Electric drive unit

An electric drive unit includes an electric motor for driving a fan. The motor has an electronic control module. An impeller wheel for producing a working air flow is mounted by bearings on an axle of the electric motor. The hub of the impeller wheel has at least one preferably two walls enclosing a cooling space or cooling space portions. At least one cooling surface of a cooling body is in contact with components of the electronic control module and projects into the cooling space. A gap formed between the hub of the impeller wheel and a carrier section communicates with an inner hub space. Holes (43, 322) communicating with the hub inner space are provided in at least one component of the electric drive unit. When the impeller wheel rotes a convection cooling air flow is established between the gap and the holes.

TITLE OF THE INVENTION

1. Field of the Invention

The invention relates to an electric drive unit with a motor cooling arrangement.

2. Background Information

Electrical drive units are used in a multitude of application areas, for example in home appliances or in the area of motor vehicles. Particularly in motor vehicles, different movable components of the motor vehicle can be adjusted by means of electrical drive units, for example seats, window lifters, sun roofs, etc., or components may be operated with a variable r.p.m. (for example fans). Electrical drive units used for ventilation comprise an electric motor (fan motor) functioning as a drive device for providing electrical drive power, an electronic control module for controlling the electric motor, for example for the r.p.m. and power regulation (closed loop control) of the electric motor and a rotatable impeller wheel driven by the electric motor as a work performing mechanism for producing a working airflow.

The electronic control module comprises structural components which, as a rule, are mounted on a printed circuit board. These structural components include particularly also power components with a high dissipation power because in the operation of the electric drive unit frequently currents flow with a very high amperage, for example 50 A. Accordingly, a high input power of the electrical drive unit and thus of the power components results. Therefore, a sufficient cooling for the electronic control module, particularly for the structural components of the electronic control module, must be provided especially for the dissipation of the power loss of the structural power components. For this purpose the structural components of the electronic control module or at least the power components thereof, are brought into contact with cooling surfaces of a cooling body. More specifically, the power components are mounted on these cooling surfaces of the cooling body.

In order to assure a compact construction and thus a small structural size of the electric drive unit, it is necessary on the one hand to build the electronic control module and the electric motor mounted on a motor carrier as small as possible while on the other hand positioning the electronic control module as close as possible to the electric motor. Particularly, the electronic control module should be directly connected to the motor carrier. In this case achieving a sufficient cooling of the structural components of the electronic control module poses a problem, particularly the dissipation of the power loss of the structural power components because the possibilities of cooling these components are substantially limited or even not available at all. In the German Patent Publication DE 41 22 529 A1, the surface of the motor carrier functioning as a cooling body is increased by forming a ring wall for the motor carrier which extends into the area of the rotor of the electric motor, whereby the heat dissipation is improved without any increase in the space requirement for the electric drive unit.

SUMMARY OF THE INVENTION

It is the object of the invention to provide a compact electric drive unit in which a simple, reliable and cost effective construction and operation are made possible in combination with an efficient cooling of the electronic control module, particularly the power components and other elements of the drive unit.

