JPH0524353B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an injection rate control device for a fuel injection pump for a diesel engine. The present invention relates to an injection rate control device capable of causing an injector to perform pilot injection by temporarily lowering fuel pressure.

[Prior art and problems]

It is known that combustion noise and _NOx emissions can be reduced by performing pilot injection prior to main injection in each injection cycle in a diesel engine. For this reason, it has been proposed to use an injection rate control device to temporarily interrupt the injection by temporarily lowering the fuel pressure in the pump chamber of the injection pump immediately after the start of injection, thereby forming a pilot injection pulse. .

Mechanical injection rate control devices can be broadly classified into an accumulator type and a relief valve type. The former, for example, as disclosed in Utility Model Application No. 56-105656, is a system in which a variable volume chamber is provided that communicates with the pump chamber of the injection pump, and a piston biased by a spring is attached to the variable volume chamber. The volume of the variable volume chamber increases or decreases depending on the injection pressure from the injection pump, and high pressure fuel from the pump chamber of the injection pump is temporarily stored in the variable volume chamber. A small depression is provided on the top surface of the piston, so that fuel pressure acts on a small diameter pressure receiving area before the piston moves. The pressure receiving area of the recess and the spring constant of the spring are set so that the piston starts moving when the injection pressure exceeds the opening pressure of the injection valve, so the piston moves immediately after fuel injection from the injection valve starts. Start. After the piston begins to move, the injection pressure acts on the entire cross-sectional area of the piston, so the piston moves rapidly against the force of the spring, and a portion of the high-pressure fuel from the injection pump flows into the variable volume chamber, causing injection. The pressure drops temporarily and a pilot injection is performed. As the pumping stroke of the injection pump further advances, the injection pressure increases again and main injection is performed. When the pressure stroke reaches its final stage and the injection pressure drops to a pressure considerably lower than the opening pressure of the injection valve, the piston returns to its initial position and the volume of the variable volume chamber becomes zero.

The problem with this accumulator-type injection rate control device is that the structure is such that injection pressure acts on the entire cross-sectional area of the piston after it moves, so the spring constant of the spring for biasing the piston must be extremely large. It is a must. A spring that can be housed in a small spring chamber behind the piston and yet has the necessary large spring constant has been impossible or extremely difficult to manufacture in practice. Another problem is that this injection rate control device exhibits an accumulator effect over the entire engine speed range and reduces the injection rate between pilot injection and main injection. This means that the required output cannot be obtained.
If an injection pump is designed to delay the end of injection in order to increase the amount of injection at high speeds and high loads, smoke will increase and fuel efficiency will deteriorate.

The relief valve type injection rate control device is configured to release fuel in the pump chamber of the injection pump when the injection pressure exceeds a predetermined pressure. (for example,
Act No. 30-9104). This device has drawbacks, such as irregular injections occurring due to valve hunting, and the pumping amount of the injection pump having to be more than doubled in order to obtain a predetermined injection amount.

[Purpose of the invention]

An object of the present invention is to provide an injection rate control device that can be easily manufactured.

An object of the present invention is to prevent the injection rate from decreasing during high-speed, high-load operation of the engine.

[Summary of means and actions for solving problems]

An injection rate control device according to the present invention, as a means for solving the above problems, includes: a casing; a valve seat formed in the casing and communicating with an inlet port communicating with a pump chamber of a fuel injection pump; a movable valve body that opens and closes the inlet port by one end; a cylinder formed within the casing that slides and guides the movable valve body; and a cylinder formed around the movable valve body within the casing that is substantially constant; a substantially dead-end closed space having a volume, the fixed volume chamber communicating with the inlet port when the valve is open when the movable valve body is spaced from the valve seat; In the closed state where the movable valve body is seated on the valve seat, the movable valve body closes the inlet port except for a part of one end of the movable valve body, and applies pressure in the pump chamber to the part. In the open state where the movable valve body is away from the valve seat, the movable valve body transfers the pressure in the pump chamber to both the part of the movable valve body and the other part of the movable valve body. and the other part of the movable valve body and the valve seat face each other with a small gap so that the inlet port and the fixed volume chamber communicate with each other through the gap. An injection rate control device for a fuel injection device is provided.

