Patent Document

[0001]    The present application claims priority from U.S. Ser. No. 60/876,900 filed on Dec. 22, 2006, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present application relates to systems for connecting remote sensors to electronic controllers and, more particularly, to systems for connecting remote sensors to electronic controllers having a single wire connection and improved signal to noise immunity. 
         [0003]    Referring to  FIG. 1 , a typical prior art sensor to controller connection system, generally designated  10 , includes a remote sensor  12 , an electronic controller  14  and a battery  16  and is connected to ground  18 . The wiring inductance L W , wiring resistance R W  and current noise source N of the system  10  represent ground noise created by transient currents in the ground path of the controller  14 . For example, a controller powering a motor load (not shown) may experience ground noise in excess of about  1  V (positive or negative). 
         [0004]    The input signal from the sensor  12  to the controller  14  is typically a relatively high impedance signal that does not allow significant current flow and, therefore, is sensitive to noise. For example, an input signal of 0.5 V to the sensor  12  may facilitate a current flow of only about 50 microamps, which is sufficiently low to be subject to ground noise. Therefore, to minimize the ground noise interference with the signal generated by the sensor  12 , a three wire connector  20  (e.g., a three pin connector) is used to supply power, by way of battery  16  and voltage regulator  17 , and ground to the sensor  12  from the controller  14  over first and second wires  22 ,  24 , while the sensor  12  supplies a signal to the controller  14  over the third wire  26 . Ideally, the three wires  22 ,  24 ,  26  are twisted together to minimize external electrical interference. 
         [0005]    Thus, the three wire system of  FIG. 1  requires increased wiring and connector cost and a significant amount of care to reduce signal noise issues. 
         [0006]    Referring to  FIG. 2 , a first alternative prior art sensor to controller connection system, generally designated  50 , includes a remote sensor  52 , an electronic controller  54  and a battery  56  and is connected to ground  58 . The wiring inductance L W , wiring resistance R W  and current noise source N of the system  50  represent ground noise created by transient currents in the ground path of the controller  54 . 
         [0007]    The sensor  52  includes a voltage regulator  60  and a pulse width modulation (“PWM”) generator  62  and may be directly connected to the battery  56  and ground  58  (e.g., by way of lines  63 ,  64 , respectively). The voltage regulator  60  regulates the battery voltage to the desired output voltage V OUT , thereby applying the proper voltage to the potentiometer R S  of the sensor  52 . The PWM generator  62  converts the analog sensor signal from the potentiometer R S  to a pulse width modulated signal and communicates the pulse width modulated sensor signal to the controller  54 . The duty cycle of the pulse width modulated sensor signal is proportional to the value of the analog sensor signal value. 
         [0008]    Thus, the connection between the sensor  52  and the controller  54  may be a single wire. Alternatively, as shown by broken line  66 , the sensor  52  may be connected to ground  58  by way of a second wire connection between the sensor  52  and the controller  54 , thereby requiring two wires between the sensor  52  and the controller  54 . Nonetheless, with either a one or two wire connection, design consideration must be given to valid signal voltages such that the signal is guaranteed to be received even in the event of large ground noise transients. Furthermore, a second design consideration requires that the input interface circuit in the controller must not adjust the PWM duty cycle of the sensor signal prior to a microprocessor reading the signal and a third design consideration is the amount of microprocessor throughput which must be used to calculate the PWM duty cycle. Still furthermore, many microprocessors must receive an interrupt at each edge of the pulse width modulated sensor signal to calculate the duty cycle of the signal. Therefore, to transmit a higher bandwidth signal, the PWM frequency must also be higher, which increases the number of microprocessor interrupts and increases the microprocessor throughput utilized to calculate the PWM duty cycle. 
         [0009]    A second alternative prior art sensor to controller connection system (not shown) is a single wire signal solution that sources a current between 4 mA and 20 mA proportional to the linear signal, wherein 4 mA represents no signal and 20 mA represents maximum signal. To provide a signal current of this magnitude requires significant power dissipation in the transistor which supplies the current, which may become cost prohibitive in the automotive environment. 
         [0010]    Accordingly, there is a need for a system for communicating a sensor signal between a sensor and a controller having improved signal to noise immunity and a single wire or pin connection between the sensor and the controller. 
