JPH11200896A - Fuel injection pump - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a sudden fluctuation in the injection starting timing when a characteristic of injection pipe internal pressure fluctuates by providing a characteristic of gradually reducing acceleration in a first stage area, and setting the acceleration to zero at switching point with a second stage area in a fuel injection pump having a two-stage cam. SOLUTION: When a cam disk 4 rotates on a roller 5 since a driving shaft interlocked/rotated by an engine, a plunger 1 is reciprocated in a pluger barrel 3 while rotating. When a suction group 9 is communicated with a suction passage 10, fuel in a chamber 11 is supplied to an actuating chamber 8 to be distributed/supplied to an injection nozzle 16 through a delivery valve 13 after pressurization. In this case, cam acceleration in a first stage area is set so as to become zero at a switching point with a second stage area by forming the cam surface of a cam disk 4 as a cam profile having the first stage area to increase in a cam speed so as to become an upward projecting curve and the second stage area to rapidly increase in the cam speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a so-called two-stage having a first stage region in which a cam speed changes at a low speed in a preceding stage with respect to a cam angle, and a second stage region in which a cam speed increases in a subsequent stage. The present invention relates to a fuel injection pump including a cam, wherein a plunger is reciprocated by rotation of the two-stage cam.

[0002]

2. Description of the Related Art As a fuel injection pump of this type, a configuration disclosed in Japanese Patent Application Laid-Open No. 62-288364 (hereinafter referred to as a first prior art) has been previously proposed by the present applicant. This is a diagram in which a low-speed region (first stage region) having a constant velocity is provided at the preceding stage with respect to the cam angle, and a mountain-shaped high-speed region (second stage region) that is convex upward is provided at the subsequent stage. This publication relates to a distribution type fuel injection pump provided with a two-stage cam, which is disclosed in the publication by an Angleich mechanism of a delivery valve to advance the injection start timing at a low speed to reduce the use area of the cam to a low speed region (first region). Stage area)
It is shown that at high speed, the injection start time is delayed so that the use area of the cam is set to the high speed area (second stage area).

Here, the Angleich mechanism is configured by providing a notch in the relief valve of the delivery valve, and when the engine speed is low, the suction amount (= cross-sectional area of the relief valve × suction stroke) is reduced. By reducing it, the residual pressure in the injection pipe is increased, and the cam lift until injection is started is reduced. On the other hand, when the engine speed is high, the suction amount is increased and the The residual pressure is reduced, and the amount of cam lift until the start of injection is increased.

As described above, by using the Angleich mechanism together with the fuel injection pump having the two-stage cam, the injection rate is reduced and the knocking noise is reduced at low engine speeds, and at the same time, the injection rate is reduced at high engine speeds. The aim is to increase the horsepower to ensure the same horsepower as before.

[0005] By the way, in the above configuration,
If the rotation speed during the period fluctuates, the injection start timing also fluctuates due to the Angleich mechanism.Therefore, it has been pointed out that if the fluctuation range is wide, the control by the timer will be hindered. A configuration disclosed in Japanese Unexamined Patent Publication No. 4-27755 (hereinafter referred to as a second prior art) has been considered.

This uses the two-stage cam shown in FIG. 4 and includes the above-described Angleich mechanism in the delivery valve, as in the first prior art. An escape passage that leaks fuel into the low-pressure chamber to slow down the boosting performance is provided, thereby delaying the injection timing in the low-speed region, thereby narrowing the fluctuation range of the injection start timing that is varied by the Angleich mechanism, and at the same time, in the low-speed region. The injection rate is further reduced to reduce knock noise. A configuration in which pressurized fuel is leaked prior to such cutoff is disclosed in Japanese Patent Application Laid-Open No. 54-155.
This is a known technique disclosed in Japanese Patent Application Publication No. 016 and the like, and is known as a step spill port (SSP).

