JPH05215031A - Fuel injection pump for internal combustion engine - Google Patents

Abstract

PURPOSE: To maintain a residual pressure to be lower than the injection pressure in an assured way by connecting a pump working chamber to a relief line at the end of fuel delivery, and opening the line by a pressure holding valve when the residual pressure is lower than the injection pressure in the pump working chamber. CONSTITUTION: A pump piston 14 is driven by a drive shaft 17 via a cam transmission device 16, thereby to limit a pump working chamber 21 connected to a delivering conduit 32 for generating injection pressure. An electromagnetic valve 38 is controlled by a control device 46 to open and close a fuel channel 22 connected to the pump working chamber 21. A residual pressure preventing the pump piston 14 from being lifted from the cam transmission device 16 is maintained in the pump working chamber 21. In the above-mentioned structure, the pump working chamber 21 is connected to a relief line 50 at the end of fuel delivery. When the residual pressure is lower than the injection pressure in the pump working chamber 21, the relief line 50 is opened by a pressure holding valve 52.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a fuel injection pump for an internal combustion engine of the type described in the preamble of claim 1.

[0002]

2. Description of the Related Art A fuel injection pump of the type DE394
Known from 3245A1. The fuel injection pump has a pump working chamber connected to at least one fuel delivery conduit, the pump working chamber being defined by a pump piston. The pump piston is driven by a rotating drive shaft via a cam drive at least during axial travel and thereby creates an injection pressure in the fuel delivery conduit. A fuel passage is connected to the pump working chamber, and the passage is controlled by a solenoid valve. The solenoid valve is closed at a predetermined point in the discharge stroke of the pump piston, which defines the start of high-pressure fuel delivery of the pump piston. When high pressure fuel delivery of the pump piston is complete, the solenoid valve is opened so that fuel can be discharged from the pump working chamber through the fuel passage. The closing and opening times of the solenoid valve are defined by the control device. After the end of the fuel discharge defined by the opening of the solenoid valve, the solenoid valve is closed and opened at a predetermined timing in order to maintain a residual pressure lower than the injection pressure in the pump working chamber. This residual pressure causes the pump piston to move away from the post-fuel delivery cam transmission by virtue of its inertia and the precise relationship of the pump piston to the rotational position of the drive shaft no longer occurs. The solenoid valve must then be opened and closed very quickly in an alternating manner in order to prevent the residual pressure in the pump working chamber from rising to the level of the injection pressure, which results in an undesired injection. The period during which the solenoid valve can be opened and closed alternately, however, is limited by its inertia, so that the occurrence of an excessively high residual pressure in the pump working chamber cannot be reliably avoided and thus can lead to undesired injection.

[0003]

The fuel injection pump of the present invention having the features of claim 1 has the following effects. That is, the pressure-holding valve ensures that the residual pressure in the pump working chamber is kept below the injection pressure and that the solenoid valve does not have to meet any special requirements regarding valve dynamics.

The following claims are advantageous features of the invention. With the arrangement characterized in claim 4, no additional costs are required for the vacuum passage. In the arrangement characterized in claim 5, fuel can be filled into the pump working chamber during the suction stroke of the pump piston via the fuel passage.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A fuel injection pump for an internal combustion engine, which is shown in a schematic longitudinal sectional view in FIG. 1, has a pump casing 10 in which a cylinder bush 12 is arranged. The pump piston 14, which also serves as a container, makes a reciprocating movement in the axial direction within the cylinder bore 13 as well as a rotating movement. The pump piston 14 is driven by a drive shaft 17 via a cam transmission 16. The drive shaft 17 rotates in synchronization with the rotation speed of the internal combustion engine operated by the fuel injection pump. The cam transmission 16, which is shown diagrammatically in FIG. 1, comprises a pawl clutch 17 for a torque-transmissible connection between the pump piston 14 and the drive shaft 17, in a known manner. The cam transmission device 16 further has an end face cam plate 18 connected to the pump piston 14, and the end face cam plate is pressed against a roller 20 held in a roller ring by a compression spring (not shown). This roller ring is held in the pump casing 10. The pump working chamber 21 is formed by the end surface of the pump piston 14 and the cylinder bush 12.
Are limited. The pump working chamber communicates with the inner chamber 24 of the fuel injection pump via the fuel passage 22. Fuel is delivered into the inner chamber 24 from a storage tank 28 by a delivery pump 26 driven by a drive shaft 17.

