WO2002066809A2

WO2002066809A2 - Sensor mounted in an injection line leading to an injection valve in a direct-injection internal combustion engine

Info

Publication number: WO2002066809A2
Application number: PCT/DE2002/000671
Authority: WO
Inventors: Ulrich Deml; Manfred Frimberger; Andreas Aumer
Original assignee: Siemens Aktiengesellschaft
Priority date: 2001-02-02
Filing date: 2002-02-22
Publication date: 2002-08-29

Abstract

The sensor comprises an element (1) made of a material having pronounced magnetoelastic properties. The element (1) is connected to the injection line (2) in a non-positive manner and surrounds the injection line (2). The sensor also has a pre-magnetizing coil (4, 5, 6, 7, 12) that surrounds the element (1). The pre-magnetizing coil (4, 5, 6, 7, 12) that is traversed by a current generates a magnetic field which premagnetizes the element (1). As a result of this change in pressure in the injection line (2), a magnetoelastic effect occurs that is augmented by the pre-magnetized element (1). In a measuring coil (8, 9, 10, 11, 13) surrounding the element (1), a tension is induced as a result of the magnetoelastic effect and a measuring signal is evaluated by a control unit.

Description

description

Sensor, which is arranged on an injection line leading to an injection valve of a direct-injection internal combustion engine

The invention relates to a sensor which is arranged on a pressurized injection line of a direct-injection internal combustion engine leading to an injection valve in order to determine an injection start into the internal combustion engine.

A known device (DE 197 57 293 C2) has a pressure sensor which is arranged on the fuel injection line in front of an injection valve. The pressure sensor has a single measuring coil made of magnetoelastic material, which is wound directly around the injection line. If an injection process is triggered and a needle stroke transmitter opens the injection nozzle by lifting the needle against the spring preload, the one that is present via the injection line

Fuel is injected into the combustion chamber of the internal combustion engine. This start of injection leads to a drop in pressure in the injection line. The pressure drop induces an electrical voltage in the measuring coil due to the magneto-elastic effect. This induced voltage is amplified and applied to a control unit as a measurement signal. In addition to the induced voltage caused by the pressure drop in the injection line, the measurement signal also has an interference component which is caused by interference from the control current for the injection valve.

The problem with the device is that this interference component in the measurement signal means that the signal-to-noise ratio of the measured signal is very small. This makes it very difficult to trace the waveform of the induced voltage generated by the pressure drop in the injection line received and from it to carry out a reliable determination of the injection timing.

Increased requirements with regard to driving comfort and exhaust gas values make it necessary to have several injection pulses per

To perform combustion cycle. For example, five injection pulses can be carried out per combustion cycle, which are designed as pre-injections and / or main injections and / or post-injections. The number of pre-injection pulses, the number of main injection pulses and the number of post-injection pulses are variable. For example, three pre-injections and two main injections can be carried out with five injection pulses. However, it may also be the case that two pre-injections, one main injection and two post-injections are carried out.

Another disadvantage of the known device is that deviations in the start of injection of the injection pulses from the defined injection times are not recognized. It is therefore also not possible to determine an exact dead time of the injection valves, that is to say the delay time between activation of the injection valves and opening of the needle of the injection nozzle, for a single injection process. Furthermore, with the known pressure sensor it is only possible to make a statement about the pressure fluctuations but not about the pressure in the injection line.

The invention has for its object to provide a generic sensor that is simple and inexpensive to build and that generates a measurement signal with a better signal-to-noise ratio.

This object is achieved by a sensor with the features of claim 1.

A direct-injection internal combustion engine has an injection line that leads to an injection valve. On a sensor is arranged in this injection line. The sensor has at least one bias coil and one measuring coil.

According to the invention, the sensor has an element which is non-positively connected to the injection line and at least partially surrounds the injection line. The element consists of a material that has pronounced magneto-elastic properties. The bias coil is arranged so that it surrounds this magneto-elastic element and biases this magneto-elastic element. Furthermore, the measuring coil is arranged in such a way that it surrounds the magnetoelastic element.

This can improve the signal-to-noise ratio of a measurement signal.

