Patent Publication Number: US-2007113549-A1

Title: Hydrostatic drive system with division of the quantity of hydraulic fluid at the pump

Description:
The invention relates to a hydrostatic drive system with division of the quantity of hydraulic fluid at the pump.  
      Hydraulic travelling drives which are designed for a cornering operation have, as is represented in EP 0 378 742 A2, two hydraulic circuits which are separate from one another, each hydraulic circuit consisting of a hydraulic pump and a hydraulic motor. In this way, it is possible to deliver separately, by two hydraulic pumps, the different quantities of hydraulic fluid for the two hydraulic motors in the case of cornering by the hydraulic travelling drive.  
      A hydraulic travelling drive according to EP 0 378 742 A2 is characterised by the difficulty of generating, by means of the two hydraulic pumps, the quantities of hydraulic fluid of equal magnitude, which are necessary in the case of straight-ahead travel, for the two hydraulic motors. Added to this is the fact that, in the case of straight-ahead travel by the hydraulic travelling drive, in the event of one drive line slipping or even spinning, the quantity of hydraulic fluid in the appertaining hydraulic circuit increases markedly, so that the hydraulic motor of the other drive line in each case, which is not slipping or spinning, is “bridged” hydraulically. In this way, the hydraulic travelling drive becomes inoperative.  
      The hydrostatic travelling drive in DE 198 33 942 A1 connects the two hydraulic circuits, which are connected in parallel in EP 0 378 742 A2, in series. There is thus obtained a single hydraulic circuit which is formed as a concatenation of the first hydraulic pump, the first hydraulic motor, the second hydraulic pump and the second hydraulic motor. This guarantees that a quantity of hydraulic fluid of equal magnitude is delivered in all the sections of the hydraulic circuit. If there is a risk of slipping or spinning in one drive line, because of the system no rise in the quantity of hydraulic fluid occurs in the hydraulic circuit. On the contrary, the slipping or spinning drive line is braked by the other drive line, which is not slipping or spinning, of the hydrostatic travelling drive.  
      What is disadvantageous about the hydrostatic travelling drive in DE 198 33 942 A1 is the use of two separate hydraulic pumps, especially as the same quantity of hydraulic fluid is delivered by both hydraulic pumps in the closed hydraulic circuit of the hydrostatic travelling drive.  
      The underlying object of the invention is therefore to further develop a hydrostatic travelling drive in such a way that, with hydraulic motors connected in series in a hydraulic circuit, use is made, in order to avoid slipping or spinning of one drive line, of a pump unit which is designed so as to be of substantially simpler construction than a pump unit consisting of two separate pumps.  
      The object of the invention is achieved by means of a hydrostatic drive system having the features in claim  1 .  
      In the minimal configuration of the first form of embodiment, the hydraulic circuit consists of two drive lines which are each driven by a hydraulic motor, which motors are, in turn, supplied with a quantity of hydraulic fluid by a hydraulic pump. The hydraulic pump has two partial delivery lines which each deliver a partial flow of hydraulic fluid in a common cylinder drum belonging to the hydraulic pump, according to the invention, of the hydrostatic drive system according to the invention. The two partial delivery lines of the hydraulic pump, according to the invention, of the hydrostatic drive system according to the invention, assume the function of the two hydraulic pumps of the hydrostatic travelling drive in DE 198 33 942 A1 and are therefore connected, within the hydraulic circuit between the two hydraulic motors, in series with the latter in each case. In this way, possible slipping or spinning of one of the two hydraulic motors can be prevented.  
      By comparison with the hydrostatic travelling drive in DE 198 33 942 A1, there is a single-pump system. This is characterised by a smaller space for construction, in particular a smaller overall length, and reduced outlay on pipework. Compared to a two-pump system, the hydrostatic drive system according to the invention needs no distributor gear unit for coupling the individual pumps mechanically, a fact which once again reduces the space required for construction and makes outlay on wear-induced maintenance and inspection unnecessary.  
      Finally, it should be mentioned that, in applications with a high hydraulic power requirement, instead of one hydraulic pump, it is possible to connect a number of hydraulic pumps in parallel.  
      Advantageous refinements of the invention are indicated in the dependent claims.  
      In a second form of embodiment of the hydrostatic drive system according to the invention, the two drive lines are driven by two mechanically coupled hydraulic motors in each case. The connections, on the feeding-in and feeding-out sides, of the first and third hydraulic motors and also of the third and fourth hydraulic motors may be connected jointly, in each case, to a connection belonging to a partial delivery line of the hydraulic pump of the hydrostatic drive system according to the invention, while the other connections, in each case, of the first and third hydraulic motors and also of the second and fourth hydraulic motors are connected in each case, on the opposite connecting side of the hydraulic pump, to a connection belonging to one of the two partial delivery lines of the hydraulic pump of the hydrostatic drive system according to the invention. This guarantees that a self-contained hydraulic circuit which, in the event of slipping or spinning of the first or second drive line, ensures braking by the other drive line in each case, exists at least over the first and second hydraulic motors and also over the two partial delivery lines of the hydraulic pump.  
