Method for controlling a generator for power generation in a motor vehicle

Abstract

Method for controlling a generator (2) for generating electricity in a motor vehicle, wherein the generator (2) is driven by an internal combustion engine (1) of the motor vehicle and is thereby controlled as a function of an excitation current (I err ) in an excitation winding (3) of the generator (2) generates electrical energy, which is fed into an energy network (BN) of the motor vehicle comprising an electrical energy store (6), wherein in one or more predetermined operating states of the motor vehicle in the excitation winding (3) of the generator (2) an excitation current (I err) with a constant excitation current value as long as the voltage of the generator (2) lies in a predetermined voltage interval (IV) which is limited by an upper and lower voltage limit value, characterized in that the predetermined operating state or states comprise an operating state which begins with the start of the internal combustion engine (1) and is ended again if the voltage of the generator (2) leaves the predetermined voltage interval (IV).

Description

[0001] The invention relates to a method for controlling a generator for generating electricity in a motor vehicle as well as a corresponding device and a corresponding motor vehicle.

[0002] To feed electrical energy into a motor vehicle's power grid, electric generators are used. These generators are connected to the vehicle's drivetrain and driven by the vehicle's internal combustion engine. Depending on an excitation current in an excitation winding, the generators convert mechanical energy into electrical energy, which is then fed into the vehicle's power grid.

[0003] Traditionally, an electric generator in a motor vehicle is operated with voltage regulation, meaning the excitation current in the generator's excitation winding is adjusted so that the voltage supplied by the generator corresponds to a target voltage. This type of operation can be disadvantageous, for example, during large load surges in the vehicle's power grid, as this causes the generator's torque to vary significantly, forcing torque control of the combustion engine to adjust the engine's torque accordingly, which in turn can lead to increased emissions.

[0004] The document DE 10 2007 035 701 A1, which forms the preamble of claim 1, discloses a device for controlling a motor vehicle generator, wherein in an emergency operation of the motor vehicle generator, its excitation winding is subjected to a constant excitation current.

[0005] Document JP H09-266700 A discloses the control of an excitation current and a torque current in a drive motor of an electric vehicle which is powered by a battery.

[0006] Document DE 196 38 357 A1 describes a voltage regulator for a generator driven by an internal combustion engine. The voltage regulator is equipped with a load response function that prevents a rapid increase in the excitation current when a high-power electrical load is connected. During driving, the load response function is disabled when the engine speed decreases, thus largely avoiding the voltage drops that occur when the load response function is active.

[0007] The document DE 10 2011 105 883 A1 discloses a method for controlling a generator, wherein an excitation current of the generator is adjusted depending on a deviation of a generator output voltage from a predetermined target voltage.

[0008] The object of the invention is to provide a method for controlling a generator for generating electricity in a motor vehicle, which method ensures efficient operation of the internal combustion engine of the motor vehicle and a defined electrical power supply.

[0009] This object is achieved by the method according to claim 1 and the device according to claim 14. Further developments of the invention are defined in the dependent claims.

[0010] The method according to the invention serves to control a generator for generating power in a motor vehicle. A preferred variant of this generator is a claw-pole generator. During operation of the motor vehicle, the generator is driven by the vehicle's internal combustion engine and, depending on an excitation current in an excitation winding of the generator, generates electrical energy. This energy is fed into a power grid of the motor vehicle, comprising an electrical energy storage device and a number of electrical consumers.

[0011] In the method according to the invention, in one or more predetermined operating states of the motor vehicle, an excitation current with a constant excitation current value is set in the excitation winding of the generator, as long as the voltage of the generator lies in a predetermined voltage range which is limited by an upper and lower voltage limit. The term upper voltage limit is understood to mean a voltage value which continues to ensure the intended operation of the motor vehicle and in particular of its energy network without damage to components. In particular, the upper voltage limit lies in the range of the maximum charging voltage of the electrical energy storage device of the energy network. In contrast, the lower voltage limit can correspond to a voltage of zero or can be selected to be higher, but always smaller than the upper voltage limit. Here and in the following, current values ​​orVoltage values ​​are always to be understood as positive values.

