Claims:We Claim:

1. A diagnostic tester to identify drift in an injector in an internal combustion engine, said diagnostic tester comprising :
- a first interface to receive compensation values of said injector for fuel quantity;
- a second interface to trigger a Morse test to collect friction data of said engine;
said diagnostic tester adapted to declare said injector having a drift if the compensation values of said injector do not correspond to the friction data
2. The diagnostic tester according to claim 1 wherein said first interface is an input port connected to a microcontroller in said diagnostic tester
3. The diagnostic tester according to claim 1 wherein said second interface is an output port connected to a microcontroller in said diagnostic tester
4. The diagnostic tester according to claim 1 wherein said diagnostic tester provides an indication when said diagnostic tester detects drift in an injector
5. A method to identify drift in an injector fitted in an internal combustion engine, said method comprising the steps:
- reading compensation values of said injectors for fuel quantity (S1)
- triggering a Morse test to collect frictional data of said engine (S2)
- declaring said injector having a drift if the compensation values of said injector do not correspond to the friction data (S3)
6. A method to identify drift in an injector according to claim 1 wherein compensation values of said injectors are stored during running of said engine
7. A method to identify drift in an injector according to claim 1 wherein compensation value of said injector indicates a correction to be applied to the quantity of fuel injected by said injector
8. A method to identify drift in an injector according to claim 1 wherein frictional data is measured by measuring torque generated by said engine
9. A method to identify drift in an injector according to claim 1 wherein frictional data is measured for individual injectors fitted in said engine
10. A method to identify drift in an injector according to claim 1 wherein frictional data corresponding to said injector is analyzed with compensation value of said injector
11. A method to identify drift in an injector according to claim 1 wherein a said injector is declared having drift if frictional loss corresponding to said injector is within acceptable range and compensation value of said injector is outside of said acceptable limits
, Description:Field of the invention
[0001] This invention relates to the field of identifying drift in an injector used in an internal combustion engine.

Background of the invention

[0002] Detecting and compensating drifts in the injectors is known in prior arts. The prior art GB201205926A discloses a method of compensating an injection drift of a fuel injector of an internal combustion engine. The method in the prior art comprises the steps of: operating the fuel injector to perform a plurality of test injections, monitoring a crankshaft speed signal of the internal combustion engine during the test injections, monitoring a signal proportional to an acceleration of the crankshaft during the test injections and integrating the monitored crankshaft signal over a range of crankshaft velocities ranging from a first value to a second value. The result of the integration is compared with an expected value and the energizing time is adjusted if the energizing time differs from the expected value. The steps are repeated until the measured integration value matches the expected integration value.

Brief description of the accompanying drawing
[0004] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:

[0005] FIG. 1 illustrates a

Detailed description of the embodiments

[0006] FIG. 1 illustrates a method to identify drift in an injector fitted in an internal combustion engine. The method comprising the steps: reading compensation values of said injectors for fuel quantity; triggering a Morse test to collect frictional data of said engine; declaring said injector having drift if compensation values of said injectors do not correspond to the friction data.

[0007] The method makes use of a diagnostic tester to detect the injectors which are having drift. The diagnostic tester is referred as tester in this document.

[0008] The drift in the injectors is the difference between the actual energizing time of the injector and the expected time of energizing the injector to inject a known quantity of fuel. In other words, if the injector is to be energized for a t1 period to inject q1 quantity of fuel, it may happen that for the energized period of t1 actual injected quantity may be q1-d or q1+d where d indicates the drift. The quantity q1 is normally calculated by an electronic control unit controlling the engine. The q1 is calculated based upon the engine parameters like engine speed, engine load, engine temperature, ambient temperature, transmission ratio etc. Based on the engine parameters the ECU calculates the quantity of the fuel q1 to be injected and accordingly energizes the injector for a period t1. But because of various factors in the injector like manufacturing tolerances, wear and tear etc. the injector may have drift and may inject q1+d or q1-d during the energization period of t1. This results in either generating less than expected torque or more than expected torque by the engine, based on whether the drift is in –ve or +ve direction. To overcome this drift, the energizing time needs to be compensated for each injector depending upon their drift. In other words, to inject q1 quantity, the ECU has to energize t1+d1 or t1-d1 duration where d1 is drift in energizing time. The drift is measured during the overrun condition of the vehicle by performing the test injections in injectors. The overrun condition is the condition where vehicle is running on its own without any torque demand by the user. This may happen when the vehicle is running on a downhill road. The drift values are measured for each injector and the drift is compensated for each injector by adjusting the energizing time. This is achieved by energizing the injector for more time (i.e.t1 +d1) for a negative drift and energizing the injector for less time (i.e. t1–d1) for a positive drift. The compensation values (d1 values) are stored for each injector.