      In a third form of embodiment of the hydrostatic drive system according to the invention, which form of embodiment is based on the first form of embodiment of the hydrostatic drive system according to the invention, a third drive line is driven by a fifth hydraulic motor. The first and third drive lines are responsible, in each case, for driving the front right-hand wheel and left-hand wheel, or the front right-hand chain and left-hand chain, of the vehicle. The second drive line drives the rear wheel or rear chain. Since the first and fifth hydraulic motors are connected in parallel, and are each connected to the second hydraulic motor and the two partial delivery lines of the hydraulic pump in series to form a closed hydraulic circuit, slipping or spinning of the first or third drive line is braked by the second drive line, and slipping or spinning of the second drive line is braked by the first and third drive lines.  
      In the fourth form of embodiment of the hydrostatic drive system according to the invention, which form of embodiment is based on the third form of embodiment and, like the latter, has three drive lines, the first and third drive lines are driven by two mechanically coupled hydraulic motors in each case. The connections, on the feeding-in and feeding-out sides, of the first and third hydraulic motors driving the first drive line, and also of the fifth and sixth hydraulic motors driving the third drive line, may be connected jointly, in each case, in a manner analogous to the second form of embodiment, to a connection belonging to a partial delivery line of the hydraulic pump, while the other connections, in each case, of the first and third hydraulic motors and also of the fifth and sixth hydraulic motors may be connected separately, on the opposite connecting side of the hydraulic pump, to one connection, in each case, belonging to one of the two partial delivery lines of said hydraulic pump. This guarantees, as in the second form of embodiment, that, in the event of slipping or spinning of the first or third drive line, braking is ensured by the second drive line, while in the case of slipping or spinning of the second drive line, braking by the first and third drive lines occurs.  
      In the fifth form of embodiment of the hydrostatic drive system according to the invention, the second hydraulic motor driving the second drive line is, in contrast to the third and fourth forms of embodiment, connected by its two connections, in each case, to the two connections of the first partial delivery line of the hydraulic pump. In the event of slipping of the second hydraulic motor, limitation of the rotational speed, and thereby avoidance of slipping of the second hydraulic motor, occurs through the fact that, if the first drive line is not slipping, the quantity of hydraulic fluid required for slipping is not diverted from the first hydraulic motor, which is likewise supplied by the first partial delivery line of the hydraulic pump, to the second hydraulic motor.  
      The sixth form of embodiment of the hydrostatic drive system according to the invention is intended for four drive lines. In this case, the fifth hydraulic motor, which drives the third drive line, is connected hydraulically in parallel with the first hydraulic motor driving the first drive line, while the seventh hydraulic motor, which drives the fourth drive line, is connected in parallel with the second hydraulic motor driving the second drive line. In the fifth form of embodiment of the hydrostatic drive system according to the invention, the first and fifth hydraulic motors are connected in series, in a manner analogous to the first form of embodiment, with the second and seventh hydraulic motors via the two partial delivery lines of the hydraulic pump in a closed hydraulic circuit. In this way it is possible, if slipping or spinning of the first, second, third or fourth drive line occurs, to prevent braking by the other two hydraulic motors which are each connected in series with the slipping or spinning hydraulic motor.  
      In the seventh form of embodiment of the hydraulic drive system according to the invention, which form of embodiment is based on the sixth form of embodiment, all four drive lines are driven by two mechanically coupled hydraulic motors. The interconnection of the hydraulic motors, of which there are eight in all, with the two connections of the two partial delivery lines of the hydraulic pump takes place in a manner analogous to the second and third forms of embodiment and thereby prevents slipping or spinning of one of the four drive lines.  
      In the case of straight-ahead travel of the vehicle, equalising flows between the two working conduits may be realised via activated 2/2-way valves in the event of non-slipping of a drive line, in order to guarantee equalisation of the differential in the case of cornering, between the two working conduits which are connected, on the feeding-in and feeding-out sides in each case, to the two connections of the two partial delivery lines of the hydraulic pump. The said 2/2-way valves may also be integrated in the hydraulic pump on the feeding-in and feeding-out sides.  
    
    
      The forms of embodiment of the invention are represented in the drawings and will be described in greater detail below.  
