GB2599122A

GB2599122A - Method for determining a rotational position of an output shaft of an engine

Info

Publication number: GB2599122A
Application number: GB2015129.6A
Authority: GB
Inventors: Fabis Radomir; Yu Zhichao
Original assignee: Daimler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2020-09-24
Filing date: 2020-09-24
Publication date: 2022-03-30
Also published as: GB202015129D0

Abstract

The invention relates to a method for determining a rotational position of an output shaft 16 of an engine 10, wherein the output shaft 16 is configured to drive and thereby rotate a rotor 22 of an electric machine 18. The output shaft 16 may be a crankshaft, the engine 10 may be an internal combustion engine and the electric machine 18 may be an integrated starter generator motor for the engine 10. A first signal indicative of a rotational speed of the rotor 22 driven and thereby rotated by the output shaft 16 is determined. The first signal is filtered by a bandpass filter. At least one positive derivative Z of the filtered first signal 36 is determined. A first position value indicative of the rotational position of the output shaft 16 at a point in time t that the positive derivative Z occurs is assigned to the positive derivative Z. The calculated position of the output shaft may then be used to control the electric machine.

Description

METHOD FOR DETERMINING A ROTATIONAL POSITION OF AN OUTPUT SHAFT OF

AN ENGINE

FIELD OF THE INVENTION

[0001] The invention relates to a method for determining a rotational position of an output shaft of an engine, in particular of a vehicle.

BACKGROUND INFORMATION

[0002] US 5 165 271 shows a single sensor apparatus and a method for determining engine position and engine speed. Moreover, US 2019/0048839 Al shows a method for controlling an integrated starter-generator.

SUMMARY OF THE INVENTION

[0003] It is an object of the present invention to provide a method to determine a rotational position of an output shaft of an engine in a particularly cost-effective way.

[0004] This object is solved by a method having the features of patent claim 1. Advantageous embodiments with expedient developments of the invention are indicated in the other patent claims.

[0005] The invention relates to a method for determining a rotational position of an output shaft of an engine. For example, the output shaft is a crankshaft such that, for example, the engine may be a reciprocating piston engine. Preferably, the engine is an internal combustion engine. For example, said engine may be part of a vehicle which may be driven by the engine via the output shaft. In other words, the engine may provide at least one torque for driving the vehicle. The output shaft is configured to drive and thereby rotate a rotor of an electric machine. Thus, preferably, the electric machine and its rotor are parts of said vehicle. For example, said rotor may be connected or connectable with the output shaft, in particular in a rotationally fixed manner, such that the rotor is drivable by the output shaft and/or vice versa. Preferably, the electric machine may be configured as an integrated starter generator (ISG).

[0006] In a first step of the method, a first signal is determined, wherein the first signal is indicative of a rotational speed of the rotor driven and thereby rotated by the output shaft. The first signal may be an electric signal. For example, the rotational speed of the rotor may be measured by a speed sensor whilst the rotor is driven and thereby rotated by the output shaft. Moreover, for example, the speed sensor may provide the first signal. Thus, for example, the first signal may be indicative of the rotational speed measured by the speed sensor. In a second step of the method, the first signal is filtered by a bandpass filter (BPF). For example, an electronic processing unit filters the first signal by using the bandpass filter. In a third step of the method, at least one positive derivative of the first signal is determined. In a fourth step of the method, a first position value is assigned to the positive derivative, in particular by the electronic processing unit. The first position value is indicative of the rotational position in which the output shaft is at a point in time at which the positive derivative occurs. In a fifth step of the method, a second signal indicative of rotational positions of the rotor is determined, wherein said rotational positions of the rotor are measured by a sensor whilst the rotor is driven and thereby rotated by the output shaft. For example, said sensor may be the afore-mentioned speed sensor. For example, said sensor measures the rotational positions of the rotor whilst the rotor is driven and thereby rotated by the output shaft such that, for example, the second signal comprises the rotational positions of the rotor. For example, the sensor provides the second signal and, thus, the rotational positions of the rotor. Preferably, the second signal is an electric signal.

