Patent Publication Number: US-6708106-B2

Title: Throttle valve opened amount calculator

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a throttle valve opened amount calculator. 
     Automobiles are provided with throttle valve sensors. A throttle valve opened amount sensor detects the opened amount of a throttle valve, which is arranged in an intake passage and opened and closed in accordance with the depressed amount of an acceleration pedal. The opened amount of the throttle valve is used as a parameter to perform engine control, such as fuel injection and ignition adjustment. In a four wheel drive vehicle, the throttle valve opened amount is used as a parameter for controlling distribution of the drive force of a transmission installed in the vehicle. 
     The throttle valve opened amount θ is calculated as described below. 
     A CPU receives a detection signal (detection voltage TPV) from a throttle valve sensor and uses the detection voltage TPV and predetermined data to obtain the throttle valve opened amount θ. More specifically, the CPU subtracts a predetermined reference value (zero point detection value TPV 0 ) from the detection voltage TPV to obtain an absolute value (TPA=TPV-TPV 0 ). 
     The CPU uses map data of the throttle valve opened amount θ corresponding to the absolute value TPA to obtain the throttle valve opened amount θ corresponding to the present detection voltage (absolute value TPA). The zero point detection value TPV 0  is the voltage value output from the throttle valve sensor when the throttle valve is fully closed (θ=0). 
     The throttle valve opened amount θ is obtained from the absolute value TPA for the following reason. There are differences between throttle valve sensors, which are installed in automobiles. Thus, the zero point detection value TPV 0  differs between sensors (e.g., 0.6±0.2V). Accordingly, the zero point detection value TPV 0  is obtained for each throttle valve sensor and the absolute value TPA is obtained from the zero point detection value TPV 0 . By obtaining the zero point detection value TPV 0  in accordance with the absolute value TPA, errors that result from differences between sensors are prevented and the throttle valve opened amount θ is accurately obtained. In this state, the same map data for obtaining the throttle valve opened amount θ is used for every automobile even though there may be differences between throttle valve sensors. 
     Changes in the sensor caused by reasons such as wear occur as time passes by. Thus, the CPU periodically corrects the zero point detection value TPV 0 . When the detection value TPV is smaller than the zero point detection value TPV 0 , the CPU sets the detection voltage TPV as a new zero point detection value TPV. The CPU obtains the throttle valve opened amount θ in accordance with the updated zero point detection value TPV 0 . Accordingly, the zero point detection value TPV 0  is replaced by a smaller value whenever the detection voltage TPV is less than the zero point detection value TPV 0 . 
     In the prior art process for correcting the zero point detection value TPV 0 , when the detection voltage TPV is less than the present zero point detection value TPV 0 , the zero point detection value TPV 0  is immediately updated with the detection voltage TPV. Thus, when the power supply voltage supplied to the sensor decreases for one reason or another or when the detection voltage TPV momentarily decreases due to noise, there is a possibility that the CPU may set the detection voltage TPV as the new zero point detection value TPV 0 . 
     The drive force transmission of a four wheel drive vehicle is normally separated from the throttle valve sensor, which is controlled by an engine controller. Thus, the signal line of the sensor is long and is apt to being affected by noise. Consequently, the zero point detection value TPV 0  may be updated when not necessary. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a throttle valve opened amount calculator that accurately calculates the throttle valve opened amount regardless of voltage fluctuation or noise. 
     To achieve the above object, the present invention provides a throttle valve opened amount calculator. The calculator includes a valve sensor for detecting an opened amount of a throttle valve to generate a detection voltage. A memory is connected to the valve sensor to store an initial zero point detection value. The initial zero point detection value is the detection voltage output from the throttle valve sensor when the throttle valve is fully closed. A calculation circuit is connected to the valve sensor and the memory to obtain the difference between the detection voltage and the initial zero point detection value and to calculate the opened amount of the throttle valve with the difference. When a plurality of detection voltages that are less than the initial zero point detection value are generated, the calculation circuit calculates a new zero point detection value that is greater than a smallest one of the plurality of detection voltages by a predetermined value and updates the initial zero point detection value with the new zero point detection value. 
