Abstract:
A system of transmitting a plurality of movement parameters of a vehicle. The system includes a supply terminal, a plurality of sensing elements, a modulation circuit, and a return terminal. The supply terminal is coupled to a power source to receive power. The sensing elements receive power from the supply terminal. Each of the sensing elements senses a movement characteristic of the vehicle, and generates movement signals indicative of the sensed movement characteristic. The modulation circuit is coupled to the sensing elements to modulate the movement signals based on the plurality of sensing elements. The return terminal is coupled to the modulation circuit to output the modulated movement signals.

Description:
BACKGROUND 
   Embodiments of the invention relate to sensing systems, particularly, to sensing systems having a 2-wire interface. 
   One type of sensing system in a vehicle uses Hall effect sensors to measure rotational velocities exhibited by electric motors. Hall effect sensors are typically placed near ring magnets of the motors to measure rotation velocities. When a motor armature rotates, poles (North and South) of ring magnets pass by the Hall effect sensors. In turn, rates at which the poles pass by the Hall effect sensors are measured. 
   Ring magnets often have a fixed number of magnetic poles that is generally predetermined when motors are constructed. Different motors have different ring magnets, and thus a different number of magnetic poles. As such, knowing the number of magnetic poles can assist in determining motor speeds, for example, by measuring times between output pulses generated by the Hall effect sensors. 
   In some instances, motors have two Hall effect sensors positioned to measure information such as direction and speed of the motor. For example, Hall effect sensors are placed near ring magnets such that outputs of the Hall effect sensors are phased 90 degrees apart. Placing Hall effect sensors 90 degrees apart allows one of the Hall sensors to sense information such as the speed of the motor, and the other Hall sensor to sense other information such as direction of the motor. The physical location of the Hall effect sensors provide an indication of an order of the output pulses, which in turn provides an indication of the direction of the motor. 
   Some motor sensing implementations use a sensor that incorporates two Hall effect sensors in a single package. These sensors typically have two outputs. One of the outputs is a pulse train that indicates a speed of the motor, while the other output indicates a rotational direction of the motor. For example, a high output voltage can indicate a clockwise rotation, and a low output voltage can indicate a counter-clockwise rotation of the motor. Outputs such as speed and direction of motors are subsequently communicated through some electrical wire connection interface to an electronic control unit for further processing. Some implementations use four-wire connections. In such cases, the first of the four-wire connections supplies a voltage to both Hall sensors; the second of the four-wire connections provides a ground for both Hall sensors; the third of the four-wire connections provides an output for speed information; and, the fourth of the four-wire connections provides an output for directional information. Other implementations use a three-wire connection interface. In such cases, one of the three-wire connections provides a ground for both Hall effect sensors, another connection acts both as an output for speed information and as a voltage supply for both Hall effect sensors, and the third connection acts as an output for directional information and as a voltage supply for both Hall effect sensors. 
   SUMMARY 
   Although 4 wire sensing systems are functional, multiple-wire configurations are less than ideal and using multiple wires often leads to increased cost and weight. Thus it would be beneficial to have a sensing system that can function with a two-wire interface and still provide both speed and direction information to an electronic control unit. 
   In one embodiment, the invention provides a system of transmitting a plurality of movement parameters of a vehicle. The system includes a supply terminal, a plurality of sensing elements, a multiplexing or multiplex circuit, and a return terminal. The supply terminal is coupled to a power source to receive power. The sensing elements receive power from the supply terminal. Each of the sensing elements senses a movement characteristic of the vehicle, and generates movement signals indicative of the sensed movement characteristic. The multiplex circuit is coupled to the sensing elements to multiplex the movement signals based on the plurality of sensing elements onto the supply terminal. The second terminal output supplies the ground return. 
   In another embodiment, the invention provides a method for transmitting a plurality of movement parameters of a vehicle. The method includes supplying power to a supply terminal, and sensing a plurality of movement characteristics of the vehicle at a plurality of sensing elements coupled to the supply terminal. The method also includes generating movement signals indicative of the sensed movement characteristics, multiplexing the movement signals based on the plurality of sensing elements, and outputting the multiplexed movement signals through a return terminal. 
