CN111608837B

CN111608837B - Method and device for supporting a starting process of an internal combustion engine

Info

Publication number: CN111608837B
Application number: CN202010111772.8A
Authority: CN
Inventors: J.米勒; W.菲舍尔
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2019-02-25
Filing date: 2020-02-24
Publication date: 2023-05-23
Anticipated expiration: 2040-02-24
Also published as: CN111608837A; DE102019202475A1

Abstract

The invention relates to a method for supporting a starting process of an internal combustion engine (60) by means of a synchronous machine (50), which can be operated as a generator in a first operating state and as an electric motor in a second operating state, comprising: -identifying (100) a rotor movement of a rotor (55) of a synchronous motor (50) starting at a first angular velocity, the first angular velocity corresponding to a first frequency; -operating (110) the synchronous motor (50) by applying an alternating voltage having a second frequency, the second frequency being greater than the first frequency; identifying (200) a transition between a first and a second operating state of the synchronous machine (50); and adapting (120) the actuation of the synchronous machine (50) on the basis of the identified transitions.

Description

Method and device for supporting a starting process of an internal combustion engine

Technical Field

The invention relates to a method and a device for supporting a starting process of an internal combustion engine, as well as a computing unit and a computer program for carrying out the method.

Background

In particular in smaller vehicles, such as in the field of motorcycles with small internal combustion engines, permanent-magnet excited synchronous generators are often used, which are rigidly coupled to the crankshaft of the internal combustion engine. The generator is used to supply the electrical energy to the on-board network (battery, control device, ignition, injection, etc.).

Here, the generator may unify three functions: in addition to supplying the on-board network with electrical energy, a firmly embodied rotor represents a rotational mass (schwungmass) for stabilizing the operating characteristics of the internal combustion engine. Furthermore, a metallic marking or tooth may be present on the rotor, which together with the rotational speed sensor generates a rotational speed signal and a crankshaft position signal for the motor control device. This is required for reliable operation of the internal combustion engine.

It is possible that an electric machine provided in the vehicle as a generator is also used as a motor in certain situations by means of a suitable design and circuit connection and is therefore used in two different operating modes. In this way, the mixing of the drive trains is achieved.

For starting the internal combustion engine, different starting methods can be used, such as an electromechanical starter or an actuator, i.e. an electric motor, the shaft of which is coupled to the crankshaft via a fixed gear and which can temporarily drive the crankshaft during starting. In motorcycles, for example, a pedal start is likewise possible, in which the crankshaft is mechanically accelerated by pedaling. The starting method pulls the motor to the necessary minimum rotational speed before the first injection and ignition takes place and the motor transitions to combustion operation. In order to be able to carry out the starting process from very low rotational speeds, the first combustion cycle is triggered by a very greasy mixture, i.e. more fuel is injected than can be completely combusted. This produces unburned carbon chains in the exhaust gases, so that a combustion which is highly loaded but rich in pollutants is achieved, and the motor speed is caused to rise significantly above the starter speed level. Even when the usual motor idle speed is reached, the fraction of fuel is reduced and the complete combustion of the fuel is used to achieve an optimized pollutant operation. However, according to current regulations, it has been necessary to achieve as effective a reduction of emissions as possible during start-up.

An electric machine that can be used as a motor can be used as a starter generator; the sizing of the motor is often just insufficient to complete the starting process alone in smaller vehicles.

Disclosure of Invention

According to the invention, a device and a method for supporting a starting process of an internal combustion engine by parallel use of a starter and an electric machine that can be used as a motor, as well as a computing unit and a computer program for carrying out the method are proposed, which have the features of the independent claims. Advantageous embodiments are the subject matter of the dependent claims and the following description.