In the present electric drive unit the cooling of the structural components of the electronic control module, particularly of the power components of the electronic control module is realized by a cooling body having at least one cooling surface in contact with the structural components to be cooled. The present drive unit comprises an impeller wheel set on the rotational axis of the electric motor provided as a drive device. The impeller wheel acts as a work unit for producing a working air stream. In the present unit at least one cooling surface, preferably all cooling surfaces are at least partially, preferably completely, reaching into the hub of the impeller wheel. Stated differently at least one cooling surface extends at least partially into the hub of the impeller wheel. For this purpose the impeller wheel is constructed with a double wall including an outer wall and an inner wall and a hub inner space formed between the outer wall and the inner wall. The cooling surfaces of the cooling body are extended into the hub inner space of the impeller wheel. Hub chambers are formed in the hub inner space between the outer wall and the inner wall by radially extending ribs (lands) which cause a stiffening of the hub of the impeller wheel. The cooling surfaces of the cooling body that reach into the hub of the impeller wheel are introduced into the hub inner space up to the vicinity of these ribs, preferably directly bordering on these ribs. When the impeller wheel is set on the rotational axis of the electric motor, a gap is formed between the hub of the impeller wheel and a carrier section. The carrier section serves for supporting the electric motor and the electronic control module as well as for the securing of the electric drive unit. For example, the gap is formed between the outer wall of the hub of the impeller wheel and a casing forming a central part of the carrier section. Further, through-holes are formed at a suitable location of the electric drive unit for the air present in the hub inner space. Preferably the through-holes are formed in the hub of the impeller wheel, particularly as bores on the upper side of the hub of the impeller wheel and/or in the rotor of the electric motor. The through-holes are formed particularly as longitudinal holes on the top side of the rotor and/or on the bottom side of the carrier section, particularly on the underside of the casing functioning as a central part of the carrier portion. During the operation of the electric drive unit and due to the rotation of the impeller wheel, a primary working air flow is produced by the rotation of the wings of the impeller wheel secured to the outer wall of the hub of the impeller wheel. Due to this primary working air flow a secondary air stream is produced in the gap between the hub of the impeller wheel and the carrier section. The secondary air stream causes a pressure differential between the air present in the area of the gap and the air present in the area of the holes in the hub when the impeller wheel rotates. As a result of the pressure differential a convection air flow is imposed by the active onflow at the gap for the air present in the hub inner space. Due to this imposed convection air flow the heated air present in the hub inner space escapes through the respective exit hole either out of the gap or out of the through-holes, whereby cooling air is introduced into the hub inner space either through the holes in the hub or through the gap, from the space outside, that is from outside of the hub of the impeller wheel. Thereby, the cooling surfaces of the cooling body present in the hub inner space are actively cooled by the imposed convection air flow from the space outside of the inner hub space whereby the convection air flow acts as a cooling medium in the inner hub space by flowing around the cooling surfaces which are correspondingly cooled.

Electric motors for use in the electric drive unit may be differently operated and configured fan motors. In this context asynchronous AC-motors which run asynchronously relative to the supply frequency, or synchronous motors which run in synchronism with the supplied frequency, may be used. These AC-motors are externally commutated. DC-motors maybe used which are self-commutating in dependency on the applied input voltage. Particularly brushless DC-motors operating as permanently excited synchronous motors may be used. In such motors the commutation is linked with a position recognition. Thus, these brushless DC-motors are operated as electronically commutated, self-commutating DC-motors (EC-DC-motors). More specifically, the self-commutation takes place depending on the input voltage applied to the individual coils. Further, different arrangements of the fixed stator relative to the rotating rotor may be selected. Particularly, in the so-called external rotor motors the rotor rotates on the outside of the stator and in so-called internal rotor motors the rotor rotates on the inside of the stator.

Advantageously, the present electric drive unit realizes a compact construction without any interference of the cooling surfaces of the cooling body provided for cooling, with the motion of the impeller wheel. This is so because the cooling surfaces are not positioned in the working air flow or they do not adversely influence the working air flow, whereby annoying noise that would otherwise result, does not occur. By utilizing the air flow that occurs when the electric drive unit operates, particularly of the active onflow at the gap between the hub of the impeller wheel and the carrier section, and the use of the pressure relationships caused thereby with the imposed convection of air out of the hub inner space, no separate cooling medium is required for cooling the cooling surfaces of the cooling body inside the hub inner space of the impeller wheel. The supply of external air for cooling into the inner space of the hub and the removal of heated air out of the hub inner space is accomplished by simple entrance holes and exit openings which possibly are already there. These holes are so constructed that a sufficient inflow of external air and thus the cooling of the cooling surfaces of the cooling body is assured. The pressure differential between the gap on the one hand and the through-holes on the other hand, the imposed convection in the hub inner space and the cooling effect are all independent of the flow direction of the working air flow produced by the motion of the impeller wheel. As a result, a good cooling effect is achieved independently of the installation or rotation direction of the impeller wheel and thus independently of the motion of the impeller wheel relative to the flow direction of the working air flow. The gap is formed between the hub of the impeller wheel and the carrier portion. The cooling effect depends on the removal of heated air from the hub inner space and on the supply of cool air from the external space. Thus, a multitude of wide ranging applications and use possibilities are achieved for the electric drive unit.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BEST MODE OF THE INVENTION

The electric drive unit1comprises, for example a brushless DC-motor3constructed as a fan motor of a motor vehicle. The motor functions as a drive device. The unit further includes an electronic control module2for controlling of the fan motor3particularly for varying the r.p.m. of the fan motor3, an impeller wheel4for producing a working air flow (useful air flow) functioning as a working device and a carrier section5for mounting the electronic control module2and the fan motor3.

