EP2467923A2

EP2467923A2 - Electric machine

Info

Publication number: EP2467923A2
Application number: EP10732994A
Authority: EP
Inventors: Martin Paetzold; Julian Roesner
Original assignee: Robert Bosch LLC
Current assignee: Robert Bosch LLC
Priority date: 2009-08-18
Filing date: 2010-07-16
Publication date: 2012-06-27
Also published as: CN102577047A; DE102009028605A1; WO2011020665A2; US9000719B2; US20120206094A1; WO2011020665A3; IN2012DN01549A

Abstract

The invention relates to an electric machine (10), particularly a generator or a starter generator for a motor vehicle, comprising a converter (64) which is arranged on a cooling element (53) and composed of semiconductor switching elements (58, 59) actuated synchronously with the phase frequency for rectifying a generator alternating voltage or supplying a motor from a DC voltage source (61). According to the invention, the cooling element (53) has a base plate (55) and cooling fins (54), wherein the ratio of the surface wetted by coolant to the volume of the cooling element (53) ranges from 0.5 to 1.5 [l/mm], preferably from 0.8 to 1.0 [1/mm].

Description

description

title

Electric machine

State of the art

The invention is based on an electrical machine with a control device, as described, for example, in EP 1 466 779 A2. The one revealed there

Inverter is designed to reduce the electrical losses with semiconductor switching elements, which in

Generator operation, the rectification of the AC voltage supplied by the generator and in engine operation

Change direction of a DC voltage source

take over the supplied voltage. Such semiconductor switching elements have good efficiency due to low voltage drops during operation, on the other hand, however, there is an increased risk of damage to the switching elements at high loads, especially when used in motor vehicles, where often strong temperature and

Load fluctuations occur.

Disclosure of the invention

The electric machine according to the invention with the features of the preceding claim has the advantage that both in

Motor operation as well as in generator mode the desired high efficiency of the circuit arrangement achieved

on the other hand, an inadmissible warming of

Circuit breaker both at short-term, very high

Load as well as continuous load under unfavorable operating conditions, especially at high

Ambient temperatures is ensured. This safety is achieved to a particularly high degree when the ratio of the surface area to the volume of the heat sink in the range of 0.8 to 1.0 [l / mm], in particular in the range of 0.87 [l / mm] to 0.96 [l / mm] is. As a result, a sufficient heat dissipation from the components both at long

Duty cycle as well as peak loads

ensured. In addition, it is ensured that the occurring when turning off MOSFETs, caused by the switching off of the current voltage spike and the resulting heating peak is dominated, the amount in particular when switching off high currents and high

Inductances in the leads to the switches can lead to overload of the semiconductor switching elements. By the safe control of the heat dissipation of the

Switching elements with improved efficiency can also by a smaller size

Reduced manufacturing costs of the machine and also reduced by the reduced fan size, the noise emission.

It has proved to be advantageous if the

Drive circuit for the semiconductor switching elements and the switching elements themselves are arranged on a common heat sink, because this reduces the manufacturing cost of the arrangement. This common arrangement is made possible in particular by the fact that the base plate of the heat sink is designed as a heat storage, which very quickly a larger amount of heat from the components can dissipate, which arises in particular by voltage peaks due to Zuleitungsinduktivitäten when switching off the current. The cooling effect of the heat sink is particularly efficient if it is mounted on the outside of a bearing plate of the machine and the cooling air reaches the heat sink with low flow losses. To further

Reduction of the flow resistance of the cooling air thereby extend the large surfaces of the cooling fins substantially in the flow direction of the cooling air and form radial

Flow channels to a central inlet for the cooling air inside the machine.

The semiconductor switching elements of the inverter are

expediently arranged on the surface facing away from the cooling ribs surface of the heat sink base plate, while the cooling fins are in turn directly facing the impinging coolant. The switching elements and their

Drive circuit are thus arranged axially on the inside of the base plate of the heat sink and the cooling fins axially on the outside of a protective cap facing side of the heat sink.

An advantageous, good heat-conducting and at the same time electrically insulated attachment of the switching elements and / or their drive circuit results when they are held on DBC (Direct Bonded Copper) substrates on the heat sink. In addition, the switching elements and / or their drive circuit can be coated with plastic, preferably potted, to further improve their mechanical protection and protection against moisture and dirt.

With regard to the further design of the heat sink, it is expedient if to achieve the greatest possible

Cooling effect, the base plate of the heat sink substantially is formed circular disc-shaped with a size of the machine corresponding diameter, wherein the

Switching elements are expediently arranged on a larger segment and the drive circuit on a smaller segment of the base plate. This results in a compact design with short leads from the

Control circuit to the individual switching elements. The switching elements are expediently evenly distributed on the segment of the heat sink occupied by them and advantageously arranged so that in each case a so-called high-side switching element and a low-side switching element of a phase radially adjacent and preferably each associated with a separate fin group. Brief description of the drawings

An embodiment of the invention is illustrated in the drawings and explained in more detail in the following description.

Show it:

Figure 1 shows a longitudinal section through a as

Alternator for motor vehicles engineered electrical machine,

Figure 2 is a circuit diagram of a three-stranded

Alternating electric machine, Figure 3 in the illustration a) the current waveform and in the representation b) the associated

Temperature profile on a MOSFET switching element during a half-wave of the phase current of the machine, Figure 4 is a schematic diagram of the inverter side

End of an electrical according to the invention

Machine and

Figure 5 is a schematic plan view of the

Cooling ribs bearing surface of the heat sink of the machine

Embodiment of the invention

FIG. 1 shows a section through an alternator 10 for motor vehicles. This has inter alia a two-part housing 13, which consists of a first bearing plate 13.1 and a second bearing plate 13.2. The bearing plate 13.1 and the bearing plate 13.2 take in a stator 16 with a

annular laminated core 17, in which inwardly open and axially extending grooves 15, a stator winding 18 is inserted. The annular stator 16 surrounds with its radially inwardly directed surface

electromagnetically excited rotor 20, which is designed as a sixteen-pole claw pole rotor. The rotor 20 consists inter alia of two claw-pole plates 22 and 23, on the outer circumference of which eight each in the axial direction

extending claw-pole fingers 24 and 25 are arranged.

Both claw pole boards 22 and 23 are arranged in the rotor 20 such that their axially extending claw pole fingers 24, 25 alternate at the periphery of the rotor 20 as N and S poles. This results in magnetically required Klauenpolzwischenräume between the

in opposite directions magnetized Klauenpolfingern 24 and 25, which tapered because of their free ends towards Klauenpolfinger slightly oblique to the machine axis. For the following description of the invention, this course is simplified referred to as axial. The rotor 20 is rotatably supported in the respective end shields 13.1 and 13.2, respectively, by means of a shaft 27 and one respective rolling bearing 28 located on each side. It has two axial end faces, on each of which a fan 30 is attached. These fans 30 are made in

Essentially from a plate-shaped or disc-shaped portion, run from the fan blades in a known manner. On the one hand, the fans 30 generate a cooling air flow over the heat sink 53 and, on the other hand, serve to exchange air between the outside and the interior of the electric machine 10 via openings 40 in the end shields 13.1 and 13.2

enable. For this purpose, the openings 40 are provided at the axial ends of the end shields 13.1 and 13.2, via which 30 cooling air is sucked into the interior of the electric machine 10 by means of the fan. The cooling air is accelerated radially outwards by the rotation of the fans 30, so that they can also pass through the cool air-permeable winding heads 45 on the drive side and 46 on the electronics side. Through this effect, the

Winding heads cooled. The cooling air decreases after the

Passing through the winding heads, or after the flow around this winding heads a way radially outward through openings not shown. In Figure 1 on the right side is a

Protective cap 47, the various components before

Environmental influences protects. Thus, this protective cap 47 covers, for example, a slip ring assembly 49, which supplies a field winding 29 with exciting current. Around Slip ring assembly 49 is a heat sink 53

arranged. Between the bearing plate 13.2 and the heat sink 53 sits a connection plate 56 for the apparent from Figure 2 semiconductor switching elements 58,59 and the drive circuit 60th

