Abstract:
The present invention relates to an electronic control circuit and method for calibrating a transmission shifter and compensating for temperature variations. The electronic control circuit includes a power supply circuit comprising a bias voltage supply and a voltage surge protection circuit; at least one position sensor that receives a surge-protected output bias voltage from the power supply circuit; and a microprocessor that receives one or more position values from the position sensor relating to the physical position of the transmission shifter. The power supply circuit provides a calibration reference signal to said microprocessor. The voltage surge protection circuit protects the calibration reference signal against a surge voltage condition.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates to electrically actuated shifting mechanisms for automated mechanical transmissions. Specifically, the invention relates to an electronic circuit used to compensate for variations in the calibration of transmission shifters in automobiles or other vehicles as a result of temperature variations in the related electronic circuitry. The invention teaches an electronic circuit and method for providing a feedback calibration reference signal to a microprocessor from a power supply circuit that allows the microprocessor to account for variations in power supply temperature and resulting measurement variations during the shifter calibration process. 
     BACKGROUND 
     Electrically actuated X-Y shifting mechanisms for effecting gear shifts in automated mechanical transmissions are well known in the art. Such mechanisms require positioning calibration in order to insure that operation of the mechanism produces accurate gear shifts. Various methods and algorithms exist for calibrating X-Y shifting mechanisms, and one such method is taught in U.S. Pat. No. 5,350,240, which is assigned to the assignee of the present invention, and incorporated herein by reference. The calibration algorithms are typically performed by a microprocessor that uses input values from one or more position sensors. 
     However, the outputs of position sensors are sensitive to variations in the temperature of the related electronic circuitry and the input power supply. When the temperature of related electronic circuitry and power supply to the position sensors is elevated as compared to ambient conditions, the outputs of the position sensors will be different from the outputs when such components are at a lower temperature, even though the shifter is in the same physical position. Accordingly, it is well-known in the art for the microprocessor to utilize a calibration reference signal to compensate for these temperature-dependent offsets in position sensor outputs. 
     In the prior art, the calibration reference signal is taken directly from the bias voltage signal that powers the position sensors. However, most microprocessors are intolerant to voltage variants above 0.5 volts. Accordingly, most systems require voltage surge protection circuitry between the calibration signal and the microprocessor. One of the problems with this methodology is that the additional circuitry may itself offset the calibration reference signal as a result of its own variations in temperature. Thus, it is desirable to have an electronic calibration circuit that includes a calibration reference signal that is treated as one of the control variables measured at the same time as the position sensors and fed directly to the microprocessor without any intervening circuitry. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an electronic circuit used to calibrate a gear shifter in a transmission. Specifically, the present invention compensates for variations in the measurements provided by the transmission position sensors resulting from differences in the temperatures of the related electronic components at different times. For example, for a vehicle transmission shifter calibrated when the vehicle and related electronic circuitry are at an elevated temperature as compared to ambient conditions, the measurements provided by the shifter position sensors will be different than when the vehicle and related circuitry are at a lower temperature, even though the transmission shifter is in the same physical position. The present invention compensates for that difference and adjusts the transmission shifter position data based upon a feedback calibration reference signal provided to the microprocessor from the power supply circuit. 
     The electronic circuit of the present invention includes a microprocessor for implementing the calibration algorithm for physically adjusting the transmission shifter relative to the various inner wall surfaces of the shift block. The present invention can be used in connection with a variety of calibration algorithms. One such algorithm is taught in U.S. Pat. No. 5,305,240. As input to the calibration algorithm, the microprocessor receives shifter position data from one or more shifter position sensors. The position sensors are powered by a power supply circuit, which includes a bias voltage supply and a voltage surge protection circuit. The voltage surge protection circuit is disposed between the bias voltage supply and the position sensors to protect the bias voltage supply and position sensors from short circuits or transient voltage or surge voltage conditions. A calibration reference signal is measured from the voltage surge protection circuit. The calibration reference signal is derived by scaling the output bias voltage supplied from the bias voltage supply to the position sensors. Because most microprocessors are intolerant to inputs that vary more than 0.5 volts, it is important that microprocessor inputs be protected from voltage surge or transient conditions. However, in this invention, because the calibration reference signal is produced by the voltage surge protection circuit, no additional voltage surge protection is necessary to protect the microprocessor from large swings in input voltage from the calibration reference signal. Accordingly, the calibration reference signal is input directly from the voltage surge protection circuit to the microprocessor through an A-D converter. A corresponding calibration reference signal is fed back to the microprocessor each time the position sensors measure and input position data to the microprocessor. 
