JP2845003B2 - Diesel engine fuel supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel supply system for a diesel engine and, more particularly, to a fuel supply system for facilitating engine start at low temperatures.

[0002]

2. Description of the Related Art In an engine using a diesel fuel such as light oil, a component such as paraffin in the fuel may crystallize at a low temperature and grow to produce wax. Since the wax generated in the fuel is captured by the fuel filter, the fuel filter may be blocked by the wax in a short time, such as when the diesel engine is started at low temperatures, which may result in poor fuel supply to the fuel injection pump. There is.

As a means for preventing the clogging of the fuel filter by the wax, for example, Japanese Utility Model Application Laid-Open No. 58-1
There is an apparatus described in 36662. The device disclosed in the publication is provided with a switching valve that recirculates excess fuel from a fuel injection pump and a fuel injection nozzle immediately upstream of a fuel filter when the fuel temperature is low and there is a possibility of wax generation. I have. Thus, after the engine is started, the high-temperature fuel passing through the fuel injection pump and the fuel injection nozzle is supplied to the upstream side of the filter, so that the fuel filter can be prevented from being clogged by the wax.

[0004]

However, in the fuel supply device according to the prior art described above, although the blocking of the fuel filter by the wax can be prevented, there may be other problems. That is, in the device disclosed in Japanese Utility Model Application Laid-Open No. 58-136662, particularly when the temperature of the recirculated fuel from the fuel injection pump or the injection nozzle is not increased, such as during engine start, the viscosity of the fuel passing through the filter is low due to the low temperature. May be higher. For this reason, in the above device, there is a case where the resistance of the fuel filter is high at the time of starting the engine at a low temperature, and there is a problem that the startability of the engine is deteriorated due to a poor fuel supply.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to improve cold startability of an engine and to prevent clogging of a fuel filter due to generation of wax.

[0006]

According to the present invention, a cold start detecting means for detecting a cold start of an engine, and a fuel passage at a cold start for supplying fuel to a fuel injection pump without passing through a fuel filter. A post-start fuel passage for supplying a mixture of surplus fuel recirculated from the fuel injection pump and the fuel injection nozzle and fuel in the fuel tank to the fuel injection pump through the fuel filter, the cold start fuel passage, Fuel passage switching means for selectively connecting the fuel passage with the fuel injection pump after the start, and when the cold start detection means detects a cold start of the engine, the fuel passage switching means switches the cold start. A fuel supply device for a diesel engine, wherein the fuel passage is connected to a fuel injection pump.

[0007]

In the cold start of the engine, the fuel passage switching means connects the fuel passage and the fuel injection pump during the cold start, so that the fuel is supplied to the fuel injection pump without passing through the fuel filter. As a result, even when the fuel temperature is low and the viscosity is high, a large flow resistance does not occur, and deterioration of the engine startability due to poor fuel supply is prevented.

After completion of the engine start, the fuel passage switching means connects the fuel passage to the fuel injection pump after the start, so that the mixture of the high temperature excess fuel recirculated from the fuel injection pump and the injection nozzle and the fuel in the tank is provided. Is supplied to the fuel injection pump through a filter. This keeps the temperature of the fuel passing through the filter higher than the wax formation temperature and prevents the fuel filter from clogging.

[0009]

FIG. 1 shows an embodiment of a fuel supply apparatus according to the present invention. In FIG. 1, 1 is a fuel oil tank, 2 is a fuel injection pump, and 3 is a fuel filter. The fuel injection pump 2 sucks fuel from the fuel supply pipe 11 and feeds the fuel to the fuel injection nozzle 4 to perform fuel injection. Excess fuel not used for fuel injection is returned from the fuel injection pump 2 and the injection nozzle 4 to the fuel return pipe 12. The fuel return pipe 12 is connected to the fuel tank 1 via the first solenoid valve 7 and the pipe 17. The fuel return pipe 12 is connected to a fuel pipe 13 at the time of cold start and a fuel return pipe 14 after the start on the upstream side of the solenoid valve 7.

A second electromagnetic valve 8 is provided in the fuel pipe 13 at the time of cold start. The fuel pipe 13 at the time of cold start is provided with a bypass passage 3 a provided in the housing of the fuel filter 3 on the downstream side of the solenoid valve 8. It is connected to the fuel supply pipe 11 of the fuel injection pump 2 without passing through the filter element. Further, a third solenoid valve 9 is provided in the post-start fuel return pipe 14, and the pipe 14 joins with the fuel pipe 16 from the fuel tank 1 downstream of the solenoid valve 9 so that the post-start fuel pipe 1
5 are formed. After the start, the fuel pipe 15 is connected to the fuel filter 3 and connected to the supply pipe 11 of the fuel injection pump 2 via a filter element.

In FIG. 1, reference numeral 5 denotes a control circuit for controlling the opening and closing of the first to third solenoid valves 7 to 9. In this embodiment, an independent control circuit for controlling the solenoid valve is not actually provided, but the solenoid valve is controlled by an electronic control unit (ECU) including a known digital computer for controlling the operation of the engine. E for performing the fuel supply control of the present invention
The output ports of the CU 5 are connected to the solenoid valves 7 to 9 via drive circuits (not shown). In addition, an input port of the ECU 5 receives an engine start signal from an ignition switch (not shown) of the engine to detect the start of the engine. Is entered.

Next, the operation of the fuel supply device of the present embodiment will be described. When the ignition switch of the engine is turned on at the time of starting the engine, an engine start signal is input to the ECU 5. At this time, the ECU 5 determines whether or not the recirculated fuel temperature detected by the temperature sensor 6 is equal to or lower than a predetermined value. If the fuel temperature is equal to or lower than the predetermined value, the first solenoid valve 7 and the third solenoid valve 9 Are closed, and only the second solenoid valve 8 is opened. At this time, since the fuel oil has a low viscosity at a low temperature, a flow through the pipes 16 and 15 and the filter 3 hardly occurs.