Figure 2 shows the circuit diagram of a three-stranded

Alternator, for example, as an alternator with a converter 64 in the form of a synchronous rectifier or as a starter generator, wherein the switching elements 58 and 59 by means of

Drive circuit 60 are connected to a DC voltage source 61. A consumer 62 is over a

Switching 63 connected to the DC voltage source 61. The three over power rails with the

Switching elements 58,59 connected strands of

Ständerwicklung 18 are designated U, V, W, the respective connections to the switching elements 58 and 59 with Ul, Vl, Wl and connected to a star strand connections with

U2, V2, W2. The phase position in the stator winding 18 is monitored by a sensor 65, which supplies corresponding signals to the drive circuit 60 for synchronous control of the switching elements 58 and 59 and for feeding the

Excitation winding 29. In case of execution of the

Electric machine according to the invention as a generator of a motor vehicle in this case replace the preferably as

MOSFETs formed switching elements 58 and 59, the diodes used in conventional generators and thereby form a synchronously driven to the phase position

Rectifier, which in operation significantly lower

Has losses as a rectifier based on semiconductor diodes. The advantage of reduced losses in the use of semiconductor switching elements for

Rectification clearly exceeds the additional effort for the drive circuit 60. In addition, the

Design of the inverter 64 with controllable semiconductor switching elements the possibility of the electric machine as a starter generator for the internal combustion engine

form so that a separate starter is eliminated.

FIG. 3 illustrates the problem when using MOSFETs as switching elements for the converter 64. FIG. 3 a shows the typical current profile in the switching element during a switch-on period, FIG. 3 b shows FIG

associated voltage curve on the switching element. The short current dip is due to the commutation of the current within a second switching element group, ie

for example, in the commutation of the current of the phase U, which changes on the lowside from phase V to phase W.

When the current is interrupted, a voltage spike occurs, which for a short time greatly increases the power loss of the switching element and thus its heating, in addition to the increasing power loss during the switch-on period. The current heat losses during the switch-on of the MOSFETs are dependent on the level of the switched current and its volume resistance. The heating due to the voltage spike when turning off the MOSFET depends on the magnitude of the current and the inductance of the supply line between the voltage source 61 and the switching element, which is why in conventional applications, in particular for the motor operation of the machine, the inverter regularly in the vicinity of the voltage source was arranged. By the measures according to the invention for improving the cooling effect on the inverter, however, it is possible, even with a

Semiconductor switching elements constructed inverter directly to the electrical machine. FIG. 4 shows, again in a schematic representation, the mechanical structure of the converter-side end of a machine according to the invention. Here, the heat sink 53 is mounted outside of the bearing plate 13.2 to the machine and covered by a protective cap 47. The protective cap has axial inlet openings 67 and radial

Inlets 69 for the cooling air, which

preferably both are arranged close to the outer end of cooling fins 54 of the heat sink 53. The cooling fins 54 themselves extend essentially radially on one side

Circular disk-shaped base plate 55 of the heat sink 53 and thus direct the cooling air flow with low flow resistance to a central opening 71 in the base plate of

Heatsink and from there axially through openings 73 in

End shield 13.2 inside the machine, the

Openings 71 in the base plate and 73 in the bearing plate are substantially aligned with each other in order to keep the flow resistance low in this area. The cooling air flow is indicated by lines 75, 76 and 77. His ride out of the machine is in a conventional manner again in the radial direction.

The semiconductor switching elements 58 and 59 are arranged on the axially inner, the cooling fins 54 opposite side of the base plate 55 of the heat sink 53 such that the switching elements of each phase are radially aligned.

In the exemplary embodiment, the (high-side) switching elements 59 connected to the positive pole of the voltage source 61 lie on an inner radius which is connected to the negative pole of the

Voltage source connected (low-side) switching elements radially outward. The drive circuit 60 for the switching elements is not visible in this illustration, but it is in the same way as the switching elements 58,59 radially inside lying on the base plate 55, as shown in dashed lines in Figure 5.