As soon as the injection pressure of the injection pump exceeds the opening pressure of the injection valve and injection starts, the movable valve body moves, the pump chamber of the injection pump is communicated with the fixed volume chamber, and the injection pressure temporarily decreases. Injection is temporarily interrupted,
Pilot injection is realized. Since the amount of movement of the movable valve body is limited, the valve mechanism acts as a type of throttle. During high-speed operation, the throttling effect of the valve mechanism increases, so the injection pressure does not decrease in the middle of injection, and the injection rate during high-speed and high-load operation increases.

In the device of the invention, the movable valve body of the valve mechanism serves only to establish or interrupt communication between the inlet port and the fixed volume chamber. That is, unlike the conventional accumulator-type injection rate control device in which the volume of the variable volume chamber expands as the piston moves and reduces the injection pressure, in the device of the present invention, the reduction in injection pressure is caused by the fixed volume chamber and the inlet port. Since the movable valve body is regulated by the stopper after the valve is opened, it is possible to use a spring with an extremely small spring constant.

In a preferred embodiment of the present invention, the biasing means for biasing the movable valve body in the valve closing direction is constituted by a hydraulic cylinder mechanism. The feed pressure of the injection pump is applied to the piston of this hydraulic cylinder. Since this feed pressure increases as the engine speed increases, the opening amount of the valve mechanism is forcibly reduced in accordance with the increase in engine speed.

〔Example〕

Although FIG. 1 shows an injection rate control device 10 according to a first embodiment of the present invention installed in a distribution type injection pump 12, the device of the present invention can also be installed in a row type injection pump. The injection pump 12 is essentially conventional, with only minor modifications to accommodate the injection rate control device 10. As is well known, a pump cylinder 16 is press-fitted into the distributor housing 14 of the injection pump 12, and a pump plunger 18 is fitted within the cylinder 16 for rotation and reciprocation. Fuel pressurized to feed pressure by a feed pump (not shown) is sent into the pump chamber 20, and is pressurized to a high pressure with the pressure stroke of the plunger 18.
As the plunger 18 rotates, the fuel is distributed to the injection valves (not shown) of each cylinder via delivery ports (not shown) for each cylinder.

The distributor housing 14 is provided with an internally threaded portion 22, into which an externally threaded portion 26 of the housing 24 of the injection rate control device 10 is screwed. This housing 24 constitutes a part of the casing 28 of the injection rate control device 10, and the pump cylinder 1
In order to seal the pump chamber 20, an annular protrusion 30 is provided on the end surface of the housing 24 to press against the end surface of the pump cylinder 16.

In the illustrated embodiment, the casing 28 of the injection rate control device 10 includes a housing 24 and a valve plate 32.
, a cylinder 34, and a stopper member 36. A cylindrical recess 38 is provided in the center of the housing 24, and the valve plate 32 and cylinder 34 are press-fitted into the recess 38, and the stopper member 36 is screwed into the recess 38 using the threaded portion 40, thereby removing the components of the casing 28. It is concluded integrally.

A bore 42 is formed in the cylinder 34 in the axial direction, into which a movable valve body 44 is slidably and precisely fitted. The cylinder 34 is provided with a cylindrical notch coaxial with the bore 42 on the side of the valve plate 32, and an annular fixed volume chamber 46 is formed between the valve plate 32, the cylinder 34, and the movable valve body 44. There is. The fixed volume chamber 46 is essentially a closed space with a dead end and has a constant volume.

The movable valve body 44 is biased toward the valve plate 32 by a spring 50 housed in a spring chamber 48, and the flat top surface of the movable valve body 44 touches the flat valve seat portion 52 of the valve plate 32. It seems to be closely attached to. A small cylindrical recess 54 is provided in the top surface of the valve body 44. An inlet port 56 is provided in the valve plate 32 and housing 24 in alignment with the recess 54 so that fuel pressure within the pump chamber 20 acts on the recess 54. Therefore, this depression 54
constitutes a pressure receiving portion that receives fuel pressure acting on the valve body 4 when the valve body 44 is closed, and the opening pressure of the valve body 44 is set by a spring 50. A stopper member 3 is used to return fuel slightly leaking from the gap between the cylinder 34 and the movable valve body 44 to the tank.
A drain pipe 58 is screwed into the spring 6, and this drain pipe 58 supports one end of the spring 50. The force of the spring 50 can be adjusted by rotating the drain pipe 58 in either direction.