Thus, the fuel pump 2 → pipe 12 → pipe 13 → bypass passage 3a → supply pipe 11 → fuel pump 2
, The fuel in this closed circuit is supplied to the fuel injection pump 2 when the engine is started. As a result, fuel is supplied to the fuel injection pump 2 without passing through the filter element, and a large flow resistance due to the filter element does not occur.
The engine is started reliably.

Next, when a predetermined time (for example, about several seconds) has elapsed after the input of the engine start signal, the ECU 5 closes the second solenoid valve 8 and opens the third solenoid valve 9 from the above state. For the above operation, the ECU 5 measures the elapsed time after the input of the engine start signal by a built-in clock. Thus, the fuel injection pump passes through the post-starting fuel pipe 15 and the filter 3 in a state where the excess fuel having a high temperature from the fuel return pipe 12 after the engine is started and the low-temperature fuel sucked from the tank 1 through the pipe 16 are mixed. Since the fuel is supplied to the filter 2, the temperature of the fuel passing through the filter 3 is maintained at a higher temperature than the wax generation temperature, thereby preventing the filter from being clogged due to the generation of wax.

Next, warm-up proceeds sufficiently and the temperature sensor 6
When the surplus fuel temperature of the fuel injection pump 2 detected in the step (5) exceeds a predetermined value, the ECU 5 opens the first solenoid valve 7 and closes the third solenoid valve 9. As a result, the high-temperature surplus fuel is returned directly to the tank 1, and the fuel pump 2
Is supplied via the filter 3. Therefore, an excessive rise in temperature of the fuel injection pump 2 is prevented.

According to this embodiment, as described above, during warm-up of the engine, excess fuel having a high temperature from a fuel pump or the like and low-temperature fuel from a fuel tank are mixed to supply an appropriate temperature fuel to the engine. Therefore, the ignition delay when the temperature of the engine combustion chamber is insufficient during warm-up can be reduced, and diesel knock during warm-up can be reduced. Immediately after the low temperature start, the relatively high temperature surplus fuel passes through the bypass passage 3a provided in the housing of the fuel filter 3, so that the fuel in the filter is heated, and the wax generated in the filter is dissolved. Filter blockage after starting can be prevented.

In the embodiment described above, three solenoid valves are used, and the three solenoid valves are used during engine startup, after engine startup and after engine startup.
Although the fuel supply system is changed as described, the fuel supply system can be further simplified. FIG. 2 shows a fuel supply system according to an embodiment when the fuel supply system is simplified. In this embodiment, surplus fuel from the fuel injection pump 2 and the nozzle 4 is directly returned to the fuel tank 1 through the fuel return passage 22. A normal fuel passage 25 for supplying fuel from the fuel tank 1 to the fuel injection pump 2 through the fuel filter 3 is provided.
In addition, a bypass passage 23 that connects the fuel tank 1 and the fuel injection pump 2 via an electromagnetic valve 28 is provided.

In this embodiment, the ECU 5 opens the solenoid valve 28 at the start of the engine and for a predetermined time after the start of the engine. When the solenoid valve 28 opens, the fuel is supplied to the injection pump 2 through the bypass passage 23 without passing through the filter 3 having a large resistance, so that the flow resistance of the fuel is reduced and the engine startability is improved. When a predetermined time elapses after the start of the engine, the solenoid valve 28 is closed, and fuel is supplied from the tank 1 to the fuel injection pump 2 through the filter 3.

In this embodiment, the surplus fuel from the fuel pump and the like is directly returned to the fuel tank. After the engine is started, the high-temperature surplus fuel and the low-temperature fuel in the fuel tank are mixed in the fuel tank, and the entire fuel in the tank is mixed. The temperature is maintained above the wax formation temperature. In this embodiment, compared to the embodiment of FIG.
While substantially simplifying the configuration of the fuel supply system, the same engine startability as that of the embodiment of FIG. 1 can be secured.

[0020]

According to the present invention, fuel is supplied to the fuel injection pump by bypassing the fuel filter at the time of low temperature start,
After starting, the excess fuel from the fuel injection pump and the injection nozzle and the fuel in the fuel tank are mixed and supplied to the fuel injection pump through the fuel filter to prevent poor fuel supply during cold start of the engine. The cold startability of the engine can be improved, and the clogging of the fuel filter due to the generation of wax can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a first embodiment of a fuel supply device for a diesel engine according to the present invention.

FIG. 2 is a schematic view showing a second embodiment of a fuel supply device for a diesel engine according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Fuel tank 2 ... Fuel injection pump 3 ... Fuel filter 3a ... Bypass passage 4 ... Fuel injection nozzle 5 ... Electronic control unit 6 ... Temperature sensor 7, 8, 9 ... Solenoid valve

Claims (1)

(57) [Claims] A cold start detecting means for detecting a cold start of the engine; a cold start fuel passage for supplying fuel to the fuel injection pump without passing through a fuel filter; a fuel injection pump and a fuel injection nozzle; The fuel passage after starting, the fuel passage during cold start, and the fuel passage after starting are selectively supplied to the fuel injection pump through the fuel filter with a mixture of surplus fuel refluxed from the fuel tank and fuel from the fuel tank. Fuel passage switching means connected to the injection pump, wherein the fuel passage switching means connects the cold start fuel passage to the fuel injection pump when the cold start detection means detects a cold start of the engine. A fuel supply device for a diesel engine, characterized in that: