Claims:We Claim:
1 An injector drive circuit (100) for gaseous fuel injection control in a dual fuel vehicle, said injector drive circuit comprising:
a microcontroller (12) connected to an input pin of a tri-state buffer (14);
a microcontroller-monitoring module (16) connected to an enable pin of said tri-state buffer (14); and
an injector drive switch (26) connected to an output pin of said tri-state buffer (14).
2 The injector drive circuit as claimed in claim 1, wherein said microcontroller-monitoring module (16) transmits an enable signal to said enable pin of said tri-state buffer (14) upon verifying normal working condition of said microcontroller (12) when said dual fuel vehicle is in a gaseous fuel mode.
3 The injector drive circuit as claimed in claim 1, wherein said tri-state buffer (14) is at least one of an active high tri-state buffer or an active low tri-state buffer;
4 The injector drive circuit as claimed in claim 1, wherein said injector drive switch (26) comprises a first field effect transistor (28) and a second field effect transistor (30).
5 The injector drive circuit as claimed in claim 4, wherein said first field effect transistor (28) is ON and said second field effect transistor (30) is OFF when an enable signal is transmitted by said microcontroller-monitoring module (16) to said tri-state buffer (14) when said dual fuel vehicle is in a gaseous fuel mode.

6 The injector drive circuit as claimed in claim 5, wherein said first field effect transistor (28) is OFF and said second field effect transistor (30) is ON when a disable signal from said microcontroller-monitoring module (16) to said tri-state buffer (14) when said dual fuel vehicle is in a gaseous fuel mode.

7 A method of driving a gaseous fuel injection circuit in a dual fuel vehicle, said method comprising:
monitoring if a microcontroller (12) is in normal working condition by a microcontroller-monitoring module (16) when said dual fuel vehicle switches to gaseous fuel mode; and
sending a gaseous fuel mode signal from said microcontroller (12) to an injector drive switch (26) through a tri-state buffer (14) based on said monitoring result, for activating a gaseous fuel injector (22).

8 The method as claimed in claim 7, further comprises transmitting an enable signal to said tri-state buffer (14) by said microcontroller-monitoring module (16) upon detecting normal working condition of the microcontroller (12).
9 The method as claimed in claim 7, said gaseous fuel mode signal of said microcontroller (12) is sent to said injector drive switch (26) upon receiving enable singal from the microcontroller-monitoring module (16).
, Description:Field of the invention
[0001] This invention relates to an injector drive circuit for gaseous fuel injection control in a dual fuel vehicle.

Background of the invention
[0002] Dual fuel engines in a vehicle are capable of running on gaseous fuel and a liquid fuel. The gaseous fuel is usually CNG or LPG. The liquid fuel may be gasoline or diesel. The advantages of using dual fuel engines are reduced costs and reduced emissions.

[0003] Attaching a CNG/LPG retrofit kit into a diesel or gasoline engine is an economically advantageous and popular choice to most of the users. The retrofit kit comprises a microcontroller and an injector drive circuit for gaseous fuel injection control. The microcontroller controls injection of the gaseous fuel when the vehicle is running in the gaseous fuel mode. The microcontroller is also responsible for passing control to a liquid fuel control that controls the injection of the liquid fuel when the vehicle is running in liquid fuel mode.

[0004] If the microcontroller malfunctions when the vehicle is running in the gaseous fuel mode, for example using CNG, then a way to switch the vehicle from the CNG mode to the liquid fuel mode, for example, to gasoline is required. By performing such switching, drivability in the gasoline mode is achieved when the microcontroller that controls CNG injection malfunctions. Hence a driver can still continue to drive the vehicle using gasoline although the microcontroller that controls CNG has failed. One way to achieve drivability in gasoline when microcontroller driving the CNG fails is achieved using a bypass switch. The bypass switch is a relay controlled switch. When the relay is energized, the vehicle is in gaseous fuel mode and a CNG injector is activated. When the relay is de-energized, the bypass switch gets connected to a gasoline injector. Hence when the microcontroller malfunctions, the relay gets de-energized and automatically the contact is made to the gasoline injector so that the vehicle can be driven using gasoline. However, use of relay leads to added mechanical component thereby increasing cost.