According to the invention, a method is proposed, which uses an electric machine, which can be used not only as an electric motor but also as a generator, wherein a rotor movement of a rotor of the synchronous machine, which starts at a first frequency, is first detected and the synchronous machine is subsequently actuated by applying an alternating voltage having a second frequency, wherein the second frequency is greater than the first frequency; in this case, a transition between generator operation and motor operation of the electric machine is detected. Once the transition is detected, it can be used as a basis for adapting the actuation of the electric machine, so that the electric machine can already be used as a motor at the beginning of the starting process. By means of a combination of a conventional starter and the motor used thereby, the starting speed can be increased significantly before the first combustion. There is thus the possibility of reducing the load and wear of the starter, reducing the noise emissions of the starter or using a smaller-sized starter (for example with smaller energy requirements or installation space). Furthermore, by increasing the starting rotational speed before the first combustion cycle, the previously described exhaust gas problems of cold starts are improved and thus future emission regulations are complied with.

The identification of the transition between generator operation and motor operation can be achieved in different ways. Exemplary embodiments are, for example:

-identifying an elevated angular acceleration of the rotor by means of a rotational speed measurement; as used herein, a significant increase in acceleration is expected in the transition from braked generator operation to accelerated motor operation.

-detecting a current flow from the battery to the use of an inverter connected between the battery and the motor; once running with the motor, current flow from the battery is expected.

-measuring the current of a phase between the inverter and the motor and identifying when the current and the voltage transition to a state of opposite phase with respect to each other.

By identifying the transition to motor operation in advance of the known rotor position or crankshaft position, the electric machine can already be used as a support at the beginning of the starting process.

According to an embodiment of the invention, the rotor of the synchronous machine is rigidly connected to the crankshaft of the internal combustion engine, and the angular speed of the rotor is measured by a rotational speed sensor of the crankshaft or of the rotor. Preferably, the crankshaft of the motor is placed in motion by the electromechanical starter. In contrast to classical devices, this implementation requires no or only a small number of changes and can therefore be easily implemented and can be implemented only by using modified power electronics, in particular also in vehicles with small internal combustion engines, such as motorcycles. For the same reason, this method is particularly suitable for permanent magnet excited synchronous motors which are inexpensive and easy to install, but can equally well be used with other motors.

The computing unit according to the invention, for example a control device of a motor vehicle or a separate control unit for an electric motor, is provided in particular in terms of program technology for carrying out the method according to the invention.

The implementation of the method according to the invention in the form of a computer program product or a computer program with program code for performing all method steps is also advantageous, since this results in particularly low costs, in particular if the implemented control device is also used for further tasks and is therefore originally present. Suitable data carriers for providing computer programs are in particular magnetic, optical and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs, etc. Downloading of programs via a computer network (internet, intranet, etc.) is also possible.

Additional advantages and design aspects of the present invention will be set forth in the description and drawings.

Drawings

The invention is schematically illustrated in the drawings by means of embodiments and is described subsequently with reference to the drawings.

Fig. 1 shows a schematic structure of a circuit for using an electric machine as a generator and a motor;

FIG. 2 shows a schematic relationship of elements for use in an exemplary embodiment of the invention; and is also provided with

Fig. 3 shows exemplary steps of an embodiment of the present invention.

Detailed Description

Common power electronics need to be changed in order to be able to use the electric machine as a generator and motor. The following description relates to a permanent magnet excited synchronous motor, but other generators may also operate in a similar manner. For this purpose, the rectifier of a typical voltage regulator or generator can be replaced, for example, by a modified circuit of an inverter with semiconductor switches, which is usually implemented as a passive diode rectifier. For example, it is possible to use active transistor bridge circuits for this purpose, with which not only the rectifier for generator operation but also the inverter for motor operation can be used. For example, a MOSFET bridge circuit can be used here, but other transistors can also be used.

A typical bridge circuit of this kind with a corresponding control unit 30, for example a motor control device, for a three-phase motor is shown in fig. 1 as an example for an inverter 10. The adaptation to the other phase numbers is achieved by adding or removing individual bridge lines. The control unit 30 can control the individual switches 20 as a function of the desired electrical power of the motor and the rotor position of the motor. The output power may be positive (generator operation) or negative (motor operation). The converter 10 is furthermore connected to a powered and rechargeable battery 40, which also feeds the on-board network 45 of the vehicle.

