Abstract:
A motor actuator control system includes a motor actuator having a motor, an output shaft for outputting rotation of the motor at reduced speed, and a gear train for transmitting rotation to the output shaft while reducing rotataional speed. The system further includes a first detector detecting current surges generated when contact between a commutator and brushes in the motor is broken, a second detector detecting a predetermined rotational position of a gear, and a control unit for controlling the motor on the basis of signals from the first detector and signals from the second detector. When the predetermined rotational position is detected, the position and the count of the current surges are correlated. Then, the motor is driven until the count reaches a predetermined number to rotate the output shaft to another predetermined rotational position.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-72327 filed on Mar. 14, 2001. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a motor actuator control system in which the number of rotations (rotational position shift amount) of a motor is detected to control the motor. The present invention is preferably applied to, for example, an air conditioning system for a vehicle in which a switching member such as a damper and an air mixing door of an air passage is driven by a motor actuator. In the air conditioning system, the position of the switching member is accurately controlled by the motor actuator control system of the present invention. 
     BACKGROUND OF THE INVENTION 
     A switching member such as a damper and an air mixing door is used to switch the air flow mode between internal air circulation and exterior air introduction, to change air flow passages leading to interior air outlet ports, and to control air mixing rate between hot air and cool air in an air conditioning system for a vehicle. Those actions in response to an operation of switches close to the driver&#39;s seat are implemented by driving the switching member using a motor actuator. To ensure that the switching member is moved to a predetermined position, the position and the position shift amount of the switching member needs to be detected, and a motor in the actuator needs to be controlled on the basis of the detected information. 
     A system using current surges periodically generated in the motor is proposed to detect the position and the position shift amount of the switching member. In the motor, a commutator rotated synchronously with a rotor slides on and discontinuously contacts brushes to pass an electric current to rotor coils, so the contact between the commutator and the brushes is periodically made and broken. A current surge (commutator surge) is generated at the moment that the contact is broken, so commutator current surges are periodically generated. Thus, the number of rotations of the motor (rotational position shift amount) is detected by counting the commutator current surges, and the position shift amount of the switching member can be determined based on the number of the surges. 
     The commutator current surges are generated a plurality of times per one rotation of the rotor, so the detection based on commutator current surge count is basically accurate. However, the commutator current surges are so weak when the motor starts and stops rotating that weak commutator current surges are not always detected. In addition, the commutator current is generated only while the motor is electrically powered, so the commutator current surge count becomes inaccurate if the rotor rotates by its own momentum or is rotated by unexpected force after the motor is switched off. Therefore, the detection based on the commutator current surge count is not reliable enough. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above aspects with an object to provide a motor actuator control system in which the number of rotations (rotational position shift amount) of a motor is accurately controlled by correlating a count of commutator surge current and a predetermined rotational position of a gear in a gear train connected to the motor. 
     In the present invention, the motor actuator control system includes a motor actuator having a motor, an output shaft for outputting rotational motion of the motor at reduced rotational speed, and a gear train constituted of a plurality of gears to transmit rotational motion of the motor to the output shaft while reducing rotational speed. The control system further includes a first detector detecting commutator current surges, a second detector detecting a predetermined rotational position of a gear, and a control unit controlling the motor on the basis of a signal from the first detector and another signal from the second detector. 
     The commutator current surges are counted by the control unit. When the second detector detects the predetermined position of the output gear which is connected to the output shaft and rotated at the slowest speed in the gear train, the count of the commutator current surges is correlated with the predetermined rotational position by substituting a predetermined number for the count. Then, the motor is driven until the count reaches another predetermined number in order to rotate the output shaft to another predetermined rotational position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. 
     In the drawings: 
     FIG. 1 is a plan view of a motor actuator according to an embodiment of the present invention; 
     FIG. 2 is a side view of a pickup used in the embodiment; 
     FIG. 3 is a schematic block diagram of a motor actuator control system according to the embodiment; 
     FIG. 4 is a schematic circuit diagram of the motor actuator control system according to the embodiment; 
     FIG. 5 is a time chart showing the correlation between commutator current and compensational signal (conduction current); 
     FIG. 6 is a flow chart showing a routine to control the motor actuator control system according to the embodiment; 
     FIG. 7 is a schematic view of an air conditioning system for a vehicle to which the motor actuator control system according to the embodiment is applied; 
     FIG. 8 is a schematic circuit diagram of a motor actuator control system according to the first modification of the embodiment; 
     FIG. 9 is a schematic block diagram of the motor actuator control system according to the first modification; 
     FIG. 10 is a time chart showing the correlation between commutator current and compensational signal (conduction current) according to the first modification; 
     FIG. 11 is a schematic circuit diagram of a motor actuator control system according to the second modification of the embodiment; 
     FIG. 12 is a schematic block diagram of the motor actuator control system according to the second modification; 
     FIG. 13 is a schematic circuit diagram of a motor actuator control system according to the third modification of the embodiment; 
     FIG. 14 is a plan view showing a modified pulse plate (conductive part, ring-shaped part) according to other modification of the embodiment; and 
     FIG. 15 is a plan view showing another modified pulse plate (conductive part, ring-shaped part) according to other modification. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will be described in detail with reference to an embodiment and various modifications of the embodiment, in which the same reference numerals designate same or similar members. 
