Patent Abstract:
A current detector used in a control system for controlling a motor for driving a vehicle is disclosed, which does not require an especially accurate power circuit, and an accurate measurement result can be obtained by using a cheap power circuit whose accuracy is relatively low. The current detector comprises a detector for outputting a voltage corresponding to a target current, wherein the detector has a current detecting element for detecting the target current; an amplifier for amplifying and outputting the output from the detector; an analog-digital converter for converting the output from the amplifier to a digital data; and a power circuit for supplying an output voltage to both the detector and the analog-digital converter.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a current detector used in a control system for controlling a motor for driving a vehicle such as an electric vehicle or a hybrid vehicle, or for use in another system which requires current detection. 
     2. Description of the Related Art 
     FIG. 4 is a block diagram showing the structure of a conventional current detector used in a control system for controlling a motor for driving a vehicle. In this figure, reference numeral  1  indicates a current sensor using a Hall element. The Hall element has a function of outputting a voltage which is proportional to (i) flowing current and (ii) generated magnetic flux density. 
     FIG. 5 is a block diagram showing the structure of the current sensor  1 . In the figure, reference numeral  7  indicates a Hall element. Reference numeral  8  indicates a core which generates a magnetic flux when current flows through wire L. Reference numeral  9  indicates a power circuit which receives 12 V voltage, and converts it to 5 V voltage and outputs the converted voltage. Reference numeral  10  indicates an amplification circuit which is driven using the 5 V voltage output from the power circuit  9 . When voltage v 1  is input from Hall element  7  to the amplification circuit  10 , the circuit  10  amplifies voltage v 1  and also adds an offset voltage to the amplified voltage, and outputs the amplified voltage including the offset as voltage v 2 . Reference numeral  11  indicates a constant current generating circuit for supplying a constant current to the Hall element  7 . The 5 V voltage output from the power circuit  9  is supplied to the constant current generating circuit  11  as a reference voltage, and the above constant current is defined by potential-dividing the reference voltage by using a resistor. 
     In FIG. 4, reference numeral  3  indicates an A/D converter which receives voltage input via terminal C from current sensor  1 , and calculates the ratio of the input voltage to a reference voltage input from the power circuit  4 , and converts the ratio to a digital value, and outputs the digital value. Here, the power circuit  4  converts input  12  V voltage to 5 V voltage and supplies the 5 V voltage to the A/D converter  3 . Reference numeral  5  indicates a CPU (central processing unit) for receiving the above digital value from the A/D converter, and calculates and outputs the value indicating a target current flowing through wire L. Reference numeral  6  indicates a power circuit for driving CPU  5 . 
     Below, the operation of the current detector (used in a control system for controlling a motor for driving a vehicle) having the above-explained structure will be explained. 
     When a 12 V voltage is input via terminal B to current sensor  1 , the power circuit  9  converts the 12 V voltage to 5 V voltage and outputs the converted voltage to the Hall element  7  and the constant current generating circuit  11 . 
     On the other hand, when a target current to be measured flows through wire L, magnetic flux is generated in core  8 . When the magnetic flux is applied to Hall element  7 , the element  7  outputs voltage v 1 , proportional to the magnetic flux, to the amplification circuit  10 . The amplification circuit  10  amplifies the input voltage v 1  and adds an offset voltage to it so as to obtain voltage v 2  (0 V ≦v 2  ≦5.0 V), and outputs voltage v 2  via terminal C to A/D converter  3 . 
     When the A/D converter  3  receives voltage v 2  via terminal C, the converter  3  calculates the ratio of v 2  to the reference voltage (i.e., 5V) input via terminal A from the power circuit  4 , and converts the calculated result to a digital value and outputs the digital value to CPU  5 . 
     In order to improve the accuracy of the current sensor  1 , a constant current (from the constant current generating circuit) should be stable, that is, should not be affected by the external environment. Accordingly, the voltage supplied to the constant current generating circuit should be accurate, and thus an accurately operable power circuit must be used as power circuit  9 . 
     In addition, the A/D converter  3  should also accurately digitize the measurement value of the current sensor  1 , and thus the power circuit  4  should also be accurate. 
     Therefore, conventionally, in order to accurately measure the target current, both the power circuits  4  and  9  must be accurate, thus the cost will be high. 
     In addition, the values of reference voltage (5 V) of the power circuits may not accurately be the same, thereby producing an error. 
     Furthermore, in the control of the motor for driving a vehicle, such an error of the current sensor certainly causes an error in the torque control of the motor. More specifically, the difference between the real value and the actually detected value functions as an error of the control value, so that overestimates or underestimates of the control may cause a shock to the vehicle, or excessive discharging or charging of the battery functioning as a power source. 
     Therefore, for example, the system must be designed in consideration of an error in the detected current; thus, the design may be limited or the system cost may be high. 