The synchronous machine 50 with the rotor 55 thus actuated can be used to support the starter during starting. Fig. 2 shows a schematic top view of an element for use in an exemplary method of the invention. In this case, an electromechanical starter 80 is often used, which is formed by an electric motor whose shaft is rigidly coupled to the crankshaft 65 of the internal combustion engine 60 via a fixed gear mechanism and can drive the crankshaft during starting. In some constructions, the rotor 55 of the synchronous motor 50 may be disposed directly on the crankshaft 65 or directly connected thereto. The synchronous machine is in this example, as already in fig. 1 (simplified here), operated by means of a converter 10, which in turn is connected to a battery 40.

The control unit 30, for example a motor control unit (ECU), however generally does not have information that a starting process has been triggered. The control device receives a signal from the rotational speed sensor 70 indicating a starting process only when the crankshaft 65 of the motor 60 is in motion.

Such a rotational speed sensor 70 can be realized, for example, by a sensor wheel (not shown) mounted on the crankshaft 65 and a corresponding sensor, for example, an inductive sensor or a hall sensor.

The sensor 70 records the passing marks (e.g. teeth) and determines the rotational speed or rotational speed by the time difference between the two marks. The absolute position of the crankshaft 65 is additionally detected by means of further markers, in particular tooth grooves on the sensor wheel, in order to determine the timing for the injection and ignition of the internal combustion engine 60, for example, correctly. Once several markers run past the rotational speed sensor 70, the sensor can recognize that the crankshaft is moving, for example, based on actuation by a starter. The current rotational or angular speed of the crankshaft can now likewise already be determined. In the rigid connection between the crankshaft 65 and the rotor 55, this also corresponds to the angular velocity of the rotor 55.

The typical function of the motor control device 30 is only used if the absolute position of the crankshaft 65 is also known based on the clearance in the rotational speed signal. However, since the starting process should be as short as possible, it is desirable to support the starter 80 directly from the beginning by the electric motor. In order to operate the inverter 10 such that the electric machine 50 operates as a motor with as much torque as possible, however the position of the rotor 55 of the electric machine must be known. In other cases, the switching process may be improperly placed, such that the electric machine 50 operates as a generator with maximum braking torque and thus prevents the starter 80. Thus, the manipulation of the motor can be ensured to a correct extent only if the synchronization with the absolute position of the shaft is actually performed.

Even before a gap in the rotational speed signal can be identified, an earlier use of the electric motor 50 can be achieved in parallel with the starter 80 in various ways. Fig. 3 shows method steps of an exemplary embodiment of the invention, wherein not all shown steps have to be carried out and further steps not shown in the figures may be used.

In step 100, a beginning rotor movement of the rotor 55 is detected by the rotational speed sensor 70.

According to an embodiment of the invention, the converter 10 is now operated in step 110 at a frequency higher than the frequency of the operating crankshaft. Once the crankshaft 65 is placed in motion by the starter 80 or otherwise placed in motion, the rotational frequency or angular velocity of the crankshaft 65 (corresponding to the frequency of the rotor 55 of the motor) may be determined by the speed sensor 70 between at least two marker passes (Markierungsdurchgaengen). As a result of the higher frequency of the operation, the voltage signal of the inverter 10 powering the stator coils of the motor and thus the magnetic field generated in the coils overruns the rotor 55 during the electrical operation cycle. From this point in time, the electric machine 50 operates as a motor. As soon as the magnetic field of the stator coil catches up with the rotor 55, the electric machine 50 operates as a generator and thus brakes the rotor 55 and the connected crankshaft 65. If a transition point between operation as a generator and operation as a motor can thus be identified in step 200, it is possible to correspondingly carry out the actuation of the electric machine 50 in a subsequent step 120 and to bring about the support of the starter 80. As soon as the play in the rotational speed signal is also detected by the rotational speed sensor 70 and thus the crankshaft or rotor position can be reliably determined, the control signal can thus be validated or correspondingly readjusted in order to maximize the available supported torque.