[0012] In the method according to the invention, the predetermined operating state(s) comprise an operating state that begins with the start of the internal combustion engine and ends again if the generator voltage leaves the predetermined voltage range. This has particular advantages because, in conventional voltage-controlled operation, a torque jump occurs when the generator is switched on during the start of the internal combustion engine. This leads to a regulation of the torque of the internal combustion engine and thus to higher engine emissions. The start of the internal combustion engine can refer to a cold start or, if necessary, a warm start within the framework of an automatic start / stop system of the internal combustion engine.

[0013] The method according to the invention has the advantage that, in certain operating states, the generator exhibits a defined torque due to the constant excitation current. Thus, the torque delivered by the combustion engine is constant and does not represent a disturbance that needs to be corrected. This ensures energy-efficient operation of the combustion engine with low emissions.

[0014] In a particularly preferred embodiment of the method according to the invention, outside of the predetermined operating state(s), the excitation current is controlled in a conventional manner based on a setpoint voltage value of the generator as a controlled variable, wherein the setpoint voltage value preferably corresponds to the upper voltage limit value of the voltage interval.

[0015] In a preferred embodiment of the invention, the operating state initiated by the start of the internal combustion engine is terminated after a predetermined period of time, provided that the generator voltage is still within the predetermined voltage range upon expiration of the predetermined period of time, wherein the predetermined period of time is preferably between 25 ms and 1 min. This ensures that the generator exits from constant excitation current operation.

[0016] In a further variant of the method according to the invention, the predetermined operating state(s) comprise an operating state that is linked to a rotational speed of the internal combustion engine and is always present when the rotational speed of the internal combustion engine is less than or equal to a predetermined rotational speed value of the internal combustion engine. The predetermined rotational speed value is in particular 1500 revolutions per minute or less and, in a preferred variant, corresponds to the idle speed of the internal combustion engine. According to this variant of the invention, stabilization of the idle speed of the internal combustion engine can be achieved.

[0017] In a further variant of the method according to the invention, the predetermined operating state(s) comprise(s) an operating state that is coupled to a speed of the motor vehicle and always exists when the speed of the motor vehicle is less than or equal to a predetermined speed value, wherein the predetermined speed value is preferably 15 km / h or less. Optionally, the predetermined operating state(s) can also comprise(s) an operating state that is coupled to a coasting operation of the motor vehicle, so that this operating state always exists when the motor vehicle is in coasting operation. Coasting operation is characterized in that, when the motor vehicle is moving, the combustion engine is decoupled from the rest of the drive train.

[0018] In a preferred embodiment, the lower voltage limit of the voltage interval is set to a value greater than zero. This value preferably does not exceed a predetermined open-circuit voltage of the electrical energy storage device in the vehicle's power grid.

[0019] In a preferred variant, the method according to the invention is used in a low-voltage on-board power supply of a motor vehicle, and in particular in a 12 V on-board power supply. In such a low-voltage on-board power supply, voltage values ​​between 14 V and 15 V or 14.5 V have proven to be particularly practical as the upper voltage limit of the voltage interval. In this case, the constant excitation current value is preferably set such that a generator output current fed into the power grid of between 15 A and 60 A results. The value should be selected such that the base current requirement of the vehicle is covered by this value. Depending on the vehicle type, suitable values ​​for the constant excitation current can be specified in advance. In a low-voltage on-board power supply, voltage values ​​between 11 V and 13 V, and preferably between 11.4 V and 12.6 V, have proven to be particularly practical as the lower voltage limit of the voltage interval.

[0020] In a particularly preferred embodiment of the method according to the invention, the voltage interval and / or the constant excitation current value and / or the predetermined time period can be varied, wherein certain criteria can be taken into account for this depending on the application.

[0021] In a further preferred embodiment of the method according to the invention, the constant excitation current value is adaptively determined or appropriately learned depending on a previous electrical energy demand in the vehicle's on-board power system. Implementing an adaptive determination of the excitation current value is within the scope of expert practice.

