Method for fault diagnosis of an electric motor, in particular a camshaft actuator, as well as corresponding control unit and computer program

Abstract

The invention relates to a method for fault diagnosis of an electric motor (100), wherein the electric motor (100) is coupled to a camshaft (121) of an internal combustion engine (120), wherein the electric motor (100) has three control lines (101, 103, 105) that are sequentially activated and deactivated for operation of the electric motor (100). The method comprises the following steps: (a) stopping the internal combustion engine (120); (b) energizing the electric motor (100); (c) receiving a movement signal indicative of a movement of the camshaft (121) in response to the energization; and (d) assessing whether a fault in the electric motor (100) exists based on the movement signal. The invention further relates to a corresponding control unit (150) and a computer program.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to methods for fault diagnosis of an electric motor operated as a camshaft actuator as well as corresponding control devices and computer programs. BACKGROUND OF THE INVENTION

[0002] In control units in the automotive industry, electrical control outputs are typically monitored electrically, meaning the outputs are continuously checked for short circuits to the supply voltage (shortcut to battery) and short circuits to ground (shortcut to ground). For this purpose, a voltage measured at a point in the control unit that exhibits a voltage difference to the supply voltage or to ground when the circuit is closed is compared with the supply voltage or the voltage at ground. If the measured difference is too small, a diagnostic function in the control unit software indicates a short circuit to the supply voltage or to ground.

[0003] Similarly, this voltage comparison also produces a voltage difference that is too small for the supply voltage or ground in the event of an open circuit (OC), depending on the hardware configuration. This is also referred to as an OC diagnosis. OC diagnostics are performed, for example, to detect damaged control cables of an electric motor. In the case of the control cables to a BLDC motor, however, this diagnosis can only be performed when the BLDC motor is safely stopped, since rotation of the rotor due to an external torque can induce a voltage despite an interrupted control cable. Induced voltages can falsify the diagnostic result.

[0004] When a BLDC motor is used as a camshaft actuator in a vehicle, such a diagnosis is therefore performed in many control units after the combustion engine has been shut down and the BLDC motor has safely come to a standstill. This way, a cable break in the camshaft actuator can always be reliably detected in the stationary phase of the combustion engine following the interruption.

[0005] However, such a diagnosis of an electric motor's control lines based on a voltage comparison with ground or supply voltage has the disadvantage that a change in the camshaft position cannot be reliably detected during the diagnostic procedure. Typically, a software driver that forms an interface to the BLDC motor must be switched to a sleep mode during the diagnostic procedure. In such a sleep mode, the position of the electric motor's rotor and thus of the camshaft cannot be detected, for example, if only a joint deactivation of the power stage for controlling the motor and the current measurement is possible. This means that the position of the camshaft cannot be reliably determined upon a subsequent engine start.Accordingly, an unfavorable position of the camshaft must be assumed, the engine start must be carried out under worst-case assumptions regarding the camshaft position and is less convenient. SUMMARY AND EMBODIMENTS

[0006] It is therefore an object of the present disclosure to provide an alternative method for fault diagnosis of an electric motor operated as a camshaft actuator, which can be carried out in particular with simultaneous position detection of the camshaft.

[0007] This problem is solved by a method for fault diagnosis of an electric motor, by a control unit, and by a computer program according to the independent patent claims. Advantageous embodiments and further developments emerge from the respective dependent claims, the following description, and the drawings.

[0008] Thus, according to a first aspect, a method for fault diagnosis of an electric motor is provided, wherein the electric motor has three control lines and is coupled to a camshaft of an internal combustion engine. The method comprises the following steps: (a) stopping or shutting down the internal combustion engine; (b) energizing the electric motor; (c) receiving a movement signal indicative of a movement of the camshaft and / or the electric motor in response to the energization; and (d) assessing whether a fault in the electric motor exists based on the movement signal.

[0009] According to a further aspect, a control unit, in particular a control unit for a motor vehicle, is provided, wherein the control unit is configured to carry out the method described above.

[0010] According to a further aspect, a computer program is provided which comprises instructions which, when executed by a computer, cause the computer to perform the method described above. In the context of the present disclosure, a computer is defined, for example, as a device that processes data using programmable computing rules. Computers can be embedded in everyday devices, for example, in control units of motor vehicles.

