FIELD OF THE INVENTION

This invention relates to a device and method for operating an engine having a common- rail type fuel injection system. More particularly, this invention relates to operating the engine when there is an error in the fuel injection system such as failure of metering unit of high-pressure pump, failure of rail pressure sensor, etc.

STATE OF THE ART

A pressure-limiting valve is provided in the common-rail of a high-pressure type fuel injection system to regulate the pressure in the common-rail. When the fuel pressure inside the common-rail reaches a maximum threshold, the pressure-limiting valve is opened to reduce the excess pressure in the common-rail. Generally, the pressure- limiting valve does not let the pressure to reduce beyond a minimum level which is required to operate the engine in a limp-home mode.

When a faulty condition is detected in the vehicle during low-idle conditions for e.g., immediately after the start of the vehicle, the engine has to be switched to the limp-home mode. In such scenario, the pressure of the common-rail is at an intermediate level which is above the minimum level pressure required for operating the engine in limp-home mode. However, in order to reduce the pressure inside the common-rail to the minimum level pressure, the pressure-limiting valve has to be opened.

The pressure inside the common-rail has to be raised to the maximum threshold for opening the pressure-limiting valve. However, if the high-pressure pump used in the fuel injection system is of small capacity, it is very difficult to raise the pressure inside the common-rail to the maximum threshold especially during low-idle conditions.

DESCRIPTION OF THE INVENTION

The apparatus and method for operating an engine in accordance with this invention comprises a controller which increases the engine speed upon detecting predetermined error conditions, when the vehicle is in low-idle condition. The controller increases the engine speed for raising the pressure inside a common-rail beyond a threshold by a high-pressure pump. When the pressure inside the common-rail reaches beyond a maximum threshold, a pressure-limiting valve in the common-rail is opened to return the excess fuel to a fuel tank. The engine speed is reduced after the pressure-limiting valve is opened. The pressure-limiting valve is closed when the pressure inside the common-rail reaches a minimum level which is required to switch the engine to limp-home mode.

The engine is switched smoothly to limp-home mode during predetermined error conditions such as during failure of the metering unit and/or the pressure sensor located in the fuel rail.

Even during low-idle conditions, transition to limp-home mode is achieved with the help of a small capacity high-pressure pump.

Problem of engine stall is avoided effectively by the controller even when the capacity of the high-pressure pump is small.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawings:

Figure 1 shows a schematic view of the apparatus for operating an engine in accordance with the present invention.

Figure 2 illustrates a flow chart showing method to operate the engine in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows a schematic view of an apparatus for operating an engine, in accordance with the embodiment of the invention. The engine described herein is a direct-injection type engine, in which high-pressure fuel is directly injected to the cylinders of the engine.

The apparatus (10) comprises a high-pressure pump (12) which is connected to the engine. The high-pressure pump (12) is driven by the engine for pressurizing and supplying the fuel from a fuel tank (14) to a common-rail (16). The common-rail (16) may be alternately termed as fuel rail or high-pressure accumulator. From the common-rail (16), the high-pressure fuel is directly supplied to the engine through one or more injectors (18).

The high-pressure pump (12) has a metering unit (20) to deliver the required quantity of the fuel to the common-rail (16) in order to maintain the required pressure in the common-rail (16). The common-rail (16) has a pressure sensor (22) to measure the fuel pressure inside the common-rail (16). When the pressure of the fuel inside the common-rail (16) exceeds a threshold, a pressure-limiting valve (24) in the common-rail (16), is opened to return the excess fuel from the common-rail (16) to the fuel tank (14).

An engine speed detector is provided to measure the speed of the engine. The engine speed detector may be a crank sensor (26) or a cam sensor (28). A controller (30) receives signals from different sensors like the pressure sensor (22), the metering unit (20), the crank sensor (26), the cam sensor (28), etc. On the basis of the status of these signals, the controller (30) detects the occurrence of predetermined error conditions. The controller (30) is otherwise called as Electronic control unit (ECU) or Engine control unit.

In an embodiment, the predetermined error condition is the failure of the pressure sensor (22).

In another embodiment, the predetermined error condition is the failure of the metering unit (20). Failure of the metering unit (20) may be an electrical contact failure or a mechanical failure. Upon occurrence of predetermined error conditions such as failure of the metering unit (20) and/or failure of the pressure sensor (22), the engine has to be switched to a limp-home mode or fail-safe mode.

However, in order to enter into limp-home mode, the pressure of the fuel inside the common-rail (16) has to be maintained at a minimum level.

During low-idle conditions, i.e., immediately after starting the vehicle, the pressure of the common-rail (16) is at an intermediate level which is above the minimum level pressure required for operating the engine in limp-home mode. However, in order to reduce the pressure inside the common-rail (16) to the minimum level pressure, the pressure-limiting valve (24) has to be opened.

The pressure inside the common-rail (16) has to be raised to the maximum threshold for opening the pressure-limiting valve (24). However, it is difficult to raise pressure inside the common-rail (16) by a small capacity high-pressure pump (12) to the maximum threshold, especially during low-idle conditions

The controller (30) recognizes the low-idle condition of the vehicle based on output of engine speed detector such as crank sensor (26) and cam sensor (28). During low-idle conditions, when the controller (30) detects the occurrence of predetermined error conditions, it checks whether the gear is neutral position. When the gear is not in neutral position, the controller (30) changes it to neutral position and then increases the engine speed to raise the pressure of the common-rail (16). The pressure of the common-rail (16) is raised beyond the threshold so that the pressure-limiting valve (24) is opened to return the excess fuel to the fuel tank (14).

