GB2123086A

GB2123086A - Fuel supply system for internal combustion engines

Info

Publication number: GB2123086A
Application number: GB08317093A
Authority: GB
Inventors: Michael Ronald Bungay; Peter Francis Bradford
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1982-07-08
Filing date: 1983-06-23
Publication date: 1984-01-25
Also published as: GB8317093D0

Abstract

Fuel flows to a high pressure pump 10 via a path 16 through a heat exchanger 15 to be heated by fuel returning from the pump 10 to a drain via a path 17. A by-pass passage 19 can convey the fuel flowing to the drain and a temperature responsive valve 20 responsive to the temperature of the fuel leaving the pump controls the flow through the path 17 and the by- pass passage 19. The path 16 is from an inlet 23 to an outlet 24 and the path 17 is from an inlet 22 to an outlet 25 shown in Fig. 2. <IMAGE>

Description

SPECIFICATION Fuel supply system for internal combustion engines This invention relates to a fuel supply system for an internal combustion engine of the compression ignition type, the system comprising a high pressure pump which in use, delivers fuel under pressure to injection nozzles of an associated engine, a low pressure pump which supplies fuel to the high pressure pump, a fuel filter through which the fuel supplied to the high pressure pump can flow and a drain passage from the high pressure pump.

It is well known that under cold conditions fractions of the fuel which is used in compression ignition engines, tends to freeze and cause clogging of the filter, thereby preventing flow of fuel to the engine. In order to overcome this problem it is known to provide electrically powered fuel heaters which are positioned upstream of or may be located in the fuel filter. Such heaters are of complex construction and require a considerable amount of electric power so their continuous use can impose a substantial load on the electrical system of the vehicle with which the engine is associated. It is also known to provide a heat exchanger upstream of the filter and to use the engine coolant as the heat source. This arrangement has the disadvantage that additional pipe work is required to connect the heat exchanger with the coolant system.

The object of the present invention is to provide a fuel system of the kind specified in a convenient form.

According to the invention a fuel system of the kind specified comprises a heat exchanger having a first fuel flow path through which fuel flows to the filter and a second flow path through which fuel flowing through said drain passage can flow, the heat exchanger acting in use, to effect heat exchange between the heated fuel in the second flow path and the fuel flowing in the first flowpath and valve means responsive in use to the temperature of the fuel leaving the fuel pump for regulating the flow of fuel in the second flow path.

An example of the fuel system in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a diagrammatic representation of the system, Figure 2 shows a sectional plan view of the heat exchanger incorporated into the system, and Figures 3 and 4 show to an enlarged scale, two valve arrangements.

Referring to Fig. 1 of the drawings, the fuel system comprises a fuel pumping apparatus generally indicated at 10 and which in known manner, incorporates a high pressure pump and a low pressure pump. The high pressure pump is provided with outlets (not shown) for connection to the injection nozzles respectively of the associated engine, and the low pressure pump has a fuel inlet which is connected to a filter unit indicated at 11.The filter unit conveniently incorporates a paper or like filter element which retains any solid particles of contaminant contained in the fuel which is drawn from a fuel supply tank indicated at 1 2. In the particular example there is interposed between the fuel filter and the tank 1 2 a sedimentation unit 1 3 which acts to retain a substantial quantity of the water which may be contained in the fuel in the fuel tank. As shown, immediately upstream of the filter unit is an electrical heater 14 which can be used to heat the fuel flowing to the filter unit.

Interposed between the filter unit and the sedimentation device is a heat exchanger generally indicated at 15, and which has first and second flow paths, the first flow path being indicated at 1 6 and forming the flow path for the fuel passing from the sedimentation unit to the filter. The second flow path indicated at 1 7 has its downstream end connected to the fuel tank by means of a suitable pipe and its upstream end connected to an outlet 18 on the pumping apparatus and through which fuel which flows into the housing of the apparatus from the high pressure pump and possibly also the low pressure pump can be returned to the fuel tank.

As is well known, the fuel leaving the pumping apparatus by way of the outlet 18 is hotter than the fuel which flows to the apparatus from the filter unit. This is because of the work done on the fuel in the pumping apparatus and by virtue of the fact that the pumping apparatus is in close proximity to the engine.

As a result of the provision of the heat exchanger, a heat exchange takes place between the fuel flowing through the outlet 18 and the fuel flowing to the filter unit. There is therefore a reduced tendency for clogging of the filter unit to occur in cold conditions. It will be appreciated that the electrical heater 14 is utilised when the engine is required for use.

Once the engine has started, however, the fuel which flows through the outlet 1 8 will increase in temperature and heat exchange will occur between this fuel and the fresh fuel drawn through the sedimentation unit. After a period therefore it will not be necessary to maintain the electrical heater in operation.

