EP1797407A1

EP1797407A1 - Combustion chamber piezoelectric pressure sensor provided with a pressure-transmitting pin

Info

Publication number: EP1797407A1
Application number: EP05779167A
Authority: EP
Inventors: Gottfried Flik; Oliver Stoll; Juergen Krueger; Sven Zinober
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2004-09-29
Filing date: 2005-08-19
Publication date: 2007-06-20
Also published as: DE102004047143A1; WO2006034928A1; KR20070062986A; JP2008514940A; US20090025468A1

Abstract

The invention concerns a sensor (SE) consisting of single-crystal and piezoelectric material (1) for measuring pressure (6) in an internal combustion engine combustion chamber, comprising a pressure-transmitting pin. Said pressure-transmitting pin is in the form of a preheating pencil (4) slidably mounted and projecting into the combustion chamber and the sensor (SE) is force-closed to the preheating pencil (4). The sensor (SE) is preferably placed between the preheating pencil (4) and a fixed stop (5). The single-crystal piezoelectric material (1) of the sensor (SE) is advantageously lithium niobate (LiNbO3). The use of the piezoelectric material (1) in Z-shaped cut and Y-shaped cut enables particularly high sensitivity to be obtained.

Description

Piezoelectric combustion chamber pressure sensor with a pressure transfer pin

State of the art

The invention relates to a piezoelectric sensor for measuring the pressure in a combustion chamber of an internal combustion engine with a pressure transfer pin.

For various applications, it is desirable to detect the pressure prevailing in a combustion chamber through a suitable sensor. A sensor made of a piezoelectric material for determining the pressure in a combustion chamber of an internal combustion engine is known, for example, from DE-692 09 132 T2. As is well known, a piezoelectric material on which a mechanical pressure is applied generates electric charges. These charges result in an electrical voltage in the piezoelectric material that can be tapped and measured. Since, in the case of direct exposure of the piezoelectric material in the combustion chamber, the sensor is damaged, inter alia, for thermal reasons, the pressure in the combustion chamber is first exerted on a pressure-receiving component which is directly exposed to the combustion chamber. The pressure-receiving component then forwards the pressure to the piezoelectric material of the sensor. According to the teaching of the cited document, the pressure is first applied to a diaphragm on the cylinder head Internal combustion engine exerted, which is then transferred via a diaphragm connected to the pressure transfer pin on the piezoelectric material.

However, the device described in the prior art has certain disadvantages in practice. First, membranes are basically problematic as a pressure receiver in a combustion chamber, since the life of such a component by z. As contamination, especially by soot particles is limited. The mechanical stability of a membrane is also critical in comparison with other components. Furthermore, in the presented device, the pressure sensor is provided as a single component on the cylinder head of the internal combustion engine. The existing on the cylinder head slot is very limited. For today's internal combustion engines but typically have multiple intake and exhaust valves per combustion chamber, and also in the direct injection technique in addition to a fuel injector for direct injection of fuel into the combustion chamber of the internal combustion engine in spark-ignited internal combustion engines also requires a spark plug to ignite the fuel. With auto-igniters a glow plug is necessary. A direct placement of the membrane with the pressure transfer pin on the combustion chamber therefore encounters difficulties.

Advantages of the invention

The inventive piezoelectric sensor SE with a pressure transfer pin with the specified features has the advantage over the prior art that an integration of the sensor in existing components of the engine allows and thus a space-saving Solution is provided. In particular, the known from the prior art membrane is omitted as a pressure-receiving component, whereby a reduction of the problem is achieved by contamination. Furthermore, the piezoelectric material of the sensor is advantageously decoupled from mechanical tightening torques and thermally induced mechanical stresses on the cylinder head and thus minimizes falsified pressure measurements.

Advantageous developments of the sensor according to the invention are specified in the subclaims and described in the description.

drawing

Embodiments of the invention will be explained in more detail with reference to the drawing and the following description. Show it:

1 shows a built-in glow plug, piezoelectric sensor with an abutment,

2a to 2c each show an embodiment of the sensor in section and in plan view,

FIG. 3 is a perspective view of a quartz crystal with the crystallographic axes X, Y and Z;

FIG. 4 a cross-sectionally hexagonal quartz crystal,

FIG. 5 shows a piezoelectric component in the X-section with a cutting angle θ, FIG. 6 shows the linear dependence of the sensitivity of the Z cut on the temperature,

7a shows a piezoelectric material 1 in the Z-section in a perspective view at a skewed force,

FIGS. 7b and 7c are vector illustrations illustrating the angles α and β, respectively;

Figure 8a and 8b, the sensitivity of the piezoelectric material in the Z-section as a function of the angle OC or ß, and

Figures 9a and 9b, the sensitivity of the piezoelectric material in the Y-section as a function of the angle OC or ß.