The controller (30) reduces the speed of the engine immediately after the pressure-limiting valve (24) is opened. The pressure-limiting valve (24) is closed when the pressure of the common-rail reaches a minimum level which is necessary to operate the engine in the limp-home mode. The engine is then switched to lymphoma mode.

Figure 2 illustrates a flow chart showing method to operate the engine in accordance with the present invention. At step SI, occurrence of predetermined error conditions such as failure of pressure sensor (22) of a common-rail (16) and/or failure of a metering unit (20) of a high-pressure pump (12) is detected by a controller (30). The speed of the engine is measured by an engine speed detector (26, 28) at step S2. Based on the detected engine speed, a controller (30) judges the low-idle condition of the vehicle. When the vehicle is in low-idle condition and the predetermined error conditions are detected, the speed of the engine is increased by the controller (30) at step S3 after ensuring that the gear is in the neutral condition. As a result, the high-pressure pump (12) operates at higher speed and the fuel pressure inside the common-rail (16) is raised beyond a maximum threshold of the pressure-limiting valve (24) provided in the common-rail (16) (Step S4).

When the fuel pressure inside the common-rail (16) is beyond the maximum threshold, the pressure-limiting valve (24) is opened to return the fuel from the common-rail (16) to a fuel tank (14) and release the excess pressure inside the common-rail (16). The pressure-limiting valve (24) is opened till the pressure inside the common-rail is reduced to a minimum level suitable for operating the engine to limp-home mode. (Step S5). Once the pressure-limiting valve (24) is opened, the engine speed is reduced by the controller (30). Finally, at step S6, when the pressure of the common-rail (16) reduces to the minimum level, the engine is switched to the limp-home mode.

Thus, the engine is switched smoothly to limp-home mode when there is a failure in the metering unit (20) or in the pressure sensor (22) located in the common-rail (16).

Transition to limp-home mode is performed easily even during low-idle conditions and even with the help of a small capacity high-pressure pump.

Even when faulty condition is detected in the vehicle immediately after the start of the vehicle, switching to limp-home mode is performed easily with this invention

Problem of engine stall is avoided effectively by the controller even when the capacity of the high-pressure pump is small.

It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiment 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.

WE CLAIM:-

1. An apparatus (10) for operating an engine, said engine is coupled to a high-pressure pump (12) for driving said high-pressure pump (12); said high-pressure pump (12) is adapted to supply high-pressure fuel from a fuel tank (14) to a common-rail (16);

said common-rail (16) has a pressure-limiting valve (24) which is opened to return the fuel from the common-rail (16) to said fuel tank (14) when pressure inside said common-rail (16) exceeds a maximum threshold;

said engine is supplied with fuel from said common-rail by at least one injector (18);

a means for detecting occurrence of predetermined error condition, said engine is adapted to operate in a limp-home mode upon occurrence of said predetermined error condition; an engine speed detector (26, 28) for measuring the speed of the engine;
said apparatus (10) is characterized by

a controller (30) which increases the engine speed for raising the pressure of the common-rail beyond the maximum threshold in order to open said pressure-limiting valve (24) based on the output of the engine speed detector (26,28) and occurrence of said predetermined condition.

2. The apparatus (10) of claim 1, wherein said predetermined error condition is a failure of a pressure sensor (22) provided in said common-rail (16).

3. The apparatus (10) of claim 1, wherein said predetermined error condition is a failure of a metering unit (20) provided in said high-pressure pump (12).

4. The apparatus (10) of claim 1, wherein said controller (30) increases the engine speed for increasing the pressure of the common-rail (16) beyond the threshold when the output of the engine speed detector (26, 28) indicates low-idle condition.

5. The apparatus (10) of claim 1, wherein said controller (30) checks if the gear is in neutral position when increasing the speed of the engine for raising the pressure of the engine.

6. The apparatus (10) of claim 5, wherein the controller (30) changes the gear to neutral position, if the gear is not in neutral position when increasing the speed of the engine.

7. The apparatus (10) of claim 1, wherein the controller (30) is further adapted to reduce the engine speed after the pressure-limiting valve (24) is opened to release the excess pressure inside the common-rail (16).

8. A method for operating an engine, said method comprising: detecting occurrence of predetermined error condition; sensing the speed of the engine;

increasing the speed of the engine by a controller (30);

raising the pressure of a common-rail (16) beyond a pressure threshold of a pressure-limiting valve (24) mounted said common-rail (16) to open said pressure-limiting valve (24) to release the excess pressure in the common-rail (16);

reducing the pressure in the common-rail (16) to a level suitable for operating the engine in a limp-home mode; and switching the engine operation from a normal mode to a limp-home mode.

9. The method of claim 8, wherein the gear is switched to neutral condition before increasing the speed of the engine.

10. The method of claim 8, wherein the engine speed is reduced after the pressure-limiting valve (24) is opened to release the excess pressure inside the common-rail (16).