High-power, low-voltage generator with starter-support function and torque compensation

Abstract

A vehicle, e.g., an off-road vehicle, may include an internal combustion engine, a starter motor coupled to the engine via a multi-stage transmission during a starting process, a further electric machine coupled to a crankshaft of the engine, and a converter arranged to supply at least one energy storage unit, e.g., a battery. The converter may be configured as a 4-quadrant regulator having a B6 circuit of MOSFETs.

Claims

1. A vehicle, including: a combustion engine with less than six cylinders, a starter motor configured to drive the combustion engine, a multi-stage transmission, wherein the starter motor is configured to drive the combustion engine during a starting process, and wherein, following the starting process, the starter motor is decoupled from the combustion engine via an uncoupling mechanism, an electric machine, distinct from the starter motor, configured to be operated as a motor and generator, having a fixed connection to a crankshaft of the combustion engine and by which the combustion engine is able to be driven, and a converter, having an electrical connection with windings of the electric machine, and which is configured to convert an alternating current generated by the electric machine to a direct current, wherein the converter is configured to supply at least one energy store in the form of a battery, and wherein the converter comprises a 4-quadrant regulator comprising a B6 bridge circuit of metal-oxide-semiconductor field-effect transistors (MOSFETs).

2. The vehicle according to claim 1, further including a control unit configured to drive the 4-quadrant regulator of the converter in such a way that the electric machine, during motor operation, works to support the starter motor.

3. The vehicle according to claim 2, wherein the control unit is configured to drive the 4-quadrant regulator of the converter in such a way that electrical compensation currents flow into the electric machine driven by the combustion engine, which compensation currents bring about compensation torques to suppress torque fluctuations of the combustion engine and thus improve the quietness and noise performance of the combustion engine.

4. The vehicle according to claim 1, wherein the electric machine is an external rotor motor, wherein the rotor is fitted with permanent magnets.

5. The vehicle according to claim 4, wherein an oil mist is provided in the electric machine, which serves to improve heat dissipation from exciter coils of a stator of the electric machine and the permanent magnets of the rotor.

6. The vehicle according to claim 4, wherein the electric machine further comprises an inner stator with exciter coils, wherein the inner stator with the exciter coils, on a side facing towards the rotor, is not, or is only partially, covered with a casting compound, wherein an uncovered part of the inner stator and/or an uncovered part of the exciter coils is/are in contact with an oil mist.

7. The vehicle according to claim 4, wherein, in order to reduce iron losses in the rotor, the rotor comprises a laminated construction or comprises a stamped laminated core inserted in the rotor.

8. The vehicle according to claim 1, wherein the electric machine comprises a laminated inner stator with exciter coils, a rotor and a metallic intermediate section, wherein the exciter coils of the inner stator are arranged across their radial longitudinal extension with an axial clearance, which is less than 2 mm from the intermediate section, and wherein the inner stator with the exciter coils and the intermediate section are filled with a filler with a heat conductance greater than that of air, wherein the intermediate section is connected to a housing of the electric machine by means of a screwed connection.

9. The vehicle according to claim 8, wherein the intermediate section is designed so that the exciter coils have the axial clearance from the intermediate section, such that a thermal resistance for generators with stator diameters of <200 mm (performance level for 500 W to 3000 W) is less than 2 k/W.

10. The vehicle according to claim 8, wherein the intermediate section or an area of the intermediate section is inset in the axial direction between the housing and the stator and rests against both, with axially aligned surfaces, such that a thermal resistance between the stator and the housing is as small as possible, and wherein the intermediate section is made from aluminium.

11. The vehicle according to claim 8, wherein the filler has a high specific conductance, and contains boron nitride and/or is formed from a thermoplastic or thermosetting plastic.

12. An assembly comprising: an inner stator with exciter coils and intermediate section in the vehicle according to claim 1, further including a filler comprising a thermoplastic, a cast material or a thermosetting plastic, wherein a space between the exciter coils and an intermediate section is filled using an injection moulding, vacuum casting or thermosetting manufacturing method, and the inner stator thereby has a positive connection with the intermediate section.

13. The vehicle according to claim 1, wherein the uncoupling mechanism comprises an overrunning clutch.

Description

DESCRIPTION OF FIGURES

(1) In the following the vehicle concept of the invention is explained in more detail using drawings.

