Abstract:
The invention relates to an automatic lubricating pump ( 1 ) for a machine having a hydraulically actuated striking tool ( 4 ), such as a hydraulic hammer for example. The lubricating pump ( 1 ) is designed such that it can be connected to a pressure line (P) of the hydraulic circuit ( 2 ). The lubricating pump ( 1 ) has a drive piston ( 8 ), designed such that it can be driven by the hydraulic circuit, and a feed piston, connected to the drive piston in a motion-transmitting manner, of a feed pump ( 9 ), by means of which lubricant is fed to a lubricating point. The service life of the lubricating pump can be prolonged compared with conventional pumps if the drive piston ( 8 ) is designed to be double-acting with two drive chambers ( 8   c,    8   d ) and a hydraulically operable changeover member ( 16 ) is provided which can be engaged in the hydraulic circuit and by means of which the drive chambers ( 8   c,    8   d ) can be alternately and automatically connected to the pressure line ( 8 ) during operation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage application under 35 USC 371 of, and claims priority to, the International Patent Application No. PCT/EP2007/004866, filed Jun. 1, 2007, which claims benefit of German Patent Application No. 10 2006 026 274.3, filed Jun. 2, 2006. The disclosures of the prior applications are considered part of (and are incorporated by reference in) the disclosure of this application. 
     TECHNICAL FIELD 
     The invention relates to an automatic lubricating pump which is designed for connection to a pressure line of a hydraulic circuit with a repeatedly increasing or a constant hydraulic pressure of a machine, such as a construction machine with a hydraulic hammer, with a drive piston shaped to be driven by the hydraulic circuit, and a feed piston, which is connected in a motion-transmitting manner to the drive piston and which borders a feed chamber which can be filled with lubricant and which is connected to at least one lubricant outlet of the automatic lubricating pump. 
     The invention also relates to a method for lubricating at least one lubricating point of machines having their own hydraulic circuit, such as construction machines, wherein a drive piston is moved by a repeatedly increasing or a constant hydraulic pressure in a pressure line of the hydraulic circuit, and the motion of the drive piston is transferred to a feed or delivery piston coupled to the drive piston, said feed piston conveying the lubricant in the direction of the at least one lubricating point. 
     BACKGROUND 
     From the state of the art a range of differently designed automatic lubricating pumps are known which are employed for the lubrication of tools on a construction machine, in particular for hydraulic striking tools such as hydraulic hammers, and are driven automatically, i.e. from the hydraulic circuit on the construction machine without their own power source. The hydraulic circuits for striking tools are characterised in that the hydraulic pressure repeatedly increases; this is achieved by interposing a periodically actuated changeover valve. The change between the rise in pressure and the drop in pressure produces the impact movement of the striking tool. The lubrication of striking tools of this nature, such as described for example in DE-A-34 43 542 or DE-A-198 03 449, is problematical, because, due to the high forces acting on the striking tool and the usually dusty environment, lubricants with a high proportion of solids and a high lubrication pressure must be used. 
     In DE-A-39 39 785 these problems with the lubrication are solved in that the feed pressure with which the lubricating grease is passed to a lubricating point is normally generated by the high operating pressure of the hydraulic circuit. If the hydraulic pressure is not applied in the operational breaks, the feed piston is moved into an initial position by a return spring. Due to the highly viscous lubricating grease, the returning force of the return spring is not sufficient for the feed piston to automatically draw in lubricating grease. Therefore, the lubricant reservoir has a compression spring in order to move the lubricating grease under pressure to the feed piston and to fill a feed chamber. With the application of the operating pressure the feed piston executes a single feed movement. With a longer operating period, to avoid the feed piston only operating once, a battery operated control device can be provided, which, starting in each case with the initial operation of the striking mechanism, opens a shut-off valve at successive times with a selectable time interval to apply the operating pressure a number of times to the feed piston and to correspondingly execute the feed movement many times. 