       FIG. 1  shows a longitudinal section through a hydraulic pump belonging to a hydraulic drive system according to the invention with division of the quantity of hydraulic fluid at the pump;  
       FIG. 2  shows an enlarged representation of a detail of the longitudinal section of the hydraulic pump of a hydraulic drive system according to the invention with division of the quantity of hydraulic fluid at the pump;  
       FIG. 3  shows a circuit diagram of a first form of embodiment of a hydraulic drive system according to the invention with division of the quantity of hydraulic fluid at the pump;  
       FIG. 4  shows a circuit diagram of a second form of embodiment of a hydraulic drive system according to the invention with division of the quantity of hydraulic fluid at the pump;  
       FIG. 5  shows a circuit diagram of a third form of embodiment of a hydraulic drive system according to the invention with division of the quantity of hydraulic fluid at the pump;  
       FIG. 6  shows a circuit diagram of a fourth form of embodiment of a hydraulic drive system according to the invention with division of the quantity of hydraulic fluid at the pump;  
       FIG. 7  shows a circuit diagram of a fifth form of embodiment of a hydraulic drive system according to the invention with division of the quantity of hydraulic fluid at the pump;  
       FIG. 8  shows a circuit diagram of a sixth form of embodiment of a hydraulic drive system according to the invention with division of the quantity of hydraulic fluid at the pump; and  
       FIG. 9  shows a circuit diagram of a seventh form of embodiment of a hydraulic drive system according to the invention with division of the quantity of hydraulic fluid at the pump. 
    
    
      An exemplified embodiment of the hydraulic pump  100  of the hydraulic drive system according to the invention with division of the quantity of hydraulic fluid at the pump will be described below with reference to  FIGS. 1 and 2 .  
      The longitudinal section represented in  FIG. 1  through the hydraulic pump according to the invention shows how the common drive shaft  1  is mounted by means of a roller bearing  2  at one end of a pump housing  3 . Said common drive shaft  1  is additionally mounted in a plain bearing  4  which is disposed in a connecting plate  5  which closes the pump housing  3  at the opposite end.  
      Constructed in said connecting plate  5  is a clearance  6  which passes right through the connecting plate in the axial direction, in which the plain bearing  4  is disposed on the one hand, and through which the common drive shaft  1  passes on the other. On that side of the connecting plate  5  which faces away from the pump housing  3 , the auxiliary pump  7  is inserted in a radial widened portion in the clearance  6 . For the purpose of driving the auxiliary pump  7 , the common drive shaft  1  has a tooth system  8 . 1  which is in engagement with the corresponding tooth system on an auxiliary pump shaft  9 . Said auxiliary pump shaft  9  is mounted in the clearance  6  by means of a first auxiliary pump plain bearing  10  and in the auxiliary pump connecting plate  12  by means of a second auxiliary pump plain bearing  11 .  
      Disposed on the auxiliary pump shaft  9  is a gear wheel  13  which is in engagement with an internal geared wheel  14 . Said internal geared wheel  14 , which is disposed in the auxiliary pump connecting plate  12  in a rotatable manner, is likewise driven, via the gear wheel  13 , by the auxiliary pump shaft  9  and thereby ultimately by the common drive shaft  1 . The suction-side and pressure-side connections for the auxiliary pump  7  are constructed in the auxiliary pump connecting plate  12 . The auxiliary pump  7  is fixed in position in the radial widened portion of the clearance  6  in the connecting plate  5  by a cover  15  which is mounted on said connecting plate  5 .  
      The inner race of the roller bearing  2  is fixed in position in the axial direction on the common drive shaft  1 . Said inner race rests, on one side, against a collar  16  on the common drive shaft  1  and, on the other side, is held in this axial position by a retaining ring  17  which is inserted in a groove in said common drive shaft  1 . The axial position of the roller bearing  2  with respect to the pump housing  3  is determined by the retaining ring  18  which is inserted in a circumferential groove in the shaft aperture  19 . A sealing ring  20  and, finally, another retaining ring  21  are also disposed in said shaft aperture  19  in the direction of the outer side of the pump housing  3 , said retaining ring  21  being inserted in a circumferential groove in said shaft aperture  19 .  
      A driving tooth system  22 , via which the hydraulic pump is driven by a driving engine which is not represented, is constructed on that end of the common drive shaft  1  which protrudes from the pump housing  3 .  
      Disposed in the interior of said pump housing  3  is a cylinder drum  23  which has a central through-aperture  24  through which the common drive shaft  1  passes. Said cylinder drum  23  is connected, via another driving tooth system  25 , to the common drive shaft  1  in a manner secured against torsion but displaceable in the axial direction, so that a rotating movement of the common drive shaft  1  is transmitted to the cylinder drum  23 .  
      Another retaining ring  26 , against which a first supporting washer  27  rests, is inserted in a groove constructed in the central through-aperture  24 . Said first supporting washer  27  forms a first spring bearing for a compression spring  28 . A second spring bearing for said compression spring  28  is formed by a second supporting washer  29  which is supported against the end face of the additional driving tooth system  25 . The compression spring  28  thereby exerts a force, in the opposite axial direction in each case, on the common drive shaft  1  on the one hand, and on the cylinder drum  23  on the other hand. The common drive shaft  1  is loaded in such a way that the outer race of the roller bearing  2  is supported against the retaining ring  18 .  
      In the opposite direction, the compression spring  28  acts on the cylinder drum  23  which is held in abutment against a control plate  31  by a spherical depression  30  constructed on the end face of the cylinder drum  23 . Said control plate  31 , in turn, rests against the connecting plate  5  in a sealing manner with the side that faces away from the cylinder drum  23 . Said cylinder drum  23  is centred by means of the spherical depression  30 , which corresponds with a suitable spherical contour on the control plate  31 .  
