Engine drive circuit and valve timing control system

Abstract

Motor drive circuit for driving an electric motor (12) of a valve timing control system (10) that adjusts the valve timing of an internal combustion engine, wherein the motor drive circuit comprises: a first abnormality countermeasure device (S20) for executing a first abnormality countermeasure process which limits a motor drive current (I) supplied to the electric motor (12) for driving the electric motor (12) when an instantaneous current of the motor drive current (I) reaches an overcurrent threshold (Io), and a second anomaly countermeasure device (S30) for executing a second anomaly countermeasure process which limits the motor drive current (I) when the motor drive current (I) exceeds a continuous current threshold (Is) which is less than the overcurrent threshold (Io) for a first predetermined time period (Ts) or longer, wherein the second anomaly countermeasure device (S30) changes the continuous current threshold (Is) according to an actual rotational speed of the electric motor (12).

Description

[0001] The present invention relates to an engine drive circuit and a valve timing control system having the same.

[0002] DE 10 2004 012 886 A1 discloses a motor control device in which an overcurrent protection circuit detects an abnormality in a motor current and forcibly turns off a MOSFET. The overcurrent protection circuit has a timer function and a timing function. In the timer mode, the overcurrent protection circuit stops an abnormality detection signal for an ON period before generating a signal for an OFF period when a current flowing through the motor exceeds a certain threshold. The timing function serves to control the OFF period to a relatively larger value compared to the ON period.

[0003] The subsequently published DE 10 2006 000 443 A1 discloses a method for controlling a motor in which an overload condition of the motor is detected. It is provided that the overload condition is given by exceeding a first predetermined limit value over a first predetermined time period, whereby a motor voltage applied to the motor is reduced by a user-detectable amount to a throttle value.

[0004] In a known motor drive circuit for driving an electric motor of an electric valve timing control system for adjusting valve timing of an internal combustion engine, when an instantaneous current of a motor drive current supplied to the electric motor for driving the motor reaches an overcurrent threshold, it is determined that an abnormality has occurred, so that the motor drive current is limited in an abnormality countermeasure process (see, for example, JP 2004-350447 A). According to this technique, for example, windings of the electric motor and switching elements of the motor drive circuit are protected from excessively large instantaneous current. Thus, failure of the electric motor and the motor drive circuit can be limited.

[0005] In the motor drive circuit of the electric valve timing control system, which adjusts the valve timing according to an operating condition of the internal combustion engine, an energization period is generally extended. In some cases, it is necessary to constantly supply electric power to the electric motor according to demand. Therefore, even if the motor drive current does not reach the overcurrent threshold, if the motor drive current continues to flow, it may cause excessive heat generation and a failure in the electric motor or motor drive circuit.

[0006] The present invention addresses the above-described disadvantage. Therefore, the present invention aims to provide a motor drive circuit of a valve timing control system that can more effectively limit an error. Another objective of the present invention is to provide a valve timing control system having such a motor drive circuit.

[0007] This object is achieved by a motor drive circuit as defined in claim 1, 2 or 3, and alternatively by a valve timing control system as defined in claim 12.

[0008] Advantageous embodiments are specified in the dependent patent claims.

[0009] The invention, together with additional objects, features, and advantages, will be best understood from the following description, the appended claims, and the accompanying drawings, in which: Fig. 1 is a flowchart illustrating a control procedure according to a first embodiment of the present invention, Fig. 2 a cross-sectional view along a line II-II in Fig. 5, which shows a structure of a valve timing control system according to the first embodiment, Fig. 3 shows a cross-sectional view along a line III-III in Fig. 2, Fig. 4 shows a block diagram of an electrical circuit system according to Fig. 2, Fig. 5 shows a cross-sectional view along a line VV in Fig. 2, Fig. 6 shows a cross-sectional view along a line VI-VI in Fig. 2, Fig. Figure 7 is a block diagram showing details of a power supply block according to Fig. 4 illustrates, Fig. Fig. 8 is a schematic diagram for describing a characteristic feature of the first embodiment, Fig. Fig. 9 is a schematic diagram for describing a characteristic feature of a second embodiment of the present invention, Fig. Fig. 10 is a schematic diagram for describing the characteristic feature of the second embodiment, and Fig. 11 is a schematic diagram for describing a characteristic feature of a third embodiment of the present invention.

[0010] Embodiments of the present invention will be described below with reference to the accompanying drawings. In the following description, similar components in the respective embodiments are indicated by the same reference numerals and will not be described repeatedly. First embodiment

[0011] Fig. 2 shows an electric valve timing control system 10 according to a first embodiment of the present invention. The electric valve timing control system 10 is installed in a vehicle and controls a relative phase (hereinafter referred to as "engine phase") between a crankshaft and a camshaft 2 of an internal combustion engine based on the rotation of an electric motor 12 of the valve timing control system 10 to control the valve timing of intake valves or exhaust valves of the engine.

