Patent Abstract:
A sensor circuit for use with a shaft assembly rotatably mounted in a housing and having an input shaft, an output shaft and a torsion bar which connects the input and output shafts together. A CR coil mounted to the housing around the shaft assembly is energized and generates an electromagnetic field. An RX coil is mounted to and rotates with the shaft assembly and has an output connected to a power circuit to generate electrical energy when excited by the electromagnetic field from the first coil. The power circuit powers an angle sensor which transmits a signal back to the first coil representative of the angle between the input and output shafts.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of U.S. Provisional Patent Application 61/448,256 filed Mar. 2, 2011, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     The present invention relates generally to angle sensors and, more particularly, to an angle sensor between an input shaft and an output shaft. 
     II. Description of Related Art 
     In steering systems of the type used in automotive vehicles, the steering system typically includes an input shaft connected to the steering wheel. The input shaft is then connected to an output shaft through a torsion bar and the output shaft, in turn, is mechanically connected through linkage to the vehicle wheels. Consequently, rotation of the steering wheel pivots the wheels of the automotive vehicle through the torsion bar, output shaft, and steering linkage. 
     In many situations, it is highly desirable to determine the angular deflection between the input shaft and output shaft of the steering mechanism. The degree of angular deflection between the input shaft and output shaft, i.e. the angular deflection of the torsion bar, is utilized by the vehicle management system to determine the steering wheel torque and the amount of assist provided by the power steering. For example, rotation of the vehicle if stopped or nearly stopped, e.g. during a vehicle parking situation, typically creates a relatively high angular deflection between the input and output shaft thus calling for increased power assistance for turning the vehicle wheels. This deflection, furthermore, rarely exceeds about 20 degrees. 
     In addition to the angular deflection between the input shaft and output shaft of the steering, in many situations it is desirable to know the angular position of the vehicle wheels. Since the steering wheel typically can completely rotate three to four revolutions, it is necessary to keep track of the revolution count in order to determine the absolute angular position of the vehicle wheels. 
     There have been previously known systems which are capable of monitoring the angular deflection between the input and output shafts of the steering wheel. These previously known systems typically employ a transducer which measures the angular torque between the steering input and output shafts. However, since the steering output shaft can rotate up to three or four times, it has been necessary for the previously known devices to provide a long length of electrical cable, typically ribbon cable, within the steering column. Sufficient ribbon cable was provided so that the ribbon cable could wind around the steering column two or three times to accommodate multiple rotations of the steering wheel. 
     This previously known solution, however, has not proven wholly satisfactory in use. For example, it is possible for the electrical connector to become entangled after extended use which can entrap or even destroy the electrical connection between the cable and the angle sensor between the steering input and output shafts. When this occurs, the overall operation of the torque sensor for the steering system is compromised. 
     Similarly, there have been previously known systems which provide an output signal representative of the angular position of the vehicle wheels during multiple rotations of the steering wheel. These previously known systems, however, have proven to be unduly complex and expensive in construction. 
     SUMMARY OF THE PRESENT INVENTION 
     The present invention provides both a torque sensor and a wheel position sensor which overcome the above-mentioned disadvantages of the previously known devices. 
     In brief, in the present invention a combination transmitter/receiver coil is coaxially mounted around the vehicle steering column which includes both the input shaft, output shaft, and the torsion bar which connects the input shaft and output shaft together. This transmitter/receiver coil, furthermore, is stationary relative to the vehicle and thus relative to the steering column. 
     Preferably, the transmitter/receiver coil comprises a PCB having a conductive trace which forms a coiled loop coaxial with the steering column. An electronic circuit, such as an ASIC, is electrically connected to the transmitter/receiver coil. This receiver coil, in turn, is electrically connected to the engine control unit (ECU) which controls the overall operation of the vehicle. 
     A floating PCB containing both an RX coil and a receiving coil is then coaxially mounted to the output shaft so that the second PCB rotates in unison with the second output shaft. The RX coil is circular in configuration. However, the receiving coil includes at least two oppositely wound receiving coils, and more preferably eight or so oppositely wound receiving coils, that are also coaxially disposed around the output shaft. Since both the RX coil and receiving coil are formed on the second PCB and the second PCB is connected to the output shaft, both the receiving coil and RX coil rotate in unison with the output shaft. Both the RX coil and receiving coil, furthermore, are coupled to an electronic circuit, such as an ASIC, also mounted to the second PCB. 
