Abstract:
A system for controlling a vehicle power sliding door having a motor supplied voltage from a power source mounted on the vehicle for opening or closing the power sliding door and a motor drive circuit for driving the motor with relays for switching direction of rotation of the motor and a FET for regulating the voltage to be supplied to the motor to change a speed of the motor rotation. In the system, a motor-drive-circuit controller is provided for outputting a command value to the motor drive circuit, thereby enabling to control the direction of rotation of a power sliding door drive motor to effect opening and closing of the power sliding door with minimal total heat loss of semiconductor devices and that, by utilizing PWM control for varying motor rotational speed, lowers product cost by decreasing the size, weight and total number of components of the power sliding door unit. In addition, the faulty operation of the controller is also detected.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a system for controlling a vehicle power sliding door, particularly to a system for controlling a power sliding door of a vehicle equipped with switching relays and a field effect transistor (FET) and capable of opening and closing a power sliding door by controlling the rotational speed and direction of rotation of a motor for driving the power sliding door.  
           [0003]    2. Description of the Related Art  
           [0004]    Japanese Patent Laid-Open Applications Hei 7(1995)-229344 and Hei 8(1996)-144633, for example, teach vehicle power sliding door control systems that are equipped with a sliding door installed to slide along one side of the vehicle and a motor or other source of driving power and is capable of opening and closing the sliding door automatically.  
           [0005]    The diagram of FIG. 20 shows the basic configuration of the motor drive circuit for controlling the direction of rotation of the motor in the conventional systems (forward rotation for opening the door and reverse rotation for closing it). As shown in FIG. 20, the motor drive circuit includes a first relay  104  having a switching relay  100  switched by a coil  102  and a second relay  110  having a switching relay  106  switched by a coil  108 .  
           [0006]    The first and second relays  104  and  106  are connected to a first power source  112  that supplies them with a voltage of, for instance, about 12 V, and their outputs are connected to the positive and negative poles of a motor (designated M)  114 . The coils  102  and  108  are connected to a second power source  116  that supplies them with a voltage of, for instance, about 12V and are further connected to the A (output port) and B (output port) of a controller  118 . The controller  118  controls the level of the current passing through the coils to different combinations of Hi (to close the relays) and Lo (to open the relays). By this, as shown in FIG. 21, the direction of rotation (forward/reverse) of the motor  114  is controlled. C, D, E and F in FIG. 20 and FIG. 22 (referred to below) are detection resistances that indicate the driven state of the motor  114 .  
           [0007]    Japanese Patent Laid-Open Application Hei 9(1997)-328960 teaches a system in which an H bridge circuit configured by use of field effect transistors (FETs) produces a pulse signal for PWM (pulse-width modulation) -controlling current from a battery to enable directional and speed control of a motor.  
           [0008]    The diagram of FIG. 22 shows the basic configuration of the motor drive circuit of the power sliding door control system using FETs.  
           [0009]    In the motor drive circuit utilizing FETs, four FETs  120  and a motor  122  are connected as illustrated to configure a conventional H bridge circuit and the gates of the FETs  120  are connected to output ports A, B, C and D of a controller  124 .  
           [0010]    In this motor drive circuit, output of drive pulse signals from the output ports A, B, C and D as shown in FIG. 23 enables production of the indicated detected values at detection resistances E and F, i.e., enables control of motor  122  direction of rotation (forward rotation: solid line, reverse rotation: broken line) and rotational speed. As shown at the A and B outputs in the same figure, by outputting pulse signals it becomes possible to vary the motor rotational speed by PWM control.  
           [0011]    Preferably, a vehicle power sliding door should be capable of being opened and closed at different speeds matched to the circumstances at the time of operation and should be capable of being opened and closed at the same speed even when the vehicle is parked or stopped on an incline. However, the foregoing systems utilizing switches, which are characterized by slow relay response of several milliseconds, are incapable of smooth sliding door operation.  
           [0012]    While the system that controls the direction of motor rotation by operating FETs incorporated in the motor drive circuit is capable of PWM control, its use of multiple FETs increases the total amount of heat loss of the semiconductor devices to the point of requiring provision of a relatively large radiator (heat sink). The weight of the heat sink and its footprint on the circuit board are therefore proportionally larger. In addition, the size and weight of the power sliding door unit increases, leading to higher product cost.  
           [0013]    In the circuit using FETs shown in FIG. 22, moreover, inadvertent reverse connection to the battery is liable to damage the FETs by producing heavy current flow through the FET parasitic diodes. Although it is conceivable to prevent such FET damage by inserting diodes or the like in the vicinity of the current source (battery), this would further increase the total amount of heat loss of the semiconductor devices.  
