CN111608837A

CN111608837A - Method and device for assisting a starting process of an internal combustion engine

Info

Publication number: CN111608837A
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: 2020-09-01
Anticipated expiration: 2040-02-24
Also published as: DE102019202475A1; CN111608837B

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 machine (50) starting at a first angular speed, the first angular speed corresponding to a first frequency; steering (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 transition.

Description

Method and device for assisting 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 smaller vehicles, in particular, such as in the field of motorcycles with small internal combustion engines, permanently excited synchronous generators are often used, which are rigidly coupled to the crankshaft of the internal combustion engine. The generator is used to supply 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 system with electrical energy, the solidly embodied rotor represents a rotating mass (Schwungmasse) for stabilizing the operating behavior of the internal combustion engine. Furthermore, metallic markings or teeth may be present on the rotor, which together with a rotational speed sensor generate 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 as a generator in the vehicle is also used as a motor in certain cases by means of a suitable design and circuit connection and is therefore used in two different operating modes. In this way, a hybrid drive system is realized.

For starting the internal combustion engine, various starting methods can be used, for example an electromechanical starter or an actuator, i.e., an electric motor, the shaft of which is coupled to the crankshaft via a fixed gear mechanism and can temporarily drive the crankshaft during starting. In motorcycles, for example, a kick start is likewise possible, in which the crankshaft is mechanically accelerated by a kick. The starting method pulls the motor to the minimum rotational speed necessary before the first injection and ignition take place and the motor is transitioned to combustion operation. In order to be able to carry out the starting process from a very low rotational speed, the first combustion cycle is triggered with a very greasy mixture, i.e. more fuel is injected than can be completely combusted. As a result, unburned carbon chains are produced in the exhaust gas, so that a high-load, but pollutant-rich combustion is achieved, and the motor speed is significantly increased to a level far above the starter speed. Even when the usual motor idle speed is reached, the fuel fraction is reduced and optimum pollutant operation is achieved by complete combustion of the fuel. But 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 may be used as a starter generator; the dimensioning of the electric machine is often not sufficient to perform the starting process alone, just 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 with the features of the independent claims. Advantageous embodiments are the subject matter of the dependent claims and the subsequent 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 starting at a first frequency is first detected and the synchronous machine is subsequently controlled 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 a generator operation and a motor operation of the electrical 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 start of the starting process. By the combination of a conventional starter and the electric machine used for this purpose, the starting speed can be increased significantly before the first combustion. There is thus the possibility of reducing the load and wear on the starter, of reducing the noise emission of the starter, or of using a starter of smaller dimensions (e.g. with a smaller energy requirement or installation space). Furthermore, by increasing the starting rotational speed before the first combustion cycle, the previously described exhaust gas problems of cold starting are improved and therefore future emission regulations are complied with.

The detection of the transition between generator operation and motor operation can be implemented 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 case of a transition from a braked generator operation to an accelerated motor operation.

-detecting a current flow from the battery to a use of an inverter connected between the battery and the electric machine; once the motor is used for operation, a current flow from the battery is expected.

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

By recognizing the transition to the motor operation in advance before the rotor position or the crankshaft position is known, it is already possible to use the electric machine as a support at the start 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 put in motion by an electromechanical starter. Compared to classical devices, such an implementation requires no or only a small amount of modification and can therefore be implemented easily and 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 machines which are inexpensive and easy to install, but can also be used with other machines.

The computing unit according to the invention, for example a control device of a motor vehicle or a separate control unit for an electric machine, 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 having program code for executing all method steps is also advantageous, since this results in particularly low costs, in particular when the implemented control device is also used for further tasks and is therefore already present. Suitable data carriers for supplying the computer program are, in particular, magnetic, optical and electrical memories, such as a hard disk, flash memory, EEPROM, DVD, etc. Downloading of the program via a computer network (internet, intranet, etc.) is also possible.

Further advantages and design aspects of the invention result from the description and the drawings.

Drawings

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

Fig. 1 shows a schematic configuration 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

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

Detailed Description

In order to be able to use the electric machine as a generator and as a motor, the conventional power electronics are modified. The following description relates to a permanent magnet excited synchronous machine, 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 they can be used not only as rectifiers for generator operation but also as inverters for motor operation. For example, a MOSFET bridge circuit may be used here, but other transistors may also be used.

Fig. 1 shows a typical bridge circuit of this type with a corresponding control unit 30, for example a motor control device, for a three-phase electrical machine as an example for an inverter 10. The adaptation to the other phase numbers is effected by adding or removing individual bridge lines. The control unit 30 can control the individual switches 20 depending on the desired electrical power of the electric machine and the rotor position of the electric machine. The output power can be positive (generator operation) or negative (motor operation). The inverter 10 is also connected to a power supply and rechargeable battery 40, which also feeds the on-board system 45 of the vehicle.

The synchronous machine 50 with the rotor 55 thus actuated can be used to support the starter during the starting process. Fig. 2 shows a schematic top view of an element used in an exemplary method of the present invention. Here, 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 which can be driven during starting. In some embodiments, the rotor 55 of the synchronous machine 50 can be arranged directly on the crankshaft 65 or can be connected directly to the crankshaft. The synchronous machine is in this example, as already in fig. 1 (simplified here), operated via an inverter 10, which is in turn connected to a battery 40.

The control unit 30, for example a motor control unit (ECU), however, usually has no information that a start process has been triggered. The control device receives a signal from the rotational speed sensor 70 indicating the starting process only when the crankshaft 65 of the motor 60 is in motion.

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

The sensor 70 registers the passing marks (e.g. teeth) and determines the rotational speed or speed from the time difference between the two marks. In addition, the absolute position of crankshaft 65 is detected by means of further markers, in particular tooth gaps on the sensor wheel, in order, for example, to correctly determine the time points for injection and ignition of internal combustion engine 60. Once the number of flags have run past the speed sensor 70, the sensor may identify that the crankshaft is moving, for example, based on being driven by a starter. The current rotational speed or angular speed of the crankshaft can now likewise 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 used only if the absolute position of the crankshaft 65 is also known on the basis of the play in the rotational speed signal. However, since the starting process should be as short as possible, it is desirable to support starter 80 directly from the outset via the electric motor. In order to operate the inverter 10 such that the electric machine 50 operates as a motor with as large a torque as possible, the position of the rotor 55 of the electric machine must however be known. In other cases, the switching process may be improperly placed such that the motor 50 operates as a generator at maximum braking torque and, thus, blocks the starter 80. In practice, therefore, only synchronization with the absolute position of the shaft is possible to ensure that the motor is actuated to the correct extent.

Even before a gap in the rotational speed signal can be recognized, an earlier use of the electric motor 50 can be achieved in various ways in parallel with the starter 80. 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 can be used.

In step 100, the starting 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 at a higher frequency than the frequency of the operating crankshaft in step 110. Once crankshaft 65 is put into motion or otherwise put into motion by starter 80, the rotational frequency or angular velocity of crankshaft 65 (corresponding to the frequency of rotor 55 of the motor) may be determined by rotational speed sensor 70 between at least two mark passes (markerungsdurcagen). Due to the higher frequency of the actuation, the voltage signal of the inverter 10, which supplies the stator coils of the electric machine, and thus the magnetic field generated in the coils, overtake the rotor 55 during the electric actuation period. From this point in time, the electric machine 50 operates as a motor. As soon as the magnetic field of the stator coils 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, in step 200, a transition point between generator operation and motor operation can be identified, it is therefore possible to carry out a corresponding actuation of the electric machine 50 in a subsequent step 120 and to cause a support of the starter 80. As soon as a gap 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 be validated or adapted again accordingly in order to maximize the available support torque.

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

A 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 in generator mode, but additionally drives the shaft in motor mode, a more pronounced increase in the angular speed should be recognizable in the transition between generator mode and motor mode. The control unit 30 (or another control unit) can thus evaluate the angular velocity obtained in step 210 and thus obtain the current angular acceleration (step 220). Because crankshaft 65 is beginning to operate, the angular acceleration is typically greater than zero during startup. As soon as the braking action of the generator 50 is cancelled and an additional motor drive is used, the angular acceleration will be increased in a recognizable manner as a result. The increase in angular acceleration represents the transition between generator operation and motor operation in step 230. Conversely, a decrease in angular acceleration also indicates whether the electric machine 50 is transitioning back into generator operation and the inverter frequency must be increased further. Alternatively, a minimum value can be determined above which the change in the angular acceleration must be increased in order to avoid misinterpretation of rotational speed fluctuations, which are caused, for example, by gas forces in the cylinder or friction forces during operation of the shaft.

According to a further embodiment, in order to determine 200 the transition between generator operation and motor operation, a current can be measured in step 240, which current flows between the rechargeable vehicle battery 40 and the inverter 10 in the case of the current measurement unit 90. In generator operation, the battery 40 is charged by the electric machine, so that there is a current flow in the direction of the battery. However, once the electric machine 50 operates 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 closer the control signal of the inverter is to the operating point of the motor with the maximum torque. By repeatedly measuring the current flow between the battery and the inverter in step 240, a transition between motoring and generating operation of the electrical machine may be determined once the current flow in the direction of the inverter is measured or once the current flow has a reversal in the direction of the inverter (step 250). The operating mode can thus be determined from the direction of the current flow and the torque can be determined from the magnitude of the current flow.

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

The voltage applied to the phase of the electric motor 50 during the actuation by the control unit and thus known can be taken into account for determining the current.

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

respective circuit

90, 95 can be integrated, for example, not only in the direction of the battery but also in the direction of the electric machine into the converter circuit or into the control unit of the converter 10.

The parallel use of the electric machine 50 and the further starter 80 can also be used to shift the point in time of the first ignition further back or to inject the internal combustion engine 60. As soon as the position information of the crankshaft required for this purpose is available, a first ignition takes place in the conventional system. However, if higher rotational speeds can be achieved by parallel operation, a desired rotational speed level can be determined according to further embodiments as a further condition for the first ignition. This rotational speed level should be dimensioned such that it is possible to achieve in the combined operation of starter 80 and electric motor 50, and the required fuel quantity or the resulting emissions are as small as possible. Other marginal conditions, such as temperature, can also be taken into account here, since in the case of cold temperatures during the start-up process, higher friction must be overcome to operate and the maximum achievable rotational speed level becomes lower.

Since the operation of the electric machine 50 as a motor requires electrical energy which must be supplied by the vehicle battery 40, the state of the battery can be monitored and too large a discharge avoided in order to avoid damage to the battery and to ensure a safe residual charge for the remaining operation.

A possibility for this is to monitor the battery voltage profile 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 a current measurement, for example the above-mentioned measurement of the current between the battery and the inverter 90 or between the inverter and the electric machine 95, is available while monitoring and regulating the state of the battery, this measurement can also relate to the battery model and improve the accuracy of the estimated state of charge and regulation.

In a too low state of charge, determined for example on the basis of a stored threshold value, the control unit may limit the extracted power at least temporarily in a different manner. The energy requirement of the starter 80 can be too high for the battery 40 used, for example, if the electric machine 50 is simultaneously used as a motor. In this case, the control unit can control the operation of the starter and the electric motor such that the starter and the electric motor are operated at least temporarily only offset in order to limit the power drawn from the battery.

For example, a specific threshold rotational speed may be determined, starting from which the electric machine is switched on (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 is related to the power consumption and/or battery data of the starter and the motor; likewise, the threshold rotational speed can be determined only during operation, for example, variably based on the current state of charge of the battery. Alternatively, it can be ascertained that the parallel operation of the starter and the electric motor is only possible for a limited time or until a limited power consumption is accepted, and otherwise only one of the two drives is used during the starting process.