     The voltage surge protection circuit of the present invention includes a switch network that initially determines if the position sensors are connected to the circuit and whether a short-circuit or excess current condition exists. If there is no short-circuit or excess current condition, the switch network permits the system to “power up”. If a short-circuit or excess current condition does exist, the switch network prevents the system power supply from providing power to the system. Thus, the bias voltage supply is protected from possible damage from the short-circuit or excess current condition. 
     The voltage surge protection circuit also includes an output current control circuit for controlling the current provided from the bias voltage supply during normal operation and for cutting off the bias voltage supply if a short-circuit or excess current condition is detected during operation. In a preferred embodiment, the output current control circuit includes a bi-polar junction output transistor connected between the system power supply and the load device. The output current of the output transistor depends upon a drive current control signal, which is the output of a drive current control circuit. Preferably, the drive current control circuit includes a pre-drive transistor, which controls the input current to the base of the output transistor, which in turn dictates the output current supplied to the position sensors. 
     During normal operation (i.e., when there is no short-circuit or an excess current condition), the pre-drive transistor determines a stable level of output current to deliver to the position sensors by receiving feedback from the output transistor. It is generally preferred that the output voltage across the position sensors be compared to a pre-determined reference voltage by an operational amplifier. The output of the operational amplifier provides the feedback to and activates the pre-drive transistor. As the output voltage across the load device approaches the pre-determined reference voltage, the currents through the pre-drive transistor and the output transistor decrease until the output voltage stabilizes. 
     If a short-circuit or excess current situation occurs, the drive current control signal deactivates the output transistor, cutting off all current flow to the position sensors. The output transistor remains deactivated until the short-circuit or excess current situation is eliminated, at which time, the switch network reactivates the circuit. 
     During system operation, the position sensors measure the physical position of the transmission shifter and input the position data to the microprocessor through an A-D converter. When the vehicle is turned off, the last set of shifter position data and the corresponding calibration reference signal are stored in a memory device. When the vehicle is turned back on and the vehicle electronics are at an ambient temperature (“cold”), the shifter position data measured by the sensors will be different from that which was measured when the vehicle was at an elevated operational temperature (“hot”), even though the physical position of the transmission shifter is the same. The microprocessor compares the calibration reference signal stored when the “hot” position data was measured with the calibration reference signal measured when the vehicle is cold. Based upon the difference in the calibration reference signals, the microprocessor adjusts the stored shifter position data. Because the calibration reference signal is input directly to the microprocessor from the voltage surge protection circuit, the potential for offset variants of the calibration reference signal resulting from additional surge protection circuitry between the calibration reference signal and the microprocessor is eliminated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a blocked diagram of the electronic circuit according to a preferred embodiment of the present invention. 
     FIG. 2 shows a blocked diagram of the power supply circuit according to a preferred embodiment of the present invention. 
     FIG. 3 shows a schematic diagram of the power supply circuit according to a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to FIG.  1  and FIG. 2, an electronic circuit  1  according to a preferred embodiment of the invention comprises a power supply circuit  10  which itself comprises a bias voltage supply  20  with a voltage surge protection circuit  11 . As discussed in greater detail below, circuit  10  includes an output current control circuit  12 , a comparison circuit  14 , a drive current control circuit  16  and a switch network  18 . The electronic circuit  1  also comprises an x-position sensor  2  and a y-position sensor  3 , which are both powered by the power supply circuit  10  and provide position data to an A-D converter  4  and microprocessor  5 . The power supply circuit  10 , and specifically the comparison circuit  14  of surge protection circuit  10 , provides a calibration reference signal  6  to the A-D converter  4  and microprocessor  5 . 
     With reference to FIG. 2, power supply circuit  10 , according to a preferred embodiment of the invention, comprises a bias voltage supply  20 ; an output current control circuit  12  connected between the bias voltage supply and position sensors  2 ,  3  for controlling the level of output current supplied to the sensors  2 ,  3 ; a comparison circuit  14  for comparing the voltage across the sensors  2 ,  3  with a pre-determined reference voltage to provide a voltage stabilization control signal; a drive current control circuit  16  responsive to the stabilization control signal for providing a drive current control signal to the output current control circuit  12 ; and a switch network  18  connected to the drive current control circuit  16  to selectively activate the power supply circuit  10 . In the disclosed embodiment, it is assumed that the bias voltage supply  20  is a common automobile 12-volt battery. 