Brief description of the accompanying drawings

[0005] Figure 1A-1B is a block diagram of an injector drive circuit for a gaseous fuel injection control, in accordance with an embodiment of the present disclosure; and

[0006] Figure 2 is a flowchart that illustrates a method of driving a gaseous fuel injection circuit, in accordance with an embodiment of the present disclosure.

Detailed description

[0007] Figure 1 is a block diagram of an injector drive circuit for a gaseous fuel injection control in a dual fuel vehicle, in accordance with an embodiment of the present disclosure.

[0008] The injector drive circuit comprises a microcontroller 12 connected to an input pin of a tri-state buffer 14, a microcontroller-monitoring module 16 connected to an enable pin of the tri-state buffer 14 and an injector drive switch 26 connected to an output pin of the tri-state buffer 14.

[0009] The tri-state buffer 14 is a logic circuit used for transmitting output of the microcontroller 12 to the injector drive switch 26. The microcontroller 12 is connected to the input pin of the tri-state buffer 14 so that the output of the microcontroller 12 is sent to the tri-state buffer 14 through the input pin of the tri-state buffer 14. To run the dual fuel vehicle in gaseous fuel mode, the microcontroller 12 outputs a gaseous fuel mode signal to the input pin of the tri-state buffer 14. The gaseous fuel mode signal is used for activating a gaseous fuel injector 22 so that gaseous fuel is injected.

[00010] The microcontroller-monitoring module 16 is connected to the enable pin of the tri-state buffer 14. The microcontroller-monitoring module 16 is adapted to monitor the normal functioning of the microcontroller 12 by sending one or more questions to the microcontroller. Upon receiving correct answers from the microcontroller, the microcontroller-monitoring module 16 will conclude that the microcontroller 12 is functioning normally. On detecting normal functioning of the microcontroller, the microcontroller-monitoring module 16 generates the enable signal that is transmitted to the enable pin of the tri-state buffer 14.

[00011] The tri-state buffer 14 acts a buffer and stores the gaseous fuel mode signal and when the enable signal is given to the tri-state buffer 14 the stored gaseous fuel mode signal is obtained at the output of the tri-state buffer 14.

[00012] The tri-state buffer 14 can either be an active high tri-state buffer 14 or an active low tri-state buffer 14. In case of active high tri-state buffer 14, the enable signal is logic-1 and if the tri-state buffer 14 is active low then the enable signal is logic-0.

[00013] For example, if tri-state buffer 14 is an active high tri-state buffer then the microcontroller-monitoring module 16 is adapted to generate a logic-1 enable signal upon determining that the microcontroller 12 is functioning normally. If tri-state buffer 14 is an active low tri-state buffer then a logic-0 enable signal is generated upon determining that the microcontroller 12 is functioning normally.

[00014] To activate the gaseous fuel mode, the microcontroller 12 generates the gaseous fuel mode signal. The activation of the gaseous fuel mode may be manually performed by the driver using a select switch or may be automatic based on pre-defined conditions. This gaseous fuel mode signal is required for activating a gaseous fuel injector 22. The gaseous fuel mode signal generated by the microcontroller 12 is given to the input pin of the tri-state buffer 14. Also, simultaneously the generated enable signal is also given to the enable pin of the tri-state buffer 14. When the enable signal is given to the tri-state buffer 14, the gaseous fuel mode signal given at the input of the tri-state buffer 14 is obtained at the output of the tri-state buffer 14. The output pin of the tri-state buffer 14 is connected to the injector drive switch 26 so that the injector drive switch 26 is operated based on the input given to the tri-state buffer 14.

[00015] The injector drive switch 26 comprises two field effect transistors, namely a first field effect transistor 28 and a second field effect transistor 30 as shown in Figure 1B. The first field effect transistor 28 is connected to a gaseous fuel injector 22 and the second field effect transistor 30 is connected to a liquid fuel injector 24. When the first field effect transistor 28 is ON, there is current flowing through the gaseous fuel injector 22. This activates the gaseous fuel injector 22 so that gaseous fuel is injected into the engine. When the second field effect transistor 30 is ON, there is current flowing through a liquid fuel injector 24. This activates the liquid fuel injector 24 and hence liquid fuel is injected into the engine. Quantity of liquid fuel injected into the engine 200 is based on a signal received from a liquid fuel controller 34.

