DEVICE COMPRISING A GENERATOR AND METHOD FOR CONTROL OF SUCH A DEVICE

Abstract: The invention relates to a device comprising a generator which during operation generates a voltage across at least one electrical load (15, 16) and comprising the regulator (12) for control of the voltage from the generator and a cooling device for cooling of loss of power from the generator. The invention is characterized in that said cooling device has dimensions which correspond to cooling of a power loss fron the generator during a continuous state which exists after reduction of the power of the generator following switching off of at least one electrical load (16) which is used during an initial load of the generator. The invention also relates to a method for controlling a generator. By means of the invention, an improved generator is obtained in which a lower sound level and a higher coefficient of efficiency of the generator is obtained.

Description: TITLE: Device comprising a generator and method for control of such a device. TECHNICAL FIELD: The present invention relates to a device comprising a generator, according to the preamble of appended claim 1. The invention also relates to a method for control of such a device, in accordance with the preamble of appended claim 4. BACKGROUND OF THE INVENTION: In the field of motor vehicles, for example cars, generators which are powered by the internal combustion engine of the vehicle and which generate electrical energy to a plurality of energy consumers in the vehicle are normally used. In recent years, the number of energy consumers has increased in many types of motor vehicles. Such energy consumers may for example be lighting arrangements and electrical heating arrangements for windows, seat heating devices for front and rear seats and active damping devices (CCD devices). The increased demand for energy in today's motor vehicles has resulted in higher requirements for the generator of the vehicle. If the generator is to be able to supply the increasing amounts of energy, increased power of the generator is required. In particular, a very high current from the generator is required during the first 5 to 10 minutes after a cold start. High power of the generator also creates high losses. This causes heat to be generated in the generator, for which reason it must be cooled. In conventional generators, the problem regarding cooling is solved by arranging a fan on the rotor shaft of the generator. When the generator's rotor and thus also the fan rotates, the losses in the form of heat will be dissipated. In order to manage to cool the generator even during the worst operating conditions, the fan is dimensioned so as to correspond to the maximum output power of the generator, as seen in relation to the cooling capacity. However, this manner of dimensioning the fan so as to withstand the worst operating conditions results in problems in the form of unwanted noise generated by the fan. Also, the total losses of the generator increase, i.e. the coefficient of efficiency of the generator is decreased. The faster the generator rotates, the higher the noise and the higher the losses are generated due to the fan. SUMMARY OF THE INVENTION: The object of the invention is thus to provide an improved generator in which the losses in the form of heat can be dissipated in a satisfactory manner, while at the same time a lower sound level and a higher coefficient of efficiency of the generator can be obtained. Said object is accomplished by means of a device of the kind initially mentioned, the characterizing features of which will be apparent from subsequent claim 1, and by means of a method of the kind initially mentioned, the characterizing features of which will be apparent from subsequent claim 4. By using a relatively small cooling device which is dimensioned according to an energy loss of the generator which arises a certain time after a cold start, when the generator has gone from an initial nominal load to a lower power level during continuous operation, a high coefficient of efficiency can be obtained by the generator. Furthermore, only a low level of noise is generated. The generator is also quickly heated. According to a certain embodiment, the temperature of the generator is detected. If the tempetature of the generator is higher than a predetermined maximum allowed temperature limit, the magnetizing current to the rotor of the generator can be limited to a level which corresponds to a heat generation in the generator which can be dissipated by the cooling device during subsequent operation. By means of the invention, a very high current can be generated by the generator during cold starting, without implying any high losses and disturbing noise. Later, when the generator is heated and the demand for current decreases, the heat generated by the generator can be dissipated by the existing cooling device. BRIEF DESCRIPTION OF THE DRAWINGS: The invention will be described in greater detail in the following with reference to the annexed drawings, in which Fig. 1 is a circuit diagram of an electrical system according to the present invention, which system comprises an alternating current generator, and Fig. 2 is a diagram showing the relationship between the voltage and temperature of the generator. PREFERRED EMBODIMENT: Fig. 1 shows a circuit diagram of an electrical system according to the present invention. The system is preferably used in a motor vehicle and comprises an alternating current generator (below referred to as "generator"), the essential components of which are a magnetization winding 1, three stator windings 2, 3, 4 and a rectifier in the form of six diodes 5, 6, 7, 8, 9, 10. The system also comprises a capacitor 11, the purpose of which is to absorb voltage transients occuring during rectification. The magnetization winding 1 is arranged on a rotor and the stator windings are arranged on a stator. When the rotor is rotated, an alternating current is generated in the stator windings 2, 3, 4. This alternating current is rectified in the rectifier 5-10. The operation of the generator is known per se and is therefore not described in detail. The electrical system comprises a voltage regulator 12 to which a temperature sensor 13 is connected. The temperature sensor 13 emits a signal corresponding to a measure of the temperature T in connection with the generator. This