FIELD

[0001] Cylinder pressure sensors are used to improve the efficiency and emissions in combustion engines. Such sensors are currently used in large diesel combustion engines in a variety of applications including marine engines. However, there are a wide variety of applications for cylinder pressure sensors and they may be deployed in a wide variety of combustion engines and other cylinder based applications such as air compressors and hydraulic systems.

BACKGROUND

[0002] Cylinder pressure is an important control parameter for closed loop control of combustion engines. Existing cylinder pressure sensors, typically based on either piezoelectric or piezoresistive measurement, suffer from poor reliability and longevity. In many cases the operational life time of existing cylinder pressure sensors is a tenth of the expected time between major engine overhaul. The poor reliability and longevity of current sensors causes drastic increases in maintenance costs and increases out of service times for engines. As an example, existing cylinder pressure sensors have a typical lifetime of about 2000 hours and the target for marine applications of such sensors is 16000 hours. [0003] Typically cylinder pressure sensors of the piezoresistive varieties include a strain gauge which is attached to a bending membrane. The bending membrane bends the gauge and the electrical resistivity of the sensor gauge changes. This change in the electrical resistivity can be measured. Piezoelectrical sensors include a piezoelectrical ceramic which is compressed with pretension in between a moving membrane and a rigid support. Applying pressure to the membrane causes an electrical charge which can be measured.

[0004] Typically, in existing sensor designs, the measuring element is in direct contact with a hot deflecting membrane. This causes high mechanical and thermal stresses to the measuring element. Therefore there is a need for thermal insulation between the sensing element and the membrane. Such implementations are difficult and often lead to difficult mechanical solutions. In the presented solution these problems are solved and a simple and reliable pressure sensor can be implemented.

SUMMARY OF THE INVENTION [0005] An object of certain embodiments of the present invention is to provide a simple and reliable capacitive pressure sensor. Through such embodiments, a simple, robust and reliable capacitive cylinder pressure sensor can be realized.

[0006] Certain embodiments of the present invention provide for a capacitive pressure sensor which may be employed in combustion engines. Such capacitive pressure sensors provide for measurement of cylinder pressure within the combustion engine.

[0007] The high temperature and repeated stress provided by the cylinder of an internal combustion engine provide a challenging employment of pressure sensors. Some embodiments of the present invention allow for measurement of these challenging environments by insulating certain components of the pressure sensor from the high heat and pressure environment of the cylinder.

[0008] Some embodiments of the present invention comprise a housing, variable capacitor and an associated circuitry. The housing may be formed of a steel cylinder having a bottom surface and an outer surface. The outer surface may be threaded to allow for installation to the cylinder head of a combustion engine. The variable capacitor may be formed by a stationary electrode and an elastically bendable electrode. Pressure exerted on the bottom surface acts to bend the elastically bendable electrode. This bending alters the capacitance of the variable capacitor. The associated circuitry may be configured to generate a signal based on the variable capacitance of the variable capacitor. This capacitance is representative of the pressure exerted on the bottom surface. As such there is no need for mechanical contact to a hot membrane and certain problems of the existing solutions are avoided.

[0009] Some embodiments of the present invention employ ceramics such as Low

Temperature Co-fired Ceramics (LTCC). These ceramics may serve to form a structure internal to the housing of the sensor. [0010] According to a first aspect of the present invention, there is provided a capacitive pressure sensor mountable to the cylinder head of combustion engine. The housing having a bottom surface and a variable capacitor. The variable capacitor is formed by a stationary electrode and an elastically bendable electrode. The stationary electrode being disposed within the housing and the elastically bendable electrode 24 being arranged to be bent by a pressure exerted on the bottom surface and thereby the variable capacitance of the variable capacitor being representative of the pressure exerted on the bottom surface. The sensor may also comprise circuitry 30 configured to generate a signal based on the pressure dependent capacitance of the variable capacitor, the signal being representative of a pressure exerted on the bottom surface.

[0011] Various embodiments of the first aspect may comprise at least one feature from the following bulleted list:

• the elastically bendable electrode forms at least a portion of the bottom surface

• the stationary electrode is substantially parallel to the elastically bendable electrode

• the bottom surface is configured to be exposed to the cylinder of the combustion engine

• the elastically bendable electrode is configured to be exposed to the cylinder of the combustion engine

• the capacitive pressure sensor further comprising a thermal insulating component disposed at least partially between the bottom surface and the circuitry

• the elastically bendable electrode is elastically bendable at pressures exerted on the bottom surface below 20 bar, 50 bar, 80 bar, 100 bar, 200 bar, 300 bar, or 400 bar

• the thermal conductivity between the bottom surface and the circuitry is less than 3.5 (W / (m*K)) the stationary electrode is comprised of ceramic such as Low Temperature Co-fired Ceramic (LTCC) • the capacitive pressure sensor further comprising a first conductive structure electrically connected to the stationary electrode and a second conductive structure electrically connected to the elastically bendable electrode

[0012] According to second aspect of the present invention, there is provided a method of installation of a capacitive pressure sensor to a cylinder head of an internal combustion engine.