[0007] In a sixth step of the method, a second position value of the second signal is determined. In other words, for example, the second signal may comprise a plurality of second position values each indicative of the respective rotational positions of the rotor. Thus, for example, the second position value of the second signal is determined in such a way that one of the second position values of the signals is selected. The second position value, which is determined or selected, is indicative of the rotational position in which the output shaft is at said point in time. In other words, the first position value is determined from the first signal, and the second position value is determined from the second signal, wherein both the first position value and the second position value relate to the same point in time at which the output shaft is in the rotational position according to the respective signals or position values. In a seventh step of the method, the rotational position of the output shaft is determined on the basis of the first and second position values. For example, in the seventh step of the method, a third position value indicative of the rotational position of the output shaft is determined, in particular calculated, on the basis of the first and second position values. For example, there may be a difference between the first position value and the second position value. Thus, for example, said difference may be determined, wherein, for example, the difference is also referred to as an offset value. Thus, for example, the rotational position of the output shaft may be determined on the basis of said offset value. Thus, the rotational position of the output shaft may be determined in a particularly easy and cost-effective way. In particular, the rotational position of the output shaft may be determined without any additional hardware components. Preferably, the determined rotational position of the output shaft may be used to control the electric machine.

[0008] Further advantages, features, and details of the invention derive from the following description of a preferred embodiment as well as from the drawings. The features and feature combinations previously mentioned in the description as well as the features and feature combinations mentioned in the following description of the figures and/or shown in the figures alone can be employed not only in the respectively indicated combination but also in any other combination or taken alone without leaving the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The drawings show in: [0010] Fig. 1 shows in a schematic view an engine for a vehicle, the engine having an output shaft configured to drive a rotor of an electric machine.

[0011] Fig. 2 shows a diagram illustrating a torque provided by the electric machine in relation of a rotational position of the output shaft.

[0012] Fig. 3 shows diagrams for illustrating a method according to the present invention.

[0013] In the figures the same elements or elements having the same function are indicated by the same reference signs.

DETAILED DESCRIPTION

[0014] In the present document, the word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment or implementation of the present subject matter described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

[0015] While the disclosure is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawing and will be described in detail below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternatives falling within the scope of the disclosure.

[0016] The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion so that a setup, device or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a system or apparatus preceded by "comprises" or "comprise' does not or do not, without more constraints, preclude the existence of other elements or additional elements in the system or method.

[0017] In the following detailed description of the embodiment of the disclosure, reference is made to the accompanying drawing that forms part hereof, and in which is shown by way of illustration a specific embodiment in which the disclosure may be practiced. This embodiment is described in sufficient detail to enable those skilled in the art to practice the disclosure, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present disclosure. The following description is, therefore, not to be taken in a limiting sense.

[0018] Fig. 1 shows in a schematic view an engine 10 of a vehicle. The engine 10 is a combustion engine. Moreover, the engine 10 is a reciprocating piston engine having a crankcase 12 having a plurality of cylinders 14. In each cylinder 14, a piston is arranged in such a way that the piston is translationally movable in relation to the crankcase 12. The engine 10 further comprises an output shaft 16 which is configured as a crankshaft. The respective piston is articulatedly connected with the crankshaft via a connecting rod in such a way that the translational movements of the pistons are converted into a rotational movement of the output shaft in relation to the crankcase 12. Thus, via the output shaft 16, the engine 10 may provide torques for driving the vehicle.

[0019] The vehicle further comprises an electric machine 18 which is configured as an integrated starter generator (ISO). The electric machine 18 comprises a stator 20 and a rotor 22, wherein the stator 20 is configured to drive and thereby rotate the rotor 22 in relation to the stator 20 and in relation to the crankcase 12. For example, the electric machine 18 is operable as an electric motor which may provide at least one torque via the rotor 22. Thus, the electric machine 18 may drive and thereby rotate the output shaft 16 in relation to the crankcase 12 via the rotor 22. Moreover, the output shaft 16 is configured to drive and thereby rotate the rotor 22 in relation to the crankcase 12 and in relation to the stator 20. Thus, alternatively or additionally, the electric machine 18 is operable in a generator mode and thus as a generator. In the generator mode, for example, the output shaft 16 drives and thereby rotates the rotor 22 in relation to the stator 20 and in relation to the crankcase 12. For example, the rotor 22 may be arranged coaxially in relation to the output shaft 16. Moreover, the output shaft 16 may be connected or connectable to the rotor 22, in particular in a rotationally fixed manner. Thus, the engine 10 may drive and thereby rotate the rotor 22 in relation to the stator 20 via the output shaft 16. For example, the electric machine 18 may be electronically controlled, for example, via an electronic control unit which is not shown in the figures. In comparison with conventional engines or vehicles, the integrated starter generator (ISO) may replace both a conventional starter and an alternator (generator). In other words, the!SG is a single device which may function both as a starter for starting the engine 10, and an alternator or generator for providing electric energy. In this regard, in the generator mode, the generator converts mechanical energy provided by the output shaft 16 into electric energy whilst the output shaft 16 drives the rotor 22. One advantage of the!SG is that the!SG may provide a high level of comfort during engine start, engine stop, and idling of the engine 10. In this regard, the ISO may be configured to provide a so-called comfort torque which is a torque to actively compensate torsional vibrations caused by the engine 10.