The method flow shown in step 200 is three alternatives, which may be used individually or at least in part together to identify transitions between operating modes.

The possibility for this is to evaluate the angular velocity, which can be measured by the rotational speed sensor 70. Since the electric machine 50 brakes the shaft during generator operation, but additionally drives the shaft during motor operation, a more pronounced increase in the angular velocity should be possible in the transition between generator operation and motor operation. The control unit 30 (or another control unit) may evaluate the angular velocity obtained in step 210 and thereby obtain the current angular acceleration (step 220). Because the crankshaft 65 begins to operate, this angular acceleration is typically greater than zero during start-up. Once the braking action of the generator 50 is removed and additional motor drive is used, the angular acceleration will thus rise in a recognizable manner. The increase in angular acceleration represents a transition between generator operation and motor operation in step 230. Conversely, a decrease in angular acceleration also indicates whether the motor 50 transitions back into generator operation, and the inverter frequency must be further increased. Alternatively, a minimum value can be determined above which the change in the angular acceleration must be raised in order to avoid misinterpretation of rotational speed fluctuations, which are caused, for example, by gas forces in the cylinder or by friction forces during operation of the shaft.

According to another embodiment, in order to determine 200 a transition between generator operation and motor operation, a current may be measured in step 240, which current flows between the rechargeable vehicle battery 40 and the converter 10 in the case of the current measuring unit 90. During generator operation, the battery 40 is charged by the motor, so that there is a current flow in the direction of the battery. However, once the electric machine 50 is operated as a motor, it is already possible to measure the current flow from the battery 40 to the inverter starting from a very small rotational speed, the greater the current flow the closer the operating signal of the inverter is to the operating point of the motor with maximum torque. By repeatedly measuring the current flow between the battery and the converter in step 240, a transition between motor operation and generator operation of the electric machine may be determined once the current flow in the direction of the converter is measured or once the current flow has a reversal in direction of the converter (step 250). The operating mode can thus be determined from the current direction and the torque from the magnitude of the current flow.

According to a further embodiment, in order to identify 200 a transition between operating modes, the current between the converter 10 and the motor for a phase may be repeatedly or continuously measured (step 260) by means of the current measuring unit 95. In most cases, a current in phase with the voltage, i.e. a measured current having the same sign as the voltage during this time period, flows during generator operation. When the current and voltage of the phase are operated in opposite phases, i.e. with different signs during the time period, the electric machine is in motor operation. In this case, it is also clearly possible to detect a transition between generator operation and motor operation (step 270) by detecting a change in the phase shift to the applied voltage during the current measurement. The operating mode, i.e. the generator operation or the motor operation and the torque of the motor, can likewise be derived from the measurements.

The voltages applied during the actuation by the control unit at the phases of the motor 50 and thus known can be used to determine the current.

The current measurement in all embodiments can be carried out in a usual manner and the

respective circuit

90, 95 can be integrated, for example, into the converter circuit or into the regulating section of the converter 10 both in the direction of the battery and also in the direction of the motor.

The parallel use of the electric machine 50 and the other starter 80 can also be used to further shift the point in time of the first ignition or the injection of the internal combustion engine 60. As soon as the position information of the crankshaft required for this is available, a first ignition is carried out in a conventional system. However, when a higher rotational speed can be achieved by parallel operation, a desired rotational speed level can be determined as a further condition for the first ignition according to a further embodiment. The rotational speed level should be metered such that it is possible in the operation of the combination of starter 80 and electric motor 50, and the amount of fuel required or emissions resulting therefrom is as small as possible. Other marginal conditions, such as temperature, can also be considered here, since in the case of cold temperatures during starting, higher friction must be overcome for operation and the maximum achievable rotational speed level becomes smaller.

Because the operation of the electric machine 50 as a motor requires electric energy that must be provided by the vehicle battery 40, the state of the battery can be monitored and excessive discharge avoided in order to avoid damaging the battery and ensure safe remaining charge for the remaining operation.