         SUMMARY OF THE INVENTION  
         [0014]    An object of the present invention is therefore to overcome the aforesaid problems of the prior art by providing a system for controlling a vehicle power sliding door that is capable of controlling the direction of rotation of a power sliding door drive motor to effect opening and closing of the power sliding door with minimal total heat loss of semiconductor devices and that, by utilizing PWM control for varying motor rotational speed, lowers product cost by decreasing the size, weight and total number of components of the power sliding door unit.  
           [0015]    Another object of the invention is to provide a system for controlling a vehicle power sliding door that is safe from FET damage even under heavy current flow caused, for example, by application of counter electromotive force.  
           [0016]    Further, when detecting whether or not the motor drive circuit of such a vehicle power sliding door control system, which switches the direction (forward/reverse) of motor rotation by use of switching relays and regulates the motor rotational speed by use of the field effect transistor (FET), is operating normally, it is preferable to be able to check the drive circuit operation with simplest possible configuration and without need for operating the motor.  
           [0017]    Still another object of the present invention is therefore to achieve such preferable checking capability by providing a system for detecting faulty operation of a vehicle power sliding door that enables current passing through a detection point to be detected and cut off without operating the motor and that is realized using a simply-configured motor drive circuit for opening and closing the vehicle power sliding door.  
           [0018]    For realizing this object, in a first aspect of this invention provides a system for controlling a power sliding door of a vehicle, comprising: a motor supplied voltage from a power source mounted on the vehicle for opening or closing the power sliding door; a motor drive circuit for driving the motor having at least a switch for switching direction of rotation of the motor and a switching element for regulating the voltage to be supplied to the motor to change a speed of the motor rotation; and a motor-drive-circuit controller for outputting a command value to the motor drive circuit. In the first aspect the present invention provides a system for controlling a vehicle power sliding door that is capable of controlling the direction of rotation of a power sliding door drive motor to effect opening and closing of the power sliding door with minimal total heat loss of semiconductor devices and that, by utilizing PWM control for varying motor rotational speed, lowers product cost by decreasing the size, weight and total number of components of the power sliding door unit.  
           [0019]    In a second aspect, the present invention provides the system further including: means for detecting an opening/closing speed of the power slide door; and wherein the motor-drive-circuit controller regulates the voltage to change the speed of the motor rotation such that the power sliding door is opened or closed at a speed inversely or substantially inversely proportional to the detected speed of the power sliding door. In the second aspect, the present invention provides a system for controlling a vehicle power sliding door that enables the power sliding door to be opened and closed at a steady speed even when, for example, opening/closing is conducted with the vehicle stopped on an incline.  
           [0020]    In a third aspect, the present invention provides the system further including a branch which is connected to the ground through a diode such that the diode is connected with its anode on the ground side. In the third aspect, the present invention provides a system for controlling a vehicle power sliding door that is safe from FET damage even under heavy current flow caused, for example, by application of counter electromotive force.  
           [0021]    In a fourth aspect, the present invention provides a system for detecting faulty operation of a power sliding door of a vehicle, comprising: a motor supplied voltage from a power source mounted on the vehicle for opening or closing the power sliding door; a power-sliding door controller provided in a motor current supply circuit for supplying current to the motor having at least a switch for switching direction of rotation of the motor and a switching element for regulating the voltage to be supplied to the motor to change a speed of the motor rotation; current detecting means for detecting supply of current to the motor; and faulty operation detecting means for detecting that faulty operation has occurred in the power-sliding door controller. In the fourth aspect, the present invention provides a system for detecting faulty operation of a vehicle power sliding door that, while being of simple configuration, enables abnormal current passing through the circuit to be detected and cut off without operating the motor.  
