Abstract:
The present invention aims at providing a rotation angle detector capable of detecting and storing information for a direction and an angle of rotation of steering wheel while maintaining a condition of reduced power consumption from a battery, when an engine is not running. In achieving the object, the invention discloses a structure, wherein the detector keeps a control means ( 8 ) including a memory unit ( 11 ) in a memory back-up mode when an ignition switch ( 7   a ), i.e. a main switch, is turned off, switches a power supply for sensor elements ( 3   a ), ( 3   b ) and ( 4 ) into a mode of low consumption of current, which is smaller than that of the normal current by a control signal of the control means ( 8 ), and allows the control means ( 8 ) to activate the sensor elements ( 3   a ), ( 3   b ) and ( 4 ) operative in the normal mode after a confirmation of an output signal from at least one of the sensor elements ( 3   a ) and ( 3   b ) when the steering wheel is moved, and thereby the detector is capable of detecting the direction and the angle of rotation out of the information for rotation of the steering wheel.

Description:
This application is a U.S. National Phase Application of PCT international application PCT/JP99/01281. 
     FIELD OF THE INVENTION 
     The present invention relates to a rotation angle detector for detecting a rotational position of a steering wheel of a vehicle. 
     BACKGROUND OF THE INVENTION 
     In general, steering for vehicles such as an automobile is provided with a lock-to-lock latitude for a steering wheel between a rightmost and a leftmost positions, when a steering wheel is turned clockwise and counterclockwise for several times (normally, 3 to 6 revolutions). 
     A reason of the above is to reduce a physical force required for an operator to turn the steering wheel by decreasing a speed of rotary movement of the steering wheel with a steering gear. Another reason is to reduce vibrations and impacts of wheels from being transmitted to the steering wheel. It is also for a reason to improve maneuverability by increasing an amount of turning the steering wheel (i.e. steering angle) necessary for changing a heading direction of the vehicle. In other words, the vehicle would require the operator to pay an excessive degree of attentiveness, if a small turning of the steering wheel should cause a substantial change in the moving direction. Stable traveling of the vehicle is thus achieved by providing a handling characteristic broad enough and suitable for a general sense of operators. 
     For the same reason, the operator is unable to determine a rotational position of the steering wheel at a glance, nor is she/he able to find a moving direction of the vehicle. A rotation angle detector for detecting a position and an angle of rotation of the steering wheel has hence been suggested. That is, an operator can easily determine a moving direction of her/his vehicle (especially, whether or not it heads straight) by using the detector. The detector is also adaptable for a variety of control devices such as (1) a device that changes firmness of a suspension according to an angle of a steering wheel, (2) a device for alarming an operator in case a steering wheel is turned beyond a predetermined angle, and (3) a device for guiding the operator for a way to return home. 
     FIG. 5 shows a structure of a rotation angle detector of the prior art. In the figure, a reference numeral  1  represents a disc having a first series of through holes  1   a  provided thereon with a predetermined pitch, and it is fixed to a rotor  2 . Reference numerals  3   a  and  3   b  respectively represent a first and a second sensor elements, each comprising a transmission type photo-interrupter consisting of a light-emitting element and a light-receiving element positioned in a manner to face each other across the first series of through holes  1   a.  The two sensor elements are provided side by side in order to detect a direction of rotation. The first sensor element  3   a  and the second sensor element  3   b  are prearranged to form a predetermined angle between them. The disc  1  also has a cutout hole  1   b,  and a third sensor element  4  comprising another transmission type photo-interrupter is provided for detecting the cutout hole  1   b,  so that the detector detects a reference position for rotation of the rotor  2  by the third sensor element  4  with the cutout hole  1   b.    
     The rotor  2 , the sensor elements  3   a  and  3   b,  and the sensor element  4  are all housed in a case  5 . The rotor  2  is so arranged that it rotates freely in synchronization with a rotation of the steering wheel in a vehicle or the like. 
