Abstract:
An electronic device for a motor vehicle, having an electronics unit designed for switching high currents in a two-part housing, a capacitor unit being arranged in the housing to suppress the interference signals produced by said high currents. 
     In an electronic device which is easy to manufacture and in which the heat produced by the electronic circuits has no further effect on the operation of the electronic circuit, the capacitor unit, which is designed to have a large surface area, is thermally connected to a first housing part ( 1 ), and the electronics unit ( 8, 9 ) is thermally connected to a second housing part ( 2 ).

Description:
FIELD AND BACKGROUND OF THE INVENTION 
     The invention relates to an electronic device for a motor vehicle, having an electronics unit designed for switching high currents in a two-part housing, a capacitor unit being present to suppress the interference signals produced by the high currents. 
     Controllers are known which, in addition to the control electronics, also contain a power output stage for driving an actuator in the motor vehicle. For driving the actuator, such as an electric motor for window lifting mechanisms or for producing a valve stroke in a motor vehicle, the power output stages supply high currents. In the case of clocked driving, the switching of the high currents produces interference signals inside the controller, the levels of these interference signals being many times higher than the levels of the signals processed by the control electronics. The physically close arrangement of these different circuits in a controller means that the signals in the control device are affected by these electromagnetic interference signals. To produce electromagnetic compatibility for these two arrangements, the controllers have electrically connected capacitors which compensate for the interference signals. 
     In operation, the power electronics and the capacitors both produce a high heat loss which is dissipated to the surroundings via the housing. 
     This requires comprehensive designs for the housing in the form of cooling ribs to dissipate the heat produced quickly. 
     SUMMARY OF THE INVENTION 
     The invention is based on the object of providing an electronic device which is easy to manufacture and in which the heat produced by the electronic circuits does not affect the operation of the electronic circuits further. 
     The invention achieves the object in that the capacitor unit, which is provided to have a large surface area, is thermally connected to a first housing part, and the electronics unit is thermally connected to a second housing part. 
     The advantage of the invention is that the two components, which produce different levels of heat loss, are thermally decoupled. The configuration of the heat sink for each housing part can be matched to the specific circumstances. 
     In one refinement, the modular capacitor unit can be fitted into a connector unit which is of modular form and is mounted on the first housing part. The modular configuration of both the capacitor unit and the connector unit enables simple installation in the housing. For the capacitor unit, separate mounting means are dispensed with completely. It is locked on the housing with the connector unit. 
     To ensure that the capacitor unit is located robustly, the capacitor unit is prestressed against the first housing part by a spring element supported on the second housing part. In addition, this arrangement makes the capacitor unit insensitive to vehicle vibrations. Vehicle movements have no effect on the electrical connections of the capacitor unit. This means that short circuits are reliably prevented. 
     In another refinement, the connector unit and the capacitor unit are mechanically mounted independently of one another on the second housing part. This arrangement ensures that the capacitor unit is located so as to withstand vibrations, so that there is no need for additional measures to ensure robustness. 
     Advantageously, a thermally conductive adhesive layer is arranged between the capacitor unit and the first housing part. This thermally conductive adhesive layer not only transfers the heat produced by the capacitor unit to the first housing part but additionally compensates for the large tolerances of the capacitor inside the housing. 
     In one refinement, contact elements of the connector unit, which are of integral design and are guided outward, run below the capacitor unit and can be connected to the electrical connections of the electronics unit at a bonding surface which faces the interior of the housing. Particularly if the contact elements are designed as a sheet metal casting, such a space-saving shape is easy to produce. 
     The electronics unit rests flat on the second housing part, which is of plate-like form, for the purpose of thermal coupling. This achieves optimum heat exchange between the electronics and the housing part. 
     The two housing parts have a rib-like outer surface which is formed with different thicknesses. The arrangement of the capacitor unit and the electronics unit in different housing parts enables a cooling-rib variation which can thus be optimally matched to the amount of heat to be dissipated which is produced by the respective device. 
     In one refinement, the first housing part is provided to hold the individual capacitor elements forming the capacitor unit with a form fit. In this arrangement, the capacitor elements are placed directly onto the housing part, which produces direct thermal contact. 
     Particularly when commercially available capacitor cells are used, the inner surface of the first housing part has semicircular depressions corresponding to the outer contour of the capacitor elements. 
     In this case, the capacitor elements form two regions which are isolated by baffle plates connected to different electrical potentials. This arrangement eliminates the need for extensive line connections for the capacitors. 
     In this arrangement, the baffle plates are approximately L-shaped, which enables space-saving installation. 
     In order to provide an electronic device which is as small as possible, the first housing part rests on a hybrid frame which is connected to the second housing part, which bears the electronics unit, with a form fit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention has numerous embodiments. Two of these will be explained in more detail with the aid of the figures shown in the drawings, in which 
     FIG.  1 : shows a first embodiment of the device according to the invention, 
     FIG.  2 : shows a plan view of the first housing part, 
     FIG.  3 : shows the design of the connector module, 
     FIG.  4 : shows a second embodiment of the device according to the invention, 
     FIG.  5 : shows a section through the second embodiment, 
     FIG.  6 : shows a third embodiment of the device according to the invention, 
     FIG.  7 : shows a plan view of the first housing part, and 
     FIG.  8 : shows a view of the closed housing. and 
    
    
     Identical features are distinguished by identical reference symbols. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows the basic design of the device according to the invention, as used to drive an electric motor which adjusts the valve stroke of an air inlet valve in an internal combustion engine. It comprises two housing parts  1  and  2 , with a hybrid circuit  3  arranged on the second housing part  2 . Cooling ribs  4  are formed on the outer surface of the second housing part  2 . 
     The cover-like housing part  1  also has cooling ribs  5 . The housing parts  1  and  2  have a connector module  6  arranged between them so as to produce a seal. The connector module  6  bears a capacitor  7  which is arranged physically close to the housing part  1 . 
     FIG. 2 shows a plan view of the second housing part  2  with connector device  6  and electronics  8 ,  9 . On the housing part  2 , there is a processor hybrid  8  which, depending on the process to be monitored, produces control signals for a power output stage module  9  which generates the appropriate switching voltages and currents for the electric motor as requested. The power output stage module  9  is also positioned on the housing part  2 . 
     In this arrangement, the connector module  6  has a connector body  10  which has a recess  14  in it. Commercially available capacitor cells  7   a  to  7   f  are fitted into this recess  14 . 
     The connector unit  6  is explained in more detail in FIG.  3 . As can be seen from this figure, the connector body  10  is of integral design and has a connector inlet  15  into which the connector elements  16  and  17  project. The connector inlet  15  serves to hold the mating connector. To simplify illustration, only two connector elements  16 ,  17  are shown in this case. A multiplicity of such connector elements is also conceivable, however. 
     The connector pins  16  and  17  are advantageously designed as sheet metal castings, which are placed into an injection mold and are encapsulated with a plastic by injection molding, the plastic then forming the connector body  10  at the same time. The surface  18  formed opposite the connector inlet  15  then serves as a bonding surface for connecting the connector pin  17  to the electronics  8  and  9 . 
     A contact device  19  for the capacitor  7   a  is fitted in the recess  14  and is bonded or held mechanically to ensure robust location. Reliable contact is made between the capacitors  7   a  to  7   f  and the contact device  19  by welding these capacitors  7   a  to  7   f  to the contact device  19  at the weld points  20 . 
     Between the housing part  1  and the capacitor  7 , there is a layer of thermally conductive adhesive  21 , which ensures that the heat produced by the capacitor  7  is transferred to the aluminum cover  1 . On the second housing part  2 , which forms the base, there is a spring  22  which presses the part of the connector body  10  which bears the capacitors  7  against the first housing part  1  (FIG.  1 ). 
     FIG. 4 shows a second embodiment of the electronic device according to the invention. In this arrangement, the connector part  6  and a capacitor unit  7 , in seven capacitor elements  7   a  to  7   g , are produced independently of one another. The capacitor module  7  is mechanically connected to the second housing part via rivet connections  36 . The connector unit  6  is then locked mechanically on the second housing part  2  at the same time. The capacitor unit  7  also has a zener diode  35  arranged on it to limit voltage spikes, and this zener diode is also cooled. 
     The sectional illustration (FIG. 5) shows that the capacitor element  7   b  projects from the capacitor unit  7  and touches the semicircular depression  23  in the first housing part  1  over the surface for heat dissipation purposes. In this case too, it is appropriate to have a thermally conductive adhesive arranged between the capacitor element  7   b  and the depression. The baffle plates  30 ,  31  connect the individual capacitor elements  7   a  to  7   g  to the connector elements  16  and  17 . 
     FIG. 6 shows a further embodiment of the invention. Here too, the housing comprises two parts, the housing parts  1  and  2  being of plate-like design. The housing part  2  is designed as a hybrid circuit having the microprocessor circuit  8  and the power output stages  9 . The respective lateral ends of the housing part  2  have a circumferentially arranged hybrid frame  34  whose outer side has the cable guide  11 , in which the cable  12  is connected (FIG.  8 ). In this case, the connector elements  16  and  17 , which extend on one side through the hybrid frame  34 , are connected to the power output stage  9  and to the processor hybrid  8  inside the housing. The first housing part  1  rests on the hybrid frame  34 . In this case, the hybrid frame  34  is sealed off against the surroundings by means of a respective circumferential seal  26 ,  27 . The supply voltage is supplied to the power electronics via the connector pin  25 . 
     That side of the housing part  1  which faces the electronics  8 ,  9  has recesses  23  distributed at regular intervals over the entire surface of the part  1 . Each such recess  23  contains a capacitor  7   a  to  7   e , the shape of the recess being matched to the outer surface of the capacitor  7   a  to  7   e . In the example shown, the recess  23  is of semicircular design. The capacitor unit  7  is supplied with voltage via a connector pin  24  on the hybrid frame  34 . 
     FIG. 7 shows a plan view of the housing part  1  with the capacitors  7   a  to  7   e , as seen from inside the housing. In each case,  5  capacitors  7   a ,  7   b ,  7   c ,  7   d ,  7   e  are arranged in parallel next to one another in the manner shown in FIG.  6 . The capacitors arranged in this manner form two adjacent rows  28  and  29 . 
     These two regions  28 ,  29  are isolated by two baffle plates  30 ,  31 . In this arrangement, each baffle plate is of L-shaped design, and its limbs enclose a respective capacitor unit  28  or  29  approximately at right angles. In this case, the baffle plate  30  is connected to the supply voltage and the baffle plate  31  is connected to the ground of the appliance. The baffle plates  30 ,  31  are calked to the housing part  1  at the points  32 . As the section corresponding to line A-A shows, the two plates  30 ,  31 , carrying different potentials, are connected via contact bridges  33  and then form the electrical connection to the capacitors  7   a  to  7   e  at the same time, said capacitors being fitted into these contact bridges  33  and soldered. Alternatively, the capacitors  7   a  to  7   e  can be inserted into the contact bridges  33  using an insulation-piercing terminal technique. 
     FIG. 8 shows a plan view of the exterior view of the first housing part  1 , which is designed as an aluminum cover. This figure once again shows the cooling ribs  5 . The two housing parts are connected to one another by means of a screw or rivet device  13 . The two housing parts  1  and  2  have the hybrid frame  34  arranged between them, which has cable guides  11  on its outer sides. When the hybrid frame  34  and the first housing part  1  are assembled, the capacitor  7  is pressed against the housing part  1 , which forms the heat sink. 
     In the application described, currents of up to 100 amps arise, and the capacitors  7  have a capacitance of approximately 3000 to 4000 μF in order to ensure reliable EMC protection for the circuit arrangement both against interference signals produced internally in the housing and against those acting externally. 
     REFERENCE SYMBOLS 
       1  First housing part 
       2  Second housing part 
       3  Hybrid circuit 
       4  Heat sink for the second housing part 
       5  Heat sink for the first housing part 
       6  Connector device 
       7  Capacitor unit 
       7   a - 7   g  Capacitor elements 
       8  Power electronics 
       9  Control electronics 
       10  Connector body 
       11  Cable guide for supply voltage 
       12  Electrical line 
       13  Screw device 
       14  Recess 
       15  Connector inlet 
       16  Connector element 
       17  Connector element 
       18  Bonding surface 
       19  Contact device for the capacitor  7   
       20  Weld points for the capacitor  7   
       21  Thermally conductive adhesive 
       22  Spring 
       23  Recess 
       24  Connector pin 
       25  Connector pin 
       26  Seal 
       27  Seal 
       28  Region with five capacitors 
       29  Region with five capacitors 
       30  Baffle plate 
       31  Baffle plate 
       32  Rivet 
       33  Contact bridge 
       34  Hybrid frame 
       35  Zener diode 
       36  Rivet connection