JP4168893B2 - Fuel supply device - Google Patents

Description

  The present invention relates to a fuel supply device for supplying a fuel that becomes a gas under normal temperature and normal pressure as a liquid to an engine.

  In recent years, DME engines that use dimethyl ether (hereinafter referred to as DME) as a fuel instead of gasoline or light oil are attracting attention. DME has a melting point of 138.5 ° C., a boiling point of −23.7 ° C. (1 atm), a cetane number comparable to that of light oil, a specific gravity greater than that of air, and is generally said to be harmless easily in air. .

  Such DME becomes a gas at normal temperature and pressure. Therefore, when DME is used as a fuel, the fuel (DME) must be pressurized and supplied to the engine as a liquid. If this is not done, bubbles are mixed into the fuel due to the vaporization of the fuel, the engine rotation becomes unstable, and cavitation occurs in the fuel passage and the fuel supply pump.

  On the other hand, when an excessively high pressure is applied to the DME, the viscosity of the DME is low, so that the DME leaks at each sliding portion, and a large recovery system is required. In addition, the horsepower consumed by the fuel supply pump itself increases, resulting in a deterioration in fuel consumption. Therefore, it is preferable to pressurize DME appropriately.

  Therefore, a device that detects the DME temperature in the fuel passage, determines a target value of the feed pressure of the supply pump based on the detected DME temperature and the vapor pressure diagram of the DME, and controls the supply pump according to the target value Has been proposed (see, for example, Patent Document 1). According to this device, DME can be appropriately pressurized and supplied to the engine.

JP 2001-115916 A

  However, as described above, since DME becomes a gas at normal temperature and normal pressure, DME in the fuel passage may be vaporized when the engine is started. In this case, accurate temperature measurement of DME becomes difficult, and the target value of the feed pressure of the supply pump cannot be set appropriately. As a result, there is a risk of causing prolonged engine start, an increase in drive power of the supply pump, damage to the supply pump due to poor sliding, and the like.

  Accordingly, an object of the present invention is to provide a fuel supply apparatus that can solve the above-described problems and can start the engine satisfactorily.

In order to achieve the above object, the present invention supplies fuel that is stored in a fuel tank and becomes a gas under normal temperature and normal pressure to a high-pressure pump as a liquid by one or a plurality of supply pumps , and rotates the crankshaft of the engine. A fuel supply device configured to supply the fuel to the engine by the high-pressure pump driven by
Engine room temperature detecting means for detecting the temperature of the engine room;
Pressure detecting means for detecting the inlet side pressure of the high-pressure pump;
A control device for controlling the supply pump and the starter motor of the engine ,
When the engine is started, the control device sets a target pressure on the inlet side of the high-pressure pump that is equal to or higher than the saturated vapor pressure of the fuel based on the engine room temperature detected by the engine room temperature detecting means and the vapor pressure diagram of the fuel. determined, while the detected pressure by the pressure detecting means is lower than the target pressure by driving only the feed pump, Do detected pressure by said pressure detecting means is equal to or higher than the target pressure mules, The supply pump and the starter motor are driven.

  In addition, fuel temperature detecting means for detecting the temperature of the fuel in the fuel passage is further provided, and the control device displays the fuel temperature detected by the fuel temperature detecting means and the fuel vapor pressure diagram during operation of the engine. Based on this, a target pressure on the inlet side of the high-pressure pump that is equal to or higher than the saturated vapor pressure of the fuel may be determined, and the supply pump may be controlled so that the pressure detected by the pressure detection means becomes the target pressure.

  According to the present invention, an excellent effect that the engine can be started satisfactorily is exhibited.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  The present embodiment is applied to a fuel supply device for a DME engine using dimethyl ether (hereinafter referred to as DME) as a fuel.

  As shown in FIG. 1, the fuel supply apparatus according to the present embodiment includes two fuel tanks 1a and 1b attached to the chassis (not shown) side of the vehicle. In the fuel tanks 1a and 1b, DME as fuel is stored in a liquid state. In each of the fuel tanks 1a and 1b, pumps 2a and 2b (primary supply pumps) for pumping DME are provided. The pressure pumps 2a and 2b are equipped with a pressure adjusting device (not shown) for adjusting the feed pressure.

