JP2656181B2 - Dual fuel 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 dual fuel engine which uses a liquid fuel such as gasoline and a gaseous fuel such as compressed natural gas, and more particularly to a dual fuel engine having a valve operating mechanism. Things.

[0002]

2. Description of the Related Art In recent years, natural gas has been reviewed as an alternative energy source to petroleum, and it has been proposed to use it as fuel for automobiles. This natural gas is usually filled in a cylinder as compressed natural gas (hereinafter, referred to as CNG), mounted on a vehicle, and used as a fuel. Further, due to the problem that the supply source of CNG is not sufficient, for example, an engine that can use both gasoline and CNG has been proposed. Such engines are used as fuel by switching between gasoline and CNG according to operating conditions (for example, see Japanese Unexamined Patent Publication No. Sho 62-62).
No. 214238).

In the above-mentioned engine, gasoline and CNG have different optimal settings such as ignition timing, lift amount and opening / closing timing of intake / exhaust valves. By burning each other at a compromised setting
Used in one engine.

[0004]

However, in particular, due to the difference in the opening / closing timing of the intake valves, the combustion characteristics when each fuel is used are deteriorated as compared with the engine using each fuel alone, and the emission is deteriorated. However, there is a problem that the torque characteristics cannot be obtained.

The present invention has been made in view of the above-mentioned problems of the prior art, and a main object of the present invention is to provide a dual fuel engine using both gaseous fuel and liquid fuel at the time of using each fuel. It is to improve combustion characteristics and torque characteristics.

[0006]

SUMMARY OF THE INVENTION According to the present invention, there is provided a dual fuel engine which switches between gaseous fuel and liquid fuel in accordance with an operating condition, wherein the opening and closing timing of an intake valve is changed. Having a possible valve train, said valve train
The valve opening timing of the intake valve is more than the time when the liquid fuel is used.
This is achieved by providing a dual fuel engine characterized in that the use of gaseous fuel is delayed .

[0007]

[Function] Assuming the same air, mixing of liquid fuel such as gasoline
Compared to aiki, the intake pressure of the mixture of gaseous fuels such as CNG
Is higher by the supply pressure of gaseous fuel.
It is better to slow down the latter than to adjust the supply to the
good. To control this by changing the valve opening timing of the valve train
To supply each fuel to the combustion chamber in a state appropriate for its properties
it can.

[0008]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a preferred embodiment of the present invention.

FIG. 1 is a configuration diagram of a main part of a dual fuel engine to which the present invention is applied. An intake port 3 and an exhaust port 4 are provided in a cylinder head 2 of an engine 1 provided in an engine room of a vehicle (not shown), and an intake manifold 5 and an exhaust manifold 6 are connected to each other. The intake manifold 5 is connected to the throttle body 7 from an upstream chamber 5a, and the upstream side of the throttle body 7 communicates with the atmosphere via an air cleaner (not shown). Further, a gasoline fuel injection device 8 is provided at a downstream side of the intake manifold 5 facing the intake port 3. The gasoline fuel injection device 8 is connected via a filter 9 to a fuel pump 10 provided in a fuel tank 11. The downstream side of the gasoline fuel injection device 8 is connected to the gasoline tank 11 via the regulator 13.

Therefore, gasoline as liquid fuel sucked up from the gasoline tank 11 by the fuel pump 10 is supplied to the gasoline fuel injection device 8 through the filter 9, and the surplus gasoline is returned to the gasoline tank 11 through the regulator 13. It is supposed to be. here,
Actually, when the engine 1 is composed of multiple cylinders, a gasoline fuel injection device corresponding to the number of cylinders is arranged between the fuel injection device 8 and the regulator 13 in series.

On the other hand, a CNG fuel injection device 14 is provided toward the inside of the intake manifold chamber 5a. The CNG fuel injection device 14 is provided with a cylinder 16 for storing CNG via a pressure reducing regulator 15 as a pressure reducing device.
It is connected to the. Therefore, CNG supplied from the cylinder 16 is decompressed in the decompression regulator 15 and
The fuel is supplied to the NG fuel injection device 14.