Japanese Patent Laid-Open Publication No. 5-33738 (hereinafter referred to as a third prior art) discloses a configuration in which a fuel injection pump and a throttle type injection nozzle are combined.
This fuel injection pump uses a two-stage cam having a low cam angle region (first stage region) and a cam angle region (second stage region) following which the cam speed increases, and the Angleich mechanism of the delivery valve is used. As shown in FIG. 5, the cam use region at idle is a low cam speed region (first stage region), and the cam use region at full load is a cam speed region following the low cam speed region (second stage region). In particular, the cam profile in the low cam angle region is assumed to gradually increase the cam speed as the cam angle increases, reducing knock noise during idling and rapid acceleration from no load To reduce the degree of smoke pollution.

[0008]

The step spill port that is effective in the low-speed, low-injection range can be dealt with by lowering the cam speed as well as lowering the rotation speed of the engine. As described above, this step spill port aims at slowing down the rise of fuel pressure in the injection pipe and reducing the injection rate. It is desirable that the increase in cam speed in the region be suppressed as much as possible, and at least the acceleration of the cam lift be set to zero as much as possible (the cam lift speed is constant) at least in the latter half near the end of injection when fuel starts to leak.

However, in the method of changing the use range of the cam by the Angleich mechanism as in the first to third prior arts described above, the injection end timing is not fixed even at the same low load. There is no guarantee that the effect of will be sufficiently obtained. For this reason, even if the effect of the step spill port is provided by using a two-stage cam, it has been studied to eliminate the Angleich mechanism of the delivery valve in order to make the injection end timing as stable as possible.

If the Angleich mechanism is eliminated, theoretically, the residual pressure in the injection pipe does not vary depending on the number of revolutions, so that the use start angle of the cam should be the same. As a reference, the width of the use area according to the load is set by operating the control sleeve. That is, as shown in FIG.
The injection period is short if the load is low (T1 shown in FIG. 4),
If the load is medium, it becomes longer and the cam speed changes suddenly (T2 shown in FIG. 4), and if the load is heavy, it is set longer (T3 shown in FIG. 4).

However, when the Angleich mechanism is eliminated, the fuel injection pump having the two-stage cam shown in FIG. 4 in which the first stage region has a constant speed can achieve the effect of the step spill port. For example, at the time of medium load where the speed rises suddenly from the middle, there is an unstable region of the injection amount, and even if the rotation speed is the same,
Since the residual pressure in the injection pipe is not always constant for each injection,
There is a problem that the injection start timing greatly fluctuates with the fluctuation of the injection pipe internal pressure.

That is, as shown in FIG. 6, the pressure in the injection pipe has a characteristic similar to the cam speed characteristic shown in FIG.
A region where the change gradient is very gentle (shown by equal pressure in the drawing) is formed in the preceding stage,
It has been confirmed that such a characteristic of the injection pipe internal pressure shifts upward as a whole as the rotational speed increases, even if the effective stroke is the same. For this reason, the timing when the injection pipe internal pressure coincides with the valve opening pressure and the injection is started is gradually advanced with an increase in the rotational speed (I1, I2...).
At a certain rotation speed, a region where the change gradient is gentle coincides with the valve opening pressure, and a slight change in the rotation speed causes a large change in the injection start timing (injection start angle) (indicated by I3 in the figure). For this reason, as shown by the solid line in FIG. 7, at a certain rotational speed, the injection amount suddenly increases, so that there is a problem that the adjustment cannot be completed even when the governor is used.

When the conventional two-stage cam shown in FIG. 4 is used, the internal pressure of the injection pipe gradually increases to the valve opening pressure before the valve is opened, but the cam speed is constant after the valve is opened. Therefore, the pressure of the injected fuel becomes constant, or the speed change becomes slower even if the fuel pressure increases. For this reason, as shown in FIG. 8A, a change in the injection start timing (Δθ) accompanying a change in the injection pipe internal pressure (a change in the residual pressure) for each injection.
1) has a disadvantage that it becomes larger than the fluctuation (Δθ2) of the injection pump having the characteristic shown in FIG.

If the emphasis is placed on the request for preventing the sudden change of the injection amount with respect to the fluctuation of the rotational speed and the request for reducing the fluctuation of the injection start timing due to the fluctuation of the injection pipe internal pressure, as shown in FIG. The characteristic is such that the cam speed is gradually increased so that the cam acceleration in the first stage region becomes positive without the speed region, and therefore, as shown in FIG. 9, the change gradient of the injection pipe internal pressure in the first stage region. It is required that the injection amount does not suddenly change even if the rotational speed changes, and that the fluctuation range of the injection start timing due to the fluctuation of the injection pipe internal pressure be reduced.