     DE-A-197 04 958 relates to a suction and pump unit which can automatically evacuate the air inclusions even with the use of lubricating grease with a high or very high solids content. To achieve this, the volume swept by a feed piston in operation is divided between a feed section which is connected to the lubricating point by a feed line closed by a non-return valve and a compression section into which a vent line opens. Due to their compressibility, air inclusions in the lubricant lead to the feed piston moving over the feed section without the non-return valve in the feed line opening. When the feed piston sweeps the compression section, the lubricant with the air inclusions is forced through the vent hole. As with the lubricating pump in DE-A-39 39 785, the feed piston in DE-A-197 04 958 also operates with a return spring. 
     The disadvantage of lubricating pumps as described in DE-A-39 39 785 and DE-A-197 04 958 is that the feed pistons execute one full feed stroke each time the operating pressure is applied. Therefore special measures must be taken to operate the feed piston a number of times during the continuous operation of the striking tool over a longer time period. One such measure is the control device of DE-A-39 39 785 described above. This is however a cost-intensive solution which is prone to faults. 
     A further measure of ensuring continuous lubrication during the complete operating period of the striking tool is described in DE-U-20 118 920. According to this solution, a progressive metering valve, which periodically extends and withdraws an actuating piston, is included in the bypass line of the hydraulic circuit. A flange shoulder of a freewheeling clutch attached to a shaft is pressed against the actuating piston under the force of a spring. The flange shoulder follows the movement of the actuating piston while the freewheeling clutch prevents reversal of the shaft when the actuating piston is withdrawn. In this way the shaft is moved gradually in a rotational direction and a cam located on the shaft is turned, driving a pump element. 
     According to the further development of DE-U-202 06 050, the progressive metering valve of DE-U-20 118 920 can be dispensed with if the flange shoulder is directly actuated by the striking mechanism via an actuating arm. 
     In EP-A-1 112 820 the freewheeling clutch is driven by a weight which moves with the vibrating motion of the striking tool. 
     In EP-A-1 626 225 a lubricant pump is shown for a vehicle or a constructional, agricultural or industrial machine. The lubricant pump switches automatically from a feed mode, in which the feed piston conveys lubricant to a lubricating point, into a filling mode when a lubricant receptacle is filled under pressure. For the changeover a changeover piston is used on the pressure-fluid side and one is also used on the lubricant side. 
     With the automatic lubrication device of EP-A-1 643 123 a hydraulic motor is used which drives a reciprocating pump via a cam. 
     Finally, reference is also made to DE-U-20 2004 008 752, according to which a differential piston arrangement can be used to convert the high hydraulic pressure into a feed pressure, suitable for lubrication. 
     It can be seen from the state of the art that it has only been possible to obtain an automatic, continuous feed of lubricant during the operation of the striking tool with a high level of constructional complexity. In addition, previous solutions have consumable parts, for example in the form of springs and freewheeling clutches, which can easily fail in continuous operation and limit the service life of the lubricant pump or require short servicing intervals. 
     SUMMARY 
     The object of the invention is therefore to improve automatic lubricating pumps for use in hydraulic striking tools such that continuous lubrication during the operation of the striking tool and at the same time a high service life for the lubricating pump can be ensured. 
     This object is resolved according to the invention for a lubricating pump of the type mentioned in the introduction in that the drive piston is designed to be double-acting with two drive chambers, and in that a changeover member is provided which can be engaged, connected or switched into the hydraulic circuit and can be actuated by the hydraulic pressure, by means of which the drive chambers can be alternately connected to the pressure line in operation. 
     For the method mentioned in the introduction this object is resolved according to the invention in that two drive chambers of the drive piston are connected alternately to the pressure line and the drive piston executes a to-and-fro movement. 
     Through this solution the wear compared to the above mentioned lubricating pumps is substantially reduced, because no mechanically susceptible components such as return springs or freewheeling clutches are used for the feed piston. The to-and-fro movement of the drive piston is basically ensured by its design as a double-acting piston and by the alternate application of pressure in the drive chambers of the drive piston by the changeover member. Compared to known mechanical solutions from the state of the art, the use of a hydraulic changeover member, which operates automatically and hydraulically, ensures a long service life due to the comparatively low wear. 