FIG. 2 and FIG. 3 show a part of the valve mechanism of the engine 1. Each cylinder of the engine 1 has a pair of intake valves 21.
a, 21b, a camshaft 22 that rotates at a rotation speed of の of the crankshaft, a cam 23a for minute lift, a cam 23b for CNG, and a cam 24 for gasoline are provided for each cylinder, On the rocker shaft 28, three rocker arms 25 to 27 are pivotally supported in parallel with each other. In the middle of these rocker arms, the cams 23a, 23
b, 24 are respectively formed with slipper surfaces, and rocker arms 25, 27 located on both left and right sides.
Of the intake valve 21 via tappet screws 29a, 29b fixed by lock nuts 30a, 30b.
a, 21b are in contact with the stem-side free ends.

As is well known, the intake valves 21a,
The valve 21b is resiliently urged in the valve closing direction by valve springs 36a, 36b via spring retainers 35a, 35b, and is driven to open and close via the right and left rocker arms 25, 27 as the camshaft 22 rotates. . The center rocker arm 26 is driven by the gasoline cam 24, but is always urged toward the sliding contact surface of the gasoline cam 24 by a lifter (not shown) provided at a portion of the cylinder head 2 corresponding to the rocker arm 26. It has been activated.

Next, a description will be given of the valve switching mechanism 34 for achieving the cooperative operation of the rocker arms 25 to 27.

As best shown in FIG. 3, each rocker arm 2
Guide holes 37, 40, 4 that are aligned with each other
1 is provided. The guide hole 37 of the rocker arm 25 located at one end thereof is a closed blind hole,
The piston 45 is received in the inside. The closed end of the guide hole 37 is connected to the passage 5 formed in the rocker arm 25.
2 and the oil supply passage 50 inside the rocker shaft 28 through a port 53 opened in the hollow rocker shaft 28. The guide hole 40 of the rocker arm 26 located at the center is formed as a through hole, and a piston 46 having a length substantially equal to the entire length of the guide hole 40 is received therein. A stopper 47 is received in the guide hole 41 of the rocker arm 27 located at the other end. The stopper 47 has a substantially cylindrical shape with a bottom, and is constantly resiliently urged toward the center rocker arm 26 by a compression coil spring 48 interposed between the inside thereof and the bottom of the guide hole 41.

According to the valve switching mechanism 34, when the oil pressure in the oil supply path 50 is low, the piston 45 is inserted into the guide hole 37 and the piston 46 is inserted into the guide hole 40 by the urging force of the compression coil spring 48. The stoppers 47 are located in the guide holes 41, respectively, so that the rocker arms 25 to 27 can move independently of each other. Accordingly, the rocker arm 26 at the center is driven by the gasoline cam 24 and performs a so-called lost motion that only pushes down the lifter repeatedly.
Since the slipper surface 25a is in sliding contact with the minute lift 23a, the intake valve 21a is brought into a rest state while being almost closed, and the rocker arm 27 is driven by the CNG cam 23b to open and close the intake valve 21b in the CNG mode. .

When the oil pressure in the oil supply passage 50 is increased, the piston 45 enters the guide hole 40 against the spring force of the compression coil spring 48 and moves the piston 46 into the guide hole 41 of the rocker arm 27. Rush. Therefore,
The three rocker arms 25 to 27 are integrally connected to each other. Here, since the cam profile of the gasoline cam 24 is relatively large with respect to the CNG cam 23b, the rocker arms 25 and 27 are also connected to the center gasoline cam 2b.
4, the intake valves 21a, 21b
Are driven to open and close in a gasoline mode.

Next, the operation of the valve train of the engine 1 according to the present invention will be described with reference to FIGS.