     SUMMARY OF THE INVENTION 
     In consideration of the above circumstances, an objective of the present invention is to provide a current detector used in a control system for controlling a motor for driving a vehicle, wherein accurate current measurement can be performed without using especially accurate power circuits (as explained above). 
     Therefore, the present invention provides a current detector used in a control system for controlling a motor for driving a vehicle comprising: 
     a detector (for example, a current sensor  21  in the following embodiment) for outputting a voltage corresponding to a target current, wherein the detector has a current detecting element (for example, a Hall element  27  in the following embodiment) for detecting the target current; 
     an amplifier (for example, an amplification circuit  30  in the following embodiment) for amplifying and outputting the output from the detector; 
     an analog-digital converter (for example, an A/D converter  23  in the following embodiment) for converting the output from the amplifier to a digital data; and 
     a power circuit (for example, a power circuit  33  in the following embodiment) for supplying an output voltage to both the detector and the analog-digital converter. 
     In a typical example, the detector comprises: 
     a Hall element (for example, a Hall element  27  in the following embodiment) functioning as the current detecting element; 
     a core (for example, a core  28  in the following embodiment) for applying a magnetic flux corresponding to the target current to the Hall element; and 
     a constant current generating circuit (for example, a constant current generating circuit  31  in the following embodiment) for supplying a constant current to the Hall element. 
     Preferably, the amplifier adds an offset voltage to the amplified voltage, and outputs the amplified voltage including the offset. 
     Also typically, the vehicle is a hybrid vehicle which uses the motor for assisting the output of an engine. 
     According to the present invention, the output voltage from a single power circuit is supplied to the detector for detecting the target current and to the analog-digital converter; thus, an especially accurate power circuit is not necessary, and an accurate measurement result can be obtained by using a cheap power circuit whose accuracy is relatively low. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing the structure of an embodiment of the current detector used in a control system for controlling a motor for driving a vehicle, according to the present invention. 
     FIG. 2 is a block diagram for showing the structure of a current sensor as a constituent of the current detector shown in FIG.  1 . 
     FIG. 3 is a graph showing the voltage output from amplification circuit  30  with respect to the current flowing through wire L. 
     FIG. 4 is a block diagram showing the structure of a conventional current detector used in a control system for controlling a motor for driving a vehicle. 
     FIG. 5 is a block diagram showing the structure of a current sensor as a constituent of the current detector shown in FIG.  4 . 
     FIG. 6 is a block diagram showing a control system of a parallel hybrid vehicle to which the current detector according to the present invention is applied. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, an embodiment according to the present invention will be explained in detail with reference to the drawings. 
     FIG. 6 is a block diagram showing a control system of a parallel hybrid vehicle (a kind of hybrid vehicle) to which a current detector according to the present invention is applied. In this figure, reference numeral  110  indicates an engine which operates by burning suitable amounts of fuel, and reference numeral  102  indicates a motor used together with the engine, and the motor  102  is operated using electric energy. The driving force generated by both the engine  110  and motor  102  is transmitted via a transmission (not shown: automatic or manual transmission) to driving wheels (also, not shown). When the vehicle decelerates, the rotation of the driving wheels is transmitted to the motor  102 , and the motor  102  functions as a generator, so that the kinetic energy of the vehicle body is recovered and stored as electric energy. 
     Reference numeral  101  indicates a main battery for supplying electric power to motor  102  when the vehicle is driven using the driving force of motor  102 . As explained above, the motor  102  functions as a generator in deceleration (of the vehicle) or the like, and the main battery  101  stores electric energy obtained by the generation using motor  102 . The main battery  101  includes a plurality of modules connected in series, and in each module, a plurality of cells are connected in series, so as to output a high voltage (here, 144 V). A temperature sensor  117  is attached to each module of the main battery  101 , and the modules are contained in a battery box which comprises an air inlet and air outlet for air-cooling the modules. In addition, cooling fan  118  is provided at the air outlet. The air inlet of the battery box is positioned suitably for taking in air from inside of the vehicle, while the air outlet is positioned suitably for discharging the air expelled by the cooling fan  118  to the outside of the vehicle. 
     Reference numeral  109  indicates an engine control unit which monitors the engine speed Ne, the vehicle speed, the degree of depression Ap of the accelerator pedal, and the like at predetermined intervals. Based on the monitored result, a driving mode determining section (not shown) included in the engine control unit  109  determines the driving mode of the vehicle. The present vehicle has four driving modes: (i) an assist mode in which the vehicle is accelerated, (ii) a deceleration mode in which the vehicle is decelerated, (iii) a cruise mode in which the vehicle drives at a fixed speed, and (iv) an idle mode in which the vehicle is stopped while the engine is active. 
