Abstract:
A fuel change indicator system for a vehicle. The system may comprise an internal combustion engine capable of combusting at least two different compositions of fuel and outputting torque to propel a vehicle; a fuel supply system configured to supply the fuel to said internal combustion engine and capable of changing the composition of the supplied fuel; an indicator capable of outputting a signal which is recognizable from outside of said vehicle; and a controller configured to control said fuel supply system to change the fuel composition; and control said indicator to output the signal in accordance with the fuel composition change.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims foreign priority to Japanese Patent Application No. 2006-183686, filed Jul. 3, 2006. 
     BACKGROUND 
     The present description relates to a dual-fuel engine, more specifically to an indicator for a vehicle having a dual fuel engine as its propelling power source. 
     When an internal combustion engine combusts fuel with air charged therein, it generates heat energy. The engine may be mounted on a vehicle, and may convert the heat energy to torque output to a drive-train to propel the vehicle. For example, in U.S. Patent Application Publication US2006/010823A1, a dual-fuel engine for an automotive vehicle is disclosed to selectively combust two different kinds of fuels, in this case, gaseous hydrogen and gasoline. Between the two different fuels, the amounts of heat energy generated from combustion of the same volume of stoichiometric mixtures are different. In a dual-fuel engine, the maximum mixture volume is constant, but maximum torque from the different kinds of fuel is different. For example, when the fuel is switched from gasoline to hydrogen, the engine output torque will decrease if, before the fuel switching, the engine outputs more torque from gasoline than the maximum torque from hydrogen. 
     Therefore, the vehicle propelling force may decrease when the fuel is switched. Then, the acceleration of the vehicle may be reduced, and the vehicle may even decelerate if the vehicle running resistance is greater for example in a high speed driving condition. As a result, when a rear vehicle follows a front vehicle with a dual-fuel engine, and the fuel supplied to the front vehicle is switched, both of the vehicle drivers may need to know about the possibility of reduced acceleration or deceleration of the front vehicle. 
     In the &#39;823 publication, when the hydrogen is supplied to the engine, it is indicated to the vehicle driver. Thus, the driver is informed that the fuel is switched from gasoline to hydrogen. However, the driver cannot tell if there is the possibility of the reduced acceleration of the vehicle. Further, other drivers who may be following the driver, for example, have no way of recognizing the possibility of the reduced acceleration of the vehicle due to the fuel switch. 
     SUMMARY 
     Accordingly, there is provided, in a first aspect of the present description, a fuel change indicator system for a vehicle, the system comprising an internal combustion engine capable of combusting at least two different compositions of fuel and outputting torque to propel a vehicle, and a fuel supply system configured to supply the fuel to the internal combustion engine and capable of changing the composition of the supplied fuel. The system further comprises an indicator capable of outputting a signal which is recognizable from outside of the vehicle, and a controller. The controller is configured to control the fuel supply system to change the fuel composition. It is further configured to control the indicator to output the signal in accordance with the fuel composition change. 
     In accordance with the first aspect, the indicator outputs the signal recognizable from the outside of the vehicle in accordance with the fuel composition change, for example from a liquid fuel to a gaseous fuel such as hydrogen. Therefore, from the outside of the vehicle, such as another vehicle driver, the possibility of reduced acceleration of the vehicle caused by the fuel composition change can be recognized. Consequently, safety of traffic in which the dual-fuel engine vehicle is involved can be improved. 
     In a second aspect of the present description, there is provided a method of controlling a vehicle system having an internal combustion engine to propel a vehicle. The internal combustion engine is capable of combusting at least two different compositions of fuel. The method comprises changing the composition of fuel supplied to said internal combustion engine, indicating a signal in accordance with the fuel composition change, and prohibiting the indicating the signal in accordance with an operating condition of the internal combustion engine. 
     In accordance with the second aspect, the signal indication in accordance with the fuel composition change is prohibited in accordance with an operating condition of the internal combustion engine. In other words, the signal indication is made only in certain engine operating conditions. Therefore, the signal indication can be limited to occasions where the vehicle behavior change caused by the fuel composition change needs to be known, for example. The limited occurrence of the signal indication can improve the effectiveness of the signal indication, for example, to the vehicle driver or the following driver. Consequently, safety of vehicle traffic in which the dual-fuel engine vehicle is involved can be improved. 