     The solution according to the invention can be further improved through further measures in each case, wherein the individual measures can be combined together as required. 
     Thus for example, in an advantageous embodiment as a changeover member a feeder or progressive metering valve with at least two outputs is used, which in each case are assigned to a drive chamber of the drive piston. Feeders or progressive metering valves are for example known from DE-C-34 16 041, EP-A-31 38 21, DE-A-29 17 863 and DE-B-24 37 473. 
     In a further embodiment the drive piston can be formed by a control piston of the progressive metering valve so that a more compact design is produced. The control piston used as the drive piston can be formed larger compared to the control piston in order to transfer larger changeover forces to the feed piston. 
     Furthermore, for the operation of the feeder or the progressive metering valve at least two connection lines, which can be alternately connected to the pressure line of the hydraulic circuit, can be routed to the drive chambers of the drive piston. If the feeder has other outputs, then they preferably open into a return line in the hydraulic circuit. Between the connection lines of the changeover member and the drive chambers preferably at least one hydraulically actuated changeover valve can be connected which in a first operating position connects the pressure line to one drive chamber and the return line to the other drive chamber and in a second operating position connects the pressure line to the other drive chamber and the return line to the first drive chamber. 
     In a further embodiment of the feeder several automatic changeover valves, capable of hydraulic actuation, can be provided. The changeover valves have control lines which in each case at one end open out into a connection to the pressure line and at the other end in drive chambers of a changeover valve. 
     The outlets of the progressive metering valve are routed outside of the changeover member and in the connected state open out for example into a connection on a preferably unpressurised or pressure-reduced return line in the hydraulic circuit. Depending on the operating position of a changeover valve, the pressure application on a control line leads to a change in the operating position of another changeover valve. The at least one changeover valve can be formed as a hydraulically actuated multiple way valve, in particular as a plunger valve with a control piston. Preferably, the feeder or the progressive metering valve provided as changeover member in the automatic lubricating pump has at least three control pistons in order to ensure adequate operating reliability. 
     In a further embodiment the progressive metering valve can have at least one pressure relief valve with a certain minimum switching pressure. The pressure relief valve opens when the hydraulic pressure exceeds the minimum switching pressure. This takes place, in particular with striking tools once in an operating cycle of the striking tool, when the hydraulic pressure is increased by a periodically actuated shuttle valve in the hydraulic circuit of the machine in order to drive the striking tools. The pressure relief valve can in particular be arranged in the control lines of at least one changeover valve. 
     Instead of progressive metering valves other differently formed changeover members can be used which connect the drive chambers of the drive piston alternately and automatically to the pressure line of the hydraulic circuit. 
     For example, in a further embodiment two pressure relief valves can be used. In one embodiment the pressure relief valves can be arranged in each case in a bypass line to the switching lines opening into the drive chambers. The bypass lines serve as pilot lines for the changeover valves. This arrangement can be used instead of a progressive metering valve, but is less advantageous due to the use of valves with spring pretensioning of the components. 
     The to-and-fro movement of the double-acting drive piston leads advantageously to a to-and-fro movement of the feed piston with which it can automatically draw lubricant out of a reserve of lubricant and pressurisation of the reserve of lubricant using spring systems susceptible to wear is no longer needed. In particular the drive piston and the feed piston can, for example, be coupled together mechanically in a fixed manner by a piston rod. 
     In order to change the amount of lubricant per unit time which is discharged by the feed piston to the at least one lubricating point, the volume flow of the hydraulic circuit can be changed in an embodiment of the invention according to the method. In the automatic lubricating pump this can be realised, for example, by arranging an adjustable throttle in the hydraulic circuit. The throttle can be connected in a return line of the changeover member, i.e. in series with the changeover member, or in a bypass line, which runs parallel to the changeover member. Of course, one or more throttles can be used, of which one is arranged in the return line and the others in the bypass line, which is however more cost-intensive. This measure enables the lubricant discharge to be changed in a constructively simple manner without complicated construction measures being required in the region of the feed piston. 
