JPH0115891Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Technical Field> The present invention relates to an improvement of a fuel injection pump for a fuel injection type internal combustion engine, and more particularly to a cam mechanism that improves oil feeding performance at the end of injection.

<Background Art> There is a fuel injection pump used in a compression ignition engine such as a fuel injection internal combustion engine, such as a diesel engine, which has a pair of plungers (Technical Manual Diesel Engine, published by Nissan Motor Co., Ltd. in 1978). , and the first example shown as an embodiment of the present invention.
As shown in the figure (as far as this figure is concerned, there is no difference from the conventional one), a distribution type fuel injection pump of a type in which a plunger is pumped using two sets of inner cam rings is known.

As will be described in detail later, such a conventional fuel injection pump has a plunger 2 built into a rotary shaft 1 that rotates in synchronization with engine rotation so as to be freely slidable in the radial direction of the shaft, and is driven to rotate together with the rotary shaft 1. , slide the plunger 2 onto the cam profile of the inner cam ring 3,
The shaft is reciprocated in the radial direction by the action of the cam lift and rotating centrifugal force. By reciprocating the plunger 2, the fuel in the pump chamber 4 is sucked into the high pressure chamber 6 through the suction port 5, and from there, the fuel is delivered to each cylinder of the engine via a delivery valve (not shown) through the discharge port 7. The fuel is fed under pressure to the injection valves located at the

Here, control of the amount of oil fed is carried out by a control sleeve 8 disposed on the outer periphery of the rotary shaft 1 so as to be freely slidable in the axial direction during the pumping stroke of the plunger 2.
This is done by closing the cut-off port 10 that communicates with the high-pressure chamber 6 and opens on a part of the outer periphery of the rotary shaft 1. Fuel supply is stopped at the stage when it communicates with the pump chamber 4.

However, with such conventional fuel injection pumps,
The delivery valve, which is installed to ensure a good injection cut-off by sucking back the fuel in the injector at the end of injection, becomes a large flow path resistance to the fuel pressure and causes a loss of pressure, resulting in a loss of fuel. This has the great disadvantage of lowering the injection pressure and deteriorating the atomization characteristics and combustion characteristics of the fuel.

Therefore, fuel injection pumps have been proposed that eliminate the above-mentioned disadvantages by eliminating the delivery valve.

In such a device, when the communication hole 11 of the control sleeve 8 and the cut-off port 10 coincide with each other at the end of fuel injection, there is no delivery valve that creates flow path resistance, so the injection valve And the pressure in the injection pipe (pipe pressure pt) connecting this and the fuel injection pump will drop rapidly. This characteristic works extremely effectively to increase the injection pressure. That is, even if the injection pressure is designed to obtain a high injection pressure, the injection pressure drops rapidly at the end of injection, so that the injection cut-off is good and it is possible to suppress trailing fuel or secondary injection.

However, when looking at this rapid fall characteristic of the injection pressure in relation to the in-cylinder pressure (combustion chamber pressure) PC, it appears that the injection pressure decreases faster than the needle valve lift of the injector decreases and the valve closes, ending injection. A region M occurs in which the pipe pressure pt rapidly decreases and becomes lower than the cylinder pressure pc. That is, the phenomenon of pc>pt occurs during needle valve lift. As a result, the gas in the combustion chamber increases to the cylinder pressure.
Due to the PC, the gas flows back into the injection pipe and mixes with the fuel, and during the next injection, this gas is compressed and the injection timing is delayed or irregular, resulting in a decrease in output torque and torque fluctuations, as well as worsening combustion and reducing fuel consumption or exhaust emissions. This causes the inconvenience of worsening.

Of course, in order to eliminate this inconvenience, it is necessary to form a cam crest profile so that the cam lift of the cam crest of the inner cam lift is steep at first, and then decreases slowly when the pipe pressure pt is slightly higher than the cylinder pressure pc. It's a good thing. This is because if the power falls slowly from the beginning, the problem of fuel dripping will occur. However, even with such a cam profile, the area of the communication opening between the communication hole 11 of the control sleeve 8 and the cut-off port 10 increases rapidly, so there is a problem that delicate injection pressure control cannot be performed at the end of injection. be.

<Purpose of the invention> In view of the above, the object of the present invention is to prevent the backflow of air in the combustion chamber at the end of injection when the delivery valve is removed while smoothly forming the cam profile of the inner cam ring.

<Summary of the invention> The gist of the invention is that a rotating plunger incorporated in a rotary shaft that rotates in synchronization with engine rotation is brought into sliding contact with an inner cam ring, and the pumping action of the fuel supplied to the injection valve is achieved. In a fuel injection pump that controls the amount of fuel pumped, especially the end of injection, by cutting off the communication of the cut-off port to the pump chamber, a plurality of plungers are provided, and correspondingly, a plurality of cam ridges are formed on the inner cam ring, A control sleeve in the end-of-injection region forms a cam profile so that the cam lifts of some of these cam crests rise when the cut-off port is opened, and a plunger that follows some of the cam crests lifts the cams at the end of injection. The in-pipe pressure pt when the injection valve is open is the in-cylinder pressure pc
To provide a fuel injection pump that prevents the fuel from decreasing further than the fuel injection pump.