     In a third aspect of the present description, there is provided a method of controlling the vehicle system described above. The method comprises changing the composition of fuel supplied to the internal combustion engine, beginning to indicate a signal in accordance with the fuel composition change, and stopping the signal indication in accordance with an operating condition of the vehicle. 
     In accordance with the third aspect, the signal indication started in accordance with the fuel composition change is stopped in accordance with the vehicle operating condition. When the fuel composition is changed, the engine output torque may be substantially reduced, and it needs to be known. But as the time goes by, the once reduced torque will be constant, and the signal will not be indicated any more. Otherwise, the redundant indication may deteriorate the effectiveness of the indication. Therefore, the limited period of the signal indication can improve the effectiveness of the signal indication, for example, to the driver or the following vehicle driver. 
     In some embodiments, the indicator may be a visual display arranged on the vehicle, visible from behind the vehicle, for example, and further integrated with a brake light of an automotive vehicle so that a following driver can recognize a possibility of reduced acceleration of the preceding vehicle. 
     The signal indication may be prohibited when the desired output torque of the internal combustion engine is below a predetermined torque, for example when the desired output torque of the internal combustion engine after the fuel switching is within a predetermined amount from the desired output torque before the fuel switching. Accordingly, the signal indication can be limited to situations with higher possibility of reduced vehicle acceleration, and the effectiveness of the signal indication can be improved. 
     The signal indication, once started, may be stopped in accordance with output torque of the internal combustion engine. The engine output torque may temporarily drop during the fuel composition change due to engine operating constraints such as requirement for reduced noise and vibration. Then, the engine torque increases again after the completion of the fuel composition change, and then the signal indication may not be necessary any more. Instead of the engine torque, acceleration of the vehicle may be accounted for. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic plan view showing a configuration of an engine according to one embodiment of the present invention. 
         FIG. 2  is a block diagram schematically showing the engine. 
         FIG. 3  is a graph showing a characteristic relationship between a target torque and a throttle opening. 
         FIGS. 4A and 4B  are torque diagrams showing relationships between an accelerator pedal opening and a vehicle traveling speed; and  FIG. 4A  shows a characteristic of gasoline, and  FIG. 4B  shows a characteristic of a gaseous fuel. 
         FIG. 5  is a flowchart showing a torque control of the engine according to the embodiment. 
         FIG. 6  is a flowchart showing the torque control of the engine where a fuel being used is switched from gasoline to gaseous fuel in the embodiment. 
         FIG. 7  is a time chart showing an example where steps S 35  and S 36  in  FIG. 6  are executed. 
         FIG. 8  is a graph illustrating an example relationship between accelerator pedal position and target torque, for explaining step S 35  in  FIG. 6 . 
         FIG. 9  is a flowchart showing a routine to cancel an indicator turned on in  FIG. 6 . 
         FIG. 10  is a time chart showing an example where steps S 37  and S 38  in  FIG. 6  are executed. 
         FIG. 11  is a graph illustrating an example of changes of accelerator pedal position and target torque, during execution of steps S 37  and S 38  in  FIG. 6 . 
         FIG. 12  is a flowchart showing the torque control where the fuel being used is switched from gaseous fuel to gasoline in the embodiment. 
         FIG. 13  is a flowchart showing an Acceleration Reducing Process Subroutine shown at step S 47  in  FIG. 12 . 
         FIG. 14  is a graph illustrating an example of accelerator pedal position and target torque, for explaining a control where the fuel being used is switched from gaseous fuel to gasoline. 
     
    
    
     DETAILED DESCRIPTION 
     Hereafter, an embodiment of the present disclosure will be explained referring to the accompanied drawings. 
       FIG. 1  is a schematic plan view showing a configuration of an engine according to one embodiment.  FIG. 2  is a block diagram schematically showing the engine. 
     Referring to  FIG. 1 , a vehicle  10  is provided with an engine compartment  11  and a trunk compartment  12 . An engine  14  is disposed in the engine compartment  11  so as to be supported by frames of the vehicle. 