[0013] According to third aspect of the present invention, there is provided a combustion engine comprising a cylinder head having a capacitive pressure sensor. [0014] According to a fourth aspect of the present invention, there is provided a cylinder head for combustion engine comprising a capacitive pressure sensor of any of embodiments of the invention.

[0015] According to a fifth aspect of the present invention, there is provided a capacitive pressure sensor apparatus for measuring pressure in a cylinder of the engine, the sensor apparatus comprising a cylindrical housing mountable to the cylinder head of an internal combustion engine and having a side wall, a stationary electrode disposed within the housing, and a movable electrode exposed and responsive to pressure changes in the cylinder, said electrodes forming a capacitor having a capacitance varying according to said pressure changes, a circuitry for generating a signal representing said varying capacitance.

[0016] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIGURE 1 illustrates schematic view of a capacitive pressure sensor in accordance with at least some exemplary embodiments having a cylindrical housing and comprising a variable capacitor formed by a stationary electrode and an elastically bendable electrode, [0018] FIGURE 2 illustrates a schematic view of a capacitive pressure sensor in accordance with at least some exemplary embodiments of the present invention wherein the elastically bendable electrode forms a portion of the housing,

[0019] FIGURE 3 illustrates a schematic view of a capacitive pressure sensor in accordance with at least some exemplary embodiments of the present invention wherein the stationary electrode is made of steel and insulated with ceramic insulators,

[0020] FIGURE 4 illustrates a schematic view of a capacitive pressure sensor in accordance with at least some exemplary embodiments of the present invention wherein both the stationary electrode and the elastically bendable electrode are formed by Low Temperature Co-fired Ceramics (LTCC), and

[0021] FIGURE 5 illustrates a capacitance readout solution according with at least some exemplary embodiments of the present invention.

EXEMPLARY EMBODIMENTS [0022] In certain embodiments of the present invention, a housing of the sensor is defined by a bottom surface, side surface and top surface. The housing may be cylindrical with circular top and bottom surfaces. In such instances the side surface would be the surface along the perimeter of the cylinder.

[0023] According to some embodiments of the present invention a capacitive pressure sensor is provide as comprising a housing having a bottom surface, variable capacitor and an associated circuitry. The variable capacitor is formed by a stationary electrode and an elastically bendable electrode. Pressure exerted on the bottom surface acts to bend the elastically bendable electrode. This bending alters the capacitance of the variable capacitor. The circuitry is configured to generate a signal based on the variable capacitance of the variable capacitor. This capacitance is representative of the pressure exerted on the bottom surface. The circuitry may be disposed inside the housing, outside on the housing or outside separate from the housing. The circuitry may be electrically connected to the variable capacitor by appropriate electrical connecting means, such as a coaxial wire. [0024] FIGURE 1 illustrates a schematic view of a capacitive pressure sensor 100 in accordance with at least some embodiments of the present invention. The capacitive pressure sensor 100 is mountable to the cylinder head of a combustion engine. The capacitive pressure sensor comprises a housing 10, variable capacitor 20 and an associated circuitry 30. The housing has a bottom surface 12. The variable capacitor 20 is formed by a stationary electrode 22 and an elastically bendable electrode 24. The stationary electrode 22 being disposed within the housing 10 and the elastically bendable electrode 24 being arranged between the stationary electrode 22 and the bottom surface 12. The sensor may also have the associated circuitry 30 being configured to generate a signal based on the variable capacitance of the variable capacitor 20, the signal being representative of a pressure exerted on the bottom surface 12.

[0025] As shown in Figure 1, in some embodiments of the present invention the elastically bendable electrode 24 may form at least a portion of the bottom surface 12.

[0026] In certain embodiments of the present invention an outer surface 14 of the housing 10 is cylindrical. The housing may form a cylinder. In such embodiments the bottom of the cylinder may be dimensioned such that it deflects as a function of pressure.

[0027] In certain embodiments the internal structure may be formed by ceramics, for example, Low Temperature Co-Fired Ceramics. In such instances LTCC layers may form the internal structure. This structure can provide for a gap between the stationary electrode 22 and the elastically bendable electrode 24 which form the variable capacitor 20. The internal structure may also function as a heat insulator between the bottom surface 12 and the remaining components.

