FIELD OF INVENTION:

The invention relates to a method and a device to diagnose the fuel supply system and to detect a malfunctioning of the components involved in the fuel supply system.

BACKGROUND OF THE INVENTION:

Diagnosing different systems and/or components in a vehicle is known in the prior arts.

The US patent 6536415 discloses one such diagnosing method. The US patent 6536415 discloses a method wherein the currents of fuel delivery units are measured, compared to each other to determine whether both the fuel delivery units are working properly.

ADVANTAGES OF THE INVENTION:

The invention proposes a simple method to detect the malfunctioning of a component in the fuel supply system. This is achieved by measuring the current in the metering unit, comparing it with the expected current for the given pressure in the fuel supply path.

The invention makes use of the existing system and the components to diagnose the fuel supply system without needing any additional components.

BRIEF DESCRIPTION OF THE DRAWINGS:

Figure 1: Shows the schematic of the fuel supply system according to the invention

DESCRIPTION OF THE INVENTION:

The present invention is described in the preferred embodiment as follows:-

FIG. 1 shows a schematic of a fuel supply system 10 for a vehicle which is not shown, involving the invention. In fig. 1 only the components which are relevant to describe the invention are shown, whereas all the other components which form essential parts of any fuel supply system for a vehicle, are not shown.

The fuel supply system 10 shown in FIG. 1 comprises a fuel tank 12, a feed pump 14, a filter 16, a high pressure pump 18 and a metering unit 20. The feed pump 14 is a low pressure pump feeding the fuel at an intermediate pressure to the high pressure pump 18.

The feed pump 14 is an electric pump of any appropriate type which are already known, with a pumping stage driven by an electric motor which is not shown in figure. In one embodiment the feed pump 14 may be outside of the fuel tank 12 and in another embodiment the feed pump 14 may be submerged in the fuel tank 12. An engine control unit (ECU) 22 controls the feed pump 14.

The feed pump 14 draws the fuel from the fuel tank 12 through a supply path and delivers the fuel to the high pressure pump 18 through the filter 16 and the metering unit 20. The high pressure pump 18 further pressurizes the fuel and delivers the fuel to the fuel accumulator 24. From fuel accumulator 24, the fuel is delivered to the next stages of the fuel supply system which are not shown. The fuel accumulator 24 contains a pressure sensor 26 which provides data on fuel pressure to the ECU 22. A bypass throttle 27 is used to ensure cooling fuel for the pump and to ensure zero delivery function when the metering unit is not sealed in fully closed condition.

Some of the components explained above may be combined and may exist in common physical units. The ECU 18 may be an existing Engine Control Unit in the vehicle which is responsible to control the engine or a separate control unit.

Downstream the filter 16, an overflow valve (OFV) 30 is provided which returns the excess fuel to the fuel tank 12. The OFV 30 is a simple mechanical spring loaded ball or plunger type valve. When the pressure in the fuel supply path 32 exceeds a pre-defined threshold, the OFV 30 opens and returns the excess fuel to the fuel tank 12.

In one embodiment, the OFV 30 may be a separate unit while in another embodiment, the OFV may be built into the filter 16 or on the pump in case the metering unit 20 is integrated on the pump. The metering unit 20 is a proportional valve controlled by the ECU 22. Based on the torque demand, the proportional valve in the metering unit 20 opens to a particular position so that required amount of fuel reaches the high pressure pump 18.

The ECU 22 contains a set of tables 34 containing current and fuel pressure values for different engine operating conditions. The different engine operating conditions may be from no load to full load condition of the engine or from minimum load to maximum load conditions. These tables 34 provide values regarding the expected current drawn by the metering unit for a given fuel pressure for a given engine operating condition.

When the OFV 30 is functioning correctly, the required amount of fuel is delivered to the high pressure pump 18 through the metering unit 20 and the excess fuel is returned to the fuel tank 12. This is achieved by the metering unit which is controlled by the ECU 22.

As explained earlier, the OFV 30 may be a part of the filter 16 or a separate unit. If the fuel supply system initially had a filter with OFV 30 built in, and if during the servicing of the vehicle if the this filter is replaced with another filter which does not have a built in OFV, then a separate OFV needs to be connected in the system. But if by chance the separate OFV is not connected in the fuel supply system, the fuel supply system may malfunction. This situation is explained below.

Assume that the filter with OFV is replaced during the servicing of a vehicle with a filter which does not have an OFV and a separate OFV is not connected in the fuel supply system. Under this condition the feed pump keeps delivering the fuel to the metering unit.
As there is no OFV and no return path for the excess fuel, the pressure in the fuel accumulator keeps increasing. The ECU which is continuously monitoring the fuel pressure in the accumulator through the pressure sensor, detects that the fuel pressure is higher than expected and operates the metering unit. The metering unit regulates the fuel flow through it by regulating the amount of opening of its valve. But as the OFV is missing, and there is no excess fuel returning to the fuel tank, the rate of closing of the valve in the metering unit will not reduce the fuel pressure as expected. This is determined by monitoring the current drawn by the metering unit and fuel pressure.