           [0022]    In a fifth aspect, the present invention provides the system wherein the faulty operation detecting means detects that the faulty operation has occurred in the power-sliding door controller if the current detecting means detects the supply of current to the motor when predetermined outputs are supplied to the switch and the switch element. In the fifth aspect, the present invention provides a system for detecting faulty operation of a vehicle power sliding door that can efficiently detect and isolate shorts arising between the relay lines, between relay lines and ground, and so on. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 is an overall schematic diagram showing a vehicle installed with a system for controlling a vehicle power sliding door according to an embodiment of the present invention;  
         [0024]    [0024]FIG. 2 is a diagram for explaining the relationship between signal inputs and outputs of an ECU that is a constituent of the system for controlling a vehicle power sliding door;  
         [0025]    [0025]FIG. 3 is a diagram showing the motor and motor drive circuit for opening and closing the power sliding door of the system of FIG. 1;  
         [0026]    [0026]FIG. 4 is a time chart showing the conducting states of controller output ports and detection resistances in the drive circuit shown in FIG. 3;  
         [0027]    [0027]FIG. 5 is a flow chart showing the sequence of power sliding door opening operations conducted by the system for controlling a vehicle power sliding door of FIG. 1;  
         [0028]    [0028]FIG. 6 is a subroutine flow chart of the operations conducted in S 28  of the flow chart of FIG. 5 when the duty ratio is 100% during power sliding door opening;  
         [0029]    [0029]FIG. 7 is a subroutine flow chart showing the operations conducted in S 28  of the flow chart of FIG. 5 when the duty ratio is 50% during power sliding door opening;  
         [0030]    [0030]FIG. 8 is a subroutine flow chart showing the operations conducted in S 28  of the flow chart of FIG. 5 when the duty ratio is 10% during power sliding door opening;  
         [0031]    [0031]FIG. 9 is a flow chart showing the sequence of power sliding door closing operations conducted by the system for controlling a vehicle power sliding door of FIG. 1;  
         [0032]    [0032]FIG. 10 is a subroutine flow chart of the operations conducted in S 428  of the flow chart of FIG. 9 when the duty ratio is 100% during power sliding door closing;  
         [0033]    [0033]FIG. 11 is a subroutine flow chart showing the operations conducted in S 428  of the flow chart of FIG. 9 when the duty ratio is 50% during power sliding door closing;  
         [0034]    [0034]FIG. 12 is a subroutine flow chart showing the operations conducted in S 428  of the flow chart of FIG. 9 when the duty ratio is 10% during power sliding door closing;  
         [0035]    [0035]FIG. 13 is a subroutine flow chart showing the operations conducted in S 28  (FIG. 5) and S 428  (FIG. 9) when opening/closing of the power sliding door is stopped;  
         [0036]    [0036]FIG. 14 is a diagram for explaining the operation of commutation (flywheel) diodes provided in the circuit of FIG. 3;  
         [0037]    [0037]FIGS. 15A and 15B are diagrams for explaining circuit locations of commutation (flywheel) diodes in a motor drive circuit of the invention;  
         [0038]    [0038]FIG. 16 is a table comparing heat loss between a conventional FET/H bridge configuration and the configuration according to the present invention;  
         [0039]    [0039]FIG. 17 is a diagram, similar to that of FIG. 3, showing a motor drive circuit in a system for controlling a vehicle power sliding door according to a second embodiment of the present invention;  
         [0040]    [0040]FIG. 18 is a diagram, similar to that of FIG. 3, showing a motor drive circuit in a system for detecting faulty operation of a vehicle power sliding door according to a third embodiment of the present invention;  
         [0041]    [0041]FIG. 19 is a flow chart showing the sequence of operations carried out by the system for detecting faulty operation of a vehicle power sliding door according to the third embodiment;  
         [0042]    [0042]FIG. 20 is a diagram for explaining the basic configuration of a motor drive circuit for controlling the direction of rotation of a power sliding door motor in a conventional system for controlling a vehicle power sliding door;  
         [0043]    [0043]FIG. 21 is a time chart showing conducting states of the motor drive circuit shown in FIG. 20;  
         [0044]    [0044]FIG. 22 is a diagram for explaining the basic configuration of a conventional motor drive circuit that uses an H bridge incorporating FETs to control the direction of rotation and rotational speed of a power sliding door motor; and  
         [0045]    [0045]FIG. 23 is a time chart showing conducting states of the motor drive circuit shown in FIG. 22. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0046]    System for controlling a vehicle power sliding door according to embodiments of the present invention will now be explained with reference to the attached drawings.  
         [0047]    [0047]FIG. 1 is an overall configuration diagram showing a vehicle installed with a system  1  for controlling a vehicle power sliding door according to an embodiment of the present invention. The vehicle power sliding door control system  1  includes an electronic control unit (ECU)  10  comprising a microcomputer (not shown) and installed at a suitable location near a power sliding door  14  in a vehicle  12  like that shown in FIG. 1. FIG. 2 is a diagram for explaining the detailed configuration of the system  1  primarily with reference to the ECU  10 .  
         [0048]    The ECU  10  incorporates a power sliding door motor (hereinafter simply referred to as “motor”)  16  for opening and closing the power sliding door  14 , an electric encoder  18  for detecting the speed and direction of door movement (opening and closing), a switch  20  installed at a suitable part of a slide portion (not shown) of the power sliding door  14  for detecting reversing-permitted/reversing-prohibited regions, and a magnetic clutch  22  disposed between the motor  16  and a drive pulley (not shown) for reducing the speed and increasing the output torque of the motor  16  (only the circuit for supplying power to the magnetic clutch is shown in FIG. 2).  