Advantageous refinements of the invention are specified in the subclaims.

It can be provided that the sensor has a second element made of soft iron or layered transformer plate and this second element at least partially surrounds the injection line and is mechanically connected directly to the ends of the magneto-elastic element.

It can thereby be achieved that the magnetic circuit of the premagnetization is closed and permeability changes in the magnetoelastic element are intensified.

It can also be provided that the sensor has a hollow cylinder which is arranged coaxially to the magnetoelastic element and the injection line, is arranged at a distance from the magnetoelastic element and the magnetoelastic element and the hollow cylinder by means of disk-shaped

Cover elements on the end faces are mechanically connected. Improved mechanical stability can be achieved in this way. Furthermore, the magnetic circuit of the premagnetization is also closed here.

In addition to the coaxial arrangement of the bias coil and the measuring coil for the injection line, it is also possible to arrange the bias coil and the measuring coil tangential to the injection line.

It can thereby be achieved that the magnetic field lines always run in the magnetoelastic material and that a closed circuit of the premagnetization is also achieved.

Several embodiments of the invention are described below with reference to the schematic drawings. Show it:

1 a shows the sensor according to the invention in the axial direction of the injection line, FIG. 1 b shows a perspective view of the sensor according to FIG. 1 a, FIG. 2 a shows a measurement signal of the sensor according to FIGS. 1 a and b without premagnetizing the magnetoelastic element in which the injection line is arranged between a high-pressure pump and an injection valve, and FIG. 2 b shows a measurement signal from the sensor according to FIGS. 1 a and b with premagnetization of the magnetoelastic element, in which the injection line is arranged between a high-pressure pump and an injection valve, FIG. 2 c shows a measurement signal from the sensor 1 a and b, in which the injection line is arranged between a high-pressure accumulator and an injection valve,

3 shows a second exemplary embodiment of the sensor, FIG. 4 shows a further exemplary embodiment of the sensor, 5 a shows a partial section through a fourth exemplary embodiment of the sensor, and FIG. 5 b shows a perspective illustration of the sensor according to FIG. 5 a.

A sensor according to the invention, which is referred to below as a pressure sensor, has a cylinder-symmetrical element 1 (FIG. 1) made of a material with pronounced magnetoelastic properties, which is referred to in the exemplary embodiment as core 1 '. The core 1 'is non-positively connected to an injection line 2 and coaxial to the injection line

2 arranged. Furthermore, the core has grooves 3 a - h. The grooves 3 a - h are arranged symmetrically in pairs. Thus, the pair of grooves 3 a, b is arranged symmetrically to the pair of grooves 3 e, f with respect to the axis of symmetry I. The pair of grooves

3 c, d is arranged symmetrically to the pair of grooves 3 g, h with respect to the axis of symmetry II.

Pre-magnetizing coils 4, 5, 6, 7 and measuring coils 8, 9, 10, 11 are incorporated into the grooves 3 a - h. The turns of the bias coils 4, 5, 6, 7 and the turns of the measuring coils 8, 9, 10, 11 are non-positively wound around the core 1 '. It is not important for the invention that the turns of the coils 4 - 11 are wound non-positively around the core 1 '. It is important, however, that they are arranged in the spaces created by the grooves 3 a - h.

The turns of each bias coil 4, 5, 6, 7 are wound in such a way that each bias coil 4, 5, 6, 7 forms a gap at approximately half the number of turns. A measuring coil 8, 9, 10, 11 is respectively arranged in this intermediate space. Both the bias coils 4, 5, 6, 7 and the measuring coils 8, 9, 10, 11 are arranged tangentially to the injection line 2. Due to the arrangement of the bias coils 4, 5, 6, 7 and the measuring coils 8, 9, 10, 11 shown, the magnetic field lines are circular in the tangential direction around the. Injection line 2 closed.

If a pressure change now occurs in the injection line 2 due to the opening of an injection valve (not shown), this leads to a change in the mechanical stresses. Via the magnetoelastic effect, the mechanical stresses have an influence on the relative permeability of the material of the injection line 2 and Materials of the pressure sensor.

