Abstract:
A positive displacement pump for pumping oil in a motor vehicle transmission comprises a pump stage that has a central kidney-shaped suction cavity and two kidney-shaped pressure cavities. Oil is selectively pumped via one kidney-shaped pressure cavity or the other kidney-shaped pressure cavity in accordance with the direction of rotation of the pump stage. This makes it possible to create, with little complexity, two operating stages for the positive displacement pump.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of PCT Application PCT/EP2015/075458, filed Nov. 2, 2015, which claims priority to German Application DE 10 2014 222 396.2, filed Nov. 3, 2014. The disclosures of the above applications are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a positive displacement pump, in particular for conveying oil in a gearbox or a combustion engine of a motor vehicle, having a pump stage that is driven by a drive unit, having a suction port for introducing oil and a pressure port for delivering oil and having a switchover device for creating two operating stages. 
       BACKGROUND OF THE INVENTION 
       [0003]    Such positive displacement pumps are used in modern-day motor vehicles, for example for conveying lubricating oil in the combustion engine or gear oil in the gearbox, and are known from practice. The areas of application mostly have different design points; however, these design points are achieved by means of corresponding operating stages of the pump stage and of the drive unit. The design points relate in particular to a small conveying quantity at high pressure or a large conveying quantity at low pressure, according to the operating state of the gearbox or of the combustion engine. 
         [0004]    A positive displacement pump has become known from DE 36 14 819 C2, in which a supply is provided to a high-pressure circuit and a low-pressure circuit by means of a divided kidney-shaped pressure cavity. The pump stage also has two pump chambers separated by a center wall. 
       SUMMARY OF THE INVENTION 
       [0005]    The invention is based on the problem of designing a positive displacement pump of the type initially mentioned so that it has a particularly compact structure. 
         [0006]    This problem is solved according to the invention by virtue of the fact that the suction port is connected to a central kidney-shaped suction cavity and the pressure port is connected to two kidney-shaped pressure cavities according to the selected operating stage. 
         [0007]    This configuration allows the suction and kidney-shaped pressure cavities to be arranged on one side of the housing. The positive displacement pump is thus particularly compact. The position and size of the kidney-shaped pressure cavities is adapted to the desired conveying volumes and conveying pressures of the intended design points. By connecting the respective kidney-shaped pressure cavity to the single pressure port, the operating stage that is appropriate to the design point is selected. The rotational speed and the torque of the drive unit may thus be adapted to the operating stages in a simple manner and the degree of efficiency is increased. 
         [0008]    According to another advantageous refinement of the invention, the switchover device is particularly simple if the switchover device is connected to the drive unit for the purpose of selectively controlling the drive direction of the pump stage. This configuration allows the operating stages to be established by the direction of rotation of the drive unit. In the simplest case, the switchover device requires switches for setting the polarity of an electric motor of the drive unit. 
         [0009]    According to another advantageous refinement of the invention, the control of the flow from the kidney-shaped pressure cavities to the pressure port is particularly simple if the two kidney-shaped pressure cavities are connected to the single pressure port via check valves. 
         [0010]    According to another advantageous refinement of the invention, pressure equalization of the kidney-shaped pressure cavity not used in the respective operating stage with the environment is ensured in a simple manner if the two kidney-shaped pressure cavities are connected to the suction port via check valves. The check valves connecting the kidney-shaped pressure cavities to the suction port are aligned in such a manner that, in case of negative pressure in the kidney-shaped pressure cavity, oil may flow in. 
         [0011]    According to another advantageous refinement of the invention, the constructional complexity for connecting the pressure port to the selected kidney-shaped pressure cavity is kept particularly low if the switchover device is designed for connecting the pressure port to one or the other of the kidney-shaped pressure cavities. 