[00016] In one example, if the gaseous fuel mode signal is given to the input pin of the tri-state buffer 14 and the enable signal is also given to the enable pin of the tri-state buffer 14 then the gaseous fuel mode signal is obtained at the output of the tri-state buffer 14. Since the injector drive switch is connected to the output pin of the tri-state buffer 14, the gaseous fuel mode signal is obtained by the injector drive switch 26. When the gaseous fuel mode signal is obtained by the injector drive switch, the first field effect transistor 28 is ON and the second field effect transistor 30 is OFF. When the first field effect transistor 28 is ON, the gaseous fuel injector 22 is activated so that the gaseous fuel injector 22 injects gaseous fuel into the engine. Since the second field effect transistor 30 is OFF, there is no current flowing to the liquid fuel injector 24 and this de-activates the liquid fuel injector 24.

[00017] Upon monitoring, if the microcontroller-monitoring module 16 determines that the microcontroller 12 is not functioning normally, then a disable signal is generated. For example, the duel fuel vehicle may be in gaseous fuel mode. However, the microcontroller 12 may not be functioning normally. When the disable signal is given to the tristate buffer 14 ( or enable signal is not given to the tri-state buffer 14), the injector drive switch 26 will not receive any signal from the tri-state buffer 14 even though the microcontroller 12 provides the gaseous fuel mode signal at the input of the tri-state buffer 14. That is, when there is no enable signal to the tri-state buffer 14, the injector drive switch 26 is isolated from the microcontroller 12. When the injector drive switch 26 does not receive any signal from the tri-state buffer, the first field effect transistor 28 is OFF and the second field effect transistor 30 is ON. When the first field effect transistor 28 is OFF, the gaseous fuel injector 22 is de-activated. Also, since the second field effect transistor 30 is ON, the liquid fuel injector 24 is activated and hence liquid fuel like gasoline may be injected into the engine based on a signal received from the liquid fuel controller 34. Therefore, with the help of the injector drive circuit disclosed in the current disclosure, one can obtain drivability in gasoline if the microcontroller that controls gaseous fuel injection malfunctions suddenly.

[00018] A working example is explained in the below paragraphs for the purpose of understanding the disclosure clearly. Let us consider that the vehicle is retrofitted with CNG/LPG kit.

[00019] It is considered that the dual fuel vehicle is in gaseous fuel mode. The microcontroller-monitoring module 16 now monitors for normal working of the microcontroller 12 that controls the gaseous fuel mode. In this case, the microcontroller 12 is a part of a CNG/LPG retrofit kit 100 that controls gaseous fuel injection.

[00020] Monitoring is performed by sending one or more questions to the microcontroller 12. The microcontroller 12 receives these questions and transmits responses to these questions to the microcontroller-monitoring module 16. If the microcontroller 12 sends correct responses to the microcontroller-monitoring module 16, then an enable signal is generated by the microcontroller-monitoring module 16. It is considered that the microcontroller 12 is functioning normally and hence the microcontroller-monitoring module 16 generates an enable signal which is logic-1. The enable pin of the tri-state buffer 14 receives this enable signal. In this example, an active high tri-state buffer 14 is considered.

[00021] To activate the gaseous fuel mode, the microcontroller 12 generates a gaseous fuel mode signal. The gaseous fuel mode signal is used for activation a gaseous fuel injector 22. The gaseous fuel mode signal is sent to the tri-state buffer 14 by the microcontroller 12. As the enable signal is received by the tri-state buffer 14, the gaseous fuel mode signal sent to the tri-state buffer 14 is obtained at the output of the tri-state buffer 14. The gaseous fuel mode signal obtained at the output of the tri-state buffer 14 is then sent to the injector drive switch 26

[00022] Once the injector drive switch 26 receives the gaseous fuel mode signal, the first field effect transistor 28 is ON and hence the gaseous fuel injector 22 is activated for injecting gaseous fuel into the engine. Quantity of gaseous fuel required to be injected into the engine 200 is based on a signal obtained from the microcontroller 12 since the microcontroller 12 is directly connected to the gaseous fuel injector 22 as shown in Figure 1.

