JP2010196471A - Fuel supply system, diesel engine, and method for controlling engine start - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve startability of a diesel engine using dimethyl ether as fuel. <P>SOLUTION: In this fuel supply system, fuel composed of dimethyl ether in a fuel tank 1 is supplied to a fuel pressurization pump P2 by a fuel forcibly feeding pump P1 and further supplied from the fuel pressurization pump P2 to the diesel engine through a common rail CR. Cranking time by the operation of the starter motor of the diesel engine E is measured. When the diesel engine E is not started within a predetermined time, the starter motor is stopped. After fuel is circulated between the fuel tank 1 and the fuel pressurization pump P2 until the predetermined time or a predetermined fuel pressure is reached, the starter motor is operated again to start the cranking. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel supply device, a diesel engine, and an engine start control method, and more particularly, to improve startability of a diesel engine (hereinafter also referred to as an engine) using dimethyl ether (hereinafter abbreviated as DME) as fuel. The present invention relates to a possible fuel supply device, a diesel engine, and an engine start control method.

  Diesel engines using DME are attracting attention as clean engines because they do not emit soot. When DME is applied to a diesel engine, it is desirable from the viewpoint of thermal efficiency that DME is directly injected into the combustion chamber of the engine and compression ignition is performed. As a method for supplying DME, a common rail type is used as a fuel injection device in the same manner as a diesel engine using light oil as a fuel. This method is a method in which fuel is pressurized by a fuel pressurization pump (hereinafter referred to as a supply pump) attached to the engine, the pressurized fuel is held in a common rail, and the fuel is injected into the engine combustion chamber by an injector. .

  In this method, there is no need to pressurize between the fuel tank and the supply pump in the case of light oil because it is liquid at room temperature, but in the case of DME, it is a gas at room temperature, so it is in a liquid state. Must be sent to supply pump. Therefore, it is necessary to provide a pressure pump on the fuel tank side and pressurize to a pressure slightly higher than the vapor pressure due to the fuel temperature at that time. At this time, since the fuel in the fuel tank is pressurized to about 5 atm, it is filled in a liquid state. During the operation of the engine, the required fuel flow rate, fuel temperature, etc. may be monitored and controlled to an appropriate supply pressure that does not vaporize the DME, depending on the operating conditions.

  However, when the engine is stopped for a long time, when the pressure of the fuel in the fuel pipe drops and the DME is in a gaseous state, the DME around the supply pump on the engine side is liquefied. There may be no state. In this state, since DME is not pumped to the common rail, it is not injected from the injector, and even if an attempt is made to start the engine with a starter, there is a problem that the engine does not start.

  In view of this, a method has been proposed in which pressure is applied to fuel in a supply pump in the front stage of the engine prior to starting the engine, and the starter is driven when the fuel pressure is detected to be a target pressure value (for example, Patent Document 1). reference).

  In addition, a method may be considered in which the fuel pump on the fuel tank side is operated before the starter motor rotates, the fuel is circulated to some extent, the fuel in the piping is made into a liquid state, and then the starter motor is rotated to start the engine. It is done.

  However, in either method, the supply pump may not completely replace the DME in the liquid state. As a result, the time required for cranking with the starter motor becomes longer, resulting in battery consumption or starter motor failure. Inconvenience, and the engine start operation becomes complicated.

JP 2005-98260 A

  An object of the present invention is to provide a fuel supply device, a diesel engine, and an engine start control method capable of improving startability of a diesel engine using DME as a fuel.

  In order to achieve the above object, a fuel supply device of the present invention supplies a fuel made of dimethyl ether stored in a fuel tank to a second pump by a first pump, and further from the second pump to a diesel engine via a common rail. In the fuel supply device to be supplied, a first opening / closing means provided in a supply pipe connecting the first pump and the second pump, and a first detection means for detecting the pressure and temperature at the inlet of the second pump; , A second opening / closing means provided in a return pipe connecting the second pump and the common rail and the fuel tank, a second detection means for detecting a pressure inside the return pipe, and the first and second And a control means for controlling the first and second opening / closing means. The control means is based on an operation of a starter motor for starting the diesel engine. When the cranking time is measured and the diesel engine does not start within the preset first time, the starter motor is stopped and the preset fuel pressure is reached until the preset second time or the preset fuel pressure. After the fuel is circulated between the fuel tank and the second pump, the starter motor is operated again to start cranking.

