Abstract:
A hydrostatic-mechanical transmission having a radial piston motor ( 1 ) with a crankshaft ( 2 ) which drives a spur gear ( 7 ). A transmission housing comprises three housing portions which define two separate spaces. The spur gear arrangement is located in one of the spaces while the radial piston motor is located in the other space.

Description:
This application claims priority from German patent application serial no. 10 2006 043 289.4 filed Sep. 14, 2006. 
     FIELD OF THE INVENTION 
     The invention relates to a hydrostatic-mechanical transmission. 
     BACKGROUND OF THE INVENTION 
     DE 10 2004 023 631 A1 discloses a hydrostatic-mechanical transmission having a radial piston motor with a crankshaft, the crankshaft driving a spur gear which is actively connected with another spur gear and powers the drive output. 
     Transmissions of this type are used for example in working machines such as wheel loaders. 
     The purpose of the present invention is to provide a hydrostatic-mechanical transmission which is of compact structure and built to ensure reliable operation. 
     SUMMARY OF THE INVENTION 
     According to the invention, the hydrostatic-mechanical transmission comprises at least one radial piston engine having a crankshaft that drives a spur gear. The transmission housing consists of three transmission housing portions which form at least two spaces, such that the spur gear transmission is located in a first space formed by a first and second housing portion, and the radial piston motor is located in a second space formed by the second and a third transmission housing portion. In particular, the cylinders of the radial piston motor are mounted in the second and third housing portions. This makes it possible to connect a valve housing to the third housing portion to accommodate the valves and the pressure medium inlets for the radial piston motor. Since the second housing portion separates the first space from the second space, the first space can be sealed tight against pressure fluid relative to the second space, so that for example the spur gear transmission can be supplied with a lubricant different from that supplied to the radial piston motor. 
     Furthermore, leakage from the radial piston motor can be drained into the second space, which can for example be connected by lines to a cooler, and the leaked oil can then be passed into a pressure medium reservoir via the cooler. 
     In a further embodiment a flushing valve is arranged in the valve housing, through which hot pressure medium passes from the radial piston motor into the second space, through which, after mixing with the leakage, the pressure medium and the leaked oil are transferred via the cooler. This arrangement enables a very compact hydrostatic-mechanical transmission to be made, which can be operated with different lubricants and in which the radial piston motor is protected against overheating by simple means. 
     Preferably, the crankshaft is supported at three bearing points, whereby the dimensions of the crankshaft can be such that at the maximum permissible deflection under load, the structural space available need not change. Preferably, one bearing point is located between the spur gear and the eccentric portion of the crankshaft and the other two bearing points are respectively in the area of the crankshaft&#39;s ends. 
     In a further embodiment of the invention the spur gear has with spiral toothing and the two bearings, close to the eccentric portion of the crankshaft, are conical roller bearings, whereby the conical roller bearing located in the area of the pressure medium inlet to the cylinders produces an axial force component that opposes the hydraulic force in the area of the pressure medium distributor, so that distortion of the housing portion in which the pressure medium inlets are located is reduced. Since the spur gear has bearing points on both sides, the radial force produced by the co-operation of the spur gears is transferred directly to the transmission housing, and this too reduces the distortion of the crankshaft under load. Since the pressure medium distributor is connected with the crankshaft via a connecting shaft, this reduction of the crankshaft&#39;s distortion also reduces the radial movement of the pressure medium distributor. 
     In another embodiment of the invention the transmission housing consists of three transmission housing portions: 
     a first housing portion in which the spur gears and the first bearing point in the area of the spur gear are located, 
     a second housing portion, which forms the middle bearing point between the spur gear and the eccentric part of the crankshaft, and 
     a third housing portion, which holds the third bearing point and contains the pressure medium inlets. 
     Connected to the third housing portion is a valve housing that contains the pressure medium distributor and the pressure medium connections and other valves, this structure makes it possible for the first and second housing portions to provide a lubricant space within which the spur gears are arranged, the second and third housing portions to provide a lubricant space in which the main components of the radial piston motor are arranged, and the valve housing to hold the valve components. 
