Patent Publication Number: US-2012029837-A1

Title: Engine revolution meter

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority to Japanese Patent Application No. 2010-171546 filed on Jul. 30, 2010, the contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to an engine revolution meter for a vehicle. 
     BACKGROUND OF THE INVENTION 
     Vehicles have been progressively electronized, and a sensor and a meter display actuator (e.g., a motor and a graphic circuit) have been sophisticated so that a meter display response speed (i.e., responsivity) can be improved. There is a concern that a pointer needle of an engine revolution meter wiggles due to an improved meter display response speed so that a meter display can flicker. JP-6-242134 discloses a technique for reducing a small motion of the pointing needle during an engine idle condition. 
     In recent years, there has been an increase in the number of vehicles equipped with a stop-idle feature that turns an engine OFF when a vehicle is stopped, for example, at a traffic light. In such a vehicle, the engine frequently switches between an idling condition and an OFF condition. Accordingly, the pointing needle of the engine revolution meter frequently moves between an engine idling RPM value and zero. The movement of the pointing needle between the engine idling RPM value and zero is relatively large. A driver may feel uncomfortable with such a large and frequent movement of the pointing needle of the engine revolution meter. 
     JP-6-242134 fails to disclose how to control the movement of the pointing needle when the engine switches between the idling condition and the OFF condition. 
     SUMMARY OF THE INVENTION 
     In view of the above, it is an object of the present invention to provide an engine revolution meter for displaying a change in an engine revolution number comfortably to a driver. 
     According to an aspect of the present invention, an engine revolution meter for displaying an engine revolution number display value includes an obtaining device, a calculating device, and a determining device. The obtaining device obtains an engine revolution number measurement value corresponding to a measured revolution number of an engine of a vehicle. The calculating device calculates the display value based on the measurement value. The determining device determines whether the measurement value is greater or less than a reference value. When the determining device determines that the measurement value is less than the reference value, the calculating device calculates the display value in such a manner that the display value changes at a first rate different from a second rate at which the measurement value changes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features, and advantages will become more apparent from the following description and drawings in which like reference numerals depict like elements. In the drawings: 
         FIG. 1  is a block diagram of an engine revolution meter according to an embodiment of the present invention; 
         FIG. 2  is a flow chart of a control process performed in the engine revolution meter; 
         FIG. 3  is a flow chart of a calculation process performed in the engine revolution meter; 
         FIG. 4  is a diagram illustrating an example of a relationship between a measurement value and a display value observed when the measurement value changes; 
         FIG. 5  is a diagram illustrating another example of the relationship between the measurement value and the display value observed when the measurement value changes; 
         FIG. 6  is a diagram illustrating an example of the relationship between the measurement value and the display value observed when an engine is stopped; 
         FIG. 7  is a diagram illustrating another example of the relationship between the measurement value and the display value observed when the engine is stopped; 
         FIG. 8  is a diagram illustrating an example of the relationship between the measurement value and the display value observed when the engine is started; 
         FIG. 9  is a diagram illustrating another example of the relationship between the measurement value and the display value observed when the engine is started; 
         FIG. 10  is a diagram illustrating the relationship between the measurement value and the display value according to a modification; and 
         FIG. 11  is a diagram illustrating a relationship among the measurement value, the display value, and the brightness for displaying the display value. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Embodiment 
     An engine revolution meter  1  according to an embodiment of the present invention is described below with reference to  FIG. 1 . The engine revolution meter  1  includes a control unit  10 , a display  20 , and a sensor unit  30 . 
     The control unit  10  has a controller  11 , a display driver  12  connected to the controller  11 , a local area network (LAN) interface (IF)  14  connected to an in-vehicle LAN  40 , and an input interface (IF)  15  connected to a sensor unit  30 . The controller  11  can perform data communication through the LAN/IF  14  with on-board devices connected to the in-vehicle LAN  40 . 
