FIELD OF THE INVENTION

This invention relates to a fuel supply apparatus and a fuel supply control method for a common rail type fuel injection system. More specifically, it relates to controlling the fuel supply to a high-pressure pump of a common rail type fuel injection system.

STATE OF THE ART

In a common rail type fuel injection system, a low-pressure pump feeds the fuel from a tank to a high-pressure pump through a metering unit. The metering unit regulates the quantity of the fuel supplied to the high-pressure pump. The high-pressure pump pressurizes the fuel and supplies it to the common rail. During certain situations, such as when the vehicle travels downhill, fuel is not supplied to the injectors. If the pump continues to supply the fuel to the common rail, the fuel pressure in the common rail may increase to an unsafe level. Therefore, the metering unit is closed when the pressure at the common rail is beyond a particular value to avoid further supply of the fuel to the high-pressure pump.

However, the fuel still leaks through the operating clearances of the metering unit and continues to flow to the high-pressure pump. As a result, the high-pressure pump continues to pressurize the fuel and supply it to the common rail.

Therefore, there is a need to control the supply of fuel to the high-pressure pump in order to avoid unintended and undesirable increase of pressure at the common rail.

BRIEF DESCRIPTION OF THE INVENTION

The present invention comprises a fuel supply apparatus and a fuel supply control method for a common rail type fuel injection system. The fuel supply apparatus comprises a unidirectional valve between a metering unit and a high-pressure pump. The high-pressure pump may be a port-controlled reciprocating pump. The unidirectional valve selectively supplies the fuel from the output of the metering unit to the high-pressure pump, based on the fuel pressure at the output of the metering unit. A return line connects the output of the metering unit to the tank. The return line has a throttle. The throttle selectively supplies a part of the fuel from the output of the metering unit back to the tank.

The unidirectional valve prevents unintended supply of fuel to the high-pressure pump and avoids undesired increase of pressure at the common rail.

The fuel leaked through the operating clearances of the metering unit does not pass through the unidirectional valve, as the unidirectional valve is opened only when the pressure at the output of the metering unit reaches a threshold.

Further, a part of the fuel leaked from the metering unit is supplied back to the tank by the throttle provided at the return line. Therefore, the fuel leaked from the metering unit does not get accumulated to a pressure that is sufficient to open the unidirectional valve.

Also, the throttle can be electronically controlled; therefore the quantity of fuel supplied to the high-pressure pump i.e. port-controlled reciprocating pump can be further regulated in addition to the metering unit.

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 a fuel supply apparatus for a common rail type fuel injection system in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The figure 1 shows a schematic view of a fuel supply apparatus for a common rail type fuel injection system, in accordance with an embodiment of the present invention. The fuel supply apparatus (100) comprises a low-pressure pump (2) which supplies a fuel from a tank (4) to a high-pressure pump (6) such as a port-controlled reciprocating pump (6) through a filter (8) and a metering unit (10).

J The metering unit (10) is otherwise called as a fuel control unit. The metering unit (10) is electronically controlled to adjust the quantity of fuel supplied to the high-pressure pump (6) based on the pressure at the common rail (12).

The high-pressure pump (6) has a port, through which the fuel is supplied from the metering unit (10) to the pump (6). The port controls the fuel flow to the pump body. A piston in the high-pressure pump (6) is moved up and down to pressurize the fuel and supply it to a common rail (12).

The metering unit (10) is controlled based on the fuel pressure at the common rail (12). At certain situations, e.g. when the vehicle is traveling in a downhill path, there is no need for supply of fuel to the common rail (12). At such situations, when the fuel pressure at the common rail (12) is already high, the metering unit (10) needs to be closed to cut-off the fuel supply to the high-pressure pump (6). For instance, the metering unit (10) is closed when the fuel supply is not required to the high-pressure pump (6). However, the fuel may still leak from the metering unit (10) through its operating clearances, even after closing the metering unit (10) completely.