      The position of the control plate  31  in the radial direction is fixed by the outer periphery of the plain bearing  4 . For this purpose, said plain bearing  4  is inserted only partially in the clearance  6  in the connecting plate  5 .  
      Cylinder bores  32 , in which pistons  33  which are longitudinally displaceable in said cylinder bores  32  are disposed, are incorporated in the cylinder drum  23  in a manner distributed over a common pitch circle. At the end that faces away from the spherical depression  30 , the pistons  33  partially protrude from the cylinder drum  23 . At this end, there is fastened to each of the pistons  33  a sliding shoe  34  via which said pistons  33  are supported on a running surface  35  on a swivelling disc  36 .  
      In order to produce a movement of stroke of the pistons  33 , the angle which the running surface  35  of the swivelling disc  36  forms with the central axis is variable. For this purpose, the swivelling disc  36  can be adjusted in its inclination by the adjusting arrangement  37 . Said swivelling disc  36  is mounted in the pump housing  3  in roller bearings in order to absorb the forces which are transmitted to the swivelling disc  36  by the sliding shoes  34 .  
      A first connection  38 , a second connection  38 ′, a third connection  56  and a fourth connection  56 ′ are provided in the connecting plate  5  for the purpose of connecting the hydraulic pump  100  to a first hydraulic circuit and to a second hydraulic circuit. Represented diagrammatically in  FIG. 1  are a first connection  38  and a second connection  38 ′ which can be connected via the control plate  31 , in a manner which is not shown, to the cylinder bores  32  and form a first partial delivery line  101  of the hydraulic pump  100  for a first hydraulic circuit. The third and fourth connections  56  and  56 ′, which are not represented in  FIG. 1 , can be connected to the cylinder bores  32  in an analogous manner, and form the second partial delivery line  102  of the hydraulic pump  100  for a second hydraulic circuit.  
      An enlarged representation of the components which interact in the interior of the pump housing  3  is represented in  FIG. 2 .  
      On its side that faces away from the running surface  35 , the swivelling disc  36  is supported on a cylindrical-roller bearing  39 , the cylindrical rollers of which are held by a bearing cage  40 . In order to ensure a reliable return of the cylindrical rollers into their original location after each swivelling movement, the bearing cage  40  is fastened to a retaining mechanism  41 , by means of which said bearing cage  40  performs a controlled movement both when swivelling out and also when swivelling back.  
      For the purpose of performing a swivelling movement, the swivelling disc  36  is coupled to a sliding block  42  which rotates said swivelling disc  36 , in a manner which is not represented, about an axis which lies in the plane of the drawing.  
      The cylinder bores, which are designated generally by  32  in  FIG. 1 , are subdivided into a first group of cylinder bores  32 . 1  and a second group of cylinder bores  32 . 2 . As has already been explained briefly in the remarks on the subject of  FIG. 1 , a sliding shoe  34  is disposed on each of the pistons  33  at the end that faces away from the control plate  31 . Said sliding shoe  34  is fastened, by means of a clearance, to a spherical head of the piston  33 , so that the sliding shoe  34  is fixed in position on said piston  33  in a movable manner, and pulling and pressing forces can be transmitted.  
      A sliding surface  43 , by which the sliding shoe  34 , and thereby the piston  33 , is supported on the running surface  35  of the swivelling disc  36 , is constructed on said sliding shoe  34 . Constructed in the sliding surface  43  are lubricating-oil grooves which are connected to the cylinder bores  32  constructed in the cylinder drum  23  via a lubricating-oil duct  44  which is constructed in the sliding shoe  34  and is continued in the form of a lubricating-oil bore  44 ′ in the piston  33 .  
      Because the sliding shoes  34  are supported against the running surface  35 , the pistons  33  perform a movement of stroke when the common drive shaft  1  rotates, as a result of which movement the pressure medium located in the cylinder spaces in the cylinder drum  23  is pressurised. Some of this pressure medium passes out at the sliding surface  43  and thus forms a hydrodynamic bearing for the sliding shoe  34  on the running surface  35 .  
      In order to convey the pressure medium from the cylinder spaces into a first or second hydraulic circuit, first connecting ducts  45 . 1  and second connecting ducts  45 . 2  are connected, in each case, to the cylinder bores of the first group  32 . 1  and the cylinder bores of the second group  32 . 2  respectively. The first and second connecting ducts  45 . 1  and  45 . 2  extend from the cylinder bores of the first group  32 . 1  and the cylinder bores of the second group  32 . 2  respectively, to the spherical depression  30  which is constructed on one end face  46  of the cylinder drum  23 .  
      A first control pocket  48  and a second control pocket  49 , which pass through the control plate  31  in the axial direction, are constructed in said control plate  31  which is connected to the connecting plate  5  in a manner secured against torsion.  
