to the one provided with the piston  21 .  
     [0030] At the end of the narrow intermediate portion  26  there is a short threaded part  27 , which is engaged in a corresponding complementarily threaded hole  28  formed at the end of the portion  23 , so as to form the screw coupling.  
     [0031] An elastic means, generally designated by the reference numeral  29 , cooperates laterally with the exchanger means  24  by virtue of levers  30  engaged in slots  31  formed on the side wall of the exchanger means  24 .  
     [0032] A diverting means D introduces air from the cavity  16  first into one chamber of the cylinder  8  and then into the other chamber, the chambers being formed by the piston  21 , and evacuates externally the air contained alternately in each one of the chambers, whose volume is gradually reduced by the piston  21 .  
     [0033] The diverting means D is associated with a front opening of the cavity  16  and interacts with the exchanger means  24  by virtue of a flat region  32  formed at the front on the exchanger means.  
     [0034] The particularity of the motor assembly  9  is that the axial through hole  25  comprises a wider end portion  33 , which is directed toward the end of the stem  20  that supports the piston  21  so as to accommodate a non-narrow part of the stem  20  during the return stroke of the piston  21 , thus delaying the exchange.  
     [0035] In this manner, the stroke of the piston shifts toward the return to an extent that is equal to the depth of the wider portion  33 .  
     [0036] As shown in particular in FIG. 5, by virtue of the wider portion  33  the stem  20  in fact penetrates more deeply into the exchanger means  24 .  
     [0037] Again with reference to FIG. 5, the non-narrow part, designated by the reference numeral  34 , is located directly behind the narrow portion  26  in the direction of the return stroke of the piston  21 . Accordingly, the length of the non-narrow part  34  is equal to the depth of the wider end portion  33 .  
     [0038] The limit of the return stroke of the piston  21  is determined by the locator  35 , which is formed between the wider end portion  33  and the axial through hole  25 , which constitutes an abutment with respect to the corresponding locator  36  formed on the stem  20  so as to straddle the narrow intermediate portion  26  and the non-narrow part  34 .  
     [0039] The above feature allows to use a guiding and sealing bush  37  associated with the first hole  18  which has a limited height, so as to not interfere with the return stroke of the piston  21 .  
     [0040] Furthermore, such feature allows to avoid the problem of the escape of the locator  36  from the gasket  38  provided on the guiding and sealing bush  37 , although the bush has a limited height. The locator  36  in fact always lies behind the conventional assemblies during the forward stroke of the piston  21 , and for this reason it does not interfere with the gasket  38 . The base of the guiding and sealing bush  37  acts as an abutment for the exchanger means  24  in the advanced position.  
     [0041] For a good operation of the assembly  9 , it is also necessary to provide a slight elongation of the exchanger means  24  on the part directed toward the riser  10 . This ensures a sufficient resting surface between the exchanger means  24  and the stem  20  during mutual sliding. Accordingly, the narrow intermediate portion  26  is also extended by the same length, so as to restore the proportions between the axial dimensions of the components that interact.  
     [0042] With the exchanger body  24  and the stem  20  thus modified, the other locator  39  formed on the stem  20  would interfere with the guiding and sealing means used on the side of the riser  10  in conventional devices. Therefore, it would be necessary to further lengthen the body, but this would entail obvious new increases in the costs of raw material.  
     [0043] In order to obviate all this, the assembly  9  includes a guiding and sealing cartridge  40 , which is engaged in the second hole  19 , protrudes along the stem  20  outside the body  15 , and is directed toward the riser  10 .  
     [0044] The cartridge  40  is formed by a first tubular segment  41 , which is provided externally with a threaded end part  42 , which is engaged in the corresponding second complementarily threaded hole  19 , and is provided internally with a likewise threaded intermediate part  43 . The head of the first segment  41  acts as an abutment for the exchanger means  24  in the retracted position.  
     [0045] A second shorter tubular segment  44  is arranged coaxially inside the first tubular segment  41  and is externally provided with a threaded end part  45 , which engages the corresponding threaded intermediate part  43  of the first tubular segment  41 .  
     [0046] Internally, the second tubular segment  44  has, at the threaded end part  45 , a hexagonal seat  46 , which accommodates a handling tool (not shown) for screwing and, at the opposite end, has an annular gasket  47 , which is adapted to form a seal on the portion  23  of the stem  20  against air seepage from the cavity  16  toward the riser  10 .  
     [0047] In order to avoid seepages of lubricant in the opposite direction, an annular gasket  48 , having an inverted U-shaped cross-section, is inserted in the first tubular segment  41  on the side of the riser  10 , just below the second tubular segment  44 .  