[0011] According to a further aspect, a storage medium is provided with a computer program, wherein the computer program comprises instructions which, when the computer program is executed by a computer, cause the computer to carry out the method described above.

[0012] According to a further aspect, a system is provided which comprises the control unit and the electric motor.

[0013] In the context of the present disclosure, the term "control line" means, for example, a line used to control the electric motor. The control line can comprise one or more switching elements that control an electric current through the control line. According to one embodiment, the control line, in particular all control lines of the electric motor, are sequentially connected to supply voltage or ground for operation of the electric motor. According to one embodiment, the control line, in particular all control lines of the electric motor, are sequentially activated and deactivated. A control line can be activated when corresponding switching elements are closed and / or when a current flows through the control line, in particular a current that is greater than a predetermined threshold value. The control line can be deactivated if at least one or both of these conditions are not met.The electric motor can have exactly three control lines, but can also have more than three control lines.

[0014] According to one embodiment, the three control lines, in particular all control lines, are electrically connected to one another at one of their ends, in particular in the region of the rotor and / or the stator of the electric motor. At the respective opposite end, the control lines can have a switching element, in particular a branch into two electrical lines, each containing a switching element. One of these switching elements can be connected to a positive voltage pole, the other switching element to a negative voltage pole. The switching elements can, but do not have to, be part of the respective control line. In other words, the control lines are connected in a star configuration.

[0015] According to one embodiment, the three control lines, in particular all control lines, are each connected at one of their ends to a further control line, wherein at least one coil of the further control line is arranged between the end of the control line and the end of the further control line. At the respective opposite end, the control lines can have a switching element, in particular a branch into two electrical lines, each containing a switching element. One of these switching elements can be connected to a positive voltage pole, the other switching element to a negative voltage pole. The switching elements can, but do not have to, be part of the respective control line. In other words, the control lines are connected in a ring or delta shape.

[0016] According to one embodiment, the switching elements are transistors, in particular MOSFETs. They can be configured to be controlled with a pulse-width modulated signal.

[0017] According to one embodiment, the electric motor is a brushless DC motor (BLDC).

[0018] In the context of the present disclosure, the term "camshaft" can mean a rod-shaped element on which at least one projection is arranged, in particular a rounded projection. Each projection can be configured to open and / or close an associated valve of the internal combustion engine upon rotation of the rod-shaped element, for example, an intake valve for a combustion mixture or an exhaust outlet valve of the internal combustion engine. The projection can be configured to exert force against a return element of the valve, for example, against a return spring. The camshaft can be driven by a crankshaft, for example, via a toothed belt or a timing chain with a ratio of one to two.

[0019] In the context of the present disclosure, the term "crankshaft" means, for example, a shaft that supports at least one crank. Each crank may be configured to move an associated piston within a cylinder upon rotation of the shaft.

[0020] In the context of the present disclosure, the term "coupling the electric motor to the camshaft" may mean that a connection, for example, mechanical or electrical, is established between the electric motor and the camshaft, such that a rotation of a rotor of the electric motor correlates with a rotation of the camshaft. The ratio of the rotational movements may be predetermined by a transmission, such as a so-called harmonic drive transmission or a three-shaft transmission. The transmission may have a high gear ratio, for example, greater than fifty to one.

[0021] According to one embodiment, a phase of rotation of the camshaft can be adjusted by means of the electric motor, in particular with respect to a rotation of the crankshaft. The phase angle can be adjustable within a predetermined angular range. The angular range can be limited by mechanical stops. The phase can be adjusted by deviating a target rotational speed of the rotor of the electric motor from the rotational speed of the camshaft, in particular by means of targeted short-term deviations. Such an embodiment can be advantageous for implementing favorable valve timing for different operating conditions, for example, for idling or maximum power.An electromechanical camshaft adjuster can have faster response times than conventional approaches, for example based on oil chambers of a vane cell adjuster, especially at low engine temperatures, and enable a more compact design.

[0022] In the context of the disclosure, the term "energizing" can be defined as a control of the electric motor, in which current flows through the control lines and / or corresponding coils of the electric motor. The associated control profile can be suitable for setting a rotor of the electric motor into rotational motion, at least when the electric motor is intact. The rotational motion corresponding to the control profile can comprise at least one complete rotation of the electric motor, in particular multiple rotations.