      A third control pocket  50  and a fourth control pocket  51  are also preferably constructed in the control plate  31 . While the first and third control pockets  48  and  50  are connected, via the connecting plate  5 , to working conduits  52  and  53 , respectively, of the first hydraulic circuit, the second control pocket  49  and the fourth control pocket  51  are connected, in a corresponding manner, to the working conduits  54  and  55 , respectively, of the second hydraulic circuit.  
      The first and third control pockets  48  and  50  are at an identical first distance R 1 ′ from the longitudinal axis  52  of the cylinder drum  23  which is smaller than the second distance R 2 ′ from the longitudinal axis  52 , which distance is again identical for the second control pocket  49  and the fourth control pocket  51 . In the course of one revolution of the common drive shaft  1 , the first connecting ducts  45 . 1  are connected in turn to the first control pocket  48  and the third control pocket  50 , so that, because of the movement of stroke of the pistons  33  disposed in the cylinder bores  32 . 1  of the first group, the pressure medium is sucked in, for example via the third control pocket  50 , and pumped into that working conduit  52  or  53  of the first hydraulic circuit which is on the pressure side, via the first control pocket  48 . For this purpose, the first connecting ducts  45 . 1  open onto the end face  46  of the cylinder drum  23  at a first distance R 1  from the longitudinal axis  52  of the cylinder drum  23  which corresponds to the first distance R 1 ′ of the first and third control pockets,  48  and  50  respectively, from said longitudinal axis  52  of the cylinder drum  23 .  
      In the exemplified embodiment represented, the first connecting ducts  45 . 1  are disposed in the cylinder drum  23  in such a way that they have a radial component of direction as a result of which the first distance R 1  of the outlet on the end face  46  is smaller than the distance on the opposite side of the first connecting ducts  45 . 1 . The second connecting ducts  45 . 2  accordingly open onto the end face  46  of the cylinder drum  23  at a second distance R 2  which corresponds with a second distance R 2 ′ of the second and fourth control pockets  49  and  51  from the longitudinal axis  52 . In the course of one revolution of the common drive shaft  1 , the cylinder bores of the second group  32 . 2  are thereby alternately connected to the second and fourth control pockets  49  and  51  via the second connecting ducts  32 . 2 .  
      In order to prevent the sliding shoes  34  from lifting off the running surface  35  of the swivelling disc  36  during a suction stroke, a holding-down plate  53  is provided, which engages round the sliding shoes  34  at an offset which is provided for that purpose. Said holding-down plate  53  has a spherical central clearance  54  with which it is supported against a supporting head  55  which is disposed on that end of the cylinder drum  23  which faces away from the end face  46 .  
       FIG. 3  shows a first form of embodiment of a hydraulic drive system according to the invention with division of the quantity of hydraulic fluid at the pump, which form of embodiment uses the hydraulic pump  100  according to the invention which has been described above, with two partial delivery lines  101  and  102 .  
      The connection  38  of the first partial delivery line  101  of the hydraulic pump  100  according to the invention is connected to the first connection  103  of the first hydraulic motor  104  via the first working conduits  52 . Said first hydraulic motor  104  drives a first wheel  106  of a vehicle via a first drive line  105 . The second connection  107  of the first hydraulic motor  104  is connected, via the working conduit  55 , to the second connection  56 ′ of the second partial delivery line of the hydraulic pump  100  according to the invention. The first connection  56  of the second partial delivery line  102  of the hydraulic pump  100  according to the invention is connected to the first connection  108  of the second hydraulic motor  109  via the working conduit  54 . Said second hydraulic motor  109  drives a second wheel  111  of a vehicle via a second drive line  111 . The second connection  112  of the second hydraulic motor is connected, via the working conduit  53 , to the second connection  38 ′ of the first partial delivery line  101  of the hydraulic pump  100  according to the invention. The leakage volume of the first and second hydraulic motors  104  and  109  is connected, in each case, to a hydraulic tank  113  for the purpose of discharging leaking hydraulic fluid.  
      The hydraulic pump  100 , which is adjustable in the quantity of its hydraulic fluid, is mechanically coupled, with its two partial delivery lines  101  and  102 , to an auxiliary pump  114  via a drive shaft which is not represented in  FIG. 3 . Said auxiliary pump  114  delivers a hydraulic fluid into a feeding conduit  116  from a tank  115 . The pressure of the hydraulic fluid in said feeding conduit  116  is set to a specific level via a pressure-limiting valve  117 . If there is a drop in pressure in the working conduits  52 ,  53 ,  54  and/or  55 , hydraulic fluid is fed into the working conduit  52 ,  53 ,  54  and/or  55  afterwards from the feeding conduit  116  via a non-return valve  117  in each case. If an excess pressure occurs in the working conduits  52 ,  53 ,  54  and/or  55 , said excess pressure is discharged into the feeding conduit  116  in known manner via an excess-pressure valve  118  in each case from the working conduit  52 ,  53 ,  54  and/or  55  which is carrying an excess pressure. The hydraulic pump  100  with its two partial delivery lines  101  and  102 , the auxiliary pump  114 , the pressure-limiting valve  117  and also the four non-return valves  118  and the four excess-pressure valves  119  together form a pump unit  120 .  
