Abstract:
In a voltage controller for a vehicle, voltage controlling means controls an output voltage of a power generator mounted on the vehicle and a terminal voltage of a battery connected to the power generator, by controlling of a field current passing through a field winding of the power generator. This control is performed by operating switching means connected to the field winding so that the switching means is conducted intermittently. Signal generating means generates a power generator state signal by measuring a state of the power generator at predetermined measurement periods. Signal averaging means performs an exponentially weighted averaging of the power generator state signal. The signal averaging means executes the averaging within a predetermined averaging period and updates the averaging at every predetermined measurement period.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is related to Japanese Patent Application NO. 2007-223217 filed on Aug. 29, 2007, the contents of which are hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a voltage controller for a vehicle and in particular, to a voltage controller that controls an output voltage of a power generator for vehicles such as a car and a truck. 
         [0004]    2. Description of the Related Art 
         [0005]    Conventionally, a voltage of a power generator mounted on a vehicle is controlled based on a detected status signal of the generator in which the signal is averaged. For example, in International Publication No. WO2005/031964, a configuration is known in which a power generator state signal is generated by a conduction rate of a switching means (e.g. a duty ratio of a power transistor) connected to a field winding of a power generator for a vehicle. The conduction rate is measured for a predetermined period and an average value being calculated. The generated power generator state signal is transmitted from a regulator to an electronic control unit (i.e., ECU). 
         [0006]    In a conventional method disclosed in International Publication No. WO2005/031964, the conduction rate is measured for the predetermined period and averaged. Therefore, the timing content of the power generator state signal is updated is each predetermined period. Even when the state of the power generator for a vehicle changes during the predetermined period, the change is not reflected in the power generator state signal in real-time. As a result, a problem occurs in that reliability of the power generator state signal is low. Because the ECU performs engine control based on an unreliable power generator state signal such as this, engine control becomes unstable. In a worst case scenario, engine control may stop. To prevent a situation such as this, the predetermined period is required to be shortened and the timing at which the content of the power generator state signal is updated is required to be made more frequent. However, in this case, the conduction rates obtained through measurement cannot be sufficiently averaged. Error increases because of the effects of noise and the like. The power generator state signals being outputted remain low in reliability, adversely affecting engine control. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention has been achieved in light of the above-described issues. An object of the present invention is to provide a voltage controller for a vehicle that can improve reliability of a power generator state signal. 
         [0008]    To solve the above-described issues, a voltage controller for a vehicle of the present invention comprises: 
         [0009]    a voltage controlling means for controlling an output voltage of a power generator mounted on the vehicle and a terminal voltage of a battery connected to the power generator, by controlling a field current passing through a field winding of the power generator by operating a switching means connected to the field winding so that the switching means is conducted intermittently; 
         [0010]    a signal generating means for generating a power generator state signal by measuring the state of the power generator at a predetermined measurement period; 
         [0011]    a signal averaging means for performing an Exponentially Weighted Moving Averaging (herein after called EWM averaging) of the power generator state signal generated by the signal generating means wherein the signal averaging means executes the averaging within a predetermined averaging period and updates the averaging at the every predetermined measurement period. 
         [0012]    Specifically, the signal generating means preferably generates at least one of a duty ratio of the switching means and a current value of a current flowing to the field winding as the power generator state signal, Alternatively, the signal generating means preferably generates at least one of a rotation frequency of the power generator for a vehicle, a temperature of the power generator for a vehicle, and an output voltage of the power generator for a vehicle as the power generator state signal. Because a result obtained by power generator state signals being averaged is transmitted to the external controller as a power generator control signal, details of a change can be reflected every time a state of the power generator for a vehicle changes. Reliability of the power generator control signal can be improved. 
         [0013]    Preferably, the switching means repeatedly switches itself on and off at a predetermined cycle. As a result, measurement accuracy of the power generator state signal, contents of which are the duty ratio of the switching means and the current value of the current flowing to the field winding, can be increased. 
         [0014]    The signal generating means preferably measures the duty ratio or the current value and generates the power generator state signal at the predetermined measurement period that is equal to the predetermined period of the switching means, regardless of whether the switching means is in operation or not. As a result of the duty ratio and the current value being measured in time with the predetermined period of the switching means, the accuracy of these measurements can be further increased. 
         [0015]    The signal averaging means preferably changes an EWM averaging period depending on a state of the power generator for a vehicle. As a result, when required response characteristics differ based on the state of the power generator for a vehicle (for example, when the power generator rotation frequency is excessively high or low, or when the power generator temperature is excessively high or low), the averaging period can be changed, and a power generator state signal of an appropriate sensitivity can be outputted. 
         [0016]    The signal averaging means preferably changes the EWM averaging period depending on a communication signal sent from the external controller. As a result, when required response characteristics differ depending on a vehicle state (for example, when the engine rotation frequency is excessively high or low, or when a coolant temperature is excessively high or low), a power generator state signal of an appropriate sensitivity can be outputted as a result of the averaging period being changed by an instruction from the external controller. 
         [0017]    The signal averaging means preferably sets the EWM averaging period to a period corresponding to a time constant of the field winding. As a result of the averaging period of the power generator state signal, contents of which are the duty ratio of the switching means and the current value of the current flowing to the field winding, being set to a frequency corresponding to the time constant of the field winding, a power generator state signal having high measurement accuracy close to actual values can be outputted. 
         [0018]    When the power generator state signals generated by the signal generating means have a same value that continues for a predetermined amount of time or a predetermined number of consecutive times, the signal averaging means outputs power generator state signals in which the same value is continued, instead of the averaged power generator state signal. As a result, a power generator state signal having high measurement accuracy close to actual values can be outputted by an averaging result being changed to 0% or 100%, when the duty ratio of the switching means is averaged and a 0%- or 100%-state continues for a predetermined amount of time or a predetermined consecutive number of times. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    In the accompanying drawings: 
           [0020]      FIG. 1  is a diagram showing a configuration of a power generator for a vehicle including a voltage controller for a vehicle according to an embodiment; 
           [0021]      FIG. 2  is a flowchart showing operations performed by the voltage controller for a vehicle related to transmission of a power generator state signal; 
           [0022]      FIG. 3  is an explanatory diagram showing a power generator state signal obtained by an EWM averaging; and 
           [0023]      FIG. 4  is an explanatory diagram showing a power generator state signal averaged by a conventional method. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    A voltage controller for a vehicle according to an embodiment of the present invention will be described with reference to the drawings  FIGS. 1 to 3 .  FIG. 1  is a diagram of a configuration showing a power generator for a vehicle including the voltage controller according to the embodiment.  FIG. 1  also shows the connection between the power generator for a vehicle and a battery, an external controller, and the like. As shown in  FIG. 1 , a power generator  2  for a vehicle according to the embodiment includes a rectifier  20 , a field winding  21 , an armature winding  22 , and a voltage controller  1  for a vehicle. The power generator  2  for a vehicle is driven by an engine, via a belt and a pulley. 
         [0025]    The field winding  21  generates a magnetic field by being electrified. The field winding  21  is wound around a field pole, thereby configuring a rotor. The armature winding  22  is a multi-phase winding (for example, a three-phase winding). The armature winding is wound around an armature core, thereby configuring an armature. The armature winding  22  generates an electromotive force as a result of change in the magnetic field generated by the field winding  21 . An alternating current output induced by the armature winding  22  is supplied to the rectifier  20 . The rectifier  20  performs full-wave rectification on the alternating current output from the armature winding  22 . The output from the rectifier  20  is outputted as the output from the power generator  2  for the vehicle. The output is then supplied to an electrical load  5 , via a battery  3 , an electrical load switch  4 , and the like. The output of the power generator  2  for a vehicle changes depending on the rotation frequency of the rotor and the amount of field current flowing to the field winding  21 . The voltage controller  1  for a vehicle is controlled by the field current. 
         [0026]    A vehicle-side controller  6 , serving as an external controller, is connected to the power generator  2  for a vehicle. The vehicle-side controller  6  controls engine rotation and the like based on a power generator state signal (described in detail hereafter) sent from the voltage controller  1  for a vehicle and other pieces of information. 
         [0027]    Next, details of the voltage controller  1  for a vehicle will be described. The voltage controller  1  for a vehicle includes a voltage control circuit  11 , a rotation frequency detection circuit  12 , a temperature detection circuit  13 , a drive duty detection circuit  14 , a field current detection circuit  15 , an output voltage detection circuit  16 , an exponentially weighted moving average circuit  17 , a communication control circuit  18 , a switching transistor  114 , a free-wheeling diode  115 , and a shunt resistor  116 . 