[0022] In a further embodiment of the method according to the invention, the constant excitation current value is set by a generator controller, which can preferably communicate with one or more other control units of the motor vehicle, such as the engine control unit or a control unit of the electrical energy storage device. The generator controller then receives the constant excitation current value and / or the voltage interval from these other control units.

[0023] In addition to the method described above, the invention further relates to a device for controlling a generator for generating electricity in a motor vehicle. The generator is driven by a combustion engine of the vehicle during operation of the motor vehicle and, depending on an excitation current in an excitation winding of the generator, generates electrical energy, which is fed into a power grid of the motor vehicle comprising an electrical energy storage device. The device is designed such that the method according to the invention or one or more preferred variants of the method according to the invention can be carried out with the device.

[0024] The invention further relates to a motor vehicle with a generator for generating electricity. The generator is driven by a combustion engine of the vehicle during operation of the motor vehicle and, depending on an excitation current in an excitation winding of the generator, generates electrical energy, which is fed into a power grid of the motor vehicle comprising an electrical energy storage device. The motor vehicle is characterized in that it contains the above-described device according to the invention for controlling the generator.

[0025] An embodiment of the invention is described below with reference to the attached Fig. 1 is described in detail. This figure shows, among other things, a schematic representation of an electric generator in a motor vehicle that is controlled based on a variant of the invention.

[0026] In Fig. Figure 1 shows the internal combustion engine 1 of a motor vehicle, indicated as a piston. The internal combustion engine drives the vehicle's drivetrain, which is schematically represented in a sectional view along an axis A. An electric generator 2 is coupled to the drivetrain. This generator is designed as a claw-pole generator and converts mechanical energy of the drivetrain into electrical energy in the form of direct current by means of a belt R. Instead of a claw-pole generator, other types of electric generators or machines can also be controlled using the method according to the invention.

[0027] To generate power, the generator contains an excitation winding 3 in its rotor, which generates a rotating magnetic field. Induces current in corresponding stator windings in a manner known per se. This current is converted into direct current via a rectifier circuit, i.e., diodes or switched MOSFETs (not shown). This direct current is fed into the vehicle's low-voltage electrical system BN. The electrical system BN comprises an electrical energy storage device in the form of a 12V battery 6, which can be charged via the generator, and a power distributor 7, which distributes the power to consumers in the electrical system, the consumers being indicated only schematically by reference numerals 8 and 9.

[0028] The generator 2 further comprises a generator controller 4, via which the excitation current I errin the excitation winding 3 and thereby controls the energy generated by the generator. In the embodiment described here, when the internal combustion engine is started, the excitation current I err set to a constant value as long as the generator voltage measured by a corresponding sensor lies within a predetermined voltage interval IV, which can be adjusted upwards by a setpoint voltage U soll is limited. The generator regulator 4 communicates with other components in the vehicle. Another component is the engine control unit 5. In this engine control unit, the target voltage value U soll which is then provided to the generator controller via a communication bus. Furthermore, the constant excitation current value is determined in a control unit (not shown) of the power grid or the electrical energy storage device 6 and is also provided to the generator controller 4 via a bus.

[0029] As already mentioned above, in the embodiment described here, a constant value of the excitation current I errin the excitation winding 3. In contrast, with a conventional generator control the excitation current is always set based on a target voltage value of the voltage generated by the generator, i.e. the excitation current is controlled such that the generator voltage has a predetermined target voltage value. With conventional control, when the engine is started, the excitation winding is slowly energized up to the control value by means of a so-called load response function, i.e. the generator attempts to regulate the target voltage. The control value is determined by the current demand of the on-board electrical system, i.e. by the demand of the corresponding consumers and the current with which the battery 6 is charged. With this type of control, the combustion engine initially sees no load on the generator when it starts, as long as the generator voltage has not yet reached the voltage of the battery 6.If the battery voltage is exceeded, a load surge occurs, as the vehicle electrical system then draws electrical energy from the generator. This requires the combustion engine to maintain a certain amount of torque to compensate for the generator's activation. However, a large torque reserve in the combustion engine or the compensation of the load surge leads to increased exhaust emissions and is therefore relevant to emissions.

