DE10242219A1 - Fuel metering unit for injection system has valve with flat characteristic for idling/low load, steep characteristic for partial/full load; transition between characteristics can be differentiated - Google Patents

Abstract

The unit has a high pressure pump driven depending on engine speed and a regulating valve actuated by an electromagnet and with a valve piston in a valve housing with control openings shaped and configured to produce at least two control ranges, one with a flat characteristic for idling and low load and one with a steep characteristic for partial and full load. The transition between the flat and steep characteristics can be differentiated. The unit has a high pressure pump driven depending on engine speed to produce the required fuel pressure and throughput in each engine operating state and a regulating valve actuated by an electromagnet and with a valve piston in a valve housing with control openings (32,34,35) shaped and configured to produce at least two control ranges, one with a flat characteristic for idling and low load and one with a steep characteristic for partial and full load. The transition between the flat and steep characteristics can be differentiated.

Description

State of the art

The invention relates to a Fuel injection system for Internal combustion engines according to the preamble of claim 1.

The general state of the art in this field is based on DE 198 52 103 A1 directed.

In particular, the invention is based on a so-called common rail system (CR system). The peculiarity in such CR systems is that the amount of fuel required by a high pressure pump to a variable from the respective operating state dependent on the internal combustion engine Pressure must be put. The high-pressure pump is driven depending on the engine speed, what z. B. happen by the camshafts of the internal combustion engine can. The possible delivery rate the high pressure pump is designed so that in any operating condition an excess of fuel, d. h, more than the rail to the desired pressure build-up needed promoted can be.

From the DE 198 53 103 A1 a fuel metering unit is known in which the flow rate is controlled by a valve piston. To control the flow, the valve piston opens one or more control openings in whole or in part. The control openings described in the cited document can be divided into two areas. The first area is used primarily for fuel metering at idle and in the lower part-load range of the internal combustion engine, while the second area is used for the medium part-load and full-load range.

Advantages of invention

By using a fuel metering unit for one Fuel injection system for Internal combustion engines with a high-speed pump driven by engine speed, the fuel pressure required to generate the respective operating state of the internal combustion engine and - throughput serves, wherein the fuel metering unit is an electromagnet actuated Has control valve with a valve piston, the valve piston in a valve housing guided is, in the wall of the valve housing at least one, preferably several radial control openings are arranged, which are shaped and / or arranged so that dependent on result in at least two control ranges from the valve piston stroke, whereby At the beginning of the valve piston stroke, the idling and the lower Partial load of the internal combustion engine assigned first control area and with a further valve piston stroke one of the partial load and the Full load of the internal combustion engine corresponding second control area of the control openings provided is, the opening cross section of the tax openings plotted over the valve piston stroke in the first control area a flat characteristic with a small pitch angle and a steep one in the second control area Characteristic curve with a large slope angle has, according to the invention the characteristic in the transition area between the flat characteristic (area 1) and the steep characteristic (area 2) is differentiable.

By designing the transition according to the invention improved between the first control area and the second control area the controllability of the flow rate through the metering unit Idling and in the lower part-load range so strong that an additional Pressure control valve on the pressure side of the high-pressure fuel pump can be dispensed with. This saves considerable costs without deteriorating the operating behavior of the internal combustion engine would.

In a variant of the fuel metering unit according to the invention has at least one tax opening in the second control area a trapezoidal cross section. Through this Geometry of the control opening in the second control area there is a very smooth transition from the first control area to the second control area, towards the end of the valve lift a very large one Increase in opening cross-section the control surface is achieved. This ensures optimal controllability of the internal combustion engine in idle and part-load range with a short valve piston travel, or the armature reached at full load.

Alternatively, the control opening in the second control area is also symmetrical and to both Have a curved outer contour on the side of their line of symmetry. That too Is it possible, the transition between the first control area and the second control area shape. Due to the concave curvature outer contours of the tax openings is a strongly progressive increase in the opening area of the control surface increasing stroke of the valve piston reached.