     A mutual relation and operation of the foregoing structural elements of the prior art detector will be described hereinafter. When the steering wheel is made in a vehicle, it rotates the rotor  2  in a link motion, as well as the disc  1  fixed to the rotor  2 , and the sensor elements  3   a  and  3   b  detect a number of the through holes  1   a  in the disc  1 . The detector is able to measure an angle of the rotation of the steering wheel and to detect a direction of the rotation, using the number of the through holes  1   a  detected by the first and second sensor elements  3   a  and  3   b  as a coefficient, since the through holes  1   a  are arranged with a predetermined angle pitch, and the first and second sensor elements  3   a  and  3   b  are disposed with a difference of 90 degrees in electrical phase between them. 
     On the other hand, the sensor element  4  can produce a reference position signal, when the cutout hole  1   b  passes through it as the rotor  2  and the disc  1  rotate. Thus, the detector is able to determine a present angle of the rotation of the steering wheel by calculating an amount of change in angle of rotation of the steering wheel obtained as above, with reference to a position where the reference position signal is obtained by the sensor element  4  from the cutout hole  1   b.    
     Accordingly, the angle and direction of the rotation of the steering wheel can be calculated by processing the number and phase of detected signals for the angle and direction of the rotation with an electronic circuit. Subsequently, a rotational position of the steering wheel can be determined from the angle and direction of the rotation of the steering wheel. 
     When an engine of the vehicle is not running (an ignition key is in an “OFF” or an “Accessory” position), electric power is not supplied to the rotation angle detector. The detector is unable to determine an angle of the rotation of the steering wheel until the cutout hole  1   b  passes through the sensor element  4  after the engine is started. Also, the detector is unable to determine how many revolutions the steering wheel has been turned at any point of time from only passage of the through holes  1   a  by the sensor elements  3   a  and  3   b,  since the steering wheel is made to turn complicatedly. In general, therefore, the detector is designed to determine a neutral position of the steering wheel by making a comparison of the passage data of the through holes  1   a  with information of number of rotations between right and left wheels, etc. In other words, the detector is unable to make a conclusive determination of an angle of rotation of the steering wheel until the vehicle makes a straight travel after the engine is started. 
     In order to solve the above problem, a method has been employed in some of the devices in that an electronic circuit is equipped with a memory element, which functions even when the engine is in a state of standstill, for storing information of a rotational position of the steering wheel immediately before the engine is turned off. 
     However, an inconsistency occurs between an actual angle of rotation and the stored angle of rotation of the steering wheel, if the steering wheel is turned while the engine is not running. This causes the detector to execute a control based on an incorrect angle of rotation of the steering wheel, and thereby giving rise to a problem that the detector is not able to carry out the intended control. 
     SUMMARY OF THE INVENTION 
     The present invention aims at solving the above-described problems, and to provide a rotation angle detector, which operate in a manner to: (1) back up memory of an angle and a direction of the rotation of a steering wheel in a memory element of an electronic circuit; (2) activate the detector by itself with own sensor element on a standby mode, when the steering wheel is turned while an engine is at a standstill; and (3) detect an angle and a direction of the rotation of the steering wheel, even when the engine is not running. 
     In order to solve the above problems, a rotation angle detector of the present invention comprises: (1) a disc having a plurality of through holes arranged with a predetermined pitch along a perimeteric direction, and a cutout portion provided in a predetermined position along the perimeteric direction; (2) a first and a second sensor elements, each comprising a light-emitting element and a light-receiving element, and disposed within a predetermined angle in a manner to correspond with the through holes in the disc; (3) a third sensor element comprising a light-emitting element and a light-receiving element, and disposed in a manner to correspond with the cutout portion in the disc; and (4) a control means comprising a signal processing unit for generating an output of detection signal corresponding to an angle and a direction of rotation of the disc using signals provided by the first, second and third sensor elements, and a memory unit for storing, as a positional information, the output provided by the signal processing unit, when a main switch is turned on. The control means includes: (a) a first means for introducing a dark current mode for maintaining the sensor elements operative with a lower supply current than that consumed under a normal operating condition, even when the main switch is in an OFF position; (b) a second means for introducing a memory backup mode for maintaining a storing condition of the positional information supplied from the signal processing unit by providing a current supply to the memory unit, even when the main switch is in the OFF position; (c) a third means for canceling the memory backup mode and the dark current mode so as to turn the sensor elements and the control means into their normal operating conditions, when the sensor elements operated under the dark current mode of the first means detect a motion of the disc; and (d) a fourth means for actuating the first means and the second means into operation so as to resume the memory backup mode and the dark current mode, if the sensor elements no longer detect motion of the disc while in a condition after the third means has canceled these modes. 
     With the foregoing structure, the detector is capable of obtaining information of an absolute steering angle immediately after the engine is started, since the detector keeps in memory a steering wheel position, monitors any movement of the steering wheel at all times, and renews the stored information if any change takes place while the engine is not running. 
    
    
     BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG.  1 ( a ) is a plan view depicting a rotation angle detector of embodiment 1 of the present invention; 
     FIG.  1 ( b ) is a sectional view of the same rotation angle detector; 
     FIG. 2 is an electrical block diagram of the same rotation angle detector; 
     FIG. 3 is a timing chart depicting outputs of sensor elements produced in conjunction with a change in angle of rotation in the same rotation angle detector; 
     FIG. 4 is an operational flow chart depicting a construct of an essential portion of the same rotation angle detector; and 
     FIG. 5 is a plan view depicting a rotation angle detector of the prior art. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
     FIGS.  1 ( a ) and  1 ( b ) depict a rotation angle detector of embodiment 1 of the present invention, wherein FIG.  1 ( a ) is a plan view, and FIG.  1 ( b ) is a sectional view. Any component represented by the same reference numeral as that of FIG. 5 is an element having identical structure, and detailed description of it will be omitted. In FIGS.  1 ( a ) and  1 ( b ), a reference numeral  6  represents an electronic circuit including a microcomputer (hereinafter referred to as “computer”) provided within the rotation angle detector. FIG. 2 is an electrical block diagram of the same rotation angle detector, and it includes an ignition switch  7   a  and an accessory switch  7   b,  both of which constitute a main switch. Electric power is supplied to the rotation angle detector directly from a battery, even if these switches  7   a  and  7   b  are turned off. A reference numeral  8  represents a control means, which executes a switching control for an operating mode of the computer and sensor elements  3   a,    3   b  and  4 , between a normal mode and a current saving mode. A reference numeral  9  represents a mode switching unit for switching the sensor elements between the normal mode and the power saving mode, and it controls a power supply to light-emitting/light-receiving elements. The control means  8  includes a computing unit  10  and a memory unit  11  for storing an absolute angular position, and that the memory unit  11  retains an absolute angular position of the disc  1  using power supplied directly from the battery, even when the ignition switch  7   a  and the accessory switch  7   b  remain turned off (in their OFF positions). The computing unit  10  calculates an amount of change in angle according to signals obtained from the sensor elements  3   a,    3   b  and  4 , obtains a new absolute angle using the information of absolute steering angle stored in the memory unit  11 , and renews the information in the memory unit  11 . On the other hand, an output unit  12  outputs the angle information stored in the memory unit  11  as an electric signal, and a control unit  13  executes an overall control of the computer. A reference numeral  14  represents a power supply circuit for converting a 12-volt supply from the battery into a 5-volt supply, and a reference numeral  15  represents a converter circuit for converting a 12-volt signal of the ignition switch  7   a  into an input signal for the computer. A reference numeral  16  represents another converter circuit for converting a 12-volt signal of the accessory switch  7   b  into another input signal for the computer. In the figure, the sensor elements  3   a,    3   b  and  4  include their respective light-emitting elements  3 La,  3 Lb and  4 L, and light-receiving elements  3 Pa,  3 Pb and  4 P. 