   In yet another embodiment, the invention provides a two-wire sensor that includes a first terminal, a first sensing element, a second sensing element, a multiplex circuit, and a second terminal. The first terminal is coupled to a power source to receive power from the power source. The first sensing element is coupled to the first terminal to receive power, and to sense a first characteristic and generates a first signal indicative of the first characteristic. The second sensing element is coupled to the first terminal to receive power, and senses a second characteristic and to generate a second signal indicative of the second characteristic. The multiplex circuit combines at least one of the first and second sensing elements into a multiplexed signal. The second terminal output supplies the ground return. 
   Other aspects of embodiments of the invention will become apparent by consideration of the detailed description and accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a schematic plan view of an exemplary vehicle. 
       FIG. 2  shows an exemplary two-wire sensing system. 
       FIG. 3  shows an output table for the two-wire sensing system of  FIG. 2 . 
       FIG. 4  shows an exemplary output current plot for the two-wire sensing system of  FIG. 2 . 
       FIG. 5  shows an exemplary receiver, demodulator, or de-multiplexer of the 2-wire sensing system. 
   

   DETAILED DESCRIPTION 
   Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
   Embodiments of the invention provides a method and a system for transmitting rotational speed and direction information via a 2-wire interface. In one particular embodiment, the system includes two terminals that act as power inputs, a sensed signal output, and a signal return. 
     FIG. 1  shows a schematic plan view of an exemplary vehicle  100 . The vehicle  100  has four wheels  104 A,  104 B,  104 C, and  104 D. The wheels  104 A,  104 B,  104 C, and  104 D are monitored by a plurality of wheel sensors  112 A,  112 B,  112 C, and  112 D. The wheel sensors  112 A,  112 B,  112 C, and  112 D are coupled to an electronic processing unit (“ECU”)  116 . The vehicle  100  also includes other sensors such as a steering wheel sensor  128 , a plurality of front window sensors  132 , and a plurality of rear window sensors  136 . The wheel sensors  112 A,  112 B,  112 C, and  112 D, the steering wheel sensor  128 , the front window sensors  132 , and the rear window sensors  136  are shown as individual sensors generically. These sensors  112 A,  112 B,  112 C,  112 D,  128 ,  132 , and  136  can also include multiple sensors in a plurality of sensor arrays that may be coupled to the ECU  116 . Although  FIG. 1  shows only the sensors  112 A,  112 B,  112 C,  112 D,  128 ,  132 , and  136 , other types of sensors such as seat-adjuster sensor, restraint device sensors, sunroof sensors, power sliding doors, power tailgate, and windshield wiper sensors can also be used in the vehicle  100 . 
   In the embodiment shown, the sensors  132  are included in a motor for driving a window (not shown) of the vehicle  100 . The sensors  132  are typically Hall effect sensors. In such cases, the sensors  132  detect and monitor a plurality of specific conditions of the window motor. For example, the sensors  132  are used to sense conditions of the window that are indicative of an amount of traveling velocity and a position of the window. Sensed conditions are then transduced and converted into signals that are indicative of the amount of traveling velocity and position of the window. Of course, the vehicle  100  may include other motors that have sensors. Examples of such motors include seat-adjusters, restraint devices, sunroofs, power sliding doors, power tailgate, and windshield wipers. 
     FIG. 2  shows an exemplary two-wire sensing system  200  that can be implemented in conjunction with a motor (not shown) such as the window driving motor in the vehicle  100  of  FIG. 1 . Although the two-wire sensing system  200  is shown directly coupled to the ECU  116  of  FIG. 1 , the two-wire sensing system  200  can also be coupled to the ECU  116  via other circuits in other embodiments, detailed hereinafter. In the embodiment shown, the two-wire sensing system  200  includes a sensor package  204  that incorporates therein a plurality of sensors  205 ,  206  (in this instance, the sensors  132  of  FIG. 1 ). An example of the sensor package  204  is an Infineon TLE4966H integrated circuit or an Infineon TLE4966L integrated circuit. In other embodiments, however, the two-wire sensing system  200  includes individual circuit components such as such as a plurality of individual Hall effect sensors and switches, rather than a prepackaged sensor package. 