     (Embodiment) 
     As shown in FIG. 1, a motor actuator  12  has a housing  14  constituted of a main case  16  and a lid (not illustrated). The case  16  is approximately box-shaped and has an opening. The lid closes the opening to shield the case  16 . The case  16  stores a DC motor  20  having a rotary shaft  22 . A worm gear  24  is coaxially attached to the end of the shaft  22 . The worm gear  24  meshes with a worm wheel  26  disposed by the gear  24 . The worm wheel  26  has a support shaft constituted of a bottom shaft and a lid shaft. The bottom shaft and the lid shaft are rotatably supported by a pair of bearings (not illustrated) respectively formed on the bottom of the case  16  and on the lid. A gear  28  is formed on the bottom shaft of the worm wheel  26  in a coaxial relation with the worm wheel  26 . The gear  28  meshes with a gear  30  disposed by the gears  26 ,  28 . The gear  30  has a support shaft constituted of a bottom shaft and a lid shaft. The bottom shaft and the lid shaft are rotatably supported by a pair of bearings (not illustrated) respectively formed on the bottom of the case  16  and on the lid. A gear  32  is formed on the bottom shaft of the gear  30  in a coaxial relation with the gear  30 . The gear  32  meshes with an output gear  34  disposed by the gear  32 . The output gear  34  has a bottom shaft and an output shaft  35 . The bottom shaft and the output shaft  35  are rotatably supported by a pair of bearings (not illustrated) respectively formed on the bottom of the case  16  and in the lid. The output shaft  35  penetrates the lid of the case  14  to be connected to a damper  90 ,  91 ,  92  or an air mixing door  96  in an air conditioning system  82  for a vehicle as shown FIG.  7 . 
     The air conditioning system  82  has three motor actuators  12 . Each actuator  12  is electrically connected to and controlled by a controller  60 . The first motor actuator  12  is mechanically connected to the damper  90  using a link  93 . The damper  90  switches air flow path between a duct  85  for introducing interior air and a duct  84  for introducing exterior air. The second motor actuator  12  is mechanically connected to the dampers  91  and  92  using links  94 . The damper  91  switches air flow path between a duct  86  leading to a defroster and a duct  87  leading to interior air outlet ports. The damper  92  switches air flow path between a duct  88  leading to an air outlet port close to the instrument panel and a duct  89  leading to an air outlet port close to passengers&#39; feet. The third motor actuator  12  is mechanically connected to the door  96  using a link  95  for controlling air mixing rate between hot air generated by a heater core  97  and cool air. 
     When the motor  20  is driven and the shaft  22  is rotated, the rotational motion of the shaft  22  is transmitted to the output gear  34  through a gear train constituted of the worm gear  24 , the worm wheel  26 , and the gears  28 ,  30 , and  32  while rotational speed is reduced. The output shaft  35 , which is connected to the link  93 ,  94 ,  95  converting rotary movement of the output shaft  35  of the actuator  12  into reciprocative movement of the damper  90 ,  91 ,  92  or the door  96 , drives a related switching member. For example, the motor actuator  12  used for moving the damper  90  closes either one of the ducts  84  and  85  to stop air flow. For the sake of brevity, explanation on this embodiment and following modifications will be made referring only to the motor actuator  12  used for moving the damper  90 . 
     A yoke  40  which doubles a housing for the motor  20  has a bearing  42  supporting rotatably the shaft  22 . The yoke  40  stores a rotor  44  which is coaxially penetrated by the shaft  22  and rotated synchronously with the shaft  22 . The rotor  44  is wound with a wire forming a coil  46 . Magnetic fields are generated when electricity is passed through the coil  46 . The rotor  44  has a commutator  48  at one end in the direction of the rotation axis of the rotor  44 . The commutator  48  is constituted of a pair of electrodes which are electrically connected to the coil  46 . Those electrodes of the commutator  48  are integrated with the rotor  44  and the shaft  22  so as to face each other around the shaft  22 . A pair of brushes  50  is disposed in the yoke  40 . One brush  50  contacts one electrode of the commutator  48 , and the other brush  50  contacts the other electrode. As shown in FIG. 3, those brushes are electrically connected to a battery  52  using a lead wire or the like. Electricity is passed from one brush  50  to the other through one electrode, the coil  46 , and the other electrode. 