[0023] In the context of the disclosure, the term "motion signal" can be defined as any signal indicating a movement of the camshaft and / or the rotor of the electric motor. The motion signal can also indicate a slight movement or the absence of movement. The motion signal can be detectable using a motion sensor and / or a position or posture sensor. The motion sensor can be configured to measure a movement of the camshaft and / or the rotor of the electric motor. The position or posture sensor can be configured to measure a position or posture of the camshaft and / or the rotor of the electric motor. A movement or the absence of movement can be derived from a comparison of positions measured at different times, in particular at times before the electric motor is energized and during or after the electric motor is energized.

[0024] The described method and the corresponding control unit can be advantageous for enabling reliable diagnosis of the electric motor, in particular the control lines, when the combustion engine is stopped. The simple, mechanical diagnostic principle is based on the possibility that a limited movement of the camshaft is possible even when the crankshaft is stationary, for example, by a fraction of a complete rotation of the camshaft, in particular up to 30 degrees. The previously described method takes advantage of this by energizing the electric motor while the combustion engine is switched off in order to move the camshaft. The fault diagnosis can be based, for example, on the extent of the resulting camshaft movement.

[0025] Thanks to this simple, mechanical method for fault diagnosis, the camshaft position can be continuously determined during the diagnostic procedure. In particular, the diagnostic procedure can be performed without having to put the electric motor's software driver into sleep mode. Camshaft position detection is not interrupted during the diagnosis, thus avoiding any loss of starting comfort due to an uncertain camshaft position after all engine idle phases.

[0026] A fault-free camshaft actuator with three functioning control lines and three functioning circuits, if appropriately designed, is capable of generating a rotating electromagnetic field in the stator and significantly rotating a camshaft from a rest position, even when the combustion engine is stopped, with the appropriate current supply. In contrast, a faulty camshaft actuator with only two functioning control lines and only one functioning circuit is not capable of generating a rotating electromagnetic field in the stator and significantly rotating a camshaft from a rest position, even when the combustion engine is stopped, with any current supply.

[0027] For the diagnostic procedure, after the combustion engine is shut down and the camshaft and camshaft actuator have safely come to rest, the camshaft actuator is selectively energized again to move the camshaft from its rest position. The position of the camshaft is continuously recorded by the engine control unit using a position sensor, specifically an incremental position sensor.

[0028] If significant camshaft movement is measured at a current supply known to be sufficient for a fault-free system, this can be sufficient evidence of the functionality of all three control lines, and the system can be identified as fault-free. If no significant camshaft movement is measured at a current supply known to be sufficient for a fault-free system, this may be caused by an interruption in a control line, and the system can be identified as faulty due to a control line interruption.

[0029] According to one embodiment, a magnetic field in the electric motor is controlled by means of the control lines, in particular via switching elements arranged in the control lines. This magnetic field can be configured to drive a rotor of the electric motor. The magnetic field can be generated by coils of the rotor of the electric motor and / or a stator of the electric motor.

[0030] According to one embodiment, the control lines are electrically conductive and supply current to coils of the electric motor, which at least partially generate the magnetic field. For example, the coils are wire coils. The control lines can encompass the coils, in particular the wire coils.

[0031] According to one embodiment, when corresponding switching elements are closed, a current flows through two of the control lines, but not through the third control line. The direction of current through the control lines can be determined by selecting the switching elements to be closed.

[0032] According to one embodiment, the presence of a fault is assumed if the movement signal indicates less than one complete revolution of a rotor of the electric motor, in particular less than two-thirds of a revolution, in particular less than half a revolution. According to one embodiment, if a fault is present, the power of the electric motor is limited. Such an embodiment can be advantageous because, with the camshaft and the electric motor at a standstill, starting the electric motor from a standstill is not possible if one of the control lines and / or corresponding circuits is faulty.

[0033] According to one embodiment, it is assumed that no error is present if the movement signal indicates more than half a revolution of the rotor of the electric motor, in particular more than one complete revolution of the rotor, in particular more than two revolutions of the rotor. Such an embodiment can be advantageous because, with the camshaft and the electric motor at a standstill, starting the electric motor from a standstill is only possible if all control lines and / or all corresponding circuits are intact.

