JP2012184747A - Diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a diesel engine that is improved in startability and wherein black smoke and a non-combusted component in exhaust gas in a normal operation are reduced.SOLUTION: The diesel engine 1 includes: an injector 30 injecting fuel into a combustion chamber provided in a cylinder head 20; a preheating means 40 wherein a heat generation part 41 is provided in the cylinder head; a first cavity 130 formed by recessing a crown surface 120 of a piston 100, and formed with a recessed curved surface part reversing at least a part of the fuel injected from the injector and advancing it toward the heat generation part; and a second cavity 140 formed around the first cavity. The injector has a first spout 31b directed to the first cavity and a second spout 31c directed to the second cavity, and includes an injection control means increasing a ratio of an injection amount from the first spout occupying the whole injection amount of the fuel to the normal operation in starting.

Description

  The present invention relates to a direct-injection diesel engine, and particularly relates to an engine that improves startability and reduces black smoke and unburned components in exhaust gas during normal operation.

In recent years diesel engines, for the purpose of improving of the NO _X reduction and net thermal efficiency, the compression ratio can be lower than conventionally been proposed.
However, in a diesel engine, there is a concern that cold startability deteriorates when the compression ratio is lowered.

For example, Patent Document 1 discloses a diesel engine in which a glow plug is surrounded by a cover and a sufficient amount of air-fuel mixture can be stored in the cover.
Further, in Patent Document 2, in order to prevent the fuel injected from the injector from directly hitting the glow plug, the fuel injection range is below the glow plug, and then the fuel is reversed in the reentrant combustion chamber (combustible mixture). Describes a diesel engine that gathers in a glow plug.
On the other hand, as a prior art related to the in-cylinder fuel injection device of a diesel engine, Patent Document 3 provides two types of nozzle holes with different angles in the nozzle, and each nozzle hole is opened and closed by an independent needle valve. Is described.

JP-A-6-221258 JP 2003-254066 A Japanese Utility Model Publication No. 64-4824

However, when the combustion chamber shape or the like is specially designed to collect the combustible air-fuel mixture around the glow plug as in the above-described prior art, a fuel rich region is locally formed during normal operation, and soot Emissions of black smoke composed of particulate matter (PM) and unburned components of the fuel will increase.
In view of the above-described problems, an object of the present invention is to provide a diesel engine that improves startability and reduces black smoke and unburned components in exhaust gas during normal operation.

The present invention solves the above-described problems by the following means.
According to a first aspect of the present invention, there is provided an injector provided in a cylinder head for injecting fuel into a combustion chamber, a preheating means provided in the cylinder head, and a crown surface of a piston being recessed, the injector A first cavity formed with a concave curved surface portion that inverts at least a part of the fuel injected from the head toward the heat generating portion side of the preheating means, and a first cavity formed around the first cavity. A diesel engine having two cavities, the injector having a first fistula directed to the first cavity and a second fistula directed to the second cavity, and starting A dee is provided with injection control means for increasing the ratio of the injection amount from the first fistula that sometimes occupies the total injection amount of fuel with respect to that during normal operation. A Le engine.
According to this, at the time of start-up, fuel can be injected mainly toward the first cavity, and the inverted combustible air-fuel mixture can be collected in the vicinity of the preheating means to improve engine startability.
On the other hand, during normal operation, by injecting fuel toward the first and second cavities, the air-fuel mixture distribution in the cylinder is made closer to uniform, the air utilization rate is increased, and an overconcentrated region is locally formed. Therefore, increase of black smoke and unburned components can be prevented.

The invention according to claim 2 is characterized in that the injection control means injects fuel only from the first hole and stops fuel injection from the second hole during start-up. It is a diesel engine as described in.
According to this, most of the fuel injected at the start can be collected around the preheating means as a combustible mixture.

According to a third aspect of the present invention, the injector is disposed in the vicinity of a cylinder central axis, and the first cavity is a shallow dish type combustion chamber formed by recessing a central portion of a crown surface of the piston, The second cavity is a reentrant combustion chamber disposed on the outer diameter side of the first cavity and at a position where the depth from the crown surface is shallow with respect to the first cavity. The diesel engine according to claim 1 or claim 2.
According to this, the effect mentioned above can be acquired reliably.

According to a fourth aspect of the present invention, the injector has a first valve body and a second valve body that can be driven independently while opening and closing the first nozzle hole and the second nozzle hole, respectively. The diesel engine according to any one of claims 1 to 3, wherein the diesel engine is provided.
According to this, it becomes possible to individually control the fuel injection amounts from the first and second injection holes, and the effects of the above-described inventions can be ensured.