     Preferably, the lubricant space containing the spur gears and the lubricant space containing the radial piston motor are sealed to be fluid-tight relative to one another. 
     In a further embodiment the spur gear actively connected with the crankshaft drives another spur gear, which powers the drive output, which has either two output flanges, one at each end of the drive output shaft, or one output flange and a bevel pinion, in order to incorporate the hydrostatic-mechanical transmission either between the front and rear axles of the vehicle, so as to drive the front and rear axles, or to incorporate it directly on the rear axle, so that the other axle is driven by the remaining drive flange via a Cardan shaft. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features emerge from the description of the figures, in which: 
         FIG. 1  in a sectional view through the hydrostatic-mechanical transmission with a radial piston motor; 
         FIG. 2  in a sectional view through the radial piston motor of the hydrostatic-mechanical transmission in  FIG. 1 ; 
         FIG. 3  in a sectional view through a hydrostatic-mechanical transmission with two radial piston motors; 
         FIG. 4  in a sectional view through the radial piston motors of the hydrostatic-mechanical transmission in  FIG. 3 ; 
         FIG. 5  in a sectional view through the other radial piston motor of the hydrostatic-mechanical transmission in  FIG. 3 ; 
         FIG. 6  is a hydraulic layout of the hydrostatic-mechanical transmission in  FIG. 1 ; and 
         FIG. 7  is a hydraulic layout of the hydrostatic-mechanical transmission in  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a hydraulic radial piston motor  1  with a crankshaft  2  having an eccentric section  3  with a cylinder  4 , which is mounted on one side in the third housing portion  5  and the second housing portion  6 . The crankshaft  2  is connected in a rotationally fixed manner to a first spur gear  7 . The first spur gear  7  is actively connected with a second spur gear  8 , which drives a drive output shaft  9 . If the driveshaft  9  has a pinion  10  and an output flange  11 , the hydrostatic-mechanical transmission can be incorporated directly on a drive axle, but the drive output shaft  9  can also be fitted, on each side, with an output flange  11 , so that the hydrostatic-mechanical transmission can be arranged between the drive axles. 
     Preferably, the first spur gear  7  and the second spur gear  8  are made with spiral toothing. The crankshaft  2  is mounted on a first bearing  12 , a second bearing  13  and a third bearing  14 . The first bearing  12  is located in the first housing portion  15  and forms the first bearing point. The second bearing  13  is located between the spur gear  7  and the eccentric section  3  in the second housing portion  6  and forms the second bearing point. For this, the second housing portion  6  has a housing wall  16 . The third bearing  14  is located in the third housing portion  5  and forms the third bearing point. Via a connecting shaft  17 , which can also be made integrally with the crankshaft  2 , the latter drives a pressure medium distributor  18 . Thanks to the special mounting of the crankshaft  2  its distortion under load is reduced, and this also improves the function of the pressure medium distributor  18 . The pressure medium distributor  18  is located in a valve housing  19 , which also contains the valves and main connections needed for the pressure medium supply  20 . Together with the second housing portion  6 , the first housing portion  15  forms a lubricant (first) space  21  which is sealed relative to the (second) space  22  by a seal  23  thus preventing leakage of pressure fluid between them. This enables different lubricants to be used in the (first and second) spaces  21  and  22 . The valves in the valve housing and any leakage from the radial piston motor  1  flow into the space  22  and pass from there, via a line (not shown) and a cooler  39 , into an external lubricant reservoir  40 . The cylinder  4  has bearing trunnions  24  by means of which the cylinder  4  is mounted and able to rotate, and which are in active connection with a rotation angle sensor, by means of which the ballast volume of the hydraulic motor can be determined. This signal serves as a control magnitude to enable appropriate regulation of the ballast volume of the hydraulic motor. The second spur gear  8  is shielded by a shield  25  in order to reduce splashing losses when the second spur gear  8  is rotating. The shield  25  is preferably made in two parts, and both can be made from a plastic, for example a polyamide. The shield  25  has at least one projection,  26  which engages in a recess  27  to fix the position of the shield  25 . The two individual parts of the shield  25  are plugged together in the axial direction and are in contact with the first housing portion  15  and the second housing portion  6  in the axial direction, so that the shield  25  remains closed. The bearing trunnions  24  have surfaces (not shown) extending in the axial direction, which prevent hydraulic pressure from building up between the blind-hole bore in the second housing portion  6  or in the third housing portion  5  and the bearing trunnion  24 , which would push the second housing portion  6  and the third housing portion  5  apart. 