         [0049]    A main switch  24  for permitting opening/closing of the power sliding door  14 , i.e., for enabling door driving, and an open/close switch  26  for inputting power sliding door  14  open/close commands are installed at suitable locations near the driver&#39;s seat (not shown) inside the passenger compartment of the vehicle. A warning lamp  28  for notifying the driver when some irregularity arises in the power sliding door  14  is provided at a suitable location on an instrument panel (not shown). In addition, a buzzer  30  is provided at a suitable location in the passenger compartment so that passengers and others can be warned that the power sliding door  14  is about to open or close.  
         [0050]    A closure unit  32  for detecting incomplete door closure and issuing a pull-in command is provided on the vehicle body near the power sliding door  14 . Moreover, at a suitable location on the power sliding door  14 , there is provided a release motor  34  for pulling in the door in response to a pull-in command from the closure unit  32  and also for releasing a junction (not shown) when the power sliding door locked at the fully closed position is to be opened.  
         [0051]    The power sliding door  14  is equipped with a switch  36  for indicating when the leading end of the power sliding door  14  in the direction of vehicle advance is not completely closed, i.e., when it is open, and a touch switch  38  for detecting power sliding door jamming, i.e., the presence of an object or person in the path of the power sliding door when it is moving in the closing direction.  
         [0052]    An inclination sensor  40  for detecting the inclination angle of the vehicle  12  relative to the axis of gravity is provided at a suitable location in the ECU  10 . A parking brake switch  42  for detecting the state of a parking brake is provided in the vicinity of a parking (hand) brake lever (not shown) installed at a suitable location near the driver&#39;s seat of the vehicle  12 .  
         [0053]    An AT parking switch  44  is provided near a shift lever (not shown) for detecting whether or not the shift lever is in park (P) position. Near a foot brake pedal (not shown) provided at a suitable location near the driver&#39;s seat, there is installed a foot brake switch  46  for detecting whether or not the foot brake is in operation. A vehicle speed sensor  48  for detecting the vehicle speed is provided at a suitable part of the vehicle drive train (not shown).  
         [0054]    The detected values of the various sensors and switches are input to a CPU  10   a  and stored in a memory  10   b  within the ECU  10 , either directly or after appropriate signal processing. In the interest of simplicity of illustration, only some of the sensors etc. are shown in FIG. 1. As best shown in FIG. 2, the vehicle power sliding door control system is supplied with electrical power by an electric power supply  50  (an onboard 12V battery, for instance) and is provided with a ground connection  52  for grounding the various circuits in the control system. The ECU  10  is further equipped with a controller  54  for controlling the driving of the motor  16 .  
         [0055]    The motor  16  and its drive circuit, which strongly reflect the features of the present invention, will now be explained.  
         [0056]    [0056]FIG. 3 is a diagram showing the motor (motor  16 ) and (motor) drive circuit  60  for opening and closing the power sliding door  14  of the system shown in FIG. 1. As shown, the drive circuit  60  includes a first relay  68  composed of a first switching relay  64  that is connected to an appropriate power supply  62  (of about 12V, for example) when open and a first coil  66  for switching the first switching relay  64 , a second relay  74  composed of a second switching relay  70  that is connected to the power supply  62  when open and a second coil  72  for switching the second switching relay  70 . The outputs of the first relay  68  and second relay  74  are connected to the motor  16 .  
         [0057]    When closed, the first and second switching relays  64  and  70  are connected to an FET  76 . Lines branching from appropriate points of the lines connecting the first and second switching relays  64  and  70  and the motor  16  pass through a first diode  78  and a second diode  80  and rejoin into a single line that connects with an appropriate point on the line connecting the first and second relays  68  and  74  with the FET  76 . In the connection state illustrated in FIG. 3, the first relay  68  is opened (Lo current level) and the second relay  74  is closed (Hi current level). The first diodes  78  and  80  are connected with their anodes on the ground side.  
         [0058]    The first and second coils  66  and  72  are connected so as to be applied with voltage from a suitable electric power supply  82  (an onboard 12V battery, for instance) and are connected to output ports A and B of the controller  54  provided in the ECU  10 , from which they are input with ON/OFF commands. The gate of the FET  76  is connected to an output port C from which it is supplied with a pulse signal. By passing Hi and Lo currents through the output ports A and B of the drive circuit  60  as shown in FIG. 4, the drive state of the motor  16  can be controlled as indicated by the detection resistances D and E, while PWM control can be effected by sending an appropriate pulse signal through the output port C.  