Description of the embodiments

FIG. 1 shows an exemplary embodiment of the sensor SE according to the invention, which is integrated into an incandescent glow plug and made of a monocrystalline, piezoelectric material 1. The sensor SE is arranged in a channel 2 relative to the combustion chamber of an internal combustion engine. However, it is not directly exposed to the pressure 6 of the combustion chamber, but positively connected to a glow plug 4. The glow plug 4 is partially arranged in the channel 2, but protrudes with one end into the combustion chamber and is displaceable, in particular axially displaceable, stored. Typically, the glow plug 4 in a gasket 3, in particular an O-ring, graphite ring or a metal bead stored. The sensor SE itself is arranged on the side facing away from the combustion chamber of the glow plug 4. Next is a rigid one Abutment 5 downstream of the sensor SE in the opposite direction of the combustion chamber.

Now, if a pressure 6 exerted on the glow plug 4, so the axially displaceably mounted glow plug 4 passes the pressure 6 on the piezoelectric material 1 on, which is mechanically deformed due to the downstream of him, rigid abutment 5. By a voltage measurement on the piezoelectric material 1, the value of the pressure 6 in the combustion chamber 3 can be derived. For picking up the voltage, the sensor SE of the piezoelectric material 1 is metallized on two sides, as shown in FIGS. 2a to 2c, to form electrodes 7, preferably with a chromium-gold (CrAu) layer, in particular alloy. The electrodes 7 are, as can be seen in Figure 1, arranged so that they are perpendicular to the pressure and are contacted with electrical leads 8 directly or alternatively indirectly via metal discs, not shown in the figures. Possible external shapes of the sensor SE are, in addition to a cuboid (FIG. 2 b) or a solid disc (FIG. 2 c), preferably those of a ring (FIG. 2 a), since the electrical leads 8 are then guided through the open center of the ring can. Through the open center of the ring and the electrical line for the glow current of the glow plug can be placed.

Due to the described arrangement of the sensor SE, the sensor SE is integrated into a glow plug or in an already existing channel 2 to the combustion chamber. Neither a separate channel 2 nor a separate pressure transfer pin for the sensor SE is necessary, but both are advantageously used for two different purposes. Also completely dispensed with a membrane as a pressure-receiving component. An additional advantage arises from that forces such as those acting through the tightening torque when screwing into the cylinder head on the Glühstiftkerzengehäuse have almost no effect on the sensor SE.

The sensor SE can be further improved by an appropriate selection of materials and by defined crystal cuts in its overall performance. In a piezoelectric sensor SE is used as the piezoelectric material 1 mainly quartz or piezoceramic. Both options, however, have certain advantages and disadvantages compared to each other. Thus, quartz is the one hand as the single-crystal version of the silicon dioxide SiO ₂ and no aging is temperature-stable up to a relatively high temperature of 573 ⁰ C. At an even higher temperature of the quartz transforms of the so-called α-modification in the ß-modification. Only then does the quartz lose its piezoelectric property. On the other hand, the quartz has only a small sensitivity of 2.3 pC / N, so that usually two piezo elements are connected in parallel in terms of charge. This requires a lot of effort and thus high costs in the construction and connection technology. In contrast, piezoelectric ceramics have a high sensitivity, which makes it possible to dispense with a complicated construction technique with a plurality of piezoelectric elements. However, disadvantageously, the sensitivity of the piezoelectric ceramics changes with the lifetime. The change is caused by depolarization in piezoelectric ceramics and severely restricts the potential for use of the material. The depolarization is accelerated at relatively large forces, so that these materials are operated only at low forces. In addition, high force effects lead to non-linear and hysteretic charge-force characteristics. This problem will at temperatures higher than 50% of the Curie temperature, further exacerbated.

In order to avoid the disadvantages of the two materials, the sensor SE according to the invention advantageously consists of the monocrystalline, piezoelectric material lithium niobate (LiNbO ₃ ). The Curie temperature of this material is above 1200 ^° C. At the same time, high sensitivity and low temperature response can be achieved through selected cuts from the crystal.

In order to be able to define the various sections from the crystal, a quartz crystal with the crystallographic axes X, Y and Z is first shown in a perspective view in FIG. Starting from the shape of a natural quartz crystal with a hexagonal cross-section and the usual definition of the mutually perpendicular axes X, Y and Z, we define as the Z-axis the imaginary axis passing through the tip of the crystal. A perpendicular axis passing through a corner of the hexagonal prism is determined to be the X axis. The Y axis is again perpendicular to the other two axes and thus passes through an area of the crystal. FIG. 4 shows the hexagonal crystal in cross section, ie the XY plane is seen in plan view. As already mentioned, the piezoelectric component can be cut out of the crystal to obtain certain properties, such as a minimum temperature response, below an optimum axial section and / or cutting angle θ. The sections are named after the crystallographic axis, which is normal to the main surface of the component. The main surface is the surface of the component, on which later the pressure or the force on the Component is coupled. For example, in FIG. 5, a piezoelectric component is shown in the X-section, since the component has been cut out of the crystal in such a way that the X-axis of the crystal is normal to the main surface of the component. The component includes a cutting angle θ simultaneously with the Y axis. The above-mentioned designations of the crystallographic axes X, Y and Z apply analogously to LiNbO ₃ crystals, wherein it should be noted that the cross section of the LiNbO ₃ crystal has the base of a ditrigonal prism. The exact geometric shape with the axis designations can be found in the literature.