     Referring to  FIG. 2 , the engine  14  is a rotary engine. This engine  14  is of two-rotor type in which two rotor housings  15  (schematically shown in a divided state in  FIG. 2 ) are integrally provided with three side housings (not shown) so that each of the rotor housings  15  is intervened between the side housings to form two rotor accommodating chambers  16 . 
     The rotor accommodating chamber  16  is provided in a cocoon shape having a trochoid inner circumferential surface, and a rotor  17  is accommodated inside the rotor accommodating chamber  16 . 
     The rotor  17  may be made of a special kind of a cast iron, and eccentrically revolves while apex seals provided to each apex constantly and slidingly contact with the inner circumferential surface of the rotor accommodating chamber  16 . Thus, the rotor  17  defines three combustion chambers in the rotor accommodating chambers  16 . Each of the rotor accommodating chambers  16  is connected with a pair of spark plugs  18  and a gaseous fuel injector  19 . It is of a direct-injection type in which a gaseous fuel (hydrogen in this embodiment) supplied from a gaseous fuel system  30  (which is a main point of this embodiment) is directly injected into one of the combustion chambers. 
     Internal gear teeth are formed in a central hole of the rotor  17  so that a revolving orbit of the rotor  17  is precisely maintained by the internal gear teeth being mated with stationary gears provided on the side housing. Further, an eccentric shaft  20  fits in the central hole of the rotor  17 . 
     Each of the rotor accommodating chambers  16  is also connected with an air-intake pipe  21  and an exhaust pipe (not illustrated). Fresh air is introduced in the combustion chamber through the air-intake pipe  21 , and exhaust gas is discharged through the exhaust pipe. 
     A port fuel injector  22  for injecting gasoline fuel is mounted to each of the air-intake pipes  21 . Each of the air-intake pipes  21  is branched for the rotor accommodating chambers  16  at a downstream end of an upstream air-intake pipe  23 . A throttle valve  24  is provided in the upstream air-intake pipe  23  so that it is opened and closed by an actuator  25 . 
     The spark plugs  18 , the fuel injectors  19  and  22 , and the actuator  25  are configured to be controlled by a control unit (PCM)  100  which will be described later. 
     Referring to  FIG. 1 , a gaseous fuel system  30  for supplying gaseous fuel to gaseous fuel injectors  19  will be explained. 
     As shown in  FIG. 1 , the gaseous fuel system  30  is provided with a gaseous fuel tank  31  arranged in the trunk compartment  12 . The gaseous fuel tank  31  may have 60 liters of volume, for example, and may be filled with hydrogen as gaseous fuel at approximately 35 MPa. 
     A main valve  32  that can be opened and closed by a solenoid is mounted to the gaseous fuel tank  31 . The main valve  32  extends in the front-and-rear direction of the vehicle  10 , and is connected with a feed pipe  33  connected with the gaseous fuel injectors  19 . A regulator valve  34  that decompresses gaseous fuel discharged from the main valve  32  to 0.6 MPa is provided in the feed pipe  33  on the upstream side (inside of the trunk compartment  12 ). 
     A cutoff valve  35  disposed in the engine compartment  11  is connected with the feed pipe  33 . The cutoff valve  35  opens and closes the feed pipe  33  by a solenoid so that it prevents leaking of gaseous fuel while the engine  14  is not running. 
     A gasoline tank  40  for storing gasoline is provided in the vehicle  10 . It is configured so that the gasoline in the gasoline tank  40  is injected from the port fuel injectors  22  to the engine  14  through a gasoline supply system. 
     In this embodiment, switching between gasoline and gaseous fuel is performed by a manual operation of a fuel switch  41  provided in an instrument panel of the automotive vehicle  10  as shown in  FIG. 1 . The driver who sits behind a steering wheel  46  of the automotive vehicle  10  can operate the fuel switch  41 . 
     Further, well-known brake lamps  42  are provided in the vehicle  10 . A message indicator light  45  is arranged on the instrument panel. The driver sitting behind the steering wheel  46  can see the message indicator light  45 . 