     The lubricating pump can furthermore have a lubricant container which accommodates the reserve of lubricant. The lubricant container is embodied as a repeatedly exchangeable cartridge. With more lengthy periods of operation cost-intensive filling of the lubricant container is unnecessary, because only the cartridge needs to be changed when the reserve of lubricant has been exhausted. 
     The reserve of lubricant can be connected through a suction pipe to the feed chamber, wherein preferably the feed chamber is arranged below the reserve of lubricant in the direction of the gravitational force, so that the gravitational force supports the further flow of lubricant into the feed chamber. A return flow of lubricant out of the feed chamber into the reserve of lubricant when pressure is applied to the feed chamber can be avoided if, according to a further advantageous embodiment, a non-return valve is positioned in the suction line between the feed chamber and the reserve of lubricant. 
     Soiling of the automatic lubricating pump can be prevented by a filter device in the pressure line in front of the changeover member. An orifice device in the pressure line advantageously limits the maximum volume flow through the changeover member. 
     In a further advantageous embodiment a bypass line, which can be constricted or closed and which is routed from the pressure line to the return line through a pump set, can be provided for the changeover member. The pump set is preferably a solid body. The bypass line can be used in winter for heating the automatic pump if the usual heated hydraulic fluid is passed through the pump set. 
     Finally, all hydraulic connections on the automatic pump are brought together on one connection plate which can be joined pressure-tight to the connections of a connection plate on the machine side depending on the type of fluid plug connectors. 
     In the following, the invention based on various embodiments of the invention is explained in more detail using examples with reference to the drawings. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  a fluid flow chart of a first embodiment of an automatic lubricating pump according to the invention in particular for striking tools; 
         FIG. 2  a schematic sectional illustration of parts of a further embodiment of the same lubricating pump according to the invention in a first operating position; 
         FIG. 3  the embodiment of  FIG. 2  in a second operating position; 
         FIG. 4  a schematic sectional illustration of parts of a further embodiment of the automatic lubricating pump according to the invention; 
         FIG. 5  a schematic side view with exposed sections of a further embodiment of the automatic lubricating pump according to the invention; 
         FIG. 6  a second operating position of an element of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     First, the structure of an automatic lubricating pump designed according to the invention will be explained based on the embodiment in  FIG. 1 . 
     The automatic lubricating pump  1  is formed with its connection lines P, R on a hydraulic circuit  2  of a construction machine (not illustrated) for connection, for example, via connections  3   a  and  3   b  formed as quick-fitting couplings. Connection  3   a  here represents the connection to the pressure line, similarly designated with P in  FIG. 1 , of the hydraulic circuit on the construction-machine side; connection  3   b  represents the connection to the essentially unpressurised return line, also designated with R in  FIG. 1 , of the hydraulic circuit. 
     If the construction machine is equipped with, for example, a hydraulic striking tool  4 , such as a hydraulic hammer, then pressure is applied to the pressure line P either constantly or, as illustrated in  FIG. 1 , periodically via a periodically actuated shuttle valve  5 , in order to periodically drive the striking tool  4  appropriately. The striking tool  4  can alternatively be connected at various points to the hydraulic circuit  2 , as schematically illustrated in  FIG. 1  using the reference numerals  1 ,  2  and  3 . Furthermore, the shuttle valve  5  can also be arranged in the return line R. 
     The automatic lubricating pump  1  is furthermore equipped with a lubricant outlet  6  to which a lubricant line  7  leading to a lubricating point can be connected. In particular the striking tool  4  can be regarded as a lubricating point. 
     The automatic lubricating pump  1  is fitted with a double-acting drive piston  8  which provides the drive for the feed pump  9 . On both of its sides the drive piston  8  has drive surfaces  8   a ,  8   b  which are bordered in each case by the drive chambers  8   c ,  8   d . The feed pump  9  conveys lubricant from a reserve of lubricant  10  through a discharge line  11  to the lubricant outlet  6 . A branch  12  from the discharge line  11  can be equipped with a pressure relief valve  13 , which leads to another connection  14 , through which lubricant can be tapped off when a certain lubrication pressure in the discharge line  11  is exceeded. 