[0020] Fig. 2 shows a diagram having an abscissa 24 and an ordinate 26. The abscissa 24 shows a so-called engine position being a rotational position of the output shaft 16 whilst the output shaft 16 rotates in relation to the crankcase 12. Since, for example, the rotor 22 is connected with the output shaft 16 in a rotationally fixed manner, the rotor 22 rotates together with the output shaft 16 when the output shaft 16 rotates in relation to the crankcase 12 and in relation to the stator 20. The ordinate 26 shows said comfort torque. This means the abscissa 24 shows respective values of the engine position (i.e. the rotational position of the output shaft 16), wherein the ordinate 26 shows values of the comfort torque provided or providable by the electric machine 18 (ISO) via the rotor 22 (i.e. by driving and thereby rotating the rotor 22 by the stator 20). A graph 28 shows the comfort torque in relation to the engine position. Particularly, the graph 28 is a comfort torque command based on the engine position being the rotational position of the output shaft 16 (crankshaft). Thus, for example, the comfort torque is provided on the basis of the engine position such that, for example, the!SG may be operated or controlled on the basis of the engine position, in particular by said electronic control unit or another electronic control unit. The electronic control unit configured to operate or control the!SG is also referred to as an electronic processing unit. The engine position is also required for engine stop positioning to ensure an upcoming or next comfort start. Thus, for example, the comfort torque is provided on the basis of the engine position. Alternatively or additionally, the engine 10 is started by the!SG on the basis of the engine position. In other words, the!SG may be operated or controlled on the basis of the engine position in order to start the engine 10 by the ISO and/or to position the output shaft 16 by the!SG when stopping or switching off the engine 10.

[0021] In conventional vehicles, the engine position which may also be referred to as crankshaft position is output from an engine control module (ECM) which may be a part of the afore-mentioned electronic control unit or another, further electronic control unit. For example, the engine position is measured and output by a sensor, wherein, for example, the!SG receives the engine position and thus the engine position sensor output from the ECM. In other words, in a conventional engine, an output shaft position sensor may measure the engine position and provide a position signal indicative of the engine position measured by the position sensor. The position signal may be an analog signal which may be amplified. The amplified signal is also referred to as a CAM-Sync signal. For example, the position signal may comprise pulses indicative of respective teeth of the position sensor, wherein said teeth are used to measure the engine position. The position sensor may comprise a gap between two of said teeth, wherein, for example, a gap between two of said pulses of the position signal may be indicative of the gap between the teeth. For example, a processor of the ISO receives the analogue CAM-Sync signal and converts the CAM-Sync signal to a digital signal and looks for the gap between the pulses and thus the gap between the teeth (i.e. the missing teeth). The gap between the teeth and thus the gap between the pulses is a zero reference for the engine position. An offset between the engine position and a motor mechanical position (i.e. an actual rotational position of the rotor 22) may then be calculated, in particular by the computer processing unit. A summation of this offset and the motor mechanical position is used as the engine position in a control software for operating and controlling the ISO. For example, for this purpose, a resistor and a capacitor for filtering are used, as well as a transistor for amplification. A power source for the transistor may be supplied by an ISO module.