Preferably LiNbO ₃ components are used with Z or Y-section, ie, the Z or Y-axis of the crystal is perpendicular to the main surface of the component or in other words, to the level of force coupling.

First, the sensitivity of a LiNbO ₃ device with a Z-cut is advantageously about three times larger than that of a quartz device. The temperature response is about 480 ppm / K and thus slightly more than in comparison to quartz, but the sensitivity S (= sensitivity), as can be seen from FIG. 6, changes linearly with the temperature T and is therefore particularly easily compensated. In addition, the Z-cut offers the advantage of a low cross-sensitivity to skew-angle force coupling. For a better illustration, the piezoelectric component with a Z-section in FIG. 7a is sketched in perspective representation with the crystallographic X, Y and Z axes. In accordance with the definition explained above, the Z-axis here extends perpendicular to the plane of a component with a Z-section Krafteinkoppelung. If a force F does not act perpendicular to this plane, but with an angle OC not equal to zero with respect to the Z-axis, then the total (total) force F _{tot can be} vectorially decomposed into a tangential component T _par parallel to the main surface or XY plane of the component, and a Z component F _z which is parallel to the Z axis. The vector decomposition of the total force F _tot into subcomponents T _par and F _z is shown in FIG. 7b, where the vectors F _tot and F _{z enclose} an angle OC. The

Tangential component T _par can in turn be decomposed into further components T _x and T _y , each of which runs parallel to the X or Y axis. The components T _par and T _x include an angle β, as shown in FIG. 7c. Further, Figs. 8a and 8b show the

Sensitivity S of the piezoelectric component in Z-section in percent change as a function of the angle OC or ß. The sensitivity S decreases only slightly.

With a sensitivity S of 20 pC / N, the Y-cut offers a significantly higher value compared to the previously mentioned values, and at the same time has a small temperature response of 240 ppm / K. However, the sensitivity depends very much on the angles OC and ß of the

Coupling in (FIGS. 9a and 9b). Oblique surfaces in the force coupling or non-parallelism of the surfaces of the piezoelectric component result in large angles OC and β, and thus influence the sensitivity. The inherently high sensitivity S can nevertheless be used if the component is installed carefully and correctly oriented in the channel 2. A certain degree of sensitivity variation can thus be adjusted and thus tolerated.

Claims

claims

A sensor (SE) of a monocrystalline, piezoelectric material (1) for measuring the pressure (6) in a combustion chamber of a

Internal combustion engine with a pressure transmission pin, that is provided as a pressure transmitting pin projecting into the combustion chamber, displaceably mounted glow plug (4), the sensor (SE) is non-positively connected to the glow plug (4).

2. Sensor (SE) with a pressure transfer pin according to claim 1, d a d e r c h e c e n e c e s in that the sensor (SE) on the side facing away from the combustion chamber of the glow plug (4) is arranged.

3. Sensor (SE) with a pressure transfer pin according to claim 1 or 2, d a d u c h e c e n e c e in that a rigid abutment (5) is downstream of the sensor (SE) in the opposite direction of the combustion chamber.

4. Sensor (SE) with a pressure transfer pin according to one of claims 1 to 3, characterized in that the glow plug (4) is slidably mounted in a seal (3), in particular an O-ring, graphite ring or a metal bead.

5. Sensor (SE) with a pressure transfer pin according to one of claims 1 to 4, characterized in that the monocrystalline, piezoelectric material (1) of the sensor (SE) is lithium niobate (LiNbO ₃ ).

6. Sensor (SE) with a pressure transfer pin according to one of claims 1 to 5, in that a single-crystal, piezoelectric material (1) of the sensor (SE) has a Z-cut or a Y-cut.

7. Sensor (SE) with a pressure transfer pin according to one of claims 1 to 6, characterized in that the monocrystalline piezoelectric material (1) on two sides, preferably with a chromium-gold (CrAu) layer, for forming electrodes (7 ) is metallized.

8. Sensor (SE) with a pressure-transmitting pin according to one of claims 1 to 7, characterized in that the sensor (SE) has the outer shape of a ring, a cuboid or a solid disc.

9. Sensor (SE) with a pressure transfer pin after

Claim 8, in that electrical lines (8) for the sensor (SE) and / or for the glow plug (4) are passed through the open center of the ring.