Radial compressive stresses are introduced into the core 1 'via the four contact surfaces between the core 1' and the injection line 2 and converted into tangential tensile stresses in the core 1 '. The magnetic field lines and the mechanical stresses therefore run parallel. The geometry of the pressure sensor therefore gives a very good measurement signal.

It is now essential that the core 1 'made of magnetoelastic material is pre-magnetized by means of the bias coils 4, 5, 6, 7. As a result, the change in the relative permeability leads to a change in the magnetic flux density B and a voltage is induced in the measuring coils 8, 9, 10, 11.

By pre-magnetizing the core 1 ', it is possible to set a fixed operating point and to achieve a significantly improved signal-to-noise ratio of the measurement signal. The voltage U _ιnd induced in the measuring coils 8, 9, 10, 11 can be described by the following equation:

U _md = a_ * P + a ₂ ⁹ P

The pre-factors Ά _X and a ₂ are in the general case both non-linear of the pressure p and the change in the pressure p dependent in the injection line 2. The pre-factors ai and a _{2 can be} influenced by a suitable choice of the current flowing through the bias coils 4, 5, 6, 7 for the purpose of biasing the core 1 '. It can be achieved that either the pressure dependency or the dependence on the pressure gradient is negligible. As a result, the induced voltage U _{ιnd is} either proportional to the pressure or proportional to the change in pressure.

In this exemplary embodiment of the pressure sensor, variable pre-magnetization of the core 1 'is therefore possible.

The signal of the induced voltage _Und is _amplified by a measured value amplifier (not shown) and applied to a control unit (not shown), which evaluates the signal. The signal can also be evaluated via a separate evaluation unit.

A number of turns of 20 for the bias coils 4, 5, 6, 7 has proven to be advantageous. A number of turns of 25 each has proven to be advantageous for the measuring coils 8, 9, 10, 11. A higher or a lower number of turns can also be used for the bias coils 4, 5, 6, 7 and for the measuring coils 8, 9, 10, 11.

For the exemplary embodiment, 1 'Vacoflux (50% cobalt, 50% iron) was used as the material with magneto-elastic properties for the core. However, only nickel or an alloy of nickel and iron, an alloy of iron and silicon or an alloy of platinum and iron can also be used.

The number of bias coils as well as the number of measuring coils can be less or more than 4. FIG. 2 a shows a curve of a voltage induced in the measuring coils 8, 9, 10, 11 of the pressure sensor according to FIGS. 1 a and b, which is referred to in the form as a slot sensor. The signal shows the voltage curve when the slot sensor is not premagnetized. The

Signal corresponds to a pressure curve on a direct-injection internal combustion engine when the injection valves are opened. Due to the pressure drop in the injection line 2 when the injection valve is opened, vibrations A, B, C of the injection line 2 are generated, which are proportional to the induced voltage U _ιnc ι and can be clearly seen in the signal curve.

In contrast to FIG. 2a, the voltage induced in the measuring coils 8, 9, 10, 11 is shown in FIG. 2a with a premagnetization of the core 1 ^'of the slot sensor. The measured signal is shown in the upper diagram and the integrated signal in the lower diagram.

In Figures 2a and b, the injection line 2 is arranged between a high pressure pump, not shown, and the injection valve. The high-pressure pump can be designed as a distributor injection pump in which pressure builds up with each combustion cycle.

FIG. 2 c shows a signal course which is exemplary of the exemplary embodiment and which represents a pressure drop in a high-pressure accumulator after an injection valve has been opened. The injection line 2 (FIG. 1 a, b) is arranged between a high-pressure fuel reservoir (not shown) and an injection valve.

In a further exemplary embodiment, the pressure sensor has an element 1, which is referred to as the core 1 ″ (FIG. 3) and made of a material that has magnetoelastic properties. The core 1 ″ is non-positively connected to the injection line 2 and surrounds the injection line 2. The pressure sensor also has a pre-magnetizing coil 12, the turns of which are wound in such a way that a gap is present at about half the number of turns. The bias coil 12 surrounds the core 1 '', and is non-positively conclusively with the core 1 ^'', respectively.