[0030] To circumvent this problem, in the embodiment described here, no control to a target voltage value is carried out for a predetermined period of time when the engine is started, but rather a fixed excitation current is set. This ensures that the generator behaves approximately like a consumer with a constant torque. The torque delivered by the combustion engine is therefore constant and does not represent a disturbance that needs to be regulated. With a constant current in the excitation winding, the generator supplies a current proportional to this. The generator therefore essentially operates like a current source whose output voltage adjusts as a function of the load. This type of operation when the combustion engine is started also inherently supports the stabilization of the idle speed of the combustion engine. Compared to control with a load response function, a higher voltage is established right from the start.This is useful both for exhaust-relevant pumps (secondary pump) and for good performance of an electric steering system.

[0031] According to the invention, the setting of a constant excitation current value is maintained as long as the generator voltage lies within the voltage interval IV. In the embodiment described here, the upper limit of the voltage interval corresponds to the target voltage value U sollto which the generator voltage is set in the case of voltage-regulated operation. The upper limit is always selected such that no voltages are reached that could lead to damage to components in the vehicle electrical system. In particular, the limit is not higher than the maximum charging voltage of battery 6. The lower limit of the voltage interval is preferably set in a range that corresponds to the open-circuit voltage of battery 6 or deviates from it by approximately 1.5 V upwards or downwards. The lower the value, the more frequently the vehicle electrical system is fed purely by the battery and not the generator. A lower lower limit is used in particular when emission-relevant operation is of great importance. In the embodiment of the Fig. 1 shows a 12V electrical system as the on-board network BN. In this case, the upper limit or target voltage value U sollA value of approximately 14.5 V is used. In contrast, the lower limit is in the range between 11.4 V and 12.6 V.

[0032] The operation of the generator with constant excitation current after starting the combustion engine is terminated when the voltage interval IV is left. The generator then switches to conventional voltage-controlled operation, as this operation of the generator is then more favorable for the power supply of the consumers in the vehicle electrical system or for charging the battery. In a preferred variant, the operation with constant excitation current is terminated in any case after a predetermined period of time, even if the voltage interval has not been left. Depending on the design of the control, this period of time is preferably between 25 s and 1 min. The constant excitation current value is Fig.1 is suitably adjusted depending on the (assumed) energy demand in the vehicle electrical system, resulting in a generator output current of typically between 15 A and 60 A. If necessary, the value of the constant excitation current can also be adaptively learned based on the energy demand at previous points in time. This means that the current energy demand is predicted using known methods based on the energy demand at previous points in time, and the excitation current value is adjusted according to the forecast.

[0033] The invention described above was based on operation with a constant excitation current during start-up of the internal combustion engine. Nevertheless, a corresponding current supply with a constant excitation current can also be implemented in other operating states of the motor vehicle, e.g., when the engine is idling or the motor vehicle is coasting, in which the engine is decoupled from the rest of the drivetrain while the vehicle is moving. Even in this case, load surges in the on-board electrical system do not lead to a readjustment of the torque of the internal combustion engine, thereby reducing emissions or stabilizing the idle speed. Reference symbol 1 engine 2 generators 3 Excitation coil 4 generator regulators 5 Engine control 6 Battery 7 power distributors 8, 9 electrical consumers I err Excitation winding IV voltage interval U soll Target voltage value of the generator BN on-board network A axis R belt