(2) These show as follows:

(3) FIG. 1: The structure of the starter-generator system;

(4) FIG. 2a: Thyristor-converter circuit of the prior art;

(5) FIG. 2b: Alternative thyristor-converter circuit of the prior art;

(6) FIG. 2c: B6 converter circuit of the invention with MOSFETs;

(7) FIG. 3: Diagram illustrating the increase in power due to the measures of the invention;

(8) FIG. 4: Possible structure of a generator of the invention;

(9) FIG. 5. Measures to improve the thermal process and to increase power;

(10) FIG. 6: Starter process with starter and starter/generator;

(11) FIG. 7: Torque-ripple compensation method.

(12) FIG. 1 shows a possible structure of the starter-generator system of the invention for a vehicle. The system consists of a combustion engine (ICE=Internal Combustion Engine) 1, connectable via a gear unit 3 with a starter motor 2. The gear unit between the starter motor and the combustion engine generally has a multi-stage design, so that a smaller starter motor can be used. The gear unit also has an overrunning clutch (X) or uncoupling mechanism (e.g. a Bendix engagement mechanism), which ensures that following a successful start of the combustion engine the starter is not driven. Apart from the starter switch 15, the control unit 11 also controls, inter alia, the converter 7. It is logical for the current of the starter motor to be cap-tured, in order to support the inverter during the starting process by synchro-nised control of the phase currents of the motor E. The crankshaft 4 of the combustion engine 1 is connected to the rotor 5 of the electric machine E, so that optionally the combustion engine 1 drives the rotor 5 and thus induces a voltage within the exciter coils 6a arranged in the inner stator 6. The electric machine E therefore works as a generator, and the electrical power it generates is then rectified via the converter 7 and fed into the vehicle electrical system 12 and inter alia the battery 13 is charged. Conversely, the control unit 11 can drive the MOSFETs of the converter 7 so that via the exciter coils 6a a driving, rotating magnetic field develops which drives the rotor 5 with its permanent magnets 9, such that the electric machine E works as a motor and to support the starter motor 2 during the starting process drives the shaft 4 and thus the combustion engine 1.

(13) On the shaft 4 a target 10 is arranged, the movement of which is detected by a sensor unit 8, whereby the activation of the B6 circuit can be performed with accuracy. Between the inner stator 6 and the housing an intermediate section 20 functioning as a heat conductor is arranged.

(14) FIG. 2a shows a conventional converter with thyristors, which can be operated merely in 2-quadrant mode. The same applies for the electronic circuit of FIG. 2b.

(15) FIG. 2c shows the B6 circuit 14 of the invention consisting of six MOSFETs, which can be operated in 4-quadrant mode.

(16) FIG. 3 shows a diagram to illustrate the increase in power as a result of using a converter, as illustrated and described in FIG. 2b. The bottom curve shows the output power with a rectifier shown in FIG. 2a. With the same generator, but using the rectifier illustrated in FIG. 2b with B6 MOSFET cir-cult, the output power increases (top curve), as a result of which a significantly better level of efficiency is achieved.

(17) FIG. 4 shows a possible structure of an electric machine E of the invention, which can be operated as a generator or motor. The electric machine E has a housing 21, which with its inner wall 22 delimits an interior space, in which the inner stator 6 with the exciter coils 6a arranged on it and the external rotor motor 5 are arranged. The rotor 5 supports on its cylindrical inner wall permanent magnets 9 and is secured against rotation via its bottom wall with the shaft via connecting elements 24, 27. On the shaft end a target 10 is secured, the rotation of which is detected by the sensor 8. The connecting lines 8a of the sensor 8 are axial fed axially out of the housing 21.

(18) The inner stator 6 is connected via an intermediate section 20 by means of screws 23 with the housing 21. The intermediate section and the inner stator 6 with its exciter coils 6a are enclosed completely or in sections by casting compound 25. Advantageously, on the side 29 turned towards the rotor 5, the casting compound 25 does not fully enclose the stator 6 or its exciter coils 6a, so that the oil mist 26 present in the interior space of the housing comes into direct contact with the inner stator 6 and/or the exciter coils 6a, so that via the oil mist 26 the heat is rapidly dissipated from the stator 6 and the exciter coils 6a to the housing. The exciter coils 6a are located with a very small clearance AB from the intermediate section 20, so that good heat dissipation via the intermediate section 20 to the housing 21 occurs.