   The sensor package  204  also includes first and second transistors or switches  208  and  212 . In the embodiment shown, the sensor package  204  has a power supply pin  216 , a ground pin  220 , a first switch pin  224 , and a second switch pin  228 . After the sensor package  204  has been powered through the power supply pin  216  and the ground pin  220 , and when the motor starts to rotate, the sensors  205 ,  206  are activated to sense a plurality of movement conditions or characteristics of the motor, such as speed, rotational direction, and proximity. The sensors  205 ,  206  then generate a plurality of outputs based on the sensed conditions. In some embodiments, the outputs from the sensors  205 ,  206  are in the form of pulses. In such cases, the output pulses generally represent the sensed conditions of the motor. For example, measuring a time between the output pulses yields a speed of the motor. For another example, measuring an order of the pulses yields a rotational direction of the motor. In the embodiment shown, the sensor  205  is a speed sensor that senses a speed of the motor, and the sensor  206  is a rotational direction sensor that senses a rotational direction of the motor. 
   In the embodiment shown, the power supply pin  216 , the ground pin  220 , the first switch pin  224 , and the second switch pin  228  are coupled to an interface module  232  to modulate or multiplex the outputs of the sensors  205 ,  206 . The interface module  232  includes first and second terminals  236 ,  240 . The first terminal  236  is generally considered a supply terminal for the two-wire sensing system  200 , and is connected to a power supply (not shown). The second terminal is generally considered a ground or return terminal, which also acts as an output terminal for the two-wire sensing system  200 . Similarly the first terminal  236  can also act as an output terminal for the two-wire sensing system  200 . 
   The interface module  232  generally includes a plurality of current sources  248 ,  252  to draw different amounts of current from the first terminal  236  to the switches  208 ,  212 . Particularly, depending on the output of the sensors  205 ,  206 , different amounts of current are drawn to signify a type of output generated by the sensors  205 ,  206 , detailed hereinafter. In the embodiment shown, the current sources  248 ,  252  are in the form of first and second resistors, respectively. Depending on the sensors  205 ,  206 , different resistor values are used for the respective outputs from the speed sensor  205  and the directional sensor  206 . In this way, different amounts of current can be drawn from the first terminal  236  depending on which of the outputs is active. In the embodiment shown with the sensor package  204 , the first current source resistor  248  has a value of 249Ω, and the second current source resistor  252  has a value of 511Ω. 
   As the motor rotates in a direction at a speed, the sensors  205 ,  206  are selectively activated to generate a plurality of active outputs signals. When the sensors  205 ,  206  are selectively generating the outputs, the outputs in turn activates the switches  208  and  212 . Due to the different resistive values of the first and second current source resistors  248 ,  252 , different amounts of currents are drawn from the first terminal  236 , and appear at the second terminal  240 .  FIG. 3  shows a table  300  indicating all possible combinations of active and inactive sensors  205 ,  206 . Since there are two sensors  205 ,  206 , there are four possible states. For example, a first state  304  indicates both of the sensors  205 ,  206  are inactive. A second state  308  indicates only the directional sensor  206  is active. A third state  312  indicates only the speed sensor  205  is active. A fourth state  316  indicates both of the sensors  205 ,  206  are active. 
     FIG. 4  shows an exemplary output current level plot  400  for the two-wire sensing system  200  of  FIG. 2 . As discussed earlier, the resistor values of the resistors  248 ,  252  are chosen such that the four different states  304 ,  308 ,  312 ,  316  as shown in  FIG. 3  have non-overlapping current boundaries based on circuit element tolerances. In this way, the ECU  116  of  FIG. 1  can accurately demodulate or de-multiplex the outputs. 