     A pair of permanent magnets  54  are disposed in the yoke  40 . Those magnets  54  are attached to the inner surface of the yoke  40  so as to face the coil  46  around the rotation axis of the shaft  22 . The yoke  40  is made of a metal to provide a magnetic flux path. The rotor  44  is rotated due to an interaction between the magnetic field of the coil  46  generated when electricity is passed through the coil  46  and the magnetic field of those magnets  54 . 
     As shown in FIG. 3, the motor  20  is electrically connected to a motor control circuit  62  in an electronic control unit  60  of a motor actuator control system  10 . The circuit  62  controls the electricity supplied from the battery  52  to the motor  20 . The motor  20  is also connected to a commutator current surge detection circuit  64  in the control unit  60 , which monitors a current (motor current) passed through the motor  20 . 
     In the motor  20 , the commutator  48  rotated synchronously with the rotor  44  discontinuously contacts and slides on the brushes  50  to pass the electric current to the coil  46 , so the contact between the commutator  48  and the brushes  50  is periodically made and broken. The commutator current surges are generated due to the self-induction of the coil  46  at the moment that the contact is broken, so the motor current passed through the motor  20  increases momentarily. 
     The circuit  64  sends a signal (commutator surge signal) to the circuit  62  when the circuit  64  detects the commutator current surges, that are larger than a predetermined threshold intensity. The circuit  62  controls the motor  20  on the basis of the count of the commutator surge signal. 
     The contact between the commutator  48  and the brushes  50  is made and broken due to the rotation of the commutator  48 . Therefore, the count of the commutator current surges is correlated to that of rotation of the motor  20  (shaft  22 ) and to the rotational position (position shift amount) of the output shaft  35  driven by the motor  20 . The count is also correlated to the position (position shift amount) of the damper  90 . Thus, the position (position shift amount) of the output shaft  35  (the damper  90 ) is accurately controlled by counting accurately the commutator current surges. 
     As shown in FIG. 1, the output gear  34  has a pulse plate  66  on the surface facing the lid of the housing  14 . The pulse plate  66  is made of an electrically conductive material such as metal, is in the shape of a ring, and is attached to the output gear  34  in a coaxial relation. A pickup  68  is disposed on the same side of the output gear as the plate  66  is formed. The pickup  68  is a resilient thin stick-like plate made of an electrically conductive material such as metal. One end of the pickup  68  is fixed to a plate  70  disposed in the proximity of the circumference of the output gear  34 . The plate  70  is supported by either of the main case  14  or the lid of the housing  14 . The other end of the pickup  68  has a V-shaped sliding part  72  at which the pickup  68  continuously contacts the pulse plate  66 , as shown in FIG.  2 . In this embodiment, the part  72  is V-shaped. However, other shapes such as U-shape may be used as well. 
     Beside the pickup  68 , a pickup  74  is disposed. The pickup  74  has substantially the same structure as the pickup  68 . A V-shaped sliding part  72  of the pickup  74  is placed outside of the pulse plate  66  so as not to contact the plate  66 . A projection part  76  protruding outwardly from the pulse plate  66  is formed on the output gear  34 . The projection part  76  is made of the same electrically conductive material as used for the pulse plate  66 . The pulse plate  66  and the projection part  76  are fixed to the output gear  34  to be rotated synchronously with the gear  34 . The sliding part  72  of the pickup  74  is disposed on the track of the projection part  76 . Therefore, the pickups  68 ,  74 , the pulse plate  66 , and the projection part  76  constitute an electrical switch. The switch is turned on when the motor  20  is driven and the projection part  76  meets the sliding part  72  of the pickup  74  at a predetermined rotational position of the output gear  34 . A current (conduction current) due to the conduction of the switch is detected by a conduction detection circuit  80  in the control unit  60 , as shown in FIG.  3 . 
     In this embodiment, the switch is formed on the output gear  34  which is rotated at the slowest speed in the gear train, so the sliding part  72  has the least sliding distance and the smallest abrasion. Therefore, the durability of the part  72  is improved. However, the switch can be formed on other gears. 