     [0048] Also, in order to avoid any wavering of the piston  21 , at the beginning of its forward stroke, it is possible to provide a secondary chamber  49  formed in the bottom of the cylinder  8 .  
     [0049] With particular reference to FIGS. 6, 7 and  8 , an elastic means, generally designated by the reference numeral  130 , cooperates laterally with the exchanger means  24  as a replacement of the conventional means shown in the other figures. A particularity of the elastic means  130  is that it is arranged between the exchanger means  24  and the side wall  17 . The elastic means  130  is constituted by two springs  131 , shown in FIG. 7.  
     [0050] Each spring  131  includes two legs  132 , two arms  133 , and a central concavity  134 , which in the active condition is directed into the cavity  16 .  
     [0051]FIG. 7 shows that, before assembly, the legs  132  are divaricated, whereas after assembly the legs  132  are substantially parallel.  
     [0052] Accordingly, before assembly, the legs  132  form an obtuse angle with the arms  133  and in the active condition they form a substantially right angle.  
     [0053] The legs  132  of each spring  131  are inserted in seats  135  and  136  formed respectively in the exchanger means  24  and in the body  15 .  
     [0054] More specifically, the seats  135  formed in the exchanger means  24  include two holes  137  in which elastic pins  138  are inserted.  
     [0055] The holes  137  are formed in the sides of the exchanger means  24  in the central area of the flat region  32 , symmetrically and at right angles to the longitudinal central axis of the exchanger means  24 .  
     [0056] The seats  136  formed in the body  15  include two holes  139 , in which elastic pins  140  are inserted.  
     [0057] The holes  139  are formed on the margin of the cavity  16 , in the central band of the body  15 , symmetrically and at right angles to the longitudinal central axis of the body  15 .  
     [0058] The holes  139  include a first portion  141  and a second portion  142 . The first portion  141  of the holes  139  has a larger diameter than the second portion  142 .  
     [0059] In this manner, during the drilling of the holes  139  straight grooves, equal in length to the first portions  141 , are formed on the side wall  17 , allowing to position the springs  131 .  
     [0060] The springs  131  are kept in position by pins  143 , inserted in the first portions  141  after the springs  131  have been arranged in the active position.  
     [0061] The pins  143  are in turn retained within the first portions  141  by the diverting means D, which closes the front opening of the cavity  16 .  
     [0062] The springs  131  are preferably made of a metal wire shaped so as to lie on a plane.  
     [0063] With reference to the accompanying figures, the general operation of the assembly  9  is per se known.  
     [0064] The operation of the elastic means  130  occurs as follows. Assume that the exchanger means  24  is in one of the two stroke limit positions. Moving from this position, the exchanger means  24  compresses the springs  131  until it reaches the position in which the diverting means D reverses the flow of the circulation of the air. From this position, the springs  131  are released, pushing the exchanger means  24  to the other stroke limit position, and so forth.  
     [0065] As described above, the improved pneumatic motor assembly achieves the intended aim and object, allowing an actual improvement in efficiency owing to the fact that the stroke available in the cylinder is utilized fully by the piston, both during the forward stroke and during the return stroke, and it allows to reduce manufacturing costs and accordingly the final price, and to improve its overall aesthetic appearance.  
     [0066] Furthermore, the guiding and sealing cartridge external to the body allows a considerable saving of material thereon which is approximately equal to 20%, because the portion of body related to the compartment for accommodating the means for guiding and sealing the stem on the riser side is no longer necessary, and because the lubricant dispensing hole is formed directly below the cavity instead of below the guiding and sealing means.  
     [0067] The same solution allows to use tubular segments instead of solid cylindrical segments in order to form the body. This feature allows to save on the purchase of raw material and allows a considerable reduction in the number of operations of the manufacturing cycle.  
     [0068] For example, it is noted that the first and second holes have the same diameter and are equally threaded.  
     [0069] Furthermore, according to the invention, it becomes possible to use a single body for a wide variety of pumps.  
     [0070] The solution adopted to provide the seats helps to reduce costs. Instead of providing very small holes in order to insert the legs of the springs, it is in fact more convenient to provide holes having a larger diameter and then insert therein elastic pins so as to bring the holes to the required diameter. The solution chosen for fitting the springs is also relevant, since it proves itself very easy. It is in fact sufficient to place the body at the end of its stroke, take each spring by compressing its legs until they are parallel, and then insert them in the already-provided seats.  
     [0071] In practical execution, the materials used, the shapes, the dimensions and the constructional details, may be different from the ones described herein but technically equivalent thereto without thereby abandoning the scope of the invention.