      The two partial delivery lines  101  and  102  of the hydraulic pump  100  according to the invention and the two hydraulic motors  104  and  109  form, together with the working conduits  52 ,  53 ,  54  and  55 , a single hydraulic first circuit. Because of this series connection of the first hydraulic motor  104  and second hydraulic motor  109  and also of the two partial delivery lines  101  and  102  of the hydraulic pump  100 , a flow of hydraulic fluid of equal magnitude flows in all the working conduits  52 ,  53 ,  54  and  55 . Possible slipping or spinning of the wheel  106  or  111  in the case of lack of adhesion of said wheel  106  or  111  on the surface of the carriageway, and an accompanying rise in the flow of hydraulic fluid in the first hydraulic motor  104  or second hydraulic motor  109 , is eliminated, since the other, non-slipping or non-spinning wheel  111  or  106 , in each case, limits the level of the flow of hydraulic fluid in the hydraulic circuit to the value that corresponds to the normal operating situation. In this way, the slipping or spinning first or second hydraulic motor  104  or  109  is braked by the non-slipping and non-spinning second or first hydraulic motor  109  or  104 . Hydraulic “bridging” of the non-slipping and non-spinning first or second hydraulic motor  104  or  109  by the slipping or spinning second or first hydraulic motor  109  or  104  is consequently not possible in the case of this configuration.  
      Because of the different paths of the wheels, cornering operations lead to asymmetrical pressure conditions at the first or second hydraulic motor  104  or  109 . Pressure differences of this kind between the working conduits  52  and  54  or  53  and  55  when the vehicle is cornering may be bridged by the interpolation of a 2/2-way valve  123  and  124  in each case. If these 2/2-way valves are switched off by the control electronics of the vehicle in the case of cornering and when no slipping of a wheel  106  or  111  occurs, the particular 2/2-way valve is switched into the open condition, in which the particular working conduits  52  and  54  or  53  and  55  are hydraulically connected to one another. In this way, hydraulic equalising flows take place between the working conduits  52  and  54  or  53  and  55  for the purpose of reducing the pressure difference between said working conduits  52  and  54  or  53  and  55 .  
      A second form of embodiment of the hydraulic drive system according to the invention with division of the quantity of hydraulic fluid at the pump, which form of embodiment uses the hydraulic pump  100  with the two partial delivery lines  101  and  102 , is represented in  FIG. 4 .  
      The second form of embodiment in  FIG. 4  is based on the first form of embodiment in  FIG. 3 , so that in the following description, as also in all the descriptions belonging to the forms of embodiment which will now follow, the same reference symbols will be used for the same features and the description thereof will not be repeated.  
      In the second form of embodiment of the hydraulic drive system according to the invention, the first drive line  105  is driven, as well as by the first hydraulic motor  104 , by a third hydraulic motor  125  which is mechanically coupled to said first hydraulic motor  104 . Said third hydraulic motor  125  is connected by its first connection  126 , via the working conduit  54 , to the first connection  56  of the second partial delivery line  102  of the hydraulic pump  100 , and by its second connection  125 , via the working conduit  55 , to the second connection  56 ′ of the second partial delivery line  102  of said hydraulic pump  100 . A fourth hydraulic motor  128 , which is mechanically coupled to the second hydraulic motor  109  and drives, with the latter, the second drive line  110 , is connected by its first connection  129 , via the working conduit  52 , to the first connection  38  of the first partial delivery line  101  of the hydraulic pump  100 , and by its second connection  130 , via the working conduit  53 , to the second connection  38 ′ of the first partial delivery line  101  of said hydraulic pump  100 .  
      Slipping or spinning of the first drive line  105  or of the second drive line  110  is realised, in a manner analogous to the first form of embodiment, by the braking effect of the closed hydraulic circuit consisting of the first hydraulic motor  104 , the second hydraulic motor  109 , the two partial delivery lines  101  and  102  of the hydraulic pump  100  and the working conduits  52 ,  53 ,  54  and  55 . A pair of hydraulic motors  104  and  126  or  109  and  128  which may possibly slip or spin is braked by the other pair of hydraulic motors,  109  and  128  or  104  and  126  respectively, which is not slipping or spinning. The fact that the third hydraulic motor  125  and the fourth hydraulic motor  128  are not interconnected cross-wise with the first and second partial delivery lines  101  and  102  of the hydraulic pump  100  is of no relevance for preventing the slipping or spinning of the first or second drive line  105  or  110 , since braking takes place via the hydraulic series connection of the first or second hydraulic motor  104  or  109 .  
      A third form of embodiment of the hydraulic drive system according to the invention with division of the quantity of hydraulic fluid at the pump, which form of embodiment uses the hydraulic pump  100  according to the invention with the two partial delivery lines  101  and  102 , is represented in  FIG. 5 .  