[00023] In another case, if the microcontroller 12 is not functioning normally then the microcontroller-monitoring module 16 will not generate an enable signal or the enable signal generated would signify that the microcontroller 12 is not functioning normally. As a result disable signal of logic-0 is generated by the microcontroller-monitoring module 16. This logic-0 signal is sent to the tri-state buffer 14. When the tri-state buffer 14 receives such a signal, the gaseous fuel mode signal is not obtained at the output of the tri-state buffer 14. Thus, the injector drive switch 26 also does not receive any gaseous fuel mode signal. When the injector drive switch does not receive the gaseous fuel mode signal, the first field effect transistor 28 is OFF and hence the gaseous fuel injector 22 does not get activated. However, there is current flow through the second field effect transistor 30 and hence the liquid fuel injector 24, for example, gasoline fuel injector is activated and hence gasoline is injected to the engine.

[00024] Therefore the injector drive circuit disclosed in this disclosure de-activates the gaseous fuel injector 22 and activates a liquid fuel injector 24 when the microcontroller controlling a gaseous fuel injection is abnormal or not operating properly. That is, when the vehicle is running in CNG mode and the microcontroller 12 malfunctions, then the injector drive circuit activates gasoline injector and thereby ensures drivability in gasoline mode. Hence, the disclosure presents a fail-safe technique in case of CNG/LPG retrofitted vehicles.

[00025] Figure 2 is a flowchart that illustrates a method of driving a gaseous fuel injection circuit in a dual fuel vehicle, in accordance with an embodiment of the present disclosure.

[00026] The method involves monitoring whether the microcontroller 12 is in normal working condition at step 105 by the microcontroller-monitoring module 16. When the dual fuel vehicle switches to gaseous fuel mode, the microcontroller-monitoring module 16 begins monitoring the microcontroller 12. Monitoring includes sending one or more questionnaire to the microcontroller 12 by the microcontroller-monitoring module 16. The microcontroller-monitoring module 16 then monitors the responses to the questionnaire given by the microcontroller 12. Based on the correctness of the responses transmitted by the microcontroller 12 to the questionnaire, the microcontroller-monitoring module 16 will determine if the microcontroller 12 is functioning normally.

[00027] If the microcontroller 12 is functioning normally then the microcontroller-monitoring module 16 transmits an enable signal to an enable pin of a tri-state buffer 14.

[00028] In response to the transmission of the enable signal to the tri-state buffer 14, at step 110, a gaseous fuel mode signal from the microcontroller 12 is sent to an injector drive switch 26 through the tri-state buffer 14. That is, the gaseous fuel mode signal given to the input pin of the tri-state buffer 14 is obtained at the output of the tri-state buffer 14 when the enable signal is given to the tri-state buffer 14. As the injector drive switch is connected to the output of the tri-state buffer 14, upon receiving the gaseous fuel mode signal, the first field effect transistor 28 present in the injector drive switch is ON and the second field effect transistor 30 is OFF. When the first field effect transistor 28 is ON, current flows to a gaseous fuel injector 22. This activates the gaseous fuel injector 22 and hence gaseous fuel injection is enabled. Since the second field effect transistor 30 is OFF, there is no current flow to a liquid fuel injector 24. This de-activates the liquid fuel injector 24.

[00029] In the absence of enable signal, the injector switch 26 does not receive the gaseous mode signal. As a result, the first field effect transistor 28 is OFF and the second field effect transistor 30 is ON. Since the second field effect transistor 30 is ON, there is current flow to the liquid fuel injector 24 and hence liquid fuel injector 24 is activated so that liquid fuel is injected into the engine 200 and the duel fuel vehicle can run on liquid fuel such as gasoline.

[00030] Hence, in this disclosure a method of switching a vehicle from gaseous fuel to liquid fuel when the microcontroller 12 controlling gaseous fuel injection fails is disclosed. By using the technique disclosed in the present disclosure a fail-safe method of vehicles fitted with CNG/LPG retrofit kit 100 is achieved.

[00031] It must be understood that the embodiments explained above are only illustrative and do not limit the scope of the disclosure. Many modifications in the embodiments with regard to the type of injectors used, method of monitoring the microcontroller are envisaged and form a part of this invention. The scope of the invention is only limited by the claims.