     An electrically conductive multi lobe coupler is mounted to the input shaft so that the inductive coupler overlies the receiving coil on the floating PCB attached to the output shaft. The angle between the coupler and the receiving coil represents the torque angle between the input and output shafts. 
     In operation, the transmitter/receiver coil on the fixed PCB is energized at a high frequency, e.g. 2-4 megahertz. The electromagnetic energy generated by the transmitter/receiver coil in turn energizes the RX coil on the floating PCB which electrically powers the circuit on the floating PCB. The floating PCB also contains circuitry, such as an ASIC, to determine the angular position between the input shaft and output shaft as a function of the voltage on the receiving coil. 
     The second circuit then generates a digital output signal at a predefined baud rate modulated by the same frequency as the transmission frequency on the transmitter/receiver coil on the fixed PCB. The circuitry on the fixed PCB demodulates the signal from the floating PCB to provide the desired information to the vehicle ECU. 
     Although the torque sensor, i.e. the angle between the input and output shafts, is preferably detected by an inductive sensor, other types of sensors, such as a Hall sensor, may alternatively be used. 
     Since the circuit on the floating PCB board is completely powered by the electromagnetic transmission from the fixed PCB and the data is also communicated by the electromagnetic transmission between the fixed and floating PCBs, the previously known requirement of an extra long electrical connector to allow multiple rotation of the steering column is completely avoided. Instead, the only electrical connection utilized by the present invention is the electrical connection from the fixed PCB. 
     In order to determine the actual angular position of the wheels, a first gear wheel is preferably mounted to either the input shaft or output shaft so that the gear wheel rotates in unison with either the input or output shaft. This gear wheel, in turn, meshes with a second gear wheel having a different number of teeth. Consequently, the first and second gear wheels rotate at different rotational speeds. 
     A position sensor is associated with each of the gear wheels so that the angular position of both gear wheels can be determined at any time. However, since the gear wheels rotate at different rotational speeds, the actual angular position of the first gear wheel, and thus the angular position of the vehicle wheels, may be precisely determined by sensors up to multiple rotations of the steering input and output shafts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the present invention will be had by reference to the following detailed description when read in conjunction with the accompanying drawing, wherein like reference characters refer to like parts throughout the several views and in which: 
         FIG. 1  is a side diagrammatic view illustrating a preferred embodiment of the invention; 
         FIG. 2  is an elevational view thereof; 
         FIG. 3  is an exploded view of the preferred embodiment; 
         FIG. 4  is a block diagrammatic view illustrating the operation of the invention; 
         FIG. 5  is a schematic view illustrating the operation of the present invention; 
         FIG. 6  is a schematic view illustrating a preferred embodiment of a modulation circuit; 
         FIG. 7  is schematic view of a portion of the fixed PCB; 
         FIG. 8  is an elevational view illustrating a portion of the preferred embodiment of the wheel position sensor; 
         FIG. 9  is a graph illustrating the operation of the wheel position sensor; 
         FIG. 10  is a graph illustrating the signal received by the fixed PCB from the floating PCB for a digital signal; and 
         FIG. 11  is a graph illustrating the signal received by the fixed PCB from the floating PCB for an analog signal. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference first to  FIGS. 1-3 , a steering column  10  of the type used in automotive vehicles is illustrated. The steering column  10  includes an input shaft  12  mechanically connected to a steering wheel  14  and an output shaft  16  which is mechanically connected by a linkage (not shown) to the vehicle wheels. 
     The input shaft  12  and output shaft  16  are axially aligned with each other and are mechanically connected together by a torsion bar  18 . The torsion bar  18  allows the input shaft  12  to rotate slightly relative to the output shaft  16  as a function of the amount of torque applied to the steering wheel  14 . The amount of rotation of the input shaft  12  relative to the output shaft  16 , however, is relatively small, typically not more than 20 degrees. 