       SUMMARY 
       [0011]    In one aspect, the disclosed sensor to controller connection system may include a power source, a controller in communication with the power source, and a sensor in communication with the power source and the controller, the sensor including sensor electronics and a current source, the current source having a control input and an output, the control input being applied by the sensor electronics and the output being applied to the controller, wherein the current source controls an electric signal communicated to the controller from the sensor based upon the control input. 
         [0012]    In another aspect, the disclosed sensor to controller connection system may include a battery, a controller in communication with the battery, and a sensor in communication with the controller by way of a single wire connection, the sensor including sensor electronics, a current source and a voltage regulator, the voltage regulator being in communication with the battery and the current source, the current source having a control input and an output, wherein the control input includes a voltage applied by the sensor electronics, and wherein the output controls an electric current communicated to the controller from the sensor. 
         [0013]    Other aspects of the disclosed system for connecting a sensor to a controller will become apparent from the following description, the accompanying drawings and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a schematic illustration of a first prior art sensor to controller connection system; 
           [0015]      FIG. 2  is a schematic illustration of a second prior art sensor to controller connection system; 
           [0016]      FIG. 3  is a schematic illustration of a first aspect of the disclosed system for connecting a sensor to a controller; and 
           [0017]      FIG. 4  is a schematic illustration of a sensor according to a second aspect of the disclosed system for connecting a sensor to a controller. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Referring to  FIG. 3 , one aspect of the disclosed system for connecting a sensor to a controller, generally designated  100 , may include a sensor  102 , an electronic controller  104  and a power source  106 , such as a battery (e.g., a 12 V automotive battery). The system  100  may be connected to ground  108 , such as a vehicle chassis. The wiring inductance L W , wiring resistance R W  and current noise source N of the system  100  may represent ground noise created by transient currents in the ground path of the controller  104 . 
         [0019]    In one aspect, sensor  102  may be a pedal feel emulator (not shown) that indicates a driver&#39;s brake request and the controller  104  may be associated with a front right electric caliper (not shown) and may generate and communicate a braking signal to the caliper based upon signals received from the pedal feel emulator. 
         [0020]    The controller  104  may include resistors R 10 , R 11 , R 12  and capacitors C 6 , C 7 . The input to the controller  104  from the sensor  102  may be in the form of a single wire  110  that supplies a current. For example, a single pin connector may be used to connect the sensor  102  to the controller  104 . The use of a single wire connection between the sensor  102  and the controller  104  may provide several advantages, including reduced costs and manufacturing time. The current supplied by the wire  110  may be converted to a signal voltage by resistor R 11 , which may be filtered by a low pass filter  112  created by resistors R 10 , R 12  and capacitors C 6 , C 7 . The low pass filter  112  may eliminate signal noise and may provide an anti-aliasing filter. 
         [0021]    The sensor  102  may include a potentiometer R S , resistors R 2 , R 3 , R 4 , R 5 , R 6 , capacitors C 1 , C 2 , C 3 , C 4 , C 5 , a transistor Q 1 , a voltage regulator  114  and an integrated circuit  116 . The potentiometer R S  may represent the sensor function of the sensor  102  and may be capable of supplying a voltage corresponding to a sensor input (e.g., pedal travel). However, those skilled in the art will appreciate that sensor  102  may have various sensor inputs. The integrated circuit  116 , resistors R 2 , R 3 , R 5 , R 6  and capacitors C 4 , C 5  may form a differential amplifier, generally designated  118 . The differential amplifier  118  and the transistor Q 1  may function as a current source. 
         [0022]    The voltage regulator  114  of the sensor  102  may be connected to the positive terminal of the power source  106  at pin  3  of the regulator  114  and to ground  108  at pin  1  of the regulator  114 . For example, the power source  106  may apply 12 V to the sensor  102  and the voltage regulator  114  may regulate the applied voltage to 5 V. The regulated output voltage (pin  2 ) from the regulator  114  may be applied to the potentiometer R S  and the first input (pin  1 ) of the amplifier  118 . The output of the potentiometer R S  may be applied to the second input (pin  2 ) of the amplifier  118 . The resulting output (pin  3 ) of the amplifier  118  may control the transistor Q 1 , thereby regulating the current output to the controller  104  by way of line  110 . 