       FIG. 2  shows the radial piston motor  1  has a crankshaft  2  whose eccentric section  3  moves pistons  28  in the cylinders  4 . 
       FIG. 3  shows the hydrostatic-mechanical transmission in  FIG. 3  differs from the hydrostatic-mechanical transmission in  FIG. 1 , in that there are two radial piston motors, each radial piston motor driving a spur gear actively connected with the spur gears arranged on a drive output shaft  9 . The first radial piston motor  1  drives the first spur gear  7 , which actively connected with the second spur gear  8  and which drives the drive output shaft  9 . The second radial piston motor  29  (see  FIG. 4 ) drives a third spur gear  30  (see  FIG. 5 ), which is actively connected with a fourth spur gear  31  that drives the drive output shaft  9 . 
       FIG. 4  shows the first radial piston motor  1  and the second radial piston motor  29  are actively connected with the drive output shaft  9 . 
       FIG. 5  shows the second radial piston motor  29  drives the fourth spur gear  31  via the third spur gear  30 , and thereby the drive output shaft  9 . 
       FIG. 6  shows the first spur gear  7  and the second spur gear  8  are located within the space  21 . In the space  22  are arranged the radial piston motor  1  and its stroke volume adjustment device  32 . The valve housing  19  accommodates the 4/2 proportional valve  33  for adjusting the stroke volume, the two-way valve  34  and the flushing valve  35  with its associated pressure limiting valve  36 . The valve housing  19  also contains the connections  20  for the main pressure medium supply. The valves in the valve housing  19  are vented through the line  37  leading to the space  22  and from there, through the line  38  and the cooler  39  into a pressure medium reservoir  40 . Thus, the radial piston motor  1  is cooled sufficiently and the hydrostatic-mechanical drive has only a small number of connections. 
       FIG. 7  shows the first radial piston motor  1  with its stroke volume adjustment device  32  and the second radial piston motor  29  with its stroke volume adjustment device  41  are in the space  22 , and the spur gears  7 ,  8 ,  30  and  31  are in the space  21 . The valve housing  19  also has a cut-off valve  42  by means of which the first radial piston motor  1  can be fully connected to the space  22 , whereby the radial piston motor  1 , when its stroke volume is adjusted to zero, can be operated at very high speed since it is completely separate from the high-pressure inlet and heat losses can be dissipated through the connection with the space  22 . Accordingly, it is no longer necessary to arrange a cut-off clutch between the first radial piston motor  1  and the first spur gear  7 . 
     INDEXES 
     
         
           1  Radial piston motor 
           2  Crankshaft 
           3  Eccentric section 
           4  Cylinder 
           5  Third housing portion 
           6  Second housing portion 
           7  First spur gear 
           8  Second spur gear 
           9  Drive output shaft 
           10  Pinion 
           11  Drive output flange 
           12  First bearing 
           13  Second bearing 
           14  Third bearing 
           15  First housing portion 
           16  Housing wall 
           17  Connection shaft 
           18  Pressure medium distributor 
           19  Valve housing 
           20  Connections 
           21  Space 
           22  Space 
           23  Seal 
           24  Trunnions 
           25  Shield 
           26  Projection 
           27  Recess 
           28  Piston 
           29  Second radial piston motors 
           30  Third spur gear 
           31  Fourth spur gear 
           32  Stroke volume adjustment device 
           33  4/2 proportional valve 
           34  Two-way valve 
           35  Flushing valve 
           36  Pressure-limiting valve 
           37  Line 
           38  Line 
           39  Cooler 
           40  Pressure medium reservoir 
           41  Stroke volume adjustment device 
           42  Cut-off valve