The pump piston 14 is provided with a longitudinal groove 30 starting from its end face, which corresponds to the rotational position of the pump piston 14 in the pump working chamber 21 into one of the delivery conduits 32. I can communicate. A pressure valve 33 is arranged in each delivery conduit 32, which opens the delivery conduit 32 when a predetermined pressure is reached. The delivery conduit 32 includes the cylinder bush 12 and the pump casing 1.
0 and the injection conduit 34, the injection nozzle 3 of the internal combustion engine
It leads to 6.

A fuel passage 22 having a solenoid valve 38 communicates with the inner chamber 24 from the pump working chamber 21. Solenoid valve 38
Comprises a valve closing member 40, which cooperates with a valve seat 42, which seats the cylinder bush 12
Alternatively, it can be formed into a valve body. The valve closing member 40 is operated by an electromagnet 44, which electromagnet 4 controls.
Controlled by 6. With this control device, the solenoid valve 38
Are controlled depending on operating parameters of the internal combustion engine, such as load, rotational speed, temperature, and the like. The closing and opening times of the solenoid valve 38 controlled by the control device 46 define the start and end of the high pressure delivery of fuel by the pump piston 14. The solenoid valve 38 is open when not energized, and is closed when energized.

During the suction stroke of the pump piston 14, the solenoid valve 38 is opened so that the fuel flows from the inner chamber 24 to the fuel passage 2
It can flow into the pump working chamber 21 through 2.
At a predetermined point in the discharge stroke of the pump piston 14, the solenoid valve 3
8 is closed by the current from the control device 46, so that the pump working chamber 21 is disconnected from the inner chamber 24 and a high pressure is created by the stroke movement of the pump piston 14. At a predetermined rotational position of the pump piston 14, the delivery conduit 32 communicates with the pump working chamber 21 via the vertical groove 30, and when the injection pressure is reached, the pressure valve 33 opens and the fuel is delivered to the injection nozzle 36.
The control device 46 causes the solenoid valve 38 to reopen at a predetermined point in the discharge stroke of the pump piston 14 by shutting off the current, and as a result, fuel is returned from the pump working chamber 21 through the fuel passage 22 into the inner chamber 34. High-voltage delivery ends. The amount of fuel actually discharged by the pump piston 14 under high pressure is only a part of the maximum amount of fuel that can be discharged in the entire discharge stroke of the pump piston 14. The solenoid valve 38 may be closed before the discharge stroke of the pump piston 14 is started,
In this way, the start of the discharge stroke of the pump piston 14 simultaneously starts the injection, and the solenoid valve 38 defines the end of high-pressure delivery or the end of injection by opening the fuel passage 22.
In this case, the change of the injection time point is controlled by, for example, a mechanical additional injection timing adjusting device.

In the first embodiment shown in FIG. 1, the circumferential surface of the pump piston 14 has an annular groove 48, which is connected to the longitudinal groove 30. A pressure reducing conduit 50 extends in a radial direction from the cylinder hole 13, and a pressure holding valve 52 is arranged in the pressure reducing conduit. This pressure holding valve is already designed to open at a pressure lower than the injection pressure. The arrangement of the vacuum conduit 50 and the arrangement of the annular groove 48 are coordinated with one another, in which case the connection between the pump working chamber 21 and the vacuum conduit 50 is formed before the pump piston 14 reaches top dead center. In FIG. 2a, the stroke of the pump piston 14 is shown in relation to the rotation angle of the drive shaft 17.
Immediately after the connection to the pressure reducing conduit 50 is controlled to be opened, the solenoid valve 38 is closed again by the control device 46, so that fuel can only flow out of the pump working chamber 21 via the pressure reducing conduit 50. The control of the solenoid valve 38 in relation to the rotation angle of the drive shaft 17 is shown in FIG. 2b. In this case, as shown in FIG.
The residual pressure in the pump working chamber 21 is maintained by this, and this residual pressure brakes the pump piston 14 before reaching the top dead center. This allows the pump piston 14
The end surface cam plate 18 is prevented from jumping away from the roller 20. The residual pressure may be, for example, 20-40 bar. After the pump piston 14 reaches top dead center, the solenoid valve 38 is opened again for the subsequent suction stroke.