In this intermediate space of the bias coil 12, a measuring coil 13 is arranged, which surrounds the core 1 ″ non-positively. Furthermore, a measuring amplifier 14 is arranged in such a way that it is as small as possible from the measuring coil 13. Due to the smallest possible distance between the measuring amplifier 14 and the measuring coil 13, interference can be reduced and thus a better signal-to-noise ratio can be achieved.

A magnetic field is generated by the magnetizing current I _mag flowing through the magnetizing coil 12, with which the core 1 ″ is magnetized.

In this exemplary embodiment of the pressure sensor, which is referred to as a cylinder sensor, the bias coil 12 and the measuring coil 13 are arranged coaxially with the hollow cylindrical core 1 ′ and the injection line 2.

In contrast to the embodiment of the slot sensor (FIG. 1 a, b), the cylinder sensor (FIG. 3) has an open magnetic circuit. To achieve a certain magnetic flux density B, a larger magnetic field strength H than in the closed magnetic circuit is therefore necessary.

In a third exemplary embodiment (FIG. 4), a cylinder sensor (FIG. 3) has a second element 15, which is referred to as a yoke 15 '. This yoke 15 'at least partially surrounds the injection line 2 and is mechanically connected to the narrow end faces of the cylinder-shaped core 1. The magnetic field lines emerging from the end faces of the core 1 ″ are closed by the yoke 15 ′. As a result, the pressure sensor referred to as a yoke sensor has a closed magnetic circuit.

It is advantageous to use soft iron or layered transformer sheet for the material of the yoke 15 '.

In a further exemplary embodiment (FIG. 5 a), the core 1 ^{″ of} a cylinder sensor (FIG. 3) is surrounded by a hollow cylinder 16 made of a magnetoelastic material. The hollow cylinder 16 is arranged coaxially to the core 1 ″ and to the injection line 2. The inner radius of the hollow cylinder 16 is designed such that there is a space between the core 1 ″, the biasing and measuring coils 12, 13 surrounding the core 1 ″ and the inner wall of the hollow cylinder 16.

On the end faces of the core 1 ″ and the hollow cylinder 16 there are cover elements 17 and 18 made of a magnetoelastic

Arranged material. The core 1 ″ and the hollow cylinder 16 are mechanically connected by means of these disk-shaped cover elements 17 and 18, and the pressure sensor referred to as the pot sensor thus has high mechanical stability.

This rotationally symmetrical pot sensor also has a closed magnetic circuit.

FIG. 5 b shows a perspective illustration of the pot sensor, in which the rotationally symmetrical arrangement of the pot sensor can be seen.

In the exemplary embodiments of the cylinder sensor, the yoke sensor and the pot sensor, there is a number of turns of approximately

1000 for the bias coil and a number of turns of about 2000 for the measuring coil advantageous. Vacoflux or nickel is advantageous for the magnetoelastic material of the cylinder sensor, the yoke sensor and the pot sensor.

A different number of turns can be used both for the pre-magnetizing coil and for the measuring coil, both for the cylinder sensor, the yoke sensor and the pot sensor. In these three embodiments, it is also possible to use alloys as magnetoelastic material that were specified in the explanations for the groove sensor.

In all exemplary embodiments, both the biasing coil and the measuring coil can be arranged at a distance from the core.

The geometric shape of the core can also be designed as a rectangle or polygon in all exemplary embodiments.

In contrast to the pre-magnetizing coil, the wire cross-section of the measuring coil should be as small as possible, since this allows the number of turns and thus the induced voltage to be maximized for a given space for the turns of the coils.

With a sufficiently large pre-magnetization of the core, it can be achieved that external magnetic fields are largely displaced from the core material. Therefore, a strong pre-magnetization of the core leads to an increase in the security against magnetic interference and to a stabilization of an operating point.

The magnetoelastic materials react differently to tensile and compressive stresses. It is therefore necessary to set a fixed working point for a pressure measurement using the magnetoelastic effect. This working point is determined by a pre-magnetization and thus by an impressed magnetic field strength H.

