ULTRASOUND MEASURING ARRANGEMENT

Description

[0001] The invention relates to an ultrasonic measuring arrangement for determining physical properties of a liquid or gaseous measuring medium within a high-pressure chamber, with an ultrasonic sensor for external arrangement on the high-pressure chamber via a coupling path.

[0002] The field of application of the invention extends primarily to automotive applications in which physical properties, such as the temperature, of high-pressure liquid or gaseous measuring media must be determined. Within the scope of such hydraulic or pneumatic measurements using an ultrasonic sensor, rapid temperature measurements in the millisecond range can be carried out using thermodynamic relationships. This allows, in particular, the injection behavior of motor vehicle injection systems, for example, gas injectors, to be investigated. In the high-pressure applications of interest here, media pressures of well over 10 bar up to approximately 260 bar prevail within the high-pressure chamber serving as the measuring chamber for the ultrasonic measuring arrangement.

[0003] Under these extreme pressure conditions, expansion of the high-pressure chamber must be avoided to prevent measurement errors during ultrasonic measurements. Ultrasonic sensors of the type of interest here cannot be directly subjected to the aforementioned high pressures, as this would result in damage. Signal coupling via conventional simple acoustic impedance layers on the high-pressure chamber fails due to their softness, as this would result in undesirable chamber expansion. State of the art

[0004] DE 10 2015 219 236 A1 discloses an ultrasonic measuring arrangement as a component of a device for flow measurement in a gas injector, comprising a high-pressure chamber for at least indirectly arranging an outlet region of the gas injector, a valve device connected to the high-pressure chamber, by means of which an outlet cross-section of the high-pressure chamber and the pressure prevailing in the high-pressure chamber can be adjusted, and measuring means for detecting physical properties of the gaseous measuring medium. These measuring means comprise at least one pressure sensor and, for example, an ultrasonic sensor for rapid temperature detection. The measuring means must be arranged in or on the high-pressure chamber in a suitable manner to ensure reliable measurement under the prevailing high-pressure conditions.

[0005] JP 2009 298157 A discloses a device for monitoring errors when testing a volume change in a sensor chamber. US 2014 / 275863 discloses a device and method for analyzing the properties of a fluid. A sensor module used therein comprises a transducer element for generating and converting acoustic signals. The sensor module is arranged, for example, in the stomach of a cow. WO 81 / 00768 A1 discloses special probes for ultrasound examination. These probes use a special working tip made essentially of titanium and provided with an aluminum coating on its tip by vacuum vapor deposition. Disclosure of the invention

[0006] It is the object of the present invention to further improve an ultrasonic measuring arrangement of the generic type so that it delivers a useful signal that can be reliably evaluated by signal processing technology with minimal expansion into the high-pressure chamber.

[0007] This object is achieved based on an ultrasonic measuring arrangement according to the preamble of claim 1 in conjunction with its characterizing features. The following claims reflect advantageous developments of the invention. The application-related claim 10 is directed to a gas injector of a fuel injection system for a motor vehicle.

[0008] The invention includes the technical teaching that the coupling section comprises a plastic layer on the high-pressure chamber side with an adjacent damped light metal layer, on which the external ultrasonic sensor is arranged. Mounting can be achieved, for example, by adhesive bonding.

[0009] Tests have shown that the impedance jumps in the ultrasonic signal resulting from this special layer structure are so small that sufficient useful signal still passes through the coupling path. On the other hand, the layer structure according to the invention also ensures sufficient rigidity of the coupling path, so that a sufficiently low chamber expansion occurs even at high pressures of up to 300 bar.

[0010] In a coupling system constructed according to the invention, the light metal layer serves to stiffen the structure, which requires a certain thickness of the light metal layer. If the layer thickness exceeds the wavelength of the ultrasonic vibration, longitudinal reflections within the layer occur. These reflections must be damped to avoid interference with the desired signal.