FIG. 3 and FIG. 4 show a second embodiment of the fuel injection pump according to the present invention. The basic structure of the fuel injection pump in the second embodiment has been described in the first embodiment. The pump working chamber 121, which is restricted in the cylinder hole 113 by the pump piston 114, is
Fuel passage 122 through a connection controlled by 38
Can be connected to. This fuel passage opens into the inner chamber 124. A pressure holding valve 152 is arranged between the solenoid valve 138 and the fuel passage 122 or in the fuel passage 122, and this pressure holding valve is an electromagnetic valve when the residual pressure rises above a specified value. When the valve 138 is opened, the connection between the pump working chamber 121 and the inner chamber 124 is opened. A check valve 154 can be provided in parallel with the pressure holding valve 152. The check valve opens in the direction opposite to the pressure holding valve 152, that is, toward the pump working chamber 121.

Since the solenoid valve 138 is opened during the suction stroke of the pump piston 114, the fuel is sucked into the pump working chamber 121 from the inner chamber 124 through the fuel passage 122 and the check valve 154. At a specified point in the discharge stroke of the pump piston 114, the solenoid valve 138 is closed and the pump working chamber 121 is shut off from the inner chamber 124, so that a high pressure is generated in the pump working chamber 121. In the defined rotational position of the pump piston 114, the pump working chamber 121 is connected to one of the delivery conduits 132, the pressure valve 133 is opened when the injection pressure is reached, and the fuel is under high pressure in the internal combustion engine. Is ejected to the injection nozzle 136 provided in the. At the specified point in the discharge stroke of the pump piston 114, the solenoid valve 138 is opened again, so that the fuel flows from the pump working chamber 121 through the pressure holding valve 152 into the inner chamber 1
24, and the fuel discharge under high pressure is terminated. In this case, the check valve 154 is loaded in the closing direction by the residual pressure in the pump working chamber 121 and is therefore closed. Due to the residual pressure maintained in the pump working chamber 121, the pump piston 114 is braked before reaching top dead center. The second embodiment eliminates the need for a separate vacuum line. This is because the fuel passage 122 is used as a pressure reducing conduit. Furthermore, a separate control for closing the solenoid valve 138 again after the end of discharge is not necessary. Pump working chamber 1 via the suction conduit controlled by the pump piston during the suction stroke of the pump piston 114
When fuel is supplied to the valve 21, the valve member of the solenoid valve 138 itself can be configured as a pressure holding valve.

The pressure valve 133 serves to separate the pump working chamber 121 and the injection nozzle 136 provided in the internal combustion engine. This prevents the combustion gas from flowing into the pump working chamber 121 via the injection nozzle 136.
The pressure valve 133 has a valve member 156 which is loaded by a spring 158 in the closing direction, i.e. towards the pump working chamber 121, and is in contact with the valve seat 160. The valve member 156 may be configured as a known pressure reducing valve, and has, for example, a throttle hole 162 that is always open. The pressure valve 133 is adapted to open when the injection pressure is reached in the pump working chamber 120, in which case the valve member 158 is lifted from the valve seat 160 against the spring force of the spring 162. The residual pressure maintained in the pump working chamber 121 by the pressure holding valve 152 after the end of the discharge stroke is also applied to the injection nozzle 136 via the throttle hole 162 provided in the valve member 156 of the pressure valve 133, whereby Combustion gas is prevented from opening the injection nozzle 136 and flowing into the pump working chamber 121. The structure of the pressure valve can also be used in the fuel injection pump of the first embodiment.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a first embodiment of a fuel injection pump.