     The reserve of lubricant can be provided with a follower piston  15  to avoid drawing air through the feed pump  9 . 
     The automatic lubricating pump  1  is furthermore provided with a hydraulically operable changeover member  16 , through which two switching lines A, B leading to the drive chambers  8   c  and  8   d  of the double-acting drive piston  8  are alternately connected to the connection  3   a  or to the connecting line or pressure line P or to the connection  3   b  or to the connecting or return line R. To achieve this, the switching lines A, B are connected via the changeover member  16  to the pressure line P and the return line R of the hydraulic circuit  2  when the automatic lubricating pump  1  is connected to the hydraulic circuit  2 . 
     An orifice  17  for limiting the volume flow of hydraulic liquid flowing through the changeover member and a filter unit  18  are fitted in the pressure line P between the changeover member  16  and the connection  3   a . An adjustable throttle  19  is arranged in the return line R and alternatively also in the pressure line P after the filter unit  18 . Additionally to or instead of the throttle  19 , a throttle  20  can also be arranged between the connection lines in a bypass line  21  in parallel with the changeover member  16 . The bypass line  21  preferably passes through a massively formed pump body and can be used for preheating the automatic lubricating pump  1 . For this use a simple switching valve can also be employed instead of the throttle  20 . 
       FIG. 1  shows that the changeover member  16  is formed for actuation without an external energy feed and only by the hydraulic circuit  2 . For example, the changeover member  16  has a hydraulically actuated changeover valve  22 , which as shown in  FIG. 1 , can be formed as a hydraulically actuated multiple way valve, in particular as a 4/2 valve. In a first operating position  23  the changeover valve connects the switching line A to the pressure line P and the switching line B to the return line R so that the drive chamber  8   c  is subjected to the hydraulic pressure in the hydraulic circuit  2  and the drive piston  8  moves in the direction of the other drive chamber  8   d . In a second operating position  24  the switching line A is connected to the return line R and the switching line B to the pressure line P. In the second operating position with the automatic lubricating pump  1  connected to the hydraulic circuit  2 , the drive chamber  8   d  is subjected to the hydraulic pressure in the hydraulic circuit  2  and the drive piston  8  moves in the direction of the drive chamber  8   c.    
     The changeover valve  22  is actuated by the pressure in two control lines  25 ,  26  which are routed back parallel to the switching lines A, B from them in each case to the changeover valve  22 . 
     In the control line  25  a pressure relief valve  27 ′ is arranged as the switching means  27  and in the control line  26  a pressure relief valve  28 ′ is also arranged as switching means  28 . The switching means  27 ,  28  ensure that a changeover of the operating position  22 ,  23  occurs in the changeover valve  22  when a predetermined minimum pressure is exceeded in one of the respective control lines  25 ,  26 . Since the switching lines A, B on connection to the pressure line P are either subjected to the hydraulic pressure or, on connection to the return line R, essentially unpressurised, the switching means  27 ,  28  only cause a changeover of operating position when the periodically changing hydraulic pressure P has exceeded the predetermined minimum switching pressure of the pressure relief valves. 
     This structure of the changeover member  16  produces the following functions: 
     Starting from the first operating position  23  in  FIG. 1 , the pressure builds up, for example, after an appropriate changeover of the shuttle valve  5  in the pressure line P, until the predetermined minimum switching pressure is exceeded in the switching line A connected in this operating position to the pressure line P. Then the pressure relief valve  28 ′ opens, the control line  26  is subjected to the hydraulic pressure and the changeover valve  22  changes over into the second operating position  24 . In the second operating position the switching line B is connected to the pressure line P and the switching line A to the return line R. If now the hydraulic pressure in the switching line B builds up at the next changeover of the switching valve  5 , the pressure relief valve  27 ′ opens, the control line  25  is subjected to the hydraulic pressure and the switching valve  22  switches back again into the first operating position  23 , as shown in  FIG. 1 . In this way alternately, at one time the switching line A is connected to the pressure line P and the return line R and then at another time the pressure line B is connected to the return line R and the pressure line P. As a consequence of this continuous switching, the double-acting drive piston  8  moves to and fro and drives the feed pump  9  via the piston rod  8   e.    