         [0023]    In one aspect, unlike conventional sensors that operate from 0 V to 5 V, sensor  102  may operate from 7 V to 12 V with respect to ground  108 . The standard acceptable automotive battery voltage range is 9 V to 16 V. For example, when the power source  106  is a battery sourcing 16 V, the sensor  102  may operate between 11 V and 16 V with respect to ground  108 . When the battery  106  is sourcing 9 V, the sensor  102  may operate between 4 V and 9 V with respect to ground  108 . Many automotive manufactures prefer electronic controllers to operate down to a controller voltage of 7 V to account for the transient ground noise. Therefore, to provide a valid signal, transistor Q 1  may source current to the controller  104  and remain in the active linear conduction range which requires a collector emitter voltage of greater than 0.5 V. When the maximum voltage across resistor R 4  is designed to be 1 V, the output voltage of the sensor  102  may be within 1.5 V of the positive battery voltage and the maximum signal generated across resistor R 11  in the controller is 5 V. With 1.5 V across the sensor output and 5 V across the controller signal input, the sensor system  100  can operate with a minimum battery voltage of 6.5 V. As the battery voltage rises above 6.5 V, the transistor Q 1  remains in the active linear conduction range, thereby increasing the power dissipation of transistor Q 1 . 
         [0024]    For cost considerations, the use of small signal transistors instead of power transistors may be preferred. To allow the use of small signal transistors, the maximum current sourced by the sensor interface electronics should be controlled to maintain acceptable power dissipation in transistor Q 1  under maximum battery voltage conditions. To maintain a power dissipation of 50 mW in transistor Q 1  with a 16 V battery, the maximum current that transistor Q 1  can source is 5 mA. Under this system condition, 1 V across resistor R 4  in the sensor interface electronics and 5 V across resistor R 11  in the controller leaves 10 V across transistor Q 1 . 
         [0025]    Referring to  FIG. 4 , one specific aspect of a sensor, generally designated  102 ′, useful with the system  100  of  FIG. 3  may include a potentiometer R S ′, resistors R 2 ′, R 3 ′, R 4 ′, R 5 ′, R 6 ′, R 7 ′, R 8 ′, R 9 ′, capacitors C 1 ′, C 2 ′, C 3 ′, C 4 ′, C 5 ′, transistors Q 1 ′, Q 2 ′, diodes D 1 ′, D 2 ′, a voltage regulator  114 ′ and amplifiers  116 A′,  116 B′ associated with integrated circuit. Amplifier  116 B′ may be unused. Diode D 2 ′ may provide reverse voltage protection for the sensor  102 ′ and diode D 1 ′ and resistor R 9 ′ may provide input voltage transient protection for standard automotive voltage transients. Capacitor C 1 ′ may filter the input battery supply. 
         [0026]    The sensor function of the sensor  102 ′ may be represented by resistors R 7 ′, R 8 ′ and potentiometer R S ′. For diagnostic reasons, many automotive sensors provide an output of 0.5 V for a signal representing a zero value and an output of 4.5 V for a signal representing the maximum value. Resistors R 7 ′, R 8 ′ provide enough voltage offset such that the full range of potentiometer R S ′ is 0.5 V to 4.5 V. At this point, those skilled in the art will appreciate that the actual sensor may be a position sensor, a force sensor, an acceleration sensor or the like and resistors R 7 ′, R 8 ′ and potentiometer R S ′ have only been used to generally represent sensor electronics. 
         [0027]    In one aspect, the voltage regulator  114 ′ may be connected to the positive input of a power source (e.g., power source  106  in  FIG. 3 ) at pin  3  of the regulator  114 ′ and to ground (e.g., ground  108  in  FIG. 3 ) at pin  1  of the regulator  114 ′ such that the regulator  114 ′ may receive a negative input voltage with respect to the regulator ground pin  3 . The voltage output (pin  2 ) of the regulator  114 ′ may deliver a regulated output voltage that is, for example, 5 V below the regulator ground pin  3 . This regulated voltage may become the common voltage for the sensor  102 ′ and associated interface electronics. For example, the regulated voltage may be about 4 V to 11 V above the vehicle chassis ground depending upon the battery voltage input. The positive battery input voltage may become the regulated +5 V above the sensor common voltage for the sensor and interface electronics. For the purpose of this description, this voltage will be referred to as +5 V although the actual voltage value is equal to the positive battery voltage with respect to ground. Capacitor C 2 ′ may filter the output of the 5 V sensor power supply. Capacitor C 3 ′ may filter the sensor supply locally at the power pins of amplifier  116 A′. Therefore, in one aspect, the sensor  102 ′ may convert a 0 V to 5 V sensor input into a 0 mA to 5 mA sensor signal. 