signal is supplied to the voltage regulator 12. The output voltage of the generator is fed to an output terminal 14 which is connected to a battery 15, which is preferably in the form of the normal storage battery of the motor vehicle. The output terminal 14 of the generator is also connected to a plurality of electrical loads in the vehicle, which loads are illustrated symbolically by means of one single variable load 16. Furthermore, the battery 15 and the load 16 are connected to an earth point 17. An ignition lock 18 is connected between the voltage regulator 12 and the battery 15. During starting of the vehicle, the voltage regulator 12 can be activated by turning the ignition lock 18. An indicator 19 is arranged between the ignition lock 18 and the voltage regulator 12. The indicator 19, which preferably is constituted by a lamp or a light emitting diode, indicates that the ignition lock 18 has been switched on. Furthermore, the device according to the invention comprises a connector 20 between the voltage regulator 12 and one of the stator windings (in this case the stator winding 4). By means of this connector 20, the voltage regulator 12 may detect one of the phases of the generated alternating voltage. In this manner, the regulator can be provided with a measure of the rotation speed of the rotor. The purpose of the voltage regulator 12 is to control the output voltage of the generator 1 so as to keep it essentially constant, regardless of the load and current of the generator. To this end, the voltage regulator 12 is adapted to supply a current to the magnetization winding 1. This current controls the degree of magnetization of the rotor of the generator. In this manner, the output voltage of the generator can be varied as a function of the current through the magnetization winding 1. The magnitude of said current can be controlled depending on the output voltage of the generator, i.e. the voltage at the output terminal 14, and depending on the temperature T. In a manner which is known, the voltage regulator 12 may comprise a field effect transistor (not shown), the conduction time of which may be controlled. In this manner, the magnitude of the current through the magnetization winding 1 can be controlled. The field effect transistor is preferably controlled by means of pulse width modulation, wherein a reduction of the duty cycle of the modulation gives rise to a reduction of the current through the magnetization winding 1. The temperature- and voltage-dependent control in the regulator 12 is shown schematically in the diagram in Fig. 2, which shows the relationship between the temperature T of the regulator 12 and the voltage U on the output terminal 14 of the generator. The relationship according to the diagram defines a voltage interval within which the output voltage U of the generator may vary, assuming a certain given temperature T. This variation is controlled by means of the control of the regulator 12. The voltage control is carried out as follows. First, the regulator 12 detects the output voltage of the generator, i.e. the voltage which is present on the output 14. This is carried out via a connector which is connected from the output 14 to the regulator 12 (see Fig. 1). Alternatively, the connector 20 from one of the stator windings 4 can be used for this purpose. The actual voltage value is compared with a predetermined set value in the regulator 12. The set value depends on the actual temperature T, in accordance with the diagram of Fig. 2, and is determined as a voltage value which is essentially "in the middle of" the voltage interval which corresponds to a certain temperature. The difference between the actual value and the set value generates a signal in the voltage regulator 12 which controls the current through the magnetization winding 1 of the rotor. When the actual value is lower than the set value, the regulator 12 increases the current through the magnetization winding 1. This is carried out by means of the regulator 12 by an increase of the conduction time of a field effect transistor which is connected in series with the magnetization winding 1. This results in an increase of the output voltage of the generator on the output terminal 14. If the actual value is higher than the set value, the current through the magnetization winding is decreased. Due to the control in the regulator 12, the battery 15 is supplied with an optimal voltage for recharging, though not such a high voltage that there is a risk for gassing in the battery 15. Preferably, the system comprises a cooling device in the form of a fan which is arranged on the rotor so that the fan rotates when the rotor rotates. In this manner, the entire generator device, including the regulator 12, can be cooled when the generator is operated. Fans for generators are known per se and are therefore not described in detail. In accordance with the invention, the fan can however be made with relatively small dimensions, i.e. it can be designed so as to provide a relatively low cooling effect, for reasons which will be explained below. The operation of the invention will now be described. When the ignition lock 18 is turned and the combustion engine (not shown) is started, the generator will be activated. This causes an alternating current to be generated in the stator windings 2, 3, 4, which current is rectified in the rectifier 5-10. The rectified output voltage is supplied to the battery 15 and the load 16. Furthermore, the generator 12 senses this output voltage via the connector between the regulator 12 and the terminal 14. Also, a value of the temperature T of the generator is supplied to the regulator 12 by means of the temperature sensor 13. In this regard, the regulator 12 controls the magnitude of the current to the magnetization winding 1 so that the voltage of the generator corresponds to the relationship shown in Fig. 2. After a while, the generator will generate an energy loss, which results in that it will be heated. This results in turn in that cooling becomes necessary. Due to the fact that the invention comprises a fan of relatively small dimensions, i.e. having a relatively low cooling effect, only a εmall fraction of the heat will be dissipated in this initial phase. In this manner, a high coefficient of efficiency can be maintained during this phase. Furthermore, only very little noise is generated by