     The above embodiment functions in the described manner also when a constant hydraulic pressure prevails in the pressure line P and the switching valve  5  is omitted. In this case the movements of the actuating pistons lead to alternating pressure conditions and thus to the opening and closing of the pressure relief valve  27 ′. 
       FIGS. 2 and 3  show a schematic sectional illustration of a further embodiment of the changeover member  16  in a schematic sectional illustration. The same reference numerals are used as in  FIG. 1 . In  FIG. 2  the changeover member  16  is located in the first operating position in which the switching line A and the drive chamber  8   c  are connected to the pressure line P and the switching line B and the drive chamber  8   d  are connected to the return line R.  FIG. 3  shows the embodiment of  FIG. 2  in the second operating position in which the switching line B is connected to the pressure line P and the switching line A to the return line R. The changeover member  16  of  FIGS. 2 and 3  can be used instead of the changeover member illustrated in  FIG. 1 . 
     In the embodiment of  FIGS. 2 and 3  the changeover member  16  is formed as a progressive metering valve with three control pistons I, II and III as well as a switching means  30  formed as a pressure relief valve  30 ′, which corresponds in its function to the switching means  27 ,  28  of the embodiment in  FIG. 1 . Apart from the two outputs of the changeover member  16 , which are connected to the switching lines A and B, all outlets  31  of the changeover member  16  are connected to the return line R. 
     At least two pairs of control lines  32  and at least one pair of outlets  31  are assigned to each control piston I, II, III. Here, the first sections  32   a  of a first pair of control lines  32  are routed through the cylinders Ia, IIa, IIIa accommodating the respective control pistons I, II, III and can be opened and closed by at least two piston sections  33   a  of the respective control piston. The first sections  32   a  open out in each case at one end in the pressure line P and at their other end pass into the second sections  32   b  of the control lines. The second sections  32   b  open out in each case at the face sides of the control pistons I, II, III in the drive chambers  33   b  arranged there. Consequently, each control line  32  connects one drive chamber  33   b  of a control piston I, II, III to the pressure line P via a piston section  33   a  of another control piston. 
     In the embodiment of  FIGS. 2 and 3  the control lines are arranged as follows: 
     The control lines  32  opening out into the drive chambers  33   b  of the control piston II are connected via the control piston I to the pressure line P ( FIG. 2 ). The control lines opening out into the drive chambers  33   b  of the control piston III are routed via the piston sections  33   a  of the control piston II. The control lines opening out into the drive chambers  33   b  of the control piston I are routed via the piston sections  33   a  of the control piston II. Apart from the control lines routed from control piston I via control piston III, the control lines  32  are in each case located on one side of the symmetrically formed control pistons. 
     The outlets  31  also run via the piston sections  33   a  parallel to the first sections  32   a  of the control lines  32  and open out like these in the second section  32   b  of the control lines. The piston sections  33   a  are in each case dimensioned here such that they either simultaneously both close the outlet  31  assigned to them and also the first section  32   a  also assigned to them or only one of them. 
     Since in each case one pair of control lines  32  passes to the drive chambers  33   b  on the face sides of the assigned control piston I, II, III, each control piston is displaced into one of its two end positions, as soon as a control line  32  of this pair is connected to the pressure line P and the other control line  32  of this pair is connected to the return line R. 