First, in the low-speed rotation range of the engine 1 (on the lower side than the rotation speed N1 shown in FIG. 4), CNG is used as fuel and the valve mechanism is set to the CNG mode. That is, the supply of gasoline from the gasoline fuel injection device 8 is stopped, the CNG is supplied from the CNG fuel injection device 14, the rocker arm 27 is driven by the CNG cam 23b, the intake valve 21a is stopped, and the intake valve is stopped. 21b
Only operate. Here, the valve opening timing of the intake valve 21b is set to be later than in the gasoline mode described later. As a result, a torque characteristic as shown by a solid line A in FIG. 4 is obtained. At this time, the intake valve 21a is also driven by a minute amount by the minute lift cam 23a via the rocker arm 25 within a range that does not actually affect the intake amount or the like. This prevents seizure of the stopped intake valve 21a.

When the rotation speed of the engine 1 increases to reach N1, gasoline is used as fuel and the valve train is switched to gasoline mode. That is, the supply of CNG from the CNG fuel injection device 14 is stopped, the supply of gasoline from the gasoline fuel injection device 8 is performed, and the rocker arm 26, the pistons 45, 46,
Via the rocker arms 25, 27, the two intake valves 21a, 21
b is operated in this gasoline mode. Here, the opening timing of the intake valves 21a and 21b is set earlier than in the case of the CNG mode. As a result, a torque characteristic as shown by a solid line B in FIG. 4 is obtained. The broken line C indicates the torque characteristic of a conventional dual fuel engine having a valve operating mechanism based on a single intake valve opening / closing timing. As can be seen by comparing the solid lines A and B with the broken line C, the torque can be changed by switching the intake valve opening / closing timing according to each fuel as compared with the case where each fuel is burned at a single intake valve opening / closing timing. The properties are significantly improved. In addition, unburned gas such as CNG is prevented from being released to the outside.

[0021]

As is apparent from the above-described structure, according to the dual fuel engine of the present invention, the valve mechanism of the dual fuel engine that switches between gaseous fuel and liquid fuel in accordance with the operating condition is used. The opening timing of the intake valve is determined by the liquid fuel
To use gas fuel more slowly than when using
Gas mixture such as gasoline and gas such as CNG
The supply of the fuel mixture to the combustion chamber depends on the properties of each fuel.
Optimize Te, the effect of the present invention since it may improve the torque characteristics with may prevent deterioration of emission and improve combustion characteristics during each fuel used is large.

[Brief description of the drawings]

FIG. 1 is a main part configuration diagram of an engine body and a fuel supply system of a dual fuel engine to which the present invention is applied.

FIG. 2 is a sectional view schematically showing a configuration of a part of a valve train of the engine shown in FIG. 1;

FIG. 3 is a sectional view of a main part of the valve train of FIG. 2;

FIG. 4 is a graph showing a relationship between a switching timing of a fuel and a valve operating mechanism according to a change in an engine rotation speed and an output torque of the engine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 2 Cylinder head 3 Intake port 4 Exhaust port 5 Intake manifold 5 a Intake manifold chamber 6 Exhaust manifold 7 Throttle body 8 Gasoline fuel injection device 9 Filter 10 Fuel pump 11 Gasoline tank 13 Regulator 14 CNG fuel injection device 15 Pressure reducing regulator 15a High-pressure chamber 15b Low-pressure chamber 16 Cylinder 21a, 21b Intake valve 22 Camshaft 23a Cam for small lift 23b Cam for CNG 24 Cam for gasoline 25-27 Rocker arm 28 Rocker shaft 29a, 29b Tappet screw 30a, 30b Lock nut 35a, 35b Spring Retainers 36a, 36b Valve springs 37, 40, 41 Guide holes 45 Pistons 46 Pistons 47 Stoppers 48 Compression coil springs 50 Oil supply 52 passage 53 port

Claims (1)

(57) [Claims] 1. A dual fuel engine that switches between gaseous fuel and liquid fuel in accordance with an operating condition, comprising a valve operating mechanism capable of changing the opening and closing timing of an intake valve . The opening timing of the intake valve is controlled by the liquid fuel
That the use of the gaseous fuel was slower than the use of
And a dual fuel engine.