[0011] Preferably, the plastic layer in the layered structure of the coupling path should be made of a synthetic resin or a lightweight glass ceramic. Due to their relatively low material density, these materials are characterized by low acoustic impedance, resulting in a significantly smaller impedance jump along the signal transmission path compared to a light metal layer.

[0012] A further improvement to the invention can be achieved by using fiber-reinforced synthetic resin for the plastic layer. Conventional glass fibers or carbon fibers are primarily used for this purpose. A suitable fiber-reinforced synthetic resin material could be, for example, carbon fiber-reinforced plastic (CFRP). The fibers contained in the plastic layer contribute to signal attenuation, so that it decays more quickly. Another suitable lightweight glass-ceramic material is Macor®, which consists of a glass matrix with mica crystals.

[0013] For good coupling of the ultrasonic signal from the light metal, the thickness of the plastic layer should be adjusted to the wavelength λ of the ultrasonic signal and should be in the range of 0.25 to 1 λ. Thus, the layer thickness must be adjusted to the transducer frequency and the speed of sound of the plastic to optimize the coupling and suppress ringing. In the example presented here, an optimum layer thickness of 1.8 to 2.2 mm, preferably approximately 2 mm, was achieved.

[0014] In order to keep the signal attenuation at the transition points between the transducer and light metal and the light metal and plastic as low as possible, the surface roughness should be compensated by a coupling medium such as silicone or machine grease.

[0015] In combination with this, the damped light metal layer preferably consists of a combination of a light metal material, such as aluminum, magnesium, titanium, or an alloy thereof, with a damping agent, such as machine grease. The light metal material provides the necessary stiffness of the coupling section to ensure the desired low chamber expansion.

[0016] According to a measure further improving the invention, it is proposed that the light metal layer be provided with a web structure running in the signal transmission direction, the interstices of which are at least partially filled with the damping agent. In the simplest case, such a web structure can be created in the form of through-holes in an aluminum plate. It is further proposed that the sensor-side opening surface be provided with a thin cover layer made of the light metal material so that the damping agent cannot escape from the holes. The plastic layer arranged on the opposite opening surface ensures a corresponding hole closure on the chamber side.

[0017] The bridge structure within the light metal layer ensures direct transmission of the sound, with the damping agent filled in the gaps, such as machine grease, dampening the signal's reverberation.

[0018] Such a light metal layer used for stiffening tends to vibrate at a layer thickness of 1 λ and should be damped. The thicker the plate, the greater the stiffness and the longer the vibration persists. In the example, a very good compromise was found with a layer thickness between 4 mm and 8 mm, preferably 6 mm. Detailed description based on drawing

[0019] Further measures improving the invention are presented below, together with the description of a preferred embodiment of the invention, with reference to the single figure. The figure shows a schematic longitudinal section through an ultrasonic measuring arrangement on a high-pressure chamber of a fuel injection system (not shown) for a motor vehicle.

[0020] The ultrasonic measuring arrangement is located at the edge of a high-pressure chamber 1 - shown here only in part - which contains a gaseous measuring medium 2 flowing through it in the form of a gaseous fuel which is under a pressure of up to 300 bar.

[0021] Physical properties of this gaseous measuring medium 2, for example its temperature, are determined via an external ultrasonic sensor 3 with transmitter and receiver functionality, which is connected via a coupling section 4 delimiting the high-pressure chamber 1.

[0022] In this embodiment, the ultrasonic sensor 3 consists of a known piezoceramic. The ultrasonic signal transmitted from the ultrasonic sensor 3 via the coupling path 4 into the gaseous measuring medium 2 is reflected by an opposite wall (not shown) of the high-pressure chamber 1 and travels in the opposite direction through the coupling path 4 back to the ultrasonic sensor 3, which receives the reflected measuring signal. From the resulting transit time differences and other signal properties, the temperature of the gaseous measuring medium 2, for example, can be calculated based on the thermodynamic relationships known to me.

[0023] For this purpose, a coupling link 4 with low transmission losses is required in order to be able to detect a sufficiently high useful signal component for signal evaluation.

