DK173815B1 - Hydraulically activated fuel pump for an internal combustion engine - Google Patents

Description

DK 173815 B1 i

The invention relates to a hydraulically actuated fuel pump for an internal combustion engine, in particular a two-stroke diesel engine, comprising a pump piston which is longitudinally displaceable in a pump cylinder and has a front end surface which together with the pump cylinder delimits a pump chamber and an actuator piston located in extension. pump plunger and is longitudinally displaceable in an actuator cylinder and has a piston surface located in a pressure chamber which faces away from the pump plunger and has a substantially larger area than the cross-sectional area of the pump plunger, where the pump plunger is loose relative to the actuator plunger and at least one fuel s flow channel a check valve opens into the pump chamber and at least one fuel outflow channel 15 leads from the pump chamber to at least one outlet port.

From the applicant's Danish patent no. 151145 a fuel pump is known, the delivery of which is controlled by turning the pump piston and where the pump piston is connected to the actuator piston. After a completed 20 delivery strokes, the pump piston can be withdrawn by the actuator piston while simultaneously refilling the pump chamber by means of a compression spring which pushes the actuator piston backwards. The pump has a complicated design with many separate parts, many of which must be machined with great precision in order for the pump piston and the actuator piston to function properly.

From an old age, a hydraulically actuated fuel pump (applicant's Danish patent no. 41046 of 1928) is known, in which fuel is used as a hydraulic fluid, 30 and in which the delivery quantity of the pump is fed from a cam controlled metering pump and in another embodiment is determined by a cam controlled control valve. which gives neither a clear starting position for the pump piston nor a unique quantity of delivery, because the camshaft drive of the control valve causes it to react differently according to the instantaneous speed of the motor, because at a higher speed of rotation it is assigned a greater amount of energy than at low rpm. The filling of the pump chamber takes place either by means of the hydraulic pressure or by suction as a result of a spring depressing the actuator piston and hence the pump piston.

From US Patent No. 3,516,395 there is known a fuel pump in which the pump filling is controlled by an electro-valve and the activation of the injection is controlled by another valve synchronized with the rotational movement of the crankshaft 10. The fuel is used as a hydraulic propellant.

For many years it has been ruled out to use the fuel on large diesel engines such as hydraulic fluid, because the properties of the fuel make it unsuitable for hydraulic purposes. The typical fuel is heavy fuel oil that requires preheating and contains aggressive and abrasive substances. In the very latest engines, liquid gas can be used as fuel, but it is also unsuitable as hydraulic fluid due to explosion risk and the risk of ice formation during cooling.

In the known hydraulic driven pumps of recent times, the fuel is kept completely separate from the hydraulic fluid and these pumps do the fuel dosing by turning the pump piston so that the location of a sloping cut-off edge is changed relative to a cut-off hole in the side cylinder of the pump cylinder. In addition to the former Danish patent, US-A-4 907 555 can be cited as an example of such pumps. The control valve for supplying high pressure hydraulic fluid can here be either cam actuated or electronically actuated. Furthermore, from the applicant's Danish patent 170121 an electronically actuated control valve is known for a hydraulically driven fuel pump, where the control valve is precise and fast operating.

The present invention has for its object to simplify the hydraulically actuated fuel pump in terms of design, operation and maintenance as well as to provide it with high reliability.

DK 173815 B1 3

To this end, the fuel pump according to the invention is characterized in that the pump cylinder and actuator cylinder are separate units which are separated by an annular spacer 5, that the actuator cylinder is an annular unit with an axially through cylinder bore, as with the actuator cylinder mounted on an upper side is in the immediate extension of a discharge port in the upper side of the distributor block, whereby the pressure chamber is radially defined by the actuator cylinder and axially defined by the piston surface of the actuator piston and the upper side of the distributor block respectively.

The two cylinders are made as independent units stacked on top of each other at the pump assembly, separated by the spacer and with relatively coarse alignment of the cylinder axes and largely without regard to whether the cylinder axes are radially displaced from each other. The lack of a requirement for very precise matching of the two cylinders provides a substantial simplification of both the manufacture of the parts and their mounting.