the fan, since the fan is relatively small. During a cold start of the vehicle, a maximum load of the generator exists since a plurality of the electric consumers of the vehicle (for example electrical heating devices for the windows and the seats) are switched on. During this phase, the generator may develop all its output power. The fan forming part of the invention has relatively small dimensions, i.e. it has a relatively low cooling effect. This results in that the temperature T of the generator rises relatively quickly during a cold start, i.e. the temperature T rises quicker than if a conventional fan had been used. Gradually, the temperature T of the generator will increase until it approaches a maximum allowed temperature limit T g , i.e. a temperature at which the components forming part of the generator may be damaged. At the same time as the temperature T increases, some of the electrical consumers in the vehicle will gradually be switched off, since some electrical consumers (for example electrical window heating devices) only have to be switched on immediately after start of the vehicle. This results in that the vehicle's demand for electric power decreases (i.e. the output power of the generator decreases). This results in turn in that the power loss of the generator, and thus also its demand for cooling, decreases. A certain time after start, the power demand of the generator will thus have decreased to a value which corresponds to continuous operation of the vehicle. This "continuous value" is of a magnitude which is approximately 35% of the maximum power of the generator. The fan forming part of the invention is dimensioned so as to provide cooling power which is required for the demand for cooling which exists in this phase. Consequently, during normal operation the generator will never reach its temperature limit T g . Instead, the temperature will be stabilized at a value which is slightly lower than the temperature limit T g . In conventional generators, the fan is dimensioned in accordance with the nominal load of the generator, so that it dissipates the power loss of the generator. In contrast to this, the invention is based on the fact that the fan does not have to dissipate such a high power loss at maximum nominal power of the generator. The fan only dissipates the power loss which exists when the electrical consumers, which in principle are only used during a cold start, have been switched off. During certain kinds of operation, there may still be a risk that the temperature T of the generator increases until it reaches the maximum allowed value T g , i.e. a limit value which corresponds to a maximum allowed temperature which the generator may have without risk that the included components may be damaged. The regulator 12 will detect if the temperature limit T g is reached. In that case, the regulator 12 decreases the current to the magnetization winding 1 to a level which corresponds to the amount of heat which the fan manages to dissipate (i.e. the current is decreased to a level which corresponds to a power level of the generator at which the temperature of the generator is lower than said temperature limit T g ) . The regulation still follows the relationship according to Fig. 2 (assuming that the capacity of the generator is sufficient) but the current is maximized to a value which corresponds to the temperature limit T g . The current to the magnetization winding 1 will be controlled to a level which corresponds to an output current from the generator at which a relatively low amount of heat is generated, more precisely an amount of heat which is not harmful to the components in the generator. This amount of heat may vary for different types of generators. The invention provides a generator operation with a higher coefficient of efficiency and with a lower level of disturbing noise from the generator. In the case where a very high number of electrical consumers are in operation in the vehicle, a very high current is required during cold starts. In modern cars, the required current for the switched-on current consumers can be approximately 200 A during starting in cold climate. The relatively small fan will be dimensioned so as to dissipate a power loss from the generator at a condition of balance which is reached at a time when the current demand in the vehicle has decreased, i.e. when for example the interior has been heated and frost on the windows has been removed. In this manner, an effective use of the generator is possible when a particularly high current demand exists. The invention is particularly intended for use in connection with motor vehicles, but can also be used together with generators in other applications. The invention uses a temperature sensor 13 which may be a separate sensor device which is connected to the regulator 12 or which alternatively can be one or several diodes which form part of the regulator 12, the temperature sensitivity of which is used as a temperature-detecting means. In the case where a separate temperature sensor is used, it can be arranged on a particular component which is arranged in or in connection with the generator and which is particularly temperature-sensitive. Furthermore, several types of cooling can be used in connection with the invention. Besides fans, water and air cooling can be used. No cooling device is needed in those cases where the current to the magnetization winding 1 is controlled down to a value corresponding to a very low generation of heat of the generator. In accordance with a possible embodiment of the invention, the current to the magnetization winding 1 can be controlled as a function of the speed of the generator. This can be accomplished by arranging an engine speed sensor in connection with the generator or by using a measure of the speed of the generator via the connector 20. This regulation is based both on the fact that a predetermined relationship between the speed and temperature of the generator exists, and the fact that a cold generator generates a higher current than a hot generator, since the resistance in the stator windings changes with temperature. Finally, the generator does not have to be provided with any temperature sensor. This applies in those cases where the fan is sufficiently well-dimensioned so as to dissipate the loss of power with a sufficient margin to the temperature limit T g .

