JPS6036779Y2 - Suction-back piston device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a suction piston device for a jerk-type fuel injection pump for an internal combustion engine.

A conventional suction/return piston device disclosed in Utility Model Registration No. 1318395 is shown in FIG.

In the figure, 1 is the pump body, 2 is the plunger, 3 is the plunger barrel, 4 is the discharge valve hardware, 5 is the discharge valve, 6 is the discharge valve spring, 7 is the discharge valve hardware holder, 8 is the pump oil supply chamber, 9
1 is an oil supply hole, and 10 is an oil drain hole.

111 is a suction piston, 112 is a suction throttle passage, 1
13 is a spring, and 114 is a spring receiver, which are fixed to the opening of the piston chamber 115 on the plunger chamber 31 side.

The piston 111 is slidably housed in a piston chamber 115.

The throttle passage 112 opens into the discharge valve chamber 71 .

The piston 111 is pressed toward the throttle passage 112 by a spring 113.

The operation starts with the plunger 2 first in the lower position (the upper surface of the plunger 2 is below the oil supply and oil drain holes 9 and 10), and as time passes, it is pushed up by a cam (not shown), and the oil supply and oil drain holes are pushed up. When the oil holes 9 and 10 are closed and the pressure in the plunger chamber 31 rises to overcome the force of the spring 6 pressing down on the discharge valve 5, the discharge valve 5 is pushed up and the fuel oil flows from the plunger chamber 31 to the discharge valve chamber 71. Outflow and further passage 10
1 and an injection pipe (not shown), the fuel is injected from a fuel injection valve (not shown) into a cylinder (not shown) of the engine, and is combusted.

When plunger 2 further rises, plunger lead 2
1 opens into the oil drain hole 10, the plunger chamber 31
The high-pressure fuel oil inside is discharged into the oil supply chamber 8 through the oil drain hole 10, the pressure in the plunger chamber 31 decreases, and the discharge valve 5 is pushed down by the spring 6 and the pressure in the discharge valve chamber 71. Take a seat.

At this time, the number of collars 51 provided on the discharge valve 5 is smaller than that of a normal discharge valve, and it is expected that only an improvement in the sharpness of the injection will be achieved.

After that, the pressure in the plunger chamber 31 further decreases, and when the pressure difference with the discharge valve chamber 71 becomes greater than the spring force of the spring 113, the piston 111 moves and performs a suction action, replenishing the high pressure that was previously sent to the nozzle side. It works by catching waves that return to the pump side and converting them into low pressure waves when they return to the nozzle side, thereby preventing secondary injection.

At this time, the diaphragm 112 appropriately controls the movement of the piston 111 and controls how the pressure waves are received.

However, the above device has drawbacks.

As the injection pressure increases, the pressure waves that return to the pump side after the end of discharge also increase, so it is necessary to make the throttle 112 relatively large in diameter and move the piston sufficiently quickly to change the pressure waves to low ones.

For this reason, it is necessary to increase the stroke of the piston 111, but the spring 11 must be moved in a limited space.
3 stress becomes severe.

The purpose of the present invention is to focus on the above-mentioned points, and to provide a suction piston device that can secure sufficient suction action and enable high-pressure injection while suppressing the stress of the spring of the suction piston within a safe range. The feature is that in the conventional suction-return piston device, a side passage is provided in the suction-return piston chamber through which the discharge valve chamber and the plunger chamber are communicated via a throttle passage by the stroke of the suction-return piston. That's true.

Embodiments of the present invention will be described below with reference to the drawings.

2 is a sectional view showing the main parts of a fuel injection pump equipped with a suction piston device according to an embodiment of the present invention; FIG. 3 is an enlarged sectional view showing the suction piston device of FIG. 2; 4
The figure is a sectional view taken along line IV-IV in FIG. 3.

In the figure, 116 is a side passage, and the suction and return piston chamber 115
A vertical groove is formed on the inner circumferential surface of the

The suction-return piston chamber 115 serves as a guide for the suction-return piston 111 throughout its entire stroke, similar to the conventional one.

