Claims:We Claim:
1. A method (100) of monitoring a status of a mechanical fuel injector (200), said mechanical fuel injector comprising at least:
a body (202), said body (202) housing a spring (204) and a strain gauge (206) attached to said spring (204); and
a nozzle holder (208) attached to said body (202) and housing a needle (210), said needle (210) mechanically engaged to said spring (204); said method comprising:
sensing (102), by said strain gauge (206) stiffness of said spring (204);

converting (104), by a control unit said sensed stiffness into a signal;

comparing (106), by said control unit, said signal with a calibrated threshold value of at least one property of said mechanical fuel injector (200); and

indicating (108), based on said comparison, to a display device said status of said mechanical fuel injector (200).

2. The method (100) of claim 1, wherein said signal is any one of a voltage and current.

3. The method (100) of claim 1, wherein said property is any one of fuel injector 200 pressure and voltage.

4. A mechanical fuel injector (200), comprising at least:
a body (202), said body housing a spring (204); and
a nozzle holder (208) attached to said body (202) and housing a needle (210), said needle (210) mechanically engaged to said spring (204); characterized in that
a strain gauge (206) attached to said spring (204), and adapted to sense stiffness of said spring (204); and

said strain gauge (206) electrically connected to an electronic control unit 300.

5. An electronic control unit (300) for monitoring the status of mechanical fuel injector (200), said mechanical injector comprising a body (202), said body (202) housing a spring (204) and a strain gauge attached to the spring (204), and a nozzle holder (208) attached to said body 202 and housing a needle (210), said needle (210) mechanically engaged to said spring (204), said electronic control unit (300) adapted to:

receive (302) from said strain gauge 206 stiffness of said spring 204 in the form of a signal;

compare (304) said signal with a calibrated threshold value of at least one property of said mechanical fuel injector 200; and

indicate (306), based on said comparison, to a display device said status of said mechanical fuel injector 200
, Description:Complete Specification:

The following specification describes and ascertains the nature of this invention and the manner in which it is to be performed.
Field of the invention
[0001]This invention relates to the field of mechanical fuel injectors.

Background of the invention
[0002] A fuel injector is used to inject fuel into an engine for combustion. Fuel injectors are of two types. The mechanical fuel injectors that are used for low cost application and electronically controlled fuel injectors that are used for injecting precise quantity of fuel. The former type of fuel injector will be the subject of interest in this patent application. In a mechanical fuel injector, the injection happens with help of a needle that is biased against a spring. The mechanical fuel injector is calibrated in dependence of the stiffness of the spring. For example, if the stiffness of the spring is around 3 N/mm2, then the fuel injector may deliver fuel at a pressure of 300 bar. During working of the mechanical fuel injector it is observed that there may be relaxation in the stiffness of the spring. This leads to slackness in compression and expansion of spring. This in turn leads improper injection (over injection of fuel and/ or under injection of fuel or no injection at all). In the absence of sensors in a mechanical injector it becomes difficult to monitor the performance of spring and take corrective actions as and when necessary.

Brief description of the accompanying drawing
[0003] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:

[0004] FIG. 1 illustrates a method of monitoring a status of a mechanical fuel injector; and

[0005] FIG. 2 illustrates a mechanical fuel injector; and

[0006] FIG. 3 illustrates an electronic control unit for monitoring the status of mechanical fuel injector.

[0007] Graph 1 illustrates the variation in pressure with respect to voltage of a mechanical fuel injector.

[0008] Graph 2 illustrates the variation in voltage with respect to stiffness of the spring in the mechanical fuel injector.

Detailed description of the embodiments
[0009] FIG. 1 illustrates a method of monitoring a status of a mechanical fuel injector 200. The mechanical fuel injector 200 comprises at least a body 202, the body 202 houses a spring 204 and a strain gauge 206 attached to the spring 204. A nozzle holder 208 is attached to the body 202 and houses a needle 210, the needle is mechanically engaged to the spring 204. The method comprises the following steps. The stiffness of the spring 204 is sensed (102) by the strain gauge 206. The sensed stiffness is converted (104) into a signal by the control unit. The signal is then compared (106) by the control unit with a calibrated threshold value of at least one property of the mechanical fuel injector 200. The property may be any one of fuel injector 200 pressure and voltage. The signal may be in the form of a voltage or current. Based on the comparison, the status of the mechanical injector is indicated (108) on a display device.