During the delivery stroke, the pistons are pressed against each other by the forward pressure on the piston surface of the actuator piston and during the return stroke, close relative to each other 25 is held by a relatively low force from the rearward pressure from the flowing fuel in the pump chamber. Furthermore, the two pistons can align with each other by small radial displacements of the rear end face of the pump piston relative to a forward facing end face of the actuator piston, thereby automatically compensating for temperature and pressure variations between the individual parts of the pump and this reduces wear on the pump and improves its reliability. The pistons may well be controlled to some extent in the radial direction by 35 elements located between the two pump cylinders, for example, pressure gauges may be located between the opposite end faces of the pump pistons, which provide information on the instantaneous pump chamber pressure to a electronic control unit.

The modular fuel pump with the two separate pump cylinders furthermore provides an advantageous option to replace only the actuator cylinder with associated piston with another unit, the diameter of the actuator piston being greater or smaller than the original unit, thereby changing the maximum injection pressure of the pump which depends by the pressure of the hydraulic fluid in the high pressure line and by the area ratio between the actuator piston and the pump piston.

The axially continuous cylinder bore in the actuator cylinder gives the actuator a very simple design, in that it has only two main parts, namely the annular bottomless cylinder unit and the cylindrical actuator piston. The pressure chamber of the actuator first appears at the fuel pump assembly on the upper side of the distributor block, which is included as an axially defining bottom surface in the chamber. At the same time, the upper side of the distributor block can act as a stop for the downward movement of the two pistons and thus determine their starting position. In this position, the pressure chamber is largely emptied of hydraulic fluid. Since the electronically actuated control valve is typically mounted on or in the distributor block so that there are only short channels to the outlet port in the upper side of the distributor block, the amount of hydraulic fluid between the control valve and the actuator piston is optimally small, giving the advantage that the energy consumption for pressure setting of 30 this amount of fluid is extremely low at the control valve opening for the pressure in the high pressure line at the start of a delivery stroke. At the same time, the minimization of the dead volume in the pressure chamber works to improve the fast acting property of an electronically actuated control valve as the time delay after valve activation due to the required pressure build-up becomes negligible.

DK 173815 B1 5

The design of the pump further allows the pump piston between each injection sequence to be returned to a fixed starting position of the effect of the fuel pressure on the end face of the pump piston in the pump chamber, and the delivery of the fuel pump is controlled electronically by interrupting the supply of hydraulic fluid to the pressure chamber, the pump plunger has delivered the desired quantity.

10 It provides a number of advantages to allow the fuel pre-pump pressure to return the pump piston to a fixed initial position and to control the delivery amount by interrupting the supply of hydraulic fluid precisely when the pump has delivered the required quantity. The adjustment of the 15 interrupt timing can thus be made right up to the time when the interruption actually occurs. When the amount of delivery is changed, the changed setting is immediately active and can affect the cylinder in which the injection takes place and subsequent injections on other cylinders at the same engine speed. This fast-acting, electronic control of the pump's delivery rate can produce injection sequences that can be varied, as desired, from a continuous injection to being composed of several consecutive injections, so-called intermittent injection.

The invention further provides the advantage that the known mechanical elements for mechanical return and filling as well as for controlling the quantities of delivery can be omitted, which opens up a number of freedoms in the design of the fuel pump. The commonly used fuel oil accumulators, also called shock absorbers, may also be omitted. It is further advantageous that the return to the starting position can be made over a relatively long period of time, since the injection itself takes place during a small part of the motor cycle. There is also no need for any specific turning position between the pump piston and the pump cylinder or actuator piston. The effective simplifications and the possible mechanical simplifications thereof result in a significant reduction in the risk of failure of the pump.

Furthermore, the effect can be achieved that energy losses in connection with the pump operation are minimized, partly because the pump piston and the consumption of high-pressure hydraulic fluid are stopped at the end of the fuel delivery, instead of continuing with simultaneous pressure relief of the pump chamber, as is usual with the known pumps. , partly because the fixed starting position makes it possible to minimize the dead volume in the actuator's pressure chamber and thus minimize the amount of hydraulic fluid to be pressurized immediately after the opening of the control valve.

In a preferred embodiment, the pump cylinder has a lower portion projecting into the spacer and a radially projecting upper portion 20 mounted by a cover pin. The division of the pump housing into two cylinders and an intermediate piece and the tensioning of the cover pins, i.e. longitudinal bolts, gives the advantage that the housing is relieved of the tensile stresses that arise when the pump chamber is pressurized and affects the upper wall of the chamber with an upward force. The spacer and the fixing between this and the two cylinder units can be made relatively flimsy because the spacer only has to withstand the compressive stresses from the compressive stress. The cap pins can clamp the three-piece pump housing to the upper side of the distributor block, which provides several advantages of servicing the fuel pump.