      The third form of embodiment in  FIG. 5 , which is based on the first form of embodiment in  FIG. 3 , has a fifth hydraulic motor  131  which drives a third drive line  144  connected to a wheel  143 . The first and third drive lines  105 ,  144  form, respectively, the left-hand and right-hand front drives of the vehicle, while the second drive line  110  represents the rear drive of said vehicle. The fifth hydraulic motor  131  is connected by its first connection  132 , via the working conduit  52 , to the first connection  38  of the first partial delivery line  101  of the hydraulic pump  100 , and by its second connection  133 , via the working conduit  55 , to the second connection  56 ′ of the second partial delivery line  102  of said hydraulic pump  100 . The fifth hydraulic motor  131  is consequently connected in parallel, hydraulically speaking, with the first hydraulic motor  104 .  
      Possible slipping or spinning of the first hydraulic motor  104  or of the fifth hydraulic motor  131  is braked by the non-slipping and non-spinning second hydraulic motor  109 , while possible slipping or spinning of said second hydraulic motor  109  is braked by the non-slipping and non-spinning first and fifth hydraulic motors  104  and  131  in a manner analogous to the way in which the first and second forms of embodiment function.  
      A fourth form of embodiment of the hydraulic drive system according to the invention with division of the quantity of hydraulic fluid at the pump, which form of embodiment uses the hydraulic pump  100  with the two partial delivery lines  101  and  102 , is represented in  FIG. 6 .  
      The fourth form of embodiment in  FIG. 6 , which is based on the third form of embodiment in  FIG. 5 , has a third hydraulic motor  125  which is mechanically coupled to the first hydraulic motor  104  and drives the first drive line  105  jointly with the latter, and a sixth hydraulic motor  134  which is mechanically coupled to the fifth hydraulic motor  131  and drives the third drive line  144  jointly with the latter.  
      The third hydraulic motor  125  is interconnected hydraulically with its first connection  126  and with its second connection  127  in a manner entirely analogous to the second form of embodiment of the hydraulic pump  134 . The sixth hydraulic motor  134  is connected by its first connection  135 , via the working conduit  52 , to the first connection  38  of the first partial delivery line  101  of the hydraulic pump  100 , and by its second connection  136 , via the working conduit  53 , to the second connection  38 ′ of the first partial delivery line  101  of said hydraulic pump  100 .  
      Slipping or spinning of the second drive line  110 , and thereby of the second hydraulic motor  109 , is braked by the non-slipping and non-spinning first drive line  105  and the first and third hydraulic motors  104  and  125  coupled thereto and by the non-slipping and non-spinning third drive line  144  and the fifth and sixth hydraulic motors  131  and  134  coupled thereto. On the other hand, slipping or spinning of the first drive line  105  and of the first and third hydraulic motors  104  and  105  coupled thereto, or slipping or spinning of the third drive line  144  and of the fifth and sixth hydraulic motors  131  and  134  coupled thereto, is braked by the non-slipping and non-spinning second drive line  110  and the second hydraulic motor  109  coupled thereto. What has been stated in the description of the second form of embodiment applies to the non-crosswise interconnection of the third and sixth hydraulic motors  125  and  134  with the two partial delivery lines  101  and  102  of the hydraulic pump  100 .  
      A fifth form of embodiment of the hydraulic drive system according to the invention with division of the quantity of hydraulic fluid at the pump, which form of embodiment uses the hydraulic pump  100  with the two partial delivery lines  101  and  102 , is represented in  FIG. 7 .  
      Unlike the fourth form of embodiment in  FIG. 6 , the second hydraulic motor  109  in the fifth form of embodiment in  FIG. 7  is connected by its first connection  108  to the first connection  38  of the first partial delivery line  101  of the hydraulic pump  100 , and by its second connection  112 , via the working conduit  53 , to the second connection  38 ′ of the first partial delivery line  101  of said hydraulic pump  100 . The first connection  132  of the fifth hydraulic motor  131  and the first connection  135  of the sixth hydraulic motor  134  is not connected, as in the fourth form of embodiment, to the first connection  38  of the first partial delivery line  101 , but to the first connection  56  of the second partial delivery line  102  of the hydraulic pump  100 .  
      In spite of the non-crosswise interconnection of the second hydraulic motor  109  with the two partial delivery lines  101  and  102  of the hydraulic pump  100 , slipping or spinning of the said second hydraulic motor  109  is braked by the non-slipping and non-spinning first hydraulic motor  104  or the non-slipping and non-spinning sixth hydraulic motor  134 . That is to say, the first connection  108  of the second hydraulic motor  109  receives the same quantity of hydraulic fluid as before from the first connection  38  of the first partial delivery line  101  of the hydraulic pump  100 , since the first connection  103  of the first hydraulic motor  104  draws the same quantity of hydraulic fluid as before from said first connection  38  of the first partial delivery line  101  of said hydraulic pump  100 . In an analogous manner, the second connection  112  of the second hydraulic motor  109  receives the same quantity of hydraulic fluid as before from the second connection  38 ′ of the first partial delivery line  101 , since the second connection  136  of the sixth hydraulic motor  134  draws the same quantity of hydraulic fluid as before from said second connection  38 ′ of the first partial delivery line  101  of the hydraulic pump  100 .  