     A further perspective of the present invention is a method for calculating an opened amount of a throttle valve. The method includes detecting the opened amount of the throttle valve to generate a detection voltage, storing an initial zero point detection value in a memory, and calculating the opened amount of the throttle valve from a difference between the detection voltage and the initial zero point detection value. The initial zero point detection value is the detection voltage when the throttle valve is fully closed. When a plurality of detection voltages that are less than the initial zero point detection value are generated, a new zero point detection value that is greater than a smallest one of the plurality of detection voltages by a predetermined value is calculated. The initial zero point detection value is updated with the new zero point detection value. 
     Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
     FIG. 1 is a schematic diagram of a four wheel drive vehicle that includes a throttle valve opened amount calculator according to a preferred embodiment of the present invention; 
     FIG. 2 is a block diagram illustrating the configuration of the throttle valve opened amount calculator of FIG. 1; and 
     FIG. 3 is a flowchart illustrating a process executed by the throttle valve opened amount calculator to correct a zero point detection value voltage. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the drawings, like numerals are used for like elements throughout. 
     A throttle valve opened amount calculator according to a preferred embodiment of the present invention is applied to a drive force transmission control circuit  50  of a four wheel drive vehicle  100 . FIG. 1 is a schematic diagram of the four wheel drive vehicle  100  in which the drive force transmission control circuit  50  is incorporated. 
     As shown in FIG. 1, the four wheel drive vehicle  100  includes an internal combustion engine  2  and a transaxle  3 . The transaxle  3  includes a transmission  3   a , a front differential  3   b , and a transfer  3   c . A left front axle  4   a  and a right front axle  4   b  are connected to the transaxle  3 . Front wheels  5   a ,  5   b  are mounted on the front axles  4   a ,  4   b , respectively. The transaxle  3  transmits the drive force produced by the engine  2  to the front axles  4   a ,  4   b . The front axles  4   a ,  4   b  further transmit the drive force to the front wheels  5   a ,  5   b.    
     As shown in FIG. 1, the transfer  3   c  is connected to a propeller shaft  6 , which is further connected to a drive force transmission  7 . A drive pinion shaft  8  connects the drive force transmission  7  to a rear differential  9 . The rear differential  9  is connected to left and right rear axles  10   a ,  10   b . Rear wheels  11   a ,  11   b  are mounted on the rear axles  10   a ,  10   b , respectively. 
     The drive force generated by the engine  2  is transmitted to the drive force transmission  7  by the transfer  3   c  and the propeller shaft  6 . Further, the drive force is transmitted to the drive pinion shaft  8 , the rear differential  9 , and the rear axles  10   a ,  10   b  from the drive force transmission  7  to rotate the rear wheels  11   a ,  11   b.    
     The drive force transmission  7  has a wet multiplate electromagnetic clutch mechanism. The electromagnetic clutch mechanism includes a plurality of separable clutch plates (not shown) and an electromagnetic coil. The electromagnetic force generated by the electromagnetic coil, which is incorporated in the drive force transmission  7 , causes the clutch plates to frictionally engage each other. In this state, the drive force of the engine  2  that is transmitted to the drive force transmission  7  is transmitted from the propeller shaft  6  to the drive pinion shaft  8 . 
     The drive force transmitted to the drive pinion shaft  8  increases as the frictional engaging force of the clutch plates increases. The frictional engaging force of the clutch plates is determined by the value of the current supplied to the electromagnetic coil  7   a . The drive force transmission  7  controls the frictional engaging force to select either one of a four wheel drive state or a two wheel drive state and to control the drive force distribution rate between the front wheels  5   a ,  5   b  and the rear wheels  11   a ,  11   b  in the four wheel drive state. 
     A drive force transmission control circuit (throttle valve opened amount calculator)  50 , which controls the drive force transmission  7 , will now be discussed with reference to FIG.  2 . The drive force transmission control circuit  50  includes a drive force distribution controller (electronic control unit, ECU)  21  and a throttle valve sensor  33 . 
     The drive force distribution controller  21  includes a CPU  22 , which serves as a calculation circuit, a ROM  23 , a RAM  24 , and an input/output circuit  25 . 