         [0059]    The opening and closing operations of the vehicle power sliding door control system described in the foregoing will now be explained.  
         [0060]    [0060]FIG. 5 is a flow chart showing the sequence of power sliding door  14  opening operations conducted by the system for controlling a vehicle power sliding door of FIG. 1. The program represented by this flow chart is activated once every 10 msec., for example.  
         [0061]    First, in S 10 , it is checked whether the ignition switch (not shown) installed in the vicinity of the driver&#39;s seat of the vehicle  12  is ON. When the result is YES, the program goes to S 12 , in which a check is made to confirm that the main switch  24  and parking brake switch  42  are ON and the vehicle speed detected by the vehicle speed sensor  48  is zero km/h. This check is made because of the danger of opening or closing (particularly opening) the power sliding door when the vehicle  12  is moving.  
         [0062]    When the result in S 12  is YES, the program goes to S 14 , in which it is checked whether a manual opening operation is in progress, i.e., whether a passenger or someone else is opening the power sliding door  14  by hand. This check is made by reading the output of the encoder  18 . When the result in S 14  is NO, the program goes to S 16 , in which it is checked whether a power sliding door open command has been input by the open/close switch  26 , i.e., whether the open/close switch  26  is in the DOOR-OPEN position.  
         [0063]    When the result in S 16  is YES, the program goes to S 18 , in which the release motor  34  is operated, and then to S 20 , in which the junction is released to unlock the power sliding door  14 . When the result in S 10  is NO, the program goes to S 22 , in which it is checked whether the main switch  24  is ON and, when it is, to S 14 . This is to enable opening of the power sliding door  14  even when the ignition switch is not ON.  
         [0064]    When it is found in S 14  that a manual opening operation is in progress, the program goes to S 24 , in which the direction of power sliding door  14  operation is confirmed by reading the pulse pattern generated from the encoder  18 . More precisely it is confirmed whether the direction of door  14  is in opening direction.  
         [0065]    When the result in S 24  is YES, the program then goes to S 26 , in which it is discriminated whether the door position detected from the output of the switch is in a reversing-permitted region (explained below). When the result in any of S 12 , S 22 , S 24  and S 26  is NO, the program returns to START.  
         [0066]    The “reversing” and “reversing-permitted region” (and “reversing-prohibited region”) will now be explained. “Reversing” refers to changing the direction of movement of the power sliding door  14  during opening or closing, i.e., changing the direction in which the power sliding door  14  is being driven to opposite direction thereto. The range over which the power sliding door  14  can move is divided into a region in which immediate reversing is permitted and regions in which immediate reversing is prohibited. Specifically, within the overall range of power sliding door  14  movement, a region of a few millimeters just before the fully closed position and a region of a few millimeters just before the fully open position are defined as “reversing-prohibited regions.” The reversing-prohibited regions are defined as regions at the full-open and full-closed positions of the sliding door for distinguishing their detection from detection of sliding door operation halt and jamming.  
         [0067]    The explanation of the flow chart of FIG. 5 will be continued. After the lock is released in S 20 , the program goes to S 28 , in which the power sliding door  14  is driven in the opening direction. FIGS.  6  to  8  are subroutine flow charts of the operations conducted in S 28 .  
         [0068]    The subroutine of FIG. 6 is for determining the Hi and Lo currents passing through the output ports A and B and the duty ratio of the pulse signal output from the output port C when the speed of the power sliding door  14  driven in the opening direction is slower than the rated opening/closing speed (opening speed: slow). A “slow opening speed” arises, for example, when the vehicle  1  is parked on a downward slope and the opening speed of the power sliding door  14  is slowed by the sliding door&#39;s own weight.  
         [0069]    The subroutine of FIG. 6 starts with S 100 , in which information is read that indicates the power sliding door  14  is in the course of an opening operation and the opening speed of the power sliding door  14  is slow. When the power sliding door  14  is in the full-closed state, the information that the opening speed is (will be) slow is obtained by analyzing the output of the inclination sensor  40 . When the power sliding door  14  is in the course of an opening operation, it is obtained by analyzing the output of the encoder  18 .  
         [0070]    The program then goes to S 102  and S 104 , in which, as shown in FIG. 4, the Lo and Hi signals are passed through output ports A and B, and then to S 106 , in which the duty ratio of the pulse signal output from the output port C is set to 100%. In the subroutines of FIGS. 7 and 8, the duty ratio of the pulse signal output from the output port C is similarly set to a value that is inversely or substantially inversely proportional to the detected opening speed of the power sliding door  14 , specifically, to 50% when the door opening speed is medium and to 10% when it is fast.  