FIG. 2 is a diagram showing a stroke characteristic curve of a pump piston, a control characteristic curve of a solenoid valve, and a pressure characteristic curve in a pump work chamber in relation to a rotation angle of a drive shaft.

FIG. 3 is a partial vertical sectional view of a second embodiment of the fuel injection pump.

FIG. 4 is a diagram showing a stroke characteristic curve of a pump piston, a control characteristic curve of a solenoid valve, and a pressure characteristic curve in a pump work chamber in relation to a rotation angle of a drive shaft.

[Explanation of symbols]

10 Pump Casing, 12 Cylinder Bush, 13 Cylinder Hole, 14 Pump Piston, 16 Cam Transmission, 17 Drive Shaft, 18
End cam plate, 20 rollers, 21 pump working chamber, 22 fuel passage, 24 inner chamber, 26
Delivery pump, 28 storage tank, 30 flutes,
32 delivery conduit, 33 pressure valve, 34 injection conduit, 36 injection nozzle, 38 solenoid valve, 4
0 valve closing member, 42 valve seat, 44 electromagnet,
46 control device, 48 annular groove, 50 pressure reducing conduit, 52 pressure holding valve, 113 cylinder hole,
114 pump piston, 121 pump working chamber, 122 fuel passage, 124 inner chamber, 13
2 delivery conduit, 136 injection nozzle, 138
Solenoid valve, 152 Pressure holding valve, 154 Check valve, 156 Valve member, 158 Spring, 16
0 valve seat, 162 throttling hole

Claims (6)

[Claims] 1. A fuel injection pump for an internal combustion engine, wherein a pump working chamber (21; 121) connectable to at least one delivery conduit (32; 132) and a pump piston (14; 114),
The pump piston is caused to move at least axially by means of a rotating drive shaft (17) via a cam transmission (16), which movement causes a pump working chamber (2).
1; 121) to form an injection pressure, and has a fuel passage (22; 122) connectable to a pump working chamber (21; 121), the fuel passage (22;
122) for controlling the discharge of the pump piston (14; 114) by opening the fuel passage during the discharge stroke of the pump piston (14; 114). A pump from the cam transmission (16), which has a control device (46) for controlling the valve (38; 138) and is below the injection pressure after the end of delivery into the pump working chamber (21; 121). Piston (14;
In the type in which the residual pressure that prevents the lifting of 114) is maintained, the pump working chamber (21; 121) is connected to the depressurizing passage (50; 122) within the range of the end of the delivery. And a pressure holding valve (52; 152) is arranged in the pressure reducing passage, and the pressure holding valve passes through the pressure reducing passage (50; 122) in the pump working chamber (21;
121) A fuel injection pump for an internal combustion engine, characterized in that it opens at a residual pressure lower than the injection pressure in 121). 2. The solenoid valve (38) is adapted to be closed again after the delivery has been completed, the pump piston (14) being guided in a cylinder bore (13) and the pump in the cylinder bore (13). 2. The fuel injection pump according to claim 1, wherein the connection between the pump working chamber (21) and the pressure reducing passage (50) is opened before the piston (14) reaches the top dead center of the pump piston. 3. A pump working chamber (21) and a pressure reducing passage (5)
Fuel injection pump according to claim 1, characterized in that the connection with (0) is opened before the solenoid valve (38) is closed again after the delivery has ended. 4. A fuel passage (122) is used as a pressure reducing passage, and a solenoid valve (138) is provided in the pump working chamber (12).
2. The fuel injection pump according to claim 1, which is arranged between 1) and the pressure holding valve (152). 5. The pump working chamber (121) is filled with fuel during the suction stroke of the pump piston (114), parallel to the pressure holding valve (152).
Check valve (15) that opens toward the pump working chamber (121)
4. The fuel injection pump according to claim 4, wherein 4) is arranged. 6. A pressure valve (33; 133) is arranged in the discharge conduit (32; 132), which opens when the injection pressure is reached, the pressure valve having a constantly open throttle point (162). The fuel injection pump according to any one of claims 1 to 5.