However, when the two-stage cam shown in FIG. 5 is used as it is, the acceleration near the cutoff becomes large, so that the above-described effect of the step spill port cannot be sufficiently exhibited.

In view of the above, the present invention satisfies the demands for preventing a sudden change in the injection amount with respect to a change in the rotational speed and reducing a change in the injection start timing due to a change in the injection pipe internal pressure.
It is another object of the present invention to provide a fuel injection pump capable of sufficiently exhibiting its function when a step spill port is provided.

[0017]

On the other hand, in order to achieve the above object, it is necessary to increase the cam speed change gradient because it is necessary to prevent a sudden change in the injection amount and to reduce the change in the injection start timing. On the other hand, the cam speed is required to be constant because the effect of the step spill port is required, and there is a problem how to balance these conflicting requirements. The present inventors have conducted intensive studies on this point, and as a result, the part where the change gradient of the cam speed is desired to be large is the part that determines the injection start timing, that is, the first part.
The part of the stage area that is on the front side of the cam angle, whereas the part that wants the cam speed to be as uniform as possible,
The cam speed is set to the first portion because the portion is near the cut angle, that is, behind the cam angle in the first stage area.
It has been concluded that it is useful to incline toward the front of the stage area and to make the inclination as gentle as possible toward the rear of the stage area to make the change gradient as zero as possible.

That is, in the fuel injection pump according to the present invention, the plunger facing the working chamber is reciprocated by the rotation of the cam, and the reciprocating movement of the plunger sucks the fuel into the working chamber and pressurizes the sucked fuel. In the above-described method, the cam has a first stage region in which the cam speed increases so as to form a convex curve with respect to the cam angle, and a second stage region in which the cam speed rapidly increases. Wherein the cam acceleration in the first stage area is continuously reduced so as to become zero at a switching point with the second stage area. 1).

Here, the cam may be an end face cam having a cam formed on a disk-shaped side surface, or may be a plate cam having a cam surface formed on a peripheral edge. The fuel injection pump is not limited to the VE type fuel injection pump, but may be a line type.

Therefore, at the time of a low load in which the beginning and end of the injection are positioned in the first stage area, the start of the injection is positioned in the portion having the gradient of the first stage area. Even when the pressure characteristics are deviated, the cam angle at which the injection is started gradually changes in the direction in which the cam angle decreases (I1 → I2 → I3...), As in FIG. Disappears. Further, the range of variation of the injection start timing due to the variation of the injection pipe internal pressure for each injection can be narrowed by having a gradient.

At the same time, the end of the injection is positioned at a portion where the cam acceleration in the first stage area is zero or close to it (the cam speed is constant or almost constant), so that a step spill port is formed. In some cases, a spill of pressurized fuel from that port can be ensured.

That is, the above-described structure forms a cut-off port in which the pressurized fuel overflows to the low-pressure side in the plunger and cuts off the injection, and controls the injection timing by adjusting the overflow timing of the pressurized fuel. In the fuel injection pump provided with the control mechanism, the plunger is further provided with a pre-leak passage which opens to the low pressure side earlier than the cutoff port and leaks the pressurized fuel to the low pressure side in the first stage region. This is useful when the amount of leakage due to the passage is set to be smaller than the overflow amount from the spill port (claim 2).

[0023]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, for example, a VE-type fuel injection pump is shown as a fuel injection pump, and a plunger 1
One end is slidably inserted into a plunger barrel 3 fixed to the housing 2, and the other end is fixed to the cam disk 4. The cam disk 4 is mounted on a roller 5 held by a roller holder, and is connected to a drive shaft that rotates in synchronization with the engine via a coupling (not shown). The cam disc 4 has a cam face 4a having cam lobes corresponding to the number of cylinders in contact with the rollers 5. Therefore, when the driving shaft is rotated by receiving driving force from the engine, the cam disc 4 is rotated. 4 is a roller 5
The plunger 1 rotates upward and reciprocates the plunger barrel 3 while rotating.