When the cover pins are tightened, the pump cylinder and associated piston can be lifted off, possibly together with the spacer, while the actuator cylinder with associated piston can be left on the distributor block. While the pump is removed, the actuator keeps the underlying hydraulic system shut off for dirt penetration. Since most of the inspections must only be carried out on the pump cylinder which is subject to the influence of the fuel, this possibility of freely lifting the pump piston and associated cylinder is a great advantage for both the maintenance and the safety of the system.

In a preferred embodiment, fully utilizing the advantages of the mutually unstable pistons, the pump piston is controlled solely in the radial direction of the associated cylinder bore of the pump cylinder, and the actuator piston is controlled exclusively in the radial direction of the cylinder bore of the associated actuator cylinder, and the two pistons. are freely adjustable in the radial direction. In this embodiment, there are a few elements, which provide easy manufacturing and high reliability.

If the fuel pump is for use in injecting liquid gas, heating the pump is not necessary. Although the pump according to the invention is considerably simplified in comparison with the known pumps for heavy fuel oil, it will be an advantage of using heavy fuel oil that preheated oil can flow through the pump even when the engine is stationary in the ready state. To achieve this, the lower section of the pump cylinder may have an annular recess, which is pressurized above and below with respect to the surrounding inside of the spacer, and a fuel supply in the wall of the spacer can lead into the annulus formed by the recess and the spacer. a discharge channel having a pressure limiting flow restriction may be in continuous communication with the annulus. The fuel thus circulates from the inlet through the annulus and out through the outlet duct, whose flow restriction prevents the pressure in the annulus from falling and the preheated fuel causes the pump cylinder to heat up in circulation.

The above advantages of being able to leave the actuator as a kind of detached skid cover over the sensitive hydraulic parts of the distributor block can be further improved by the fact that the actuator cylinder has on its upper side an upright annular wall with a larger internal diameter than the cylinder bore in the actuator cylinder, and there is at the lower end of the pump piston an upwardly closed cup-shaped screen which is spaced from the underside of the pump cylinder and projects down around the annular wall. When the cylinder and piston of the pump are lifted off, the upright wall around the actuator's cylinder bore protects against dirt particles being inserted at the top of the actuator piston, from which they could be moved out to the gap between the cylinder and piston during continued operation and causing wear and tear on the sliding surfaces. . The cup-shaped shield of the pump piston, together with the wall, provides protection against the fact that fuel is forced into the actuator piston during operation, the amount of fuel leaking down through the annular gap between the pump piston and cylinder landing on the upper side of the screen. As the screen projects down around the wall, the fuel from the top of the screen runs exclusively down to the outside of the wall, preventing the fuel from reaching the actuator piston. A fuel drain in the cavity between the actuator and the pump can prevent larger amounts of fuel from settling around the wall.

The cup-shaped screen is located in the cavity formed by the height of the spacer, and this cavity has no practical use other than to allow the screen to participate in the pump piston movements and to produce the just-mentioned separation of the fuel and hydraulic systems. The three-part structure thus allows the space to be utilized for other purposes. Since all known elements for determining the pump delivery quantity by mechanical means when turning the pump piston are replaced by volume control on the basis of a temporal control of the application of hydraulic fluid to the actuator, in practice small variations in the delivery quantity of the pumps may occur due to DK 173815 B1 9 small variations between the pumps of the hydraulic fluid delivery rate, when the control valve has connected the actuator pressure chamber with the high pressure line. It is possible to detect such differences in the delivery quantities of the pumps by continuously measuring one or more parameters of the combustor in the cylinder, and then compensate for this by the electronic activation of the control valve. An alternative to this is to utilize the available space in the cavity to configure the fuel pump such that the cup-shaped screen has downward decreasing wall thickness and that there are at least two sensors mounted in the spacer outside and on opposite sides of the screen of the pump piston. immediate position. The two opposing sensors simultaneously measure at the piston position, and the electronic control unit receiving the measurement signals can therefore compensate for the variations in the measurements at one of the sensors which may occur due to the piston's ability to adjust freely in the radial direction.

The sensors are well known and may, for example, be based on inductive measurement of the position.