[0022] In the following, a method will be explained by which the engine position may be determined in a particularly easy and cost-effective way. For example, the method is realized by an algorithm executed by the electronic processing unit. The method is used to determine or detect the engine position (i.e. the rotational position of the output shaft 16) without the need for any additional hardware. For example, at engine start, comfort torque is not applied since the engine position or a signal indicative of the engine position is not available. This may also be the case when a hardware-line is available.

[0023] In said method, a first signal is determined, the first signal being indicative of a rotational speed of the rotor 22 driven and thereby rotated by the output shaft 16. In other words, for example, whilst the rotor 22 is driven and thereby rotated by the output shaft 16, the rotational speed is measured by a speed sensor. For example, the speed sensor provides the first signal which may be also referred to as a motor speed signal since, for example, the ISO may also be referred to as a motor. There may be an oscillation in the motor speed signal, in particular during start and idling of the engine 10, at a frequency corresponding to the engine speed and the number of cylinders 14 of the engine 10. Said engine speed may be a rotational speed of the output shaft 16, wherein the engine speed may correspond to the rotational speed of the rotor 22 since, for example, the rotor 22 may be connected to the output shaft 16 in a rotationally fixed manner. In the method, the first signal is filtered by a bandpass filter. Thus, said oscillation may be filtered out from the motor speed signal by the bandpass filter (BPF).

[0024] Fig. 3 shows a diagram 30 having an abscissa 32 and an ordinate 34. For example, the time is plotted on the abscissa 32, wherein the diagram 30 further comprises a graph 36 illustrating the filtered first signal which is also referred to as a BPF motor speed signal. Thus, values of the BPF motor speed signal are plotted on the ordinate 34. A cutoff frequency of the BPF may be computed or calculated from the engine speed and the number of the cylinders 14. Moreover, in the method, at least one positive derivative of the filtered first signal is determined. Preferably, the highest positive derivative or at least one of the highest positive derivatives of the filtered first signal is determined. In this regard, the highest positive derivative of the filtered first signal corresponds to the maximum positive torque provided by the engine 10 via the output shaft 16 (i.e. provided by the output shaft 16). Moreover, in the method, a first position value is assigned to the determined positive derivative wherein the first position value is indicative of the rotational position in which the output shaft 16 is at a point in time at which the positive derivative occurs. In other words, the rotational position in which the output shaft 16 is at said point in time at which the positive derivative occurs is an engine position in which the engine 10 provides, via the output shaft 16, maximum torque. This engine position may be defined as an upper dead center (UDC) which may vary by engine model and engine load.

[0025] Fig. 3 further shows a diagram 38 having an abscissa 40 on which the time is plotted. The diagram 38 further comprises an ordinate 42. A graph 44 illustrates an ideal engine position such that, in Fig. 3, a relationship between the BPF motor speed signal and said UDC or a so-called UDC position in which the output shaft 16 is when providing maximum torque is shown. As shown in Fig. 3, zero-crossing points at which the BPF motor speed signal (first signal) turns from negative to positive are used as highest positive derivative points at which the first signal has its highest positive derivatives. The engine position is detected in a limited speed range (idle speed) for consistent engine load, corresponding to a constant UDC position. The UDC position may be modified by a modifying value provided by a look-up table depending on engine load. In Fig. 3, one of said zero-crossing points is indicated by Z, and the UDC is indicated by U. [0026] Moreover, in the method, a second signal indicative of rotational positions of the rotor 22 driven by the output shaft 16 is determined, wherein the rotational positions of the rotor 22 are measured by a sensor whilst the rotor 22 is driven by the output shaft 16. For example, said sensor may be the afore-mentioned speed sensor. In the diagram 38, a further graph 46 illustrates the second signal which may be also referred to as a quasi-motor mechanical position or a quasi-motor mechanical position signal. In other words, the graph 44 illustrates a quasi-motor mechanical position which is measured and provided by said sensor which may be configured as a position sensor. For example, said sensor is installed as a shaft of the electric machine 18, in particular of the rotor 22. The shaft is also referred to as a motor shaft, wherein, for example, said sensor is configured to measure the rotational positions of the rotor 22, in particular the shaft. As shown in Fig. 3, there may be a difference or an offset between the quasi-motor mechanical position and the real or ideal engine position illustrated by the graph 44. This difference or offset between the quasi-motor mechanical position and the ideal engine position may be obtained as will be described in greater detail below: In the method, a second position value of the second signal (graph 44) is determined, the second position value being indicative of the rotational position in which the output shaft 16 is at said point in time. In Fig. 3, said point in time is indicated by t. Moreover, in said method, the rotational position of the output shaft 16 is determined on the basis of the first and second position values. Particularly, a third position value indicative of the rotational position of the output shaft 16 is determined on the basis of the first and second position values. Moreover, preferably, the determined rotational position of the output shaft 16, in particular the third position value, is used to operate or control the ISO. In other words, preferably, the!SG is operated or controlled on the basis of the determined rotational position of the output shaft 16, in particular on the basis of the third position value.