The fuel in the fuel tanks 1 a and 1 b is sent into the fuel pipe 3 by the pressure feed pumps 2 a and 2 b and is boosted by the secondary supply pump 4. Thereafter, the fuel is supplied to the high-pressure pump 5 provided on the engine E side and driven by the rotation of the crankshaft of the engine . A common rail 7 for accumulating fuel is connected to the high-pressure pump 5, and a plurality of fuel injection valves (injectors) 6 for injecting fuel into the combustion chamber of each cylinder of the engine E are connected to the common rail 7. The high-pressure pump 5 raises the fuel to a pressure suitable for injecting the fuel into the combustion chamber and sends the fuel to the common rail 7.

  The secondary supply pump 4 and the high-pressure pump 5 are provided with a pressure adjusting valve so that the feed pressure can be adjusted. These pumps 4 and 5 are connected to fuel recovery pipes 8a and 8b for returning surplus fuel discharged from the pressure regulating valve to the fuel tanks 1a and 1b. A fuel recovery pipe 8c for returning surplus fuel discharged from the common rail 7 to the fuel tanks 1a and 1b is connected in the middle of the fuel recovery pipe 8b. A pressure adjustment valve (PCV) 10 is interposed in the fuel recovery pipe 8c, and the fuel in the common rail 7 is adjusted to an optimum pressure by the pressure adjustment valve 10. As the pressure regulating valve 10, a mechanical type, an electric type, or a combination type of a mechanical type and an electric type can be used.

  The fuel recovery pipes 8 a and 8 b are joined and connected to one main fuel return pipe 9. Excess fuel from the secondary supply pump 4, the high-pressure pump 5 and the common rail 7 is all recovered in the main fuel return pipe 9. Two auxiliary fuel return pipes 14a and 14b are connected to the downstream end of the main fuel return pipe 9, and these auxiliary fuel return pipes 14a and 14b are connected to the fuel tanks 1a and 1b, respectively. The surplus fuel collected in the main fuel return pipe 9 is distributed to the fuel tanks 1a and 1b through the sub fuel return pipes 14a and 14b. In the figure, 13 indicates a fuel cooler, and 15 indicates a fuel cutoff valve.

  The fuel supply apparatus includes a plurality of detection means, and the detection values of the detection means are transmitted to a control device (ECU) 12. As detection means, a secondary supply pump inlet pressure sensor 20 for detecting the inlet side pressure of the secondary supply pump 4 and a high pressure pump inlet pressure for detecting the fuel pressure on the inlet side of the high pressure pump 5 (hereinafter simply referred to as inlet side pressure). Sensor 19 (pressure detection means), engine room temperature sensor 16 (engine room temperature detection means) for detecting the temperature of the engine room, fuel temperature sensor 21 (fuel) for detecting the fuel temperature in the fuel passage on the inlet side of the high-pressure pump 5 Temperature detecting means).

  The ECU 12 controls switching of driving / non-driving of the pumps 2a and 2b, the secondary supply pump 4 and the high-pressure pump 5, feed pressure, and the like according to the detection values of the detection means. The ECU 12 also controls the pressure adjustment valve 10.

  Further, the engine E includes a starter motor (not shown) for forcibly rotating the crankshaft when the engine is started, and the ECU 12 also drives and controls the starter motor.

  Now, fuel supply control at the time of engine start and engine operation by this fuel supply device will be described.

  First, the control at the time of engine start will be described using the flowchart of FIG. This flowchart is executed by the ECU 12.

  First, when the engine start mode is started by, for example, the driver turning the ignition key, the ECU 12 proceeds to step S1, and the ECU 12 drives the pressure pumps 2a and 2b in the fuel tanks 1a and 1b. Thereby, the fuel in the fuel tanks 1 a and 1 b is supplied to the inlet side of the secondary supply pump 4.

  Next, in step S2, the ECU 12 determines whether or not the pressure detected by the secondary supply pump inlet pressure sensor 20 is equal to or higher than the target value M1 input to the ECU 12 in advance. This target value M1 is set to an appropriate value that ensures that the fuel (DME) is liquid and that it is not excessively high pressure. The determination in step S2 is repeated until the inlet side pressure of the secondary supply pump 4 detected by the secondary supply pump inlet pressure sensor 20 reaches the target value M1. Meanwhile, the secondary supply pump 4 is not driven, and only the pressure pumps 2a and 2b are driven. Accordingly, the inlet side pressure of the secondary supply pump 4 increases.

  If the inlet side pressure of the secondary supply pump 4 becomes equal to or higher than the target value M1, the process proceeds to step S3, and the ECU 12 drives the secondary supply pump 4. Thereby, the fuel is supplied to the inlet side of the high-pressure pump 5. At this time, since the fuel supplied to the secondary supply pump 4 is pressurized to the target value M1 or more, bubbles are not mixed into the supplied fuel.