The r.p.m. of the fan motor3shall, for example be variable within the r.p.m. range between 400 r.p.m. and 2400 r.p.m. (rated r.p.m.). The r.p.m. change is achieved by varying a DC-voltage supplied to the fan motor3. The fan motor3delivers its defined power at the rated r.p.m. of, for example 2400 r.p.m. The fan motor3has, for example a maximum input power of 600 W with a motor input voltage of 12 V, whereby the maximum motor current is 50 A. This current is distributed onto the coil windings of the fan motor3by commutation (commutation of the motor sections of the fan motor3).

The components of the fan motor3separated from one another are shown inFIG. 3, including the electronic control module2, the impeller wheel4, and the carrier section5of the electric drive unit1. Structural components, for example electronic elements21of the electronic control module2which is arranged on the underside332of the motor support33are secured on a printed circuit board22(compareFIG. 3). Structural components or electronic elements21are particularly provided as commutation transistors for commutating the motor sections of the fan motor3. For example, four commutation transistors constructed as field effect transistors are provided having connector pins in contact with contact points on the printed circuit board22or with a stamped grid24. The housings of the field effect transistors are, for example arranged on cooling surfaces71, for example made of aluminum, of the cooling body7. In order to protect the structural components or electronic elements21of the electronic control module2the printed circuit board22is mounted in a housing23, for example made of synthetic material. The stamped grid24is provided for the electrical connection of the structural components or electronic elements21and for providing an external connector possibility. The stamped grid24is formed of a plurality of stamped grid connector tabs26enclosed by synthetic material25by spraying. The stamped grid connector tabs26leading outside are integrated in at least one plug-in connector27. Particularly at least one connector plug can be connected to the plug-in connector27for connecting the electric drive unit1with further structural packages, for example for connecting the electric drive unit1with the onboard power supply net of the motor vehicle for a voltage supply and/or with a switching unit for feeding a control signal for switching on the fan motor3. Furthermore, the stamped grid24forms connector elements28which lead perpendicularly away from the plane of the printed circuit board22. For example, six such connector elements28are provided, whereby for example two connector elements28are provided for the voltage supply of the fan motor3and four connector elements28are provided for the commutation of the fan motor3. The connector elements28are made, for example of electrolytic copper with a thickness of, for example 0.8 mm and comprise, for example a square diameter of, for example 6 mm. The length of the connector elements28is selected in accordance with the height of the stator31of the fan motor3and thus depending on the power of the electric drive unit1. The length of the connector elements28is, for example, about 70 mm.

The fan motor3, for example constructed as an external rotor motor, comprises a circular stator31formed of a plurality of stator coils35with coil windings351. The stator31is mounted on a top side331of the motor support33. This “top side”331faces upwardly inFIG. 1. The fan motor3further comprises a rotor32rotating about the stator31on the outside of the stator31. The stator coils35are formed as circular segments and are assembled to form a coil assembly in such a way that a central opening38is formed in the center of the coil assembly so that a stationary axle39of the fan motor3can pass through the opening38. A plurality of holes, for example in the form of elongated holes322, is formed in a side wall323of the rotor32. This side wall323faces upwardly inFIG. 1. The longitudinal holes322are, for example arranged in a star shape fanning out radially away from the stationary axle39of the fan motor3. The rotor32rotates on bearings (FIG. 3) about the axle39. The motor support33comprises lead-throughs34(compareFIG. 3) for the connector elements28extending from the stamped grid24of the electronic control module2. The connector elements28are led through the lead-throughs34to the individual stator coils35. Contact elements in the form of contact hooks36and/or contact surfaces37are attached to the ends of the coil winding351of the stator coil35for realizing the connector contacts for the stator31or rather the stator coils35. The contact elements28reach through the lead-throughs34and along the inside of the central opening38. The contact elements28are electrically connected in a suitable manner, either with the contact hooks36or with the contact surfaces37. For example, the connector elements28are welded to the contact surfaces37. The holes333formed in the motor support33serve for securing the motor support33and thus the electric motor3and the electronic control module2to the carrier section5.