Claims: CLAIMS : 1. Device comprising a generator which during operation generates a voltage across at least one electrical load (15, 16) and comprising a regulator (12) for control of the voltage from the generator and a cooling device for cooling of power loss from the generator, c h a r a c t e ¬ r i z e d i n that said cooling device has dimensions which correspond to cooling of a power loss from the generator during a continuous state which exists after reduction of the power of the generator following switching off of at least one electrical load (16) which is used during an initial load of the generator. 2. Device according to claim 1, further comprising a temperature sensor (13) for measuring a temperature (T) in connection with the generator, the regulator (12) being adapted to supply a current to the magnetization winding (1) depending on the temperature (T), for control of the voltage from the generator, c h a r a c t e r i z e d i n that the regulator (12) comprises means for detecting whether values from the temperature sensor (13) are higher than a temperature limit (T g ) corresponding to the maximal allowed temperature of the generator, and that the regulator (12) comprises current feeding means which, in the case where the temperature is higher than the temperature limit (T g ), is adapted to feed a current to the magnetization winding (1) , the magnitude of which current corresponds to a heat generation of the generator at which its maximal allowed temperature is not reached. 3. Device according to any one of claim 1 or 2, c h a r a c t e r i z e d i n that the cooling device is constituted by a fan. 4. Method for control of a generator which during operation generates a voltage across at least one electrical load (15, 16), the generator comprising a magnetization winding (1) and a regulator (12) which supplies a current to the magnetization winding (1) depending on a temperature (T) which is measured in connection with the generator, for control of the voltage from the generator, c h a r a c ¬ t e r i z e d i n that it comprises the following steps: - detection whether the measured temperature (T) is higher than a temperature limit (T g ) corresponding to the maximum allowed temperature of the generator and, in the case where the temperature is higher than the temperature limit (T g ), - reduction of the current supplied to the magnetization winding (1) to a magnitude which corresponds to a heat generation of the generator at which itε maximal allowed temperature is not reached. 5. Method according to claim 4, comprising cooling of the generator, c h a r a c t e r i z e d i n that said current magnitude is chosen so that it results in a heat generation of the generator at which the cooling is sufficient to maintain the generator below its maximal allowed temperature (T g ). 6. Method according to any one of claim 4 or 5, c h a r a c t e r i z e d i n that the output voltage of the generator is fed to the regulator (12) and that the supply of current to the magnetization winding (1) is also carried out depending on the level of said output voltage. AMENDED CLAIMS [received by the International Bureau on 07 January 1997 (07.01.97) original claims 1 and 3 amended ; original claims 4-6 cancelled; remaining claim unchanged (2 pages)] 1. Device comprising a generator which during operation generates a voltage across at least one electrical load (15, 16) and comprising a regulator (12) for control of the voltage from the generator and a cooling device for cooling of power loss from the generator, c h a r a c t e ¬ r i z e d i n that said cooling device is constituted by a fan having dimensions which correspond to cooling of a power loss from the generator during a continuous state which exists after reduction of the power of the generator following switching off of at least one electrical load (16) which is used during an initial load of the generator. 2. Device according to claim 1, further comprising a temperature sensor (13) for measuring a temperature (T) in connection with the generator, the regulator (12) being adapted to supply a current to the magnetization winding (1) depending on the temperature (T), for control of the voltage from the generator, c h a r a c t e r i z e d i n that the regulator (12) comprises means for detecting whether values from the temperature sensor (13) are higher than a temperature limit (T g ) corresponding to the maximal allowed temperature of the generator, and that the regulator (12) comprises current feeding means which, in the case where the temperature is higher than the temperature limit (T g ), is adapted to feed a current to the magnetization winding (1), the magnitude of which current corresponds to a heat generation of the generator at which its maximal allowed temperature is not reached. Ql U IBRCSTITUTE SHEET (RULE 28$ 3. Device according to claim 1, c h a r a c t e ¬ r i z e d i n that the dimensions of the fan are chosen so that the fan provides a cooling effect which ensureε that the temperature of the generator does not exceed a temperature limit (T g ) which corresponds to the maximal allowed temperature of the generator.

Inventors: MLAKAR ZVONKO, MLAKAR, ZVONKO
Applicants: MLAKAR ZVONKO, VOLVO AB, AB VOLVO, MLAKAR, ZVONKO
Application year: 1996
Main classification: H02P9
IPC codes: H02P9