     The pickup  68  is connected to the positive pole of the battery  52 . The pickup  74  is connected to a resistor  78 , and the resistor  78  is connected to the conduction detection circuit  80 , as shown in FIGS. 3 and 4, so the conduction current is output separately from the current passed through the motor  20  when the switch is turned on. The circuit  80  is electrically connected to the motor control circuit  62  to send a signal (conduction signal) caused by the conduction current. 
     The motor control circuit  62  controls the motor  20  on the basis of a control routine shown in FIG.  6 . After the motor actuator control system  10  is set to function at step  200 , whether an operation signal from an operation switch (not illustrated) is received or not is determined at step  202 . If not, step  202  is repeated awaiting the operation signal. If the operation signal is detected at step  202 , a count N of the commutator current surges is reset by substituting zero for the count N at step  204 . Then, the commutator current surge detection circuit  64  is set to monitor the motor current passed through the motor  20  at step  206 . The conduction detection circuit  80  is set to monitor the conduction current. Afterward, the motor  20  is driven at step  210 . 
     At step  212 , whether the circuit  62  receives the conduction signal or not is determined. If the conduction signal is received, whether the count N of the commutator current surge is equal to a predetermined count NA or not is determined at step  224 . 
     The count N is bound to be equal to the predetermined count NA if the rotational position of the shaft  22  is at a predetermined position when the motor  20  is turned on and the commutator current surges generated right after the motor  20  is turned on are strong enough to be detected by the commutator current surge detection circuit  64 . If the count N is equal to the predetermined count NA, step  212  is repeated. 
     The count N is not equal to the predetermined count NA if the rotational position is shifted from the predetermined position due to an expected external force or if the commutator current surges are weak. In the case that the count N is not equal to the predetermined count NA, the count N is corrected by substituting the predetermined count NA for the count N. Then, step  212  is repeated. In this correction, even if the real rotational position of the shaft  35  is shifted from a detected position based on the count N, the correlation between them is retrieved using the conduction signal. Therefore, the reliability in controlling the rotational position of the shaft  35  is improved. 
     If the conduction signal is not received at  212 , whether the circuit  62  receives the commutator surge signal or not is determined at step  214 . As described above, the commutator surge signal is sent from the circuit  64  to the circuit  62  when the circuit  64  detects the commutator surge current larger than a predetermined threshold intensity. If the commutator surge signal is not received at step  214 , step  212  is repeated. If received, one is added to the count N at step  216 , and then step  218  is executed. At step  218 , whether the count N reaches another predetermined count NS or not is determined. If not, step  212  is repeated. If the count N reaches the count NS, step  220  is executed to stop the motor  20 , and then the routine is ended at step  222 . 
     In the motor actuator  12  used for moving the damper  90 , the count NS is the count of the commutator current surges generated while the damper  90  closing one of the ducts  84  and  85  is moved to the position where the damper  90  closes the other. Therefore, the damper  90  is surely moved to the position by turning off the motor  20  when the count N reaches the predetermined count NS. 
     A commutator current surge is generated at the moment that the contact between the commutator  48  and the brushes  50  is broken. In addition, the rotational motion of the shaft  22  is transmitted to the output shaft  35  with reduced rotational speed in the motor actuator  12 . Therefore, the count of the commutator current surges generated while the output gear  34  spins once is the product of the inverse of the overall speed reduction ratio and the number of electrodes constituting the commutator  48 . Thus, the motor  20  is precisely controlled on the basis of the count of the commutator current surges in the motor actuator control system  10 . 
     (First Modification) 
     As shown in FIG. 8, the motor  20  and the pickups  68 ,  74  are connected electrically in parallel in a motor actuator control system  100 . The pickup  68  is electrically connected to the positive pole of the battery  50 , to which one brush  50  is electrically connected, with a resistor  102  interposed between the pole and the pickup  68 . The pickup  74  is electrically connected to the negative pole of the battery  50  to which the other brush  50  is electrically connected. In this modification, the positive and the negative poles of the battery  52  are respectively assigned to the pickups  68 ,  74 . However, the opposite assignment may be used. 
     As shown in FIG. 9, the motor actuator control system  100  has a control unit  104  constituted of the motor control circuit  62  and a commutator surge and conduction signal detection circuit  106 . The detection circuit  106  monitors the motor current passed through the motor  20  and sends the commutator surge signal to the motor control circuit  62  in the control unit  104  when the circuit  106  detects a commutator current surge. The detection circuit  106  also detects the conduction current passed between the pickups  68 ,  74  and sends the conduction signal to the motor control circuit  62  when the circuit  106  detects the conduction current. The conduction current provides a much higher peak T than a peak due to the commutator current surges in the motor current, as shown in FIG.  10 . The motor control circuit  62  controls the motor  20  on the basis of the commutator surge signals and the conduction signals according to the control routine shown in FIG.  6 . 