<Examples> Examples of the present invention will be described below based on the drawings.

FIGS. 1 and 2 show an example in which the present invention is applied to a distribution type fuel injection pump used in a four-cylinder diesel engine. In the figure, fuel is sucked in by a vane-type transfer pump 13 driven by a drive shaft 12 connected to the crankshaft of the engine, and is sent to a pump chamber 4 in the housing, and is also fed through an inflow port 14. It is supplied to the rotary shaft 1 of the plunger pump 15.

The rotary shaft 1 is rotationally driven by a drive shaft 12 in the same manner as the transfer pump 13, and when the suction port 5 coincides with and communicates with the inflow port 14 as the rotary shaft 1 rotates, the fuel in the pump chamber 3 flows through the guide hole 18. It is guided into the high pressure chamber 6.

A number of plungers 2a to 2d corresponding to the number of cylinders (four in this embodiment) are arranged in a radial direction with a high pressure chamber 6 in the center so as to reciprocate in the radial direction of the rotary shaft 1 inside the cylinders. , the plungers 2a to 2d are biased in the centrifugal direction in accordance with the rotation of the rotary shaft 1.

Further, an inner cam ring 3 is disposed on the outer periphery of the plungers 2a to 2d, and the plungers 2a to 2d are in rotational sliding contact with the inner cam profile via a roller 21. Cam profile is plunger 2a~2
It has four cam ridges 22a to 22d corresponding to the number d, and plungers 2a to 2d are attached to these cam ridges.
When the plungers 2a to 2d ride on each other, the plungers 2a to 2d are pushed in the centripetal direction against the centrifugal force, thereby pressurizing the fuel in the high pressure chamber 6.

During this pressurization stroke, the discharge port 7 of the rotary shaft 1 coincides with and communicates with the distribution port 24 of each cylinder, so that high-pressure fuel is delivered to the injection valve corresponding to each cylinder via the injection pipe without a delivery valve. and is pumped.

It should be noted that two sets of the pump section consisting of the plunger 2, the inner cam ring 3, and the high pressure chamber 6 are provided, and the diameter of the plunger of one set is made smaller.
As a result, a pilot injection is performed using a set of small-diameter plungers, and then a main injection is performed using a set of large-diameter plungers. Shortens ignition delay, performs slow combustion, reduces combustion noise, and reduces emissions of carbon, etc. in exhaust gas.

Here, the amount of fuel injected is controlled to increase or decrease by controlling the position of the control sleeve 8 and controlling the injection end timing. That is, the cut-off port 10 communicates with the high pressure chamber 6 through the guide hole 18.
has an opening edge inclined to the axis of the rotary shaft 1, and the cut-off port 10 opens in a part of the outer periphery of the rotary shaft 1 so as to be able to communicate with the pump chamber 4. A circumferentially sliding control sleeve 8 closes off the cut-off port 10. When the communication hole 11 formed through the control sleeve 8 and the cut-off port 10 coincide, the high-pressure fuel in the high-pressure chamber 6 in the pressurizing stroke passes through the cut-off port 10 and the communication hole 11 to the low-pressure side. The fuel is relieved into the pump chamber 4, and the fuel injection is completed. This injection end timing control is performed for the main injection, and is not performed for the pilot injection that is advanced.

The position of the control sleeve 8 is controlled by a cam 25 whose rotation is controlled by a torque motor 30. That is, the control sleeve 8 is freely slidable in the axial direction on the fixing pin 26, and is pressed against the cam 25 by the spring force of the spring 27. Then, the torque motor 30 is actuated via a control device (not shown) according to the engine rotational speed output from an engine operation state detection device (not shown), the amount of accelerator pedal depression, and the engine cooling water temperature, etc. The optimum axial position of 8 is controlled by the lift of cam 25. This controls the fuel injection period from when the discharge port 7 communicates with the distribution port 24 to start fuel injection until the cut-off port 10 and the communication hole 11 align and the fuel injection ends. It controls the amount of fuel injection.

Also, the timing of fuel injection is determined by the timer piston 44.
Controlled by That is, the fuel pressure in the pump chamber 4 according to the engine rotational speed is regulated by the control valve 41 and introduced into the pressure chamber 42, and the pressure in the pressure chamber 42 and the spring force of the sling 43 are balanced. The positioned timer piston 44 rotates the inner cam ring 3 via the rod 45, thereby adjusting the positions of the cam ridges 22a to 22d. As a result, as the engine speed increases, the compression timing, that is, the injection timing of the plungers 2a to 2d is advanced.
The injection timing control described above is performed only on the set of large-diameter plungers for main injection, and the inner cam ring of the set of small-diameter plungers for pilot injection is fixed.

Incidentally, the fuel in the pump chamber 4 lubricates the moving parts within the pump, and the excess fuel overflows from the return port 47 and is returned to the fuel tank or the like.

The configuration of the distribution type fuel injection pump as described above is the same as the conventional one.

In the present invention, as shown in FIGS. 2 and 3, one of the cam ridges 22a to 22d of the inner cam ring 3 is
Only one cam ridge 22d is replaced with another cam ridge 22 of equal shape.
Compared to a to 22c, the rotary shaft 1 is delayed.
The cam shape of the cam ridge 22d is raised in the fuel injection timing region where the cutoff port 10 and the communication hole 11 of the control sleeve coincide with each other as the cutoff port 10 rotates.

With this configuration, during the pressure feeding stroke of the plunger, the cutoff port 10 and the communication hole 11 of the control sleeve coincide, and the high pressure fuel in the high pressure chamber 6 is relieved to the pump chamber 4, so that the injection pressure, that is, the pressure inside the pipe pt suddenly increases. Even if an attempt is made to lower the pressure, one cam ridge 22d lifts the plunger 2d in the direction of compressing the fuel in the high pressure chamber 6, and the pressure drop rate of the pipe pressure pt becomes smaller (see Figure 4, point 1). (chain line), cylinder pressure when the injection valve is open
It cannot be lower than PC. This eliminates the risk of high-pressure gas in the combustion chamber flowing back into the injection valve, and prevents inconveniences such as a delay in injection timing due to compression of gas in the injection valve and injection pipe during the next fuel injection. The fuel injection rate characteristics of are made uniform.

In addition, by appropriately selecting the timing at which the cam lift of the cam ridge 22d at the end of injection is started, the pressure in the pipe pt is lowered all at once during fuel injection, and the cam lift of the cam ridge 22d is gradually lowered after the pressure in the cylinder approaches pc. It is also possible to reduce the internal pressure pt.

Throughout the entire injection stroke, there is no delivery valve that acts as a flow path resistance in the injection pipe that connects the fuel injection pump and the injection valve (not shown). This makes high-pressure fuel injection possible.

As a result, the spray properties become better, the air utilization rate improves, and the fuel quality improves.

In this embodiment, only one of the cam peaks is retarded relative to the others, but it goes without saying that the number of cam peaks is not critical.

In addition, in this embodiment, a four-cylinder engine has been described, but when applied to a multi-cylinder engine such as a six-cylinder engine, it is sufficient to provide the number of cam ridges and plungers corresponding to the number of injection valves; It doesn't have to be the same number.

<Effects of the invention> As described above, according to the invention, in a fuel injection pump using an inner cam ring, where it is difficult to obtain a complicated injection rate, it is possible to achieve a simple cam profile without complicating the individual cam profile of the inner cam ring. By simply creating a cam profile with a certain cam lift characteristic that rises when the cut-off port communicates with the communication hole of the control sleeve, a sudden drop in pressure in the pipe at the end of injection can be prevented and the needle valve lift can be reduced. In addition, it is possible to prevent combustion gas within the combustion chamber from flowing back into the injection valve and injection pipe. This prevents delays in the injection timing of each cycle and stabilizes the injection rate.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional view showing an example of the fuel injection pump of the present invention, Fig. 2 is a cross-sectional view taken in the direction of the arrow - Fig. 3 is a cam lift curve diagram showing the profile of the cam crest of the above, and Fig. 4 is a sectional view showing an example of the fuel injection pump of the present invention. FIG. 3 is an injection rate characteristic curve diagram comparing the above embodiment and a conventional example. DESCRIPTION OF SYMBOLS 1... Rotary shaft, 2a-2d... Plunger, 3... Inner cam ring, 4... Pump chamber, 5... Suction port, 6... High pressure chamber, 7... Discharge port, 8... Control sleeve, 10 …
...Cut-off port, 11...Communication hole, 22a~
22d...Cam mountain, 25...Cam, 30...Torque motor.

Claims (1)

[Scope of utility model registration request] A rotary shaft that rotates in synchronization with engine rotation, an inner cam ring, and a fuel pump that is incorporated into the rotary shaft and rotates and slides in sliding contact with the inner cam ring to reciprocate in the radial direction of the rotary shaft and supply fuel to the injection valve. a control sleeve that slides on the outer periphery of the rotary shaft in order to communicate with and cut off the low-pressure side and a cut-off port that is opened in a part of the outer periphery of the rotary shaft and into which the fuel pumped by the plunger is guided; In the fuel injection pump, a plurality of cam ridges of the plunger and the inner cam ring are provided so as to correspond to each other, and a cam lift of some of the cam ridges occurs when a cut-off port is opened by a control sleeve in an injection end region. A fuel injection pump for an internal combustion engine characterized by having a cam profile that stands up.