     The controller  11  includes a central processing unit (CPU)  11   a , a read only memory (ROM)  11   b , and a random access memory (RAM)  11   c . The ROM  11   a  stores control program performed by the CPU  11   a . The CPU  11   a , the ROM  11   b , and the RAM  11   c  are connected together through a bus line  11   d . Thus, data is transmitted among the CPU  11   a , the ROM  11   b , and the RAM  11   c  so that the controller  11  can serve as a microcomputer. 
     The display driver  12  drives and controls the display  20 . 
     The input/IF  15  receives an engine RPM signal from an engine revolution sensor  31  incorporated in the sensor unit  30  and outputs the an engine RPM signal to the controller  11 . For example, the input/IF  15  can include a voltage converter or a waveform shaper for converting the an engine RPM signal into a signal form that can be processed by the controller  11 . 
     The display  20  is located on an instrument panel solely or together with another meter or display apparatus. The display  20  includes at least one of a mechanical meter  201  and a digital meter  21 . 
     The mechanical meter  201  includes a dial  202  and a needle  203 . 
     The dial  202  is made of a translucent thin plate. Numbers (or characters)  205  and corresponding markings  206  are printed on the outer edge of the front side of the dial  202  and arranged at approximately regular intervals in a circumferential direction of the dial  202 . The numbers  205  and markings  206  indicate an engine revolution number, for example, in units of revolutions per minute (RPM). A non-translucent, colored layer  204  is formed on the dial  202  in such a manner that the numbers  205  and markings  206  are not covered with the colored layer  204 . 
     The number  205  and the corresponding marking  206  are illuminated from the back side of the dial  202  by a common light source (not shown), such as a light-emitting diode (LED), located at a position corresponding to the number  205  and the marking  206 . Each light source is controlled and illuminated by a light source driver (not shown) incorporated in the display driver  12 . For example, the light source driver PWM-controls the brightness of the light source according to a command from the controller  11 . Alternatively, the number  205  and the corresponding marking  206  can be illuminated by separate light sources. 
     A root of the needle  203  is attached to a rotating shaft (not shown) of a motor  203   m . For example, the motor  203   m  can be a step motor. The display driver  12  calculates the rotation amount and direction of the motor  203   m  based on the present position of the motor  203   m  and an engine RPM display value received from the controller  11 . Then, the display driver  12  drives the motor  203   m  so that the motor  203   m  can rotate by the calculated rotation amount in the calculated rotation direction. For example, the present position of the motor  203   m  can be measured from an origin point corresponding to the marking  206  with the number  205  of “0”. 
     The front side of the needle  203  is translucent. A light source  203   c , such as a LED, is located near the root of the needle  203  and emits light in a direction toward the tip of the needle  203  so that the needle  203  can be illuminated. A cover  203   b  is attached to the root of the needle  203  to cover the light source  203   c . Thus, the light source  203   c  is hidden from user&#39;s view. 
     As described above, the number  205 , the marking  206 , and the needle  203  on the dial  202  of the mechanical meter  201  are illuminated by separate light sources. Alternatively, a lamp  207  can be placed in a lower position on the front side of the dial  202  to illuminate the entire mechanical meter  201 . 
     The digital meter  21  has a display area  22  for displaying a bar graph constructed with multiple segments  22   a  arranged in one direction. Each segment  22   a  has an approximately rectangular light-emitting surface. A number and/or marking can be displayed along with the corresponding segment  22   a  in the display area  22 . 
     Each segment  22   a  is formed with a light source such as a LED or a vacuum fluorescent display (VFD) and controlled by a segment driver incorporated in the display driver  12 . Specifically, the display driver  12  illuminates the segments  22   a  based on the engine RPM display value received from the controller  11  so that the bar graph indicative of the engine RPM display value can be displayed on the display area  22 . 