     The CPU  22  performs various calculations to control the electromagnetic coil  7   a  of the drive force transmission  7  in accordance with various types of programs stored in the ROM  23 . The ROM  23  stores various programs, which control the electromagnetic coil  7   a , various types of data, and various types of map data. In addition to storing various types of data, the RAM  23  temporarily stores calculation results of the CPU  22 . 
     The control programs stored in the ROM  23  are used to calculate the value of the current supplied to the electromagnetic coil  7   a  in accordance with the present driven state of the automobile and to control the electromagnetic coil  7   a  by means of the input/output circuit  25  in accordance with the calculated current value. 
     The ROM  23  stores a program for calculating the opened amount θ of a throttle valve and a program for correcting a zero point detection value TPV 0 , which is used to calculate the opened amount θ. The map data stored in the ROM  23  is used to perform four wheel drive. The ROM  23  stores map data related to duty ratio control of the electromagnetic coil  7   a . The map data related to the duty ratio is used to produce the frictional engaging force (target frictional engaging force) corresponding to the drive force distribution rate that is optimal under the present driving state. 
     A left front wheel velocity sensor  31   a , a right front wheel velocity sensor  31   b , a left rear wheel velocity sensor  32   a , and a right rear wheel velocity sensor  32   b  are connected to the CPU  22  via input/output circuit  25 . 
     The left front wheel velocity sensor  31   a  detects the wheel velocity of the left front wheel  5   a . The right front wheel velocity sensor  31   b  detects the wheel velocity of the right front wheel  5   b . The front wheel velocity sensors  31   a ,  31   b  generate detection signals corresponding to the present velocity of the left front wheel  5   a  and the right front wheel  5   b , respectively, and send the detection signals to the input/output circuit  25 . In the same manner, the left rear wheel velocity sensor  32   a  detects the wheel velocity of the left rear wheel  11   a , and the right rear wheel velocity sensor  32   b  detects the wheel velocity of the right rear wheel  11   b . The rear wheel velocity sensors  32   a ,  32   b  generate detection signals corresponding to the present velocity of the left rear wheel  11   a  and the right rear wheel  11   b , respectively, and send the detection signals to the input/output circuit  25 . 
     The CPU  22  calculates the present wheel velocities VFL, VFR, VRL, VRR of the wheels  5   a ,  5   b ,  11   a ,  11   b  from the detection signals of the wheel velocity sensors  31   a ,  31   b ,  32   a ,  32   b , respectively. The CPU  22  calculates the front wheel average velocity VFN ((VFL+VFR)/2) from the wheel velocities VFL, VFR and calculates the rear wheel average velocity VRN ((VRL+VRR)/2) from the wheel velocities VRL, VRR. 
     The CPU  22  calculates a differential velocity ΔN(|VFN−VRN|/2) from the front wheel average velocity VFN and the rear wheel average velocity VRN. In the preferred embodiment, the CPU  22  obtains the vehicle velocity from the wheel velocities VFL, VFR, VRL, VRR. 
     A throttle valve sensor  33 , which detects the opened amount θ of the throttle valve of the engine  2 , is connected to the CPU  22  via the input/output circuit  25 . In the preferred embodiment, the throttle valve sensor  33  is controlled by an engine controller (not shown). The throttle valve sensor  33  generates a detection signal (detection voltage) TPV corresponding to the throttle valve opened amount θ and provides the CPU  22  with the detection voltage TPV via the input/output circuit  25 . The throttle valve opens and closes in accordance with the depression of an acceleration pedal (not shown). The CPU  22  uses the detection voltage TPV to calculate the throttle valve opened amount θ as described below. 
     The CPU  22  subtracts a predetermined reference value (zero point detection value TPV 0 ) from the detection voltage TPV to obtain an absolute value TPA (TPV−TPV 0 ). The zero point detection value TPV 0  is updated periodically and stored in the RAM  24 . The CPU  22  uses map data of the throttle valve opened amount θ corresponding to the absolute value TPA, which is stored in the ROM  23 , to obtain the throttle valve opened amount θ corresponding to the present detection voltage (absolute value TPA). 