An electronic control of the fuel pump delivery amount by interrupting the pump piston delivery stroke starting from a fixed, lower starting position provides an advantageous opportunity to further improve the pump's reliability as the pump cylinder has a lower section that fits pressure-tightly around the pump piston and a chamber section with a larger internal diameter than the lower section that the fuel inlet duct opens into the side wall of the chamber section and that at least two fuel outflow ducts exit from the side wall of the chamber section. From the known pumps with fuel outflow ducts and / or pressure relief holes which are opened or closed by an edge of the piston passing through the duct or the hole, it is well known that the sudden pressure changes as the passage of the control edge of the piston can cause cavitation and DK 173815 B1 10 other erosion damage to piston and cylinder. According to this preferred embodiment of the invention, to make the chamber section with a larger internal diameter than the lower pressure-sealing section, the cylinder surface of the pump piston 5 moves at a radial distance within the side wall of the chamber section. The fuel inlet and outlet ducts end or begin in the chamber wall sidewall, which means that the fuel has full access to the channel openings in the pump chamber, regardless of the piston position, with at least a fuel-filled annular area between the piston cylinder surface and chamber section sidewall.

This removes the sudden, eroding pressure fluctuations and improves the reliability of the fuel pump.

Furthermore, abrasive particles in the fuel may cause wear on the rim of the channel openings. The location of the openings at a radial distance from the cylinder surface of the pump piston prevents wear damage to the hollow rim from propagating to the piston as scratches, which provides a further improvement in operational safety.

In one embodiment, the increased diameter of the upper cylinder of the pump cylinder is utilized for a further simplification of the design of the fuel pump. In this embodiment, the fuel outflow channels are connected to upwardly discharging ports, and the flanges of the pressure lines leading to the fuel injectors are mounted on the upper side of the upper section of the pump cylinder. This facilitates mounting of the pressure lines and 30 gives these a design without tubing bends near the mounting location of the pumps. The good space on the upper side of the pump cylinder allows mounting up to four pressure lines on the upper side.

In one embodiment it is possible that the pump cylinder 35 in the area above the chamber section has a smaller diameter section constituting an upwardly closed damper chamber and that the pump piston has an upper section DK 173815 B1 11 with a height corresponding to the height of the damper chamber and an outer diameter slightly smaller than the damper chamber diameter. The damper chamber improves the reliability of the fuel pump, reducing the risk of damage to the pump in the event of failure to interrupt the high pressure of the actuator pressure chamber, for example as a result of a hanging control valve or a delay or failure of the electronic control signal to the control valve. If, as a result of such failure, the pump piston is driven all the way up to the top of the pump chamber, it continues up into the damper chamber and forms, with the side wall of this closed chamber, an annular slot through which the fuel in the damper chamber is expelled during simultaneous pressure rise in the damper chamber, slowing down the piston movement. The damper chamber thus forms a hydraulic cushion which prevents hard impact of the pump piston against the top of the chamber. The upper section of the pump piston fills approximately the same volume as the damper chamber, which gives the advantage that the total fuel volume in the pump cylinder, when the piston is in its initial position, is not substantially increased as a result of the addition of the damper chamber. Since the total fuel volume must be pressurized to the injector's opening pressure before the injection of fuel begins, an energy saving is achieved by minimizing this volume because the pump piston's path to the pressure setting becomes shorter, thereby minimizing the consumption of high pressure hydraulic fluid.

An operating advantage can be obtained by having the actuator piston near its underside have a recess and a stop mounted in the wall of the actuator cylinder protruding into the recess. The stop prevents the actuator piston from falling out of the cylinder by raising it. This effect is particularly important when dismantling the actuator after a long period of operation, where perhaps untrained personnel can make the separation without being aware that the actuator cylinder is bottomless.

An example of a preferred embodiment of the invention will now be described in more detail with reference to the schematic drawing, in which fig. 1 is a side view of a fuel pump according to the invention mounted by a cylinder in an internal combustion engine; FIG. 2 is a longitudinal section through the fuel pump of FIG.

10 and FIG. 3 the fuel pump seen from above.

A fuel pump 1 is mounted on the upper side of a distributor block 2 carried by a bracket 3. The bracket is connected to a high-pressure hydraulic fluid line 15 which is supplied with the hydraulic fluid from a pump station not shown, for example, which may be located in the range of 125 to 325 bar. The pressure may be fixed, but is preferably adjustable depending on the load of the motor. The pump station may be supplied from a hydraulic fluid storage tank, which may, for example, be a standard hydraulic oil, but it is preferred that the engine lubricating oil be used as hydraulic fluid and that the system be fed from the engine oil sump.