     Referring to  FIGS. 1 and 2 , the control unit  100  is a unit whose main components are a microprocessor, a main storage device, an auxiliary storage device, and an input/output device. An input component to be connected with the control unit  100  includes the fuel switch  41 , an accelerator pedal opening sensor SW 4 , an engine speed sensor SW 5 , a vehicle speed sensor SW 6 , and a throttle opening sensor SW 7 . Further, an output component to be connected with the control unit  100  includes the spark plugs  18 , fuel injectors  19  and  22 , actuator  25 , main valve  32  of gaseous fuel tank  31 , cutoff valve  35 , brake lamps  42 , and indicator light  45 , as mentioned above. 
       FIG. 3  is a graph showing a relationship between a target torque T and a throttle opening K. 
     Referring to  FIG. 3 , the auxiliary storage device of the control unit  100  stores a gasoline map Mg and a gaseous fuel map Mh (refer to  FIGS. 6 and 12 ) for switching a fuel type. The maps Mg and Mh are created based on experimental values of the relationship between the target engine torque Ti and the throttle opening K. 
     The gasoline map Mg is set based on gasoline characteristics G 1 -G 3  in  FIG. 3 , and gaseous fuel map Mh is set based on gaseous fuel characteristics H 1 -H 3  in  FIG. 3 . In the illustrated example, G 1  and H 1  are at 1,000 RPM of the engine speed V, G 2  and H 2  are at 2,500 RPM, and G 3  and H 3  are at 4,000 RPM, respectively. 
       FIGS. 4A and 4B  are graphs showing relationships between an accelerator pedal opening AOF and a vehicle traveling speed V.  FIG. 4A  shows the relationship in the case in which gasoline is used, and  FIG. 4B  shows the relationship in the case in which gaseous fuel is used. 
     Referring to  FIG. 4 , the auxiliary storage device of the control unit  100  also stores a torque control map Mt (refer to  FIG. 13 ) for reducing torque fluctuations during the fuel switching. The torque control map Mt is for absorbing rapid fluctuations of the torque when the fuel being used is switched from gaseous fuel to gasoline based on the relationship between the accelerator pedal opening AOF and the vehicle traveling speed V. As illustrated, one graph of  FIG. 4  defines torques to be equal to those torques illustrated in the other graph of  FIG. 4 . That is, G 1  is equal to H 1 , G 2  is equal to H 2 , and Gn is equal to Hn (n being an integer). By utilizing a torque control map Mt populated with data based on  FIGS. 4A and 4B , when the fuel being used for the traveling vehicle is switched from gaseous fuel to gasoline at a certain target torque Ti, the accelerator pedal opening AOF and the vehicle traveling speed V to which the value of the target torque Ti becomes equal may be selected immediately after the switching. Thus, it is possible to make the torque fluctuations slower and to buffer shock that may occur upon executing the switching of the fuel being used from gaseous fuel to gasoline, as will be described later. 
     The control unit  100  also includes a nonvolatile memory as a part of the auxiliary storage device for storing a fuel flag used as an identifier to identify the fuel type currently selected. 
       FIG. 5  is a flowchart showing a torque control routine of the engine according to this embodiment. 
     Referring to  FIG. 5 , while the engine  14  is running, the control unit  100  determines which type of fuel is selected based on the fuel flag (step S 20 ), and a map M corresponding to the selected fuel (for example, gasoline) is set (step S 21 ). In this step S 21 , if the fuel being used is gasoline, the gasoline map Mg is set as the map M. On the other hand, if the fuel being used is gaseous fuel, gaseous fuel map Mh is set as the map M. 
     Next, the control unit  100  determines whether a predetermined time has passed after the fuel flag is switched (step S 22 ). If the predetermined time has not passed in step S 22  (NO in step S 22 ), the control unit  100  further determines whether the switching of the fuel being used is from gasoline to gaseous fuel (step S 23 ). As will be described later, if the fuel being used is switched from gasoline to gaseous fuel (YES in step S 23 ), the flowchart shown in  FIG. 6  is executed. On the other hand, if the fuel being used is switched from gaseous fuel to gasoline (NO in step S 23 ), the flowchart shown in  FIG. 12  is executed. 