The possibility for this is to monitor the battery voltage change during the starting process. The battery model evaluated or calculated in the control unit 30 may then provide an estimate of the state of charge of the battery from the voltage variation process. If the above-mentioned measurement of the current, for example between the battery and the converter 90 or between the converter and the motor 95, is available when monitoring and adjusting the state of the battery, this measurement may also relate to the battery model and improve the accuracy of the estimated state of charge and adjustment.

In a too low state of charge, which is determined, for example, from a stored threshold value, the control unit may limit the extracted power at least temporarily in different ways. The energy requirement of the starter 80 may be too high for the battery 40 used, for example, when the electric machine 50 is simultaneously used as a motor. In this case, the control unit may control the operation of the starter and the motor so that the starter and the motor are operated at least temporarily only with a stagger in order to limit the power extracted from the battery.

For example, a specific threshold rotational speed can be determined, from which the motor is started (and the starter is deactivated if desired) in order to bring the crankshaft further to the target rotational speed. The rotational speed may be predetermined, for example, and may be related to the power consumption of the starter and the motor and/or battery data; likewise, the threshold rotational speed may be variably determined only during operation, for example, based on the current state of charge of the battery. Alternatively, it can be determined that the parallel operation of the starter and the motor is only accepted for a limited time or until a limited power consumption is accepted, and that otherwise only one of the two drives is used during the starting process.

Typically, the starter 80 also has an idle state in which little electrical energy is required, and once the rotational speed of the crankshaft 65 rises above the rotational speed of the starter 50, the starter is in idle state. This may occur, for example, after expansion of the first cylinder, but also before the first combustion. At this point in time, the energy-intensive phase of the starting process ends, so that even after the rotational speed has fallen again to the maximum starter rotational speed, there is still a lower energy demand than at the beginning. If, starting from the idle phase of the starter 80, the electric machine 50 is driven during motor operation, the energy no longer required in the starter can be used for this purpose in order to further increase the rotational speed level by means of the electric machine. As long as the rotational speed remains above the starter rotational speed and thus idling is active, the full available electrical power can be used almost for the motor operation of the electric machine and thus the rotational speed level is significantly increased before the first combustion even in the case of small batteries with a limited output of electrical energy and thus the emissions in cold starts are improved.

By the possibility of supporting the electromechanical starter with the electric motor during operation of the motor, a further design of the starter can be achieved. For example, a smaller sized starter may be used, which is not capable of actuating the motor alone. As a result, the installation space of the starter and/or the cost of the starter can be optimized, which is in turn attractive in particular in small vehicles. Alternatively, the transmission between the starter and the crankshaft can be simplified if necessary and its cost optimized. The aspect to be optimized may also be noise emission during start-up as much as possible. If the starter is not designed in a smaller size, the transmission can alternatively be changed such that a smaller torque is transmitted to the crankshaft and the rotational speed thereof is increased for this purpose, while an insufficient torque is fed via the electric machine. Thus, higher rotational speed levels during start-up and thus improved cold start emissions can be achieved. With a constant dimensioning of the starter and the gear mechanism, the support by the electric motor can be used to reduce the load on the components and thus optimize their service life and wear.

The above embodiments may also be used when other starting methods are used, such as a mechanical starter, which initially puts the crankshaft in motion. The invention also provides the advantage that emissions in the first combustion cycle can be reduced and the rotational speed can be increased from the beginning in a simple manner by means of the support of the electric machine.

The method or device as described above may preferably be used in a vehicle with a small internal combustion engine (synchronous motor equipped with permanent magnet excitation), for example in a motorcycle. In general, however, all of the described embodiments can be transferred to each arbitrary internal combustion engine, which is used with an electric generator. However, if there is no rigid coupling between the engine shaft (crankshaft) and the generator shaft, the rotational speed sensor of the crankshaft cannot be used directly and other suitable determination of the position of the generator shaft must be used. If an externally excited motor is used instead of a permanently excited motor, a change in the excitation regulation must be made if necessary.