     Still referring to  FIGS. 1-3 , a fixed printed circuit board (PCB)  20  is coaxially mounted around the steering column  12 , preferably adjacent one end of the torsion bar  18 . This fixed PCB  20 , furthermore, is fixed relative to the vehicle itself and, thus, does not move relative to the steering column  10 . 
     A circular transmitter/receiver CR coil  22  is formed on the fixed printed circuit board  20  so that the CR coil  22  is coaxial with the steering column  10 . The CR coil  22  is coupled to an electronic circuit  24 , such as an ASIC, which, in turn, is electrically connected by a cable  26  to the electronic control unit  28  for the vehicle. 
     Still referring to  FIGS. 1-3 , a floating PCB  30  is connected to the output shaft  16  so that the floating PCB  30  rotates in unison with the output shaft  16 . A circularly wound RX coil  32  is formed by conductive traces on the PCB board at a position such that the CR coil  22  on the fixed PCB  20  inductively couples, when activated, with the RX coil  32  on the floating PCB  30 . Preferably, the coils  22  and  32  are coaxially aligned with each other. A receiving coil  34  having at least two oppositely wound loops  36  ( FIG. 2 ) is also formed by conductive traces on the floating PCB  30 . 
     An electrically conductive coupler  38  is attached to the input shaft  12  so that the coupler  38  rotates in unison with the input shaft  12 . This coupler  38 , furthermore, may take any of several shapes, such as a multi lobe shape as shown in  FIG. 3 . Since the coupler  38  is attached to the input shaft  12  and the floating PCB  30  attached to the output shaft  16 , the relative angle between the coupler  38  and the floating PCB  30  is proportional to the amount of torque applied to the steering wheel  14 . 
     With reference now to  FIGS. 1-4 , the ASIC  24  on the fixed PCB  20  includes an oscillator  50  which oscillates at a high frequency, e.g. 2-4 megahertz. This oscillator  50  is electrically connected to and thus excites the CR coil  22  on the fixed PCB  20 . 
     The signal generated by the CR coil  22  is inductively coupled to the RX coil  32  on the floating PCB  30 . The RX coil  32 , furthermore, is electrically connected to an ASIC  52  which, through a power regulator  54 , converts the incident electromagnetic radiation from the CR coil  22  to electrical power sufficient to power the ASIC  52  on the floating PCB  30 . Consequently, no external power lines are required to power the second ASIC  52 . 
     The receiving coil  36  on the floating PCB  30  is also electrically connected as an input signal to the second ASIC  52 . Since the receiving coil includes an even number of oppositely wound loops  36  ( FIG. 3 ), the voltage on the receiving coil  36  varies as a function of the rotational position of the coupler  38  relative to the floating PCB  30 . For example, a zero voltage on the receiving coil  32  would be indicative of a zero deflection between the input shaft  12  and output shaft  16  of the steering column  10 , while a positive voltage would be indicative of torque in one direction between the input shaft  12  and output shaft  16 , and a negative voltage would be an indication of torque in the opposite rotational direction between the input shaft  12  and output shaft  16 . 
     With reference now to  FIG. 5 , one scheme, i.e. the Jordi Sacristan-Riquelme system, is illustrated for powering the second ASIC  52  by the transmission of electromagnetic radiation from the CR coil  22  on the fixed PCB  20 . Although the circuitry illustrated in  FIG. 4  is self-explanatory, in brief the oscillator  50  on the first ASIC  24  energizes an LC circuit at its resonant frequency to generate the electromagnetic radiation. That radiation is detected by an LC circuit including the RX coil  32 , to power the second ASIC  52 . 
     With reference now to  FIG. 6 , the second ASIC  52  is programmed to generate a fixed digital signal back to the fixed PCB board  20  at a predefined baud rate, e.g. 50,000 Hz. For example, as shown in  FIG. 6 , the power from the power circuit illustrated in  FIG. 4  is coupled at port  60  in order to power a modulation circuit  62 . A switch  64  is opened and closed at the same frequency as the oscillator  50  to selectively power an RC network. A data input port  66 , however, controls a second switch  68  at the modulation frequency, e.g. 50K, to selectively ground the capacitor Cmod in the RC network. This, in turn, causes a change in amplitude received by the transmitter/receiver CR coil  22  on the fixed PCB  20 . 
     As shown in  FIG. 10 , when the output of ASIC  52  is digital, the data is sent back to the fixed PCB the same way as RFID. The sequence of the binary data is encoded to a waveform per IEEE802.3, the rising edge representing “1”, the falling edge representing “0”. The waveform is then amplitude-modulated to the signal through the circuit shown in  FIG. 6 . ASIC  24  decodes the data in a reversed order, i.e. it demodulates the signal to an encoded waveform using the circuit shown in  FIG. 7 , then decodes the waveform to the binary data sequence. 
     As shown in  FIG. 11 , when the output of ASIC  52  is analog, the result is converted to PWM waveform first, where the duty cycle (td/tp shown in the figure) represents the torsion angle. For example, 50% duty cycle indicates no torsion angle between the input and output shaft. Less than 50% duty cycle indicates the torsion angle in one direction, greater than 50% duty cycle indicates the torsion angle in the other direction. The PWM waveform is then amplitude-modulated to the signal through the circuit shown in  FIG. 6 . ASIC  24  demodulates the signal to PWM waveform using the circuit shown in  FIG. 7  for further signal processing. 
     The circuit may contain a processor programmed to output the magnitude and direction of the angle between the input and output shafts. 
     With reference now to  FIG. 7 , the ASIC  24  on the fixed PCB board receives the signal on the CR coil  22  via an attenuator  70  and then couples the signal through a band pass filter  72  and amplifier  74  as a data output signal on line  26  to the ECU  28 . 
     When both the torque sensor and the angle sensor on the first gear wheel use an inductive sensor, they can share the same transmitter and the same conductive coupler. Such arrangement saves components and completely eliminates the possible interference between those two sensors. 
     From the foregoing, it can be seen that the present invention provides an effective torque sensor for two rotating elements that are connected together by a torsion bar, such as a steering column in an automotive vehicle. Since the rotating portion of the sensor, i.e. the floating PCB, is completely powered by incident radiation from the fixed PCB  20 , the use of extraneous wires to power the ASIC  52  on the floating PCB  30  is rendered unnecessary. 
     It will also be understood that, even though the sensor for the relative angle between the input shaft  12  and the output shaft  16  has been described as an inductive sensor, other sensors may be used without deviation from the spirit of the invention. For example, Hall effect sensors may alternatively be used to detect the angle between the input shaft  12  and the output shaft  16 . Still other types of sensors may also alternatively be used. 
     With reference now to  FIG. 8 , in many applications, such as an automotive steering column, the output shaft  16  may rotate a number of revolutions. In order to determine the actual angular position of the vehicle wheels, it is necessary to not only know the instantaneous angular position of the output shaft  16 , but also the number of rotations of the output shaft  16  from a known position. 
     In order to determine the number of rotations of the output shaft  16 , a first pinion  80  is attached to the output shaft  16  (or input shaft  12 ) so that the pinion  80  rotates in unison with the output shaft  16 . This pinion  80 , furthermore, has a known predetermined number of teeth. 
     The first pinion  80  meshes with a second pinion  82  that is rotatable about a fixed axis in the vehicle. The second pinion  82 , however, has a different number of teeth from the first pinion  80  so that the pinions  80  and  82  rotate at different rotational speeds. 
     As best shown in  FIG. 9 , the actual angular positions of the two pinions  80  and  82  are shown over a plurality of rotations, for example four rotations. As shown in  FIG. 8 , the actual angular positions of both pinions  80  and  82  are only the same at a predetermined number of full revolutions of the output shaft  16 . 
     A sensor  84 , which may be any kind of conventional sensor, is operatively coupled with both pinions  80  and  82  so that the sensor  84  can determine the rotational position of both pinions  80  and  82  at any time. Given the positions of the sensors  80  and  82  at any given time, the actual rotational position and number of rotations of the output shaft  16  can be determined from the chart shown in  FIG. 8  as programmed by an appropriate processor. 
     Consequently, with both the torque sensor illustrated in  FIGS. 1-6 , and the position illustrated in  FIGS. 7-8 , all desired information from the steering system of an automotive vehicle may be determined for use by the engine ECU. 
     Having described my invention, many modifications thereto will become apparent to those skilled in the art without deviation from the spirit or scope of the appended claims.

Technology Classification (CPC): 6