[0027] Preferably, the afore-mentioned offset between the quasi-motor mechanical position and the real engine position is obtained by calculating an offset value indicative of said offset (i.e. the difference between the quasi-motor mechanical position and the ideal engine position). This means, that, preferably, once a zero-crossing or a zero-crossing point (i.e. a rotational position at which the first signal turns from negative to positive) is determined (i.e. once a zero crossing from negative to positive) event occurs, the offset or difference between the ideal engine position (i.e. the UDC position) and the quasi-motor mechanical position is calculated. A number of such offset calculations varies by the number of the cylinders 14, with the average being used as a final offset value. A summation of the learned or final offset value and the quasi-motor mechanical position is used as the engine position (i.e. the rotational position of the output shaft 16), and in an ISO control software to operate or control the!SG for comfort function and engine stop positioning. For systems, which may already have a hardware connection and thus the CAM-Sync signal, the ISO is still able to provide the same level of comfort with said method or algorithm during a hardware failure. Moreover, CAM-Sync signal related hardware failures may be eliminated. Moreover, in particular for future products, CAM-Sync signal related hardware may be removed in comparison with conventional solutions which will reduce both, costs and manufacture assembly time. Related diagnostic functions may also be eliminated. Moreover, the method of the present invention may provide the same comfort level with all the savings mentioned above.

Reference signs Engine 12 Crankcase 14 Cylinders 16 Output shaft 18 Electric machine Stator 22 Rotor 24 Abscissa 26 Ordinate 28 Graph Diagram 32 Abscissa 34 Ordinate 36 Graph 38 Diagram Abscissa 42 Ordinate 44 Graph 46 Graph t Point in time U upper dead center Z zero-crossing point

Claims

CLAIMS1. A method for determining a rotational position of an output shaft (16) of an engine (10), wherein the output shaft (16) is configured to drive and thereby rotate a rotor (22) of an electric machine (18), and wherein the method comprises: determining a first signal indicative of a rotational speed of the rotor (22) driven and thereby rotated by the output shaft (16); filtering the first signal by a bandpass filter; -determining at least one positive derivative (Z) of the filtered first signal (36); assigning, to the positive derivative (Z), a first position value indicative of the rotational position in which the output shaft (16) is at a point in time (t) the positive derivative (Z) occurs; determining a second signal indicative (46) of rotational positions of the rotor (22), the rotational positions of the rotor (22) being measured by a sensor whilst the rotor (22) is driven by the output shaft (16); determining a second position value of the second signal (46), the second position value being indicative of the rotational position in which the output shaft (16) is at the point in time (t); and determining the rotational position of the output shaft (16) on the basis of the first and second positions values.
2. The method according to claim 1, wherein an offset value is determined by subtracting one of the positions values from the other position value.
3. The method according to claim 2, wherein the rotational position of the output shaft (16) is determined by summating the offset value and the second position value.
4. The method according to any one of the preceding claims, wherein a cutoff frequency of the bandpass filter is determined at least on the basis of a number of cylinders (14) of the engine (10).
5. The method according to any one of the preceding claims, wherein the positive derivative (Z) of the filtered first signal (36) is the highest positive derivative (Z) of the filtered first signal (36).
6. The method according to any one of the preceding claims, wherein the positive derivative (Z) is at a zero-crossing point at which the filtered first signal (36) turns from negative to positive.
7. The method according to any one of the preceding claims, wherein the electric machine (18) is configured to: -start the engine (10); and/or -convert mechanical energy provided by the output shaft (16) when driving the rotor (22) into electric energy.