         [0012]    According to another advantageous refinement of the invention, a large number of check valves is avoided in a simple manner if a multi-directional valve is connected downstream of the pump stage and if the switchover device is designed for activating the multi-directional valve, so that a selective connection of one kidney-shaped pressure cavity or the other kidney-shaped pressure cavity to the pressure port is established. As a result of this, the number of components susceptible to faults is kept low. It is simultaneously ensured that in each case only the intended kidney-shaped pressure cavity is connected to the pressure port. A further advantage of this configuration is that the positive displacement pump is consequently of particularly compact structure. In the case of a positive displacement pump intended for conveying oil in a gearbox of the motor vehicle, the multi-directional valve may, in the simplest case, be arranged in a gearbox control system that is present anyway. As a result of this, the installation space required for the positive displacement pump is kept particularly small. 
         [0013]    According to another advantageous refinement of the invention, pressure equalization of the kidney-shaped pressure cavity not used in the respective operating stage with the environment is realized in a simple manner, when using a multi-directional valve, if the multi-directional valve has two switching stages, wherein the switching stages are configured for connecting the suction port to the kidney-shaped pressure cavity not used in the respective operating stage. 
         [0014]    According to another advantageous refinement of the invention, a drop in the oil pressure in the gearbox or the combustion engine, with the positive displacement pump switched off, is avoided in a simple manner if the multi-directional valve has a switching stage in which the pressure port is shut off. 
         [0015]    According to another advantageous refinement of the invention, in case of use in a motor vehicle, the positive displacement pump has a long service life if the pump stage is designed as an internal gear pump or as a G-rotor pump. Of course, it is also possible for two pump stages arranged in parallel to be able to be driven by a single drive unit. 
         [0016]    According to another advantageous refinement of the invention, differing conveying volumes and conveying pressures is established in a simple manner in the operating stages if a separation region between the kidney-shaped suction cavity and one of the kidney-shaped pressure cavities, in the case of the pump stage designed as an internal gear pump, is arranged inside the region of maximum eccentricity between an inner rotor and an outer rotor and another separation region of the kidney-shaped suction cavity and the other of the kidney-shaped pressure cavities is arranged outside the region of maximum eccentricity. 
         [0017]    Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The invention permits numerous embodiments. For the purpose of further clarifying its basic principle, several of the embodiments are illustrated in the drawing and are described below. The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0019]      FIG. 1  is a diagrammatic illustration of a positive displacement pump, according to embodiments of the present invention; 
           [0020]      FIG. 2  is a sectional view of a pump stage with adjacent regions of a positive displacement pump, according to embodiments of the present invention; 
           [0021]      FIG. 3  is a sectional view of an alternate embodiment of a pump stage with adjacent regions of a positive displacement pump, according to embodiments of the present invention; and 
           [0022]      FIGS. 4 a -4 c    are sectional views of various switching positions of a multi-directional valve used as part of a pump stage of a positive displacement pump, according to embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
         [0024]      FIG. 1  diagrammatically shows a positive displacement pump  1  having a motorized drive unit  2  and a pump stage  3 . The motorized drive unit  2  is connected to a switchover device  4  and selectively drives the pump stage  3  in one or the other direction of rotation. The positive displacement pump  1  has a suction port  5 , via which oil is sucked in from a tank  6  or an oil pan, and a pressure port  7 , via which oil is conveyed to a consumer (not shown), such as lubrication points of a combustion engine or of a gearbox of a motor vehicle. The pump stage  3  is connected to the pressure port  7  and to the suction port  5  via a total of four check valves  8 - 11 . 
         [0025]    As  FIG. 2  diagrammatically shows in a sectional illustration, the pump stage  3  from  FIG. 1  has two kidney-shaped pressure cavities  12 ,  13  and one central kidney-shaped suction cavity  14 . Oil is sucked in via the kidney-shaped suction cavity  14  in both directions of rotation of the pump stage  3 . The kidney-shaped pressure cavities  12 ,  13  are connected to the pressure port  7  via two of the check valves  8 ,  9 . Furthermore, the kidney-shaped pressure cavities  12 ,  13  are connected to the suction port  5  via the further check valves  10 ,  11 . The pump stage  3  is designed as an internal gear pump and has an inner rotor  15  and an outer rotor  16 . The kidney-shaped suction cavity  14  and the kidney-shaped pressure cavities  12 ,  13  are arranged in a housing  17  that seals off the front faces of the rotors. 