     FIG. 3 depicts timing at which the sensor elements produce outputs in conjunction with a change in angle of rotation, and reference characters A, B and Z respectively represent outputs of the sensor elements  3   a,    3   b  and  4 . The sensor elements  3   a  and  3   b  change signal levels of their outputs A and B alternately between H and L at intervals of 1 degree in the rotational angle of the disc  1 , and they are so positioned that the changes in signal level shift by 0.5 degree from each other. The sensor elements  3   a,    3   b  and  4  are positioned with respect to each other so that the change in signal level of the output Z coincides with that of the signal A. 
     The rotation angle detector constructed as above operates in a manner which will be described hereinafter with reference to FIG.  4 . 
     FIG. 4 depicts an operational flow covering an essential portion of the same rotation angle detector. In the step  10   a,  the detector is initialized (e.g. setting up an I/O port of the computer, setting up a variety of registers, and setting up a RAM), when electric power is supplied for the first time from the battery, or the computer is reset. The detector checks a position of the accessory switch and a position of the ignition switch in the main switch in the steps  10   b  and  10   c.  When the ignition switch is turned on, that is, the engine is started or rotated, the detector wakes up the computer into operation (functional mode) in the step  10   d,  and operates the sensor elements under the normal mode in the step  10   e.  If the sensor elements are in their OFF state upon checking signals of photo-transistors in the sensor elements in the step  10   f,  the detector resumes the step  10   d  for wake-up operation of the computer. If the sensor elements are in their ON state upon checking signals of the photo-transistors in the sensor elements in the step  10   f,  the detector determines a direction of rotation in the step  10   h,  calculates a number of rotations in the step  10   k,  stores the direction and the number of rotations resulted from the calculation according to the direction of rotation determined in the step  10   h  into the memory unit in the step  10   m,  and outputs them externally in the step  10   n.  The detector then resumes again the step  10   b  for checking a position of the accessory switch. 
     The memory unit having a storage function dictated in the step  10   m  may be replaced by any one of; 
     (a) a RAM unit in the computer, or in case the battery run down, 
     (b) an electrically erasable programmable ROM (hereinafter referred to as “EEPROM”) provided external of the computer, and 
     (c) a RAM provided external of the computer, and connected with a battery (e.g. lithium-ion battery) or a capacitor of large capacity as a supplementary power supply for the external RAM. 
     The routine of operation described above shows that the detector functions under the normal mode of power consumption for detecting an angle and a direction of the rotation of a steering wheel during the engine running. In this instance, the computer consumes an electric current of approximately 5 mA under the normal mode for its wake-up in the step  10   d.  A light-emitting element for each of the sensor elements consumes approximately 6 mA in the step  10   e,  for a total current of nearly 12 mA between two of them. Therefore, the detector consumes a current of approximately 17 to 18 mA in all for the wake-up operation of the computer in the step  10   d  and for functioning the light-emitting elements of the sensor elements in the step  10   e.    
     On the other hand, the detector controls its operation under a different routine than what is described in the above, if the accessory switch and the ignition switch within the main switch are both in their OFF positions in the steps  10   b  and  10   c.  In this routine, the steps  10   b  and  10   c  fulfil a determining function for selecting a mode that does not consume power of the battery during the engine not running, and these steps can be substituted by other signals if available. 
     When both switches are in their OFF positions in the steps  10   b  and  10   c,  the detector turns on the light-emitting elements of the sensor elements under a low current consumption mode in the step  10   r,  if a door-lock signal as well as a steering shaft-lock signal are OFF in the respective steps  10   p  and  10   q.  The detector increases a gain of the phototransistors of the sensor elements in order for them to be operative even with the light-emitting elements of the sensor elements in the low current consumption mode, and checks for a state of inputs in the step  10   t.  The detector then resumes again the step  10   b  for a check of position of the accessory switch, after turning the computer into a sleep mode (i.e. for backing up memory) in the step  10   u,  if the inputs are in the OFF state. However, if power of the inputs are ON in the step  10   t  as a result of checking the state of inputs under the condition of increased gain of the phototransistors of the sensor elements, the detector takes the step  10   d  for executing the detecting operation of a direction and an angle of rotation by the sensor elements under the normal operating mode. 