The internal combustion engine may be a mid-speed four-stroke engine, but is typically a slow-moving two-stroke cross-head engine which may be a propulsion engine in a ship or a stationary drive unit in a power plant.

The engine can be designed in different sizes with performance per cylinder from 400 kW to 5500 kW and with 30 rpm at full load from, for example, 200 rpm for the smallest engines down to, for example, 60 rpm for the largest engines. With specific fuel consumption ranging from typically 160 g / kWh to 185 g / kWh, the need for injected fuel per 35 full load injection sequence can range from about 6 g for the smallest engines to around 250 g for the largest. The fuel pump according to the invention is particularly useful for injecting the larger amounts, for example quantities of more than 30 g of fuel per sequence at full load.

The high pressure line from the pumping station is mounted 5 on the side of the bracket 3 which carries on its upper side the distributor block 2. From the block a pressure line 4 extends to the exhaust valve actuator. From the fuel pump 1, several, such as three, comprise pressure pipes 5 for injectors 6 which inject the fuel into the combustion chamber of a motor cylinder 7. The lower flakes 8 of the pressure pipes are bolted to the pump 1.

Each cylinder of the motor is connected to an electronic control unit 9, which receives overall synchronization, ringing and control signals through lines 10 and 15, providing electronic control signals to, inter alia, a control valve 11 through a line 12. The control unit can receive signals through a line 13 from the control valve. about the instantaneous setting of the control valve. There may be one control unit 9 per cylinder, or several cylinders 20 may be associated with the same control unit. The control unit may also receive signals for an overall control unit common to all the cylinders.

In the bracket, a branched duct 14 from the high-pressure line leads the pressurized hydraulic fluid up to a high-pressure port on the control valve 11. The duct 14 is provided with a plurality of fluid accumulators 15, which supply most of the liquid quantity when the control valve opens and is reborn from the high-pressure line while the control valve is closed. A control port on the control valve 30 is connected via a relatively short channel 16 in the distributor block to an outlet port on the upper side of the block 17. The control valve further has a tank port which is connected via a channel 18 to a return line for used hydraulic fluid. The return line pressure can range from 35 atmospheric pressure to a few bar excess pressure.

When the fuel pump is to start delivering fuel, a control signal from the control unit 9 DK 173815 B1 14 activates the control valve 11 to the position where the high pressure port is connected to the control port, so that the high pressure liquid has free access to the outlet port through the duct 16. When the pump delivery stroke is to stop, the control valve is activated. to 5 the position where the tank port is connected to the control port, whereby the high pressure in the duct 16 is drained away.

Thus, the control valve 11 has at least three gates and at least two positions. It may have a fast-acting pilot glider which, by hydraulic actuation, sets a main glider. The control valve may, for example, be of the type described in the applicant's Danish patent No. 170121.

The upper side of the fuel pump 1 is raised by means of the bracket 3 to be approximately equal to the cover 19 of the engine cylinder, so that the pressure pipes 5 have a short length, and thus an advantageously small volume to be pressed at the beginning of each injection. The fuel pump is supplied with fuel from a fuel line 20 which, by means of a pre-pump 20, distributes the fuel to the pumps at a pressure which can typically be in the range of 4 to 15 bar overpressure, typically about 8 bar overpressure. A branch line 21 leads from the fuel line to a fuel access 22 shown in FIG. 2. The pump is additionally connected to a drain line 23 which removes leakage fuel.

The fuel pump is made up of two cylinder units, namely, an actuator cylinder 24 and a pump cylinder 25, which are separated from each other by an intermediate piece 26, 30 whose underside abuts an upwardly facing ring surface on the upper side of the actuator cylinder and whose upper side abuts a downwardly facing ring surface of the pump cylinder. . The spacer is annular and substantially cylindrical and has a relatively small wall thickness that is less than half the wall thickness of the two cylinders. The intermediate piece is screwed to the two cylinders by means of small machine screws 27 to hold the three housing parts together when moving the pump.

The pump cylinder 25 has a substantially circular cylindrical lower portion 28 and an upper portion 29 having substantially greater outer diameter than the lower portion.

5 The downwardly facing ring face of the abutment 26 is formed by the underside of the radially projecting portion of the upper section and is immediately outside the lower portion 28, so that it is pressurized at its top and bottom by its cylindrical outer surface 10 with respect to the inside of the abutment. two O-rings 29 located in grooves on the outside of the lower section.