[0012] First, the electric motor 12 of the electric valve timing control system 10 is Fig. 2. The electric motor 12 is a brushless motor (commutatorless motor) and has a motor housing 13, a motor shaft 14, and windings 15 (see Fig. 7). The motor housing 13 is attached to the machine via a strut. The motor shaft 14 is supported by the motor housing 13 such that the motor shaft 14 is rotatable in both forward and reverse directions. In addition, the respective windings 15 are securely held by the motor housing 13. In the electric motor 12, when each of the windings 15 is energized to form a rotating magnetic field in the forward rotation direction, ie, in Fig. 3 is fed clockwise, the motor shaft 14 is rotated in the forward direction of rotation. In contrast, if each of the windings 15 is used to form a rotating magnetic field in the reverse direction of rotation, ie in Fig. 3 is fed counterclockwise, the motor shaft 14 is driven to rotate in the opposite direction (reverse direction).

[0013] As it is in Fig. As shown in Figure 4, the electric motor 12 further includes rotation angle sensors 16. The rotation angle sensors 16 are arranged sequentially in the rotation direction of the motor shaft 14, and each rotation angle sensor 16 comprises, for example, a Hall element. The rotation angle sensor 16 outputs a sensor signal whose voltage changes based on the locations of the magnetic poles N, S of the motor shaft 14 relative to the rotation angle sensor 16.

[0014] The following is a phase control mechanism 10 of the electric valve timing control system 10 according to Fig. 2. The phase control mechanism 20 includes a drive-side rotor (rotor on the driving side) 22, a driven-side rotor (rotor on the driven side) 24, a planetary gear unit 30, and a link unit 50.

[0015] The drive-side rotor 22 is a timing gear around which a timing chain is wound to establish a connection between the crankshaft of the internal combustion engine and the timing gear. When the crankshaft outputs torque to the drive-side rotor 22, the drive-side rotor 22 is rotated synchronously with the clockwise rotation of the crankshaft according to Fig. 5, maintaining the relative phase with respect to the crankshaft. The output-side rotor 24 is coaxially attached to the camshaft 2 of the internal combustion engine and is integrally formed with the camshaft 2 according to Fig. 5 is rotated clockwise. According to the present embodiment, the forward rotation direction of the motor shaft 14 is set to be the same rotation direction as that of the internal combustion engine. Furthermore, the reverse rotation direction (reverse rotation direction) of the motor shaft 14 is set to be opposite to the rotation direction of the internal combustion engine.

[0016] As it is in Fig. 2 and Fig. 3, the planetary gear unit 30 includes a sun gear 31, a planet carrier 32, a planetary gear 33, and a transmission rotor 34. The sun gear 31 is made of an internal gear and is coaxially fixed to the drive-side rotor 22 by bolts, so that the sun gear 31 rotates integrally with the drive-side rotor 22 upon transmission of output torque from the crankshaft. The planet carrier 32 is connected to the motor shaft 14 via a joint 35, so that the planet carrier 32 rotates integrally with the motor shaft 14 upon transmission of torque from the motor shaft 14. The planet carrier 32 has a cylindrical outer peripheral surface portion eccentric with the drive-side rotor 22 and forms an eccentric portion 36.The planetary gear 33 is an external gear and is fitted (fixed) to the eccentric portion 36 through a bearing 37, so that the planetary gear 33 is arranged eccentrically relative to the sun gear 31. The planetary gear 33 meshes with the sun gear 31 from the radially inner side of the sun gear 31 and performs a sun and planetary motion in response to the relative rotation of the motor shaft 14 relative to the drive-side rotor 22. The transfer rotor 34 is concentrically fitted (fixed) to an outer circumferential surface of the driven-side rotor 24. The transfer rotor 34 has a plurality of engagement holes 38 arranged sequentially at equal intervals in the rotation direction. In addition, the planetary gear 33 has a plurality of engagement protrusions 39, each projecting into a corresponding one of the engagement holes 38.These engagement projections 39 are respectively engaged with the engagement holes 38, so that the planetary rotation of the planetary gear 33 is converted into the rotation of the transmission rotor 34.

[0017] As it is in Fig. 5 and Fig. 6, the connecting unit 50 comprises primary connections 52, secondary connections 53, a guide 54 and movable bodies 56. In Fig. 5 and Fig. 6, for the sake of simplicity, no hatching is used to indicate the cross-sections of the components. The primary links 52 are connected to the drive-side rotor 22 such that the primary links 52 form a rotating pair (revolute pair). The secondary links 53 are connected to the driven-side rotor 24 such that the secondary links 53 form a rotating pair (revolute pair). Furthermore, each secondary link 53 is connected to the corresponding primary link 52 via the corresponding movable body 56 such that the secondary link 53 and the primary link form a rotating pair (revolute pair). As shown in Fig. 2 and Fig. As shown in Fig. 6, the guide 54 is formed as a portion of the transmission rotor 34, which has an axial end surface of the transmission rotor 34 located on a side opposite to the planetary gear 33. The guide 54 has guide grooves 58, in each of which a corresponding one of the movable bodies 56 is slidably received. Each guide groove is formed as a spiral groove such that a radial distance from the rotation center of the guide 54 to the spiral groove changes in the longitudinal direction of the spiral groove.