[0034] According to one embodiment, the movement signal is determined by means of a position sensor for the rotor of the electric motor. The position sensor can be configured to determine, in particular to directly measure, a rotation of the rotor. Such an embodiment can be advantageous because the position sensor for the rotor is typically more accurate than a position sensor that directly measures the rotation of the camshaft. For example, a camshaft sensor on the camshaft sensor wheel can be configured to distinguish between four and twelve flanks. The engine sensor, on the other hand, can be configured to measure with an angular resolution of less than twenty degrees, in particular less than ten degrees. Accordingly, some movements of the camshaft may not be detectable at all with the camshaft sensor. Alternatively or additionally, the movement signal can be determined by means of a position sensor for the camshaft.

[0035] According to one embodiment, the electric motor is coupled to the camshaft by means of a gear mechanism, wherein a gear ratio of the gear mechanism, which indicates the ratio of revolutions of the electric motor to revolutions of the camshaft, is greater than 10, in particular greater than 50. The gear ratio can be 73 or greater. The gear mechanism can be a so-called harmonic drive, which has a particularly compact design. Such an embodiment can be advantageous, in particular when the movement signal is determined using the position sensor for the rotor of the electric motor, because the gear ratio allows a movement of the camshaft to be determined with great accuracy. This applies in particular if the position sensor for the rotor of the electric motor already has a greater angular resolution than the position sensor for the camshaft.In other words, a large gear ratio of the position sensor of the rotor of the electric motor can enable a particularly precise determination of the camshaft position.

[0036] According to one embodiment, the method further comprises: after stopping the internal combustion engine and before energizing the electric motor, checking using a position sensor whether the camshaft and / or the rotor of the electric motor are at rest. The position sensor can be a position sensor for the camshaft and / or preferably a position sensor for the rotor of the electric motor. In particular, signals from both sensors can also be taken into account for the check. As described in connection with the two previous embodiments, the position sensor for the rotor of the electric motor can have a higher level of accuracy compared to the position sensor of the camshaft sensor. In this respect, a rest position can be determined more precisely based on signals from the position sensor of the electric motor.

[0037] According to one embodiment, a position of the rotor of the electric motor and / or the camshaft actuator is continuously determined during the method. Such an embodiment can be advantageous because, as already described, the position of the camshaft is reliably known the next time the engine is started. The mechanical method for fault diagnosis described in this disclosure can enable continuous detection of the camshaft position, for example, because the software driver of the electric motor does not need to be switched to a sleep mode for diagnosing the electric motor.

[0038] According to one embodiment, the fault comprises at least one of a broken connection in one of the control lines and a malfunction of one of the switching elements. Such an embodiment can be advantageous because all of these faults, especially the broken connection, can lead to damage to the electric motor and / or the control unit if they remain undetected.

[0039] According to one embodiment, the error indicates a damaged control line and / or a damaged circuit of the electric motor. Such an embodiment can be advantageous because, as already explained, damaged control lines can lead to overloading of the electric motor.

[0040] According to one embodiment, the method is performed during a start-stop operation of the internal combustion engine. Such an embodiment can be advantageous because the internal combustion engine is stopped several times during the start-stop operation, allowing the diagnostic method to be performed more frequently, in particular several times during a driving cycle, for example, when the vehicle is stopped at a traffic light or in a traffic jam.

[0041] According to one embodiment, the method further comprises: setting the camshaft to a predetermined rest position after energizing the electric motor and / or after the diagnostic procedure has ended, for example, to a position that the camshaft assumed before the diagnostic procedure began. The predetermined rest position can be a position in which a comfortable engine start is possible.

[0042] According to one aspect, a method for fault diagnosis of an electric motor comprises the following steps: (a) checking whether a suspected fault variable is set, wherein the suspected fault variable indicates a previously determined suspected fault, in particular a suspected fault determined during operation of the internal combustion engine; (b) performing a method as previously described in this disclosure if the suspected fault variable is set, in particular only if the suspected fault variable is set.

[0043] For a method for setting such a suspected error variable, the method disclosed in DE 10 2023 206 485 A1, for example, can be used, the disclosure content of which is incorporated into the present disclosure. The method disclosed therein can be advantageous because it can also be carried out during operation of the internal combustion engine, i.e., even when the engine is running. However, it is subject to greater uncertainty.

[0044] Therefore, the method described here can be more reliable and can therefore be used to confirm or refute a previously identified suspected fault during a subsequent engine idle phase. If the suspected fault is refuted, any power limitation of the electric motor imposed due to the suspected fault can be lifted. If the suspected fault is confirmed, the power limitation can be retained. Such an embodiment can be advantageous, for example, if the diagnostic procedure is only performed in the subsequent engine idle phase when the suspected fault variable is set. It therefore does not have to be performed during all engine idle phases.