[0028] As illustrated in Figure 1 , in certain embodiments, the internal structure may be mechanically compressed within the housing 10. This may be accomplished by a mechanical clamping structure. The mechanical clamping structure can consist of a compressing nut 76, PCB 70 and first conductive structures 62. The compressing nut may be separated from the mechanical clamping structure by springs 74. In such instances the springs 74 ensure the proper clamping force.

[0029] Also illustrated within Figure 1 are electrical contacts 60 and first conductive structures 62. The conductive structures may electrically connect the stationary electrode 22 to the circuitry 30, e.g. via the printed circuit board (PCB) 70. The circuitry 30 may be affixed to the printed circuit board 70. The circuitry 30 may be electrically connected to the first conductive structures 62 through the PCB 70.

[0030] As further illustrated by Figure 1, in certain embodiments the stationary electrode may be comprised of ceramic such as LTCC. This may be formed in a layered fashion.

[0031] Also illustrated in Figure 1 is a wire 32 for transmitting of the signal generated by the circuitry. This wire 32 may transmit the signal to an engine control unit for close control of an engine to which the sensor is equipped.

[0032] In certain embodiments of the capacitive pressure sensor may further comprise threads 40 disposed on at least a portion of the outer surface 14 of the housing 10.

[0033] In some embodiments of the present invention, the housing 10 may have a threaded 40 outer surface 14.

[0034] In some embodiments of the capacitive pressure sensor the elastically bendable electrode 24 may be arranged to elastically bend responsive to the pressure exerted on the bottom surface 12.

[0035] In certain embodiments of the present invention the measurement resolution of the capacitive pressure sensor can be estimated with the aid of the following equations: APmin = (d/β) * ( V/V), where β = ( d )/ P. Within the equations APmin refers to the measurement resolution, d is the distance between the stationary electrode 22 and elastically bendable electrode 24 and d is the displacement of elastically bendable electrode, P is a pressure change, V is representative of electronics noise and V is the applied measurement voltage. As an example of estimation as per the supplied equations, if the mechanical sensitivity is P=7n/bar, electrode gap is d = 50 μιη, electronics noise is AV =3nV/VHz and measurement voltage is V = 3V the resolution of the 10 kHz band is -lmbar. For example, the required measurement resolution for diesel engine having a capacity greater than 1 MW is 10 bar@10 kHz BW.

[0036] In certain embodiments the stationary electrode 22 may be disposed substantially perpendicular relative to the outer surface 14 of the housing 10. [0037] In some embodiments of the present invention, the bottom surface 12 may be configured to be exposed to the cylinder of the combustion engine.

[0038] In certain embodiments of the present invention the elastically bendable electrode 24 may be configured to be exposed to the cylinder of the combustion engine. [0039] FIGURE 2 illustrates a schematic view of a capacitive pressure sensor 100 according to certain exemplary embodiments of the present invention wherein a compressing nut 76 may provide a mechanical clamping force. The clamping force affixes the stationary electrode 22 to the housing 10. Insulators 52 may be positioned at least partially between the stationary electrode 22 and the housing 10. The insulators may be ceramic. The insulators may also be MICA. The insulators electrically insulate the stationary electrode 22 from the housing 10.

[0040] Some embodiment may comprise springs 74 disposed at least partially between the compressing nut 76 and stationary electrode 22. The stationary electrode 22 may be electrically insulated from the springs 74 by further insulators 52. [0041] A thermal insulating component may be disposed between the compressing nut 76 and support plate 72.

[0042] Figure 3 illustrates a schematic view of a capacitive pressure sensor 100 according to certain embodiments of the present invention. The stationary electrode 22 may be comprised of steel and insulated with insulators 52. The insulators may be ceramic. The insulators may also be MICA. The insulators electrically insulate the stationary electrode 22 from the housing 10. The stationary electrode 22 may be fastened to the housing via tightening bolts or screws 82. The tightening bolts or screws 82 may be also insulated from the stationary electrode 22 by the insulators 52. Springs 74 may be disposed between the stationary electrode 22 and the tightening bolts or screws 82. [0043] A thermal insulating component may be disposed between the stationary electrode 22 and a support plate 72. The PCB 70 may be supported at least partially by the support plate 72. Affixed to the PCB may be circuitry 30 configured to generate a signal based on the variable capacitance of the variable capacitor 20. The circuitry 30 may alternatively be disposed in various other ways inside the housing, outside on the housing or outside separate from the housing. A wire 32 may provided that is electrically connected to the variable capacitor and/or the PCB 70 and may be connected to another component or to the circuitry 30 disposed separate from the housing.