         [0071]    The explanation of flow chart of FIG. 5 will be resumed. Next, in S 30 , another check is made to confirm that the main switch  24  and parking brake switch  42  are ON and the vehicle speed detected by the vehicle speed sensor  48  is zero km/h. When the result in S 30  is YES, the program goes to S 32 , in which it is checked whether the open/close switch  26  is in the DOOR-CLOSE position.  
         [0072]    When the result in S 32  is NO, the program goes to S 34 , in which it is checked whether the power sliding door  14  is in a reversing-prohibited region. When the result in S 34  is NO, i.e., when the door is in the reversing-permitted region, the program goes to S 36 , in which it is checked whether the amount of change in pulse width at the encoder  18  exceeds a prescribed value A. This check is made because the fact that the rotational speed of the motor  16  has reached or exceeded a prescribed value many mean that a person or object has been caught in the sliding door so that driving of the motor  16  must be halted. The prescribed value A is the upper limit of pulse width change amount in the reversing-permitted region.  
         [0073]    When the result in S 36  is NO, the program goes to S 38 , in which it is checked whether an overcurrent is flowing through the drive circuit  60 . Like S 36 , S 38  is also for fail detection and is carried out by a fail detection circuit (not shown) provided at a suitable place in the drive circuit  60 . When the result in S 38  is NO, the program returns to S 28  and the power sliding door operation is continued.  
         [0074]    When the result in S 34  is YES, the program goes to S 40 , in which it is checked whether the amount of change in pulse width at the encoder  18  exceeds a prescribed value B. When the result in S 40  is NO, the program goes to S 42 , in which a check like that in S 38  is made to determine whether an overcurrent is present. When the result in S 42  is NO, the program returns to S 28  and the power sliding door operation is continued. The prescribed value B is the upper limit of pulse width change amount in the reversing-prohibited regions.  
         [0075]    When the result in S 30  is NO or the result in one of S 32 , S 36 , S 40  and S 42  is YES, the operation of the power sliding door  14  must be halted. In these cases, therefore, the program goes to S 44 , in which the operation of the motor  16  is immediately stopped, and to S 46 , in which the motor  16  is rotated in the reverse direction. When the result in S 42  is NO, the program goes to S 47  in which it is determined whether the power sliding door  14  is completely opened. If not the program goes back to S 28 , while if so, the program goes to S 48 , in which the motor  16  is stopped and the program terminated.  
         [0076]    The sequence of the power sliding door  14  closing operations will now be explained with reference to the flow chart of FIG. 9.  
         [0077]    The program represented by this flow chart is activated once every 10 msec, for example. Aspects of the power sliding door  14  closing operation that are the same as those of the opening operation will not be explained again. The steps in FIG. 9 that are the same as those in FIG. 5 are assigned reference numerals whose last two digits are the same as those of the corresponding step in FIG. 5. It should be noted here that the motor  16  is rotated in reverse when jamming has occurred S 450  and is stopped in S 452 .  
         [0078]    An explanation will now be made centering on points in which the flow chart of FIG. 9 differs from that of FIG. 5. At the beginning of the closing operation, a check is made in S 412  regarding the same points as in the corresponding S 12  of FIG. 5 plus the additional point of the touch switch  38  being OFF. This is because the fact that the touch switch  38  is ON may mean that the power sliding door  14  is in the full-closed position or that jamming has occurred owing to the presence of an obstacle or the like at the end of the power sliding door in the direction of vehicle advance. Similarly, the ON/OFF state of the touch switch  38  is checked in S 435 .  
         [0079]    The steps of operating the release motor and releasing the lock (S 18  and S 20 ) of the opening operation are omitted from the closing operation. On the other hand, S 450  and S 452  for carrying out reversing and halting operations when jamming occurs are added in order to prevent catching of, for example, a passenger&#39;s hand in the door.  
         [0080]    Subroutine flow charts of the operations conducted in S 428  are shown in FIGS. 10, 11 and  12 . As indicated by S 500  to S 506  of FIG. 10, S 600  to S 606  of FIG. 11 and S 700  to  706  of FIG. 12, the duty ratio of the pulse signal output from the output port C is determined so as to maintain the closing speed of the power sliding door  14  constant.  
         [0081]    When the power sliding door  14  is not in the course of an opening or closing operation, i.e., when it is stationary, the motor  16  is stopped by setting the outputs of the output ports A, B and C of the drive circuit  60  to Hi, Hi and Hi as shown in FIGS. 4 and 13.  
