JP2929398B2 - Fuel supply system for two-stroke engine - 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 two-stroke engine, and more particularly, to a fuel injection method in which a piston can be sufficiently cooled at a high speed when fuel is directly injected into a cylinder. About improvement.

[0002]

2. Description of the Related Art There is known a two-cycle engine in which compressed air and fuel are directly injected into a cylinder by an air fuel injection device mounted on a cylinder head. In this type of two-stroke engine, most of the combustion air is sucked into the crank chamber via the intake pipe and supplied to the cylinder from the scavenging port.

[0003]

In the case of a normal two-stroke engine, a mixture of fuel and air is sucked into the crank chamber, and the compressed air is primarily compressed by lowering the piston. Side). Therefore, the piston is cooled on the back side and the front side by the fuel. On the other hand, in the case of the air-fuel injection type two-stroke engine, only air is sucked into the crank chamber and fuel is directly injected to the surface side of the piston, so that the cooling of the piston tends to be insufficient. In particular, it is conceivable that the amount of cooling of the piston is insufficient during high-speed rotation of the engine, making it difficult to increase the speed and output of the engine.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems. By cooling the piston not only from the front side but also from the rear side or the side, high speed rotation is enabled to increase the output. It is an object of the present invention to provide a fuel supply device for a two-stroke engine that can be achieved.

[0005]

According to the present invention, air is supplied to a cylinder through an intake passage including an intake pipe, a crank chamber, and a scavenging port, and fuel is supplied by a main fuel injection valve attached to a cylinder head. In a fuel supply system for a two-stroke engine in which fuel is injected directly into a cylinder, fuel is injected into the intake passage when the engine speed is equal to or higher than a predetermined value, and fuel injection is stopped when the engine speed is lower than the predetermined value. A fuel injection valve is provided in the middle of the intake passage, and fuel injection amount control means for reducing a fuel supply amount from the main fuel injection valve per one rotation of the crankshaft as the engine speed increases is provided. .
Here, the auxiliary fuel injection valve may inject into any of the intake pipe, the crank chamber, and the scavenging port.

[0006]

According to the fuel supply device of the present invention, fuel is injected into the intake passage by the auxiliary fuel injection valve,
When the engine speed is higher, the injection amount from the main fuel injection valve is reduced.As the engine speed is higher, the injection amount from the auxiliary fuel injection valve can be increased. Therefore, when the fuel is injected into the intake pipe or the crank chamber, The back side of the piston is also cooled, and when injected into the scavenging port, the side of the piston is also cooled. As a result, cooling of the piston is sufficiently performed, and high-speed rotation and high output of the engine can be achieved.

[0007]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. FIGS. 1 to 5 are views for explaining a fuel supply apparatus for an air-fuel-injected two-stroke engine according to a first embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a water-cooled, two-cycle, parallel three-cylinder engine configured to directly inject air and fuel into a cylinder. The cylinder body 3 formed in parallel in the direction of the shaft 6 is mounted and fixed with bolts, and the cylinder head 4 is fixed on the cylinder body 3 with bolts. The piston 5 slidably inserted into the cylinder 3a is connected to a crank arm 6a of the crankshaft 6 by a connecting rod 6b.

The cylinder head 4 is provided with an air-fuel injection device 19 for directly injecting compressed air and fuel into the cylinder 3a. The air-fuel injection device 19 comprises a main fuel injection valve 19a provided for each cylinder. And an air rail, a fuel rail and the like common to each injection valve. The crankcase 2a of the crankcase 2 in which the crank arm 6a is accommodated communicates with the cylinder 3a via a scavenging port 3b.

An intake manifold 8 is connected to the crank chamber 2a, and a reed valve 7 is provided in the connection.
Is installed. Merging section 1 of intake manifold 8
0, a throttle valve 9 is interposed. An auxiliary fuel injection valve 13 for injecting fuel into the intake manifold 8 is provided downstream of the throttle valve 9, and an air flow meter for detecting an air flow rate is provided upstream. 11 are provided respectively. Here, since the air flow rate is proportional to the opening of the throttle valve 9, that is, the load, the air flow rate or the throttle valve opening will be described below as representing the load state. Reference numeral 12 denotes a rotation speed sensor that detects the engine rotation speed.

Reference numeral 27 denotes an ECU that controls the amount of fuel injected from the air fuel injection device 19 and the auxiliary fuel injection valve 13 in the following manner. That is, as shown in FIG. 4, the fuel injection from each main fuel injection valve 19a is performed three times with the timing shifted per engine rotation, and the fuel injection from the auxiliary fuel injection valve 13 is performed once per engine rotation. Let Also, as shown in FIG. 2B, during low-speed rotation to medium-speed rotation medium load to high-speed rotation low load represented by the region C, fuel is injected only from the main fuel injection valve 19a, At the time of the medium speed rotation high load, the high speed rotation medium load, and the high speed rotation high load, the fuel is injected from both the main fuel injection valve 19a and the sub fuel injection valve 13.