According to a fifth aspect of the present invention, the fuel that is injected into the first cavity from the first injection hole and then reversed and wound up on the cylinder head side is injected into the second injection hole by the injection control means. From the fuel injected from the first nozzle hole to the cylinder head side after being injected into the second cavity, the fuel trajectory injected from the first nozzle hole and the fuel injected from the second nozzle hole 2. The fuel injection timing from the second nozzle hole is delayed with respect to the fuel injection timing from the first nozzle hole so as to pass through a region where the fuel trajectory intersects first. The diesel engine according to any one of claims 1 to 4.
According to this, it is possible to prevent the mixture flow formed by the injection from the first injection hole from interfering with the flow of the mixture formed by the injection from the second injection hole. The combustion state can be improved by optimizing the mixture flow.

  As described above, according to the present invention, it is possible to provide a diesel engine with improved startability and reduced black smoke and unburned components in exhaust gas during normal operation.

FIG. 2 is a schematic cross-sectional view of a combustion chamber portion in an embodiment of a diesel engine to which the present invention is applied, taken along a plane perpendicular to the crankshaft and including the cylinder center axis, and shows a state at the time of starting. FIG. 2 is a schematic cross-sectional view of an injector tip (injection hole) in the diesel engine of FIG. 1. FIG. 2 is a schematic cross-sectional view of a combustion chamber portion of the diesel engine of FIG. 1 and shows a state during normal operation.

  The present invention aims to provide a diesel engine with improved startability and reduced black smoke and unburned components in exhaust gas during normal operation. A second cavity, which is a reentrant combustion chamber disposed around it, is formed, and fuel is injected only into the first cavity during startup, and fuel is injected into both the first and second cavities during normal operation. Solved by.

Embodiments of a diesel engine to which the present invention is applied will be described below.
The diesel engine according to the embodiment is a common rail type direct-injection four-stroke diesel engine mounted as a driving power source in an automobile such as a passenger car.
FIG. 1 is a schematic cross-sectional view of a combustion chamber portion of a diesel engine according to an embodiment taken along a plane orthogonal to a crankshaft and including a cylinder center axis, and shows a state at the time of starting.
The engine 1 includes a cylinder block 10, a cylinder head 20, an injector 30, a glow plug 40, a piston 100, and the like.
The space between the cylinder head 20 and the crown surface of the piston 100 functions as a combustion chamber in which the injected fuel burns as an air-fuel mixture.

The cylinder block 10 includes a cylinder 11 having a cylindrical inner surface into which the piston 100 is inserted.
The cylinder head 20 is provided by closing one end of the cylinder 11.
The cylinder head 20 includes an intake port and an exhaust port (not shown) that suck in fresh air (unburned air and EGR gas) and exhaust burned gas.
The cylinder head 20 includes a valve that opens and closes an intake port and an exhaust port, a valve drive system that drives the valve, and the like.

The injector 30 is pressurized by a high-pressure supply pump (not shown) and atomizes fuel stored in a common rail that is a pressure accumulating chamber and injects the fuel into a cylinder.
The injector 30 is fixed to the cylinder head 20 so as to face the center of the crown surface of the piston 100 in a state where the central axis direction (needle driving direction) is substantially coincident with the central axis of the cylinder 11.

FIG. 2 is a schematic cross-sectional view of the vicinity of the nozzle portion of the injector.
As shown in FIG. 2, the injector 30 includes a nozzle body 31, a first needle 32, a second needle 33, and the like.
The nozzle body 31 is formed in a cylindrical shape, and its end on the combustion chamber side is closed by an end surface portion 31a.
The end surface portion 31a is formed to protrude in a cone shape on the piston 100 side.
The inner surface of the end surface portion 31a is a seal surface portion that is in close contact with the protruding end portions of the first needle 32 and the second needle 33 and seals the fuel.

A first nozzle hole 31b and a second nozzle hole 31c are formed in the end surface portion 31a.
The first injection hole 31 b is a through hole that injects fuel in a direction inclined by a predetermined angle with respect to the central axis of the injector 30.
The second injection hole 31 c is a through hole that injects fuel in a direction inclined by a predetermined angle larger than the first injection hole 31 b with respect to the central axis of the injector 30.
The second injection hole 31c is disposed on the inner diameter side (protrusion end side) of the end surface portion 31a with respect to the first injection hole 31b.
A plurality of the first injection holes 31b and the second injection holes 31c are arranged in the circumferential direction around the central axis of the injector 30.

The first needle 32 is formed in a cylindrical shape concentric with the nozzle body 31 and is inserted on the inner diameter side of the nozzle body 31.
The end surface of the first needle 32 is in close contact with the end surface portion 31a of the nozzle body 31, and the first injection hole 31b can be closed.
The gap between the outer peripheral surface of the first needle 32 and the inner peripheral surface of the nozzle body 31 is filled with high-pressure fuel supplied from the common rail.