The inner diameter of the stopper member 36 is made slightly smaller than the diameter of the bore 42 so that the movable valve body 44 abuts against a shoulder 60 thereof. The shoulder portion 60 constitutes a stopper means for regulating the lift amount of the valve body 44, and in this embodiment, the lift amount of the valve body 44 is set to about 0.1 mm.

A valve mechanism 62 is constituted by the above-mentioned valve seat portion 52, movable valve body 44, spring 50, and stopper means.

As mentioned above, when the movable valve body 44 is closed, fuel pressure from the pump chamber 20 of the injection pump acts on the recess 54 of the valve body 44 through the port 56, and this force is opposed by the spring 50. Therefore, the valve opening pressure of the movable valve body 44 is determined by the pressure receiving area of the recess 54 and the force of the spring 50. If the opening pressure of the injection valve is 120 kg/cm ² and the diameter of the recess 54 is 2 mm, if you want the opening pressure of the movable valve body 44 to be 140 kg/cm ² , the spring force of the spring 50 should be 4.4 kgf. There must be.

After the valve is opened, the fuel pressure acts on the entire cross-sectional area of the movable valve body 44, so the valve-closing pressure of the movable valve body 44 is determined by the total cross-sectional area. If the valve closing pressure is desired to be 10 kg/cm ² , the ratio of the pressure-receiving area of the recess 54 to the total cross-sectional area of the valve body 44 should be 1:14.

Next, the operation of this embodiment will be explained with reference to FIGS. 1 and 2. In FIG. 2, solid lines indicate operation during low-speed operation, and broken lines indicate operation during high-speed operation.

At low speed, the pressure stroke of the pump plunger 18 begins and the pressure in the pump chamber 20 is 120Kg/cm ²
When this happens, the injection valve (not shown) opens and fuel injection begins (FIG. 2D). When the pressure in the pump chamber 20 further advances and the pressure in the pump chamber 20 reaches 140 kg/cm ² , the movable valve body 44 opens (FIG. 2B), and the pump chamber 20 and the fixed volume chamber 46 communicate with each other. At that time, the movable valve body 4
4 moves until it abuts the shoulder 60 of the stopper member 36 and remains in that position until the fuel pressure drops to the valve closing pressure. As a result of said conduction, the pressure within the fixed volume chamber 46 increases and at the same time the pressure within the pump chamber 20 decreases (FIGS. 2A and C). Since the pressure falls below the opening pressure of the injection valve, fuel injection is temporarily interrupted. Pilot injection is performed in this manner. As the pumping stroke further progresses and the pressure in the pump chamber 20 rises again while balancing the pressure in the fixed volume chamber 46,
Injection from the injection valve is resumed. Plunger 18
When the pressure feeding stroke approaches the end and the pressure inside the pump chamber 20 drops to 120 kg/cm ² or less, injection from the injection valve ends. The main injection is performed in this manner. The pressure stroke is completed and the pressure in the pump chamber 20 is 10
When the pressure falls below Kg/cm ² , the movable valve body 44 closes. At this time, fuel with a pressure of 10 kg/cm ² is confined within the fixed volume chamber 46. Pump room 20
The pressure inside is the feed pressure of the injection pump (1~5Kg/
^cm2 ). This completes one injection cycle and prepares for the next cycle.

At high speeds, the amount of movement of the movable valve body 44 is limited (for example, 0.1 mm), and the valve mechanism 62 has a throttling effect. Pressure transmission to is delayed. For this reason, as shown by the broken line in Figure 2,
The rise in pressure in the fixed volume chamber 46 is delayed, and the pressure drop in the pump chamber 20 is reduced. Therefore, the injection rate waveform becomes as shown by the broken line D in FIG. 2, and no pilot injection is performed. In this way, the injection amount increases at high speeds, resulting in a large engine output. This tendency becomes stronger as the rotational speed increases.

Next, a second embodiment of the present invention will be described with reference to FIG. The difference from the first embodiment is that a hydraulic cylinder mechanism is provided behind the movable valve body, and the amount of movement of the movable valve body is forcibly restricted as the feed pressure of the injection pump increases. This embodiment focuses on the fact that the feed pressure of the injection pump increases in proportion to the rotational speed, and attempts to make the amount of opening of the movable valve body zero at a certain rotational speed or higher.