      A sixth form of embodiment of the hydraulic drive system according to the invention with division of the quantity of hydraulic fluid at the pump, which form of embodiment uses the hydraulic pump  100  with the two partial delivery lines  101  and  102 , is represented in  FIG. 8 .  
      On the basis of the third form of embodiment in  FIG. 5 , in which the first and fifth hydraulic motors  104  and  131  are connected in parallel, in the sixth form of embodiment in  FIG. 8 , a seventh hydraulic motor  137  is connected in parallel with the second hydraulic motor  109 . The first connection  138  of the seventh hydraulic motor  137  is connected, via the working conduit  54 , to the first connection  56  of the second partial delivery line  102  of the hydraulic pump  100 , and by its second connection  139 , via the working conduit  53 , to the second connection  38 ′ of the first partial delivery line  101  of said hydraulic pump  100 . This seventh hydraulic motor  137  drives a fourth drive line  146  connected to a wheel  145 .  
      Slipping or spinning of the first drive line  105 , and thereby of the first hydraulic motor  104 , or slipping or spinning of the fifth hydraulic motor  131 , which is connected in parallel, and thereby of the third drive line  144 , is prevented by the non-slipping and non-spinning second drive line  110  and the second hydraulic motor  109  coupled thereto, and by the non-slipping and non-spinning fourth drive line  146  and the seventh hydraulic motor  137  coupled thereto, since the first hydraulic motor  104  and the fifth hydraulic motor  131 , which is connected in parallel therewith, are connected in series, via the closed hydraulic circuit, with the second hydraulic motor  109  and the seventh hydraulic motor  137 , which is connected in parallel therewith.  
      A seventh form of embodiment of the hydraulic drive system according to the invention with division of the quantity of hydraulic fluid at the pump, which form of embodiment uses the hydraulic pump  100  with the two partial delivery lines  101  and  102 , is represented in  FIG. 9 .  
      On the basis of the sixth form of embodiment in  FIG. 8 , the first hydraulic motor  104  is mechanically coupled, in a manner analogous to the second form of embodiment in  FIG. 4 , to the third hydraulic motor  125  for the purpose of driving the first drive line  110 , the second hydraulic motor  109  is mechanically coupled, in a manner analogous to the second form of embodiment in  FIG. 4 , to the fourth hydraulic motor  128  for the purpose of driving the second drive line  105 , the fifth hydraulic motor  131  is mechanically coupled, in a manner analogous to the fourth form of embodiment in  FIG. 6 , to the sixth hydraulic motor  134  for the purpose of driving the third drive line  144 , and the seventh hydraulic motor  137  is mechanically coupled to the eighth hydraulic motor for the purpose of driving the fourth drive line  146 . Said eighth hydraulic motor  140  is connected by its first connection  141 , via the working conduit  54 , to the first connection  56  of the second partial delivery line  102  of the hydraulic pump  100 , and by its second connection  142 , via the working conduit  55 , to the second connection  56 ′ of the second partial delivery line  102  of said hydraulic pump  100 .  
      If slipping or spinning of the first, second, fifth or seventh hydraulic motor  104 ,  109 ,  131  or  137  occurs, what has been stated in the description of the sixth form of embodiment applies in an analogous manner. Non-crosswise hydraulic interconnection of the third, fourth, sixth and eighth hydraulic motors  125 ,  128 ,  134  and  140  with the two partial delivery lines  101  and  102  of the hydraulic pump  100  does not result, if slipping or spinning of the third, fourth, sixth and/or eighth hydraulic motors  125 ,  128 ,  134  and/or  140  occurs, in braking of the particular hydraulic motor failing to occur, since the third, fourth, sixth and eighth hydraulic motors  125 ,  128 ,  134  and  140  are mechanically coupled, in each case, to the first, second, fifth and seventh hydraulic motors  104 ,  109 ,  131  and  137 , the braking of which is ensured, in the event of slipping or spinning, because of the cross-wise hydraulic interconnection with the two partial delivery lines  101  and  102  of the hydraulic pump  100 .  
      The invention is not limited to the forms of embodiment represented. The elements described can be combined with one another in any desired manner within the scope of the invention. In this connection, attention may be drawn, in particular, to the hydraulic interconnection which is complementary to the hydraulic interconnection of the hydraulic motors  104 ,  109 ,  125 ,  128 ,  131 ,  134 ,  137  and  140  in the second form of embodiment in  FIG. 4 , the fourth form of embodiment in  FIG. 6 , the fifth form of embodiment in  FIG. 7  and the eighth form of embodiment in  FIG. 9 , and in which, instead of the first connections  103 ,  108 ,  126 ,  129 ,  132 ,  138  and  141 , the second connections  107 ,  112 ,  127 ,  130 ,  133 ,  136 ,  139  and  140  are connected to one another hydraulically in each case.