     In an example shown in  FIG. 1 , the rectangular-shaped segments  22   a  are arranged in one direction so that the engine RPM display value can be displayed as a bar graph. The shape and arrangement of the segment  22   a  are not limited to the example shown in  FIG. 1 , as long as the number of the segments  22   a  to be illuminated varies depending on the engine RPM display value. For example, the segments  22   a  can be shaped and arranged so that the engine RPM display value can be displayed as a line graph, a circular graph, or the like. Likewise, the display area  22  is not limited to a rectangular shape. For example, the display area  22  can be polygonal, circular, ellipsoidal, or the like. 
     The display  20  can be configured as a graphic meter using an organic electroluminescence (EL), a dot-matrix liquid crystal display (LCD), a plasma display, or the like. 
     As mentioned previously, the sensor unit  30  includes the engine revolution sensor  31 . The engine revolution sensor  31  measures the engine RPM and outputs the engine RPM signal indicative of the engine RPM measurement value. The engine RPM signal is inputted through the input/IF  15  to the controller  11  so that the controller  11  can obtain the engine RPM measurement value. Thus, the input/IF  15  can serve as an engine revolution number obtaining device. It is noted that when the engine RPM signal is an analog signal, an analog-to-digital (A/D) converter  13  can be interposed between the input/IF  15  and the controller  11 , as shown in  FIG. 1 . 
     Alternatively, engine RPM information associated with the engine RPM measurement value can be inputted from the on-board device connected to the in-vehicle LAN  40  to the controller  11  through the LAN/IF  14  so that the controller  11  can obtain the engine RPM measurement value. In such an approach, wiring between the control unit  10  and the sensor unit  30  can become unnecessary. In this case, the LAN/IF  14  can serve as an engine revolution number obtaining device. 
     An engine switch  35  shown in  FIG. 1  can be a traditional ignition switch or a push switch used to start and stop an engine of a vehicle with an electronic smart key system. When the engine switch  35  is turned ON to start the engine, the engine switch  35  outputs an engine start command signal to the control unit  10 . In contrast, when the engine switch  35  is turned OFF to stop the engine, the engine switch  35  outputs an engine stop command signal to the control unit  10 . In an example shown in  FIG. 1 , the engine switch  35  is connected directly to the control unit  10 . Alternatively, the engine switch  35  can be connected through the in-vehicle LAN  40  to the control unit  10 . 
       FIG. 2  is a flow chart illustrating a control process that is performed by the CPU  11   a  of the controller  11  in accordance with the control program. 
     The control process starts at S 11 , where the controller  11  obtains the engine RPM measurement value. Specifically, at S 11 , the engine RPM signal outputted from the engine revolution sensor  31  is converted by the A/D converter  13  into engine RPM data, and the controller  11  obtains the engine RPM measurement value based on the engine RPM data. Alternatively, at S 11 , the controller  11  can receive engine RPM information through the LAN/IF  14  from the on-board device connected to the in-vehicle LAN  40  and obtain the engine RPM measurement value based on the engine RPM information. 
     Then, the control process proceeds to S 12 , where the controller  11  compares the engine RPM measurement value, obtained at S 11 , with a predetermined reference value prestored in the ROM  11   b . For example, the reference value can be an engine idle RPM, an engine RPM during charging of a battery of a hybrid vehicle, or an upper limit (e.g., 2000 rpm) of an engine RPM range a user usually uses. 
     If the engine RPM measurement value is greater than the reference value corresponding to No at S 12 , the control process proceeds to S 20 . At S 20 , the controller  11  displays the display  20  as usual. Specifically, at S 20 , the controller  11  calculates the engine RPM display value without any processing on the engine RPM measurement value and outputs the engine RPM display value (i.e., the engine RPM measurement value) to the display driver  12 . Thus, the display  20  displays the exact engine RPM measurement value. 
     In contrast, if the engine RPM measurement value is equal to or less than the reference value corresponding to YES at S 12 , the control process proceeds to S 13 . At S 13 , the controller  11  determines, based on the engine RPM measurement value, whether the engine is in a stopped condition. For example, when the engine RPM measurement value less than a predetermined threshold value (e.g., 100 rpm) is kept for a predetermined period, the controller  11  can determine that the engine is in the stopped condition. 