[0045] As part of the power limitation, the current supply to the electric motor can be reduced to such an extent that there is no risk of overheating, even at the expense of reduced dynamic performance. Reducing the current supply can be advantageous to prevent the electric motor from being impaired or damaged by the fault. This can occur, for example, due to excessive heat generation if only two of the three control lines are intact and / or activated, resulting in higher currents in the control lines, switching elements, and motor coils in the remaining circuit than if all three control lines were intact and / or activated.

[0046] The aforementioned DE 10 2023 206 485 A1 describes, among other things, a method for testing for line dropouts based on a histogram of the total phase currents of the camshaft actuator during combustion engine operation—i.e., not during an engine idle phase. If a suspected fault is detected, the current supply to the BLDC motor is limited for the remainder of the combustion engine's current driving cycle in such a way that overheating does not occur, even with the additional heating described above due to a line interruption.

[0047] In summary, the diagnostic procedure described here can be used either only to confirm a suspected fault found in the subsequent engine idle phase or independently of the suspected fault procedure described above in every engine idle phase. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Further advantages and advantageous embodiments and further developments of the method, the control device and the computer program emerge from the following exemplary embodiments shown in conjunction with the figures.

[0049] They show: Fig. 1 an electric motor for control by a control unit according to an embodiment of the present disclosure, and Fig. 2 an electric motor coupled to a camshaft of an internal combustion engine, which is suitable for carrying out a method according to an embodiment of the present disclosure.

[0050] Identical, similar, or functionally identical elements are provided with the same reference symbols in the figures. In some figures, individual reference symbols have been omitted for clarity. The figures and the relative sizes of the elements depicted in the figures are not to scale. Rather, individual elements may be exaggerated for clarity and / or clarity. DETAILED DESCRIPTION OF EMBODIMENTS

[0051] Fig. Figure 1 shows an electric motor 100 with six switching elements 108-113 for control by a control unit according to an exemplary embodiment of the present disclosure. The control unit is configured to perform a method for fault diagnosis of an electric motor 100, in this case a BLDC motor.

[0052] The electric motor 100 has three control lines 101, 103, 105, which are sequentially activated and deactivated for operation of the electric motor 100. For this purpose, the switching elements 108, 109, 110, 111, 112, 113, which can be implemented as transistors, for example, are sequentially switched such that one of the control lines 101, 103, 105 is connected to a negative pole of a voltage source and another of the control lines 101, 103, 105 is connected to a positive pole of the voltage source. Thus, two switching elements 108, 109, 110, 111, 112, 113 are closed, and all other switching elements 108, 109, 110, 111, 112, 113 are open. Accordingly, a current flows through two of the control lines 101, 103, 105 and through two of the coils 102, 104, 106 assigned to the two control lines. This generates a magnetic field that depends on the current direction through the control lines 101, 103, 105.This magnetic field drives a rotor of the electric motor 100. The total current through all control lines 101, 103, 105 can be measured using the ammeter 107.

[0053] Brushless DC (BLDC) motors 100 are used in a variety of applications, including automotive engineering. One application example is the drive of an electromechanical camshaft actuator for controlling the rotational speed of a camshaft in an internal combustion engine.

[0054] BLDC motors 100 are controlled by a control unit via three control lines 101, 103, 105. In the stator of the BLDC motor 100, the lines connected to the control lines 101, 103, 105 are electrically interconnected and mechanically arranged such that alternating electrical currents through the control lines 101, 103, 105—the so-called phase currents—induced by the control unit by varying the control voltage generate a rotating magnetic field in the stator. This rotating field rotates the rotor of the BLDC motor 100. The change in the rotor position is measured by the control unit using an incremental position sensor, for example, integrated Hall sensors. Thus, the BLDC motor 100 is controlled in a closed control loop with the rotor speed as the controlled variable and the phase currents through the control lines 101, 103, 105 as the manipulated variables.

[0055] The control unit generates the phase currents by pulse-width modulation (PWM) of a control voltage on the control lines 101, 103, 105 of the BLDC motor 100. Any desired current profile can be generated, e.g., in the form of a sine or square wave, the course of which can be described using the parameters frequency, amplitude, and phase position. For the desired operation of the BLDC motor 100, a current of the desired intensity must flow in the desired direction through two of the three control lines 101, 103, 105 at all times. The third control line 101, 103, 105 is not energized by the control unit.

[0056] An important prerequisite for the full functionality of this drive system is the secure electrical connection between the control unit and the BLDC motor 100 via the three control lines 101, 103, 105. A temporary or permanent interruption of a control line 101, 103, 105 can make the operation of the BLDC motor 100 impossible. However, this is not necessarily the case.

[0057] At any given moment during motor operation, current flows alternately through one of the three circuits formed by the control unit, two of the three control lines 101, 103, 105, and the BLDC motor 100. Three phase-shifted alternating currents flow in the three control lines 101, 103, 105. If one control line 101, 103, 105 is interrupted, then two of these three circuits are interrupted. An alternating current in the remaining circuit can only generate an oscillating, but no longer a rotating, magnetic field in the stator of the BLDC motor 100. Without a rotating magnetic field, the BLDC motor 100 cannot start from a standstill under its own power.However, if (i) the BLDC motor 100 is already rotating at the time the control line is interrupted or (ii) the BLDC motor 100 is set in rotation by a torque acting externally on its rotor, then, with a low torque tapped at the rotor shaft, it is possible for the control unit operating in the closed control loop to permanently maintain the rotation of the BLDC motor 100 by increasing the current in the remaining circuit to minimize the speed control deviation.

[0058] However, such continued operation with an interrupted control line 101, 103, 105 represents a completely different operating point for the BLDC motor 100 and the control unit than fault-free operation with three control lines 101, 103, 105. After the interruption of one control line 101, 103, 105, the control unit must increase the current in the circuit via the remaining two control lines 101, 103, 105 in a controlled manner to such an extent that the BLDC motor 100 generates the same torque as in fault-free operation with the help of all three circuits in order to achieve the desired target speed of the BLDC motor 100. The critical components of the BLDC motor 100 (the active motor coils) and the control unit (the transistors of the remaining circuit) are then subjected to a larger current and heat up more than in fault-free operation. The current I is quadratically added to the heating power P at a resistor R, P = R * I 2For example, doubling the current quadruples the heating power. Since, for cost reasons, it is common practice to operate the fault-free overall system close to the limits of its thermal capacity, at least at certain operating points, additional heating due to an interruption in a control line 101, 103, 105 threatens overheating and thermal destruction of the system.

[0059] This necessitates reliably detecting an interruption in a control line 101, 103, 105, for example, using the method described above, in order to prevent overheating through active countermeasures. If a fault is detected, the current supply to the BLDC motor 100 can be reduced to such an extent that, at the expense of reduced dynamic performance of the BLDC motor 100, no risk of overheating occurs during subsequent continued operation of the combustion engine 120.

[0060] With reference to Fig. 2, the use of an electric motor 100, as in Fig. 1, explained as a camshaft actuator. For this purpose, the electric motor 100 is immovably supported against the vehicle via the mechanical connection 130 and coupled to a camshaft 121 of an internal combustion engine 120, for example, by means of a transmission 122. The camshaft 121 is configured to open and close corresponding valves 123 of the internal combustion engine 120 by means of the cams, for example, intake valves for a fresh charge or exhaust valves for exhaust gases. The camshaft 121 is coupled, for example, by means of a timing chain 125, to a crankshaft 124 of the internal combustion engine 120. The crankshaft 124 is configured to move pistons in corresponding cylinders of the internal combustion engine 120 in order to compress the combustion mixture in the cylinder.

[0061] The rotor of the BLDC motor 100 usually rotates synchronously with the camshaft 121 of the internal combustion engine 120. By means of brief, targeted deviations between the target rotational speed of the rotor of the BLDC motor 100 and the rotational speed of the camshaft 121, the phase position of the camshaft 121 is adjusted. The angular adjustment range of the rotor of the BLDC motor 100 relative to the camshaft 121 is limited by mechanical stops. With the electromechanical camshaft actuator, both cases of continued operation are possible despite an interrupted control line: (a) The control line 101, 103, 105 can be interrupted by vibrations during driving of the internal combustion engine 120, while the rotor of the BLDC motor 100 rotates approximately at the camshaft speed. (b) Before the internal combustion engine 120 starts, the BLDC motor 100 is also stationary.If the BLDC motor 100 does not begin to rotate as intended when the internal combustion engine 120 starts due to an interrupted control line 101, 103, 105, then it is rotated by the rotating camshaft 121.