         [0026]    In the case of a rotation of the inner rotor  15 , as a result of a corresponding current feed to the drive unit  2 , in the anticlockwise direction, oil is sucked in from the tank  6  or the oil pan via the central kidney-shaped suction cavity  14  and conveyed to the pressure port  7  via the kidney-shaped pressure cavity  12  illustrated on the left in the diagram. 
         [0027]    In case of negative pressure, the kidney-shaped pressure cavity  13  illustrated on the right in the diagram also sucks in oil from the suction port  5  and thus complements the function of the kidney-shaped suction cavity  14 . The connection of the kidney-shaped pressure cavities  12 ,  13  to the suction port  5  or the pressure port  7  is realized via the check valves  8 - 11 . In case of the inner rotor  15  being driven in the clockwise direction, the oil is conveyed to the pressure port  7  via the kidney-shaped pressure cavity  13  illustrated on the right in the diagram.  FIG. 2  furthermore shows that the pump stage  3  has separation regions t 1 , t 2  of differing sizes between the common kidney-shaped suction cavity  14  and the kidney-shaped pressure cavities  12 ,  13  that are used, according to the selected direction of rotation. The kidney-shaped suction cavity  14  is arranged outside the region of maximum eccentricity of the pump stage  3 . Consequently, one of the separation regions t 1  is arranged in the region of maximum eccentricity and the other of the separation regions t 2  is arranged outside the maximum eccentricity. Additionally, the kidney-shaped pressure cavities  12 ,  13  have differing dimensions, so that the pump stage  3  has differing conveying pressures and conveying volumes according to the kidney-shaped pressure cavity  12 ,  13  that is used for conveying. 
         [0028]      FIG. 3  diagrammatically shows a further embodiment of a pump stage  18 , which differs from the embodiment of  FIG. 2  only in that a multi-directional valve  19  is provided for controlling two kidney-shaped pressure cavities  20 ,  21  with the suction port  23  and with the pressure port  24 . One kidney-shaped suction cavity  22  is, as in the case of the embodiment according to  FIG. 2 , connected to the suction port  23  without control. Control lines for controlling the multi-directional valve are illustrated in dotted form in the drawing, via which lines the position of the multi-directional valve  19  is controlled according to the direction of rotation of the pump stage  18 . Alternatively, the multi-directional valve  19  may be connected to the switchover device  4  illustrated in  FIG. 1  and is activated at the same time as the switchover of the direction of rotation of the pump stage  18 . 
         [0029]    The multi-directional valve  19  has three switching positions, wherein one of the switching positions shuts off the kidney-shaped pressure cavities  20 ,  21  and the pressure port  24 . 
         [0030]      FIGS. 4 a  to 4 c    show a multi-directional valve  25  which, for example, is used in the embodiment according to  FIG. 3  and has a valve body  26  and a valve housing  27 . The multi-directional valve  25  respectively has a port  28 ,  29  which is led to a kidney-shaped pressure cavity, a suction port  30  and two pressure ports  31 . In the middle position illustrated in  FIG. 4 a   , all ports  28 - 31  are closed. In  FIGS. 4 b  and 4 c   , one or the other of the ports  28 ,  29  that is led to the kidney-shaped pressure cavities is selectively connected to the pressure port  31 . At the same time, the port  29 ,  28  not used for conveying oil in each case is connected to the suction port  30 . Spring elements  32 ,  33  preload the multi-directional valve  25  into the middle position illustrated in  FIG. 4 a   . The position of the valve body  26  may, for example, be controlled by the switchover device  4  by means of an electromagnet (not shown). Control lines  34 ,  35  are provided for controlling the multi-directional valve  25 , via which lines the position of the multi-directional valve  19  is controlled according to the direction of rotation of the pump stage  18 . 
         [0031]    The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.