JPH01280672A - Fuel injection pump - Google Patents

Abstract

PURPOSE:To decrease an amount of air bubbles generated in fuel due to a negative pressure, by a method wherein the edge on the delivery port side of a suction port opened to the inner peripheral surface of a cylinder is positioned further rearwardly than the maximum advance position of the tip surface of a plunger contained forward and backward movably in a cylinder. CONSTITUTION:When an engine is started and rotation of a crank wheel 6 is transmitted to a drive shaft 5, a plunger 11 is moved forward and backward through a cam mechanism formed with a roller 17 and a disc cam 13. Along with backward movement of the plunger 11, a pressure in a cylinder 12 is reduced. In this case, a suction port 22 is released before the plunger 11 is moved backward to an intermediate position between a maximum advance position and a maximum reversing position, and fuel is sucked in the cylinder 11 through the working of a valve device 24. Meanwhile, along with forward movement of the plunger 11, a pressure in the cylinder 12 is increased, and fuel is delivered through the delivery port of a delivery valve device 31. This constitution causes suction of fuel before a negative pressure in the cylinder 12 is reduced to a low value, and suppresses the generation of air bubbles in fuel.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fuel injection pump used, for example, in high-speed diesel engines.

[Conventional technology]

A fuel injection pump used in a diesel engine is a plunger pump in which a plunger is held in a cylinder so that it can move forward and backward, and when the plunger moves back, the fuel is sucked in from the suction port, and when the plunger moves forward, it pressurizes and discharges it. It is composed of By the way, conventionally, in this type of fuel injection pump, there are those in which the suction port is opened facing the top surface of the plunger, and those in which the suction port is opened in the inner circumferential surface of the cylinder. In the former case, a check valve device is provided in the suction passage connected to the suction port, and in the latter case, the desired discharge pressure can be obtained by opening the suction port close to the maximum retracted position of the plunger. I have to.

[Problem to be solved by the invention]

However, in the former case, the maximum pressure of the fuel injection pump acts on the suction side as well, and the check valve device and seal structure must be configured to withstand the maximum pressure, so a strong pressure-resistant structure is required. There was a problem that required . on the other hand,
In the latter case, when the plunger retreats, the pressure inside the cylinder is reduced to negative pressure. As a result, many air bubbles are generated before the plunger approaches its maximum retracted position, which reduces the amount of fuel that can be sucked in. Also, when air bubbles get mixed into the fuel, it becomes difficult to function as a high-pressure pump. There was also the problem that the operating efficiency deteriorated due to the significant decrease in the amount of energy. The present invention has been made in view of these circumstances, and it is an object of the present invention to provide a fuel injection pump that can eliminate the need for a strong pressure-resistant structure while suppressing deterioration in operating efficiency.

[Means to solve the problem]

The fuel injection pump according to the present invention has a discharge port opening opposite to the plunger tip surface, and a suction port opening in the inner circumferential surface of the cylinder. It is positioned slightly behind the forward position.

[Effect]

In the present invention, when the plunger retreats, the pressure inside the cylinder is reduced, but before the plunger retreats that much, the suction port is opened and fuel is sucked in.

When the plunger moves forward, the pressure inside the cylinder increases, and after the plunger closes the suction port, it reaches the maximum pressure.
Fuel is discharged from the discharge port.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing the main parts of a fuel injection pump according to the present invention, FIG. 2 is a longitudinal sectional view showing the whole, and FIG. 3 is a -
■It is a line sectional view. In Figures 2 and 3, the reference numeral 1 indicates a fuel injection pump, and the trochoid pump 2 has a low discharge pressure (approximately 3 kg/cJ), and the trochoid pump 2 has a high discharge pressure (150 to 600 kg/cJ). ) is configured in combination with a plunger pump 3. Reference numeral 4 denotes a casing having a hollow chamber opened to the front, and a drive shaft 5 is rotatably supported with its front end facing into the hollow chamber and its rear end protruding outside. The protruding end of the drive shaft 5 and the crankshaft 6 of the engine are connected by a power transmission member such as a gear. Here, the number of teeth of the power transmission member is set so as to reduce the rotation of the crankshaft 6 by half. 7 is a cover that closes the opening of the casing 4, and 8 is a partition plate that is screwed onto the inner circumferential surface of the casing and defines a hollow chamber from front to rear. The trochoid pump 2 is housed in a rear chamber defined by the partition plate 8. Reference numeral 9 denotes a suction passage provided in the casing 4, and although not shown, a discharge port is opened in the partition plate 8 through which fuel pressurized by the trochoid pump 2 is discharged to the front side of the hollow chamber.