The upper end of the side passage 116, that is, the end on the discharge valve chamber 71 side, is connected to the plunger chamber 3 from the end surface of the piston chamber 115 on the discharge valve chamber side.
The length of the side passage 116 is L.
is formed to be larger than the length h of the piston 111.

Therefore, when the piston 111 makes a sufficient stroke, the discharge valve chamber 71 and the plunger chamber 31 communicate with each other via the throttle passage 112.

The rest is the same as the conventional one, and the same parts are indicated by the same symbols.

The operation in the case of the above configuration will be described.

The process is the same as the conventional one until the discharge valve 5 closes at the end of discharge.

Thereafter, the pressure wave returning from the nozzle to the pump side is stopped by the piston 111 descending.

When the piston 111 descends to a certain extent, the side passage 116 opens, and the piston 111 no longer descends, but this side passage 116 opens.
Therefore, the discharge valve chamber 71 and the plunger chamber 31 are connected to the throttle passage 1.
12, the pressure waves returned from the nozzle are appropriately blocked by the size of the throttle passage 112.

Moreover, it differs from conventional ones in that it can maintain this state as long as high pressure waves are returned.

On the other hand, regarding the initial stroke of the piston 111, as in the conventional piston, when the pressure in the discharge valve chamber 71 decreases, it increases again, and the function of preventing the pressure from decreasing too much is maintained.

The above case has the following effects.

Injecting fuel at high pressure to atomize it is very effective in improving engine combustion, but when injecting at high pressure, a high pressure wave returns from the nozzle side to the pump side at the end of pump discharge. However, in order to stop this, the throttle passage 1
It is necessary to make the piston a relatively large diameter and move the piston quickly to generate a low pressure wave, but with this invention, even if the piston stroke is within the allowable limit of the spring stress, the pressure wave will not return. Since this can be stopped as long as the fuel is injected, high-pressure injection becomes easy.

In addition, the initial stroke of the piston 111 rises again as in the conventional piston 111, thereby preventing the pressure from dropping too much, especially at low loads.

That is, in terms of operating points, at high speeds and high loads where the injection pressure is high, the piston 111 descends until the side passages 116 open and provides sufficient suction, and at low rotation speeds and low loads, the side passages 116 do not open, and the piston 111 does not open as before. Similar to the above, it prevents pressure from dropping too much and prevents cavitation and irregular injection.

In this way, high-pressure injection is possible, and improved combustion results in low fuel consumption and low pollution for the engine.

[Brief explanation of the drawing]

Figure 1a is a sectional view showing the main parts of a conventional fuel injection pump;
FIG. 1 is an enlarged cross-sectional view of the suction-return piston device shown in FIG. ,
3 is an enlarged sectional view of the suction/return piston device shown in FIG. 2, and FIG. 4 is a sectional view taken along line IV--IV in FIG. 3. 1...Fuel injection pump body, 31...
Plunger chamber, 71...Discharge valve chamber, 111...
... Suction and return piston, 112 ... Throttle passage, 113 ... Spring, 115 ... Suction and return piston chamber, 116 ... Side passage.

Claims (1)

[Scope of utility model registration request] The discharge valve chamber and the plunger chamber of the jerk type fuel injection pump communicate with each other through a passage that opens into the discharge valve chamber and a suction piston chamber that is connected to the passage and opens into the plunger chamber, and the suction piston A suction piston is slidably built into the chamber and is pressed by a spring toward a passage opening into the discharge valve chamber, and a throttle restricts the movement of the suction piston through the passage opening into the discharge valve chamber. In the suction piston device formed in the passage, a groove is provided in the vertical direction on the inner circumferential surface of the suction piston chamber, and the end on the discharge valve chamber side is connected to the end surface of the suction piston chamber on the discharge valve chamber side. a side passage that is shifted toward the plunger chamber and has a length greater than the length of the suction-return piston so that the discharge valve chamber and the plunger chamber communicate with each other via the throttle passage through the stroke of the suction-return piston; A suction-return piston device characterized by: