EP1586765B1 - Method and control system for positioning the crankshaft during shutdown of a combustion engine - Google Patents

Description

FIELD OF THE INVENTION

The invention relates to a method and a control system for positioning a crankshaft of an internal combustion engine.

BACKGROUND OF THE INVENTION

Internal combustion engines must be started by means of a starter e.g. be launched in the form of an electric motor which is directly or indirectly coupled to the crankshaft of the internal combustion engine. The crankshaft is then accelerated by the starter to an engine speed required to start the engine.

Depending on the position angle of the crankshaft, the starting torque, which the starter must initially apply, varies. In particular, when a cylinder is just in the compression stroke, this causes a high starting torque, which has an unfavorable effect on the starting behavior of the internal combustion engine.

To improve the starting behavior of the internal combustion engine is from the document DE 198 17 497 Al the Applicant known to bring the crankshaft of the internal combustion engine before starting to a certain starting angle, starting from which the starting operation is performed. In this way, an unfavorable position of the crankshaft at the beginning of starting can be avoided and the starting time of the internal combustion engine or the initial torque to be overcome by the starter during the starting process can be reduced. The Positioning of the crankshaft may be performed after stopping the engine or before starting the engine.

Normally, starter motors are used to start combustion engines, which are controlled by means of a field-oriented control. These electric motors are, in particular, asynchronous or synchronous motors. Such electric motors are operated by means of a motor control, which require the speed of the rotor or the crankshaft as an input variable for the realization of the field-oriented control.

For this purpose, the crankshaft is provided, for example, with a position sensor which determines the positional angle of the crankshaft and determines therefrom the rotational speed of the crankshaft. However, the accuracy of the determined speed depends on how accurately the attitude angle was determined by the position sensor. Also, speed sensors are often provided to detect the speed directly.

In both cases, the determined speed is relatively inaccurate. This results in particular at low speeds of the crankshaft to the fact that the relative error is very large and a field-oriented control for driving the electric motor is no longer possible. Thus, the active positioning of the crankshaft, in particular when stopping the internal combustion engine, shortly before the standstill of the crankshaft, can no longer be performed reliably with the aid of the electric motor.

With the help of more accurate sensors for detecting attitude angle and / or speed, it would be possible to solve this problem. However, it is desirable to position the crankshaft at a starting angle while maintaining the previous components of the engine system.

EP 1 136 696 A discloses a method and apparatus for positioning a crankshaft of an internal combustion engine for adjusting a starting angle. For this purpose, the internal combustion engine is braked by means of an electric machine such that the crankshaft is in its predetermined angular position at the time of complete standstill of the internal combustion engine. The deceleration of the internal combustion engine takes place by the angle position signals of the rotating crankshaft are detected by a position sensor after switching off the engine and forwarded to the electronic control of the electric machine. The electronic control controls the electric machine such that a counter-torque acting on the crankshaft is generated.

DE 100 30 001 A discloses a device for the controlled shutdown of an internal combustion engine, wherein at least one adjusting device can be activated, which is controlled after completion of the regular operation of the internal combustion engine and the crankshaft of the internal combustion engine and / or the camshaft of the internal combustion engine moves to a predeterminable angular position.

DE 44 30 651 A1 discloses a method and system in which an electric motor is first reversely operated for positioning. A crankshaft angle sensor detects the (absolute) angle of the crankshaft using an absolute value rotary encoder.

DE 100 30 000 A1 describes an arrangement with a controllable clutch, which allows a frictional connection between a crankshaft of an internal combustion engine and a shaft which is connected to an electric drive system. In addition, the arrangement includes a sensor that detects the crank angle, that is, an absolute value position sensor.

EP 1 365 145 A2 describes a device for starting an engine, which comprises a crankshaft angle detection device, that is, an absolute value position sensor. In addition, the crankshaft of the internal combustion engine is rotated in the reverse direction for positioning by an electric motor.

It is an object of the present invention to provide an improved method and an improved control system for positioning the crankshaft of an internal combustion engine.

This object is solved by the subject-matter of independent claims 1 and 8.

Further embodiments of the invention are specified in the respective dependent claims.

In the control of the electric motor for positioning the crankshaft to the starting angle is switched to a control mode, so that the electric motor is controlled independently of the speed. This is advantageous since the speed detection and evaluation in conventional engine systems is generally too imprecise to operate the electric motor at low speeds with a field-oriented control. Especially at very low speeds, as occur, for example, when the crankshaft of the internal combustion engine comes to a stop shortly before the crankshaft stops, the inaccuracy of the rotational speed can cause the relative deviation to become very large, so that field-oriented engine control is no longer possible without significantly to maintain running disturbances during operation of the electric motor.