         [0028]    The amplifier  116 A′, resistors R 2 ′, R 3 ′, R 5 ′, R 6 ′ and capacitors C 4 ′, C 5 ′ may form a differential amplifier, generally designated  118 ′. In one aspect, the value of resistor R 2 ′ may equal the value of resistor R 5 ′, the value of resistor R 3 ′ may equal the value of resistor R 6 ′ and the value of capacitor C 4 ′ may equal the value of capacitor C 5 ′, such that the gain of the differential amplifier  118 ′ may be defined by the ratio of resistor R 3 ′ to resistor R 2 ′. For example, resistor R 3 ′ may have a resistance of 49,900 Ohms and resistor R 2 ′ may have a resistance of 249,000 Ohms, resulting in a gain of the differential amplifier  118 ′ of about 0.2 (49,900/249,000). Therefore, in one example, the differential amplifier  118 ′ may provide an output voltage that is equal to 0.2 times the input voltage. 
         [0029]    The output voltage (pin  3 ) from the differential amplifier  118 ′ may be converted to a sensor output current by the transistors Q 1 ′, Q 2 ′ and the sensor output current may be supplied to the controller ( FIG. 3 ) by line  110 ′. Transistors Q 1 ′, Q 2 ′ may be configured as a Darlington transistor pair  120 ′, which may be two individual transistors or a single transistor package designed specifically as a Darlington transistor. The collectors of transistors Q 1 ′, Q 2 ′ may be the output current source of the sensor  102 ′ to the controller ( FIG. 3 ). The Darlington transistor configuration  120 ′ may be used since the collector current of a transistor equals the emitter current minus the base current. Therefore, the Darlington transistor configuration  120 ′ may increase the gain of the transistors Q 1 ′, Q 2 ′ such that the base current is very small with respect to the emitter current. Therefore, the emitter current and collector current are very nearly equal. Resistor R 4 ′ may be configured to sense and ultimately control the emitter current of transistor Q 1 ′. 
         [0030]    The output voltage from the potentiometer R S ′ (e.g., between 0.5 and 4.5 V) may be applied to pin  2  of the differential amplifier  118 ′. As discussed above, the sensor output voltage range may be, for example, between 0.5 and 4.5 V and, therefore, the input voltage to the differential amplifier  118 ′ may be, for example, between 0.5 and 4.5 V. 
         [0031]    If a sensor voltage of zero volts were possible, the output voltage of the differential amplifier  118 ′ would be zero. However, since resistor R 3 ′ is connected to +5 V (with respect to the sensor voltage), the voltage on resistor R 6 ′ may be +5 V and the output voltage of the differential amplifier  118 ′ will be at a voltage near +5V such that transistors Q 1 ′, Q 2 ′ are in a non-conducting state. With a sensor voltage of 0.5 V applied to the input voltage (pin  2 ) of the differential amplifier  118 ′, the output voltage goes lower in voltage below +5 V. This change in voltage causes the amplifier  116 A′ to sink current from the base of transistor Q 2 ′. The emitter of transistor Q 2 ′ sinks current from the base of transistor Q 1 ′ which causes current flow in the emitter of transistor Q 1 ′. This current flow is sensed by resistor R 4 ′ by creating a voltage as the output voltage of the differential amplifier  118 ′. The output pin  3  of amplifier  116 A′ continues to decrease in voltage until the gain equation (e.g., output voltage=0.2×input voltage) of the differential amplifier  118 ′ is satisfied. For example, the final voltage across resistor R 4 ′ with a sensor voltage of 0.5 V is 0.1 V. With the value of resistor R 4 ′ at 200 Ohms, the emitter current of transistor Q 1 ′ is 500 microamps, for example. Since the collector current of transistors Q 1 ′, Q 2 ′ is nearly equal to the emitter current, the sensor and interface electronics source 500 microamps to the controller ( FIG. 3 ). This current is significantly greater than prior art systems, thereby significantly improving the signal to noise immunity. Similarly, with a sensor voltage of 4.5 V as the input voltage to the differential amplifier  118 ′, the output voltage of the differential amplifier  118 ′ across resistor R 4 ′ is 0.9 V, which, following the example above, sources 4.5 mA to the controller ( FIG. 3 ). 
         [0032]    Although various aspects of the disclosed sensor to controller connection system have been shown and described, modifications may occur to those skilled in the art upon reading the specification. The present application includes such modifications and is limited only by the scope of the claims.

Technology Category: 3