[0018] When the motor shaft 14 is not rotated relative to the drive-side rotor 22, the planetary gear 33 in the phase control mechanism does not perform sun and planetary motion and is rotated integrally with the drive-side rotor 22 and the transmission rotor 34. Therefore, the movable bodies 56 are not guided along the guide grooves 58, whereby the positional relationship between the links 52 and the links 53 does not change. As a result, the motor shaft 14 and the camshaft 2 are rotated synchronously, so that the relative phase between the drive-side rotor 22 and the driven-side rotor 24 is maintained, and the engine phase, which determines the valve timing, is also maintained. When the motor shaft 14 is rotated in the forward direction relative to the drive-side rotor 22, the transmission rotor 34 is Fig. 6 is rotated counterclockwise relative to the drive-side rotor 22 due to the sun and planetary movement of the planetary gear 33. Thus, the movable bodies 56 are guided along the guide grooves 58, thereby changing the positional relationship between the primary links 52 and the secondary links 53. As a result, the driven-side rotor 24 is rotated according to Fig. 5 is rotated clockwise relative to the drive-side rotor 22, thereby advancing the valve timing and the engine phases. In contrast, when the motor shaft 24 is rotated in the reverse direction relative to the drive-side rotor 22, the driven-side rotor 24 is rotated according to Fig. 5 is rotated counterclockwise relative to the drive-side rotor 22 in the opposite direction. In this way, the valve timing and the engine phase are delayed.

[0019] The following is an electrical circuit system 60 of the electrical valve timing control system 10 according to Fig. 2. The electrical circuit system 60 includes a control circuit 62 and a motor drive circuit 80. According to Fig. 2, the control circuit 62 and the motor drive circuit 80 are arranged outside the electric motor 12. However, the locations of the control circuit 62 and the motor drive circuit 80 can be changed to any other locations based on, for example, design specifications.

[0020] The control circuit 62 has a microcomputer as its main component and is connected to the motor drive circuit 80 as shown in Fig. 4. The control circuit 62 receives a current rotational speed (actual rotational direction) Rr and a current rotational direction (actual rotational direction) Dr of the electric motor 12 from the motor drive circuit 80. The control circuit 62 determines current valve timing (actual valve timing) based on the actual rotational speed Rr and the actual rotational direction Dr received from the motor drive circuit 80. Then, the control circuit 62 sets target valve timing based on engine information such as a throttle opening degree (i.e., an opening degree of a throttle valve). Thereafter, the control circuit 62 sets a target rotational speed Rt and a target rotational direction Dt of the electric motor 12 based on a phase difference between the actual valve timing and the target valve timing.Then, the control circuit 62 outputs the target rotational speed Rt and the target rotational direction Dt as a control signal to the motor drive circuit 80.

[0021] The motor drive circuit 80 includes a signal generation block 81, a control block 82, and a power supply block 83. Each of the blocks 81 to 83 according to the present embodiment is implemented as hardware including specific (dedicated) circuit elements.

[0022] The signal generation block 81 is connected to the respective rotation angle sensors 16 of the electric motor 12, the control circuit 62, and the control block 82. The signal generation block 81 determines the actual rotational speed Rr and the actual rotational direction Dr of the electric motor 12 based on the sensor signals received from the rotation angle sensors 16. The signal generation block 18 then supplies the determined actual rotational speed Rr and the determined actual rotational direction of the electric motor 12 to the control circuit 62 and the control block 82.

[0023] The control block 82 is connected to the control circuit 62, the signal generation block 81, and the power supply block 83. The control block 82 determines a power supply command value E to be supplied to the power supply block 83 based on the target rotational speed Rt and the target rotational direction Dt received from the control circuit 62 as the control signal, and the actual rotational speed Rr and the actual rotational direction Rr received from the signal generation block 81.

[0024] As it is in Fig. As shown in Figure 7, the power supply block 83 includes an inverter assembly 84 and a circuit drive assembly 85. The inverter assembly 84 includes a bridge circuit and is connected to a vehicle battery 87 for receiving an electric power source voltage. In the inverter assembly 84, a plurality of switching elements 86 are connected to the windings 15 of the electric motor 12. In addition, the circuit drive assembly 85 is connected to the control block 82 and each of the switching elements 85 of the inverter assembly 84. The circuit drive assembly 85 performs pulse width modulation on the drive signal (drive signal) of each switching element 86 based on the power supply command value E received from the control block 82.As a result, each switching element 86 is turned on and off by turning the drive signal on and off, so that the electric motor 12 is energized (powered) to rotate in the target rotation direction Dt.

[0025] A characteristic part of the first embodiment is further described below.

[0026] As it is in Fig. As shown in Figure 7, the power supply block 83 further includes a sensing arrangement 88 in addition to the inverter arrangement 84 and the circuit drive arrangement 85. The sensing arrangement 88 is connected to a load transistor 89 arranged in a power supply path of the inverter arrangement 84. The sensing arrangement 88 is also connected to the control block 82. The sensing arrangement 88 detects an electric current I flowing in the load transistor 89 and supplies the detected electric current I to the control block 82. The current I detected by the sensing arrangement 88 coincides with the motor drive current flowing in the windings 15 through the inverter arrangement 84.

[0027] As it is in Fig. 4 and Fig. As shown in Figure 7, the control block 82 monitors the measurement of the motor drive current I received from the power supply block 83 and determines whether an abnormality exists in the measurement of the motor drive current I. If an abnormality is detected, the control block 82 takes appropriate countermeasures. The determination of the abnormality is based on the relationship between the threshold values ​​Io, Ioc, Is and the motor drive current I according to Fig. 8 carried out.