[0062] If the position detection of the camshaft 121 is not possible without interruption, then either the line drop diagnosis in engine idle phases can only be carried out when the camshaft is in a randomly non-critical stop position, or after line drop diagnosis even in critical stop positions of the camshaft, a lower starting comfort must be accepted in fault-free systems.

[0063] Such disadvantages can be avoided if a method for diagnosing faults of the electric motor 100 is carried out with the following steps: (i) stopping the internal combustion engine; (ii) checking whether the camshaft is at rest; (iii) energizing the electric motor; (iv) receiving a movement signal representative of a movement of the camshaft in response to the energization; and (v) assessing whether a fault of the electric motor exists based on the movement signal.

[0064] The method has the advantage that, unlike with a voltage comparison against ground or supply voltage, a software driver forming the interface to the BLDC motor does not need to be switched to sleep mode. Consequently, the position of camshaft 121 can be continuously detected. With active rotor position detection using the incremental position sensor, the engine control unit can correctly map the rotation of camshaft 121 even after the internal combustion engine 120 has been shut down. The camshaft position is already available at the beginning of the subsequent start of the internal combustion engine 120, and the engine can start normally with minimal jerking.

[0065] The invention is not limited to the embodiments described herein. Rather, the invention encompasses any novel feature and any combination of features, including, in particular, any combination of features in the embodiments and claims. REFERENCE SYMBOL 100 electric motor 101 first control line 102 first coil 103 second control line 104 second coil 105 third control line 106 third coil 107 ammeter 108 first switching element 109 second switching element 110 third switching element 111 fourth switching element 112 fifth switching element 113 sixth switching element 120 combustion engine 121 camshaft 122 gearboxes 123 Valve 124 Crankshaft 125 timing chain 130 mechanical connection to the vehicle

Claims

[1] Method for fault diagnosis of an electric motor (100) of an electromechanical camshaft actuator, wherein the electric motor (100) has three control lines (101, 103, 105) and is coupled to a camshaft (121) of an internal combustion engine (120), the method comprising the following steps: - stopping the combustion engine (120); - energizing the electric motor (100); - receiving a movement signal indicative of a movement of the camshaft (121) in response to the energization; and - Assessing whether there is a fault in the electric motor (100) based on the movement signal. [2] Method according to the preceding claim, wherein the presence of an error is assumed if the movement signal indicates less than one complete revolution of a rotor of the electric motor (100). [3] Method according to one of the preceding claims, wherein it is assumed that no error is present if the movement signal indicates more than one complete revolution of the rotor of the electric motor (100). [4] Method according to one of the preceding claims, wherein the movement signal is determined by means of a position sensor for the rotor of the electric motor (100). [5] Method according to the preceding claim, wherein the electric motor (100) is coupled to the camshaft (121) by means of a gear (122), wherein a gear ratio of the gear (122), which indicates the ratio of revolutions of the electric motor (100) to revolutions of the camshaft (121), is greater than 10, in particular greater than 50. [6] Method according to one of the preceding claims, further comprising, after stopping the internal combustion engine (120) and before energizing the electric motor (100), checking by means of a position sensor whether the camshaft (121) is at rest. [7] Method according to one of the preceding claims, wherein a position of the rotor of the electric motor (100) is continuously determined during the method. [8] Method according to one of the preceding claims, wherein the error indicates a damaged control line (101, 103, 105). [9] Method according to one of the preceding claims, wherein the method is carried out during a start-stop operation of the internal combustion engine (120). [10] Method according to one of the preceding claims, further comprising: setting the camshaft (121) in a predetermined rest position after energizing the electric motor. [11] Method for fault diagnosis of an electric motor (100) of an electromechanical camshaft adjuster, comprising the following steps: - Check whether a suspicion variable is set, where the suspicion variable indicates a previously identified suspicion; - Carrying out the method according to one of the preceding claims when the error suspicion variable is set. [12] Control device which is arranged to carry out a method according to one of the preceding claims. [13] A computer program comprising instructions which, when executed by a computer, cause the computer to carry out a method according to any one of claims 1 to 11.

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