         [0082]    The first and second diodes  78  and  80  installed in the drive circuit  60  will now be explained.  
         [0083]    [0083]FIG. 14 is a simplified explanatory diagram of the configuration in the vicinity of the motor  16  of the drive circuit  60  in the present embodiment. When switch SW is turned ON with the FET in the ON state, current flows in the direction of the arrow (a). When the FET is thereafter turned OFF, energy stored in the reactance component of the motor M produces current in the direction of the arrow (b).  
         [0084]    Without the illustrated diode D (commutation diode or flywheel diode), the release of the energy stored in the reactance component of the motor M produces a positive voltage (counter electromotive force) on the FET side. If the reverse electromotive energy is great, the rated voltage of the FET is liable to be exceeded and, in the worst case, the FET may be damaged. In this embodiment, the counter electromagnetic energy released by the reactance component of the motor  16  is prevented from damaging the FET by the first and second diodes  78  and  80 , which act as commutation (flywheel) diodes.  
         [0085]    Diodes incorporated in the circuit as indicated by the encircled portions in FIGS. 15A and 15B can also function as commutation diodes. However, if the battery should be connected backward, current flowing as indicated by the arrows may result in damage to the FET  76  by overcurrent. In contrast, when branch points are formed between the motor  16  and the switches and grounding is established from the branch points through diodes as in the system in the present embodiment, the controller  54  cannot operate when the battery is connected backward and, therefore, the relays  68  and  74  do not turn ON. As the system in the embodiment calls for use of two diodes, moreover, the loss arising during commutation is divided between them so that use of relatively small diodes suffices. The circuit ( 90 ) shown in FIG. 15B relates to the second embodiment set out later.  
         [0086]    The total heat losses of the conventional motor drive circuit configured as an H bridge circuit using FETs and the system of the present invention were compared. The comparison was made under conditions of: FET ON,  10  A current, and motor not driven.  
         [0087]    The results of the loss comparison are shown in FIG. 16. The total heat loss of the conventional configuration was 17.5 W and that of the configuration in the invention was 6.4 W, thus demonstrating the lower total heat loss of the invention system in comparison with the conventional FET/H bridge configuration.  
         [0088]    [0088]FIG. 17 is a diagram, similar to that of FIG. 3, showing a motor drive circuit  90  in the system according to a second embodiment of the present invention. All constituent elements of the motor drive circuit  90  are the same as those shown in FIG. 3 and are therefore assigned the same reference symbols.  
         [0089]    In the circuit according to the second embodiment, the FET  76  is disposed between the power supply  62  and the first and second relays  68  and  74 . The effects obtained with this circuit arrangement are exactly the same as those provided by the (motor) drive circuit  60 . The discussion made with reference to the first embodiment should therefore be applied to the second embodiment.  
         [0090]    [0090]FIG. 18 is a diagram, similar to that of FIG. 3, showing a motor drive circuit  90  in a system for detecting faulty operation of a vehicle power slide door according to a third embodiment of the present invention.  
         [0091]    Explaining this with focus on the difference from that of FIG. 3, a detection resistor  86  is added at a position downstream of the FET  76  and the ground. A sensor (current detecting means)  86  is provided at a position between the FET  76  and the resistor  86  for detecting current flowing the path. The sensor  86  is connected to a current detection port F of the controller  54  provided in the ECU  10  to forward the output indicative voltage at a position upstream of the resistor  86 .  
         [0092]    The output of the sensor  86  is amplified by an operational amplifier (not shown) and is A/D converted by an A/D converter such that the controller  54  is able to detect current flow by the voltage drop between the detection resistor  86 . Since this type of a sensor is well-known, no further explanation will be made.  
         [0093]    The faulty operation detection in the aforesaid vehicle power sliding door control system will now be explained.  
         [0094]    [0094]FIG. 19 is a flow chart showing the sequence of operations carried out by the system for detecting faulty operation of the vehicle power sliding door according to this embodiment. The program represented by this flow chart is activated once every suitable period of, for example, 10 msec. or shorter, while the motor  16  is stopped.  
         [0095]    First, in S 900  and S 902 , the system is set to pass Hi current from the output ports A and B through the first and second relays  68  and  74 . The program then goes to S 904 , in which the output from the output port C is set to Hi, i.e., the duty ratio of the pulse signal output from the output port C is set at 100%.  
         [0096]    Next, in S 906 , a check is made as to whether the output from the output port A is Hi. When the result is NO, the faulty operation detection is terminated. When it is NO, the program goes to S 908 , in which a check is made as to whether the output from the output port B is Hi.  