     In the end positions of the control piston an outlet is in each case opened and simultaneously the section  32   a  of a control line in parallel to this outlet is closed by one piston section  33   a  so that the second section  32   b  of this control line is connected to the return line R. In addition, the first section  32   a  of the other control line passing through the control piston is opened, while simultaneously the outlet  31 , which is parallel on this section  32   a , is closed by the other piston section  33   a  so that the opened control line is connected to the pressure line P. Thus, each control piston I, II, III has a first operating position and a second operating position which correspond to both of its end positions in the cylinder Ia, IIa, IIIa. In the first operating position one drive chamber of the control piston connected via the control line  32  is subjected to the hydraulic pressure and the other drive chamber is connected to the return line R via the outlet  31 . In the second operating position the other drive chamber of this control piston is subjected to the hydraulic pressure and the other drive chamber is connected to the return line R. Correspondingly, in switching to and fro between the drive chambers of a control piston connected to the control lines, connection is made to the pressure line P alternately in the two operating positions. 
     The pressure relief valve  30  is positioned in front of the two control lines  32  through the control piston III and formed such that it only opens when a predetermined hydraulic pressure in the pressure line P is exceeded and, depending on the position of the control piston III, connects one of the drive chambers  33   a  of the control piston I to the pressure line P. 
     The function of the changeover member  16  of  FIGS. 2 and 3  is as follows: 
     In  FIG. 2  the switching line A of the drive piston  8  is connected via the drive chambers  33   b  of the control piston III and the control piston II to the pressure line P. The drive piston  8  is accordingly moved into the right end position in  FIG. 2 , because the drive chamber  8   c  is subjected to hydraulic pressure. The movement of the drive piston  8  is transferred to the feed pump  9  (not shown in  FIGS. 2 and 3 ) via the piston rod  8   e . The operating position of  FIG. 2  thus corresponds to the operating position  23  of  FIG. 1 . 
     If the pressure line P is subjected to pressure by the hydraulic valve  5  ( FIG. 1 ) switching over, the pressure in the pressure line P increases until the predetermined minimum switching pressure of the pressure relief valve  30  is reached and it opens. With the pressure relief valve  30  open the left control line  32  of the control piston III in  FIG. 2  is connected to the right drive chamber  33   b  of the control piston I in  FIG. 2 . The control piston I is subjected on its right face side to the hydraulic pressure in the pressure line P and moves into its left end position in which it connects the right control line  32  to the right drive chamber  33   b  of the control piston II, while it simultaneously connects the left drive chamber  33   b  of the control piston II to the return line R via an outlet  31 . Consequently, the control piston II moves from the right end position illustrated in  FIG. 2  into the left end position as soon as the control piston I is also moved into the left end position. 
     In the left end position the control piston II in turn connects the right control line  32  to the right drive chamber  33   b  of the control piston III and thus the switching line B to the pressure line P. Simultaneously, the control piston II closes the left control line  32  and connects the left drive chamber  33   b  of the control piston III and thus the switching line A to the outlet  31  assigned to it. Thus the drive piston  8  can move from one end position on the right to the other end position on the left. 
     At the end of this changeover process all control pistons I, II, II and the drive piston  8  are moved into their left end position, as illustrated in  FIG. 3 . This operating position corresponds to the operating position  24  in  FIG. 1 . The to-and-fro movement of the drive piston is indicated symbolically in  FIGS. 2 and 3  by the arrows H 1  and H 2 . 
     If, during the next switching cycle of the switching valve  5 , the pressure again increases in the pressure line P beyond the minimum switching pressure, then the pressure relief valve  30  opens again and the control pistons I, II, III move in this order successively from their left end position illustrated in  FIG. 3  into the right end position illustrated in  FIG. 2  until the drive chamber  8   c  is connected to the pressure line P and the drive piston  8  has also moved in the direction H 2  into its right end position. With that, one changeover process and one drive cycle of the double-acting drive piston  8  have finished. 
       FIG. 4  shows in a schematic sectional illustration a further embodiment of the changeover member  16 . With this embodiment the same reference numerals are used as for the aforementioned embodiments, provided the function and the structure of the elements are the same. 
     In contrast to the embodiment of  FIGS. 2 and 3 , in the embodiment of  FIG. 4  the control piston III is also used as the drive piston, which drives the feed pump  9  (cf.  FIG. 1 ) via the piston rod  8   e . As illustrated in  FIG. 4 , the control piston III can be formed with a larger cross-section than the other control pistons in order to produce greater driving forces. One of the other control pistons can also be used as the drive piston instead of the control piston III. 