     If the controller  11  determines that the engine is in the stopped condition corresponding to YES at step S 13 , the control process proceeds to S 18 . At S 18 , the controller  11  determines whether the engine start command signal is received from the engine switch  35 . If the controller  11  does not receive the engine start command signal from the engine switch  35  corresponding to NO at S 18 , the control process proceeds to S 20 . In contrast, if the controller  11  receives the engine start command signal from the engine switch  35  corresponding to YES at S 18 , the control process proceeds to S 19 . At S 19 , the controller  11  performs a display value calculation process for calculating the engine RPM display value by correcting the engine RPM measurement value. The calculation process is discussed in detail later. 
     In contrast, if the controller  11  determines that the engine is not in the stopped condition corresponding to NO at step S 13 , the control process proceeds to S 14 . At S 14 , the controller  11  determines whether the engine stop command signal is received from the engine switch  35 . If the controller  11  receives the engine stop command signal from the engine switch  35  corresponding to YES at S 14 , the control process proceeds to S 19 . In contrast, if the controller  11  does not receive the engine stop command signal from the engine switch  35  corresponding to NO at S 14 , the control process proceeds to S 15 . 
     At S 15 , the controller  11  determines whether there is a change in the engine RPM measurement value. For example, when a difference between the present engine RPM measurement value and the next previous RPM measurement value exceeds 5 rpm, the controller  11  can determine that there is the change in the engine RPM measurement value. If the controller  11  determines that there is the change in the engine RPM measurement value corresponding to YES at S 15 , the control process proceeds to S 19 . In contrast, if the controller  11  determines that there is no change in the engine RPM measurement value corresponding to NO at S 15 , the control process ends so that the present display condition can be continued. 
     Next, the calculation process performed at S 19  in the flow chart of  FIG. 2  is described below with reference to a flow chart of  FIG. 3 . The calculation process starts at S 31 , where the controller  11  determines whether a timing of calculation of the engine RPM display value arrives. For example, the calculation timing can arrive when the controller  11  determines that there is the change in the engine RPM measurement value, or when a predetermined time is elapsed after the controller  11  determines that there is the change in the engine RPM measurement value. Alternatively, the calculation timing can arrive when the controller  11  receives the engine start or stop command signal, or when a predetermined time is elapsed after the controller  11  receives the engine start or stop command signal. Alternatively, the calculation timing can arrive when the controller  11  determines that the engine is in the stopped condition after receiving the engine stop command signal. Alternatively, the calculation timing can arrive when the controller  11  determines that the engine RPM measurement value exceeds a predetermined threshold after receiving the engine start command signal. 
     If the controller  11  determines that the calculation timing arrives corresponding to YES at S 31 , the calculation process proceeds to S 32 . At S 32 , the controller  11  calculates the rate of the change in the engine RPM measurement value. For example, the controller  11  can calculate the engine RPM measurement value change rate by dividing the difference between the present engine RPM measurement value and the next previous RPM measurement value by a time interval at which the calculation process is performed. Alternatively, the previous engine RPM measurement values can be stored as historical data in the RAM  11   c , and the engine RPM measurement value change rate can be calculated based on the historical data. 
     Then, the calculation process proceeds to S 33 , where the controller  11  calculates the rate of the change in the engine RPM display value based on the engine RPM measurement value change rate, which is calculated at S 32 . Specifically, the controller  11  calculates the engine RPM display value change rate in such a manner that the engine RPM display value change rate becomes less than the engine RPM measurement value change rate. If the next previous engine RPM display value change rate remains less than the engine RPM measurement value change rate, the next previous engine RPM display value change rate can be used as the engine RPM display value change rate. 
     Then, the calculation process proceeds to S 34 , where the controller  11  calculates the engine RPM display value based on the engine RPM display value change rate, which is calculated at S 33 , and the next previous engine RPM display value, which is stored in the RAM  11   c . Then, the calculation process proceeds to S 35 , where the controller  11  outputs the engine RPM display value, which is calculated at S 34 , to the display driver  12  so that the display driver  12  can drive the display  20  based on the engine RPM display value. Then, the calculation process ends. 