It has also proven to be advantageous if the control opening is rectangular in the area of the first control area, since with this geometry a linear increase in the opening cross section of the control surface is achieved in the first control area. This linear increase makes it easier to control the amount of fuel flowing through the fuel metering unit in the particularly sensitive idling and lower part-load range. In addition, the rectangular cross section in this area ensures that even the smallest strokes of the valve piston open an opening cross section of the control opening that is at least as large as the annular gap area between the valve piston and the housing wall through which a certain amount of leakage flows. If the flow cross-section released through the control opening is smaller than the annular gap area between the valve piston and the housing wall, this is also the case Leakage amount is generally greater than the amount of fuel flowing through the control opening, which at least complicates the controllability of the fuel flow through the fuel metering unit.

Alternatively, the rectangular part the tax opening also be rounded at the end facing away from the second region.

It has proven to be advantageous if several small control surfaces instead of a big one control surface be provided. In particular, it is advantageous if one is straight Number of control surfaces, i.e. the number of control surfaces is divisible by two, is provided. Then there is a symmetric Load on the valve piston, so that this in all operating points always smooth in the wall of the valve housing can be moved back and forth.

It has further proven beneficial proven if only one control surface protrudes into the first control area and there is a rectangular one Has cross-section. If only one tax opening in the first tax area protrudes, can be particularly sensitive and with a particularly flat characteristic curve the flow through the fuel metering unit according to the invention can be regulated in idle and lower part load range.

Other advantages and beneficial Embodiments of the invention are the following drawing, their description and the claims can be found.

drawing

It shows:

1 an embodiment of a fuel metering unit in vertical longitudinal section,

2 a variant of a control valve of the fuel metering unit 1 with three tax openings (shown in processing over the circumference),

3 the detail "A" 2 in separate representation,

4 an alternative embodiment of a control opening,

5 a diagram, wherein the opening cross-section of the control opening after 3 is applied over the stroke of the valve piston, and

6 an enlarged view of a section 5 ,

description of the embodiments

The fuel metering unit after 1 is based on an electromagnet 10 with integrated control valve 11 , The electromagnet exists in detail 10 essentially from a magnetic coil 12 , an anchor 13 with anchor bolt 14 and a magnetic pot 15 which is the solenoid 12 and the anchor 13 partially encloses.

The entire electromagnet assembly 10 with integrated control valve 11 is arranged in a high-pressure fuel pump (not shown). The magnetic pot 15 serves at the same time as a sealing element, as a magnetic yoke and as a fastening element ( 16 ) of the electromagnet 10 in the high pressure pump.

The solenoid 12 after being in the magnetic pot 15 is completely overmolded. By with 17 overmolding is an optimal heat transfer from the coil 12 to the magnetic pot 15 guaranteed. This can counteract overheating in critical operating states. The encapsulation continues 17 good vibration and vibration resistance, which means that the fuel metering unit is attached 10 . 11 at highly stressed places, e.g. B. the high-pressure fuel pump, in relation to vibrations, temperature and environmental pollution is made possible.

Furthermore, the extrusion coating 17 the solenoid 12 in cooperation with two sealing points 18 . 19 ensures that the contact points of the coil 12 to the connector lugs (not shown) are "dry". Magnet coil winding and contact points are thus optimally protected against attacks by corrosive media.

To check that the encapsulation 17 the solenoid 12 completely encloses are on the circumference of the magnetic pot 15 Overflow holes " 20 . 21 intended.

The control valve 11 has a valve housing 22 , which in a flange-like widening 23 passes, which at the same time the front end of the magnetic pot 15 forms. In the valve housing 22 is an axial bore 24 formed coaxially to the anchor bolt 14 of the electromagnet 10 is arranged. The axial bore 24 takes a sliding sleeve-shaped valve piston 25 on, in its interior 26 a compression spring 27 is arranged. The compression spring 27 is supported on the front on a floor 28 of the valve piston 25 and on the back of one in the axial bore 24 of the valve housing 22 located spring plate 29 from. A paragraph 30 on the inner wall of the valve piston 25 ensures that the compression spring 27 largely contact-free from the inner wall in the valve piston 25 lies. The valve piston head is on the outside 28 and thus the valve piston 25 with the front end of the anchor bolt 14 in Appendix.

An opening 31 connects the interior 26 of the valve piston 25 with a (not shown) feed pump of the fuel injection system. In the valve housing 22 several radially directed control openings are also arranged (see also 2 to 4 ), one of which is out 1 can be seen and is numbered 32. The tax opening 32 is in hydraulic operative connection with the low pressure area of the high pressure pump (not shown).