         [0028]    The voltage control circuit  11  includes resistors  111  and  112 , and a voltage comparator  113 . In the voltage comparator  113 , a reference voltage Vref is inputted into a plus input terminal. A detection voltage is inputted into a negative input terminal. The detection voltage is an output voltage of the power generator  2  for a vehicle (B terminal voltage or terminal voltage of the battery  3 ) divided by a voltage dividing circuit formed by the resistors  111  and  112 . Instead of the B terminal voltage being divided, the terminal voltage of the battery  3  can be introduced and divided. The divided terminal voltage can then be applied to the negative input terminal of the voltage comparator  113 . The reference voltage Vref can be a constant voltage (such as a value equivalent to a regulated voltage). However, according to the embodiment, to intermittently control the switching transistor  114  at a predetermined period, a reference voltage Vref of which a voltage value periodically changes to form a saw-tooth waveform or a triangular waveform is used (a method of intermittently controlling the switching transistor  114  at a predetermined period is not limited thereto, and other methods can be used). An output terminal of the voltage comparator  113  is connected to the switching transistor  114 . In the switching transistor  114 , the base is connected to the output terminal of the voltage comparator  113 . The collector is connected to the output terminal (B terminal) of the power generator  2  for the vehicle, via the free-wheeling diode  115 . The emitter is grounded, via the shunt resistor  116  and a grounding terminal (E terminal). The collector of the switching transistor  114  is also connected to the field winding  21 . When the switching transistor  114  is turned ON, the field current flows to the field winding  21 . When the switching transistor  114  is turned OFF, the current flow is stopped. The free-wheeling diode  115  is connected in parallel to the field winding  21 . When the switching transistor  114  is turned OFF, the free-wheeling diode  115  recirculates the field current flowing to the field winding  21 . 
         [0029]    The rotation frequency detection circuit  12  detects the rotation frequency of the power generator  2  based on a phase voltage of the armature winding  22  inputted via a P terminal. The temperature detection circuit  13  detects the temperature of the power generator  2  for a vehicle using a predetermined temperature sensor (not shown). The drive duty detection circuit  14  detects the drive duty of the switching transistor  114  as the duty ratio. The field current detection circuit  15  detects the field current flowing to the field winding  21  based on the value of voltage drop in the shunt resistor  116 . The output voltage detection circuit  16  detects an output voltage appearing at the B terminal of the power generator  2 . Detection values detected (measured) at each detection circuit are inputted into the exponentially weighted moving average circuit  17  as power generator state signals before averaging. 
         [0030]    The exponentially weighted moving average circuit  17  performs an EWM averaging process on the power generator state signals respectively inputted from the rotation frequency detection circuit  12 , the temperature detection circuit  13 , the drive duty detection circuit  14 , the field current detection circuit  15 , and the output voltage detection circuit  16 . An averaged power generator state signal is inputted into the communication control circuit  18  and transmitted to the vehicle-side controller  6  according to a protocol decided with the vehicle-side controller  6 . 
         [0031]    The above-described switching transistor  114  corresponds to a switching means. The voltage control circuit  11  corresponds to a voltage controlling means. The rotation frequency detection circuit  12 , the temperature detection circuit  13 , the drive duty detection circuit  14 , the field current detection circuit  15 , and the output voltage detection circuit  16  correspond with a power generator state signal generating means. The exponentially weighted moving average circuit  17  corresponds to a signal averaging means. The communication control circuit  18  corresponds to a communicating means. 
         [0032]    The voltage controller  1  for a vehicle according to the present invention is configured as described above. Next, operations performed from detection to transmission of the power generator state signal will be described.  FIG. 2  is a flowchart of operations performed by the voltage controller  1  for a vehicle related to transmission of the power generator state signal. 
         [0033]    The rotation frequency detection circuit  12 , the temperature detection circuit  13 , the drive duty detection circuit  14 , the field current detection circuit  15 , and the output voltage detection circuit  16  measure the newest power generator state signals V (Step  100 ). Next, the exponentially weighted moving average circuit  17  performs an EWM averaging using the newest power generator state signals V and calculates a newest average value AV (Step  101 ). The communication control circuit  18  transmits the newest average value AV towards the vehicle-side controller  6  as an averaged power generator state signal (Step  102 ). Because the newest average value AV calculated at Step  101  is used in a subsequent averaging process, the newest average value AV is stored in the exponentially weighted moving average circuit  17  (Step  103 ). The series of operations described above is repeated at a predetermined cycle, preferably the same cycle as the intermittent cycle of the switching transistor  111 . 
         [0034]    Next, details of the EWM averaging process performed at Step  101  will be described. When the newest power generator state signal obtained by a measuring operation at Step  100  is V n+1 , the newest average value calculated at Step  101  is AV n+1 , the average value of a previous cycle recorded at Step  103  is AV n , and the averaging frequency is N, the newest average value AV n+1  can be calculated using an equation below. 
         [0000]        AV   n+1 =( V   n+1 +( N− 1)× AV   n )/ N    
         [0000]    Calculation of the newest average value AV n+1  at Step  101  is performed using the equation. Storage of the average value at Step  103  is performed by the average value AV n  of the previous cycle being overwritten with the newest average value AV n+1 . 