The second needle 33 is formed in a cylindrical shape concentric with the nozzle body 31 and the first needle 32, and is inserted on the inner diameter side of the first needle 32.
The end surface of the second needle 33 is in close contact with the end surface portion 31a of the nozzle body 31, and the second injection hole 31c can be closed.

  The first needle 32 and the second needle 33 described above are individually lifted (in FIG. 2) by an actuator such as a solenoid coil (not shown) or a piezoelectric element based on a control signal from an engine control device (injection control means) (not shown). (Upward) can be driven. Accordingly, the engine control device can individually adjust the fuel injection timing and the injection amount from the first injection hole 31b and the second injection hole 31c, and further, by stopping the driving of the second needle 33 It is also possible to inject fuel only from the first injection hole 31b.

A glow plug 40 shown in FIG. 1 and the like is preheating means used when the engine 1 is cold started.
The glow plug 40 is fixed to the cylinder head 20 so that the heat generating portion 41 provided at the tip thereof is exposed adjacent to the injector 30 in the combustion chamber.

The piston 100 is a substantially cylindrical member that is inserted into the cylinder 11 and receives the combustion pressure in the cylinder and transmits it to a crankshaft (not shown) via a connecting rod (not shown).
The piston 100 includes a side surface 110, a crown surface 120, a first cavity 130, a second cavity 140, and the like.

The side surface 110 is a surface portion arranged to face the inner peripheral surface of the cylinder 11, and a first ring groove 111, a second ring groove 112, and a third ring groove 113 are formed in order from the cylinder head 20 side. Yes.
The first ring groove 111, the second ring groove 112, and the third ring groove 113 are, for example, circumferential grooves having a substantially rectangular cross section, and a first compression ring, a second compression ring, and an oil ring (not shown) are provided. This is the part that is inserted.

  The crown surface 120 is an end surface on the side where the piston 100 faces the cylinder head 20 and is formed substantially in a substantially flat shape.

The first cavity 130 is a shallow dish type combustion chamber in which the central portion of the crown surface 110 is recessed toward the crankshaft. As shown in FIG. 1 and the like, the inner surface of the first cavity 130 facing the injector 30 is formed as a concave curved surface having a circular cross section when viewed along the central axis.
The outer peripheral wall 131 of the first cavity 130 is disposed substantially in parallel with the central axis direction of the piston 100.
A cone-shaped protrusion 132 is formed at the center of the first cavity 130. The height of the protrusion 132 is set to be smaller than the depth of the first cavity 130, and the top of the protrusion 132 is formed in a rounded convex curve shape.

The second cavity 140 is a reentrant combustion chamber provided on the outer diameter side of the first cavity 130 and at a shallow depth from the crown surface 120 with respect to the first cavity 130. As shown in FIG. 1 and the like, the inner surface of the second cavity 140 facing the injector 30 is formed as a concave curved surface having a circular cross section when viewed along the central axis.
The outer peripheral wall 141 of the second cavity 140 is formed so as to be inclined so that the end on the crown surface 120 side is on the inner diameter side of the cylinder 11 with respect to the end on the crankshaft side.
A lower surface portion (surface portion far from the cylinder head 20) 142 of the second cavity 140 is disposed so as to be inclined so that the inner diameter side is the cylinder head 20 side with respect to the outer diameter side.
Further, the connection portion 143 between the lower surface portion 142 of the second cavity 140 and the outer peripheral wall portion 131 of the first cavity 130 is rounded and formed in a convex curved surface shape.

Hereinafter, injection control in the engine of the embodiment will be described.
First, when the engine 1 is started, the engine control device stops driving the second needle 33 of the injector 30 and drives only the first needle 32 to inject fuel only from the first injection hole 31b.
At this time, the flow F1 of the air-fuel mixture formed by the injection from the first injection hole 31b collides with the bottom of the first cavity 130 and changes direction along the inner surface as shown in FIG. It is wound up to the cylinder head 20 side along the portion 131.
A portion of the air-fuel mixture thus wound is collected near the heat generating portion 41 of the glow plug 40 and ignited thereby.

On the other hand, during normal operation of the engine 1, the engine control device performs fuel injection using both the first injection hole 31b and the second injection hole 31c of the injector 30.
FIG. 3 is a schematic cross-sectional view showing a cross-section corresponding to FIG. 1, and shows a state during normal operation.
At this time, in addition to the mixture flow F1 described above, the cylinder is formed by injection from the second injection hole 31c, enters the upper portion of the second cavity 140, and then reverses along the inner surface thereof. A flow F2 flowing toward the center side of the combustion chamber is formed.
In addition, a flow F3 that flows between the cylinder head 20 and the crown surface 120 of the piston 100 from above the second cavity 140 is also formed by the injection from the second injection hole 31c.
Each of these mixed airflows forms a substantially uniform mixture distribution in the combustion chamber, and is ignited and combusted in each part in the combustion chamber.
The engine control device delays the injection timing from the second fistula with respect to the injection timing from the first fistula, so that the flow F1 is changed from the first cavity 130 side to the cylinder head 20 side. Since it passes through the part with a time difference after flowing to the point, it is prevented from interfering with each other.

In the embodiment described above, the following effects can be obtained.
(1) During start-up, fuel can be injected toward the first cavity 130 and the inverted combustible mixture F1 can be collected in the vicinity of the glow plug 40 to improve the startability of the engine 1.
On the other hand, during normal operation, by injecting fuel toward the first cavity 130 and the second cavity 140, the air-fuel mixture distribution in the cylinder is made to be close to uniform, the air utilization rate is increased, and the overconcentrated region is locally localized. Formation of black smoke and unburned components can be prevented.
(2) By stopping fuel injection from the second injection hole 31c of the injector 30 at the time of starting, most of the fuel injected at the time of starting can be collected around the glow plug 40 as a combustible air-fuel mixture.
(3) The injector 30 has the first needle 32 and the second needle 33 that individually open and close the first injection hole 31b and the second injection hole 31c, so that the fuel injection amount from each injection hole 31b, 31c can be appropriately adjusted. Can be controlled.
(4) The mixture flow F1 formed by the injection from the first injection hole 31b and the mixture flow F2 formed by the injection from the second injection hole 31c are prevented from interfering with each other. It is possible to improve the combustion state by optimizing the flow of the air-fuel mixture.

(Modification)
The present invention is not limited to the embodiments described above, and various modifications and changes are possible, and these are also within the technical scope of the present invention.
For example, the specific shapes of the first and second cavities and the arrangement of the injectors and glow plugs can be changed as appropriate.
Further, the configuration of the fuel injection means that can individually adjust the fuel injection amounts from the first and second nozzle holes is not particularly limited. Further, depending on the operating state of the engine, fuel may be injected only from the second injection hole.
In the embodiment, the fuel injection from the second nozzle hole is stopped at the time of starting, but a small amount of fuel may be injected from the second nozzle hole at the time of starting to the normal time.

DESCRIPTION OF SYMBOLS 1 Engine 10 Cylinder block 11 Cylinder 20 Cylinder head 30 Injector 31 Nozzle main body 31a End surface part 31b 1st injection hole 31c 2nd injection hole 32 1st needle 33 2nd needle 40 Glow plug 41 Heat generating part 100 Piston 110 Side surface 111 1st ring Groove 112 Second ring groove 113 Third ring groove 120 Crown surface 130 First cavity 131 Outer wall portion 132 Protrusion 140 Second cavity 141 Outer wall portion 142 Lower surface portion 143 Connection portion F1 to F3 Flow of air-fuel mixture

Claims (5)

An injector provided in the cylinder head for injecting fuel into the combustion chamber;
Preheating means provided with a heat generating part in the cylinder head;
A first cavity formed with a concave surface of the piston, and formed with a concave curved surface portion that inverts at least a part of the fuel injected from the injector toward the heat generating portion side of the preheating means; ,
A diesel engine having a second cavity formed around the first cavity,
The injector has a first slot directed to the first cavity and a second slot directed to the second cavity, and the first occupying the total fuel injection amount at the time of start-up. A diesel engine comprising an injection control means for increasing a ratio of an injection amount from a fistula to that during normal operation. 2. The diesel engine according to claim 1, wherein the injection control unit injects fuel only from the first hole and stops fuel injection from the second hole at the time of start-up. The injector is disposed in the vicinity of the cylinder central axis,
The first cavity is a shallow dish type combustion chamber formed by denting the central portion of the crown surface of the piston,
The second cavity is a reentrant combustion chamber disposed on the outer diameter side of the first cavity and at a position where the depth from the crown surface is shallow with respect to the first cavity. The diesel engine according to claim 1 or 2. The said injector has the 1st valve body and 2nd valve body which can drive independently, respectively opening and closing the said 1st nozzle hole and the said 2nd nozzle hole. The diesel engine according to any one of claims 1 to 3. The injection control means injects fuel that is injected from the first nozzle hole into the first cavity and then reversed and wound up to the cylinder head side from the second nozzle hole to the second cavity. A region where the trajectory of the fuel injected from the first injection hole intersects the trajectory of the fuel injected from the second injection hole with respect to the fuel that is reversed and wound up to the cylinder head side 5. The fuel injection timing from the second nozzle hole is delayed with respect to the fuel injection timing from the first nozzle hole so as to pass through the first nozzle hole first. 5. The diesel engine according to item 1.

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