     The CPU  22  calculates the optimal drive force distribution rate using map data, which is stored in the ROM  23 , in accordance with the throttle valve opened amount θ, the differential velocity ΔN, and the vehicle velocity. The CPU  22  generates a current generation signal, which determines the current value of the electromagnetic coil  7   a , in accordance with the calculation result. More specifically, the CPU  22  generates a current generation signal to obtain the duty ratio resulting in a drive force distribution rate that is optimal for the present driven state of the automobile in accordance with the map data stored in the ROM  23 . 
     The CPU  22  is connected to a drive circuit  35 , which controls the electromagnetic force of the electromagnetic coil  7   a  incorporated in the drive force transmission  7 , via the input/output circuit  25 . The drive force  35  generates drive current having a predetermined value and supplies the electromagnetic coil  7   a  of the drive force transmission  7  with the generated current. Accordingly, the drive force transmission  7  properly controls the drive force distribution rate. 
     The correction of the zero point detection value TPV 0 , which is used to calculate the throttle valve opened amount θ for the drive force transmission control circuit (throttle valve opened amount calculator)  50  will now be discussed with reference to the flowchart of FIG.  3 . The CPU  22  periodically performs the process illustrated in the flowchart of FIG.  3 . 
     The CPU  22  retrieves the detection voltage TPV and compares the detection voltage TPV with the zero point detection value TPV 0 , which is stored in the RAM  24  (step S1). When the detection voltage TPV is less than the zero point detection value TPV 0 , the CPU  22  proceeds to step S2 and compares the detection voltage TPV with a minimum detection voltage value TPVMIN, which is stored in the RAM  24  (step S2). 
     When the detection voltage TPV is less than the minimum detection voltage value TPVMIN, the CPU  22  sets the detected detection voltage TPV as the new minimum detection voltage value TPVMIN and rewrites the minimum detection voltage value TPVMIN (step S3). Afterward, the CPU  22  proceeds to step S4. At step S2, if the detection voltage TPV is greater than the minimum detection voltage value TPVMIN, the CPU  22  proceeds to step S4 without rewriting the minimum detection voltage value TPVMIN. The minimum detection voltage value TPVMIN is set at the value of the zero point detection value TPV 0  when the initial value is set. 
     In step S4, the CPU  22  adds “1” to a zero point detection counter value CT 0 , which is stored in the RAM  24 , and than compares the zero point detection counter value CT 0  with a reference detection number KT 0  (step S5). The reference detection number KT 0 , which is stored in the ROM  23 , is the number of times the detection voltage TPV is successively less than the zero point detection value TPV 0 . In the preferred embodiment, when the number of times in which the detection voltage TPV is less than the zero point detection value TPV 0  reaches the reference detection number KT 0  within a predetermined period, the zero point detection value TPV 0  is corrected. 
     In step S5, when the zero point detection counter value CT 0  is less than the reference detection number KT 0 , the CPU  22  temporarily terminates the process. Accordingly, when the detection voltage TPV being less than the zero point detection value TPV 0  is successively detected for a number of times that is less than the reference detection value KT 0  and the detection voltage TPV is less than the minimum detection voltage value TPV, the smallest detection voltage TPV is stored in the RAM  24  as the minimum detection voltage value TPVMIN (steps S2, S3). 
     When the zero point detection counter value CT 0  reaches the reference detection number KT 0 , the CPU  22  performs a calculation to correct the zero point detection value (step S6). The correction calculation is performed based on formula (1) using the zero point detection value TPV 0  and the minimum detection voltage value TPVMIN. 
     
       
         TPV 0 ←(TPV 0 −TPVMIN)/a+TPVMIN  (1) 
       
     
     In formula (1), “a” is a constant. In the preferred embodiment, “a” is set to, for example “2”. 
     As apparent from formula (1), in the correction calculation of the zero point detection value, the difference between the zero point detection value TPV 0  and the minimum detection voltage value TPVMIN is divided by two and the minimum detection voltage value TPVMIN is added to the divided difference. 
     The CPU  22  sets the calculation result as the new zero point detection value TPV 0  and rewrites the former zero point detection value TPV 0 . The CPU  22  then uses the new zero point detection value TPV 0  to calculate the throttle valve opened amount θ. 
     Subsequently, the CPU  22  sets the new zero point detection value TPV 0  as the minimum detection voltage value TPVMIN (step S7) and resets the zero point detection counter value CT 0  to “0” (step S8). Afterward, the CPU  22  temporarily terminates the correction process. 