Claims

[1] Method for controlling a generator (2) for generating electricity in a motor vehicle, wherein the generator (2) is driven by an internal combustion engine (1) of the motor vehicle and is thereby controlled as a function of an excitation current (I err ) in an excitation winding (3) of the generator (2) generates electrical energy, which is fed into an energy network (BN) of the motor vehicle comprising an electrical energy store (6), wherein in one or more predetermined operating states of the motor vehicle in the excitation winding (3) of the generator (2) an excitation current (I err ) with a constant excitation current value as long as the voltage of the generator (2) is within a predetermined voltage interval (IV) limited by an upper and lower voltage limit, characterized bythat the predetermined operating state(s) comprise an operating state which begins with the start of the internal combustion engine (1) and is ended again if the voltage of the generator (2) leaves the predetermined voltage interval (IV). [2] Method according to claim 1, characterized by that outside the specified operating condition(s) the excitation current (I err ) based on a target voltage value (U soll ) of the generator (2) is controlled as a control variable, whereby the target voltage value (U soll ) preferably corresponds to the upper voltage limit of the voltage interval (IV). [3] Method according to one of the preceding claims, characterized bythat the operating state initiated by the start of the internal combustion engine (1) is ended after a predetermined period of time has elapsed, provided that at the end of the predetermined period of time the voltage of the generator (2) is still in the predetermined voltage interval (IV), wherein the predetermined period of time is preferably between 25 msec and 1 min. [4] Method according to one of the preceding claims, characterized by that the predetermined operating state(s) comprise an operating state which is coupled to a rotational speed of the internal combustion engine (1) and is always present when the rotational speed of the internal combustion engine (1) is less than or equal to a predetermined rotational speed value of the internal combustion engine (1), wherein the predetermined rotational speed value is in particular 1500 rpm or less and preferably corresponds to the idling speed of the internal combustion engine (1). [5] Method according to one of the preceding claims, characterized bythat the predetermined operating state(s) comprise an operating state which is coupled to a speed of the motor vehicle and is always present when the speed of the motor vehicle is less than or equal to a predetermined speed value, wherein the predetermined speed value is preferably 15 km / h or less. [6] Method according to one of the preceding claims, characterized by that the specified operating state(s) include an operating state which is linked to a coasting operation of the motor vehicle and is always present when the motor vehicle is in coasting operation. [7] Method according to one of the preceding claims, characterized by that the lower voltage limit value of the voltage interval (IV) is greater than zero and preferably does not exceed a predetermined open-circuit voltage of the electrical energy storage device (6) in the energy network (BN) of the motor vehicle. [8] Method according to one of the preceding claims, characterized by that the energy network (BN) of the motor vehicle is a low-voltage electrical system and in particular a 12V electrical system. [9] Method according to claim 8, characterized by that the upper voltage limit of the voltage interval (IV) is between 14 V and 15 V and in particular 14.5 V and / or the constant excitation current value is set such that the generator output current fed into the power grid (BN) is between 15 A and 60 A. [10] Method according to claim 8 or 9 in combination with claim 7, characterized by that the lower voltage limit of the voltage interval (IV) is between 11 V and 13 V, in particular between 11.4 V and 12.6 V. [11] Method according to one of the preceding claims, characterized by that the voltage interval (IV) and / or the constant excitation current value and / or the predetermined time period can be varied. [12] Method according to one of the preceding claims, characterized by that the constant excitation current value is determined adaptively depending on a previous demand for electrical energy in the energy network (BN) of the motor vehicle. [13] Method according to one of the preceding claims, characterized by that the setting of the constant excitation current value is carried out by a generator controller (4) which can preferably communicate with one or more other control units (5) of the motor vehicle, from which the generator controller (4) receives the constant excitation current value and / or the voltage interval (IV). [14] Device for controlling a generator (2) for generating electricity in a motor vehicle, wherein the generator (2) is driven by an internal combustion engine (1) of the motor vehicle and is thereby controlled as a function of an excitation current (I err) generates electrical energy in an excitation winding (3) of the generator (2), which is fed into an energy network (BN) of the motor vehicle comprising an electrical energy store (6), characterized by that the device is designed such that a method according to one of the preceding claims can be carried out with the device. [15] Motor vehicle with a generator (2) for generating electricity, wherein the generator (2) is driven by an internal combustion engine (1) of the motor vehicle and, in this case, as a function of an excitation current (I err ) generates electrical energy in an excitation winding (3) of the generator (2), which is fed into an energy network (BN) of the motor vehicle comprising an electrical energy store (6), characterized by that the motor vehicle comprises a device for controlling the generator (2) according to claim 14.

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