In FIG. 3, an injection rate control device 100 is attached to an injection pump 102. In FIG. Injection pump 102
are pump cylinder 104, pump plunger 1
06, a distributor housing 108, and a pump chamber 110.

Similar to the first embodiment, a housing 114 forming a part of the casing 112 of the injection rate control device 100
is screwed into the distributor housing 108 and also serves as a side plate of the pump cylinder 104. The valve plate 11 is located in the central recess of the housing 114.
6. The first cylinder 118 and the second cylinder 120 are press-fitted in this order and fixed by a cap 122 screwed onto the housing 114. It can be considered that the housing 114, the valve plate 116, and the first cylinder 118 constitute the casing 112. A movable valve body 126 of a valve mechanism 124 is fitted into the central bore of the first cylinder 118 in a fluid-tight and slidable manner. Between the movable valve body 126, the valve plate 116, and the first cylinder 118, there is a fixed space that is a closed space with a constant and constant volume, similar to the fixed volume chamber 46 of the first embodiment. A volume chamber 128 is formed. Movable valve body 126
A central recess 130 provided on the top surface of the inlet port 1
It communicates with the pump chamber 110 via 32 and 134.

The movable valve body 126 is urged toward the valve plate 116 by a hydraulic cylinder mechanism 136. This hydraulic cylinder mechanism 136 has a piston 138 that is fluid-tightly and slidably fitted into the second cylinder 120,
A pressure chamber 140 is formed between the piston 138, the second cylinder 120, and the cap 122. A seal between the housing 114 and the cap 122 is provided by an O-ring 142. Feed pressure generated by an internal feed pump (not shown) of injection pump 102 is transferred to passages 144, 14.
6,148 to the pressure chamber 140.
The fuel leaking into the space 150 from between the first cylinder 118 and the movable valve body 126 is removed from the drain port 15.
2,154 and is returned to the fuel tank.

In this embodiment, the recess 13 of the movable valve body 126
The ratio of the pressure receiving area of 0 and the total cross-sectional area of the valve body is approximately 1:13.5
It is set as. Further, the ratio of the total cross-sectional area of the movable valve body to the cross-sectional area of the piston 138 is approximately 1:6.5.
That is, the diameters of the recess 130, the movable valve body 126, and the piston 138 are 1.5 mm, 5.5 mm, and 14 mm, respectively. The end of the skirt portion 156 of the piston 138 abuts against the inner end surface 158 of the cap 122 to limit the maximum lift amount of the movable valve body 126, and the distance therebetween can be 0.1 mm.

Next, the operation of the second embodiment will be explained with reference to FIGS. 3 and 4.

During idle operation (for example, 700 rpm), the feed pressure of the injection pump is approximately 1.6 kg/cm ² , and this pressure is transmitted to the pressure chamber 140 and acts on the piston 138 . The diameter of the piston 138 is
Since it is 14mm, a load of 2.46Kgf is applied to piston 13.
8. When the pump plunger 106 is in the suction stroke, the pump chamber 110 is also under feed pressure, and the pressure acting on the recess 130 of the movable valve body 126 is also the feed pressure of 1.6 kg/cm ² . Therefore,
The hydraulic pressure acting on the piston 138 is dominant, and the movable valve plate 126 is seated on the valve body 116.

The pumping stroke of the pump plunger 106 begins,
Injection starts when the pressure in the pump chamber 110 rises and exceeds the opening pressure of the injection valve (for example, 120 kg/cm ² ). If the pressure increases further and exceeds 140Kg/ ^cm2 ,
The load acting on the movable valve body 126 from the recess 130 is 2.47 kgf, which overcomes the load from the piston 138. Therefore, the movable valve body 126 begins to rise away from the valve plate 116. Once the movable valve body 126 is lifted up, the pressure from the pump chamber acts on its entire cross-sectional area, so the movable valve body 126 rises until the skirt portion 156 of the piston 138 hits the cap 122. Therefore, the pump chamber 110 communicates with the fixed volume chamber 128, and due to the increase in volume, the pump chamber 11
Since the zero pressure temporarily decreases, the injection is interrupted and the pilot injection ends (solid line in FIG. 4). When the pumping stroke further progresses, injection resumes again and main injection is performed. Since the diameter of the movable valve body 126 is 5.5 mm, when the pressure inside the pump chamber 110 is 10 Kg/cm ² , the entire cross-sectional area of the movable valve body 126 has a load equal to the aforementioned load of 2.46 Kgf acting on the piston 138 due to the feed pressure. will come into play. Therefore, when the pressure stroke reaches the final stage and the pressure inside the pump drops to 10 kg/cm ² or less, the movable valve body 126 moves to the piston 138.
The valve is pushed to seat on the valve plate 116 and close the valve. The above cycle is repeated.