         [0097]    When the result in S 908  is NO, the faulty operation detection is terminated. When the result is YES, the program goes to S 910 , in which the current value detected by the sensor  88  at the current detection port F is read. As explained earlier, when the outputs of the output port A and B are Hi, it follows that the first and second relays  68  and  74  have burned out. When the result in S 910  is NO, therefore, it is likely that a faulty operation has occurred. For example, a short (short-circuiting) has occurred between the first or second relay and ground or that the first and second relays have shorted with each other.  
         [0098]    The program therefore goes to S 912 , in which the outputs of output ports A and B are set to Hi and the output of output port C is set to Lo, i.e., the duty ratio is set to 0%, and a command is issued to cut off current flow. Next, in S 914 , the warning lamp  28  is turned on to warn the passengers that the circuit has failed.  
         [0099]    Being configured in the foregoing manner, the system of this embodiment can, without operating the motor, achieve detection and cut-off abnormal current flow in the circuit with a simple configuration. In addition, it can efficiently detect and isolate shorts arising between the relay lines, between relay lines and ground, and so on.  
         [0100]    In the third embodiment, although the sensor  88  is located between the FET  76  and the resistor  86 . The point at which the sensor  88  is incorporated is not limited to this location, however, but can be installed at any point where current flows when the first and second relays short.  
         [0101]    Moreover, although the sensor  88  detects current state (presence/absence of current), it can instead be configured to similarly detect whether or not voltage is applied at a prescribe point.  
         [0102]    Thus, the first and the second embodiments are configured to have a system  1  for controlling a power sliding door  14  of a vehicle, comprising: a motor  16  supplied voltage from a power source mounted on the vehicle for opening or closing the power sliding door; a motor drive circuit  60  for driving the motor having at least a switch (first relay  68 , a second relay  74 ) for switching direction of rotation of the motor and a switching element (FET  76 ) for regulating the voltage to be supplied to the motor to change a speed of the motor rotation; and a motor-drive-circuit controller (ECU  10 , controller  54 ) for outputting a command value to the motor drive circuit.  
         [0103]    The system further includes: means (electric encoder  18 , inclination sensor  40 ) for detecting an opening/closing speed of the power slide door; and wherein the motor-drive-circuit controller regulates the voltage to change the speed of the motor rotation such that the power sliding door is opened or closed at a speed inversely or substantially inversely proportional to the detected speed of the power sliding door, as illustrated in FIGS.  6  to  8  and FIGS.  10  to  12 .  
         [0104]    The system further includes a branch which is connected to the ground through a diode (first diode  78 , second diode  80 ) such that the diode is connected with its anode on the ground side.  
         [0105]    Being configured in the foregoing manner, the systems according to the first and second embodiments can, at the time of driving the motor  16  to open and close the power sliding door  14 , implement PWM control and enable the motor  16  to be switched between forward and reverse rotation and varied in rotational speed while holding down the total heat loss of the semiconductor devices. Since the motor  16  is PMW-controlled at a duty ratio approximately inversely proportional to the opening/closing speed of the power sliding door  14 , moreover, the door can be opened and closed at a steady speed even when, for example, opening/closing is conducted with the vehicle stopped on an incline. In addition, the FET is protected from damage by application of counter electromotive force or the like.  
         [0106]    The third embodiment is thus configured to have system for detecting faulty operation of a power sliding door  14  of a vehicle, comprising: a motor  16  supplied voltage from a power source mounted on the vehicle for opening or closing the power sliding door; a power-sliding door controller provided in a motor current supply circuit for supplying current to the motor having at least a switch (first relay  68 , second relay  74 ) for switching direction of rotation of the motor and a switching element (FET  78 ) for regulating the voltage to be supplied to the motor to change a speed of the motor rotation; current detecting means ( 88 ) for detecting supply of current to the motor; and faulty operation detecting means (controller  54 , S 20 , S 24 ) for detecting that faulty operation has occurred in the power-sliding door controller.  
         [0107]    In the system, the faulty operation detecting means detects that the faulty operation has occurred in the power-sliding door controller if the current detecting means detects the supply of current to the motor (S 20 , S 24 ) when predetermined outputs are supplied to the switch and the switch element (S 10 , S 12 , S 14 ).  
         [0108]    Although the invention was described with reference to embodiments in which the duty ratio of the pulse signal sent to the gate of the FET is set at 10%, 50% and 100%, these values were merely used as examples and other values can be used instead.  
         [0109]    While the invention has thus been shown and described with reference to specific embodiments, it should be noted that the invention is in no way limited to the details of the described arrangements; changes and modifications may be made without departing from the scope of the appended claims.