Vehicle diagnosis device and method
A diagnostic unit for determining the operational status of a fuel delivery system of an engine, the engine comprising a plurality of cylinders, each one of the cylinders comprising a combustion chamber into which fuel is injected by an associated fuel injector and within which, in use, combustion events repeatedly occur to define a combustion cycle of the cylinder between successive combustion events, the diagnostic unit comprising: inputs for receiving data related to engine rotation; processing means arranged: (i) to determine, from the data received at the inputs, a first engine rotation parameter for a cylinder under test at a first point within the combustion cycle of the cylinder and to determine a second engine rotation parameter for the cylinder under test at a second, different point within the combustion cycle of the cylinder; and (ii) to compare the two engine rotation parameters for the test cylinder in order to identify the operational status of the fuel delivery system associated with the cylinder under test.
1 . A diagnostic unit for determining the operational status of a fuel delivery system of an engine, the engine comprising a plurality of cylinders, each one of the cylinders comprising a combustion chamber into which fuel is injected by an associated fuel injector and within which, in use, combustion events repeatedly occur to define a combustion cycle of the cylinder between successive combustion events, the diagnostic unit comprising:
inputs for receiving data related to engine rotation
a processor arranged: (i) to determine, from the data received at the inputs, a first engine rotation parameter for a cylinder under test at a first point within the combustion cycle of the cylinder and to determine a second engine rotation parameter for the cylinder under test at a second, different point within the combustion cycle of the cylinder; and (ii) to compare the two engine rotation parameters for the test cylinder in order to identify the operational status of the fuel delivery system associated with the cylinder under test.
2 . A diagnostic unit as claimed in claim 1 , wherein the processor is arranged to determine the two engine rotation parameters at two points towards the end of the combustion cycle of the cylinder under test.
3 . A diagnostic unit as claimed in claim 2 , wherein the processor is arranged to determine the first engine rotation parameter at the cylinder's top dead centre position and to determine the second engine rotation parameter at a point in the combustion cycle after the top dead centre position.
4 . A diagnostic unit as claimed in claim 1 , wherein the engine rotation parameters are determined at the same combustion cycle positions for the cylinder under test over a plurality of combustion cycles.
5 . A diagnostic unit as claimed in claim 1 , wherein the processor is arranged to derive a relative engine rotation parameter and to use the relative parameter to identify the operational status of the cylinder under test, the relative engine rotation parameter being the difference between the first and second engine rotation parameters.
6 . A diagnostic unit as claimed in claim 5 , further comprising an output arrangement for outputting an indication of the operational status of the engine
7 . A diagnostic unit as claimed in claim 6 , wherein the output arrangement outputs a notification signal indicating a severe combustion fault for the cylinder under test if the processor determines that the relative engine rotation parameter is a negative value.
8 . A diagnostic unit as claimed in claim 5 , wherein the relative engine rotation parameter derived by the processor is compared to a predicted relative engine rotation parameter in order to determine the operational status of the cylinder under test.
9 . A diagnostic unit as claimed in claim 8 , wherein predicted relative engine rotation parameters are stored in a function map as a function of engine speed and injected fuel quantity.
10 . A diagnostic unit as claimed in claim 8 , further comprising an output arrangement for outputting an indication of the operational status of the engine
11 . A diagnostic unit as claimed in claim 10 , wherein the output arrangement outputs an over-fuelling notification signal for the cylinder under test if the processor determines that the predicted relative engine rotation parameter is less than the determined engine rotation parameter.
12 . A diagnostic unit as claimed in claim 11 , wherein the output arrangement outputs a needle stuck open notification signal for the cylinder under test.
13 . A diagnostic unit as claimed in claim 10 , wherein the output arrangement outputs a cylinder reduced combustion quantity/quality notification signal for the cylinder under test if the processor determines that the predicted relative engine rotation parameter is greater than the determined engine rotation parameter.
14 . A diagnostic unit as claimed in claim 13 , wherein the output arrangement outputs a cylinder misfire notification signal for the cylinder under test if the processor determines that the predicted relative engine rotation parameter is greater than the determined engine rotation parameter.
15 . A diagnostic unit as claimed in claim 1 , wherein the processor is arranged to determine, from the data received at the inputs, engine speed variations between cylinders in order to identify cylinders within the engine that are potentially exhibiting a fault.
16 . A diagnostic unit as claimed in claim 9 , further comprising a correction arrangement arranged to correct engine rotation parameters stored in the function map.
17 . A diagnostic unit as claimed in claim 16 wherein:
the processor is arranged to determine, from the data received at the inputs, when engine speed variations across all the cylinders is approximately zero and
the correction arrangement is subsequently arranged to compare the determined relative engine rotation parameter with the corresponding relative engine rotation parameter stored in the function map and to apply a correction factor in the event of any discrepancy.
18 . A diagnostic unit as claimed in claim 16 , wherein the correction arrangement comprises a feedback loop with a PID controller and a feed forward term from the function map.
19 . A diagnostic unit as claimed in claim 1 , wherein the data relating to the engine rotation comprises data relating to the rotation of a crank wheel within the engine.
20 . A diagnostic unit as claimed in claim 19 , wherein the processor is arranged to determine the speed of the crank wheel for the cylinder under test at two different points within the combustion cycle of the cylinder.
21 . A diagnostic unit as claimed in claim 20 , wherein the crank wheel comprises a group of regularly spaced crank teeth associated with each cylinder within the engine and the processor is arranged to monitor the time taken for a given crank tooth to move past a crank tooth sensor and to subsequently determine the speed of the crank wheel.
22 . A diagnostic unit as claimed in claim 19 , wherein the crank wheel comprises a group of regularly spaced crank teeth associated with each cylinder within the engine and the processor is arranged to determine the time taken for two different crank teeth for the cylinder under test to move past a crank tooth sensor within the combustion cycle of the cylinder.
23 . A diagnostic unit as claimed in claim 22 , wherein the processor is arranged to determine the first engine rotation parameter at the cylinder's top dead centre position and to determine the second engine rotation parameter at a point in the combustion cycle corresponding to the final crank tooth associated with the cylinder under test.
24 . A diagnostic system of a vehicle comprising a diagnostic unit according to claim 1 , a crank wheel, the crank wheel comprising a group of regularly spaced crank teeth associated with each cylinder within the engine, and a crank tooth sensor for sensing movement of the crank teeth, the output of the crank tooth sensor being input to the diagnostic unit.
25 . An electronic control unit for a vehicle comprising a diagnostic unit according to claim 1 .
26 . A method of determining the operational status of a fuel delivery system of an engine, the engine comprising a plurality of cylinders, each one of the cylinders comprising a combustion chamber into which fuel is injected by an associated fuel injector and within which, in use, combustion events repeatedly occur to define a combustion cycle of the cylinder between successive combustion events, the method comprising:
receiving data related to engine rotation
determining, from the data received, a first engine rotation parameter for a cylinder under test at a first point within the combustion cycle of the cylinder;
determining a second engine rotation parameter for the cylinder under test at a second, different point within the combustion cycle of the cylinder; and
comparing the two engine rotation parameters for the test cylinder in order to identify the operational status of the fuel delivery system associated with the cylinder under test.
27 . A data carrier comprising a computer program arranged to configure a diagnostic unit or an engine control unit to implement the method according to claim 26 .