     If the predetermined time has passed in step S 22  (YES in step S 22 ), the control unit  100  reads a current throttle opening K, engine speed Ne, accelerator pedal opening AOF, and vehicle traveling speed V from the accelerator pedal opening sensor SW 4 , engine speed sensor SW 5 , vehicle traveling speed sensor SW 6 , and throttle opening sensor SW 7 , respectively (step S 24 ). 
     Next, based on the read values, the target torque Ti corresponding to the current traveling state is set based on the map M (step S 25 ). 
     Next, based on the map M, the actuator  25  is driven based on the set target torque Ti to control the throttle valve  24  (step S 26 ). It will be appreciated that, to adjust engine torque, a fuel amount supplied to the engine through fuel injectors  19  or  22  is typically adjusted. When a throttle opening K of the throttle valve  24  is adjusted at step S 26 , an amount of fresh air is inducted into the engine. An airflow meter (not shown) arranged in the intake air passage  23  upstream of the throttle valve  24 , detects airflow in the intake air passage  23 , and thus the amount of air inducted into the engine. Based on the detected airflow, an engine speed Ne and a target air-fuel ratio, the amount of fuel may be computed, for example, by controller  100 . Usually, the target air-fuel ratio is a constant value, that is, a stoichiometric air-fuel ratio which depends on the kind of fuel to be combusted. Therefore, the throttle valve opening is adjusted, and the engine output torque will be adjusted accordingly. 
     Next, the throttle opening K and engine speed Ne after driving the actuator  25  are read again (step S 27 ). 
     Next, an actual torque Tq is calculated based on the read throttle opening K and the engine speed Ne (step S 28 ). 
     The calculated actual torque Tq and target torque Ti are compared, and the throttle opening K is corrected (step S 29 ), and by returning to step S 26 , a feedback control for matching the target torque Ti and the actual torque Tq is realized. 
     If the fuel being used is switched from gasoline to gaseous fuel, referring to  FIG. 6 , the control unit  100  reads the current throttle opening K and the engine speed Ne (step S 30 ). Next, the target torque Ti is set by the read values based on the gasoline map Mg (step S 31 ). 
     Next, the control unit  100  reads a maximum torque Th obtained from gaseous fuel based on gaseous fuel map Mh (step S 32 ). Next, the control unit  100  calculates a torque difference Tgp between the target torque Ti and the maximum torque Th (step S 33 ). 
     Next, the control unit  100  determines whether the torque difference Tgp is less than a predetermined gap value Ts (step S 34 ). 
     If the torque difference Tgp is less than the gap value Ts (YES in step S 34 ), the control unit  100  sets a torque value Th as the target torque Ti where an absolute value of the torque difference Tgp is the minimum (step S 35 ). Then, the map M is updated with gaseous fuel map Mh (step S 36 ), and it returns to step S 26 . 
     On the other hand, if the torque difference Tgp is greater than the gap value Ts (NO in step S 34 ), the control unit  100  causes an indicator turned ON (step S 37 ) and then shifts to step S 35 . By forcing the indicator to be turned ON, the control unit  100  functions as a vehicle deceleration alerting control device. The indicator may be a visual indicator, for example, a brake lamp  42 , an in-cabin indicator light  45  configured to be visible by a driver of the vehicle, and/or an audio indicator, such as an recorded voice message, alarm, etc. In some embodiments, both the in-cabin indicator light  45  and the brake lamp  42  are provided and configured to light at substantially the same time, giving the driver and indication of when the brake lamps  45  are illuminated. In other embodiments, the audio signal and brake lamps may be provided and configured to be emitted and lighted simultaneously. And, in other embodiments, only one indicator may be provided. 
       FIG. 7  is a timing graph showing an example where steps S 35  and S 36  in  FIG. 6  are executed, and  FIG. 8  is a graph illustrating example accelerator pedal position and torque, for explaining step S 35  in  FIG. 6 . 
     First, referring to  FIG. 7 , during steady travel with a small accelerator pedal opening AOF, if the operator switches the fuel being used from gasoline to gaseous fuel at a time t 1 , since the torque difference Tgp is relatively small, the actual torque Tq relatively promptly returns to the same level as operating with gasoline, and the vehicle traveling speed V hardly changes. Therefore, the indicator will not be turned ON in this case (described later). As a result, it is possible to control excessive alerts to an operator of a follow-on vehicle. 