A plunger 11 is held by a cylinder 12 fixed to the cover 7 so as to be slidable in the axial direction. A disc cam 13 is connected to the rear end of the plunger 11, and is always urged rearward by a plunger spring 14. A cam is formed along the circumferential direction on the rear surface of the disk cam 13 and is engaged with a roller to be described later and moves in the front-rear direction.

A claw 13a that engages with a concave portion 5a provided on the outer periphery of the drive shaft 5 is integrally provided on the inside of this cam, and the disc cam 13 and the drive shaft 5 are coaxially connected at the center thereof. Shaft part 13
b is provided. Reference numeral 15 denotes a holding cylinder rotatably interposed between the disc cam 13 and the partition plate 8. Four support shafts 16 extending in the radial direction are mounted on the holding cylinder 15 at equal intervals in the circumferential direction. Engaging roller 17
is rotatably supported. Reference numeral 18 indicates a worm gear integrally provided on the lower outer circumferential surface of the holding cylinder 15 within a range of approximately 90 degrees, and 19 indicates a worm that meshes with the worm gear 18. 21 is a motor that rotates the worm 19. Therefore, the holding cylinder 15 is held in a state where its rotation is restricted by the engagement between the worm gear 18 and the worm 19, and when the drive shaft 5 rotates, the plunger 11 moves forward and backward due to the engagement between the roller 17 and the disk cam 13. By rotating the holding cylinder 15 with the motor 21 via the worm 19, the position of the roller 17 is shifted in the circumferential direction with respect to the cam of the disc cam 13, and the timing when the plunger 11 advances and retreats is determined by rotating the crankshaft 6. It can be shifted relative to the rotation angle.

22 is a suction port for supplying fuel into the cylinder 12. This suction port 22 is opened on the inner peripheral surface of the cylinder 12 and is opened and closed by moving the plunger 11 back and forth.

Here, as shown in FIG. 1, the opening position of the suction port 22 is such that the edge on the discharge port side, which will be described later, is positioned slightly rearward of the maximum forward position A of the plunger tip surface. ing. To be more specific, in this embodiment, the suction port 22 has the tip surface of the plunger 11 at the maximum forward position A.
When the distal end surface is in the vicinity, it is closed, and when the distal end surface is at an intermediate position C between the maximum forward position A and the maximum retracted position B, at least a portion on the maximum forward position A side is opened. A suction passage 23 is connected to the suction port 22 and communicates the inside of the cylinder 12 with the hollow chamber of the casing 4. 24 is a suction valve device provided in the middle of this suction passage 23. This suction valve device 24 includes a suction valve body 25 made of a steel ball, a suction valve seat 26 provided on the hollow chamber side of the suction valve body 25, and a biasing force for the suction valve body 25 toward the suction valve seat 26. It is a check valve device consisting of a compression spring 27 that
It opens only when the pressure in the cylinder 12 becomes lower than the pressure in the upstream casing 4, and is closed otherwise. 28 is a blind plug that fixes the suction valve seat 26.

31 is a discharge valve device disposed in front of the plunger 11. This discharge valve device 31 is fixed in front of the plunger 11 with a nut 32, and includes a main body 34 having a discharge port 33 that opens opposite to the distal end surface of the plunger 11, and
4, a discharge valve body 36 inserted into this discharge pipe 35, a discharge valve seat 37 arranged on the plunger side of this discharge valve body 36, and a discharge valve body 36 that is constantly This is a check valve device consisting of a compression spring 38 that biases toward the discharge valve seat 37, and is provided in the discharge passage 39.