         [0035]    Averaging described above is equivalent to a moving average of a predetermined number of power generator state signals that are consecutively measured. The predetermined number subjected to the moving average is equivalent to the averaging frequency N. In other words, in the series of operations shown in  FIG. 2 , an average of measured values of an N-number of newest power generator state signals is calculated. In the next series of operations performed after a return from Step  103  to step  100 , an oldest power generator state signal among the previous N-number of power generator state signals is deleted. A power generator state signal obtained by a latest measuring operation is added instead. The average of the measured values of the N-number of newest power generator state signals at this point is calculated. The newest average value can be determined by the operation being repeated. 
         [0036]      FIG. 3  is an explanatory diagram of the power generator state signal obtained by averaging. In  FIG. 3 , “drive duty measured value” indicates the drive duty (duty ratio) serving as the power generator state signal measured by the drive duty detection circuit  14 . “Average value” indicates the average value calculated by the exponentially weighted moving average circuit  17 . A horizontal axis indicates an elapsed time t.  FIG. 4  is an explanatory diagram of a power generator state signal averaged by a conventional method. 
         [0037]    As shown in  FIG. 3 , according to the embodiment, a new averaging value is calculated every time a new power generator state signal is measured. On the other hand, as shown in  FIG. 4 , in the conventional method, an average value (power generator state signal) is calculated every predetermined amount of time (in the example shown in  FIG. 4 , an amount of time equal to four intermittent cycles of the switching transistor). Therefore, once a power generator state signal is outputted, even when the state of the power generator changes, the change is not reflected in the content of the power generator state signal during the subsequent four cycles. 
         [0038]    In this way, according to the voltage controller  1  for a vehicle according to the embodiment, a result obtained by a power generator state signal being averaged is transmitted to the vehicle-side controller  6  as the power generator control signal. Therefore, every time a state of the power generator  2  for a vehicle changes, details of the change can be reflected. Reliability of the power generator control signal can be improved. 
         [0039]    As a result of the switching transmitter  114  being intermittently controlled at a predetermined cycle, measurement accuracy of the power generator state signal, contents of which are the duty ratio of the switching transistor  114  and a current value of the current flowing to the field winding  21 , can be increased. 
         [0040]    The duty ratio and the current value are measured (measurement operation subsequent to V n+10  in  FIG. 3 ) and the power generator state signal is generated at the same cycle as the intermittent cycle of the switching transistor  114 , regardless of whether intermittent control is actually performed. As a result of the duty ratio and the current value being measured in time with the intermittent cycle of the switching transistor  114 , accuracy of these measurements can be further increased. 
         [0041]    The present invention is not limited to the above-described embodiment. Various variation embodiments within the scope of the spirit of the present invention are possible. For example, the exponentially weighted moving average circuit  17  can change the averaging frequency N depending on the state of the power generator  2  for a vehicle. As a result, when required response characteristics differ based on the state of the power generator  2  for a vehicle (for example, when the power generator rotation frequency is excessive high or low, or when the power generator temperature is excessive high or low), the averaging frequency can be changed, and a power generator state signal of an appropriate sensitivity can be outputted. 
         [0042]    The exponentially weighted moving average circuit  17  can change the averaging frequency N depending on a communication signal sent from the vehicle-side controller  6 . For example, the communication signal is received by the communication control circuit  18  or another circuit and inputted into the exponentially weighted moving average circuit  17 . As a result, when required response characteristics differ depending on a vehicle state (for example, when an engine rotation frequency is excessively high or low, or when a coolant temperature is excessively high or low; it is assumed that the communication signal sent from the vehicle-side controller  6  includes information on the engine rotation frequency and the coolant temperature), a power generator state signal of an appropriate sensitivity can be outputted by the averaging frequency being changed by an instruction from the vehicle-side controller  6 . 
         [0043]    The exponentially weighted moving average circuit  17  can set the averaging frequency N to a frequency corresponding to a time constant of the field winding  21 . As a result of the averaging frequency of the power generator state signal, contents of which are the duty ratio of the switching transistor  114  and the current value of the current flowing to the field winding  21 , being set to a frequency corresponding to the time constant of the field winding  21 , a power generator state signal having high measurement accuracy close to actual values can be outputted. 
         [0044]    When, in the inputted power generator state signals, the same value continues for a predetermined amount of time or for a predetermined consecutive number of times, the exponentially weighted moving average circuit  17  can output power generator state signals in which the same value is continued, instead of the averaged power generator state signal. As a result, a power generator state signal having high measurement accuracy close to actual values can be outputted by an EWM averaging result being changed to 0% or 100%, when the duty ratio of the switching transistor  114  is averaged and a 0%- or 100%-state continues for a predetermined amount of time or a predetermined consecutive number of times.