[0044] A coaxial wire 34 may be provided for electrically connecting the stationary electrode 22 with the circuitry 30. The circuitry may be disposed inside the housing, outside on the housing or outside separate from the housing. The coaxial wire 34 may be connected to the stationary electrode 22 via a clamped contact 66. The coaxial wire 34 or corresponding connecting electrode and clamped contact 66 may be an integrated part of the stationary electrode 22.

[0045] The variable capacitor 20 may be formed by the stationary electrode 22 and the elastically bendable electrode 24 which forms a portion of the housing 10.

[0046] As illustrated by Figure 3, in certain embodiments of the present invention a thermal insulating component 50 may be disposed at least partially between the bottom surface 12 and the circuitry 30. This thermal insulating component may be, for example, stone wool. [0047] According to certain embodiments of the present invention the capacitive pressure sensor is mountable to the cylinder head of an internal combustion engine.

[0048] Figure 4 shows a schematic view of a capacitive pressure sensor according to certain embodiments of the present invention. In the illustrated embodiment the internal structure of the sensor may be adhered to the housing via an adhesive 80. This adhesive may be applied to the housing such that it is between the bottom surface 12 and the internal structure. In such applications a high temperature glue may be used, for example a ceramic adhesive.

[0049] When the portion of the housing forming the bottom surface 12 elastically bends, it causes the elastically bendable electrode to bend and the variable capacity of the variable capacitor to change.

[0050] As also shown in Figure 4, the elastically bendable electrode 24 may be comprised of ceramic such as LTCC.

[0051] As shown in Figure 4, in certain embodiments of the present invention there are first conductive structures 62 electrically connected to the stationary electrode 22 and a second conductive structure 64 electrically connected to the elastically bendable electrode 24. These structures electrically connect the electrodes to the PCB 70 and/or circuitry 30.

[0052] In some embodiments of the present invention a thermal insulating component 50 may be disposed at least partially between the bottom surface 12 and the elastically bendable electrode 24.

[0053] Also shown in figure 4 are structural material layers 78. These layers may also be comprised of a ceramic such as LTCC.

[0054] Figure 5 illustrates a capacitance readout solution according to certain embodiments of the present invention. [0055] In certain embodiment of the present invention electrical conducting components are integrated within ceramic, for example, LTCC.

[0056] In some embodiments of the present invention, the elastically bendable components may be elastically bendable when exposed to pressures seen within the combustion chamber of combustion engine. In some instances the elastically bendable electrode 24 may be elastically bendable at pressures exerted on the bottom surface 12 below 20 bar, 50 bar, 80 bar, 100 bar, 200 bar, 300 bar, or 400 bar .

[0057] In certain embodiments of the present invention the circuitry 30 may be thermally isolated from the bottom surface 12. The thermal conductivity between the bottom surface 12 and the circuitry 30 may be, for example, less than 3.5 (W / (m*K)).

[0058] In some embodiments of the present invention the bottom surface 12 of the housing 10 may be elastically bendable. In such instances the components between the bottom surface 12 and the elastically bendable electrode 24may also be elastically bendable. [0059] A method of installation of the capacitive pressure sensor according to an embodiment of the present invention comprises the steps of affixing the capacitive pressure sensor to a cylinder head of combustion engine.

[0060] An internal combustion engine according to some embodiments of the present invention comprises a cylinder head having the capacitive pressure sensor according to an embodiment of the present invention affixed to said cylinder head. [0061] A cylinder head for a combustion engine according to some embodiments of the present invention comprises the capacitive pressure sensor according to an embodiment of the present invention affixed to said cylinder head.

[0062] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0063] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[0064] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0065] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0066] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[0067] The verbs "to comprise" and "to include" are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, a singular form, throughout this document does not exclude a plurality.

INDUSTRIAL APPLICABILITY [0068] At least some embodiments of the present invention find industrial application in control systems of combustion engines. Some embodiments comprise pressure sensor applications in other harsh environment at high temperature and/or at high pressure such as air compressors and hydraulic systems.

REFERENCE SIGNS LIST

10 Housing

12 Bottom Surface

14 Outer Surface

20 Variable Capacitor

22 Stationary Electrode

24 Elastically Bendable Electrode

30 Circuitry

32 Wire

34 Coaxial Wire

40 Threads

50 Thermal Insulating Component

52 Insulator

60 Electrical Contacts 62 First Conductive Structure

64 Second Conductive Structure

66 Clamped Contact

70 Printed Circuit Board (PCB)

72 Support Plate

74 Spring

76 Compressing Nut

78 Structural Material Layer

80 Adhesive

82 Tightening Screw

100 Pressure Sensor

P Pressure