Both the base plate 55 and the cooling fins 54 of the heat sink 53 are made of aluminum or a

Aluminum alloy with good thermal conductivity. The entire heat sink 53 is designed such that

on the one hand, in particular by the cooling fins 54, a sufficiently large surface, and on the other hand a

Sufficient storage volume of the standing in direct thermal contact with the semiconductor switching elements and the drive circuit base plate 55 results in the rapid dissipation of the heat generated during switching of the components. For this purpose, the ratio of the total surface area to the total volume of the heat sink 53 should be in the range of 0.5 to 1.5 [l / mm]. An optimum ratio of the surface to the volume of the heat sink with regard to heat dissipation on the one hand and heat absorption on the other hand is in the range of 0.8 to 1.0 [l / mm], in particular in the range of 0.87 to 0.98 [l / mm]. In this embodiment, the cooling effect of

Heatsink 53 so effective that it can be integrated into the machine without difficulty, resulting in significant structural and cost advantages over a

separate, arranged at this point component. It is both a sufficient heat to the

In stationary operation ensures as well as a rapid heat dissipation occurring temperature peaks.

In particular, the higher efficiency of a constructed with semiconductor switching elements synchronous rectifier with respect to a diode rectifier can thus without endangering the

Switching elements are used.

Good thermal coupling between the switching elements 58 and 59 designed as MOSFETs and the baseplate 55 of the heat sink 53 is achieved by the

Use of indicated in Figure 4 by the reference numeral 57 DBC (Direct-Bonded-Copper) substrates, which the switching elements in a basically known manner

electrically isolated, but with very good thermal

Connect coupling with the base plate 55 of the heat sink.

An additional permanent protection of the switching elements 58,59 and the drive circuit 60 against corrosion and against mechanical effects results from the fact that the electronic components are coated on the axially inner surface of the base plate 55 with plastic, preferably encapsulated. FIG. 5 shows a plan view of the surface of the heat sink 53 provided with cooling fins 54. From this

Representation can be seen that the base plate 55 is formed substantially circular disc-shaped, wherein the on the invisible back of the base plate

arranged switching elements 58,59 on a larger segment of more than 200 ° and the drive circuit 60 are arranged on the remaining smaller segment. The

Switching elements 58, 59 are distributed uniformly on the larger segment of the baseplate, and preferably in pairs, with a radial alignment of a separate one

Cooling fin group 54a-54e assigned. The single ones

Cooling fins 54 are preferably integral with the

Base plate 55 made as a casting. Alternatively, however, it is also possible to manufacture the base plate and the cooling ribs or cooling rib groups separately and subsequently to connect them to one another.

The advantageous design and design of the heat sink 53 ultimately results from a variety of General conditions: First of all, the length of the machine in the axial direction and its weight are fundamentally limited, taking into account the respective required performance. On the one hand, this results in a limitation of the height of the

Cooling ribs 54 and on the other hand, a limitation of the thickness of the base plate. In addition, the heat sink should be manufactured as a casting as far as possible, which is why the cooling fins must have a certain minimum thickness. In addition, the shape and size of the cooling fins is limited by an allowable maximum flow resistance of the cooling air, otherwise the fan power must be increased, causing the

Total generator efficiency drops. From these

General conditions results in the claimed ratio between the surface wetted by the coolant and the volume of the heat sink 53 responsible for the direct heat dissipation from the semiconductor switching elements. The wetted surface is that surface which is in direct contact with the coolant (here: the cooling air) and not by other components, for example by

Fastener is covered.

An embodiment of the heat sink according to the invention was designed as follows: thickness of the base plate 55: 3mm

Height of cooling fins 54: 15mm

Inner radius of the base plate 55 in the region of the central

Opening 71: 28mm

Outer radius of the base plate 55: 60mm Volume of the entire heat sink 53: 48241mm ³

Heatsink wetted surface 53: 46100mm ² ratio of heat sink surface to its

Volume: 0.96 l / mm

Claims

claims

1. Electrical machine, in particular generator or

Starter generator for a motor vehicle, with a arranged on a heat sink (53), in synchronism with

Phase frequency controlled semiconductor switching elements

(58,59) constructed converter (64) for rectifying a generator AC voltage or for supplying a motor from a DC voltage source (61), wherein the heat sink (53) has a base plate (55) and cooling fins (54) and the ratio of the Coolant wetted surface to

Volume of the heat sink (53) in the range of 0.5 [l / mm] to 1.5 [l / mm]].