The outer section of the lower section has between these two axially spaced pressure seals a recess, which together with the inside of the intermediate part delimits a circular annular chamber 30 which communicates partly with the fuel supply 22 and partly with an outlet duct 31 leading from the annular chamber to a circulation line not shown. for preheated fuel. At the connection of the circulation line, there is a throttle member 32 with a flow restriction which limits the amount of circulating fuel.

When mounted on the upper side 17 of the distributor block, the fuel pump with the actuator cylinder 25 is positioned around the outlet port of the duct 16, and the pump cylinder is clamped to the distributor block by cover pin 33 which is passed through through holes 34 in the protruding portion of the upper section 29 of the cylinder. .

The actuator cylinder 24 is an annular unit with an axially continuous cylinder bore 35, in which an actuator piston 36 is pressure-sealing and longitudinally displaceable. The actuator piston is rotated down to a slightly smaller diameter at its lower edge, so that it has a circumferential recess 37, which includes a stop 38 in the form of the end of a screw inserted through an inclined bore through the cylinder wall. The front section of the screw DK 173815 B1 16 fits pressure-sealing into the associated bore, and in addition there is a pressure-sealing gasket under the screw head. By removing the screw, the actuator piston can be lowered by the cylinder. The underside 59 of the actuator piston, together with the cylinder bore and upper side 17, defines a pressure chamber 60 which, in the initial position shown, is substantially empty because the underside abuts the upper side 17.

A pump piston 39 is inserted longitudinally into the pump cylinder, which in a lower section 40 fits pressure-sealing around the pump piston. The lower section passes via a tapered section into an upper chamber section 41 having a larger internal diameter than the lower section 40, and at the top of the chamber section, the cylinder bore enters an upper damper chamber 42.

The actuator piston has a flat upwardly facing end face 43 perpendicular to the longitudinal axis of the actuator, and the pump piston has a downward-facing end face 44 which, in the illustrated starting position of the pistons, abuts against the end face 43. The two end faces can move freely relative to each other in the radial direction under the control forces between pump piston 39 and cylinder section 40 and between actuator piston 36 25 and cylinder bore 35. It is to be understood that the directional upward and downward directions are used for clarity and apply to the fuel pump assembly shown. Other mounting methods, such as sideways mounting on a vertical surface, are also possible. Instead, as forward directions, forward and backward or front and rear can be used, where forward and forward indicate the direction of movement of the pump piston in the active delivery stroke.

On the top of the actuator cylinder 24, inside the cavity 45, formed by the intermediate piece 26, is mounted an upright annular wall 46 which has a larger internal diameter than the cylinder bore 35. An upwardly closed cup-shaped cup is mounted on the lower end of the pump piston DK 173815 B1 17 screen 47 whose downwardly projecting sidewall 48 passes down around the outside of wall 46. The screen and wall prevent impurities such as leaked fuel and dirt particles from entering the top of the actuator piston. Instead of the mounting of the screen 47 shown in the drawing, by being raised on a tapered guide surface by means of a nut inserted into the end of the pump piston, the screen 47 may be crimped onto a cylindrical guide surface of the pump piston. A drain opening not shown near the upper side of the actuator cylinder connects the cavity 45 with the drain line 23.

The side wall 48 of the screen has a decreasing wall thickness downwards. In the intermediate piece 26, diametrically opposed 15 sides of the side wall 48 are mounted two sensors 49 which, through wires 50, give signals to the control unit 9. The signals may, for example, be a voltage, the size of which depends on the distance between the end of the sensor and the outside of the side wall 48. is oblique, the distance increases as the pump piston moves upward, and thus the sensors provide feedback to the controller regarding the instant piston position.

A fuel inlet duct 51 connects pump chamber 52 to annulus 30 through outlet duct 25 31. In the flow path between outlet duct 31 and pump chamber is a non-return valve 53 which only allows fuel to flow into the pump chamber. When the pressure in the pump chamber rises above the pre-pump pressure in the annulus 30, the check valve closes and it reopens and allows the flow of fuel at the pump pressure as soon as the pressure in the pump chamber drops again at the stop of the pump stroke delivery stroke. The non-return valve is screwed into a lateral bore 54 in the upper section 29, giving the advantage that the non-return valve does not take up space on the upper side of the pump cylinder.

Three fuel outflow ducts 55 exit from the chamber section 41 and terminate in upwardly discharging outlet ports 56 at pressure pipe connections to the injectors 6.