Only a core made of magnetoelastic material that is non-positively connected to the injection line 2 will reduce the mechanical vibrations caused by pressure fluctuations due to its rigidity. Therefore, the diameter of a cylindrical core made of magneto-elastic material cannot be chosen to be as large as desired. The pre-magnetization coils, however, can be used to set an optimal pre-magnetization and thus to achieve an optimum working point for the magnetoelastic material used.

With the sensors according to the invention it can be achieved that the signal-to-noise ratio of the measurement signal is considerably improved. This makes it possible to determine the start of injection into the combustion chamber of the internal combustion engine more precisely. It is thus possible for a single injection process - pre-injection, main injection or post-injection - to determine a dead time between triggering the injection valve and opening the needle of the injection nozzle more precisely.

This also enables the function of the injection valves to be checked continuously. This is particularly necessary for pre-injections and post-injections, because the small injection quantities result in small needle strokes of an injection nozzle needle. The illustrated embodiments of the pressure sensor make it possible to check the function of the injection valve, which is arranged on the same injection line as the pressure sensor, with regard to the pre-injection and the main injection.

It is also possible to check the main injections on injection valves which are not arranged in the injection line on which the pressure sensor with which the measurement is made is arranged. The variable bias in certain embodiments of the pressure sensor also makes it possible to make qualitative statements about both the pressure fluctuations and the pressure in the injection lines.

Claims

claims

1. Sensor, which is arranged on a pressure-injected injection line (2) of a direct-injection internal combustion engine leading to an injection valve

- An element (1) which is non-positively connected to the injection line (2), the element (1) surrounds an entire length of the injection line (2) at least in sections and the element (1) consists of a material that has pronounced magneto-elastic properties , at least one bias coil (4, 5, 6, 7, 12) for biasing the element (1) and the bias coil surrounds the element (1), and with at least one measuring coil (8, 9, 10, 11, 13) that surrounds the element (1) and in which an electrical voltage is induced in the element (1) when a magnetoelastic effect occurs.

2. Pressure sensor according to claim 1, characterized in that the bias coil (4, 5, 6, 7, 12) and the measuring coil (8, 9, 10, 11, 13) non-positively or at a distance from or to the element (2) are connected or arranged.

3. Pressure sensor according to one of the preceding claims, characterized in that the bias coil (4, 5, 6, 7,

12) and the measuring coil (8, 9, 10, 11, 13) are arranged coaxially with the injection line (2).

4. Pressure sensor according to one of the preceding claims, characterized in that the pressure sensor has a second element (15) which at least partially surrounds the injection line (2) and the second element (15) directly with the end faces of the element (1) is mechanically connected.

5. Pressure sensor according to claim 4 _/ characterized in that the second element (15) is made of soft iron or layered transformer sheet.

6. Pressure sensor according to one of claims 1 to 3, characterized in that a hollow cylinder (16) is provided which is spaced from the element (1) and coaxial to the injection line (2) and the element (1) and the hollow cylinder (16) and the element (1) is mechanically connected to the two end faces by disk-shaped cover elements (17, 18).

7. Pressure sensor according to claim 6, characterized in that the hollow cylinder (16) and the disc-shaped cover elements (17, 18) are made of magnetoelastic material.

8. Pressure sensor according to one of claims 1 or 2, characterized in that the bias coil (4, 5, 6, 7,

12) and the measuring coil (8, 9, 10, 11, 13) are arranged tangentially to the injection line (2).

9. Pressure sensor according to claim 8, characterized in that the bias of the element (1) by means of a bias current through the bias coil (4, 5, 6, 7) is variably adjustable.

10. Pressure sensor according to claim 8, characterized in that depending on the set bias of the element

(1) the induced voltage detected by the measuring coil (8, 9, 10, 11) is proportional to the pressure or a pressure change in the injection line (2).

11. Pressure sensor according to one of the preceding claims, characterized in that the windings of the bias coil (4, 5, 6, 7, 12) are wound such that the bias coil (4, 5, 6, 7, 12) at least at one point has a space.

12. Pressure sensor according to claim 11, characterized in that the measuring coil (8, 9, 10, 11, 13) is arranged in the intermediate space of the bias coil (4, 5, 6, 7, 12).