  The engine start control method of the present invention is an engine start control method for supplying a fuel made of dimethyl ether to a diesel engine. The engine start control method has a start mode and a subsequent normal operation mode. The start mode includes the diesel engine. A fuel pressurizing step for pressurizing the fuel to promote liquefaction of the fuel supplied to the engine; and when the detected pressure of the fuel at the fuel pressurizing step reaches a preset first fuel pressure, the diesel A starter process for starting cranking by the operation of an engine starter motor and measuring the cranking time. If the diesel engine does not start within a preset first time, stop the starter motor operation. And the fuel until the preset second time or preset second fuel pressure is reached. A fuel circulating step circulating the, after the fuel circulating process, in which once again has a starter re-activation step of starting the cranking by operating the starter motor.

  Further, in the engine start control method of the present invention, the first fuel pressure and the second fuel pressure in the fuel pressurizing step are the fuel temperature detected by the first detecting means and the vapor pressure diagram of the dimethyl ether. And a pressure at which the dimethyl ether is not vaporized.

  In the engine start control method of the present invention, the fuel supply pressure to the diesel engine in the normal operation mode is lower than the fuel supply pressure to the diesel engine in the start mode.

  According to the present invention, the cranking time of a diesel engine using DME as fuel is measured, and if the diesel engine does not start within a preset time, the starter motor is stopped and the preset time or Since the fuel is circulated between the fuel tank and the second pump until the set fuel pressure is reached, the starter motor is operated again to start cranking. Therefore, the startability of the diesel engine using DME as fuel is started. Can be improved.

It is the figure which showed the structure of the fuel supply apparatus of embodiment of this invention. It is the figure which showed the flow of the engine starting control method using the fuel supply apparatus of FIG. It is the figure which showed the state of the fuel supply apparatus at the time of a fuel pressurization process. It is the figure which showed the state of the fuel supply apparatus at the time of a fuel circulation process. It is the graph which showed together the vapor pressure line of DME, and the target fuel pressure line.

  Hereinafter, a fuel supply device, a diesel engine, and an engine start control method according to embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  The fuel supply apparatus according to the present embodiment illustrated in FIG. 1 is configured such that fuel in a fuel tank 1 is supplied to a fuel pressurizing pump (first pump: hereinafter simply referred to as a pressure pump) P1 by a fuel pressurizing pump ( Second rail: hereinafter referred to as supply pump) P2 and further supplied to the combustion chamber of each cylinder of a diesel engine (hereinafter simply referred to as engine) E from the supply pump P2 via a common rail CR. It is. The fuel supply device and the engine E are illustrated as being mounted on a vehicle such as a truck, but are not limited thereto, and may be mounted on a ship, for example.

The fuel tank 1 stores a fuel made of dimethyl ether (DME: C ₂ H ₆ O). 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 easily decomposed in air. is doing. The DME in the fuel tank 1 is in a liquid state when the inside of the fuel tank 1 is maintained in a high pressure state (pressurized at about 5 atm). Although FIG. 1 illustrates the case where there is one fuel tank 1, the present invention is not limited to this, and a plurality of fuel tanks 1 may be provided.

  The pressure pump P1 in the fuel tank 1 is connected to the supply pipe 2a through the outlet valve V1 and the first electromagnetic valve (first opening / closing means) MV1 in order, and further connected to the supply pump P2 through the supply pipe 2a. Yes. The pressure feed pump P1 is provided with a pressure adjusting device that adjusts the fuel supply pressure (feed pressure), and the fuel in the fuel tank 1 is supplied in a state where the fuel supply pressure is adjusted by the adjustment device of the pressure feed pump P1. Pumped to pump P2.

  The pressure pump P1 is electrically connected to a control device (control means) C, and the operation of the pressure pump P1 is controlled by the control device C. That is, the control device C controls the supply of fuel from the fuel tank 1 to the supply pump P2, the fuel supply pressure, the fuel supply amount per unit time, the supply stop, and the like by controlling the operation of the pressure pump P1.

  The first electromagnetic valve MV1 is provided immediately after the outlet valve V1 of the pressure pump P1. The first electromagnetic valve MV1 is electrically connected to the control device C, and the opening / closing operation of the electromagnetic valve is controlled by the control device C. That is, the control device C controls the supply and shutoff of fuel from the fuel tank 1 to the supply pump P2 by controlling the opening / closing operation of the first electromagnetic valve MV1.

  In addition, a sensor (first detection means) S1 is provided at the inlet of the supply pump P2 in the supply pipe 2a. This sensor S1 is a sensor for detecting the fuel pressure and the fuel temperature at the inlet of the supply pump P2. The sensor S1 is electrically connected to the control device C, and a signal detected by the sensor S1 is transmitted to the control device C.

  The supply pump P2 is a pressure regulating pump that raises the pressure up to a pressure (several tens to several hundreds of MPa) suitable for injecting fuel into the combustion chamber of each cylinder of the engine E, and sends the fuel to the common rail CR. And a pressure adjusting valve capable of adjusting the discharge pressure.

  The supply pump P2 is connected to the common rail CR through a plurality of pipes 2b. A plurality of injectors (fuel injection valves) J are connected to the common rail CR through a plurality of pipes 2c. The common rail CR is a component for stocking the fuel to be supplied to the injector J.

  The injector J is a component for injecting fuel into the fuel chamber of each cylinder of the engine E, and has an injection nozzle and an electromagnetic valve. The injection nozzle of the injector J is a component that injects and supplies high-pressure fuel into the combustion chamber. The electromagnetic valve of the injector J is a component that performs lift control of the needle in the injection nozzle, and is electrically connected to the control device C to control its operation.

  The engine E is a power source when the vehicle travels, and includes a starter motor for forcibly rotating the crankshaft when the engine is started. This starter motor is electrically connected to the control device C, and its operation is controlled. The engine E is provided with a rotation sensor (not shown) that detects the rotation of the engine E. The rotation sensor is electrically connected to the control device C, and the rotation detection signal detected by the rotation sensor is transmitted to the control signal C. The control device C detects the start of the engine E based on the rotation detection signal from the rotation sensor.

  A main return pipe 2e to the fuel tank 1 is connected to the supply pump P2 through a return pipe 2d connected to the fuel inlet. A check valve 3a is interposed in the middle of the return pipe 2d so that the fuel flowing from the supply pump P2 to the main return pipe 2e does not flow back to the supply pump P2.

  A return pipe 2f is connected to the common rail CR via a pressure control valve 3b and a solenoid valve V2. The return pipe 2f is connected to the return pipe 2d and the main return pipe 2e. The pressure control valve 3b is a pressure safety valve that opens when the fuel pressure in the common rail CR exceeds the limit set pressure, and suppresses the pressure in the common rail CR to a limit set pressure or less. The electromagnetic valve V2 is installed so that it can be opened when the fuel pressure in the common rail CR is lowered depending on the operating state of the engine E.

  In the main return pipe 2e to the fuel tank 1, a second electromagnetic valve (second opening / closing means) MV2 is provided immediately before the return valve V3 of the fuel tank 1. The second electromagnetic valve MV2 is electrically connected to the control device C, and the opening / closing operation of the electromagnetic valve is controlled by the control device C. That is, the control device C controls the return and shutoff of the fuel from the engine E side to the fuel tank 1 by controlling the opening / closing operation of the second electromagnetic valve MV2.

  The main return pipe 2e is provided with a pressure sensor (second detection means) S2. The pressure sensor S2 is a sensor that detects the fuel pressure in the return pipe 2e. The pressure sensor S2 is electrically connected to the control device C, and a signal detected by the pressure sensor S2 is transmitted to the control device C. Note that F denotes a filter.

  The control device C is an electronic control unit such as an ECU (Engine Control Unit). The control device C includes a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a timer, and the like, and a program recorded in the ROM and DME vapor pressure diagram information described later. Various arithmetic processes are performed based on various sensor (detection) information read into the RAM, and the operation of the fuel supply device, the engine E, and the like can be controlled.

  Moreover, the said control apparatus C measures the operating time (namely, cranking time) of the said starter motor with the said timer. Further, the control device C determines that the engine E does not start within a preset time (for example, about 5 seconds) (that is, even if the time measured by the timer exceeds the preset time). In the case of not starting, the starter motor is instructed to stop, and the fuel pressure at the inlet of the supply pump P2 detected by the sensor S1 for a preset time (eg, about 5 seconds) or the preset fuel pressure (eg, 3 MPa) In order to circulate the fuel between the fuel tank 1 and the supply pump P2 by controlling the pressure feed pump P1, the supply pump P2, the first electromagnetic valve MV1, and the second electromagnetic valve MV2. Further, after the fuel circulation step, the control device C instructs to start the cranking again by operating the starter motor.

  Next, the engine start control method according to the present embodiment will be described with reference to FIGS. 3 and 4 along the flow of FIG. 3 and 4 show the states during the fuel pressurization process and the fuel circulation process, respectively, and the arrow A indicates the flow of fuel.

  First, when the driver turns on the engine key, the pressure pump P1 of the fuel tank 1 is activated (step 101 in FIG. 2). Subsequently, as shown in FIG. 3, the first electromagnetic valve MV1 is opened with the second electromagnetic valve MV2 closed. At this time, the rotational speed of the pressure pump P1 is set higher than the rotational speed of the pressure pump P1 in the normal operation mode. As a result, the fuel pressure in the supply pipe 2a can be quickly increased, so that the DME in the supply pipe 2a can be liquefied in a short time and the startability of the engine E can be improved (see FIG. Step 102 of 2). Subsequently, it is determined whether or not the fuel pressure at the inlet of the supply pump P2 (that is, the fuel pressure detected by the sensor S1) becomes a preset first fuel pressure (step 103 in FIG. 2). When the fuel pressure detected by the sensor S1 does not become the first fuel pressure, the process returns to step 102.

  On the other hand, when the fuel pressure detected by the sensor S1 becomes the first fuel pressure or higher, as shown in FIG. 4, the first and second electromagnetic valves MV1 and MV2 are opened and the starter motor is allowed to rotate. (Step 104 in FIG. 2). In this state, the starter motor will not operate even if the engine key is set to the starter position. The first fuel pressure is determined by the control device C based on the vapor pressure diagram of the DME so that the DME does not vaporize at the fuel temperature at the inlet of the supply pump P2 detected by the sensor S1. The first fuel pressure in the start mode is higher than that in the normal operation mode. Thereby, since liquefaction of DME can be promoted, startability of the engine E can be improved.

  After such a fuel pressurizing step, when the start switch is turned on (the engine key may be used instead of the starter position), the starter motor rotates to start cranking. The fuel injection device for the engine E is controlled by the control device C, and normal engine start is started (starter step, step 105 in FIG. 2). In this state, it waits for the engine E to start. At this time, the control device C measures the cranking time (starter motor operating time) due to the operation of the starter motor, and determines whether or not the engine E starts within a preset time (for example, about 5 seconds). judge. The start of the engine E is determined by the rotation detection signal of the rotation sensor (step 106 in FIG. 2).

  In step 106, if the engine E starts within a preset time, the fuel system start mode is canceled and the process returns. After returning, the mode is changed to the normal operation mode. The fuel pressure at the inlet of the supply pump P2 in the normal operation mode (that is, the fuel supply pressure to the engine E) is the fuel pressure at the inlet of the supply pump P2 in the start mode (that is, the fuel supply pressure to the engine E). ) (However, DME is not vaporized). Thereby, the power consumption in the normal operation mode can be reduced. For this reason, since the load of the engine E can be reduced, fuel consumption performance can be improved. In addition, battery consumption can be reduced.

  On the other hand, when the engine E does not start within the preset time in step 106, the process proceeds to step 107 and the following fuel circulation control is performed. First, the operation of the starter motor is stopped. Thereby, since useless rotation operation of the starter motor can be reduced, failure of the starter motor can be reduced or prevented. Secondly, after the starter motor is stopped, until a preset time (for example, about 5 seconds) or the fuel pressure detected by the sensor S1 reaches a preset second fuel pressure (for example, 3 MPa), The fuel is circulated between the fuel tank 1 and the supply pump P2 (fuel circulation process). That is, as shown in FIG. 4, by operating the pressure pump P1 with both the first and second electromagnetic valves MV1 and MV2 open, fuel is supplied from the fuel tank 1 to the supply pipe 2a and the supply pump P2. Then, it is circulated to return to the fuel tank 1 through the return pipe 2d and the main return pipe 2e. The second fuel pressure is the same as the first fuel pressure (step 107 in FIG. 2). After such a fuel circulation step, the same pressure determination as described above is made in step 103, and then, through step 104, the starter motor is rotated again to start cranking (starter restarting step, step 105 in FIG. 2). . This is automatically repeated until the engine starts.

  Next, FIG. 5 is an example of a graph showing the DME vapor pressure diagram information and the target fuel pressure map together. In the vapor pressure diagram, the horizontal axis indicates the fuel temperature (° C.), and the vertical axis indicates the DME vapor pressure (atm). Further, in the target fuel pressure map, the horizontal axis indicates the fuel temperature (° C.), and the vertical axis indicates the DME target fuel pressure (atm).

  VP0 (solid line) indicates the DME vapor pressure line, VP1 (solid line) indicates the target fuel pressure line in the start mode, and VP2 (broken line) indicates the target fuel pressure line in the normal operation mode. This target fuel pressure is a target value of the fuel pressure detected by the sensor S1 at the inlet of the supply pump P2. The pressure value of the target fuel pressure line VP1 corresponds to the first and second fuel pressures set in advance.

  In the present embodiment, the fuel pressure (target fuel pressure line VP1, VP2) at the inlet of the supply pump P2 in the start mode and the normal operation mode is lower than the vapor pressure (vapor pressure line VP0) so that DME does not vaporize. It is set to be higher. However, as described above, the fuel pressure (target fuel pressure line VP2) at the inlet of the supply pump P2 in the normal operation mode is lower than the fuel pressure (target fuel pressure line VP1) at the inlet of the supply pump P2 in the start mode. It is trying to become. As a result, the power consumption during the normal operation mode can be reduced and the load on the engine E can be reduced, so that the fuel consumption performance can be improved. In addition, battery consumption can be reduced. Note that the difference between the fuel pressure in the start mode and the fuel pressure in the normal operation mode is, for example, about 0.5 MPa. In addition, information as illustrated in FIG. 5 is recorded in advance in the ROM of the control device C, and the control device C performs the control operation based on this information.

  According to the present embodiment, since the starter motor can be operated and cranking can be started after the DME is completely replaced with the liquid state on the supply pump P2, smooth operation can be performed without performing complicated operations. The engine E can be started.

  Further, since the starter motor is operated and cranking is started after the DME is completely replaced with the liquid state on the supply pump P2, the cranking time can be shortened. For this reason, failure of the starter motor and battery consumption at the time of engine start can be reduced or prevented. Therefore, the startability of the engine E using DME as fuel can be improved.

1 Fuel tank 2a Supply pipe 2b, 2c Pipe 2d Return pipe 2e Main return pipe 2f Return pipe 3a Check valve 3b Pressure control valve 4 Fuel cooler P1 Fuel pump (first pump)
P2 Fuel pressurizing pump (second pump)
CR Common rail E Diesel engine V1 Outlet valve V2 Solenoid valve V3 Return valve MV1 First solenoid valve (first opening / closing means)
MV2 second solenoid valve (second opening / closing means)
C Control device (control means)
S1 sensor (first detection means)
S2 Pressure sensor (second detection means)
J Injector F Filter

Claims (5)

In a fuel supply device that supplies fuel composed of dimethyl ether stored in a fuel tank to a second pump by a first pump, and further supplies the diesel engine from a second pump via a common rail.
First opening / closing means provided in a supply pipe connecting the first pump and the second pump;
First detection means for detecting pressure and temperature at the inlet of the second pump;
A second opening / closing means provided in a return pipe connecting the second pump and the common rail to the fuel tank;
Second detection means for detecting the pressure inside the return pipe;
Control means for controlling the first and second pumps and the first and second opening / closing means,
The control means measures a cranking time due to an operation of a starter motor that starts the diesel engine, and stops the starter motor if the diesel engine does not start within a preset first time, The fuel is circulated between the fuel tank and the second pump until the fuel pressure reaches a predetermined second time or a preset fuel pressure, and then the starter motor is operated again to start cranking. A fuel supply device.   A diesel engine using the fuel supply device according to claim 1. In an engine start control method for supplying a fuel made of dimethyl ether to a diesel engine,
It has a start mode and a normal operation mode after that,
The starting mode is:
A fuel pressurizing step of pressurizing the fuel to promote liquefaction of the fuel supplied to the diesel engine;
A starter step of starting cranking by an operation of a starter motor of the diesel engine when the detected pressure of the fuel becomes a first fuel pressure set in advance by the fuel pressurization step;
When the cranking time is measured and the diesel engine does not start within the preset first time, the starter motor is stopped and the preset second time or the preset first time A fuel circulation step for circulating the fuel until the fuel pressure reaches 2;
An engine start control method comprising: a starter restarting step of starting cranking again by operating the starter motor after the fuel circulation step.   The first fuel pressure and the second fuel pressure in the fuel pressurizing step are obtained based on the fuel temperature detected by the first detection means and the vapor pressure diagram of the dimethyl ether, and the dimethyl ether is vaporized. The engine start control method according to claim 3, wherein the pressure is not applied.   The engine start control method according to claim 3 or 4, wherein a fuel supply pressure to the diesel engine in the normal operation mode is lower than a fuel supply pressure to the diesel engine in the start mode.

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