  On the other hand, the ECU 12 determines the inlet side target pressure M2 of the high-pressure pump 5 based on the engine room temperature detected by the engine room temperature sensor 16 in steps S4 and S5. The target pressure M2 is a value that changes according to the engine room temperature, and is input to the ECU 12 as a map in advance.

  The inlet side target pressure M2 of the high pressure pump 5 will be described with reference to FIG.

  FIG. 3 shows a vapor pressure diagram of the fuel (DME) and a map of the target pressure M2. In the figure, a line indicated by a solid line A is a vapor pressure diagram of DME, and a line indicated by a dotted line B is an inlet-side target pressure M2 of the high-pressure pump 5. That is, when FIG. 3 is viewed as a vapor pressure diagram, the horizontal axis is the fuel temperature T (° C.), the vertical axis is the fuel pressure P (atm), and when viewed as a map of the target pressure M2, the horizontal axis is the fuel temperature. As an alternative, the engine room temperature Te (° C.) and the vertical axis represent the target pressure M2 (atm).

  As is apparent from the figure, the inlet-side target pressure M2 of the high-pressure pump 5 is set to a value equal to or higher than the saturated vapor pressure of DME. That is, the value is set such that DME becomes liquid. This is to prevent air bubbles from being mixed into the supplied fuel. Therefore, the target pressure M2 needs to be set to the saturated vapor pressure of DME at the minimum.

  In the present embodiment, the inlet side target pressure M2 of the high pressure pump 5 is set to a value higher by ΔP than the saturated vapor pressure of DME. The value of ΔP is set to an appropriate value so that DME leakage does not occur in each sliding part of the engine and the power consumption of the pumps 2a and 2b and the secondary supply pump 4 is not excessively increased. Note that the value of ΔP may be constant regardless of the fuel temperature (engine room temperature) or may be different. Thus, the target pressure M2 of the high-pressure pump 5 is set to an optimum value for each fuel temperature (engine room temperature).

  Returning to FIG. 2, in step S5, the ECU 12 determines the target pressure M2 from the map based on the detection value of the engine room temperature sensor 16. Accordingly, it can be said that the target pressure M2 is determined based on the engine room temperature and the DME vapor pressure diagram.

  If the inlet-side target pressure M2 of the high-pressure pump 5 is determined, the process proceeds to step S6, and whether the actual inlet-side pressure of the high-pressure pump 5 detected by the high-pressure pump inlet pressure sensor 19 is equal to or higher than the target pressure M2. Determine whether. This determination is repeated until the pressure on the inlet side of the high-pressure pump 5 reaches the target pressure M2. Meanwhile, the high-pressure pump 5 is not driven, and only the pressure-feed pumps 2a and 2b and the secondary supply pump 4 are driven. Therefore, the inlet side pressure of the high-pressure pump 5 increases.

  When the inlet side pressure of the high pressure pump 5 reaches the target pressure M2, the process proceeds to step S7, and the ECU 12 drives the starter motor of the engine. As a result, the crankshaft of the engine rotates to start driving the high-pressure pump 5, and fuel is injected into the combustion chamber of each cylinder to start the engine. At this time, since the fuel supplied to the high pressure pump 5 is pressurized to the target pressure M2 or higher, bubbles are not mixed into the supplied fuel. Therefore, no sliding failure occurs in the high-pressure pump 5 and engine rotation does not become unstable.

  As described above, the fuel supply device of the present embodiment detects the engine room temperature when starting the engine, and determines the inlet-side target pressure M2 of the high-pressure pump 5 based on the engine room temperature. In other words, since the fuel in the fuel passage may be vaporized when the engine is started, the engine room temperature is measured instead of the fuel temperature. Since the engine room temperature can be regarded as substantially equal to the fuel temperature when the fuel is supplied to the engine E side (the inlet side of the high-pressure pump 5), the inlet-side target pressure M2 of the high-pressure pump 5 is appropriately determined thereby. It becomes possible. Therefore, bubbles are not mixed in the supplied fuel, and the secondary supply pump 4 and the high pressure pump 5 are not damaged due to poor sliding.

  Further, since the starter motor is not driven until the pressure on the inlet side of the high-pressure pump 5 reaches the target pressure M2, unnecessary (meaningless) driving of the starter motor can be prevented, and power consumption can be reduced. .