[0028] Specifically, when an instantaneous current of the motor drive current I reaches the overcurrent threshold value Io, it is determined that an instantaneous high-load abnormality occurs. Hereinafter, the condition that the instantaneous current of the motor drive current I reaches the overcurrent threshold value Io is referred to as “Condition A.” Thus, in such a case, the power supply command value E (see Fig. 7) that limits the motor drive current I below a termination threshold Ioc that is smaller than the overcurrent threshold Io, and is applied regardless of the control signal supplied to the control circuit 82. This countermeasure process is stopped when the motor drive current I is reduced to below the termination threshold Ioc.

[0029] The overcurrent threshold Io is set to a value that limits the occurrence of a fault of, for example, the windings 15 of the electric motor 12 or the switching elements 86 of the inverter assembly 84 caused by the instantaneous overcurrent. The termination threshold Ioc is set based on the overcurrent threshold Io to limit the motor drive current I from reaching the overcurrent threshold Io even in a case where the motor drive current I is changed within a tolerable range after the termination of the above-described countermeasure process against the instantaneous high-load abnormality. According to the present embodiment, as shown in Fig. 8, the overcurrent threshold Io and the termination threshold Ioc are both kept generally constant with respect to the actual speed Rr of the electric motor 12.

[0030] After starting the countermeasure process against the instantaneous high load abnormality, when the instantaneous current of the motor drive current I reaches the overcurrent threshold value Io, if this countermeasure process against the instantaneous high load abnormality is maintained for a predetermined period of time Tos or longer due to the still high motor drive current I (ie, I ≥ Ioc), it is determined that a continuous high load abnormality occurs. Hereinafter, the above-described condition that the countermeasure process against the instantaneous high load abnormality is maintained for the predetermined period of time Tos or longer is referred to as “Condition B”. Thus, in such a case, a countermeasure process against the continuous high load abnormality is started so that the power supply command value E (refer to FIG. Fig. 7) is determined, which limits the motor drive current I to zero (0) to stop the power supply to the electric motor 12, and is set regardless of the control signal. This countermeasure process is maintained until the vehicle's ignition switch is turned off.

[0031] The predetermined time period Tos is set to a relatively short time period in such a manner as to prevent the occurrence of the fault of, for example, the windings 15 of the electric motor 12 or the switching elements 86 of the inverter assembly 84 caused by the continuous high load current.

[0032] Furthermore, when the motor drive current I is continuously maintained above a continuous current threshold value Is, which is an intermediate value (a middle value) smaller than the overcurrent threshold value Io and the termination threshold value Ioc, for a predetermined period of time Ts or longer after increasing the instantaneous current of the motor drive current I above the continuous current threshold value Is, it is determined that a continuous intermediate load abnormality occurs. Hereinafter, the above-described condition in which the motor drive current I is continuously maintained above the continuous current threshold value Is for the predetermined period of time Ts or longer is referred to as "Condition C." Thus, in such a case, a countermeasure process against the continuous intermediate load abnormality is started so that the power supply command value E (refer to FIG. Fig. 7), which limits the motor drive current I below the continuous current threshold Is, is determined and adjusted regardless of the control signal. This countermeasure process is terminated when the motor drive current I remains below the threshold Is for a predetermined period of time Tsc or longer.

[0033] The continuous current threshold value Is and the predetermined time period Ts are each set according to a value that limits the occurrence of a fault (failure) caused by the instantaneous overcurrent, for example, of the windings 15 of the electric motor 12 or of the switching elements 86 of the converter arrangement 84. Thus, according to the present embodiment, the predetermined time period Ts is longer than the predetermined time period Tos. Furthermore, according to the present embodiment, as shown in Fig. 8, the continuous current threshold value Is is set to change according to the actual rotational speed Rr. The relationship between the continuous current threshold value Is and the actual rotational speed Rr is determined in advance based on the relationship between the motor drive current I required to drive the electric motor 12 and the actual rotational speed Rr. Thus, even if the motor drive current I required to drive the electric motor 12 is changed according to the actual rotational speed Rr, the occurrence of the continuous inter-load abnormality can be appropriately determined based on the threshold value Is reflecting the change in the motor drive current I.

[0034] Furthermore, the motor drive current I used in the continuous inter-load abnormality countermeasure process is preferably an intermediate value between zero and the value Is. However, it should be noted that this motor drive current I used in the continuous inter-load abnormality countermeasure process can be reduced to zero. Furthermore, the predetermined time period Tsc used to determine whether the continuous inter-load abnormality countermeasure process needs to be terminated is set to a value long enough to prevent unintentional termination of the continuous inter-load abnormality countermeasure process caused by the motor drive current I accidentally falling below the threshold value Is.A random or erroneous drop in the motor current I below the threshold Is may potentially cause the motor drive current I to oscillate (hunt) around the threshold Is due to repeated termination and execution of the countermeasure process against the continuous intermediate load abnormality. This will cause an undesirable condition similar to the continuous maintenance of the motor drive current I above the threshold Is.

[0035] The instantaneous high load abnormality or the continuous high load abnormality may potentially occur simultaneously with the continuous intermediate load abnormality. However, the instantaneous high load abnormality or the continuous high load abnormality represent a higher degree of urgency than the continuous intermediate load abnormality.According to the present embodiment, when the time period for which the motor drive current I is continuously maintained above the threshold value Is reaches the predetermined time period Ts during the countermeasure process against the instantaneous high load abnormality or the continuous high load abnormality, that is, when the condition C is satisfied during the countermeasure process against the instantaneous high load abnormality or the continuous high load abnormality, the countermeasure process against the instantaneous high load abnormality or the continuous high load abnormality is executed and maintained with higher priority than the countermeasure process against the continuous intermediate load abnormality. Hereinafter, the condition of satisfying the condition C during the countermeasure process against the instantaneous high load abnormality or the continuous high load abnormality is referred to as "condition D."Furthermore, according to the present embodiment, when the instantaneous current of the motor drive current I reaches the overcurrent threshold Io during the countermeasure process against the continuous intermediate load abnormality, that is, when Condition A is satisfied during the countermeasure process against the continuous intermediate load abnormality, the countermeasure process against the instantaneous high load abnormality is executed with higher priority than the countermeasure process against the continuous intermediate load abnormality. Hereinafter, the condition of satisfying Condition A during the countermeasure process against the continuous intermediate load abnormality is referred to as "Condition E."Furthermore, according to the present embodiment, when the continuous execution time of the countermeasure process against the continuous high load abnormality reaches the predetermined time period Ts during the countermeasure process against the continuous intermediate load abnormality, that is, when Condition B is satisfied during the countermeasure process against the continuous intermediate load abnormality, the countermeasure process against the continuous high load abnormality is executed with higher priority than the countermeasure process against the continuous intermediate load abnormality. Hereinafter, the condition of satisfying Condition B during the countermeasure process against the continuous intermediate load abnormality is referred to as "Condition F."

[0036] As it is in Fig. 4 and Fig. As shown in FIG. 7, a monitor signal indicating an occurrence of an abnormality type (abnormality type) K is output from the control block 82 to the control circuit 62 during the execution of the countermeasure process against the corresponding abnormality upon satisfaction of any one of the conditions A to F. Thus, the control circuit 62 determines the abnormality type K indicated by the monitor signal received from the control block 82, which corresponds to the instantaneous high-load abnormality, the continuous high-load abnormality, or the continuous intermediate-load abnormality. Then, the control circuit 62 generates the control signal indicating the appropriate target rotational speed Rt (for example, 0) corresponding to the abnormality.According to this embodiment, the countermeasure process against the abnormality is autonomously executed by the control block 82 before the control circuit 62 generates the control signal corresponding to the abnormality. Thus, during the occurrence of the abnormality, it is possible to quickly protect, for example, the windings 15 of the electric motor 12 and the switching elements 86 of the inverter assembly 84.

[0037] According to the first embodiment, the countermeasure process against the instantaneous high load abnormality executed when condition A is satisfied and the countermeasure process against the continuous high load abnormality executed when condition B is satisfied correspond to a first abnormality countermeasure process according to the present invention. Furthermore, the countermeasure process against the continuous intermediate load abnormality corresponds to a second abnormality countermeasure process according to the present invention. The control block 82 according to the present embodiment serves as both a first abnormality countermeasure means and a second abnormality countermeasure means according to the present invention.

[0038] The following is the control flow of the control block 82 with reference to Fig. 1. The current sequence starts when the ignition switch is turned on.

[0039] In step S10, the electric motor 12 is driven by a normal control operation in which the power supply command value E is determined based on the control signal received from the control circuit 62 and indicating the target rotational speed Rt and the target rotational direction Dt. Thereafter, according to the present embodiment, the control block 82 executes in parallel both step S20 for executing the countermeasure process against the instantaneous high load abnormality and the countermeasure process against the continuous high load abnormality, and step S30 for executing the countermeasure process against the continuous intermediate load abnormality.

[0040] First, details of step S20 for executing the countermeasure process against the instantaneous high load abnormality and the countermeasure process against the continuous high load abnormality are described.

[0041] More specifically, in step 201 of step S20, it is determined whether the motor drive current I has reached the overcurrent threshold Io or not.

[0042] If NO is returned in step S210, the operation returns to step S10 to continue the normal control operation. In contrast, if YES is returned in step S201, it is determined that condition A is satisfied, that is, it is determined that the momentary high-load abnormality occurs, thereby proceeding to steps S202 and S203. At this time, in step S202, an increment of a continuous high-load abnormality indicator is started. Then, in step S203, the countermeasure process against the momentary high-load abnormality is executed with higher priority than the countermeasure process against the continuous intermediate load abnormality, so that the motor drive current I is immediately limited, and the monitor signal indicating the momentary high-load abnormality is output to the control circuit 62.

[0043] Thereafter, in step S204, it is determined whether the elapsed time measured by the continuous high load abnormality timer has become equal to or greater than the predetermined time period Tos.

[0044] If NO is returned in step S204, the operation proceeds to step S205. In step S205, it is determined whether the motor drive current I has been reduced below the termination threshold Ioc. If NO is returned in step S205, the operation returns to step S203 to perform the countermeasure process against the momentary high load abnormality. Conversely, if YES is returned in step S205, it is determined that the momentary high load abnormality has been resolved, whereby the operation proceeds to steps S206 and S207. Here, in step S206, the countermeasure process against the momentary high load abnormality is terminated. Then, in step S207, the continuous high load abnormality timer is stopped and reset, and then the operation returns to step S210 to resume the normal control operation.

[0045] If YES is returned in step S204, it is determined that condition B is satisfied, that is, it is determined that the continuous high-load abnormality occurs. Thus, the operation proceeds to step S208. In step S208, the countermeasure process against the continuous high-load abnormality is executed until the ignition switch is turned off, so that the power supply to the electric motor 12 is stopped. Also, at this time, the monitor signal indicating the continuous high-load abnormality is output to the control circuit 62.

[0046] The details of step S20 have been described above. Step S30 for executing the countermeasure process against the continuous intermediate load abnormality is described in detail below.

[0047] In the individual step S301 of step S30, it is determined whether the motor drive current I has been increased above the continuous current threshold value Is.

[0048] If a NO is returned in step S301, the operation returns to step S10 to continue the normal control operation. Conversely, if a YES is returned in step S301, the operation proceeds to step S302. In step S302, in a state where the continuous inter-load abnormality timer is stopped, the counting of the continuous inter-load abnormality timer is started. In contrast, in a state where the continuous inter-load abnormality timer is counting up, this counting is maintained.

[0049] Thereafter, in step S303, it is determined whether the elapsed time measured by the continuous intermediate load abnormality timer has become equal to or longer than the predetermined time period Ts.

[0050] If NO is returned in step S303, the operation returns to step S10 to continue the normal control operation. Conversely, if YES is returned in step S303, it is determined that condition C is satisfied, that is, it is determined that the continuous inter-load abnormality occurs, and the operation proceeds to steps S304 and S305. At this time, in step S304, the continuous inter-load abnormality timer is stopped and reset. Then, in step S305, the countermeasure process against the continuous inter-load abnormality is executed so that the motor drive current I is limited, and the monitor signal indicating the continuous inter-load abnormality is output to the control circuit 62.

[0051] Here, according to the present embodiment, the execution of the countermeasure process against the continuous intermediate load abnormality in step S305 may overlap with the execution of the countermeasure process against the instantaneous high load abnormality in step S203 or the execution of the countermeasure process against the continuous high load abnormality in step S203. Thus, when the execution of the countermeasure process against the continuous intermediate load abnormality overlaps with the execution of the countermeasure process against the instantaneous high load abnormality, the countermeasure process against the continuous intermediate load abnormality is stopped, and the countermeasure process against the instantaneous high load abnormality, which has higher priority than the countermeasure process against the continuous intermediate load abnormality, is executed.In this way, the above-described countermeasure process is executed with the higher priority in the case where Condition D or Condition E is satisfied. Furthermore, when the execution of the countermeasure process against the continuous intermediate load abnormality overlaps with the execution of the countermeasure process against the continuous high load abnormality, the countermeasure process against the continuous intermediate load abnormality is stopped, and the countermeasure process against the continuous high load abnormality, which has the higher priority than the countermeasure process against the continuous intermediate load abnormality, is executed. In this way, the above-described countermeasure process is executed with the higher priority in the case where Condition D or Condition F is satisfied.

[0052] In step S306, which is executed after step S305, it is determined whether the motor drive current I has been reduced below the continuous current threshold Is.

[0053] If YES is returned in step S306, steps S307 and S308 are executed to determine whether the countermeasure process against the continuous inter-load abnormality can be terminated. In step S307, a termination timer starts counting up. Then, in step S308, it is determined whether the elapsed time measured by the termination timer has become equal to or longer than the predetermined time period Tsc.

[0054] If NO is returned in step S308, the operation returns to step S305 to continue the countermeasure process against the continuous inter-load abnormality. Conversely, if YES is returned in step S308, it is determined that the continuous inter-load abnormality has been resolved, and the operation proceeds to execute steps S309 and S310. At this time, in step S309, the countermeasure process against the continuous inter-load abnormality is terminated. Then, in step S310, the termination timer is stopped and reset, and the operation returns to step S10 to resume normal control operation.

[0055] If NO is returned in step S306, the operation proceeds to step S311. In step S311, in a state where the termination timer is stopped, the stopped state of the termination timer is maintained. Conversely, in a state where the termination timer is counting up, the counting up is stopped. With the latter operation, even in a case where the motor drive current I is reduced below the threshold value Is by chance or within a tolerable range, and the motor drive current I returns to a previous value after the termination timer starts counting up, the termination of the countermeasure process against the continuous inter-load abnormality is denied. Thus, it is possible to protect, for example, the windings of the electric motor 12 and the switching elements 86 of the inverter assembly 84.After step S311, the operation returns to step S305 to continuously execute the countermeasure process against the continuous intermediate load abnormality.

[0056] According to the first embodiment, the motor drive current I can be limited not only during the instantaneous high-load abnormality or the continuous high-load abnormality, but also during the continuous intermediate-load abnormality by a corresponding appropriate countermeasure process. Thus, even in the case of a structure in which the power supply period is relatively long, such as a structure requiring continuous power supply to the electric motor 12, the failure of, for example, the windings 15 of the electric motor 12 and the switching elements 86 of the inverter assembly 84 can be sufficiently limited. Second embodiment

[0057] As it is in Fig. As shown in Fig. 9, the second embodiment of the present invention is a modification of the first embodiment. In the control block 82 according to the second embodiment, the continuous current threshold Is used to determine whether the condition C for executing the countermeasure process against the continuous inter-load abnormality is satisfied is changed not only according to the actual rotational speed Rr of the electric motor 12, but also according to whether the actual rotational direction Dr of the electric motor 12 agrees with the target rotational direction Dt of the electric motor 12.