Each of the channels 55 is composed of a radial bore, the outer end of which is blocked by an ice-screwed element 57 and an axial bore. As seen in FIG.

3, the three radial bores and the bores 51, 54 may be evenly distributed in the circumferential direction of the cylinder. In connection with the connection of the pressure tube, a check valve can be placed in the pressure tube if desired, so that back flow of fuel to the pump chamber is prevented after the completion of the delivery stroke. Further, there may be an axial central bore 58 leading up from the top of the damper chamber 42. The bore 58 is blocked by an element 57 but may serve, if desired, for insertion of a lifting tool which can be screwed into the top of the pump piston. so that this can be lifted off together with the pump cylinder.

The pump piston has a front end face which is step-shaped with an annular, radially outer portion 61 20 and a central, radially inner portion 62 which is upwardly displaced relative to the portion 61. Thus, between the two portions, the pump piston has an upper section 63, if height corresponds to the height of the damper chamber 42 and whose outer diameter is slightly smaller than the inner diameter of the damper chamber 25.

The fuel pump works as follows. When the control valve 11 holds the pressure chamber 60 in the actuator in connection with the drain, i.e. valve valve port, the fluid pressure in the pressure chamber is low, such as 0.5 bar overpressure. In the present context, drainage means in the broad sense a drainage possibility for used hydraulic fluid. Thus, the drain is not necessarily at atmospheric pressure. The drain connected to the valve port of the valve may be pressurized to a smaller overpressure, for example the said 0.5 bar. At the same time as the chamber is connected to the drain, the check valve 53 is open and allows fuel at pre-pump pressure to flow into the pump chamber 52, for example the pressure herein is 8 bar overpressure. When the drain pressure is set to be greater than atmospheric pressure, the ratio of the actuator piston to the pump piston area must be less than the ratio of the pre-pump pressure in the pump chamber and the drain in the actuator pressure chamber so that the downward force on the pump piston exceeds the actuated force on the actuator piston. . In the illustrated embodiment, the ratio of piston areas 10 is 4: 1, while the ratio of absolute pressure values is approximately 6: 1.

As long as the control valve 11 is in the said position, the pump piston and the actuator piston are pressed downward by the pressure in the pump chamber, and they are therefore returned to the indicated starting position with the pistons abutting against each other and the underside 59 of the actuator piston abutting the upper side 17 of the distributor block.

When the control valve is actuated to connect its high pressure port to the duct 16, the pressure in the pressure chamber 60 increases suddenly to the pressure in the high pressure line, for example to 250 bar. The actuator piston is pushed forward by this pressure and drives the pump piston into the pump chamber 52, whereby the pressure rise causes the check valve 53 to close and the pressure in the pressure pipes 5 to increase. After a brief migration of the pistons, the fuel pressure in the pipes 5 reaches the opening pressure of the injectors, which can be, for example, 400 bar and the fuel injection starts.

When the control unit 9 decides that the injection 30 must be switched off and gives an activation signal for switching the control valve 11, the duct 16 is reconnected to the tank port and the pressure in the pressure chamber drops abruptly to the drainage pressure with simultaneous pressure drop in the pump chamber to the pre-pump pressure and the pump piston stops. Thereafter, the check valve 53 opens and the fuel again starts flowing into the pressure chamber, thereby pushing the pump piston and actuator piston back to the starting position, after which the process can be repeated at the subsequent injection sequence.

It is worth noting that during the return movement, the pump chamber need only be supplied with a fuel quantity corresponding to the amount injected in the previous sequence, and that injection into a two-stroke engine typically takes place during about 1/15 part of an engine revolution, after which there are 14/15 parts of the rotation to return the pistons, or to 10 to inject on other cylinders using the same pump. Even with relatively small resultant downward forces on the pistons, there is a particularly good time to return to the fixed starting position.

Of course, a variety of variations of the above embodiment can be made. For example, it is possible to perform the closed-bottom actuator cylinder by making an inlet passage for the pressure chamber in the cylinder. It is also possible to design the upper side of the actuator piston in another way, such as the step shape. The pump piston can be made without the screen when the position feedback is not desired. It is possible, but not desirable, to perform the fuel pump with housing which is traditionally capable of absorbing the tensile stresses. Furthermore, the two pump cylinders may be made in one piece without any actual cavity, the actuator's cylinder bore being able to go, for example, stepwise or tapered into the pump's cylinder bore, giving a fuel pump of 30 short length, with neither an internal wall nor an inner screen being raised. . If the pump is to supply fuel for four injectors, the flow restriction may be located in a side bore just like the check valve. Furthermore, the outlet ports 56 may be side-facing, so that the pressure pipes 5 are mounted on the side wall of the pump.