Although not shown, a fuel injection valve is connected to the downstream side of the discharge passage 39.

Reference numeral 41 denotes a control device for controlling the motor 21. This control device 41 receives a signal corresponding to the engine rotation speed output from the engine rotation speed detector 42 and the motor 2.
The motor 21 is controlled by a signal corresponding to the rotation angle of the motor shaft output from the potentiometer 43 provided in the motor 21.
It controls the rotation of. By the way, if the motor 21 is driven to rotate the holding cylinder 15, the timing of the forward and backward movements of the plunger 11 will be shifted from the crankshaft rotation angle, and accordingly the discharge pressure will be adjusted to a certain crankshaft rotation angle. can be varied within a wide range. The control device 41 utilizes such an effect to control the discharge pressure of the fuel injection pump 1 at the fuel injection timing so that it is low in the low engine speed range and increases as the engine speed increases. .

In the fuel injection pump configured in this manner, when the engine is started, the rotation of the crankshaft 6 is transmitted to the drive shaft 5, so that the plunger 11 is rotated by the cam mechanism of the roller 17 and the disk cam 13. Advance and retreat. Plunger 1
When the cylinder 1 retreats, the pressure inside the cylinder 12 is reduced, but before the plunger 11 retreats to the intermediate position C between the maximum forward position A and the maximum retreat position B, the suction port 22 is opened and fuel is sucked into the valve device 24. can be sucked into the cylinder 12 via. When the plunger 11 moves forward, the pressure inside the cylinder 12 is increased and the plunger 11
After closing, the maximum pressure can be reached and fuel can be discharged from the discharge port 33.

Therefore, in the stroke of the plunger 11 retreating,
The volume of the cylinder 12 that becomes negative pressure is small, and fuel can be sucked while the negative pressure is small. In other words, it is possible to reduce the influence of negative pressure on the fuel during fuel suction, thereby reducing the amount of bubbles generated in the fuel. In addition, during the forward movement of the plunger 11, when the pressure in the cylinder 12 is low, the suction valve device 24 prevents the pressure from escaping, and after the pressure increases, the plunger 11 itself can prevent the pressure from escaping, so the suction passage It is possible to prevent large pressure from acting on 23.

〔Effect of the invention〕

As explained above, according to the present invention, the discharge port is opened to face the plunger tip surface, and the suction port is opened to the inner circumferential surface of the cylinder, and the edge of the suction port on the discharge port side is connected to the plunger tip surface. Since the plunger is positioned slightly behind the maximum forward position of the plunger, when the plunger moves back, the suction port is opened and fuel is sucked in before the plunger moves back that far, and when the plunger moves forward, the pressure inside the cylinder increases and the plunger moves forward. After the suction port is closed, the maximum pressure can be reached and fuel can be discharged from the discharge port.

Therefore, the influence of negative pressure on the fuel can be reduced, reducing the amount of bubbles generated in the fuel, and the plunger can prevent large pressure from acting on the suction passage, which would reduce operating efficiency. It is possible to eliminate the need for a strong pressure-resistant structure while suppressing the

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the main parts of a fuel injection pump according to the present invention, FIG. 2 is a longitudinal sectional view showing the whole, and FIG.
It is a sectional view taken along the line -■. 3...Plunger pump, 11...Plunger, 12...Cylinder, 22...Suction port, 23...
...Suction passage, 24...Suction valve device, 31...
・Discharge valve device.

Claims (1)

[Claims] In a fuel injection pump that communicates the interior of a cylinder that holds a plunger so that it can move forward and backward with a suction passage and a discharge passage each equipped with a check valve device, the discharge port is opened opposite to the tip surface of the plunger, and the suction port is connected to the cylinder. A fuel injection pump having an opening on the inner circumferential surface and having the edge of the suction port on the discharge port side positioned slightly rearward of the maximum forward position of the plunger tip surface.