[0024] For this purpose, the coupling section 4 according to the invention has a special layer structure which consists of a plastic layer 5 adjacent to the high-pressure chamber 1 with a damped light metal layer 6 adjacent thereto, which is connected to the external ultrasonic sensor 3 via a thin cover layer 7.

[0025] In this embodiment, the plastic layer 5 has a thickness of approximately 2 mm and consists of a fiber-reinforced synthetic resin, specifically CFRP.

[0026] The adjacent damped light metal layer 6 has a layer thickness of approximately 6 mm in this embodiment and is made of a light metal material, in this case aluminum, which is provided with a damping agent. For this purpose, the light metal layer 6 has a web structure 9 running in the signal transmission direction, the interstices of which are filled with the damping agent 8, in this case a conventional machine grease.

[0027] Experimental tests with such a layer structure for a coupling section 4 have shown that when the high-pressure chamber 1 is filled with nitrogen as the test gas, an attenuation of 86.9 dB occurs at a pressure of 30 bar and an attenuation of 50.8 dB occurs at a pressure of 250 bar. This shows that the transmission losses are so low that sufficient useful signal still reaches the ultrasonic sensor 3 for signal evaluation. At the same time, the layer structure of the coupling section 4 according to the invention ensures sufficiently high rigidity to prevent excessive chamber expansion, even at high pressures of up to 300 bar.

[0028] The invention is not limited to the preferred embodiment described above. Rather, modifications thereof are also conceivable, which are also encompassed by the scope of the following claims. For example, it is also possible to use a different plastic material for the plastic layer 5. For the damped light metal layer, magnesium or the like can also be considered as the base material, and the longitudinal web structure preferably incorporated therein can also be formed in a manner other than with a drilled hole pattern, for example, as a columnar structure or the like.

Claims

1. Ultrasonic measuring arrangement for determining physical properties of a liquid or gaseous measuring medium (2) inside a high-pressure chamber (1) of the ultrasonic measuring arrangement, comprising an ultrasonic sensor (3) for arrangement on the high-pressure chamber (1) via a coupling path (4) of the ultrasonic measuring arrangement, characterized in that the ultrasonic sensor is arranged externally on the high-pressure chamber and the coupling path (4) comprises a layer of plastic (5) on the high-pressure chamber side with an adjoining layer of light metal (6), which is damped with respect to layer-internal reflections in the longitudinal direction and on which the external ultrasonic sensor (3) is arranged, and in that the damped layer of light metal (6) consists of the combination of a light-metal material with a damping means (8).

2. Ultrasonic measuring arrangement according to Claim 1, characterized in that the layer of plastic (5) consists of a synthetic resin.

3. Ultrasonic measuring arrangement according to Claim 2, characterized in that the synthetic resin of the layer of plastic (5) is fibre-reinforced.

4. Ultrasonic measuring arrangement according to Claim 3, characterized in that the layer of plastic (5) consisting of a fibre-reinforced synthetic resin has a thickness corresponding to 0.25 to 1 λ of the ultrasonic signal.

5. Ultrasonic measuring arrangement according to Claim 1, characterized in that the damped layer of light metal (6) has a rib structure (9) of the light metal extending in the direction of signal transmission, the gaps of which are at least partially filled with the damping means (8).

6. Ultrasonic measuring arrangement according to Claim 1, characterized in that aluminium, titanium, magnesium or an alloy containing at least one of these light metals is used as the light-metal material and in that machine grease is used as a damping means (8) combined therewith.

7. Ultrasonic measuring arrangement according to Claim 1, characterized in that the damped layer of light metal (6) has a thickness of between 4 and 8 millimetres.

8. Ultrasonic measuring arrangement according to Claim 1, characterized in that the ultrasonic sensor (3) is produced from a piezo ceramic and is provided with a combined transmitter and receiver functionality.

9. Gas injector of a fuel injection system for a motor vehicle comprising an ultrasonic measuring arrangement according to one of the preceding claims.