(19) The left side of FIG. 5 shows a conventional electric machine, often used as a generator, where the inner stator with the exciter coils is secured to a cylindrical projection in the inside of the housing. With this type of construction, the heat from the inner stator and its exciter coils can primarily drain away via the path designated Rth1 or heat transfer resistances, since the remainder of the stator is in contact with the air and in the heat conduction effect, due to the very low specific conductance of the air (0.026 W/mK), can be ignored. The heat transfer between exciter coils and stator can be quite unfavourable if the coils have not been drizzled with oil or the coils are in contact with one another and with the stator insulation. This can only be achieved through a highly precise coiling technique. The heat transfer resistances Rth1 are conse-quently relatively high, so that the power of the electric machine is limited due to the heating that occurs and the poor heat dissipation.

(20) The right side shows the electric machine of FIG. 4. The various effectively operating heat transfer resistances R.sub.th1-R.sub.th4 of the electric machine of the invention are designated by R.sub.thi. R.sub.th1: Thermal resistance coil.fwdarw.inner stator.fwdarw.housing R.sub.th2: Thermal resistance coil head SK1.fwdarw.housing via casting compound R.sub.th3: Thermal resistance coil head SK2.fwdarw.housing via copper line and casting compound R.sub.th4: Thermal resistance coil head SK2.fwdarw.oil mist

(21) The total thermal resistance Rth.sub.ges is given by the following formula (compara-ble to the connection in parallel of electric resistances):

(22) ${\mathrm{Rth}}_{\mathrm{ges}}=\frac{1}{\underset{i=1}{\overset{n}{.Math.}}\frac{1}{{\mathrm{Rth}}_i}}$

(23) Compared the prior art, R.sub.th1 has been reduced in such a way that the cross-sectional area between the stator and housing through advantageous design of an intermediate section is increased and the path to the housing is as short as possible.

(24) Due to the close fit or short distance AB between the intermediate section 20 and the exciter coils 6a, the thermal resistance R.sub.th2 is relatively small, so that the heat is properly dissipated from the exciter coils of the exciter coil head SK1 directly to the housing.

(25) R.sub.th3 represents the thermal resistance of the exciter coil head SK2, the rotor of which is turned towards the intermediate section 20, which is thereby improved, since copper is an extremely good heat conductor and the heat of the coils can be dissipated both via the casting and via the stator.

(26) R.sub.th4 represents a further effective heat path, since the coil head SP2 is in open contact with an oil mist, in that the coil head SP2 is not completely cast. Since it is at the coil head SP2 that the highest temperatures usually arise, the heat conduction can be effectively used to reduce the drop in temperature in the stator and stresses in the casting.

(27) Even if the resistance R.sub.th2 through the use of a filler material with good thermal conductance properties as a result, inter alia, of minimum distances of the exciter coils (approximately 1 mm) to the intermediate section is higher than the primarily effective thermal resistance R.sub.th1 (greater by a factor of 3-5), through this measure the thermal resistance can be reduced by 20%-30%, since the higher resistance is effective in the parallel connection of the resistances. Since apart from the thermal resistance, account has to be taken of the fact that the resistance of copper increases as it heats up and the power loss increases further, due to the lower thermal resistance at a given housing temperature the dissipated power loss, limited by the maximum temperature of the coils, can be increased by more than 50%. The further resistances R.sub.th3 and R.sub.th4 continue to have a favourable effect on the power of the electric machine.

(28) FIG. 6 shows the starter process with starter and starter/generator. The lower diagram shows for the torque Mstarter_old of the starter motor to be applied for the starting process. In a conventional concept with a single, large starter motor, not supported by the generator, this must be designed so that it can provide the necessary motor torque Mstarter_old on its own.

(29) With the concept of the invention, the starter motor merely has to apply the torque Mstarter_new. The electric machine operated during motor operation provides the remaining motor torque Mgenerator.

(30) The top diagram shows the power required for the starter process, wherein the curve P_old shows the necessary power for a single, unsupported starter motor and rectifier with thyristor circuit. The curve P_new shows the electrical power needed for the concept of the invention, wherein the saving is achieved by the B6 MOSFET circuit of the converter and the structural features of the electric machine.

(31) FIG. 7 shows a possible torque-ripple compensation method, in which the electric machine simultaneously generates a torque through corresponding activation of the rectifier, but simultaneously also electrical energy via the rotor driven by the combustion engine. Through the corresponding activation of the B6 MOSFET circuit, the compensation torque (dashed line) is generated, which is added to the torque of the combustion engine (solid line) to give a drive torque, the amplitude of which is significantly smaller than the torque fluctuations, which result solely from the combustion engine.