Shown in fig. 2A is the current versus expected change in fuel pressure, the X axis representing the change in fuel pressure and the Y axis representing the current. This graph is shown as an example. There will be different graphs for different operating conditions of the engine. The table 34 contains these graphs in the form of values of change in current for expected change in fuel pressure. These tables are prepared for the values when the OFV is functioning correctly. The current refers to the current drawn by the metering unit 20.

The table 34 contained in the ECU is shown in the figure 2B. The table shown in Fig. 2B has two columns. The first column contains the change in current i.e. ΔI. The second column contains the values for expected change in pressure i.e. Δ Pe.

Shown in fig. 3A is a graph of the fuel pressure versus time, X axis representing the time and the Y axis representing the fuel pressure for a case where the OFV is either absent or the OFV is malfunctioning.

As shown in the graph in Fig. 3A, when the filter with OFV is replaced in the vehicle with a filter without an OFV and the vehicle is started, then suddenly there will be pressure building up in the accumulator as shown on graph at the point 100. The ECU continuously monitors the current drawn by the metering unit and the fuel pressure in the accumulator. The monitored fuel pressure in the accumulator is referred as Pa (Pressure actual).

The ECU monitoring the fuel pressure Pa detects that there is pressure build up above a threshold and operates the metering unit to reduce the pressure. The current I drawn by the metering unit starts decreasing as the solenoid valve in the metering unit starts closing the proportional valve. This is shown in fig. 3B. But the rate of closing of the solenoid valve may not bring down the pressure at the expected rate. This is checked by comparing the actual change in pressure ΔPa with the expected change in pressure Δ Pe stored in the table 34 corresponding to the change in current Δl.

The ECU computes the actual change in pressure ΔPa by taking some consecutive readings of Pa. ECU also computes the change in current Al by taking the corresponding readings of I. The ECU retrieves expected change in pressure ΔPe which is corresponding to the Δl, from the table.

ECU compares ΔPa and ΔPe, i.e. actual change in pressure and the expected change in pressure. If the difference between ΔPa and ΔPe is within an acceptable limit, then there is no malfunction in the fuel supply system, otherwise there is a malfunction in the fuel supply system.

There are different tables like table 34 for different operating conditions. Based on the engine operating conditions, the right table is selected for retrieving the expected change in pressure, ΔPe. Thus for a given operating condition of the engine, if the change in current (delta I) of the metering unit does not result in expected change in pressure, then there is malfunction in the fuel supply system. Once the ECU determines that there is a malfunction in the fuel supply system, it generates a warning 34 to the user or to the technician in the service station. The warning may be in the form of an audio beep or a lamp. The error information is also registered in the ECU 22 to provide information to service.

The embodiment is explained with reference to the malfunctioning of the OFV, but same method is applicable to detect the malfunction of the metering unit itself. If the metering unit is malfunctioning, the same can be detected by monitoring the current of the metering unit and the fuel pressure. In this case tables containing expected change in current drawn by the metering unit for known change in the fuel pressure for different conditions are stored. Whenever there is pressure build up beyond the threshold, then by comparing the actual change in current of the metering unit and the actual change in pressure to the expected values stored in the tables the malfunctioning is detected. If the actual readings are beyond acceptable limits when compared to the expected values, there is malfunction in the metering unit.

Thus the invention proposes a simple method to detect a malfunction in the fuel supply system which would have been caused by incompatible overflow valve or absence of the overflow valve in the fuel filter. This may happen during the servicing of the car when fuel filter with overflow valve is replaced.

The invention makes use of the existing system and the components to diagnose the fuel supply system without needing any additional components.

WE CLAIM:

1. A method to diagnose a fuel supply system, the method comprising the steps:

- Monitoring a current drawn by a metering unit

- monitoring an actual fuel pressure of the fuel in a fuel accumulator

- comparing the actual fuel pressure to the expected fuel pressure for the current monitored to determine if there is any malfunction in the fuel supply system

2. A method according to claim 1 wherein, comparing the actual fuel pressure with the expected fuel pressure comprises comparing the actual change in fuel pressure with the expected change in fuel pressure.

3. A method according to claim 1 wherein the expected change in fuel pressure is retrieved from a table, the expected change in fuel pressure corresponds to the monitored current.

4. A method according to claim 1 wherein a warning signal is generated if the actual change in fuel pressure is beyond acceptable limit when compared to the expected change in fuel pressure.

5. A method according to claim 1 wherein the information regarding the malfunction is stored in an Engine control Unit (ECU).

6. A fuel supply system (10) comprising;

a fuel tank (12) to store fuel

a feed pump (14) to draw fuel from the fuel tank (12)

a filter (16) to receive the fuel from the feed pump (14) and filtering the fuel passing through the said fuel filter (16)

a metering unit (20) receiving fuel from the filter (16) and supplying fuel to a high pressure pump (18)

a high pressure pump (18) receiving fuel from the filter (16) and delivering the fuel at high pressure to a fuel accumulator (24)

an engine control unit (ECU) (22), the said engine control unit characterized by a means to diagnose the fuel supply system by comparing a change in fuel pressure to an expected change in fuel pressure for a given current drawn by the metering unit (20)

7. A fuel supply (10) system according to claim 6 wherein the metering unit is a proportional valve

8. A fuel supply system according to claim 5 wherein the ECU has a table containing values of change in current and corresponding expected change in pressure.