The use of the control mode for the electric motor also has the advantage that the electric motor is operated independently of the detected rotational speed of the crankshaft. This is possible by the electric motor to achieve a predetermined torque with a specific drive frequency and a certain voltage or current is operated. Thus, the electric motor can be operated so that the attitude angle can be approached. Current or voltage and frequency are chosen so that the applied torque is sufficient to prevent turning back of the internal combustion engine. This makes it advantageously possible to determine the exact position of the internal combustion engine with position / speed sensors that have no left / right rotation detection.

Further features of the invention will be apparent from the disclosed objects and methods, or will become apparent to those skilled in the art from the following detailed description of embodiments and the attached drawings.

DESCRIPTION OF THE DRAWINGS

• Fig. 1 eine schematische Darstellung eines Startersystems für einen Verbrennungsmotor; und
• Fig. 2 ein Flussdiagramm einer bevorzugten Ausführungsform.

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings. Show it:

• Fig. 1 a schematic representation of a starter system for an internal combustion engine; and
• Fig. 2 a flowchart of a preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1 is an engine system z. B. illustrated for a motor vehicle. It has, for example, a four-cylinder internal combustion engine 1 operating according to the four-stroke cycle, which transmits torques via a crankshaft 2 to other (not shown) parts of a drive system of the motor vehicle to the drive wheels of the motor vehicle.

In the present embodiment, an electric motor 4 serving as a starter / generator is arranged directly on the crankshaft 2. The electric motor 4 has a firmly connected to the crankshaft 2 rotor (not shown), and a z. B. on the housing of the internal combustion engine 1 supported stator (not shown). The electric motor 4 is formed in the embodiment shown as an asynchronous motor 4, but may also be designed as a synchronous motor öder similar.

Such an electric motor 4 has a high torque for the starter operation. In other (not shown) embodiments of the electric motor 4 is coupled via a transmission gear with the crankshaft 2, possibly via an intermediate Einspurgetriebe. The electric motor 4 is designed so that it can apply the required torque in the running direction of the internal combustion engine to set a desired crank angle position and also when starting the required starting power for directly driving the crankshaft 2 to the required starting speed.

In the embodiment according to Fig. 1 the electric motor is controlled by a control unit 5. The control unit 5 comprises a drive unit 6 in order to control the electric motor 4 with the aid of drive signals, in particular with the aid of PWM signals (pulse width modulation signals). The drive signals are generally generated depending on the current engine speed, the desired target speed and / or the attitude angle of the rotor of the electric motor 4. The control unit 5 further controls the operation for starting angle adjustment and the starting operation.

By a position sensor 7 which is mounted in the embodiment shown on the crankshaft, the control unit 5 receives the current position angle of the crankshaft. The position sensor can also be integrated in the electric motor 4 and z. B. be designed as a Hall effect rotation angle sensor to measure the rotor angle. The measured rotor angle corresponds due to the direct coupling of the rotor with the crankshaft 2, the attitude angle.

The starting process of the internal combustion engine 1 is prepared in a special way: After completion of the engine operation, for. B. at or shortly after switching off the ignition of the motor vehicle, the control unit 5 controls the electric motor 4 via the drive unit 6 so that the crankshaft 2 is brought into a favorable for the next start crank angle position, the starting angle. Here, the electric motor 4, the crankshaft 2 of the expiring internal combustion engine 1, to set the desired starting angle.

The position sensor 7 is used primarily for attitude angle detection. However, it is also used for speed detection for a variety of functions within the engine system, in particular for the injection control of the internal combustion engine. The commonly used position sensors, however, usually have only an accuracy that is sufficient for the conventional functions. The reaching of the starting angle can be indicated by a signal edge of the position sensor 7. In particular, the achievement of the starting angle can be indicated by a CAN signal.

The electric motor 4 is usually operated in a closed-loop control mode, ie depending on, for example, the speed and the desired setpoint speed, the control signals are generated by the control unit 6. If However, the rotational speed of the crankshaft 2 or the current position angle is detected only with a low accuracy, this leads, especially at low speeds of the crankshaft 2 to significant relative errors that prevent precise operation of the electric motor 4 in the control mode. Low speeds, however, occur when the crankshaft is coasting shortly before stopping. It is just when setting the attitude angle when the crankshaft after the end of the engine operation, a particularly precise operation of the electric motor 4 is necessary to adjust the starting angle.