Claims (10)

A hydraulically actuated fuel pump for an internal combustion engine, in particular a two-stroke diesel engine, comprising a pump piston (39) longitudinally displaceable 5. a pump cylinder (29) and a front end surface defining together with the pump cylinder a pump chamber (52) and a an actuator piston (36) extending in extension of the pump piston and longitudinally displaceable in an actuator cylinder (24) and having a piston surface (59) located in a pressure chamber 10 which faces away from the pump piston and has a substantially larger area than the cross sectional area of the pump piston, wherein the pump piston is loose relative to the actuator piston and wherein at least one fuel inflow channel (51) with a check valve (53) 15 opens into the pump chamber and at least one fuel outlet channel (55) leads from the pump chamber to at least one outlet port, characterized in that the pump cylinder (25) and actuator cylinder (24) are separate units separated by an annular 20 spacer piece (26) that the actuator cylinder (24) is an annular unit with an axially continuous cylinder bore (35) which, with the actuator cylinder mounted on the upper side (17) of a distributor block (2), is in the immediate extension of a discharge port in the upper side of the distributor block, whereby the pressure chamber is radially defined by the actuator cylinder and axially defined by the piston surface of the actuator piston and the upper side of the distributor block, respectively. Hydraulically actuated fuel pump according to claim 30 1, characterized in that the pump cylinder has a lower section (28) protruding into the spacer and a radially projecting upper section (29) mounted by a cover pin ( 33). Hydraulically actuated fuel pump according to claim 35 1 or 2, characterized in that the pump piston (39) is guided exclusively in the radial direction by the associated cylinder bore in the pump cylinder (25), that the DK 173815 B1 actuator piston (36) is guided exclusively in the radial direction. of the cylinder bore (35) in the associated actuator cylinder and that the two pistons are freely adjustable in the radial direction. Hydraulically actuated fuel pump according to one of claims 1-3, characterized in that the lower portion (28) of the pump cylinder has an annular recess which is pressurized at the top and bottom with respect to the surrounding inside of the spacer (26). ), that a fuel supply (22) in the wall of the spacer leads to the annulus (30) formed by the recess and the spacer, and that a discharge duct (31) with a pressure-limiting flow restriction is in continuous communication with the annulus. Hydraulically actuated fuel pump according to one of claims 1-4, characterized in that the actuator cylinder (24) has on its upper side an upright annular wall (46) with a larger internal diameter than the cylinder bore in the actuator cylinder and that at the pump piston ( 39) the lower end is an upwardly closed cup-shaped shield (47) spaced from the underside of the pump cylinder and projects down around the annular wall. Hydraulically actuated fuel pump according to claim 25 5, characterized in that the cup-shaped screen (47) has a downwardly decreasing wall thickness and that there are at least two sensors (49) mounted in the spacer outside and on opposite sides of the screen of the pump piston. (39) immediate position. Hydraulically actuated fuel pump according to one of claims 1-6, characterized in that the pump cylinder has a lower section (40) which fits pressure-sealing around the pump piston (39) and a chamber section (41) with a larger internal diameter than the lower section that the fuel inlet duct (51) opens into the side wall of the chamber section and that at least two fuel outflow ducts (55) exit from the side wall of the chamber section. DK 173815 B1 Hydraulically actuated fuel pump according to claim 7, characterized in that the fuel outflow ducts (55) are connected to upward discharge ports (56) and that the flanges (8) for the pressure pipes 5 (5) leading to the fuel injectors (6) are mounted on the upper side of the pump cylinder. upper section. Hydraulically actuated fuel pump according to claim 7 or 8, characterized in that the pump cylinder (25) in the area above the chamber section (41) 10 has a smaller diameter section which forms an upwardly closed damper chamber (42) and the pump piston has a upper section (63) having a height corresponding to the height of the damper chamber and an outer diameter slightly smaller than the damper chamber diameter. Hydraulically actuated fuel pump according to one of claims 1-9, characterized in that the actuator piston (36) has a recess (37) near its underside and a stop (38) mounted in the wall of the actuator cylinder protrudes into the recess. 20