The impeller wheel4comprises the hub41attached to the rotor32of the fan motor3and the wings42which are radially arranged on the radially outer cylindrical wall411of the hub41, seeFIG. 3. For example seven wings42are provided. Through-holes, for example in the form of bores43are formed in a radially outer side portion412of the hub41. The bores43serve just as the elongated holes322on the side wall323of the rotor32for the supply of external cooling air into the hub inner space414formed between the radially outer wall411and the radially inner cylindrical wall413of the hub41seeFIG. 2. These bores43and elongated holes322alternatively serve for the discharge of the air present in the hub inner space414. The impeller wheel4is rotatably secured by bearings to the carrier section5whereby a rim or inner side415of the hub41faces a central portion51of the carrier section5to form a gap6to be described below.

The central portion51of the carrier section5is, for example, shaped as a casing in the form of a circular ring. A plurality of radially arranged lands52shown inFIG. 1are provided on the outer wall511of the central portion51for securing the carrier section5and thus the electrical drive unit1. The inner space54of the central portion51is adapted for the installation of the electronic control module2, whereby a plurality of chambers53are formed on the inner wall512of the central portion51for receiving the cooling surfaces71of the cooling body7of the electronic control module2. Furthermore, a plurality of retainer openings55are provided on the inner wall512of the central portion51neighboring to the chambers53and corresponding to the holes333in the motor carrier33. The motor carrier33and thus the fan motor3are secured through these retainer openings55from the top side513of the carrier section5by means of suitable securing means for example by means of screws in the central portion51of the carrier section5. The carrier section5in turn is secured by means of the lands52to the installation location provided for and suitable for the installation on the chassis or aggregates of the motor vehicle, for example screwed to the radiator of the motor vehicle.

FIG. 2shows a bottom view of the assembled electrical drive unit1. The hub41of the impeller wheel4is constructed with an axially extending double wall including the radially outer cylindrical wall411and the radially inner cylindrical wall413. These cylindrical walls411and413enclose the hub inner space414formed between the outer wall411and the inner wall413. This hub inner space414is subdivided in a partial circumferential area into hub chambers45by ribs44. The ribs44are arranged between the outer wall411and the inner wall413of the hub41and cause a stiffening of the hub41of the impeller wheel4. The wings42are secured to the radially outer wall411of the hub41of the impeller wheel4. The radially inner wall413of the hub41of the impeller wheel4is connected to the rotor32of the electric motor3. The rotor32rotates about the stator31with the aid of the bearings shown inFIGS. 3 and 5. Space radially inwardly of the wall13is also part of the hub inner space. The cooling surface71of the cooling body7of the electronic control module2are inserted into the hub inner space414, preferably to such an extent that they border directly on the hub chambers45formed in the hub inner space and thus on the ribs44.

A sectional view of the assembled electric drive unit is shown inFIG. 3.FIG. 4shows a side view thereof. The stationary axle39of the rotor32rotating about the stator31, is fixed in the opening38. The rotor32is secured on the axle39by bearings, seen inFIGS. 3 and 5. The magnets321of the rotor32are for example secured to the inside of the rotor32. The electronic control module2is centrally arranged below the motor support33. Hence, the module2is positionable completely within the dimensions of the stator31, more specifically the control module2does not extend at any point beyond the motor support33. This is possible due to the central arrangement of the electronic control module2and particularly due to the electrical connection of the electronic control module2and the fan motor3through the connector elements28that are centrally positioned in the electric drive unit1.

A gap6is formed between the inwardly facing side or edge513of the central portion51of the carrier section5and the also inwardly facing side or edge415of the hub41of the impeller wheel4. The gap6communicates with the inner hub space414and thus also with the circumferentially radially outwardly positioned bores or holes43. The gap6also communicates with the radially inwardly positioned elongated holes322. Due to the rotation of the impeller wheel4a pressure differential arises between the air present in the area of the gap6and the air present in the area of the bores43and the area of the elongated holes322. This pressure differential is independent of the flow direction of the primary working air flow produced by the rotation of the wings42of the impeller wheel4. As a result, a convection air flow of the air between the gap6on the one hand and the bores43and the elongated holes322on the other hand occurs through the inner hub space414, whereby the air which has been heated due to the contact with the cooling surfaces71of the cooling body7, discharges from the inner hub space414and cool outer air from the surrounding space is supplied into the hub inner space414. As a result the cooling surfaces71of the cooling body7are cooled and the structural components21of the electronic control module2arranged on these cooling surfaces71are also cooled. The cooling surfaces71extend into the hub inner space414preferably directly into the hub chambers45, i.e. they border directly on the hub chambers45.