     Below, relationships between the engine RPM measurement value and the engine RPM display value in the control process are described. Firstly, a relationship between the engine RPM measurement value and the engine RPM display value observed when the engine RPM measurement value below a reference value NE 1  changes is described with reference to  FIGS. 4 and 5 . 
     As shown in  FIG. 4 , when the engine RPM measurement value decreases below the reference value NE 1 , the controller  11  determines that the calculation timing arrives. Thus, the engine RPM display value change rate is set less than the engine RPM measurement value change rate. Therefore, the engine RPM display value changes at a rate less than a rate at which the engine RPM measurement value changes. Then, when the engine RPM measurement value below the reference value NE 1  starts to increase, the controller  11  determines that the calculation timing arrives. Thus, the engine RPM display value change rate is set less than the engine RPM measurement value change rate. Therefore, until the engine RPM measurement value increases above the reference value NE 1 , the engine RPM display value changes at the rate less than the rate at which the engine RPM measurement value changes. 
     It is noted that a user may want to know as soon as possible when the engine starts. To satisfy such a user demand, as shown in  FIG. 5 , only when the engine RPM measurement value below the reference value NE 1  decreases, the engine RPM display value change rate can be set less than the engine RPM measurement value change rate. In other words, when the engine RPM measurement value below the reference value NE 1  increases, the engine RPM display value change rate can be set equal to the engine RPM measurement value change rate. Alternatively, according to user demands, only when the engine RPM measurement value below the reference value NE 1  increases, the engine RPM display value change rate can be set less than the engine RPM measurement value change rate. 
     In the examples shown in  FIGS. 4 and 5 , the calculation process is started (i.e., the calculating timing arrives) at the same time the engine RPM measurement value decreases below the reference value NE 1  or the engine RPM measurement value below the reference value NE 1  starts to increase. Alternatively, the calculation process can be started (i.e., the calculating timing can arrive), when a predetermined delay time is elapsed after the engine RPM measurement value decreases below the reference value NE 1  or the engine RPM measurement value below the reference value NE 1  starts to increase. 
     Secondary, a relationship between the engine RPM measurement value and the engine RPM display value observed when the engine is stopped is described with reference to  FIGS. 6 and 7 . As shown in  FIG. 6 , when the running engine is commanded to be stopped (i.e., when the controller  11  receives the engine stop command signal), the controller  11  determines that the calculation timing arrives. Thus, the engine RPM display value change rate is set less than the engine RPM measurement value change rate. In some types of engines, the engine RPM measurement value change rate during a time period from when the engine is commanded to be stopped to when the engine is completely stopped may depend on the engine RPM measurement value obtained at the time the engine is commanded to be stopped. In such an engine, a first mapping table between the engine RPM measurement value at the time the engine is commanded to be stopped and the engine RPM measurement value change rate during the time period from when the engine is commanded to be stopped to when the engine is completely stopped can be prestored in the ROM  11   b . In such an approach, when the engine is commanded to be stopped, the engine RPM display value change rate can be set less than the engine RPM measurement value change rate by referring to the first mapping table. 
     In the example shown in  FIG. 6 , the calculation process is started (i.e., the calculating timing arrives) at the same time the controller  11  receives the engine stop command signal. Alternatively, the calculation process can be started (i.e., the calculating timing can arrive), when a predetermined delay time is elapsed after the controller  11  receives the engine stop command signal. 
     Alternatively, as shown in  FIG. 7 , the controller  11  can determine that the calculation timing arrives, when the engine RPM measurement value becomes zero after the running engine is commanded to be stopped (i.e., after the controller  11  receives the engine stop command signal). In this case, the engine RPM measurement value change ratio can be calculated by dividing the engine RPM measurement value at the time the engine is commanded to be stopped by the time period from when the engine is commanded to be stopped to when the engine RPM measurement value becomes zero. Thus, the engine RPM display value change rate can be set less than the calculated engine RPM measurement value change rate. Alternatively, the controller  11  can determine that the calculation timing arrives, when the engine RPM measurement value decreases below a predetermined value after the running engine is commanded to be stopped. 