The flow principle can also be reversed be returned. This would be the opening 31 hydraulically connected to the low pressure area of the high pressure pump while the control opening 32 would be connected to the pressure side of the pre-feed pump and would thus form the inlet into the metering unit.

The top half of the 1 - above the common central axis 33 from valve bore 24 , Valve piston 25 and anchor bolts 14 - shows the control valve 11 in the open position in which the control opening 32 through the valve piston 25 is fully released. In the lower half of the 1 against it is the control valve 11 shown in the fully closed position. The magnetic force of the energized electromagnet acts here 10 over the anchor bolt 14 on the valve piston 25 and moves it against the resistance of the compression spring 27 in the said closed position of the control valve 11 , Conversely, the compression spring can 27 the valve piston 25 in the open position (upper half of 1 ) move when energizing the electromagnet 10 and therefore its anchor 13 and anchor bolts 14 acting magnetic force is reduced accordingly. In the open position of the control valve 10 flows to the control valve 11 at 31 supplied fuel through the control opening 32 towards the elements of the high pressure pump.

As already indicated above, it has proven to be practical in practice, not just one, but several, on the circumference of the valve housing 22 to provide distributed, radial control openings.

2 shows a variant with a total of three control openings - with 32 . 34 and 35 designated - are provided.

As from the enlarged representation in 3 results from the special design of the central control opening 32 two control areas of the control valve 11 on the one hand an area 1 with correspondingly low fuel delivery and another area 2 with depending on the stroke of the valve piston 25 sharply increasing fuel delivery (cf. 5 ). The stroke of the valve piston 25 is equal to the stroke of the anchor bolt 14 ,

Here is the area 1 (low fuel delivery) assigned to the engine idling up to the lower partial load. The area 2 (sharp increase in fuel delivery), on the other hand, corresponds to the average partial load up to the full load of the internal combustion engine.

Area 1 is characterized by the fact that initially only the opening cross-section of the rectangular part 36 the tax opening 32 a hydraulic operative connection between pressure side 31 the feed pump (not shown) and suction side of the high pressure pump (not shown). Hence the in 5 With 37 numbered flat linear characteristic of the opening cross-section plotted against the stroke of the valve piston 25 (or the anchor bolt 14 ). This allows good control of the idling and the lower partial load of the internal combustion engine. This is achieved through the narrow, rectangular design of the slit-shaped part 36 the tax opening 32 , The radius R at the beginning of the rectangular part 36 the control opening is opposite the rest of the rectangular part 36 only of minor importance for the control behavior of the internal combustion engine at idle and in the lower partial load. This narrow slot can be produced by eroding, punching or laser cutting.

In the area 2 are three characteristics 38 . 39 and 40 applied. The characteristic 38 results from the opening cross section of the control opening 32 alone; while the characteristic curve 40 results when the opening cross-sections of the control openings 32 . 34 and 35 be added.

The area 2 is characterized by the fact that the opening cross-sections - in this case all three control openings involved 32 . 34 and 35 (please refer 2 ) - is trapezoidal. Plotted over the stroke of the valve piston 25 or the anchor bolt 14 , results in the range 2 an increasingly steeper characteristic curve (compare the curve sections 38 . 39 . 40 in 5 ). This ensures that a correspondingly large opening cross-section is available after a defined stroke. This means that the electromagnet has a short overall length and requires little energy 10 possible.

Because the top of the trapezoid of the control opening 32 the same width as the rectangular slot 36 is the course of the opening cross-section over the stroke of the valve piston 25 differentiable. In other words, the course of the characteristic curve is without kinks or jumps. This improves the controllability of the metering unit in the transition area between the area 1 and the area 2 ,

The fuel metering unit in question can be used equally for different types of vehicles (cars, commercial vehicles, special vehicles, ships, etc.), provided they are operated with internal combustion engines. The required adjustment can be easily made by designing the opening cross-sections of the valve control openings (e.g. 32 . 34 . 35 in 2 ) accomplish.