     Referring to FIG. 3, which shows circuit  10  in detail, bias voltage supply  20  with output potential V L  provides output current to sensors  2 ,  3  through a resistor R 1  and an output transistor Q 1 , which together comprise the output current control circuit  12 . The output potential Vout across the sensors  2 ,  3  is scaled by a voltage divider R 4 /R 5  comprising resistors R 4  and R 5 . A reference voltage Vcc is scaled by a voltage divider R 6 /R 7  comprising resistors R 6  and R 7 . The scaled output voltage Vout and the scaled reference voltage Vcc comprise inverting  24  and non-inverting  25  inputs, respectively, to an operational amplifier U 1 . Together, the R 4 /R 5  voltage divider, the R 6 /R 7  voltage divider, and operation amplifier U 1  comprise the comparison circuit  14 . Calibration reference signal  6  is taken as the output of the R 4 /R 5  voltage divider. 
     The output of U 1  provides current to the base terminal of a pre-drive transistor Q 3 . The collector terminal of transistor Q 3  is connected to resistor R 3 , which is connected to resistor R 2 , which is connected to the bias voltage supply  20 . The potential at the R 2 /R 3  node provides the input to the base terminal of transistor Q 1 . Resistor R 2 , R 3 , and transistor Q 3  comprise the drive current control circuit  16 . Transistor Q 1  comprises the output current control circuit  12 . 
     The switch network  18  comprises resistor R 10 , diodes D 1  and D 2 , and switch transistor Q 2 . The emitter terminal of transistor Q 3  is connected to the collector terminal of switch transistor Q 2 , and the emitter terminal of transistor Q 2  is connected to ground. Vcc provides current through resistor R 10  and diode D 1  to the base terminal of transistor Q 2 . Vcc is also connected through resistor R 10  and diode D 2  to the Vout node. 
     When a short-circuit or excess current condition exists at the sensors  2 ,  3 , the switch network  18  passes bias current from Vcc through transistor R 10  and diode D 2  because the Vout potential is close to zero. During this condition, transistor Q 2  is inactive because there is insufficient current being delivered to the base of transistor Q 2  to activate it. Accordingly, transistor Q 2  cuts off the path to ground from transistor Q 3 , which essentially makes the power supply circuit  10  inactive and cuts off the bias voltage supply  20  from the sensors  2 ,  3 . Thus, the power supply circuit  10  is prevented from “powering up” if there is a short-circuit or excess current condition. 
     Assuming that sensors  2 ,  3  provide sufficient resistance to reduce the load current and increase the Vout potential to a level greater than two diode junction voltage drops (diode D 1  and the emitter of transistor Q 2 ), transistor Q 2  is activated, providing a current flow path from transistor Q 3  to ground. The collector current of transistor Q 3  is delivered from V L  through resistors R 2  and R 3 . As a result, a drive current is delivered to the base of transistor Q 1 , which causes output current to be delivered to the sensors  2 ,  3  and Vout to increase. 
     The rising potential at the Vout node is scaled by the R 4 /R 5  voltage divider. In the preferred embodiment, resistors R 4  and R 5  are of equal magnitudes so as to scale Vout down by one half. Similarly, the Vcc potential is scaled down by the R 6 /R 7  voltage divider. In the preferred embodiment, R 6  and R 7  are of equal magnitudes so as to scale Vcc by one half. The difference between the scaled Vcc and Vout potentials comprises the input to amplifier U 1 . The amplified difference is applied to the base of transistor Q 3 . The current supplied to the base of transistor Q 3  controls the current drawn by the collector of transistor Q 3  and thus the voltage drops across resistors R 2  and R 3 . The potential at the R 2 /R 3  node controls the activation of transistor Q 1 . As current is supplied to the sensors  2 ,  3  and the Vout potential increases, the difference voltage input to amplifier U 1  decreases. As a result, emitter current of transistor Q 3  decreases until a stable Vout potential is established. In the preferred embodiment, the stable Vout potential is approximately 5 volts. After a stable Vout is achieved, the system operates in steady state until a short-circuit or excess current condition is detected. 
     If a short-circuit or excess current condition occurs at the sensors  2 ,  3 , the voltage surge protection circuit  11  shuts down and cuts the bias voltage supply  20  off from the short-circuit or excess current condition. In such a situation, the short-circuit or excess current condition at the sensors  2 ,  3  causes the current pushed through resistor R 1  to increase and the voltage drop across R 1  to increase. This removes potential for bias current from transistor Q 3 . As collector current of transistor Q 3  decreases, the potential at the R 2 /R 3  node decreases, driving transistor Q 1  into cutoff. As cutoff is approached, emitter current of transistor Q 1  is reduced, and the Vout potential approaches zero. As the Vout potential decreases, current from Vcc is drawn away from the base of transistor Q 2  until the transistor is deactivated. Once the short-circuit or excess current condition is eliminated, the switch network  18  reactivates the circuit  10 , as described above. 
     In a preferred embodiment of the invention, additional components are included in the control circuit  10  for such things as temperature compensation, device gain variances, general circuit stabilization, and protection against short circuits to high voltage or reverse polarity. Specifically, linear three-terminal voltage regulator U 2  is connected between the collector of transistor Q 1  and the Vout node. Regulator U 2  provides a high precision output voltage and closely regulates Vout to a stable voltage while maintaining the short-circuit and over-current protection features of the invention. A resistor R 11  is connected in parallel with sensors  2 , 3  to stabilize the circuit by dampening any overshooting of the 5-volt stabilized Vout potential on initial power-up of the control circuit  10 . Capacitors C 4  and C 5  are also connected in parallel with sensors  2 ,  3  and resistor R 11  to prevent the control circuit  10  from oscillating as a result of the high gain in the system. Capacitor C 3  is connected between the inverting input node of amplifier U 1  and ground, and it acts as a filter against negative input to the system. A diode D 3  is connected between a resistor R 8  and the base terminal of transistor Q 3  to prevent back leakage from the collector of transistor Q 3  when transistor Q 2  cuts off. The base terminal of transistor Q 3  is connected to reference ground through a resistor R 9 , and resistor R 9  acts as an emitter follower to stabilize potential gain at high temperatures. A diode D 4  is connected between the inverting input to amplifier U 1  and Vcc to clamp the Vout potential at its stable voltage and prevent damage from electrostatic discharge. A diode D 5  is connected between an inverting input node  24  of amplifier U 1  and resistor R 9 , providing a flow path from the base of transistor Q 3  to the inverting input node  24  and preventing back leakage. Diode D 5  also prevents the bias on inverting input node  24  from exceeding one diode drop below ground. A capacitor C 1  is connected across inverting input node  24  and an output terminal  26  of amplifier U 1 , and a capacitor C 2  is connected in parallel with resistor R 4 . Capacitors C 1  and C 2  maintain a stable circuit by reducing unwanted oscillations. R 12  is connected between the inverting input  24  and the A-D converter  4  to protect the A-D converter  4  from potential electrostatic discharge damage. 
     During operation, power supply circuit  10  provides power to sensors  2 ,  3  from bias voltage supply  20  through voltage surge protection circuit  11 . Sensors  2 ,  3  detect the physical position of the transmission shifter (not shown) and provide related position data to microprocessor  5  through A-D converter  4 . A calibration reference value is provided by calibration reference signal  6  to microprocessor  5  through A-D converter  4 . Microprocessor  5  implements one of a variety of available calibration algorithms, such as the one disclosed in U.S. Pat. No. 5,305,240, for example. The position data for each measurement and the calibration reference value may be stored in memory devices (not shown). 
     When the vehicle is turned off, the vehicle, transmission and associated electronic circuitry all cool down to an ambient temperature. When the vehicle is turned back on, the bias voltage supply  20  has an offset in output bias voltage compared to when the bias voltage supply  20  was at an elevated temperature compared to ambient. The shift in output voltage causes the sensors  2 ,  3  to provide different position measurements to the microprocessor  5  even though the physical position of the transmission shifter is the same. When the vehicle is turned back on, calibration reference signal  6  provides a new calibration reference value to the microprocessor  5 . The microprocessor  5  compares the new calibration reference value to the previous calibration reference value. Based upon the difference between the two calibration reference values, the microprocessor adjusts the stored position values provided by the sensors  2 ,  3  according to methods that are well-known in the art. 
     One of the benefits of the present invention is that calibration reference signal  6  is directly derived from Vout and it is protected against voltage surges and transients by voltage surge protection circuit  11 . Thus, the need for additional surge protection circuitry between the calibration reference signal  6  and the microprocessor  5  is eliminated, which in turn eliminates the undesirable possibility of calibration reference signal  6  being offset by additional surge protection circuitry prior to reaching microprocessor  5 . As a result, the adjustments to the position data made by the microprocessor  5  are more accurate and the system overall becomes more stable as compared to prior art systems. 
     Furthermore, the present invention provides a mechanism for monitoring and adjusting Vout based upon the feedback signal provided to the base of transistor Q 3 . Because the feedback signal provided to the base of transistor Q 3  is a function of inverting input  24  of amplifier U 1 , any load or temperature effects of microprocessor  5  on calibration signal  6  will affect the feedback signal provided to the base of transistor Q 3  and assist to stabilize the system. 
     While preferred embodiments of the present invention have been described herein, it is apparent that the basic construction can be altered to provide other embodiments which utilize the processes and compositions of this invention. Therefore, it will be appreciated that the scope of this invention is to be defined by the claims appended hereto rather than by the specific embodiments which have been presented hereinbefore by way of example.