     Otherwise the function and structure of the embodiment of  FIG. 4  correspond to the function and structure of the embodiment of  FIGS. 2 and 3 . 
       FIG. 5  shows a further embodiment of an automatic lubricating pump  1 , wherein the same reference numerals are used as in the aforementioned figures provided they are similar in their structure or function. 
     The automatic lubricating pump  1  of  FIG. 5  is equipped with a changeover member  16  which can be constructed according to one of the aforementioned embodiments. 
     The drive piston  8 , the two chambers  8   c ,  8   d  of which are connected to the switching lines A, B of the changeover member  16 , is connected in a motion-transmitting manner via the piston rod  8   e  to the single or double-acting feed piston  35  of the feed pump. As can be seen in  FIG. 5 , the feed piston  35  can be formed in particular as one piece by the piston rod  8   e.    
     The feed pump  9  furthermore has a feed chamber  36  which is connected to the reserve of lubricant  10  via a suction line  37 . The part  36 ′ of the feed chamber  36 , which is closely sealed to the feed piston and leads to the lubricant line  11 , is used as the metering chamber, which determines the amount of lubricant delivered to the lubricating point per stroke of the feed piston  35 . The reserve of lubricant  10  is accommodated in a repeatedly exchangeable cartridge  38  which is placed sealed on a pump housing  39 . 
     The end position of the follower piston  15  with an empty or almost empty cartridge  38  can be read via an inspection window  40  in the cartridge  38  or in the pump housing  39 . 
     The reserve of lubricant  10  is arranged in the direction G of the gravitational force above the feed chamber  36  so that the gravitational force supports the filling of the feed chamber  36  with lubricant from the reserve of lubricant. In addition, due to the to-and-fro movement of the double-acting drive piston  8 , the feed piston  35  automatically draws lubricant from the reserve of lubricant  10 . A reverse flow of lubricant out of the metering chamber  36 ′ into the reserve of lubricant is eliminated, because the feed piston  35  plunges into the metering chamber  36 ′ in a sealed manner. 
     The feed piston  35  presses the lubricant out of the metering chamber  36 ′ through a non-return valve  41  in the direction of the lubricant outlet  6 . 
     The drive piston  8  and the feed pump  9 , preferably together with the non-return valve  41 , are inserted into preferably a single hole  42  in the pump housing  39 . The hole  42  has at least on one end, preferably as illustrated in  FIG. 5  on both of its ends, screw plugs  43 , which can be easily removed for servicing purposes and enable access to the drive piston  8  or the feed pump  9  with optionally the non-return valve  41 . 
     A three-way valve  44 , for example in the form of a ball valve, is arranged in the suction line  37 . The three-way valve  44  is formed for actuation outside of the automatic lubricating pump and, in the position illustrated in  FIG. 5 , connects the reserve of lubricant to the feed chamber  36 . In the position illustrated in  FIG. 6  the three-way valve  44  is formed for transfer in that the suction line  37  is connected to a filling line  45  so that if required, the cartridge  38  can be filled via a filling connection  46  which is externally accessible. 
     With a cartridge unintentionally emptied during feeding, there is the possibility of venting the suction channel  37  and filling with grease after changing the cartridge by exerting manual pressure on the usual follower plate and releasing the venting screw. 
     Finally, the automatic lubricating pump  1  has according to the embodiment of  FIG. 5  an actuating element  47 , with which the throttle  19 ,  20  ( FIG. 1 ) can be actuated, the hydraulic flow changed and the amount of lubricant discharged per unit time by the automatic lubricating pump can be set. 
     The embodiments described above can be modified further. For example, the pressure relief valve can be omitted if at least one further control piston is used appropriate to control pistons I, II. 
     Furthermore, instead of the connections illustrated in  FIG. 4 , which can be connected singly to appropriate lines, a connection plate can be provided to which all fluid connections are brought together. This connection plate forms part of a fluid plug, with which the automatic lubricating pump can be connected to the machine in one step.