Abstract:
A motor-pump unit, in particular for a power steering system of a motor vehicle, comprises a housing, a pump, and a drive motor. The pump is constructed as a prefabricated pump module. Both the pump module and the motor are received directly in the housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/EP2004/001488 filed Feb. 17, 2004, the disclosures of which are incorporated herein by reference, and which claimed priority to German Patent Application No. 203 02 534.2 filed Feb. 17, 2003, the disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to a motor-pump unit, in particular for a power steering system of a motor vehicle, comprising a housing, a pump, and a drive motor. 
     Such a motor-pump unit, which can also be used in other areas of application, for example in a rolling stabilizing system, is known from German Utility Model No. 202 05 936.7 and comprises an outer housing, a pump housing and a motor housing. In the known unit, the pump housing and the motor housing are arranged inside the outer housing, which also serves as a storage container for the hydraulic fluid which is to be delivered. 
     The invention provides an extremely compact and favorably priced motor-pump unit, which is distinguished by a simple structure and a simple installation. 
     BRIEF SUMMARY OF THE INVENTION 
     According to the invention, in a motor-pump unit of the type initially mentioned, provision is made that the pump is constructed as a prefabricated pump module and that both the pump module and the motor are received directly in the housing. The housing constitutes an integral housing for all the essential components of the motor-pump unit. A separate housing for the motor can be dispensed with. The installation is simplified, because the pump module is a pre-assembled structural unit which is simply inserted into the housing. As the motor-pump unit according to the invention has fewer and simpler interfaces, the tolerance problem is also simplified. 
     In the preferred embodiments of the invention, the motor is a wet rotor motor, so that it can be fluid-cooled. The motor can be an inside rotor electric motor, which is distinguished by its compactness, or alternatively an outside rotor electric motor. 
     According to a further development of the invention, a sensorless motor control is provided. The elimination of Hall sensors or the like for closed-loop control of the motor permits a more compact design of the structural space for the motor. During installation of the motor, no tolerances have to be taken into consideration with respect to the position of the motor relative to such sensors. 
     Preferably, in the housing a motor space is formed which serves as a hydraulic fluid reservoir, from which the pump module sucks hydraulic fluid. The flow which is thereby automatically introduced in the motor space regulates the heat balance of the motor, because the motor heat occurring in operation can be taken up by the hydraulic fluid in an optimum manner and carried away. The emission of thermal energy of the motor to the hydraulic fluid in addition improves the cold start performance of the hydraulic pump. The effective utilization of the motor space as main component of the hydraulic fluid reservoir of the motor-pump unit in addition allows the part of the hydraulic fluid reservoir which is provided for volume equalization to be designed so as to be very compact. 
     In the housing an electronic unit arranged adjacent to the motor space can be received, which is constructed on a carrier plate, the carrier plate sealing the motor space. Therefore, all the motor, electronic and pump components are held in a single housing. The electronic unit can contain power electronics components, which are arranged on a side facing away from the motor space, or alternatively on a side of the carrier plate facing the motor space. According to the first alternative mentioned, the power electronics components are protected from contact with the hydraulic fluid and are cooled indirectly by the dissipation of heat via the carrier plate to the hydraulic fluid. According to the second alternative mentioned, the power electronics components are cooled directly by the hydraulic fluid. 
     In the preferred embodiments, a resonator space is provided for the reduction of pulsations, which occur in particular with the use of an outside gear pump. The resonator which is formed in this way can be constructed largely independently of the pump, i.e. the rigidity of the resonator walls can be designed independently of the actual pump function. This promotes an optimum design of the damping behavior. 
     According to a first embodiment, the resonator space is formed in the housing and is closed by a resonator cover which is constructed as a flat punched part. Such a resonator cover is sturdy and can be produced at a favorable cost. According to a second embodiment, the resonator space is formed substantially by a bell-shaped resonator cover, which is mounted on the housing. Such a cover can be constructed as a diecast or deep-drawn part. Both embodiments are distinguished by the direct or indirect integration of the resonator into the housing, in contrast to conventional motor-pump units, in which a resonator is constructed in the pump or is arranged as a separate component for example on an end face of the pump. 
