DE10259955A1 - Fuel injection device for an internal combustion engine - Google Patents

Abstract

The fuel injection device has a high-pressure fuel pump (10) and a fuel injection valve (12) connected to it for each cylinder of the internal combustion engine. The high pressure fuel pump (10) has a pump piston (18) which is tightly guided in a cylinder bore (16) and which delimits a pump working chamber (22) in the cylinder bore (16) which is connected to the fuel injection valve (12). The pump piston (18) is driven by a cam drive (20, 21, 23) of the internal combustion engine in one stroke. The pump piston (18) has a plurality of micro-depressions (80) at least in a partial area of its surface which is tightly guided in the cylinder bore (16).

Description

State of technology

The invention is based on one Fuel injector for an internal combustion engine according to the preamble of claim 1.

Such a fuel injector is due to the EP 0 987 431 A known. This fuel injection device each has a high-pressure fuel pump and a fuel injection valve connected to it for each cylinder of the internal combustion engine. The high-pressure fuel pump has a pump piston which is tightly guided in a cylinder bore and which delimits a pump work space in the cylinder bore and is connected to the fuel injection valve. The pump piston is driven by a cam drive of the internal combustion engine in one stroke. The cam drive also causes transverse forces on the pump piston, which, due to insufficient lubrication of the pump piston, can lead to seizure and therefore heavy wear on the pump piston and the cylinder bore. As a result, the function of the fuel injection device is impaired, since the pump working chamber can no longer be reliably sealed by the pump piston and fuel can escape from the pump working chamber.

The fuel injection device according to the invention with the features according to claim 1 has in contrast the advantage that the lubrication of the pump piston through the microwells is improved and thus increased wear resistance of the pump piston and the cylinder bore is reached.

In the dependent claims are advantageous refinements and developments of the fuel injection device according to the invention specified. The microwells of the pump piston also reduces the leakage of fuel from the pump work space, causing a thinning of the lubricating oil the internal combustion engine in an oil-lubricated according to claim 2 Cam drive can be reduced. By training according to claim 7 can wear resistance of the pump piston can be further improved.

An embodiment of the invention is shown in the drawing and explained in more detail in the following description. Show it 1 sections of an internal combustion engine with a fuel injection device in a schematic representation, 2 detail of the surface of a pump piston of the fuel injection device in an enlarged view according to a first embodiment, 3 the pump piston surface according to a second embodiment, 4 the pump piston surface according to a third embodiment and 5 the pump piston surface according to a fourth embodiment.

description of the embodiments

In 1 A section of an internal combustion engine of a motor vehicle is shown, only part of a cylinder of the internal combustion engine being shown. The internal combustion engine is preferably a self-igniting internal combustion engine and has one or more cylinders. For each cylinder of the internal combustion engine, a fuel injection device is provided, which is preferably designed as a so-called pump-nozzle unit and which has a high-pressure fuel pump for each cylinder of the internal combustion engine 10 and a fuel injector connected to it 12 has, which form a common structural unit. Alternatively, the fuel injection device can also be designed as a so-called pump-line-nozzle system, in which the high-pressure fuel pump and the fuel injection valve of each cylinder are arranged separately from one another and are connected to one another via a line. The high pressure fuel pump 10 has a pump body 14 with a cylinder bore 16 on, in which a pump piston 18 is tightly guided. The pump piston 18 is at least indirectly through a cam 20 a camshaft 21 the internal combustion engine against the force of a return spring 19 is driven in one stroke. Between the cams 20 and the pump piston 18 can, for example, a rocker arm 23 be arranged on the one hand on the cam 20 expires and on the other hand at least indirectly on the pump piston 18 attacks. The pump piston 18 limited in the cylinder bore 16 a pump work room 22 , in the delivery stroke of the pump piston 18 Fuel is compressed under high pressure. The pump work room 22 becomes fuel from a fuel tank 24 of the motor vehicle supplied, for example by means of a feed pump 25 ,

The fuel injector 12 has one with the pump body 14 connected valve body 26 on, which can be formed in several parts, and in which at least one injection valve member 28 in a hole 30 is guided longitudinally. The valve body 26 has at least one, preferably a plurality of injection openings at its end region facing the combustion chamber of the cylinder of the internal combustion engine 32 on. The injector member 28 has, for example, an approximately conical sealing surface on its end region facing the combustion chamber 34 on that with one in the valve body 26 in its valve seat formed end region facing the combustion chamber 36 cooperates, from or after which the injection openings 32 dissipate. In the valve body 26 is between the injection valve member 28 and the bore 30 to the valve seat 36 towards an annulus 38 present in its the valve seat 36 end area facing away from the radial expansion of the hole 30 in one the injector member 28 surrounding pressure chamber 40 transforms. The injector member 28 points to the level of the pressure chamber 40 by reducing the cross-section, a pressure shoulder 92 on. At the end of the injection valve member facing away from the combustion chamber 28 grips a preloaded closing spring 44 through which the injector member 28 to the valve seat 36 is pressed down. The closing spring 44 is in a spring chamber 46 of the valve body 26 arranged, which is attached to the bore 30 followed. It can be provided that the first injection valve member 28 of the fuel injector 12 is hollow and a second injection valve member is slidably guided therein, through which at least one second injection opening is controlled.