It is important that the fuel flowing to the pumping apparatus should not be too hot, since excessive leakage may occur within the apparatus due to the reduced viscosity of the fuel, and this may cause erratic operation of the apparatus. Means is therefore provided to prevent the fuel flowing through the outlet 1 8 following the flow path 1 7. This is achieved by means of a by-pass passage 19 through which the fuel flowing through the outlet 18 can flow in preference to the second flow path 17. The control of this flow of fuel is by means of a temperature responsive valve indicated at 20.It will be appreciated that the heat exchanger may be disposed upstream of the sedimentation unit but it is important to ensure in this case, that the sedimentation unit is not too far removed from the filter unit otherwise the fuel leaving the sedimentation unit may cool sufficiently to allow freezing of the fractions of fuel. It will also be appreciated that the electrical heater may be associated with the sedimentation unit. Moreover, there may be cases where the provision of an electrical heater may not be required. Such a case would be where the vehicle is protected from extreme cold during the time the engine is not in operation.

Referring now to Fig. 2, the heat exchanger comprises a body 21 in which is defined a fuel inlet 22 for connection to the outlet 18, a fuel inlet 23 for connection to the sedimentation unit, and a fuel outlet 25 for connection to the tank 1 2. The fuel inlet 23 and the outlet 24 lead into a flow path which is defined by a number of partitions 26 extending from opposite sides of a chamber formed in the body. The flow path is therefore of a length which is substantially longer than that of the body.

The so-called second flow path is defined by an insert which locates in the chamber and which is shown in dotted outline, the flow path defined by the insert having a length substantially the same as the first flow path.

The insert is connected by passages one to the outlet 25 and the other to a branch passage 27 communicating with the inlet 22.

Also communicating with the inlet 22 is the by-pass passage 1 9 and this extends to the outlet 25. The temperature responsive valve includes a first valve element 28 to control the flow of fuel into the branch passage 27 and a second valve element 29 of cup-shaped form, which controls the flow of fuel into the by-pass passage. A temperature responsive spring 30 is used to control the positions of the valve elements which are coupled together. The valve elements are biased against the action of the temperature responsive spring by a resilient means conveniently in the form of a coiled compression spring.The arrangement is such that when the fuel leaving the outlet 1 8 is cold, the valve element 29 covers the by-pass passage 1 9 so that all the fuel flows by way of the branch passage 27 and from the branch passage 27 through the insert so as to effect heat exchange with the fuel flowing to the filter unit. As the temperature of the fuel leaving the outlet 18 increases, the valve elements move to ensure that more fuel flows through the by-pass passage 1 9 and in this manner, the temperature of the fuel flowing to the filter unit is controlled. The fuel flowing into the by-pass passage flows by way of a port formed in the stem connecting the two elements together, the port communicating with a passage in the stem opening into the base wall of the cupshaped element 29.

Figs. 3 and 4 show to an enlarged scale, the construction of the temperature responsive valve. The construction of the valve shown in Fig. 3 corresponds with that shown in Fig. 2.

The temperature responsive spring 30 is of the type which expands with increasing temperature so that as the temperature increases the valve members are moved downwardly against the action of the spring 31 to allow fuel flow through the by-pass passage 1 9 and to restrict the flow through the passage 27.

In the example shown in Fig. 4 the temperature responsive spring is of the type which contracts as the temperature increases. Hence the positions of the spring 30 and 31 are reversed.

In the system described the fresh fuel flowing to the pump and the hot fuel leaving the pump never mix but at the same time exchange of heat can take place. The fact that no mixing occurs eases the problem of venting the pump of air as compared with a system in which the heated fuel is allowed to mix with the fresh fuel. In such a system recirculation of the air can take place. Moreover, whether or not heat exchange is taking place, flow through the heat exchanger will be substantially unaffected and therefore any settings in the pump which might be affected by variations in pressure as a result of varying flow through the outlet 18 will be unaffected.

Claims

1. A fuel supply system for an internal combustion engine of the compression ignition type, the system comprising a high pressure pump which in use, delivers fuel under pressure to injection nozzles of an associated engine, a low pressure pump which supplies fuel to the high pressure pump, a fuel filter through which the fuel supplied to the high pressure pump can flow, a drain passage from the high pressure pump, a heat exchanger having a first fuel flow path through which fuel flows to the filter and a second flow path through which fuel flowing through said drain passage can flow, the heat exchanger acting in use, to effect heat exchange between the heated fuel in the second flow path and the fuel flowing in the first flow path and valve means responsive in use to the temperature of the fuel leaving the fuel pump for regulating the flow of fuel in the second flow path.

2. A system according to Claim 1 including a by-pass passage connected at one end to a drain, the other end of the by-pass passage being connected by said valve means to said drain passage, so that as the valve means reduces the flow of fuel through said second flow path, the flow of fuel through said by-pass passage is increased and viceversa.

3. A system according to Claim 2 in which said valve means comprises first and second valve elements which are coupled together for controlling the flow through the second flow path and the by-pass passage respectively.

4. A system according to Claim 3 in which the flow of fuel into the by-pass passage takes place through passage means formed in a stem connecting the valve members.

5. A system according to any one of the preceding claims in which said valve means incorporates a temperature responsive spring.

6. A fuel supply system for an internal combustion engine of the compression ignition type comprising the combination and arrrangement of parts substantially as hereinbefore described with reference to the accompanying drawings.