2. Electrical machine according to claim 1, characterized

in that the ratio of the surface wetted by the coolant to the volume of the heat sink (53) is in the range from 0.8 [l / mm] to 1.0 [l / mm], in particular in the range from 0.87 [l / mm] to 0.96 [l / mm].

3. Electrical machine according to claim 1 or 2, characterized in that the cooling body (53) made of Al or an Al alloy with good thermal conductivity, preferably with a thermal conductivity above 200 W / m-K exists.

4. Electric machine according to one of the preceding

Claims, characterized in that they as

Three-phase, electrically excited generator with one

Synchronous rectifier, in particular in the execution as Full bridge rectifier arrangement, for charging a

Battery (61) is formed.

5. Electrical machine according to one of the preceding

Claims, characterized in that serve as semiconductor switching elements (58,59) MOSFETs.

6. Electrical machine according to one of the preceding

Claims, characterized in that a

Drive circuit (60) and controlled by it

Semiconductor switching elements (58,59) on a common heat sink (53) are arranged.

7. Electrical machine according to one of the preceding

Claims, characterized in that the heat sink (53) with the inverter (64) and / or the drive circuit (60) attached to the outside of a bearing plate (13,2) of the machine (10) and covered by a protective cap (47).

8. Electrical machine according to claim 7, characterized

in that the protective cap (47) has axial and / or radial openings (67, 69) for the targeted access of cooling air (67, 69) to the cooling body (53).

9. Electrical machine according to one of the preceding

Claims, characterized in that the cooling body (53) has at least one central opening (71) for the passage of cooling air.

10. Electric machine according to one of the preceding

Claims, characterized in that the base plate (55) of the heat sink (53) is formed as a heat sink.

11. Electrical machine according to one of the preceding claims, characterized in that the base plate (55) of the cooling body (53) on its side remote from the cooling ribs (54) surface carries the switching elements (58,59).

12. Electrical machine according to one of the preceding claims, characterized in that the cooling ribs (54) of the cooling body (53) extend with their large surfaces substantially in the flow direction (77) of the coolant.

13. Electrical machine according to one of the preceding claims, characterized in that the cooling ribs (54) form radial flow channels.

14. Electrical machine according to one of the preceding

Claims, characterized in that the switching elements (58,59) and the drive circuit (60) axially on the inside of the base plate (55) of the heat sink (53) and the cooling fins (54) axially outside on the protective cap (47) facing side of Heatsink (53) are arranged.

15. Electrical machine according to one of the preceding claims, characterized in that the switching elements

(58, 59) and / or their drive circuit (60) via DBC (direct bond copper) substrates (57) to the heat sink

(53) are thermally coupled and electrically isolated.

16. Electrical machine according to one of the preceding claims, characterized in that the switching elements

(58,59) and / or the drive circuit (60) with plastic (79) wrapped, preferably encapsulated.

17. Electrical machine according to one of the preceding claims, characterized in that the base plate (55) of the heat sink (53) is formed substantially circular disk-shaped, wherein the switching elements (58,59) on a larger segment and the drive circuit (60) on a smaller segment are arranged.

18. Electrical machine according to one of the preceding claims, characterized in that the switching elements (58,59) are evenly distributed on a segment of the heat sink (53).

19. Electrical machine according to one of the preceding claims, characterized in that in each case one

Highside switching element (59) and a lowside switching element (58) of a phase radially adjacent to the heat sink (53) are arranged and together assigned to a cooling fin group (54a-54e).

20. Electrical machine according to one of the preceding claims, characterized in that the cooling body (53) is made in one piece as a casting.