[0009] In the prior arts, as the drift is measured only in terms of variation in engine speed for known injector energizing time, it may not be conclusive as there may be also drift in the engine related components. For example if the friction between the piston and the cylinder has increased over the time, then this will influence the engine speed for known quantity of fuel injection. For example, if earlier the energizing time t1 was varying engine speed by N, if there is increased friction in engine, then the same energizing time may vary the speed by N-d. If the friction data has come down over a period of time, then the same energizing time may vary the speed by N+d where d is the drift.

[0010] Hence, the frictional losses in the engine plays important role in deciding the drift in the injectors.

[0011] In the conventional vehicle service, if a vehicle was suspected of injector drifts, then the mechanic needs to remove all the injectors from the engine and test the injectors individually to conclusively identify the injectors which are having drifts.

[0012] The invention proposes a simple method where the engine friction data is also considered when deciding about the drift in the injector. This will conclusively identify which injector is having a drift, without removing the injectors form the engine.

[0013] When a vehicle which is suspected of injector drift comes to a service station, the diagnostic tester is connected to the ECU which is controlling the engine in the vehicle. In step S1 the diagnostic tester receives the compensation values of each injector which are stored in the ECU. Normally the compensation values are computed by ECU during overrun condition. During overrun condition, there is no demand from the user for torque. During this time, the ECU performs test injections and monitors the variation in engine speed. The ECU injects a known quantity of fuel as part of the test injection. This known quantity of fuel should vary the speed by a known value which is pre-stored. If there is any deviation from the known value, then the percentage deviation is calculated. The percentage deviation is the compensation value which is either added or subtracted to the fuel quantity while injecting fuel into the cylinders. Such multiple compensation values are stored for each injector. Example of compensation values are shown in fig. 2. The X axis represents the time t and Y represents the quantity drift q that is compensated in mg/hub. The different curves show the compensation for different injectors. Ex. the graph i1 indicates compensation values for injector 1, similarly the graphs i2, i3 and i4 represent compensation values for injector 2, injector 3 and injector 4 respectively.

[0014] The diagnostic tester receives these compensation values for each of the injectors. In step S2 the tester triggers a Morse test on the engine. The Morse test is the test where power output of the engine corresponding to each of the injectors is calculated. The power output may be also plotted as friction data corresponding to each of the cylinders. One example of friction data are shown in fig. 3. The X axis represents the engine speed N and the Y axis represents the friction Nm in Newton Meters. The graph G1 represents the friction measurements when the engine was fitted for the first time in the vehicle. The graph G2 and G3 represent the friction measurements when the engine comes for servicing subsequently. Friction data and friction measurements refer to same values.

[0015] In step S3, the tester analyzes the friction data, ex, the values of G3 and the compensation values for each of the cylinders and injectors respectively. Also the friction data of the engine stored during the previous service of the vehicle are retrieved ex. G2. If the present friction data G3 are lower compared to the previous set of friction data G2, then the amount of fuel to be injected into the cylinder to get known variation in the engine speed should be lesser. This means the compensation values should be negative. If the friction has reduced but the compensation value is positive, then the injector is having drift in negative direction. Similarly if the friction data has increased but the compensation value is negative, then the injector is having drift in positive direction. The tester detects which of the injectors is having the drift and generates an indication in step S5 to the mechanic operating the tester. In step S4, the injector is not having drift and tester my indicate the same.The indication may be in the form of an audio signal or a message on the display of the tester.

[0016] The diagnostic tester comprises typically a microcontroller, memory, input and output interfaces and a display. The diagnostic tester has a first interface which may be a simple input port. The diagnostic tester has a second interface which may be a simple output port. The diagnostic tester may communicate with the ECU using either a wired link or a wireless link to receive the compensation values. The diagnostic tester performs the above method steps through a set of instructions stored in its memory, to identify the injectors which have drifts and generate an indication through the display or an audio indication. As diagnostic testers are known, the details are not explained here.