To the spring chamber 46 can of which the bore 30 opposite end in the valve body 26 another hole 48 connect in the control spool 50 is tightly guided with the injection valve member 28 connected is. The hole 48 is smaller in diameter than the spring chamber 46 , The control piston 50 is about a piston rod smaller in diameter than this 51 with the injection valve member 28 connected. The control piston 50 can be made in one piece with the injection valve member 28 be formed, but is preferably for reasons of assembly as a separate part with the injection valve member 28 connected.

From the pump work room 22 leads through the pump body 14 and the valve body 26 a channel 60 to the pressure room 40 of the fuel injector 12 , From the pump work room 22 or from the channel 60 runs a channel 62 to the control pressure room 52 , In the control pressure room 52 A channel also opens 64 , which forms a connection to a relief area, than the at least indirectly the fuel tank 24 or serve another area where there is little pressure. From the pump work room 22 or from the channel 60 makes a connection 66 to a relief area 24 than the at least indirectly the fuel tank 24 can serve by a first electrically operated control valve 68 is controlled. The control valve 68 can like in 1 shown to be designed as a 2/2-way valve.

The connection 64 the control pressure chamber 52 with the relief area 24 is operated by a second electrically operated control valve 70 controlled, which can be designed as a 2/2-way valve. In connection 62 the control pressure chamber 52 with the pump work room 22 is a throttling point 63 provided and in the connection of the control pressure chamber 52 with the relief room 24 is a throttling point 65 intended. By appropriate dimensioning of the throttling points 63 . 65 can the inflow of fuel from the pump work space 22 in the control pressure room 52 and the outflow of fuel from the control pressure chamber 52 to the extent necessary. Adequate inflow of fuel into the control pressure chamber 52 is for a quick closing of the fuel injector 12 required and a sufficient outflow of fuel from the control pressure chamber 52 is for a quick opening of the fuel injector 12 required. The control valves 68 . 70 can have an electromagnetic actuator or a piezo actuator and are controlled by an electronic control device 72 driven.

Through the in the control pressure room 52 the prevailing pressure is via the end face of the control piston which delimits this 50 a the closing spring 44 supporting force in the closing direction on the injection valve member 28 generated. Through the second control valve 70 the pressure in the control pressure chamber 52 controlled, with the control valve closed 70 at least approximately the same pressure in the control pressure chamber 52 as in the pump work room 22 while with the control valve open 70 due to the connection with the relief area 24 a lower pressure in the control pressure chamber 52 set as in the pump work room 22 , The on the injector member 28 the total closing force that is dependent on the force of the closing spring 44 and of that in the control pressure room 52 prevailing pressure by the second control valve 70 is controlled. The control pressure room 52 and the second control valve 70 can also be omitted, so that the opening pressure of the fuel injector 12 only by the closing spring 44 is determined.

The pump piston 18 the high pressure pump 10 is in the 2 to 5 each shown enlarged in sections. The pump piston 18 is at least in a partial area of it in the cylinder bore 16 dense surface with a variety of microwells 80 Mistake. The width of the microwells 80 is, for example, between approximately 10 μm and approximately 30 μm, their depth is, for example, between approximately 2 μm and approximately 30 μm and their distance from one another is, for example, between approximately 30 μm and approximately 150 μm. The microwells 80 are preferably even over the surface of the pump piston 18 distributed. When operating the fuel injector is in the microwells 80 of the pump piston 18 the fuel acting as a lubricant is stored and enables good lubrication and thus low friction between the pump pistons 18 and the cylinder bore 16 , The microwells 80 also act as a laby Rinth seal, so that no or very little fuel from the pump work space 22 between the pump piston 18 and the cylinder bore 16 exit and to the cam drive 20 . 21 . 23 the internal combustion engine can get. This avoids dilution of the lubricating oil of the internal combustion engine.

At one in 2 The first exemplary embodiment shown are the microwells 80 trained as a cup. At one in 3 The second exemplary embodiment shown are the microwells 80 formed as grooves which are inclined in the longitudinal direction or in the transverse direction or at any inclination over the circumference of the pump piston 18 can run. At one in 4 The third exemplary embodiment shown are the microwells 80 formed as intersecting grooves. At one in 5 The fourth exemplary embodiment shown are the microwells 80 as a spiral over the circumference of the pump piston 18 extending grooves formed.

The microwells 80 can in the surface of the pump piston 18 for example by means of laser processing, hard turning, spark erosion or by means of a lithographic process. To minimize the play between the pump piston 18 and the cylinder bore 16 to reach the pump piston 18 and the cylinder bore 16 can be processed by pairing loops.

The pump piston 18 can in addition to the microwells 80 at least in a partial area of it in the cylinder bore 16 tightly guided surface with a coating 82 be made of wear-resistant material. The coating 82 can consist in particular of carbon or carbon compounds which have a high hardness.

The function of the fuel injection device is explained below. During the suction stroke of the pump piston 18 this is with the first control valve open 68 Fuel from the fuel tank 24 by means of the feed pump 25 fed. During the delivery stroke of the pump piston 18 fuel injection begins with a pre-injection, the first control valve 68 by the control device 72 is closed so that the pump work space 22 from the relief area 24 is separated and located in the pump work room 22 with the delivery stroke of the pump piston 18 increasingly builds high pressure. By the control device 72 also becomes the second control valve 70 closed so that the control pressure chamber 52 from the relief area 24 is separated. In this case, builds up in the control pressure room 52 High pressure at least approximately as in the pump work room 22 on. A fuel injection cycle begins with a pre-injection of a small amount of fuel. To one from the control device 72 depending on the operating parameters of the internal combustion engine, such as speed, load, temperature and other specific point in time and for a specific period of time, the second control valve is used for the pre-injection 70 by the control device 72 opened so that the control pressure chamber 52 with the relief area 24 connected is. From the control pressure room 52 can then fuel through the throttle 65 to the relief area 24 flow out so that the pressure in the control pressure chamber 52 sinks. When the pressure in the pump work space 22 and thus in the pressure room 40 of the fuel injector 12 is so big that through this over the pressure shoulder 42 on the injector member 28 pressure applied is greater than the sum of the force of the closing spring 44 and the one on the control piston 50 through in the control pressure room 52 acting residual pressure acting pressure force, the injection valve member moves 28 in the opening direction 29 and gives the at least one injection port 32 free. The control device ends the pre-injection 72 the second control valve 70 closed, so the control pressure chamber 52 from the relief area 24 is separated. The first control valve 68 remains in its closed position. In the control pressure room 52 high pressure builds up like in the pump work room 22 on so that on the spool 50 a large pressure force acts in the closing direction. Now that on the injection valve member 28 in the opening direction 29 acting force is less than the sum of the force of the closing spring 44 and the pressure force on the control piston 50 closes the fuel injector 12 , Several consecutive fuel pre-injections can also be provided.

For a subsequent main injection, the second control valve 70 by the control device 72 again open at a certain time and for a certain period of time, so that the pressure in the control pressure chamber 52 sinks. The fuel injector 12 then opens due to the reduced pressure force on the control piston 50 and the injector member 28 moves in the opening direction 29 , With the second control valve open 70 a small amount of fuel flows through the throttling points 63 . 65 to the relief room 24 off, however, the throttling points 63 . 65 be formed with a small flow cross-section, so that the outflowing amount of fuel and the reduction in pressure in the pump work space 22 is low.

To end the main injection, the second control valve 70 by the control device 72 brought into its closed switching position, so that the control pressure chamber 52 from the relief area 24 is separated and located in the control pressure room 52 High pressure builds up. On the injector member 28 then acts due to the high pressure in the control pressure chamber 52 and the closing spring 44 a greater force in the closing direction than in the opening direction 29 and the fuel injector 12 closes. The first control valve 68 can stop the main injection in its open or closed position. Subsequent to the main injection, a post-injection can take place during the fuel injection cycle. The second control valve is used for post-injection 70 by the control device 72 opened again at a point determined by this, so that the fuel injection valve 12 due to the falling pressure in the control pressure chamber 52 opens. The control device ends the post-injection 72 the first control valve 68 opened and / or the second control valve 70 closed so the fuel injector 12 closes.

Claims (7)

Fuel injection device for an internal combustion engine, each with a high-pressure fuel pump ( 10 ) and a fuel injector connected to it ( 12 ) for each cylinder of the internal combustion engine, the high-pressure fuel pump ( 10 ) one in a cylinder bore ( 16 ) tightly guided pump piston ( 18 ) which is in the cylinder bore ( 16 ) a pump work room ( 22 ) limited with the fuel injection valve ( 12 ) is connected, the pump piston ( 18 ) by a cam drive ( 20 . 21 . 23 ) the internal combustion engine is driven in a stroke movement, characterized in that the pump piston ( 18 ) at least in a partial area of it in the cylinder bore ( 16 ) dense surface a variety of microwells ( 80 ) having. Fuel injection device according to claim 1, characterized in that the cam drive ( 20 . 21 . 23 ) the internal combustion engine is oil-lubricated. Fuel injection device according to claim 1 or 2, characterized in that the microwells ( 80 ) are designed as cups. Fuel injection device according to claim 1 or 2, characterized in that the microwells ( 80 ) are designed as grooves. Fuel injection device according to claim 4, characterized in that the grooves ( 80 ) cross each other. Fuel injection device according to claim 4, characterized in that the grooves ( 80 ) spiraling over the surface of the pump piston ( 18 ) run. Fuel injection device according to one of the preceding claims, characterized in that the pump piston ( 18 ) at least in a partial area of it in the cylinder bore ( 16 ) tightly guided surface with a coating ( 82 ) is made of wear-resistant material, in particular carbon or carbon compounds.