When the engine speed rises above the idle speed, the feed pressure of the injection pump increases in proportion to this, so the valve opening pressure of the movable valve body 126 also increases in accordance with the speed. Therefore, as shown in Fig. 4, as the rotational speed increases, the injection rate reduction timing shifts to the latter half of the injection cycle, and at 2500 rpm, the movable valve body 126 does not open and control of the injection rate stops. be done. Needless to say, the rotation speed at which injection rate control is stopped can be freely selected by changing the area ratio.

In the above embodiments, the injection rate control device of the present invention has been explained as being applied to a distribution type injection pump, but the present invention is not limited to such an example of application; Needless to say, it can also be applied to control.

〔Effect of the invention〕

The first effect of the present invention is that, while making pilot injection possible at low speeds and light loads, the injection amount at high speeds and high loads can be increased to ensure high output. That is, the casing is provided with a fixed volume chamber that is essentially a closed space with a dead end, and the injection rate is controlled by opening and closing communication with the pump chamber using a valve mechanism with a limited opening amount. This is because at high speeds, the throttling effect of the valve mechanism increases and the injection amount increases.

The second effect of the present invention is that since the amount of movement of the movable valve body of the valve mechanism is extremely small, when the movable valve body is biased toward the valve closing position with something like the spring 50, This makes it possible or easy to manufacture an injection rate control device using a spring with a small spring constant.

In addition, since the amount of movement of the movable valve body of the valve mechanism is small, changes in stress applied to the spring are reduced.
Spring deterioration is prevented and the initial set load is maintained over a long period of time.

A hydraulic cylinder mechanism 136 acts as a biasing means for the movable valve body.
In the embodiment configured as above, the opening amount of the valve mechanism can be forcibly limited as the engine speed increases, so injection rate control can be forcibly stopped in the high-speed rotation range and high output can be obtained. can.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing the injection rate control device according to the first embodiment attached to an injection pump, and Fig. 2 is a sectional view showing the pump chamber pressure, valve body position, and fixed volume during one injection cycle of the first embodiment. 3 is a graph showing changes in chamber pressure and injection rate, the horizontal axis represents the crank angle, and FIG. 3 is a cross-sectional view showing the injection pump equipped with the injection rate control device according to the second embodiment,
FIG. 4 is a graph showing changes in the injection rate at various engine speeds in the second embodiment. 10,100...Injection rate control installation, 12,102
...distribution type injection pump, 20,110...pump chamber,
28,112...Casing, 32,116...Valve plate, 44,126...Movable valve body, 46,128...Fixed volume chamber, 50...Spring, 56,132,1
34...Inlet port, 62, 124...Valve mechanism, 13
6... Hydraulic cylinder mechanism, 138... Piston, 14
0...Pressure chamber.

Claims (1)

[Claims] 1. A casing, a valve seat formed in the casing and communicating with an inlet port leading to a pump chamber of a fuel injection pump, a movable valve body that opens and closes the inlet port with one end, and a movable valve body formed in the casing and communicating with an inlet port leading to a pump chamber of a fuel injection pump. a substantially dead-end closed space formed around the movable valve body in the casing and having a substantially constant volume; a fixed volume chamber that communicates with the inlet port when the valve is open and away from the seat, and in a closed state where the movable valve body is seated on the valve seat, the movable valve body The inlet port is closed by a portion other than a portion of one end, so that only the portion receives the pressure of the pump chamber, and the valve is in an open state in which the movable valve body is separated from the valve seat. Well then,
The movable valve body receives the pressure of the pump chamber at both the part and the other part of the movable valve body, and there is a small gap between the other part of the movable valve body and the valve seat. An injection rate control device for a fuel injection device, characterized in that the inlet port and the fixed volume chamber are configured to face each other at the rim and communicate with the fixed volume chamber through the gap.