[0058] In particular, as stated in Fig. 10, in the case where the target rotation direction Dt received from the control circuit 62 and the actual rotation direction received from the signal generation block 81 agree with each other, that is, both are the forward rotation direction or the reverse rotation direction, the continuous current threshold value Is is set to a small threshold value Iss. In contrast, in the case where one of the target rotation direction Dt and the actual rotation direction is the forward rotation direction, whereas the other of the target rotation direction Dt and the actual rotation direction is the reverse rotation direction, the continuous current threshold value Is is set to a large threshold value Isl that is larger than the small threshold value Iss. However, as shown in Fig. 9, both the small threshold Iss and the large threshold Isl are set to change relative to the actual rotational speed Rr, while maintaining a predetermined relationship therebetween in a range where the large / small relationship therebetween can be maintained.

[0059] As described above, according to the second embodiment, the large threshold Isl is used as the continuous current threshold Is for determining the occurrence of the continuous intermediate load abnormality in the case where the target rotational direction Dt is different from the actual rotational direction Dr, thereby requiring a larger motor drive current I, whereas the small threshold Iss is used as the continuous current threshold for determining the occurrence of the continuous intermediate load abnormality in the case where the target rotational direction Dt and the actual rotational direction Dr coincide with each other.Thus, even if the motor drive current I is increased due to the discrepancy between the target rotation direction Dt and the actual rotation direction Dr, the determination of the occurrence of the continuous intermediate load abnormality can be made correctly, thereby avoiding excessive execution of the countermeasure process against the continuous intermediate load abnormality. Third embodiment

[0060] As it is in Fig. As shown in Figure 11, the third embodiment of the present invention is a modification of the second embodiment. In the control block 82 according to the third embodiment, the continuous current threshold Is used to determine whether the condition C for executing the countermeasure process against the continuous inter-load abnormality is satisfied is changed according to the power supply voltage V of the battery 87 applied to the inverter assembly 84, instead of according to the actual rotational speed Rr of the electric motor 12.

[0061] In particular, in a low range VI according to Fig. 11, in which the power supply voltage V is lower than a predetermined value Vth, the continuous current threshold value Is is set to have a linear relationship with the power supply voltage V. Furthermore, in a range Vh according to Fig.11, in which the power supply voltage V is equal to or greater than the predetermined value Vth, the continuous current threshold Is is set to maintain a substantially constant value relative to the power supply voltage V. According to the present embodiment, the overcurrent threshold Io and the termination threshold Ioc are also set to have a similar relationship to that of the continuous current threshold Is to the power supply voltage V.

[0062] According to the third embodiment, even if the motor drive current I required to drive the electric motor 12 is changed according to the power supply voltage V, the occurrence of the continuous inter-load abnormality can be correctly determined based on the threshold value Is reflecting the change in the motor drive current I. Another embodiment

[0063] The embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and the above-described embodiments can be modified within the scope of the present invention.

[0064] For example, the function of the control block 82 can be implemented by executing a corresponding program in the microcomputer.

[0065] Furthermore, the continuous current threshold value Is can be changed according to the actual rotational speed Rr of the electric motor 12 and / or the state of agreement between the target rotational direction Dt and the actual rotational direction Dr of the electric motor 12 and / or the power supply voltage V of the battery 87, that is, depending on whether the target rotational direction Dt and the actual rotational direction Dr agree with each other. Specifically, according to the second embodiment, the continuous current threshold value Is can be set based only on the state of agreement between the target rotational direction Dt and the actual rotational direction Dr of the electric motor 12. Furthermore, according to the third embodiment, the continuous current threshold value Is can be set based on a two-dimensional relationship, that is,based on the state of agreement between the target rotation direction Dt and the actual rotation direction Dr as well as the power supply voltage V. Furthermore, according to the second embodiment, the continuous current threshold value can be set based on a three-dimensional relationship, that is, based on the actual rotation speed Rr, the state of agreement between the target rotation direction Dt and the actual rotation direction Dr, and the power supply voltage V.

[0066] Furthermore, the electric motor 12 may be a motor other than a brushless motor (commutatorless motor). The structure of the power supply block 83 may be appropriately modified based on the type of the electric motor 12.

[0067] The phase control mechanism (or phase change mechanism) combined with the electric circuit system 60 may be changed to any other suitable one as long as the valve timing can be adjusted by adjusting the engine phase by using the rotation of the electric motor 12.

[0068] Additional advantages and modifications will be apparent to those skilled in the art. The invention, in its broader sense, is therefore not limited to the specific details, representative devices, and illustrated examples shown and described.

[0069] A control block (82) of a motor drive circuit executes a countermeasure process against a momentary high-load abnormality to limit a motor drive current (I) when an instantaneous current of the motor drive current (I) reaches an overcurrent threshold (Io). Furthermore, the control block (82) executes a countermeasure process against a continuous intermediate load abnormality to limit the motor drive current (I) when the motor drive current (I) exceeds a continuous current threshold (Is) that is smaller than the overcurrent threshold (Io) for a predetermined period of time or longer.