     In the resonator cover, preferably a combined pressure control and non-return valve is installed, which brings savings of time and cost compared with an installation of individual valves. 
     The arrangement of the pump module in the resonator space proves to be particularly space-saving, which leads to an extremely compact structure of the pump with the associated components. This further development of the invention is based on the finding that instead of a separate resonator or a resonator provided in the pump, the reduction of the pressure pulsations generated by the pump can also be achieved by a resonator space filled with hydraulic fluid and surrounding the pump module. 
     A very effective mounting of the pump module is achieved in that the pump module is mounted in the housing at least in a supporting manner by a differential force on a wall delimiting the motor space, the differential force resulting from surfaces of different size, acted upon with pressure by the hydraulic fluid, on the side of the pump module facing the motor or facing away from the motor. In this way, a coupling to the motor can be achieved without screws which may become loose in the course of time, and without or with simpler damping or equalization elements, a good acoustic disconnection of the pump module from the housing being provided. In addition, the installation costs and the installation effort are reduced. 
     The installation of the motor-pump unit according to the invention can be further simplified by the motor and preferably also the electronic unit being able to be installed from a first side of the housing and the pump module and preferably also the resonator cover and the container cover from a second side. 
     The housing is preferably constructed in one piece as a diecast part or formed from diecast and deep-drawn parts. 
     Other advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exploded view of a motor-pump unit according to the invention in accordance with a first embodiment; 
         FIG. 2  shows a sectional view of the motor-pump unit of  FIG. 1 ; 
         FIG. 3  shows a view, partially in section, of a variant of the motor-pump unit in accordance with the first embodiment; and 
         FIG. 4  shows a simplified exploded view of a motor-pump unit according to the invention in accordance with a second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In  FIGS. 1 and 2 , a motor-pump unit  10  is shown, the illustrated orientation of the motor-pump unit  10  corresponding approximately to the later installation position in a motor vehicle. The motor-pump unit  10  comprises a drive motor  12 , an electronic unit  14 , and a pump module  16 . These components of the motor-pump unit  10  are received in a housing  18  which is open on two sides. The lower side of the housing  18  is closed by a housing cover  20 . In the housing  18 , a motor space  22  (see  FIG. 2 ) and a resonator space  24  are formed, which is closed by a resonator cover  26 . In the resonator cover  26 , a combined pressure control and non-return valve  28  is mounted. The motor-pump unit  10  additionally comprises a cup-shaped container cover  30  with a cap  32  and a return connection  34 . The container cover  30  closes the upper side of the housing  18  and delimits a hydraulic fluid reservoir, the interior of the housing  18  being constructed substantially “open”, so that all the components of the motor-pump unit  10  received in the housing  18  are surrounded by hydraulic fluid. 
     The drive motor  12  of the unit is therefore constructed as a wet rotor motor and is an integral component of the internal fluid circuit. The motor  12  is an inside rotor electric motor, mounted in the housing  18 , with a rotor  36 , a shaft  38  connected with the rotor  36 , and a stator  40  arranged around the rotor  36 . The corresponding bearing region of the housing  18  is constructed as a pin which receives two ball bearings and one or two sliding bearings or a hydrodynamic bearing unit. Alternatively to the inside rotor motor, the motor may also be constructed as an outside rotor motor. A sensorless controlling of the motor is provided, i.e. the open- and closed-loop control of the motor takes place without a Hall sensor arrangement. 