A vertical hole 6 is formed in the plunger 1 from one end inserted into the plunger barrel 3 along the axial direction. A portion protruding from the plunger barrel 3 is connected to the vertical hole 6 and is connected to the plunger 1. A cut-off port 7 is formed in the radial direction. An operating chamber 8 is formed in a closed space surrounded by one end of the plunger 1 in which the vertical hole 6 opens and the plunger barrel 3.
The plunger 1 is formed with a number of suction grooves 9 extending in the axial direction from one end facing the working chamber 8 in a number corresponding to the number of cylinders.
When the suction groove 9 communicates with the suction passage 10 formed in the housing 2 and the plunger barrel 3, fuel is supplied from the chamber 11 in the pump to the working chamber 8 via the suction passage 10 and the suction groove 9. I have.

The plunger 1 is formed with a discharge port 12 having one end connected to the vertical hole 6 and the other end opened to the outer peripheral surface covered with the plunger barrel 3. The plunger barrel 3 and the housing 2 are formed with a number of distribution passages 14, one end of which is open on the inner peripheral surface of the plunger barrel 3 and the other end of which is opened to the outside, in accordance with the number of cylinders. Thus, the discharge port 12 sequentially communicates with the distribution passage 14. For example, in the case of four cylinders, four distribution passages 14 are formed in the plunger barrel 3 at a phase interval of 90 degrees, and a delivery valve 13 is attached to the opening 15 of each distribution passage 14.
A pipe 17 leading to 6 is connected via this delivery valve 13.

The delivery valve 13 is composed of a valve having no Angleich mechanism. The relief valve shown in the first to third prior arts is not formed with an Angleich slit, but is provided with such an Angleich slit. It comprises a standard relief valve that does not have it, a well-known equalizing valve that keeps the residual pressure in the injection pipe constant, and the like.

Therefore, when the plunger 1 moves to the left in FIG.
Is supplied to the working chamber 8 through one of the suction grooves 9 at the tip of the plunger. When the plunger 1 moves rightward in FIG. 1, the suction passage 10 and the suction groove 9 are separated from each other and compressed in the pump chamber. Fuel is pumped from the discharge port 12 through the vertical hole 6 of the plunger 1 to one of the distribution passages 14, sent from the delivery valve 13 to the injection nozzle 16 via the pipe 17, and from the injection nozzle 16 into the cylinder of the engine. It is designed to inject.

A control sleeve 18 for covering the cut-off port 7 is slidably fitted to the plunger 1. The control sleeve 18 can be relatively moved in the axial direction of the plunger 1 by a governor (not shown). The more the control sleeve 18 is moved toward the plunger barrel 3, the longer the injection period and the greater the injection amount. I can do it. When the cut-off port 7 of the plunger 1 is disengaged from the side edge of the control sleeve 18 and opens to the chamber 11 during the process in which the discharge port 12 communicates with the distribution passage 14 and the pressurized fuel is pumped, the compressed fuel is released. Chamber 1
1 flows into the injection nozzle 1
In this case, the valve opening pressure falls shortly and the injection ends.

The cut-off port 7 is connected to a pre-leak passage 19. This pre-leak passage 19
Is formed, for example, to extend further from the open end of the cutoff port 17 in the axial direction of the plunger 1 by a length S. The pre-leak passage 19 is not limited to such a configuration, and is constituted by a passage formed with a phase shift in the circumferential direction separately from the cutoff port 7. Similarly, the open end covered by the control sleeve 18 is cut off. The length S in the axial direction of the plunger 1 is larger than the port 17
It may be formed as long as possible. Further, the pre-leak passage 19 may be constituted by a passage formed by shifting the axial position from the cutoff port 7.

In any structure, such a pre-leak passage 19 functions as a passage for leaking fuel at low speeds, but is formed in a shape that behaves as if it were not formed at high speeds.
A configuration in which the passage cross section of the pre-leak passage is smaller than the passage cross section of the cutoff port is useful.

FIG. 2 shows a cam speed curve and a cam acceleration curve representing the cam characteristics of the cam ring 4. The cam characteristic of the cam ring 4 is represented by a change in cam speed, as shown by a solid line, a first stage region having a gentle curve and an upward convex curve, followed by a rapid increase in speed. And a second stage area having a speed curve having the following speed curve. The speed curve of the first stage area gains a cam lift by gradually increasing the speed by making a gradient in the first half. The gradient is set to zero so that the speed becomes constant at the switching point with the second stage area.

That is, when the above-mentioned cam characteristics are viewed as a change in cam acceleration, as shown by a broken line, the curve also becomes an upwardly convex curve in the first stage region, and the first stage region in the second stage region. Following the region, the acceleration suddenly increases, and the cam profile in the first stage region is a cam profile in which the cam acceleration is gradually reduced so as to become zero at the switching point with the second stage region.

The relationship between such a cam and its use area is the same as in the case where there is no Angleich mechanism shown in FIG. 4, the use start angle is substantially constant regardless of the load, If there is, the use area of the cam is shortened and only the first stage area is used (in the drawing, indicated by T1 of θ0 to θ1). If the load is medium, the use area is somewhat longer and the cam speed changes suddenly. (Θ
If the load is high, the use area is further expanded (indicated by T3 of θ0 to θ3).

In the above configuration, since the cam speed gradually increases in the first half of the first stage area, the internal pressure of the injection pipe in that part has a large change gradient as shown in FIG. Thus, at the beginning of the injection, the injection amount does not suddenly change in the middle even if the rotation speed changes, and has a characteristic as shown by the one-dot chain line in FIG.

Further, since the change gradient of the injection pipe internal pressure is made large at the beginning of the injection, it is possible to prevent the injection start timing from fluctuating largely due to the injection pipe internal pressure (residual pressure) that can fluctuate with each injection. it can.

In particular, when the load is low, the injection ends at the rear end of the first stage area, so that the cam speed becomes almost constant (cam acceleration is almost zero) around the end of the injection. Accordingly, the suction passage 10 is separated from the suction groove 9 and the pre-leak passage 19 is disengaged from the side edge of the control sleeve 18 in the process of moving the plunger 1 rightward in FIG. When opened to the chamber 11, the compressed fuel flows out of the chamber 11 via the pre-leak passage 19. The amount of the outflow is smaller than the overflow flow rate at the time of cutoff because the cross section of the pre-leak passage 19 is formed smaller than the cross section of the cutoff port. As a result, as shown in FIG. 3, the rise in the pressure in the injection pipe is slowed down, and the time until the pressure in the injection pipe reaches the valve opening pressure, that is,
The injection start timing is delayed.

At the same time, the amount of oil supply is
Since the pressure is reduced by the amount leaked into the chamber 11 via the nozzle 9, the internal pressure of the injection pipe also decreases as shown by a broken line.
For this reason, the injection rate is smaller than in the case where the pre-leak passage 19 is not provided, so that knock noise can be reduced.

Thereafter, when the plunger 1 is further moved and the cutoff port 7 is disengaged from the side edge of the control sleeve 18 and opens into the chamber 11, the compressed fuel overflows into the chamber 11 at once, and the internal pressure of the injection pipe is opened. The pressure drops at once, and the injection ends.

On the other hand, at the time of medium load and high load operation, since the use area of the cam is expanded so as to cover the second stage area, the cam acceleration around the end of the injection becomes large, and the pre-leak passage 19 becomes large. It behaves as if it has not been formed. Therefore, the suction passage 1
In the process in which the plunger 1 is moved to the right in FIG. 1 and the fuel is compressed in the working chamber, the pre-leak passage 19 is disengaged from the side edge of the control sleeve 18 so that the plunger 1 moves to the right side in FIG. Even if opened, the compressed fuel does not leak from the pre-leak passage 19,
When the cutoff port 7 is disengaged from the side edge of the control sleeve 18 and opens into the chamber 11, the internal pressure of the injection pipe drops at a stretch, and the injection ends. For this reason, the injection rate is maintained at the same level as when the pre-leak passage 17 is not provided.