The control unit 5 is therefore designed so that it runs when the internal combustion engine, the electric motor 4 below a limit speed in a control mode (open loop). That the electric motor 4 is no longer operated in a field-oriented control, which takes into account the current rotor speed in the generation of the drive signals, but now independent of the current speed with fixed quantities such. the drive frequency, as well as fixed current and voltage curves operated to turn the crank angle with a torque determined thereby a short distance on the starting angle. The reaching of the starting angle can be indicated by a signal edge of the position sensor 7. The control unit 5 then stops the control of the electric motor 4 immediately.

The control unit 5 thus controls the electric motor 4 below the limit speed in the control mode to start the starting angle. The limit speed is at a speed at which the conventional speed detection becomes too inaccurate to allow trouble-free operation of the electric motor with field-oriented control. This limit speed is for example in the range of 5 to 50 rev / min at speeds, but may also be lower or higher. Current or voltage and frequency are chosen so that the applied torque is sufficient to prevent turning back of the internal combustion engine. This makes it possible to determine the exact position of the internal combustion engine with position / speed sensors that have no left / right rotation detection.

In conventional speed sensors, such as are commonly used in motor systems, or in the use of position sensors, the direction of rotation is not detected, since the internal combustion engine is operated in one direction only. For this reason, it is necessary that the control unit 5 controls the electric motor 4 in the control mode so that the crankshaft 2 is further rotated in the usual rotational direction of the crankshaft to adjust the starting angle. Current or voltage and frequency must be selected so that the applied torque is sufficient to prevent turning back of the internal combustion engine. This makes it possible to determine the exact position of the internal combustion engine with position / speed sensors that have no left / right rotation detection.

When stopping the internal combustion engine, the control unit 5 controls the internal combustion engine 1 so that below a further limit speed, which is greater than the limit speed, a fuel supply for the internal combustion engine is switched off. The limit speed is preferably in a range under which no independent engine operation of the internal combustion engine 1 or no continuous engine operation is possible. In particular, the further limit speed is about 800 rpm, but may also assume larger or smaller values. Further, the electric motor 4 below the further limit speed in accordance with the control mode with a field-oriented control can be further controlled depending on the speed to dampen vibrations of the crankshaft, which occur when stopping the engine. For this purpose, the leakage of the crankshaft 2 by means of the electric motor 4th led, ie the electric motor 4 reduces by an additional torque fluctuations in the decrease of the speed when the internal combustion engine 1.

When falling below the limit speed is then switched from the field-oriented control of the control mode to the control mode of the control mode to set the start angle as accurate as possible at the end of the discharge process. In this case, the electric motor 4 is controlled so that it starts the starting angle with a predetermined torque, ie a predetermined speed, or with a predetermined torque curve.

The "optimal" attitude angle for starting an internal combustion engine, ie the starting angle, depends on various factors, such as the engine type, number of cylinders and firing order, and also on the desired starting behavior, whether z. B. for the next start a small starting torque at the beginning of the startup process, a shortened start time or at least a reproducible starting behavior with always constant starting conditions is desired. For a like in Fig. 1 shown four-cylinder four-stroke engine 1 is for example a possible favorable starting angle with reduced starting torque in a range immediately after top dead center of the first ignited cylinder. Since in a four-cylinder inline engine usually the two outer cylinders are operated in synchronism with each other, but in the opposite direction to the two inner cylinders, therefore, a possible favorable starting angle is immediately after top dead center of the two outer cylinders of the internal combustion engine. 1

The advantage of this set starting angle is that the breakaway torque to be applied by the starter machine 4 at the beginning of the following starting operation is considerably lower than in known starter systems. If the internal combustion engine 1 is started out of this set crank angle position, at least the two outer cylinders of the internal combustion engine 1 of the electric machine 4 counteract a relatively low, predominantly friction-related torque. Until the next compression stroke (of the two inner cylinders), the electric machine 4 can supply enough (start) energy to the system to overcome the compression.

Alternatively, a favorable starting angle may also be just before the bottom dead center, if it is primarily a question of achieving a reproducible starting behavior with constant starting conditions, because this starting angle position is more stable against any vehicle movements between the switching off of the internal combustion engine and the next starter.

In the flowchart according to Fig. 2 an embodiment of the method according to the invention for positioning the crankshaft is illustrated to a starting angle: In step S1, first asked whether the internal combustion engine 1 should be turned off. The user of the motor vehicle can do so by turning off the ignition or the like. In this case, the supply of fuel to the internal combustion engine is stopped by the control unit and the rotational speed of the crankshaft decreases.

If the current speed of the crankshaft 2 drops below the further limit speed (step S2), then the control operation for the electric motor 4 is set (step S3). Then, the electric motor 4 is controlled by the control unit 5, the leadership of the crankshaft 2 (step S3) to dampen vibrations occurring during the leakage of the internal combustion engine 1. The electric motor is operated with the field-oriented control and can be controlled in an optimal manner by the drive unit 6.

If the speed falls below the limit speed (step S5), the value of which indicates that the detection of the speed is now too inaccurate to operate the electric motor in the control mode, the control operation of the electric motor 4 is switched over in step S6. In the control mode, the starting angle can then be approached.

Claims (10)

1. A method for positioning a crankshaft (2) of an internal combustion engine (1) at a starting angle with the aid of an electric motor (4) which is arranged directly on the crankshaft (2) and serves as a starter/generator, wherein:

   - the electric motor (4) can be actuated depending on the rotational speed of the crankshaft (2) according to a closed-loop mode of operation,

   - the crankshaft (2) is moved so as to be at the starting angle once the internal combustion engine (1) has stopped in order to start the internal combustion engine (1) from said starting angle when it is started again,

   characterized in that

   - below a rotational speed threshold, the electric motor (4) is actuated independently of the rotational speed in open-loop operation in an open-loop mode of operation in such a manner that the crankshaft (2) continues to be rotated in the usual direction of rotation of the crankshaft in order to set the starting angle, and the current or the voltage and the frequency are selected such that the torque applied is sufficient to prevent the internal combustion motor from rotating back.
2. A method according to claim 1, characterized in that a switch is made from field-oriented regulation of the closed-loop mode of operation to open-loop operation of the open-loop mode of operation when the rotational speed decreases below the rotational speed threshold when the internal combustion engine (1) stops.
3. A method according to any one of claims 1 or 2, characterized in that an edge of a rotational speed sensor or an edge of a position sensor indicates that the starting angle has been reached.
4. A method according to any one of claims 1 to 3, characterized in that a CAN signal indicates that the starting angle has been reached.
5. A method according to any one of claims 1 to 4, characterized in that the starting angle selected is the crank angle at which the time required to start the internal combustion engine is reduced.
6. A method according to any one of claims 1 to 4, characterized in that the starting angle selected is the crank angle at which the starting torque is reduced.
7. A method according to any one of claims 1 to 4, characterized in that the starting angle selected is a crank angle shortly before the bottom dead centre of the cylinder.
8. A control system for actuating an electric motor (4) which is arranged directly on a crankshaft (2) of an internal combustion engine (I) and serves as a starter/generator in order to position the crankshaft (2) at a starting angle, wherein the control system comprises:

   - a detection device (7) for receiving and/or determining an angular position and/or the rotational speed of the crankshaft (2); and

   - a control unit (5) which is suitable for actuating the electric motor (4) depending on the rotational speed of the crankshaft in a closed-loop mode of operation and to move the crankshaft (2) so as to be at the starting angle once the internal combustion engine (1) has stopped, so that the internal combustion engine (1) is started from said starting angle when it is started again,

   characterized in that

   - the control unit is designed to actuate the electric motor (4) independently of the rotational speed in open-loop operation according to an open-loop mode of operation below a predefined rotational speed threshold, so that the crankshaft (2) continues to be rotated in the usual direction of rotation of the crankshaft in order to set the starting angle, and the current or the voltage and the frequency are selected such that the torque applied is sufficient to prevent the internal combustion motor from rotating back.
9. A control system according to claim 8, characterized in that the control unit (5) makes a switch from field-oriented regulation of the closed-loop mode of operation to open-loop operation of the open-loop mode of operation when the rotational speed decreases below the rotational speed threshold when the internal combustion engine (1) stops.
10. A control system according to any one of claims 8 or 9, characterized in that the control unit is designed to actuate the electric motor (4) with a predefined torque in the open-loop mode of operation in order to move the crankshaft (2) so as to be at the starting angle, wherein the torque can be adjusted by means of the actuating frequency as well as the voltage or the current.

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