Claims

[1] Motor drive circuit for driving an electric motor (12) of a valve timing control system (10) which adjusts valve timing of an internal combustion engine, the motor drive circuit comprising: a first abnormality countermeasure device (S20) for executing a first abnormality countermeasure process that limits a motor drive current (I) supplied to the electric motor (12) for driving the electric motor (12) when an instantaneous current of the motor drive current (I) reaches an overcurrent threshold value (Io), and a second abnormality countermeasure device (S30) for executing a second abnormality countermeasure process that limits the motor drive current (I) when the motor drive current (I) exceeds a continuous current threshold value (Is) that is smaller than the overcurrent threshold value (Io) for a first predetermined period of time (Ts) or longer, wherein the second abnormality countermeasure device (S30) changes the continuous current threshold value (Is) according to an actual rotational speed of the electric motor (12). [2] A motor drive circuit for driving an electric motor (12) of a valve timing control system (10) that adjusts valve timing of an internal combustion engine, the motor drive circuit comprising: a first abnormality countermeasure device (S20) for executing a first abnormality countermeasure process that limits a motor drive current (I) supplied to the electric motor (12) for driving the electric motor (12) when an instantaneous current of the motor drive current (I) reaches an overcurrent threshold value (Io), and a second abnormality countermeasure device (S30) for executing a second abnormality countermeasure process that limits the motor drive current (I) when the motor drive current (I) exceeds a continuous current threshold value (Is) that is smaller than the overcurrent threshold value (Io) for a first predetermined period of time (Ts) or longer, wherein the second abnormality countermeasure device (S30) changes the continuous current threshold value (Is) according to whether an actual rotation direction (Dr) of the electric motor (12) agrees with a target rotation direction (Dt) of the electric motor (12). [3] A motor drive circuit for driving an electric motor (12) of a valve timing control system (10) that adjusts valve timing of an internal combustion engine, the motor drive circuit comprising: a first abnormality countermeasure device (S20) for executing a first abnormality countermeasure process that limits a motor drive current (I) supplied to the electric motor (12) for driving the electric motor (12) when an instantaneous current of the motor drive current (I) reaches an overcurrent threshold value (Io), and a second abnormality countermeasure device (S30) for executing a second abnormality countermeasure process that limits the motor drive current (I) when the motor drive current (I) exceeds a continuous current threshold value (Is) that is smaller than the overcurrent threshold value (Io) for a first predetermined period of time (Ts) or longer, wherein the second abnormality countermeasure device (S30) changes the continuous current threshold value (Is) according to a power supply voltage (V) applied to the motor drive circuit. [4] The motor drive circuit according to claim 2, wherein, in a case where the actual rotation direction (Dr) of the electric motor (12) does not agree with the target rotation direction (Dt) of the electric motor (12), the second abnormality countermeasure means (S30) sets the continuous current threshold value (Is) to a first value (Isl) that is larger than a second value (Iss) that is set in a case where the target rotation direction (Dt) of the electric motor (12) agrees with the actual rotation direction (Dr) of the electric motor (12). [5] The motor drive circuit according to any one of claims 1 to 4, wherein the first abnormality countermeasure means (S20) terminates the first abnormality countermeasure process when the motor drive current (I) is reduced to below a termination threshold value (Ioc) which is smaller than the overcurrent threshold value (Io). [6] The motor drive circuit according to claim 5, wherein the first abnormality countermeasure means (S20) stops the power supply to the electric motor (12) in the first abnormality countermeasure process when the first abnormality countermeasure process is continuously executed for a second predetermined time period (Tos) or longer which is shorter than the first predetermined time period (Ts). [7] The motor drive circuit according to claim 5 or 6, wherein the first abnormality countermeasure means (S20) continuously executes the first abnormality countermeasure process with higher priority than the second abnormality countermeasure process even when a period of time in which the motor drive current (I) continuously exceeds the continuous current threshold value (Is) reaches the first predetermined period of time (Ts) during the execution of the first abnormality countermeasure process. [8] The motor drive circuit according to any one of claims 1 to 7, wherein the first abnormality countermeasure process (S20) performs the first abnormality countermeasure process with higher priority than the second abnormality countermeasure process when the instantaneous current reaches the overcurrent threshold value (Io) during the execution of the second abnormality countermeasure process. [9] The motor drive circuit according to any one of claims 1 to 8, wherein the second abnormality countermeasure means (S30) terminates the second abnormality countermeasure process when the motor drive current (I) is reduced to below the continuous current threshold value (Is). [10] The motor drive circuit according to claim 9, wherein the second abnormality countermeasure means (S30) terminates the second abnormality countermeasure process when the motor drive current is maintained below the continuous current threshold (Is) for a third predetermined period of time (Tsc) or longer. [11] Motor drive circuit according to one of claims 1 to 10, wherein the motor drive circuit drives the electric motor (12) based on a control signal generated by an external control circuit (62) connected to the motor drive circuit, and the first abnormality countermeasure means (S20) and the second abnormality countermeasure means (S30) respectively execute the first abnormality countermeasure process and the second abnormality countermeasure process while ignoring the control signal. [12] Valve timing control system with an electric motor (12) the motor drive circuit (80) according to any one of claims 1 to 11, which drives the electric motor (12), and a phase control mechanism (20) that adjusts valve timing of the internal combustion engine by adjusting a relative phase between a crankshaft and a camshaft (2) of the internal combustion engine according to the rotation of the electric motor (12).

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