     Further, when both switches are judged to be in their OFF positions in the steps  10   b  and  10   c,  and if the door-lock signal and the steering shaft-lock signal are ON in the respective steps  10   p  and  10   q,  the detector turns the light-emitting elements of the sensor elements into the OFF mode in the step  10   v  after lapse of a predetermined time determined by the step  10   s.  The detector then turns the phototransistors of the sensor elements into the OFF mode in the step  10   w,  and the computer into the sleep mode in the step  10   u.  The computer keeps its condition of backing up memory during the sleep mode in the step  10   u.    
     In the above-described routine of operation, where the engine is at a standstill state, the detector consumes only about 0.01 to 0.1 mA during a part of the routine designated as a second dark current mode, in which the door-lock signal and the steering shaft-lock signal are ON and the computer is in the sleep mode, whereas it consumes approx. 0.6 mA during the other part of the routine designated as a first dark current mode, in which the door-lock signal and the steering shaft-lock signal are OFF. In these routines, the door-lock signal and the steering shaft-lock signal are signals implying that the steering wheel is not moved while the engine is not running. It needs no mentioning that the same function can be attained using a signal signifying a seated/unseated condition of a driver&#39;s sheet or a sheet next to it (i.e. a signal implying that no person is present within a space wherein the steering wheel can be moved), as an example of other signals. 
     When an engine of an automobile is standstill and a door-lock signal in its ON state, a battery normally supplies its electric power only to a limited devices such as a clock and a key-less entry receiver. The key-less entry receiver consumes a current of approximately 5 mA among these devices. On the contrary, the rotation angle detector consumes a mere current of approx. 0.6 mA during the above-stated first dark current mode and approx. 0.1 mA during the second dark current mode, which are not significant for a concern of the buttery running down while the engine is not running. 
     Although the described exemplary embodiment is a detector which employs transmission type photo-interrupters as the sensor elements  3   a,    3   b  and  4 , they may be substituted by reflection type photo-interrupters. If this is the case, the detector is to be provided with a disc  1  having light-reflecting portions in place of the through holes  1   a  and a cutout portion  1   b.    
     Industrial Applicability 
     As has been described, the present invention is able to realize a rotation angle detector which is characterized by comprising: (1) a disc having a plurality of through holes arranged with a predetermined pitch along a perimeteric direction of it, and a cutout portion provided in a predetermined position along the perimeteric direction; (2) a first and a second sensor elements, each comprising a light-emitting element and a light-receiving element, and disposed within a predetermined angle in a manner to correspond with the through holes in the disc; (3) a third sensor element comprising a light-emitting element and a light-receiving element, and disposed in a manner to correspond with the cutout portion in the disc; and (4) a control means comprising a signal processing unit for generating an output of detection signal corresponding to an angle and a direction of rotation of the disc using signals provided by the first, second and third sensor elements, and a memory unit for storing, as a positional information, the output provided by the signal processing unit when a main switch is turned on. The control means includes: (a) a first means for introducing a dark current mode for maintaining the sensor elements operative with a lower supply current than that consumed under a normal operating condition, even when the main switch is in an OFF position; (b) a second means for introducing a memory backup mode for maintaining a storing condition of the positional information supplied from the signal processing unit by providing a current supply to the memory unit, even when the main switch is in the OFF position; (c) a third means for canceling the memory backup mode and the dark current mode so as to turn the sensor elements and the control means into their normal operating conditions, when the sensor elements operated under the dark current mode of the first means detect a motion of the disc; and (d) a fourth means for activating the first and the second means into operation so as to resume the memory backup mode and the dark current mode, if the sensor elements no longer detect motion of the disc while in a condition after the third means has canceled these modes. With the simple structure as described above, the rotation angle detector is able to detect an angle and a direction of the rotation of the steering wheel even when the engine is not running, since the detector stores information of the rotation of the steering wheel by activating the control means using signals from the photo-transistors of the sensor elements, if the steering wheel is turned while the engine is not running.