     Referring to  FIG. 8 , even if Tgp is small, when the torque setting control is not executed, a control point becomes as a phantom line in  FIG. 8  and, thus, a large torque shock may occur. On the other hand, in this embodiment, it is possible by adopting step S 35  in  FIG. 6  to reduce the torque difference Tgp during the switching as much as possible. In the meantime, during the steady travel, although the value of Tgp may be a negative value in rare cases, since the absolute value is set to become a minimum in step S 35 , the control point shifts so that Tgp may be zero in this case. 
     Next, referring to  FIG. 9 , in an Alert Canceling Process Subroutine, first, the control unit  100  determines whether indicator lights  45  are turned ON (step S 380 ). If the indicator is tuned ON (YES in step S 380 ), the control unit  100  reads a vehicle traveling speed V 1  (step S 381 ). Next, the control unit  100  holds for a predetermined period of time (0.1 second in the illustrated example) after reading the vehicle traveling speed V 1  (step S 382 ), and when the predetermined period of time has passed, the control unit  100  reads a vehicle traveling speed V 2  after the predetermined time has passed (step S 383 ). Next, the control unit  100  calculates a deceleration rate-dv based on the vehicle traveling speed V 1  and V 2  (step S 384 ). Next, the control unit  100  compares an absolute value of the calculated deceleration rate-dv with a predetermined changing rate dvs, and determines whether the absolute value of the deceleration rate-dv is reducing (step S 385 ). If the absolute value of the deceleration rate decreases below to the changing rate dvs (YES in step S 385 ), the control unit  100  turns OFF the indicator (step S 386 ). As a result, it is possible to reduce discomfort to the operator of a following vehicle caused by turning ON the brake lights  42 . On the other hand, if the absolute value of the deceleration rate is still high (NO in step S 385 ), the control unit  100  updates the vehicle traveling speed V 2  read in step S 383  to the initial vehicle traveling speed V 1  (step S 387 ), and returns to step S 382 . 
     As described above in relation to  FIG. 9 , canceling or stopping the indicator after the indicator has already begun emitting a signal, or prohibiting the indicator from emitting a visual or audio signal, may be based on a vehicle operating condition, such as vehicle speed and change in vehicle speed. Alternatively or in addition, the vehicle operation condition upon which the signal indication from the indicator is cancelled, stopped or prohibited may be engine torque. For example, a change of the actual torque Tq determined at the step S 28  of  FIG. 5  may be used for this determination. Accordingly, when the change is not negative, the signal indication may be stopped. Also, a change of the vehicle acceleration can be considered by differentiating the vehicle speed detected by the vehicle speed sensor SW 6 . 
     In one embodiment, for example, indication of the signal may be prohibited when a desired output torque, also referred to as target torque, of said internal combustion engine is below a predetermined torque. Further, indication of the signal may be prohibited when the desired output torque of said internal combustion engine after said switching the fuel is within a predetermined amount from the desired output torque before said switching. 
     Next, referring to  FIGS. 10 and 11 , an example in which the brake lights  42  or indicator light  45  is turned on will be explained. 
     Referring to  FIGS. 10 and 11 , for example, if the traveling state of the vehicle  10  is accelerating, when the fuel being used is switched from gasoline to gaseous fuel at a time t 2 , a large torque difference Tgp occurs even if the throttle opening K is fully open (WTO). In this case, the brake lamp  42  is turned ON when the fuel being used is switched (step S 37  in  FIG. 6 ). 
     Then, when the vehicle traveling speed V gradually decreases and the absolute value of the deceleration rate-dv becomes small, the brake lamp  42  is turned OFF by control of the Alert Canceling Process Subroutine illustrated in  FIG. 9 . 
     Next, referring to  FIGS. 12 ,  13 , and  14 , control routines in which the fuel being used is switched from gaseous fuel to gasoline will be explained. 
       FIG. 12  is a flowchart showing a torque control routine where the fuel being used is switched from gaseous fuel to gasoline in this embodiment.  FIG. 13  is a flowchart showing the Acceleration Reducing Process Subroutine in  FIG. 12 .  FIG. 14  is a graph illustrating an example of accelerator pedal position and target torque, for explaining a control where the fuel being used is switched from gaseous fuel to gasoline. 
     First, referring to  FIG. 12 , if the operator switches the fuel being used from gaseous fuel to gasoline, the control unit  100  reads the current throttle opening K and engine speed Ne (step S 40 ). Next, the target torque Ti is set by the read values based on gaseous fuel map Mh (step S 41 ). 
     Next, based on gasoline map Mg, the control unit  100  obtains a torque Tg outputted by the throttle opening K and the engine speed Ne corresponding to the target torque Ti with gasoline (step S 42 ). The control unit  100  then calculates the torque difference Tgp between the target torque Ti and the torque Tg (step S 43 ). 
     Next, the control unit  100  determines whether the torque difference Tgp is less than the predetermined gap value Ts (step S 44 ). 
     If the torque difference Tgp is less than the gap value Ts (YES in step S 44 ), the control unit  100  sets the torque value Tg as the target torque Ti where the absolute value of the torque difference Tgp is the minimum (step S 45 ). Then, the map M is updated to the gasoline map Mg (step S 46 ), and it returns to step S 26 . 
     On the other hand, if the torque difference Tgp is greater than the gap value Ts (NO in step S 44 ), the control unit  100  executes the Acceleration Reducing Process Subroutine S 47 , and then shifts to step S 45 . By executing the Acceleration Reducing Process Subroutine S 47 , the control unit  100  functionally constitutes an acceleration reducing control device. 
     Next, referring to the Acceleration Reducing Process Subroutine S 47  shown in  FIGS. 13 and 14 , first, the control unit  100  sets the target torque Th by the gaseous fuel immediately before the switch as the target torque Ti after the switch (step S 471 ). Further, the map M is set as the gasoline map Mg (step S 472 ), and based on the torque control map Mt, K is set by the torque line that is equal to the target torque Ti set in step S 471  (step S 473 ). 
     In this control routine, referring to  FIGS. 4A and 4B , if the target torque Th by the gaseous fuel immediately before the switch is H 3  in  FIG. 4B , the target torque Ti after the switch is set as G 3  irrespective of the values of the current throttle opening K and vehicle traveling speed V, and the throttle opening K is controlled based on G 3 . 
     Returning to  FIG. 13 , next, in the embodiment, the control routine is configured to determine whether an acceleration request exists based on whether the accelerator pedal opening AOF increases after the switch of the fuel being used (step S 474 ). In this determination, if the acceleration request exists, it is considered to be recognized by the operator that the vehicle  10  will accelerate suddenly in accordance with switching the fuel. Therefore, after setting the target torque Ti as the torque Tg by gasoline (step S 475 ), it immediately returns to the original routine, and inhibits the Acceleration Reducing Process. 
     On the other hand, in step S 474 , if the acceleration request does not exist, the control unit  100  holds for a predetermined time (step S 476 ). This predetermined time may be 60 seconds, for example. The predetermined time does not have to be a constant time, and may be a variable time. 
     If the predetermined time has passed, the control unit  100  updates the target torque Ti by a value adding a predetermined value n to the target torque Ti as a new target torque Ti (step S 477 ). 
     Next, the control unit  100  determines whether the target torque Ti has reached the torque Tg by the gasoline to be set originally for the traveling state during the fuel switch (step S 478 ). In step S 473 , this determination is realized by reading and storing the torque line G equivalent to the torque Tg by the gasoline to be set originally from the accelerator pedal opening AOF when referring to the torque control map Mt. 
     If the target torque Ti has reached the torque Tg (YES in step S 478 ), control of the control unit  100  returns to the main routine. On the other hand, if the target torque Ti has not reached the torque Tg (NO in step S 478 ), it resets the count time (step S 479 ), and repeats the control from step S 474 . 
     Referring to  FIG. 14 , when the Acceleration Reducing Process Subroutine S 47  is executed, the torque difference Tgp resulting from the switch of fuel being used is reduced as much as possible, and after that, it is possible to resume the original torque as time passes. Therefore, it is possible to accelerate smoothly without causing discomfort to the operator. 
     As described above, in this embodiment, since the brake lamp  42  as the vehicle deceleration alerting device indicates the deceleration of the vehicle  10  when the fuel being used is switched from gasoline to gaseous fuel, in a traveling state in which a deceleration of the vehicle  10  resulting from the torque decrease tends to occur, it is possible to report the deceleration of the vehicle  10  and urge cautions to the operator on the follow-on vehicle, in order to improve the road traffic safety. 
     Further, in this embodiment, the vehicle deceleration alerting device turns ON the brake lamp of the vehicle  10 . Thus, in this embodiment, with the existing equipments, since it can turn ON the brake lamp  42 , it is possible to certainly inform the operator of the follow-on vehicle that the vehicle  10  may decelerate with a less expensive configuration that is easy to realize. 
     In this embodiment, when the fuel being used is switched from gasoline to gaseous fuel, the control unit  100  functionally constitutes the alert controlling device that executes the alerting to the follow-on vehicle when the torque difference Tgp between the engine torque Tg by gasoline in the current traveling state and the engine torque Th when switched to gaseous fuel is greater than the gap value Ts, while controlling the brake lamp  42  so that it inhibits the alerting when less than the gap value Ts. For this reason, in this embodiment, since the alert to the operator of a following vehicle is executed only when a relatively large deceleration occurs, it is possible to avoid excessive alerting, and prevent discomfort to the operator on the follow-on vehicle. 
     Further, in this embodiment, the control unit  100  functionally constitutes the deceleration rate detecting device for detecting the deceleration rate of the vehicle  10 , and an alert ending device for terminating the alert by the brake lamp  42  when the calculation result by the deceleration rate detecting device is less than the predetermined changing rate dvs of the vehicle  10  after the switching the fuel being used from gasoline to gaseous fuel. For this reason, in this embodiment, by continuing the alert until the deceleration rate of the vehicle becomes small, it is possible to secure safe travel of the following vehicle, while avoiding excessive alerting when it becomes less than the predetermined changing rate dvs, and preventing the discomfort to the operator of the follow-on vehicle. 
     Further, in this embodiment, the vehicle traveling speed sensor SW 6  as the vehicle traveling speed detecting device for detecting a value related to the traveling speed of the vehicle  10  is provided, and the control unit  100  as the deceleration rate detecting device detects the deceleration rate-dv based on the detection by the vehicle traveling speed sensor SW 6 . For this reason, in this embodiment, since the deceleration rate-dv is detected based on the vehicle traveling speed V, it is possible to achieve the deceleration determination in a deceleration state apparently viewed by the operator of the follow-on vehicle, and realize a control closer to human sense. 
     Further, in this embodiment, the control unit  100  as the alert controlling device may determine the torque difference Tgp based on the maximum engine torque by gaseous fuel. The control unit  100  functionally constitutes a target torque setting device for setting the target torque so that the torque difference Tgp is the minimum when the torque difference Tgp is less than the gap value Ts. For this reason, in this embodiment, it is possible to reduce the torque decrease as much as possible when the fuel being used is switched from gasoline to gaseous fuel. 
     As described above, in the embodiment, during a traveling state in which deceleration of the vehicle  10  resulting from the torque decrease tends to occur, it produces an effect that it alerts the deceleration of the vehicle  10  to the operator on the follow-on vehicle of the vehicle  10 , and it is possible to improve the road traffic safety. 
     The above-mentioned embodiment is only a one example and is not to be considered as exclusive or limiting as various modifications are possible. For example, the switching method of the fuel being used is not limited to a manual type as described in the embodiment above, and may be an automatic type in which a control unit automatically switches according to the traveling state. 
     Further, as an example of the vehicle deceleration alert may be an alert of “vehicle will decelerate” or other suitable phrase by an audible signal which a sound generating device such as a speaker system emits to the inside or outside of the automotive vehicle. 
     Further, the vehicle deceleration alert may be a viewable display of “vehicle will decelerate” on a rear window of the vehicle. This method can be easily realized by an image projection device like a so-called head-up display. 
     It should be understood that the embodiments herein are illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.