Finally, the cam characteristics in the first stage area are shown in FIG.
By providing a step spill port, the advantage of promoting a low injection rate at a low load while maintaining a high injection rate at a high load,
At the same time, it is possible to prevent a sudden change in the injection amount with respect to the above-described fluctuations in the rotational speed, and to reduce a fluctuation range of the injection start timing due to a fluctuation in the injection pipe internal pressure (residual pressure).

[0041]

As described above, according to the present invention,
In a fuel injection pump having a two-stage cam, the first
Since the acceleration is gradually reduced in the stage area and the acceleration is set to zero at the switching point with the second stage area, the beginning of the injection is positioned in the part having the velocity gradient of the first stage area. Even when the rotation speed fluctuates and the characteristics of the injection pipe internal pressure fluctuate, it is possible to prevent rapid fluctuation of the injection start timing. At the same time, it is possible to prevent the injection start timing from greatly fluctuating due to the injection pipe internal pressure that can fluctuate for each injection.

In addition, when the load is low, the end of the injection is positioned at a position where the acceleration of the first stage region is zero or in the vicinity thereof. Therefore, when the step spill port is formed, its function is fully exhibited. Therefore, the injection rate at the time of low-load operation is reliably reduced, and effects such as reduction of knock noise are obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a main part of a distribution type fuel injection pump according to the present invention.

FIG. 2 is a characteristic diagram showing a cam speed (a lift speed of a cam lift) and a cam acceleration (a lift acceleration of a cam lift) representing characteristics of the cam disk used in FIG.

FIG. 3 shows the characteristics of the injection pipe internal pressure and the injection rate of the distribution type fuel injection pump according to the present invention.
This is the characteristic when the pre-leak passage is not formed,
The broken line shows the characteristics when the pre-leak passage is formed.

FIG. 4 is a diagram showing a conventional cam characteristic, and shows a cam speed curve and a cam acceleration curve of a two-stage cam having a constant velocity portion in a first stage area.

FIG. 5 is a diagram showing a conventional cam characteristic, and shows a cam speed curve of a two-stage cam in which a first stage region is inclined.

FIG. 6 is a schematic diagram showing a change in injection pipe internal pressure when a two-stage cam having the cam characteristics shown in FIG. 4 is used, and a change in a characteristic diagram accompanying a change in rotation speed. FIG. 5 is a diagram showing a change in the injection start angle.

FIG. 7 is a characteristic diagram showing a relationship between a rotation speed and an injection amount of the injection pump having the characteristics of FIG.

FIG. 8 is an explanatory diagram showing a variation amount of an injection start angle with respect to a variation of an injection pipe internal pressure. FIG. 8A shows a case where a slope of a characteristic line of the injection pipe internal pressure with respect to a cam angle is gentle. FIG. 8B shows a case where the inclination is steep.

9 is a diagram schematically showing a change in injection pipe internal pressure when a two-stage cam having the cam characteristics shown in FIG. 5 is used. FIG. FIG. 4 is a diagram showing a change and a change of an injection start angle.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plunger 3 Plunger barrel 4 Cam disk 4a Cam surface 8 Working chamber 11 Chamber 12 Discharge port 13 Delivery valve 14 Distribution passage 16 Injection nozzle 17 Pipe

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02M 59/10 F02M 59/10 C

Claims (2)

[Claims] 1. A fuel injection pump for reciprocating a plunger facing a working chamber by rotation of a cam to draw fuel into the working chamber and pressurize and inject the sucked fuel by the reciprocating movement of the plunger. The cam has a cam profile having a first stage region in which the cam speed increases so as to form a convex curve with respect to the cam angle, and a second stage region in which the cam speed rapidly increases. A fuel injection pump, wherein the cam acceleration in the first stage area is continuously reduced so as to become zero at a switching point with the second stage area. 2. A control mechanism for forming, in the plunger, a cutoff port for overflowing pressurized fuel to a low pressure side to cut off injection, and adjusting an overflow timing of the pressurized fuel to control an injection period. Further, the plunger is provided with a pre-leak passage that opens to the low pressure side earlier than the cutoff port and leaks the pressurized fuel to the low pressure side in the first stage region. 2. The fuel injection pump according to claim 1, wherein a leak amount is smaller than an overflow amount from the spill port.