As mentioned and out 1 the control valve is visible 11 in the magnetic pot 15 . 33 of the electromagnet 10 integrated and the complete fuel metering device 10 . 11 is screwed directly into the high pressure pump. This guarantees an optimally small installation space and cost-effective production. The minimum dead volume that can be achieved thereby ensures exact metering of the amount of fuel required in each case and fast reaction times to changing volume requirements of the high-pressure pump or the internal combustion engine.

It is already clear from the preceding explanations that exact controllability is important for the valve of a fuel metering device. The control of the electromagnet 10 is pulse width modulated. This leads to reduced friction terese and good dynamics of the fuel metering unit.

In 4 is an alternative embodiment of a control opening 32 shown. The control surface 32 is, as well as the embodiment according to 3 , symmetrical with respect to a line of symmetry 52 formed and in a first area with a rectangular cross section 36 and a second area. In the first control area (area 1) the control opening is rectangular without radius R (see 3 ) at the beginning of the tax opening 32 executed. In the second control area (area 2 ) is the outer contour 54 the tax opening 32 executed curved. This results in a very smooth transition between the areas 1 and the area 2 and a strong progression of the increase in the opening cross section in the area of the full load of the internal combustion engine.

According to the invention, any geometries can be in the first control area and in the second control area of the control opening 32 can be combined with each other if the transition between the first area and the second area is selected so that the transition of the flat characteristic curve from the area 1 into the steep curve in the area 2 is differentiable.

6 shows a section B. 5 in an enlarged view. The control areas area 1 and area 2 are also in 6 registered again. If one assumes that with a full stroke of the valve piston, which should be 2.7 mm in the exemplary embodiment shown here, the valve piston opens the control opening 36 (please refer 3 and 4 ) closes completely and therefore no fuel through the control opening 32 can flow, zero delivery is set when the valve piston is at full stroke and as the stroke decreases, an ever larger part of the control surface 32 Approved.

A first line 55 shows the cross section of the annular gap between the valve piston 25 and the axial bore 24 in which the valve piston 25 is sealingly led. This cross-sectional area of the gap between valve pistons 25 and axial bore 24 is independent of the stroke of the valve piston 25 so the line 50 in 6 is entered as a horizontal line. In the case of the fuel metering unit according to the prior art, which is in series production, there is an annular gap between the valve pistons 25 and axial bore 24 a cross-sectional area of about 0.11 mm ² . A leakage flow flows through this annular gap during operation of the pre-feed pump, which then reaches the high-pressure pump and there, as well as that through the control openings 32 . 34 and 35 flowing fuel that is pressurized.

Using a second line 56 is the increase in the opening cross-section over the stroke of the valve piston 25 shown when the control surface 32 has a purely trapezoidal cross-section. The course of the second line is in the area of zero delivery or idling operation, ie with abscissa values between 2.7 mm and 2.6 mm 56 relatively flat.

A third line 57 which in the area 1 the line 37 out 5 and in the area 2 the line 38 out 5 shows the course of the opening cross-section over the stroke of the valve piston 25 with a control opening according to the invention 32 according to the embodiment 3 , After that is the slope of the third line 57 in the range between 2.7 mm and 2.6 mm steeper than with a purely trapezoidal control opening (line 56 ) and takes a linear course in the range between 2.6 mm and 2.3 mm. This is due to the rectangular part 36 the tax opening 32 , In this range between 2.6 mm and 2.3 mm stroke of the valve piston, the idling and the lower partial load of the internal combustion engine are regulated. It can be clearly seen that the average slope of the third line 57 in the range between 2.3 mm and 2.6 mm is much less than that of the second line 56 , Therefore, a fuel metering unit with a control opening according to the invention 32 better controllable in this area than with a purely trapezoidal geometry of the control opening.

With a stroke of less than 2.3 mm, the second control area (area 2 ) the tax opening 32 , How to draw the third line 57 out 6 can be seen is the transition between the area 1 (Stroke> 2.3 mm) and the range 2 (Stroke <2.3 mm) differentiable; that means it is a "rounded" transition without kinks or jumps. This means that even in the transition area between area 1 and area 2 the fuel metering unit according to the invention can be regulated very well. With decreasing valve lift (valve lift <2.0 mm) the progression of the line becomes 38 always larger, so that with the same travel of the valve piston 25 (please refer 1 ) the same opening cross section of the control opening 32 is achieved as with a purely trapezoidal control opening according to the prior art. Since in the area of full-load operation of the internal combustion engine, the control quality is not as high as that of idling and lower part-load operation, the line has a large slope 38 in the area 2 not disadvantageous.

In 6 is also a fourth line 58 shown which is just like the first line 55 represents a constant opening cross-section. This characteristic curve represents a metering unit in which the annular gap between valve pistons 25 and axial bore 24 compared to the state of the art (see first line 55 ) was reduced. The smaller the opening cross-section of the annular gap, the smaller the leakage quantity and the better the control quality of the fuel metering unit in idling and in the lower part-load range.

Claims (11)

Fuel metering unit for a fuel injection system for internal combustion engines with a mo High-pressure pump driven as a function of the door speed, which is used to generate the fuel pressure and throughput required for the respective operating state of the internal combustion engine, the fuel metering unit being operated by an electromagnet ( 10 ) operated control valve ( 11 ) with a valve piston ( 25 ), the valve piston ( 25 ) in a valve housing ( 22 ) is guided, whereby in the wall of the valve housing ( 22 ) at least one, preferably several radial control openings ( 32 . 34 . 35 ) are arranged, which are shaped and / or arranged such that there are at least two control ranges depending on the valve piston stroke, with a first control range (range 1 ) and with a further valve piston stroke a second control area (area. corresponding to the partial load and the full load of the internal combustion engine) 2 ) the control openings ( 32 . 34 . 35 ) is provided, the opening cross section of the control openings, plotted over the valve piston stroke, in the first control area (area 1 ) a flat characteristic ( 37 ) with a small pitch angle and in the second control area (area 2 ) a steep characteristic curve ( 38 respectively. 39 respectively. 40 ) with a large pitch angle, characterized in that the transition of the flat characteristic curve (area 1 ) in the steep characteristic curve (area 2 ) is differentiable. Fuel metering unit according to claim 1 or 2, characterized in that the control openings ( 32 . 34 . 35 ) have a trapezoidal cross-section in the second control area. Fuel metering unit according to claim 1 or 2, characterized in that the control openings ( 32 . 34 . 35 ) in the second control area (area 2 ) are symmetrical and have a curved outer contour on both sides of their symmetry line (). Fuel metering unit according to one of the preceding claims, characterized in that at least one of the control openings ( 32 . 34 . 35 ) has a rectangular cross-section in the first control area. Fuel metering unit according to one of the preceding claims, characterized in that an end (R) of the first control region of the control openings (averted from the second control region) 32 ) is rounded. Fuel metering unit according to one of the preceding claims, characterized in that the valve piston ( 25 ) is sleeve-shaped and in its interior ( 26 ) the compression spring acting on it in the open position ( 27 ) and that the compression spring ( 27 ) on the back of one in the valve bore ( 24 ) of the valve housing ( 22 ) arranged spring plate ( 29 ) supports. Fuel metering unit according to one of the preceding claims, characterized in that the control valve ( 11 ) by appropriate axial displacement and subsequent fixation of the spring plate ( 29 ) in the valve bore ( 24 ) is adjustable. Fuel metering unit according to one of the preceding claims, characterized in that the valve piston ( 25 ) has a recess on its cylindrical peripheral surface and in the valve housing ( 22 ) a radial bore connected to the suction side of the prefeed pump is arranged such that in the closed position of the valve piston ( 25 ) the radial control openings ( 32 ) due to the valve piston bore with the radial bore in the valve housing ( 22 ) are hydraulically connected. Fuel metering unit according to one of the preceding claims, characterized in that on the valve piston ( 25 ) facing edge of the spring plate ( 29 ) an axial sealing seat ( 51 ) is formed, which is in the closed position of the valve piston ( 25 ) with the spring plate ( 29 ) facing edge ( 52 ) interacts in a sealing manner. Fuel metering unit according to one of the preceding claims, characterized in that an even number of control surfaces ( 32 ) is provided. Fuel metering unit according to one of the preceding claims, characterized in that only one control surface ( 32 ) a rectangular part ( 36 ) in the first control area (area 1 ) having.