     The electronic unit  14  contains the electronic components necessary for operating and controlling the motor-pump unit  10 . The electronic unit  14  constitutes an independent module and is constructed on a carrier plate  42  (e.g. of aluminum). The carrier plate  42  on the one hand constitutes a thermal capacity to receive the heat produced in the electronic components, and on the other hand it serves as a plate for sealing against the motor space  22  and therefore promotes the transfer of heat to the hydraulic fluid. The power electronics components of the electronic unit  14  are arranged on the side of the carrier plate  42  facing away from the motor space  22 , so that they are cooled indirectly by the hydraulic fluid through the emission of heat to the carrier plate  42 , the side of which facing the motor space  22  is in contact with the hydraulic fluid. Alternatively, the power electronics components can also be arranged on the side facing the motor space  22 , so that a direct cooling by the hydraulic fluid takes place. 
     The compact pump module  16  forms a pre-assembled structural unit and contains all the essential pump components. The pump module  16  is preferably constructed as an outside gear pump, but other types of pump may also be realized. The pump module  16  is placed inside the resonator space  24 , which is described in more detail further below, and is coupled to the shaft  38  of the motor by means of a coupling  44 . For a correct positioning of the pump module  16 , positioning pins are formed integrally with the pump module  16 . An actual fastening of the pump module  16  to the wall, delimiting the motor space  22 , in the housing  18  is not absolutely necessary, because the pump module  16  in the resonator space  24  filled with hydraulic fluid is pressed against this wall by a differential force on application of pressure after the start-up of the pump module  16 . The differential force results from surface areas of different sizes, which are acted upon with pressure, with respect to the side of the pump module  16  facing the motor  12  and the side facing away from the motor  12 . Alternatively or in addition, however, a fastening of the pump module  16  can be provided, for example by a screw connection. 
     The resonator of the motor-pump unit  10  formed by the resonator space  24  serves to reduce the pulsations of the hydraulic fluid caused in particular by an outside gear pump, the resonator being constructed as a largely integral component of the housing  18 . The resonator is closed by the resonator cover  26 , a largely flat punched metal part. The resonator cover  26  is fastened by screws on the housing  18 , but can alternatively also be constructed as a screw cover. 
     Instead of the combined pressure control and non-return valve  28  mounted in the resonator cover  26 , alternatively also two corresponding individual valves can be provided, the valves or the components thereof being able to be mounted at least partially also in the resonator region of the housing  18  or integrated therein. 
     A main component of the hydraulic fluid reservoir of the motor-pump unit  10  is constituted by the motor space  22 , from which the pump sucks hydraulic fluid. The remaining region of the reservoir for volume equalization, principally arranged around the resonator, is of a very compact configuration. However, this region can alternatively also be constructed as a separate equalization tank connected to the motor-pump unit  10  by a hose, or as an equalization connection piece arranged on the motor-pump unit  10 . 
     The housing  18  is preferably constructed as a diecast part or as a combination of diecast and deep-drawn parts. As already mentioned, the housing  18  contains parts of the resonator and of the hydraulic fluid reservoir. In addition, the housing  18  has a pressure outlet and several outer fastening points  48  in the central housing region (in relation to the height of the housing). 
     The structure of the motor-pump unit  10  is designed such that the motor components and the electronic components can be installed into or onto the housing  18  from one side and the hydraulic components (in particular pump module  16 , resonator cover  26 , pressure control and non-return valve  28 ) from the opposite side. 
     In  FIG. 3  a variant of the motor-pump unit  10  according to the invention is illustrated, in which the installation takes place the other way round, for reasons of structural space. Apart from the reversed orientation, according to which the pump module  16  is arranged under the motor  12 , the structure is largely unchanged. The pressure control and non-return valve  28 , however, is not held here in the resonator cover  26 , but rather is arranged in the housing region between the pump module  16  and the motor  12  such that it discharges into the motor space  22 . 
     In the embodiment of the motor-pump unit  10  shown in  FIG. 4 , in contrast to the embodiment previously described, the resonator space  24  is defined substantially by a bell-shaped resonator cover  26 ′. The bell-shaped resonator cover  26 ′ is not constructed here as a flat punched part, but rather as a diecast or deep-drawn part. 
     In accordance with the provisions of the patent statutes, the principle and mode of operation of this invention have been explained and illustrated in its preferred embodiments. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.