[0010] FIG. 2 illustrates a mechanical fuel injector 200. The mechanical fuel injector 200 comprises at least a body 202 housing a spring 204, and a nozzle holder 208 attached to the body 202 and housing a needle 210, the needle 210 is mechanically engaged to the spring 204. A strain gauge 206 is attached to the spring 204, and adapted to sense stiffness of the spring 204. The strain gauge 206 is electrically connected to an electronic control unit 300.

[0011] With reference to FIG. 1, the method for monitoring the status of the mechanical fuel injector 200 will be explained in further detail. The status disclosed herein may refer to stiffness of the spring 204 and in turn pressure at which the mechanical fuel injector 200 is working. However, it should be noted that the status is not restricted to stiffness alone and it could include any other parameter that is required for arriving at the pressure with which the injector is operating. For example, the speed of traverse of needle 210 within the housing. For the purpose of this explanation, the stiffness of the spring 204 is considered as an input for arriving at the status of the mechanical fuel injector 200.

[0012] For the purpose of better understanding, attention is directed towards the below mentioned table (table 1). From the table let us consider that the mechanical injector is designed to operate at a pressure of 300 bar. The value of 300 bar in this instance may refer to the calibrated threshold value of pressure. In order to achieve this pressure the stiffness of 5 N/mm2 by supply current at 3V. From the corresponding Table. 1, the variation of pressure with voltage may be stored in the form of a data map in the electronic control unit 300 (ECU). This is illustrated in the form of a graph (Graph 1)

Pressure (Bar) Spring stiffness (N/mm2) Voltage (V)
Calibrated 300 5 3
Actual X Y 2
Actual X1 Y1 4

(Table. 1)

[0013]Now, under actual working condition the spring 204 being an elastic member is subjected to stress, in this case stress due to compression. This stress may cause a change in at least one property of the spring 204, and stiffness being the factor that decides the pressure at which fuel is injected into the engine, any change in stiffness may cause variation in pressure and hence may affect engine performance.

[0014]Consider (from table 1) the stiffness of the spring 204 changes from 5 N/mm2 to Y N/mm2 during working of the injector. For stiffness of Y N/mm2 the pressure at which the injector operates may be X bar. Now, the method disclosed herein will monitor if said X bar of pressure corresponds to normal working of injector (in this case 300 bar) and in case of non-correspondence provide an alert in the form of a display.

[0015]The method comprises the following steps. The stiffness of the spring 204 is sensed 102 by the strain gauge 206 (Y N/mm2). The sensed stiffness (Y N/mm2) is converted 104 into a signal by the control unit. The signal is then compared 106 by the control unit with a calibrated threshold value of at least one property of the mechanical fuel injector 200. From graph 1, the stiffness of the spring 204 is converted to voltage (2V) and this is compared with the threshold values as illustrated in Graph 1. The signal may be in the form of a voltage or current. Referring again to the Table. 1 and Graph. 1, if the magnitude of stiffness of spring 204 as obtained from control unit in the form of voltage is 2V, then comparing the same from graph 1, for magnitude of 2V, the pressure at which the injector is operating is 200 bar. This pressure of 200 bar is less than pressure for which the injector is designed for (in this case 300 bar). Based on the comparison, the status of the mechanical injector is indicated 108 on a display device. The display device may be any one of handheld mobile device, dashboard of a vehicle.

[0016]In another example, consider the voltage that is obtained after conversion of stiffness (Y1 N/mm2) into signal to be 4V. In this case from Graph 1, for threshold value of 4V, the mechanical injector should operate at 400 bar which may approximately correspond to X1 bar pressure. This would imply that for 4V signal, the mechanical injector is operating at a pressure higher than the pressure for which it is designed to operate (in this case 300 bar). Hence, deviation in this case too is displayed on the display device.

[0017]In another example, referring to table 2, consider the spring 204 to operate under a stiffness of Y N/mm2. It is assumed that the injector is calibrated to work at voltage of 3V and the spring 204 stiffness is set at 1.5 N/mm2. The stiffness is set for varying the tension in the spring 204.