     The engine control unit  109  also sends data related to the driving mode to motor control unit  108 . When the motor control unit  108  receives the data related to the driving mode from the engine control unit  109 , a gain switching section (not shown) in the control unit  108  switches (i.e., selects) the gain based on the data, and a feedback processing section (also not shown) controls a power drive unit  103  according to the selected gain, so that the power drive unit  103  controls the amount of electric power sent to or received from motor  102 . 
     Reference numeral  119  indicates a battery control unit, which calculates the remaining battery charge (called “SOC (state of charge)”) of main battery  101 . In order to protect main battery  101 , the battery control unit  119  also controls the cooling fan  118  built into the battery box which contains the main battery  101 . In this control, the temperature of the main battery  101  is maintained equal to or below a predetermined value. 
     The above engine control unit  109 , motor control unit  108 , and battery control unit  119  are realized using a CPU (central processing unit) and a memory, and the function of each control unit is realized by executing a specific software program. 
     Reference numeral  103  indicates a power drive unit comprising three parallel-connected sets of two switching elements which are connected in series. The ON/OFF switching operations of the switching elements in the power drive unit  103  are performed by a feedback processing section (not shown) provided in the motor control unit  108 . According to the ON/OFF switching operations, the direct current supplied from the main battery  101  to the power drive unit  103  is converted to three-phase alternating current, and the converted three-phase alternating current is supplied to the motor  102  via three phase lines  103   u ,  103   v , and  103   w.    
     Reference numeral  120  indicates a 12V battery for driving various kinds of electrical equipment  105 . This 12V battery  120  is connected via DC-DC converter  104  to the lines for connecting the main battery  101  and the power drive unit  103 . The DC-DC converter  104  reduces the voltage (144 V) supplied from main battery  101  to 12 V, and supplies the reduced voltage to the electrical equipment  105  and 12V battery  120 . 
     Reference numeral  121  indicates a precharge contactor, and reference numeral  122  indicates a main contactor. The main battery  101  and the power drive unit  103  are connected via these contactors. The ON/OFF switching operations of the precharge contactor  121  and main contactor  122  are performed by the motor control unit  108 . Reference numeral  123  indicates a resistor for limiting the precharge current to the main battery  101  at the precharge operation, that is, when the precharge contactor  121  is switched on. 
     Reference numeral  124  indicates a rotation sensor for detecting the speed of rotation of motor  102 . Reference numerals  125   u ,  125   v , and  125   w  indicate current detectors in the present control system for controlling the motor for driving the vehicle, and current detectors  125   u ,  125   v , and  125   w  respectively detect currents flowing through three phase lines  103   u ,  103   v , and  103   w . The rotation speed detected by the rotation speed sensor  124  and the current values detected by the above current detectors  125   u ,  125   v , and  125   w  are input into the motor control unit  108 . The internal structure of each current detector ( 125   u ,  125   v , and  125   w ) will be explained later in detail with reference to FIG.  1 . 
     Reference numeral  106   a  indicates a voltage sensor positioned very close to the terminals  101   a  of the main battery  101 , between the terminals  101   a  of the main battery  101  and the terminals  103   a  of the power drive unit  103 . Reference numeral  106 b indicates a current sensor positioned very close to a terminal  101   a  of the main battery  101 . That is, the voltage sensor  106   a  detects the voltage between the terminals  101   a  of the main battery  101 , while the current sensor  106   b  detects the current flowing through the relevant terminal  101   a  of the main battery  101 . These two sensors, that is, voltage sensor  106   a  and current sensor  106   b , form the first power detecting section  106 . The voltage value detected by the voltage sensor  106   a  and the current value detected by the current sensor  106   b  are input into the motor control unit  108  and the battery control unit  119 . 
     Reference numeral  107   a  indicates a voltage sensor positioned very close to the terminals  103   a  of the power drive unit  103 , between the terminals  101   a  of the main battery  101  and the terminals  103   a  of the power drive unit  103 . Reference numeral  107   b  indicates a current sensor positioned very close to a terminal  103   a  of the power drive unit  103 . That is, the voltage sensor  107   a  detects the voltage between the terminals  103   a  of the power drive unit  103 , while the current sensor  107   b  detects the current flowing through the relevant terminal  103   a  of the power drive unit  103 . These two sensors, that is, voltage sensor  107   a  and current sensor  107   b , form the second power detecting section  107 . The voltage value detected by the voltage sensor  107   a  and the current value detected by the current sensor  107   b  are input into the motor control unit  108 . 
     The DC-DC converter  104  is connected to a position between current sensors  106   b  and  107   b  which are provided on the line for connecting the relevant terminal  101   a  of the main battery  101  and the relevant terminal  103   a  of the power drive unit  103 ; thus, the current detected by the current sensor  107   b  is the sum of the current detected by the current sensor  106   b  and the current flowing through the DC-DC converter  104 . 