A unidirectional valve (14) is provided between the outlet of the metering unit (10) and an inlet of the high-pressure pump (6). The unidirectional valve (14) selectively supplies the fuel from the output of the metering unit (10) to the high-pressure pump (6) based on the fuel pressure at the output of the metering unit (10).

Normally, the unidirectional valve (14) is in a closed position so that there is no supply of fuel to the high-pressure pump (6). The unidirectional valve (14) opens only when the fuel pressure at the output of the metering unit (10) reaches a threshold.
Therefore, the fuel leaked from the metering unit (10) does not reach the high-pressure pump (6); thereby undesired increase in fuel pressure at the common rail (12) is avoided.

In an embodiment of the present invention, the unidirectional valve (14) is integrally provided at an inlet of the high-pressure pump (6). That is, the unidirectional valve (14) is provided as a part of the port-controlled reciprocating pump (6).

In another embodiment, the unidirectional valve (14) is integrally provided at an outlet of the metering unit (10).

A return line (16) is provided connecting the output of the metering unit (10) to the tank (4). The return line (16) has a throttle (18). The throttle (18) supplies a part of the fuel from the output of metering unit (10) back to the tank (4).

When the metering unit (10) is closed, fuel still leaks from the metering unit (10). The throttle (18) returns a part of this leaked fuel back to the tank (4). As most of the leaked fuel is returned back to the tank (4), the chance of pressure build-up to open the unidirectional valve (14) is almost made impossible. Remaining part of the leaked fuel stays in the path between the metering unit (10) and the high-pressure pump (6). However, the remaining part of the leaked fuel is very less in quantity; therefore there is no increase in pressure to cause the opening of the unidirectional valve (14).

Further, during normal operation, when the metering unit (10) is opened, the throttle (18) still supplies a part of the fuel from the output of the metering unit (10) back to the tank (4). But a remaining part of the fuel from the output of the metering unit (10) will reach the threshold pressure and opens the unidirectional valve (14). Thus the throttle (18) returns the excess fuel back to the tank (4) and helps in regulating the fuel supply to the high-pressure pump (6).

In an embodiment of the present invention, the throttle (18) has a very small clearance, which is suitably designed to return most of the fuel leaked from the output of the metering unit (10) back to the tank (4).

In another embodiment of the present invention, the throttle (18) has a variable clearance. For example, the throttle (18) can be an L-shaped lever or rotary plate. The throttle (18) is pivotally rotated by the flow of the fuel entering the return line (16). Thus, clearance for the entry of the fuel to be returned to the tank (4) is varied based on the pressure at the output of the metering unit (10).

In yet another embodiment of the invention, the throttle (18) is an electronic throttle (18). The electronic throttle (18) is controlled based on the pressure at the output of the metering unit (10). The electronic throttle (18) can also be controlled based on the pressure at the common rail (12).

A fuel supply control method for a high-pressure pump of a common-rail type injection system, in accordance with the present invention is explained as follows. Pressure at the common rail (12) is monitored continuously and a metering unit (10) is adjusted based on the fuel pressure at the common rail (12). When the pressure at the common rail (12) is already at a threshold value, the metering unit (10) is closed completely.

Fuel supply to a high-pressure pump (6) such as a port-controlled reciprocating pump (6) is controlled by selectively opening a unidirectional valve (14) depending on the fuel pressure at the output of the metering unit (10). The unidirectional valve (14) is opened only when the fuel pressure at the output of the metering unit (10) reaches a threshold. Therefore, undesired increase of fuel pressure at the common rail (12) by the fuel leaked from the metering unit (10) is avoided. A remaining part of the fuel from the output of the metering unit (10) is returned selectively back to the tank (4) by a throttle (18) provided at a return line (16).

The fuel supply control method further comprises adjusting the throttle (18) based on the pressure at the output of the metering unit (10). The throttle (18) can also be adjusted based on the pressure at the common rail (12).

As the pressure at the common rail (12) reaches a threshold value, the throttle (18) is progressively opened so that the supply of the fuel to the pump (6) is stopped when the pressure at the common rail (12) reaches the threshold value. Similarly, when the pressure at the common rail (12) is less, then the throttle (18) is closed so that most of the fuel is supplied to the pump (6).

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. A fuel supply apparatus (100) for a common rail type fuel injection system,

said apparatus comprises a low-pressure pump (2) supplying a fuel from a tank (4) to a high-pressure pump (6)through a filter (8) and a metering unit (10), said high-pressure pump (6)supplying the fuel to a common rail (12), characterized in that, said apparatus comprises,

— a unidirectional valve (14) selectively supplying the fuel from the output of the metering unit (10) to the high-pressure pump (6) , based on the fuel pressure at the output of the metering unit (10); and
— a return line (16) connecting the output of the metering unit (10) to the tank (4), said return line (16) having a throttle (18), said throttle (18) selectively supplying a part of the fuel from the output of the metering unit (10) to the tank (4).

2. The fuel supply apparatus (100) of claim 1, wherein the high-pressure pump (6) is a port-controlled reciprocating pump (6).

3. The fuel supply apparatus (100) of claim 1, wherein the unidirectional valve (14) is integrally provided at an inlet of the high-pressure pump (6).

4. The fuel supply apparatus (100) of claim 1, wherein the unidirectional valve (14) is integrally provided at an outlet of the metering unit (10).

5. The fuel supply apparatus (100) of claim 1, wherein the unidirectional valve (14) is provided between an outlet of the metering unit (10) and an inlet of the high-pressure pump (6).

6. The fuel supply apparatus (100) of claim 1, wherein the unidirectional valve (14) opens when the fuel pressure at the output of the metering unit (10) reaches a threshold.

7. The fuel supply apparatus (100) of claim 1, wherein the metering unit (10) is controlled based on the fuel pressure at the common rail (12).

8. The fuel supply apparatus (100) of claim 1, wherein the metering unit (10) is closed when fuel supply is not required to the high-pressure pump (6).

9. The fuel supply apparatus (100) of claim 1, wherein the throttle (18) in the return line (16) supplies a part of the fuel leaked from the metering unit (10) to the tank (4).

10. The fuel supply apparatus (100) of claim 1 and 9, wherein the throttle (18) supplies a part of fuel leaked from the metering unit (10) so as to avoid opening of the unidirectional valve (14).

11. The fuel supply apparatus (100) of claim 1, wherein the throttle (18) has a variable clearance.

12.The fuel supply apparatus (100) of claim 1, wherein the throttle (18) is an electronic throttle (18).

13. The fuel supply apparatus (100) of claim 12, wherein said electronic throttle (18) is controlled based on pressure at the output of the metering unit (10).

14. The fuel supply apparatus (100) of claim 12, wherein the electronic throttle (18) is controlled depending on the pressure at the common rail (12).

15. A fuel supply control method for a high-pressure pump (6) of a common rail type injection system, the method comprising the steps of monitoring the pressure at common rail (12); adjusting a metering unit (10) based on the monitored pressure at the common rail (12), characterized in said method,

— opening an unidirectional valve (14) at the output of said metering unit (10) depending on the fuel pressure at the output of the metering unit (10); and

— returning a part of the fuel from the output of the metering unit (10) back to the tank (4), selectively.

16. The fuel supply control method of claim 15, wherein the high-pressure pump (6) is a port-controlled reciprocating pump (6).

17. The fuel supply control method of claim 15 further comprises :

— adjusting a throttle (18) provided at a return line (16) based on the pressure at the output of metering unit (10), said return line (16) connecting the output of the metering unit (10) to the tank (4). 18. The fuel supply control method of claim 15, wherein adjusting said throttle (18) based on the pressure at the common rail (12).