Although in the present embodiment the motor control device is exemplarily referred to as a control unit for controlling the electric machine (comprising an inverter as well as a rotational speed sensor), the control unit may also be a separate regulator which assumes the task mentioned for controlling the inverter and which derives the required signals from the rotational speed sensor. It is also understood that the inverter described in connection with the embodiments is shown by way of example only, and that other circuits and designs are conceivable that are capable of operating the connected electric machine (as a generator and motor).

Claims

1. Method for supporting a starting process of an internal combustion engine (60) by means of a synchronous electric machine (50), which can be operated as a generator in a first operating state and as an electric motor in a second operating state, wherein an electromechanical starter (80) is used, the shaft of which is rigidly coupled to a crankshaft (65) of the internal combustion engine (60) by means of a fixed transmission, wherein the method comprises:

-identifying (100) a rotor movement of a rotor (55) of the synchronous motor (50) starting at a first angular velocity, said first angular velocity corresponding to a first frequency,

manipulating (110) the synchronous motor (50) by applying an alternating voltage having a second frequency, the second frequency being greater than the first frequency,

a transition between a first and a second operating state of the synchronous machine (50) is detected (200), and a manipulation of the synchronous machine (50) is adapted (120) based on the detected transition.

2. The method of claim 1, wherein identifying (200) a transition between the first and second operating states comprises:

-measuring (210) the angular velocity of the rotor (55);

determining (220) angular acceleration from the measured plurality of angular velocities; and is also provided with

Upon an increase in angular acceleration, it is determined (230) that the synchronous machine (50) transitioned from the first operating state to the second operating state.

3. The method of claim 1 or 2, wherein identifying (200) a transition between the first and second operating states comprises:

-measuring (240) a current (90) between an inverter (10) connected to the synchronous motor (50) and a battery (40) connected to the inverter (10);

upon initiating a current flow from the battery (40) to the inverter (10), a transition of the synchronous motor (50) from a first operating state to a second operating state is determined (250).

4. The method according to any one of the preceding claims, wherein the applied alternating voltage is a multiphase alternating voltage, and wherein identifying (200) a transition between the first and second operating states comprises:

-measuring (260) the current of a phase (95) between the converter (10) and the synchronous motor (50), and-determining (270) that a transition between said first and second operating states has occurred as soon as the measured current (95) and the associated voltage of said phase transition from a state in phase with respect to each other to a state in phase with respect to each other.

5. The method according to any of the preceding claims, wherein a rotor (55) of the synchronous motor is rigidly connected with a crankshaft (65) of an internal combustion engine (60), and wherein the angular speed of the rotor (55) is measured by a rotational speed sensor (70) of the crankshaft (65) or the rotor (55).

6. The method of claim 5, wherein a crankshaft (65) of the motor (60) is placed in motion by an electromechanical starter (80).

7. Method according to any of the preceding claims, wherein the point in time of the first injection and ignition of the internal combustion engine (60) is preset during the start-up according to a rotational speed threshold.

8. The method according to any of the preceding claims, wherein the synchronous motor (50) is a permanent magnet excited synchronous motor.

9. -a computing unit (30) arranged to perform all method steps of the method according to any of the preceding claims.

10. A machine readable storage medium having a computer program stored thereon, which, when implemented on a computing unit, causes the computing unit to perform all the method steps of the method according to any of claims 1 to 8.

11. Apparatus for supporting a start-up procedure of an internal combustion engine, comprising:

a synchronous machine (50) which can be operated as a generator in a first operating state and as an electric motor in a second operating state;

a rotational speed sensor (70) arranged for measuring an angular speed of a rotor (55) of the synchronous motor (50), and a calculation unit (30) according to claim 9 arranged for receiving an output signal of the rotational speed sensor (70) and for controlling the synchronous motor (50).

12. The device according to claim 11, wherein the rotor (55) of the synchronous motor is rigidly connected to a crankshaft (65) of the internal combustion engine (60), wherein the device furthermore comprises an electromechanical starter (80) which is connected to the crankshaft (65) of the internal combustion engine (60) and is provided for driving the crankshaft.

13. The device according to claim 11 or 12, wherein the synchronous motor (50) is permanently excited.