     If the detection voltage TPV is greater than the zero point detection value TPV 0  is step S1, the CPU  22  proceeds to step S9 and sets the zero point detection value TPV 0 , which is stored in the RAM  24 , as the minimum detection voltage value TPVMIN. Then, the CPU  22  resets the zero point detection counter CT 0  to “0” (step S10) and temporarily terminates the process. Thus, even if the detection voltage TPV becomes much smaller than the minimum detection voltage value TPVMIN momentarily due to, for example, noise, the minimum detection voltage value TPVMIN is replaced by the present zero point detection value TPV 0  when the detection voltage TPV is detected as being greater than the zero point detection value TPV 0  Accordingly, an erroneous minimum detection voltage value TPVMIN is not used to calculate the new zero point detection value TPV 0 . 
     The throttle valve opened amount calculator  50  has the advantages described below. 
     (1) When the detection voltage TPV being less than the zero point detection value TPV 0  is detected for a predetermined number of times during a predetermined period, the zero point detection value TPV 0  is replaced by the corrected, new zero point detection value TPV 0 . The new zero point detection value TPV 0  is obtained by adding the minimum detection voltage value TPVMIN to a value that is one half of the difference between the zero point detection value TPV 0  and the minimum detection voltage value TPVMIN. Thus, the throttle valve opened amount is calculated with high accuracy. 
     (2) When the detection voltage TPV is greater than the zero point detection value TPV 0 , the CPU  22  rewrites the zero point detection value TPV 0 , which is stored in the RAM  24 , to the minimum detection voltage value TPVMIN. Accordingly, even if the detection voltage TPV becomes much smaller than the minimum detection voltage value TPVMIN momentarily due to, for example, noise, as long as the subsequently detected detection voltage TPV is greater than the zero point detection value TPV 0 , the detection voltage, which is abnormal due to noise, is set as the minimum detection voltage value TPVMIN and not used for subsequent calculation. Thus, even if the power supply voltage supplied to the sensor decreases for one reason or another or even if the detection voltage TPV becomes abnormally low due to noise, the throttle valve opened amount θ is calculated with high accuracy. 
     (3) When the detection voltage TPV being less than the zero point detection value TPV 0  is successively detected for a number of times that is equal to the reference detection number KT 0  within a predetermined period, the zero point detection value TPV 0  (minimum detection voltage value TPVMIN) is corrected. Accordingly, even if the detection voltage TPV becomes lower than the zero point detection value TPV 0  due to momentary voltage fluctuation or noise, the zero point detection value TPV 0  is not corrected. As a result, the calculation of the throttle valve opened amount θ is hardly affected by voltage fluctuation or noise. 
     (4) If the detection voltage TPV is detected as being greater then the zero point detection value TPV 0  after the zero point detection value TPV 0  is corrected, the minimum detection voltage value TPVMIN is replaced by the corrected zero point detection value TPV 0 . Accordingly, when the detection voltage TPV is successively detected as being less than the zero point detection value TPV 0  within the predetermined time, the minimum detection voltage value TPVMIN, which was obtained in the past, is not used in the correction process. As a result, the minimum detection voltage value TPVMIN is obtained with high accuracy. 
     It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, it should be understood that the present invention may be embodied in the following forms. 
     The constant “a” may be a value that is “1” or greater. 
     The reference detection number KT 0  may be a value in which the detection voltage TPV is only less than the zero point detection value TPV 0  during the predetermined time. 
     In formula (1), instead of the smallest detection voltage TPV that is less than the zero point detection value TPV 0  (minimum detection voltage value TPVMIN), the voltage value of the second smallest detection voltage TPV may be used to correct the zero point detection value TPV 0 . 
     In formula (1), the average value of a plurality of detection voltages TPV, which are smaller than the zero point detection value TPV 0 , may be calculated to update the zero point detection value TPV 0  with the average value of the detection voltage TPV. The average value of the detection voltage TPV may be calculated without the smallest detection voltage TPV. 
     The present invention may be embodied in a front engine rear drive (FR) or rear engine rear drive (RR) based four wheel drive vehicle. 
     The present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.