   In the embodiment shown in  FIG. 2 , the output generated by the speed sensor  205  is configured to draw more current than the output generated by the direction sensor  206 . In this way, outputs having a relatively high current level can be directly interpreted by the ECU  116  without knowing if the directional sensor  206  is active or inactive. As such, a single threshold can be set between a maximum current value generated by only the directional sensor  206  and a minimum current value generated by only the speed sensor  205 . In the embodiment shown in  FIG. 2 , an exemplary level  404  positioned between a maximum current value generated by only the directional sensor  206  and a minimum current value generated by only the speed sensor  205  is shown as threshold A in  FIG. 4 . Accordingly, the ECU  116  will recognize that a speed of the motor is available when the current level of the output pulses is above threshold A or level  404 . Moreover, since speed is often required in processing decisions, having a threshold such as level  404  allows information regarding the speed of the motor to be communicated to and processed by the ECU  116  directly and with minimum or no delay. 
   As for the outputs generated by the directional sensor  206 , two levels or thresholds are used to differentiate between inactive and active states. For example, a second level  408  (threshold B) can be positioned between a maximum current value generated by only the speed sensor  205 , and a minimum current value generated by both the speed sensor  205  and the directional sensor  206 . In other embodiments, the level  408  can also be positioned above the maximum current value generated by only the speed sensor  205 . Similarly, a third level  412  (threshold C) can be positioned between a maximum current value that can be generated by both inactive sensors  205 ,  206 , and a minimum current value generated by only an active directional sensor  206 . In some embodiments, the level  412  can also be positioned just above the maximum current value that can be generated by both inactive sensors  205 ,  206 . Once the ECU  116  has determined that the current level of the output is above level  208 , the ECU  116  recognizes that the directional sensor  206  is active. For example, if an inactive directional sensor  206  indicates a counter-clockwise rotation, the motor is rotating clockwise when the current value of the output is above level  208 . 
   Although the ECU  116  can de-multiplex the outputs generated by the 2-wire sensing system  200  of  FIG. 2 , other optional circuits can also be used to receive the outputs.  FIG. 5  shows an exemplary embodiment of a receiver, demodulator, or de-multiplexer  500  that receives and demodulates or de-multiplexes the outputs of the 2-wire sensing system  200  of  FIG. 2 . In the embodiment shown, a third resistor  504  is connected in series with the first terminal  236  to sense a change in the amount of current drawn from the 2-wire sensing system  200 . The third resistor  504  is sized such that current drawn by the third resistor does not reduce the output voltage between terminals  236  and  240  below the minimum operating voltage required by the sensing system  200  when the maximum amount of current is drawn by the sensing system  200 . In other embodiments, the third resistor  504  is connected in series with the second terminal  240  to sense a change in the amount of current drawn from the 2-wire sensing system  200 . Furthermore, the outputs from the 2-wire sensing system  200  are amplified in an amplifier section  508  based on applications and components selected for the 2-wire sensing system  200 . In some embodiments, the amplifier section  508  includes an LM2904 operational amplifier. 
   After the outputs have been amplified by the amplifier section  508 , the amplified outputs are optionally demodulated or de-multiplexed with a comparator section  512 . As discussed earlier, the speed information from the speed sensor  205  can be readily determined by comparing the current level of the outputs with the threshold A or the level  404 . The comparator  512 , as shown in  FIG. 5 , compares the current level of the outputs with a fixed current amount indicative of the threshold A. In some embodiments, the comparator  512  includes an LM2904 operational amplifier. Also as discussed earlier, the directional information can be readily extracted from the amplified outputs by the ECU  116  depending on the current level of the outputs. Optionally, the direction information can be determined with a comparator (not shown) that has an adjustable threshold based on the output of the speed sensor  205 . In some embodiments, the directional information from the directional sensor  206  is an analog signal. 
   Various features and advantages of the invention are set forth in the following claims.