  Furthermore, since the inlet side target pressure M2 of the high pressure pump 5 is appropriately set according to the engine room temperature (fuel temperature), the fuel is not pressurized more than necessary. Therefore, it is possible to prevent DME leakage due to each sliding portion of the engine. In addition, the power consumption of the pressure pumps 2a and 2b and the secondary supply pump 4 can be reduced, and the engine start period can be shortened. That is, when the target pressure M2 is constant, the target pressure M2 must be set according to the high pressure side, so that the fuel is pressurized more than necessary when the engine room temperature (fuel temperature) is low. . As a result, problems such as an increase in power consumption of the pumps 2a and 2b and the secondary supply pump 4 and a prolonged engine start period occur. Such a problem does not occur in the fuel supply device of the present embodiment.

  Next, control during engine operation by the fuel supply device of this embodiment will be described.

  During engine operation, the ECU 12 determines the inlet-side target pressure of the high-pressure pump 5 based on the fuel temperature detected by the fuel temperature sensor 21 from a map similar to the map indicated by the dotted line B in FIG. Then, the pumps 2a and 2b and / or the secondary supply pump 4 are controlled so that the pressure detected by the high pressure pump inlet pressure sensor 21 becomes the target pressure. Thereby, the inlet side pressure of the high-pressure pump 5 is always controlled to an appropriate value. Thus, during engine operation, the fuel temperature is directly detected, and the inlet side target pressure of the high-pressure pump 5 is determined based on the fuel temperature. This is because the fuel in the fuel passage is liquid during engine operation.

  The present invention is not limited to the above-described embodiment, and various modifications can be considered.

  For example, the target value M1 of the inlet side pressure of the secondary supply pump 4 is also determined as an optimum value for each engine room temperature or fuel temperature and input as a map in the same manner as the high-pressure pump 5. Alternatively, it may be determined from the map based on the engine room temperature or the fuel temperature during engine operation.

  In the above embodiment, the supply pumps that supply the fuel in the fuel tanks 1a and 1b to the high-pressure pump 5 are described as having the tank internal pressure feed pumps 2a and 2b and the secondary supply pump 4. Only one supply pump may be provided, or three or more supply pumps may be provided.

  Also, only one fuel tank or three or more fuel tanks may be provided.

  Furthermore, the present invention is not limited to a DME engine, but can be applied to an engine using another fuel that becomes a gas at normal temperature and pressure.

It is the schematic of the fuel supply apparatus which concerns on one Embodiment of this invention. It is a control flow figure at the time of engine starting by the fuel supply device concerning one embodiment of the present invention. It is a graph which shows the vapor pressure diagram of DME, and the inlet side target pressure of a high pressure pump.

Explanation of symbols

1a, 1b Fuel tank 2a, 2b Pressure feed pump (supply pump)
4 Secondary supply pump 5 High pressure pump 12 ECU (control device)
16 Engine room temperature sensor (Engine room temperature detection means)
19 High pressure pump inlet side sensor (pressure detection means)
21 Fuel temperature sensor (fuel temperature detection means)

Claims (2)

Fuel that is stored in a fuel tank and becomes a gas under normal temperature and normal pressure is supplied to a high-pressure pump as a liquid by one or more supply pumps, and the fuel is supplied by the high-pressure pump that is driven by the rotation of the crankshaft of the engine. A fuel supply device for supplying to an engine,
Engine room temperature detecting means for detecting the temperature of the engine room;
Pressure detecting means for detecting the inlet side pressure of the high-pressure pump;
A control device for controlling the supply pump and the starter motor of the engine ,
When the engine is started, the control device sets a target pressure on the inlet side of the high-pressure pump that is equal to or higher than the saturated vapor pressure of the fuel based on the engine room temperature detected by the engine room temperature detecting means and the vapor pressure diagram of the fuel. determined, while the detected pressure by the pressure detecting means is lower than the target pressure by driving only the feed pump, Do detected pressure by said pressure detecting means is equal to or higher than the target pressure mules, A fuel supply apparatus for driving the supply pump and the starter motor . A fuel temperature detecting means for detecting the temperature of the fuel in the fuel passage;
The control device determines a target pressure on the inlet side of the high-pressure pump that is equal to or higher than the saturated vapor pressure of the fuel based on the fuel temperature detected by the fuel temperature detecting means and the fuel vapor pressure diagram during engine operation. 2. The fuel supply apparatus according to claim 1, wherein the supply pump is controlled so that the pressure detected by the pressure detection means becomes the target pressure .

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