The injection ratio between the total fuel injection amount A1 from the three sets of main fuel injection valves 19a and the fuel injection amount B1 from the auxiliary fuel injection valves 13 is as shown in FIGS. Controlled. FIGS. 2A and 3 show the fuel supply amount per one rotation of the crankshaft. However, in FIG. 2A, the fuel supply amount per unit time has the same tendency. For example, when the engine speed is X2, the throttle valve opening is Y2 (P
At two points or more, the total injection amount from the main fuel injection valve 19a is kept at G2, and the shortage is controlled so as to be compensated by the injection amount from the auxiliary fuel injection valve 13. When the engine speed is X1 (X1 <X2), the throttle valve opening Y1 (P1
At this point, the injection amount from the main fuel injection valve is constant at G1. In this case, the injection amount from the main fuel injection valve decreases from G1 to G2 as the engine speed increases from X1 to X2. In FIG. 3, curve B indicates the injection amount from the main fuel injection valve, and curve A indicates the required fuel supply amount when the throttle valve is fully open. Further, as shown by the curve A ', even if the engine speed increases and the required fuel amount decreases, the injection amount from the auxiliary fuel injection valve may be controlled to be constant.

Next, the function and effect of this embodiment will be described. The ECU 27 reads the engine speed signal a and the air flow rate signal (throttle valve opening) b, calculates the required fuel supply amount Q according to the input signals a and b, and realizes the required fuel supply amount Q. The drive signals d and e are applied to the main fuel injection valve 1 respectively.
9a, output to the auxiliary fuel injection valve 13. First, when the engine speed and the throttle valve opening are within the region C in FIG. 2B, all of the necessary fuel supply amount Q is supplied to the main fuel injection valve 19.
Inject from a. On the other hand, when the engine speed and the throttle valve opening are within the range D, the injection amount from the main fuel injection valve 19a is fixed to a fixed amount (for example, G1, G2, or the like) corresponding to the engine speed at that time. And the rest is
Inject from In this case, the certain amount (G1 etc.)
It is set smaller as the engine speed increases.

As described above, in the present embodiment, when the engine speed and the throttle valve opening (load) are in the predetermined ranges, fuel is injected into the intake manifold 8 by the auxiliary fuel injection valve 13 and the engine speed increases as the engine speed increases. Since the injection amount from the main fuel injection valve 19a is reduced to increase the fuel amount ratio from the auxiliary fuel injection valve 13, the piston 5 can also be cooled from the back side, and the cooling performance of the piston at high speed and high load can be secured. High speed and high output of the engine can be achieved.

In this embodiment, more fuel is supplied from the intake manifold 8 in a state of being mixed with air as the engine rotates at a higher speed, so that variations in the air / fuel ratio of each cylinder can be reduced. . Incidentally, the higher the speed, the greater the pulsating inertia of the intake and exhaust, and the more likely the difference is in the amount of intake air for each cylinder. Therefore, if fuel is supplied only by direct injection, the air / fuel ratio will vary greatly.

Here, when the injection amount ratio from the auxiliary fuel injection valve is increased at the time of high speed and high load as in the present embodiment, the advantage of this type of engine in which air fuel is directly injected into the cylinder may be impaired. There is. However, as shown in FIG. 5, this type of air-fuel injection type two-cycle engine performs so-called premixed combustion at the time of high speed and high load, similar to a normal two-cycle engine.
Therefore, there is no particular problem even if the injection amount ratio from the auxiliary fuel injection valve is increased.

In the above embodiment, the injection amount from the main fuel injection valve is fixed at G1, G2, etc. even if the throttle valve opening (engine load) is increased to a predetermined value or more. It is sufficient to decrease the injection amount from the main fuel injection valve as the speed increases, and thereby increase the injection amount from the auxiliary fuel injection valve as the rotation speed increases, and the injection amount itself from the main fuel injection valve increases in load. However, it is not always necessary to fix as in the above embodiment. That is, as shown in FIG. 6A, the injection amount from the main fuel injection valve may be increased or decreased as the throttle valve opening increases (G2 ', G in FIG. 6).
2 ''). As shown in FIG. 6B, the ratio between the injection amount A3 from the main fuel injection valve and the injection amount B3 from the auxiliary fuel injection valve is constant, that is, B3 '/ A3' = B3.
3 '' / A3 ''. FIG.
(a) and (b) show a state where the engine speed is constant.

In the case where an auxiliary fuel injection valve which starts fuel injection when the engine speed reaches a predetermined value is provided, the minimum injection amount of the auxiliary fuel injection valve is injected at the start of the fuel injection. Become. Therefore, in order to make the total fuel supply amount equal to the required fuel amount, it is necessary to reduce the fuel amount from the main fuel injection valve by the minimum injection amount. FIGS. 7 and 8 are diagrams for explaining a second embodiment of the present invention in which the fuel amount ratio from the main and auxiliary fuel injection valves is set in consideration of the minimum injection amount of the auxiliary fuel injection valve. FIG. 7 shows the fuel amount ratio per one rotation of the crankshaft when the throttle valve opening is changed in a state where the engine speed is constant at X2, and FIG. 8 shows the throttle valve opening being constant at any one of the openings. The graph shows the fuel amount ratio per crankshaft rotation when the engine speed is changed in this state. In FIG. 7, the fuel supply amount per unit time has the same tendency.

In FIG. 7, for example, when the throttle valve opening reaches Y2, fuel injection from the auxiliary fuel injection valve 13 is started. In this case, the main injection amount from the main fuel injection valve 19a is temporarily reduced by the minimum injection amount Q3 of the sub fuel injection valve 13. The main injection amount increases with the throttle valve opening increased while the sub-injection amount remains fixed at the minimum injection amount Q3, and becomes constant when the main injection amount reaches G2. The sub-injection amount increases as the valve opening increases. G after the main injection amount is reduced by the minimum injection amount Q3.
For the return to 2, various modes can be adopted. For example, as shown by a dashed line in FIG.
Alternatively, as indicated by the two-dot chain line, the throttle valve opening may be returned to G2 at the maximum point in time.

In FIG. 8, curves a to c show the relationship between the engine speed and the fuel supply amount when the throttle valve opening is fully open, 1/2 open, and 1/4 open. It shows the injection start timing and the main and sub injection amount ratios. For example, when the throttle valve is fully opened, the auxiliary fuel injection is started at the engine speed n. When the throttle valve is fully opened and the engine speed is 5000 rpm, the required fuel injection amount is Q5, of which Q4 is injected from the main fuel injection valve and the rest is injected from the auxiliary fuel injection valve. Curve e shows the relationship between the fuel injection start timing from the main fuel injection valve and the exhaust port closing timing,
S1 is a region where fuel injection starts after the exhaust port is closed, S2
Indicates an area where fuel injection is started before the exhaust port is closed. Also in the present embodiment, the auxiliary fuel injection is started when the engine speed exceeds a predetermined value, and the main fuel injection amount is reduced as the engine speed increases, thereby increasing the auxiliary fuel injection amount. . Looking at the relationship between the start timing of the main fuel injection and the exhaust port closing timing, as the throttle valve opening increases, the fuel is injected before the exhaust port is closed at a point in time when the engine speed is lower.

As described above, according to the fuel supply system for a two-stroke engine according to the present invention, the auxiliary fuel injection valve for injecting fuel into the intake passage is provided. Since the amount of fuel from the injection valve has been reduced, the injection amount from the auxiliary fuel injection valve can be increased, cooling from the back or side of the piston can be sufficiently performed, and the effect of achieving high speed and high output of the engine can be achieved. is there.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a fuel supply device for a two-stroke engine according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a throttle valve opening-fuel supply characteristic and an engine speed-throttle valve characteristic of the embodiment.

FIG. 3 is a characteristic diagram of an engine speed and a fuel supply amount according to the embodiment.

FIG. 4 is a view showing an injection order of the embodiment.

FIG. 5 is a view showing injection conditions of the embodiment.

FIG. 6 is a diagram showing a modified example of the throttle opening-fuel supply amount characteristic in the embodiment.

FIG. 7 is a throttle valve opening-fuel supply amount characteristic diagram according to a second embodiment of the present invention.

FIG. 8 is a graph showing the relationship between engine speed and fuel supply amount according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 2 cycle engine 2a Crank chamber 3a cylinder 8 Intake manifold (intake pipe) 13 Auxiliary fuel injection valve 19 Air fuel injection device 27 ECU (fuel injection amount control means)

Continuation of front page (56) References JP-A-2-140460 (JP, A) JP-A-62-113821 (JP, A) JP-A-4-132842 (JP, A) JP-A-63-255539 (JP, A) JP-A-63-106330 (JP, A) JP-A-61-279737 (JP, A) JP-A-63-255536 (JP, A) JP-A-4-203335 (JP, A) 63-106332 (JP, A) Fully open 1983-102, 738 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB name) F02D 41/00-41/40 F02B 17/00-23 / Ten

Claims (1)

(57) [Claims] An air supply system supplies air into a cylinder through an intake passage including an intake pipe, a crank chamber, and a scavenging port, and directly injects fuel into the cylinder by a main fuel injection valve attached to a cylinder head. In the fuel supply device for a two-stroke engine, when the engine speed is equal to or higher than a predetermined value, fuel is injected into the intake passage, and when the engine speed is lower than the predetermined value, fuel injection is stopped. A fuel supply device for a two-stroke engine, further comprising a fuel injection amount control means provided on the way to reduce the fuel supply amount from the main fuel injection valve per one rotation of the crankshaft as the engine speed increases.