Spring stiffness (N/mm2) Voltage (V)
Calibrated 1.5 3
Actual Y 2

(Table. 2)

[0018] Referring to Table 2 and graph 2, for a spring 204 whose stiffness has changed from 1.5 N/mm2 to Y N/mm2, the strain gauge 206 that is attached to the spring 204 senses the stiffness of Y N/mm2 and this stiffness is converted into a signal by the control unit. In an embodiment the signal may be a voltage value and the corresponding voltage for stiffness of Y N/mm2 is 2V. Now, this is compared with the calibrated threshold value of the mechanical fuel injector 200 from Graph 2. For a voltage of 2V the spring 204 stiffness is 1 N/mm2, this may approximately correspond to Y N/mm2. This may indicate that there is loss in stiffness of the spring 204 and this information will now be available on the display device. The above mentioned method discloses a method of arriving at the pressure at which the mechanical fuel injector 200 works in real time and then compare the same with the pressure for which the mechanical fuel injector 200 is designed for. Deviation if any is then displayed for proper corrective actions.

[0019] The above examples are for the purpose of illustration only and it should not be construed that the mechanical fuel injector 200 is designed to work only under the above mentioned pressure values or stiffness of spring 204. The spring 204 may be designed to operate under varied stiffness ranges in order to calibrate the pressure at which mechanical fuel injector 200 injects fuel.

[0020]The mechanical fuel injector 200 will be explained in further detail with reference to FIG.2. The mechanical fuel injector comprises at least a body 202 housing a spring 204, and a nozzle holder 208 attached to the body 202 and housing a needle 210, the needle 210 is mechanically engaged to the spring 204. A strain gauge 206 is attached to the spring 204, and adapted to sense stiffness of the spring 204. The strain gauge 206 is electrically connected to an electronic control unit 300.

[0021]The construction of the mechanical fuel injector 200 will be explained in further detail. The mechanical fuel injector 200 is used to inject fuel into the engine cylinder at a pressure as per the requirements of engine, which again depends upon the speed and load under which the engine operates. The mechanical fuel injector 200 is calibrated to operate at a pressure and then the stiffness of the spring 204 is set so that the needle 210 opens to inject fuel at the calibrated pressure. The stiffness of the spring 204 in the mechanical fuel injector 200 is set using a shim 212.

[0022] FIG. 3 illustrates an electronic control unit (300) for monitoring the status of mechanical fuel injector 200. The mechanical fuel injector 200 comprises a body 202, the body 202 houses a spring 204 and a strain gauge 206 attached to the spring 204, and a nozzle holder 208 attached to the body 202 and housing a needle 210. The needle 210 is mechanically engaged to the spring 204, the electronic control unit 300 is adapted to receive (302) from the strain gauge 206 the stiffness of the spring 204 in the form of a signal. The received signal is then compared (304) with a calibrated threshold value of at least one property of the mechanical fuel injector 200. The property may be any one of fuel injector 200 pressure and voltage. Based on the comparison the status of the mechanical fuel injector 200 is indicated (306) on to a display device.

[0023]The above mentioned electronic control unit 300 receives the stiffness of the spring 204 in the form of a signal from the strain gauge 206. The electronic control unit 300 may store data maps of calibrated threshold value of at least one property of the mechanical fuel injector 200. The signal received from the strain gauge 206 is then compared with the values stored in the data maps to ascertain whether the stiffness of the spring 204 is in accordance with the calibrated requirements of the mechanical fuel injector 200. The results of the comparison may be displayed onto a display device for further corrective action (if any) of the mechanical fuel injector 200.

[0024] ‘Adapted’ or ‘arranged’, in the context of the instant disclosure, refers to the technical capability or the technical capacity of a component, in relation to which the term ‘adapted’ or ‘arranged’ is used, to carry out or executed a specified action or actions, upon the requirement of the specified action or actions to be carried out or executed. Moreover, the usage of the term ‘adapted’ or ‘arranged’ here, is in reference with the normal technical capability or technical capacity of the component, imparted by the design or the structure or the composition of the component, and not in reference with any special or extraneous capability or capacity, beyond the scope of the normal technical capability or technical capacity. Therefore there is a need to address this problem.

[0025]It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention in terms of the type of mechanical fuel injector used. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.