     Below, the operation of the control system of the hybrid vehicle, having the above-explained structure, will be explained. First, the battery control unit  119  calculates the-remaining battery charge SOC of the battery  101  based on the current and voltage at the terminals  101   a  of main battery  101 , and sends the calculated value to the motor control unit  108 . The motor control unit  108  sends the received SOC to the engine control unit  109 . 
     A target power calculating section (not shown) provided in the engine control unit  109  calculates a target power value based on the remaining battery charge SOC, the degree of depression Ap of the accelerator pedal, engine speed Ne, vehicle speed, air-intake passage (negative) pressure Pb, the ON/OFF state of the engine, and the like. In addition, a driving mode determining section (not shown) determines the current driving mode of the vehicle, among the assist mode, deceleration mode, cruise mode, and idle mode. 
     According to the target power, the feedback processing section (not shown) provided in the motor control unit  108  calculates the power necessary for the motor  102 . In addition, when the motor control unit  108  receives data related to the driving mode from the engine control unit  109 , the control unit  108  performs control operation suitable for the driving mode. More specifically, when the driving mode is the assist or deceleration mode, the motor control unit  108  executes a feedback control for matching the power measured at the terminals  103   a  of the power drive unit  103 , that is, the power detected by the second power detecting section  107 , to the above target power. On the other hand, when the driving mode is the cruise or idle mode, the motor control unit  108  executes a feedback control for matching the power measured at the terminals  101   a  of the main battery  101 , that is, the power detected by the first power detecting section  106 , to the above target power. In addition, when the engine  110  is started, the motor control unit  108  controls the power drive unit  103  so as to control the start operation of engine  110  by using the motor  102 . 
     The engine control unit  109 , motor control unit  108 , and battery control unit  119  operate as explained above at predetermined operation timing so as to control the engine  110 , motor  102 , and main battery  101 , thereby controlling the hybrid vehicle. 
     FIG.,  1  is a block diagram showing the structure of current detector  125   u  (see FIG. 6) in the above control system for controlling the motor for driving the vehicle. Here, the other current detectors  125   v , and  125   w  have the same structure. 
     In FIG. 1, reference numeral  21  indicates a current sensor using a Hall element. 
     FIG. 2 is a block diagram showing the structure of current sensor  21 . In the figure, reference numeral  27  indicates a Hall element, reference numeral  28  indicates a core, reference numeral  30  indicates an amplification circuit, and reference numeral  31  indicates a constant current generating circuit. These structural elements are the same as those shown in FIG.  5 . Here, the operational amplifier used in the amplification circuit  30  has the function of outputting a voltage up to approximately the same level as that of the supplied voltage. 
     The distinctive feature of the circuit shown in FIG. 2 in comparison with the circuit shown in FIG. 2 is that the power circuit  9  in FIG. 5 is omitted. 
     In FIG. 1, reference numeral  23  indicates an A/D converter, and reference numeral  25  indicates a CPU, and these elements are also the same as those shown in FIG.  4 . Reference numeral  33  indicates a power circuit for converting input voltage (i.e., 12 V) to 5 V, and outputting the converted voltage. This power circuit  33  is not an especially accurate one. 
     As explained above, in the current detector  125   u  in the control system for controlling the motor for driving the vehicle, the output from the power circuit  33  is applied to both the A/D converter  33  and the constant current generating circuit  31 . 
     Below, the operation of the sensor for controlling the motor, having the above-explained structure, will be explained. 
     The power circuit  33  converts the 12V-DC power supply voltage to 5V stabilized voltage Vs, and outputs the voltage Vs. As explained above, the power circuit  33  is not an especially accurate one; thus, it is assumed that the output voltage Vs changes within the range from 4.8 to 5.2 V due to variations in the 12V power source, variations in the temperature, or the like. 
     If it is assumed that the target current to be detected is within the range from −100 A to +100 A, as shown in FIG. 3, the output from the amplification circuit  30  changes from 4.8 V to 5.2 V with respect to the maximum current 100A. Also with respect to the current below 100 A, the output voltage from the amplification circuit  30  changes due to variations in the voltage Vs. On the other hand, the voltage Vs is also applied to the A/D converter  23 ; thus, if the voltage Vs varies, then the reference voltage used for the A/D conversion varies in the same direction as that of the output voltage of the amplification circuit  30 . As a result, the A/D converter is not affected by the variation of the voltage Vs, and outputs a stable conversion result regardless of the variation of the voltage Vs. 
     The current detector in the above embodiment can also be used as a current sensor  106   a  and  107   b.    
     The embodiment of the present invention has been explained in detail with reference to the drawings, but specific embodiments are not limited to the above, and any design modification or variation is possible within the scope and spirit of the present invention.

Technology Classification (CPC): 8