Typically, starter 80 also has an idle mode in which little electrical energy is required, and once the rotational speed of crankshaft 65 rises above the rotational speed of starter 50, the starter is in the idle mode. This may occur, for example, after the first cylinder is expanded, 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 again dropped to the maximum starter rotational speed, there is a lower energy requirement than at the beginning. If, starting from the idle phase of the starter 80, the electric machine 50 assumes drive during the 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 therefore idling is active, the full available electrical power can be used almost for the motor operation of the electric machine, and therefore the rotational speed level is increased significantly even with small batteries with a limited output of electrical energy before the first combustion, and therefore emissions in cold starts are improved.

By the possibility of supporting the electromechanical starter with the electric machine during operation of the motor, a further design of the starter can be achieved. For example, a starter of a smaller size may be used, which starter is not capable of activating the motor alone. The installation space of the starter and/or the cost of the starter can thereby be optimized, which in turn is 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 the noise emission during the start-up as far as possible. If the starter is not designed with a small size, the transmission can alternatively be modified in such a way that a lower torque is transmitted to the crankshaft and, for this purpose, its rotational speed is increased, while insufficient torque is supplied by the electric machine. Higher rotational speed levels during starting and thus improved cold start emissions may be achieved. With a constant dimensioning of the starter and the gear mechanism, the support by the electric machine can be used to reduce the load on the components and thus to optimize their service life and wear.

The above-described embodiments can also be used when other starting methods are used, for example a mechanical starter, which initially sets the crankshaft in motion. The invention also offers the advantage that the emissions in the first combustion cycle can be reduced and the rotational speed can be increased from the beginning in a simple manner by the assistance of the electric machine.

The method or device as described above can preferably be used in vehicles with small internal combustion engines (equipped with permanently excited synchronous machines), such as motorcycles. In general, however, all of the described embodiments can be transferred to any arbitrary internal combustion engine, which is used with a 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 determinations of the position of the generator shaft must be used. If an externally excited electric machine is used instead of a permanently excited electric machine, a change in the excitation regulation must be carried out if necessary.

Although in the present exemplary embodiment the motor control device is referred to as a control unit for controlling the electric machine (including the inverter and the rotational speed sensor) by way of example, it can also be a separate controller which assumes the mentioned task for actuating the inverter and receives the required signals from the rotational speed sensor. It is also understood that the inverter described in connection with the embodiments is only shown by way of example, and that other circuits and designs are conceivable, which are capable of operating the connected electrical machine (as a generator and a motor).

Claims

1. 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 the synchronous machine (50) starting at a first angular speed, the first angular speed corresponding to a first frequency,

steering (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 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) an angular acceleration from the measured plurality of angular velocities; and is

-determining (230) that a transition between said first and second operating states has occurred once the angular acceleration has risen.

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 with the synchronous machine (50) and a battery (40) connected with the inverter (10);

determining (250) a transition occurring between the first and second operating states once current flow from the battery (40) to the inverter (10) is initiated.

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

measuring (260) the current between the inverter (10) and the synchronous machine (50) in a phase (95), and

determining (270) that a transition has occurred between the first and second operating states once the measured current (95) and the accessory voltage of the phase transition from being in phase with respect to each other to being in anti-phase with respect to each other.

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

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

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

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

9. A computing unit (30) arranged for performing all method steps of the method according to any one of the preceding claims.

10. Computer program which, when being implemented on a computing unit, causes the computing unit to carry out all the method steps of the method according to any one of claims 1 to 8.

11. A machine-readable storage medium having stored thereon a computer program according to claim 10.

12. Device for supporting a starting process 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 the angular speed of the rotor (55) of the synchronous machine (50), and

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

13. The device according to claim 12, wherein the rotor (55) of the synchronous machine is rigidly connected to a crankshaft (65) of the internal combustion engine (60), wherein the device further 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.

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