     In this modification, the motor  20  and the pickups  68 ,  74  are connected electrically in parallel in a motor actuator control system  100 , so a wiring harness connecting the pickup  74  to the conduction detection circuit  80  in the embodiment is needless and the system  100  becomes simpler in structure than the system  10 . 
     (Second Modification) 
     As shown in FIGS. 11 and 12, the motor circuit including the motor  20  and another circuit including the pickups  68 ,  74  are separately connected to the battery  52  in a motor actuator control system  120 . Therefore, the conduction current passed between the pickups  68 ,  74  is not affected by a fluctuation of the motor current. Thus, the detection of the conduction current by the conduction detection circuit  80  is improved. 
     (Third Modification) 
     As shown in FIG. 13, a resistor  142  is disposed between the pickup  68  and the positive pole of the battery  52 , which is connected to one brush  50  in a motor actuator control system  140 . Another resistor  144  is disposed between the pickup  68  and the negative pole of the battery  52 , which is connected to the other brush  50 . The pickup  74  is connected to the conduction detection circuit  80  as in the system  10  in the embodiment. 
     In the case that the resistors  142 ,  144  have the same resistance, the circuit  80  incurs half the voltage of the battery  52  when the conduction between the pickups  68 ,  74  is made. This circuit structure also enables the conduction detection circuit  80  to detect preferably the conduction current between the pickups  68 ,  74 . 
     (Other Modifications) 
     In above embodiment and modifications, a single projection part  76  is formed. However, a plurality of projection parts  76  may be formed at constant angular interval X 1 , as shown in FIG.  14 . Eight projection parts are formed with forty-five degree angular intervals in FIG.  14 . In this case, at least one conduction between the pickups  68 ,  74  is made, namely at least one conduction signal is sent from the conduction detection circuit  80  to the motor control circuit  62 , when the output gear  34  is rotated by forty-five degrees or more. 
     In the case that the circuit  62  is programmed to cancel a second and later conduction signals, a motor actuator control system in this modification performs in the same manner as the system  10  in the embodiment. In the case that the circuit  62  is programmed to correct the count N using a plurality of predetermined counts NA every time the conduction signal is detected, the motor  20  is more accurately controlled due to the multiple correction. 
     In the above embodiment and modifications, each projection part  76  protrudes outwardly from the pulse plate  66 . However, each projection part  76  may protrudes inwardly from the pulse plate  66 . In FIG. 15, a plurality of projection parts  76  protruding inwardly from the pulse plate  66  is formed with constant angular intervals X 2 . Twelve projection parts are formed with thirty degree angular interval in FIG.  15 . 
     The constant angular interval X 1 , X 2  is set to be smaller than a predetermined operation angle of the output shaft  35  formed on the output gear  34  in order to reliably detect the rotational position of the output gear  34  within the operation angle. For example, in the case that the predetermined angle is sixty degrees, at least seven projection parts  76  are needed to provide the constant angular interval X 1 , X 2  that are smaller than the operation angle. 
     In the case that only one projection part  76  is formed on the output gear  34 , the position of the gear  34  in the rotational direction needs to be adjusted such that the projection part  76  contacts the pickup  74  within the operation angle of the output shaft  35  when the output gear  34  is assembled. However, if a plurality of projection parts  76  is formed at the constant angular interval X 1 , X 2  that are smaller than the operation angle, the position adjustment is needless. Therefore, the assembly becomes easier. 
     In the above embodiment and modifications, the rotational position of the output gear  34  is correlated with the count N of the commutator current surges by substituting a predetermined number NA for the count N unless the count N and the number NA are equal at the moment that the motor control circuit  62  receives the conduction signal from the conduction detection circuit  80 . However, the rotational position of the output gear  34  may be correlated with the count N of the commutator current surges by starting to count the commutator current surges at the moment that the circuit  62  receives the conduction signal from the circuit  80 . 
     In the above embodiment and modifications, the rotational position of the gear  34  is detected using the electric signal generated by a mechanical switch constituted of the pickups  68 ,  74 , the pulse plate  66 , and the projection part  76 . However, instead of the mechanical switch, other means such as an optical sensor and a magnetic sensor may be used. 
     In the above embodiment and modifications, the motor actuator control system  10 ,  100 ,  120 ,  140  according the present invention is used in the air conditioning system  82 . However, as a matter of course, the system is not limited to the application and may be applied to other systems in which at least one motor actuator is used.