     Thirdly, a relationship between the engine RPM measurement value and the engine RPM display value when the engine is started is described with reference to  FIGS. 8 and 9 . As shown in  FIG. 8 , when the stopped engine is commanded to be started (i.e., when the controller  11  receives the engine start command signal), the controller  11  determines that the calculation timing arrives. Thus, the engine RPM display value change rate is set less than the engine RPM measurement value change rate. In some types of engines, the engine RPM measurement value change rate during a time period from when the engine is commanded to be started to when the engine is completely started may depend on the engine RPM measurement value obtained at the time the engine is commanded to be started. In such an engine, a second mapping table between the engine RPM measurement value at the time the engine is commanded to be started and the engine RPM measurement value change rate during the time period from when the engine is commanded to be started to when the engine is completely started can be prestored in the ROM  11   b . In such an approach, when the engine is commanded to be started, the engine RPM display value change rate can be set less than the engine RPM measurement value change rate by referring to the second mapping table. 
     Alternatively, as shown in  FIG. 9 , the controller  11  can determine that the calculation timing arrives, when the engine RPM measurement value reaches a predetermined value NE 2  after the stopped engine is commanded to be started (i.e., after the controller  11  receives the engine start command signal). In this case, the engine RPM measurement value change ratio can be calculated by dividing the predetermined value NE 2  by a time period from when the engine is commanded to be started to when the engine RPM measurement value reaches the predetermined value NE 2 . Thus, the engine RPM display value change rate can be set less than the calculated engine RPM measurement value change rate. 
     In the above examples shown in  FIGS. 4-9 , the engine RPM display value changes at a constant rate. Alternatively, as shown in  FIG. 10 , the engine RPM display value can change at a non-constant rate.  FIG. 10  illustrates a relationship between the engine RPM measurement value and the engine RPM display value from when the running engine is stopped to when the stopped engine is started. In this case, for example, the engine RPM display value change rate can be calculated by subtracting a predetermined value from the engine RPM measurement value change rate or by multiplying the engine RPM measurement value change rate by a predetermined coefficient less than one. In such an approach, the engine RPM display value can change at a non-constant rate by following the change in the engine RPM measurement value. The subtracted value and the multiplied coefficient can vary depending on the engine RPM display value. 
     When the calculation process shown in  FIG. 3  is performed so that the engine RPM display value change rate can be different from the engine RPM measurement value change rate, a design of a meter display displayed on the display  20  can be different than usual. For example, as shown in  FIG. 11 , the brightness of the needle  203  of the mechanical meter  201  can change between when the calculation process is performed and when the calculation process is not performed. In an example shown in  FIG. 11 , when the calculation process is performed, the brightness of the light source  203   c  is set to a first value L 0 , and when the calculation process is not performed, the brightness of the light source  203   c  is set to a second value L 1  greater than the first value L 0 . Thus, when the calculation process is performed, the needle  203  is illuminated more darkly than usual. Thus, a user can recognize that the calculation process is performed. Alternatively, when the calculation process is performed, the needle  203  can be illuminated more brightly than usual. Alternatively, the color of the needle  203  can change between when the calculation process is performed and when the calculation process is not performed. 
     Likewise, at least one of the brightness and color of the display area  22  can be changed between when the calculation process is performed and when the calculation process is not performed. 
     Likewise, when the display  20  is configured as a graphic meter, at least one of the brightness, color, and contrast can be changed between when the calculation process is performed and when the calculation process is not performed. 
     (Modifications) 
     The embodiment described above can be modified in various ways. For example, in the case of  FIG. 11 , when the brightness changes from a normal value or returns to the normal value, the brightness can change at a predetermined rate. 
     Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims.