WO2008097227A2

WO2008097227A2 - Glow plug integrated pressure sensor improvements

Info

Publication number: WO2008097227A2
Application number: PCT/US2007/003468
Authority: WO
Inventors: Marek T. Wlodarczyk
Original assignee: Wlodarczyk Marek T
Priority date: 2007-02-08
Filing date: 2007-02-08
Publication date: 2008-08-14
Also published as: WO2008097227A3

Abstract

A pressure-sensing element for an internal combustion engine is located in the sleeve of a ceramic glow plug heater having axial and radial pressure channels connecting a pressure-sensing element diaphram to a combustion chamber.

Description

IN THE UNITED STATES PATENT AND TRADEMARK OFFICE

PATENT APPLICATION GLOW PLUG INTEGRATED PRESSURE SENSOR IMPROVEMENTS

The field of the invention pertains to internal combustion engines with pressure sensors adapted to directly measure individual cylinder pressures in real time and, in particular, fiber optic pressure sensors in spark plugs and glow plugs. Diesel engines can significantly benefit from cylinder pressure-based controls resulting in reduced harmful emissions, better fuel economy and drivability, and lower engine noise levels. Recently, as much as a 24% reduction in soot emissions and a 12% reduction of NOx emissions were demonstrated by a closed loop control of fuel injection timing and duration based on information provided by pressure sensors located in all engine cylinders. In passenger car and light duty truck engines, where glow plugs are used, a preferred way of introducing a cylinder pressure sensor into a combustion chamber is through a glow plug.

Applicant's fiber optic pressure sensors have been successfully used to measure the dynamic component of the combustion engine cylinder pressure. In the existing design based on two fibers applicant's sensor compensates for such error sources as LED temperature and aging effects, photodiode thermal dependence, fiber to LED/photodiode coupling dependence on temperature, as well as low frequency fiber bending. However, the current sensor only responds to the dynamic component of total cylinder pressure. Furthermore the present design does not compensate for light intensity changes associated with rapidly occurring fiber bending.

In addition, by providing an aperture in a glow plug for a fiber optic pressure sensor, a separate aperture into the combustion chamber is not necessary. However, the glow plug environment can be extreme with instantaneous temperatures in thousands of degrees Fahrenheit, rapid cyclic pressure changes and befouling combustion products. To control some of the effects of the extreme environment and provide more accurate pressure measurements over long-term operation, the following improvements to glow plug integrated pressure sensors have been developed. Summary of the Invention.

This invention teaches a novel glow plug with a built-in cylinder pressure sensor for use in diesel and other internal combustion engines. The pressure- sensing element is located in the sleeve of a ceramic glow plug heater having axial and radial pressure channels connecting the sensor diaphragm to the combustion chamber. The sensor signal conditioner is encapsulated in an automotive-type connector either directly attached to the glow plug body or located at the end of a cable pigtail containing the sensor fibers and the heater positive potential wire. A high temperature rated fiber optic pressure sensor capable of measuring either dynamic or absolute pressure is used.

The novel absolute pressure sensor of this invention relies on 3 optical fibers combined in a common ferrule in the sensor head area and connected to one light source (LED) and two detectors (photodiodes) in the signal conditioner area. The fibers can either be identical but spaced unequally in the ferrule or can have different diameters, numerical apertures, or both and be spaced equally or unequally. The fiber parameters or their spacing are selected to maximize the difference in the response of the "measurement" and "reference" detectors to changing pressure.

The sensor output is derived from the detectors' ratio resulting in the rejection of the common mode errors, such as LED output temperature dependence and aging, fiber bending, or thermal dependence of fiber to LED or photodiode coupling. For maximum linearity and sensitivity the sensor output is proportional to the ratio of the measurement detector signal divided by a difference of the measurement detector signal and the reference detector signal multiplied by a constant factor. This factor is selected for each sensor in such a way that the ratio denominator is independent of pressure resulting in an absolute pressure sensor with high linearity.

As an option, the aperture or axial pressure passage of the integrated glow plug and pressure sensor is provided with a porous filter inserted therein. The purpose of the filter is four-fold: (1) the filter acts as a trap for combustion deposits, (2) the filter burns combustion deposits when the glow plug heater is on, (3) the filter acts as a heat shield for reducing thermal shock error of the pressure sensor, and (4) the filter damps acoustic high frequency ringing associated with the pressure passage. The filter is preferably made of a corrosion-resistant wire mesh, such as already used in diesel particulate filters. The wire mesh filter can be easily modified in dimensions and porosity to accomplish all of the four functions above. With the radial pressure access hole located in the glow plug section that heats to over 600⁰C, the combustion deposits burn out whenever the glow plug is turned on. As an alternative, the filter may be made of a suitably porous ceramic material.

Brief Description of the Drawings.

FIG. 1 illustrates in cross-section a ceramic glow plug having the new sensor therein;

FIG. 2 illustrates in cross-section a ceramic glow plug having an alternative configuration for the new sensor therein;

FIG. 3A illustrates the external appearance of the ceramic glow plug of FIG. 2; FIG. 3B illustrates the directly attached glow plug connector;

FIG. 4 illustrates a pigtail glow plug connector;

FIG. 5 illustrates a ferrule arrangement for the optical fibers;

FIG. 6 is a graph of diaphragm distance versus voltage for the new sensor;

FIG. 7 illustrates in cross-section a ceramic glow plug having an alternative construction for the heater and new sensor therein;

FIG. 8 is a cross-section of a first version of the integral glow plug and filter therein;

FIG. 8 A is an external view of the first version of the integral glow plug of FIG. 8; FIG. 8B is an external view of the socket end of the first version of the integral glow plug of FIG. 8;

FIG. 9 is a cross-section of a second version of the integral glow plug and filter therein;

FIG. 9A is an external view of the second version of the integral glow plug of FIG. 9;

FIG. 9B is an external view of the socket end of the second version of the integral glow plug of FIG. 9;

FIG. 10 is a cross-section of a third version of the integral glow plug and filter therein; FIG. 1OA is an external view of the third version of the integral glow plug of FIG. 10;

FIG. 1OB is an external view of the socket end of the third version of the integral glow plug of FIG. 10; FIG. 11 is a cross-section of a ceramic heater integral glow plug with optical-electrical interface; and

FIG. 12 is a cross-section of a metal sheath heater integral glow plug with optical-electrical interface.

Description of the Preferred Embodiments.

This invention teaches a number of designs for a glow plug 6 with a built- in cylinder pressure sensor having a pressure-sensing element 10 mounted close to the ceramic heater 8 and heater wires 4 and with an axial bore and radial passages connecting the sensing element to the combustion chamber. The sensing element 10, sealed and welded 11 into a bore of the metal heater sleeve 12, is exposed to combustion gases in one of the two ways shown in FIG. 1 and FIG. 2. In the embodiment of FIG. 1, an axial bore pressure channel 14 and one or multiple radial holes 16 are located in the ceramic heater itself. By having the radial holes 16 located in the mid/upper section of the glow plug, high temperature in this area minimizes potential for soot clogging. In the design shown in FIG. 2, the axial channel 18 and the radial holes 20 are located in the glow plug metal sleeve 22. In order to minimize potential for soot deposits the radial holes 20 are located as close as practical to the top section of the sleeve 22 - for maximum temperature in the area where the holes are located. A diaphragm-type 2 intensity-modulated fiber optic pressure sensor 10 capable of measuring either dynamic pressure (previously patented by applicant) or a novel absolute pressure sensor is used. When a dynamic sensor is utilized the total cylinder pressure is established as the sum of a dynamic sensor output and the output of the Manifold Absolute Pressure (MAP) sensor. No MAP sensor is required when an absolute cylinder pressure sensor is used.

The absolute pressure sensor of this invention is based on three fibers cemented in a common ferrule in the sensor head area and connected in the signal conditioner section to a light source (LED) and two detectors (photo diodes). Compared to the dynamic sensor the purpose of the extra fiber and detector of the absolute sensor is to provide a "reference" channel required for cancellation of the common mode errors of the "measurement" and "reference" signals. In an "ideal" design the measurement and reference signals should behave identically under the effect of interfering factors but show maximum difference in their responses to pressure. In a preferred embodiment, "self-aligning" LED and photodiodes are used, as described in U.S. Pat. No. 6,758,086 by this applicant, for high LED coupling efficiency, thermal stability, and fiber- to-photodiode coupling consistency. Due to the miniature size of the "self-align" devices the sensor signal conditioner can be encapsulated into an automotive-type connector 24, either directly attached to the glow plug body 26 or located at the end of a pigtail cable 28 containing the sensor fibers 36, 38, 40 and the heater wire 4, as shown in FIG. 3 and FIG. 4, respectively. Three 30 (smaller diameter) out of four pins of the connector are for the sensor (power, ground, and output) while the fourth (larger in diameter) pin 32 is for the glow plug positive potential heater wire 4. The differential response of the measurement and reference detectors is due to the different responses of the two fiber pairs (formed by three fibers) to diaphragm deflection. The different responses are either due to different core, cladding, or buffer diameters of the fibers used, or their different numerical apertures, or all of the above. Alternatively, identical fibers can be cemented in the ferrule 34 such that their spacing is different between the two pairs, as shown in FIG. 5. The position of the fibers connected to the light emitting diode (LED) 36, measurement detector (MD) 38, and reference detector (RD) 40 are shown. The response of the measurement and reference detectors to changing diaphragm to fiber distance is shown in FIG. 6 for a sensor having fibers spaced as in FIG. 5. It is to be noted that in this invention all the fibers have their ends located the same distance from the sensor diaphragm.

Depending on the distance between the fibers ends and the diaphragm Do (set during sensor assembly), the measurement and reference detectors can respond differently to pressure. When the fibers are located in the ascending region 42 of the two curves, the outputs of both detectors decrease with pressure (fiber to diaphragm distance is reduced). When fibers are positioned near the reference curve peak location 44, the reference signal changes little with pressure while the measurement signal 46 decreases with increasing pressure. Conversely, when the fibers are located near the measurement curve peak 48, the reference signal 50 increases with increasing pressure. Finally, when fibers are located sufficiently away from the diaphragm, both measurement 52 and reference signals 54 increase with increasing pressure.

In a preferred design, the fiber to diaphragm distance of this novel sensor is set in the ascending part 42 of the curves at a point of maximum slope and linearity of the measurement channel Do- The radial separation between the fibers, or their dimensions and/or numerical aperture, are selected in such a way that the reference signal responds linearly to pressure for a given fiber location Do. For example, the optimum fiber location is approximately 100 microns (Do) away from the diaphragm for the fiber tip shown in FIG. 5.

If the measurement (V_m) and reference (V_r) signals depend linearly on pressure, then their dependencies can be expressed as:

Vi = I_c ( v_Oj + Sj x p) , for i = m, r , (1) where v_o,- and S; are the offset voltage and sensitivity, respectively, of the measurement (m) or reference (r) signals. I₀ is a pressure independent factor common to both channels and is a multiplicative product of LED intensity (I _LED), LED-to-fiber coupling efficiency (C _LED ), fiber-to-detector coupling efficiency (C_p), detector sensitivity (D_p), diaphragm reflectivity (R), and the square of the fiber transmission (T): I_c = I _LED x C _LED x C_p x D_p x R x T² . (2)

In a novel approach of this invention the sensor output is derived from the ratio of the measurement signal divided by the difference of the measurement signal and the product of the reference signal and a constant factor F:

V_0Ut - V_1nZ (V_n1- F x VO . (3) For maximum linearity of the sensor response the factor F is selected in such a way that the denominator of Eq. (3) is independent of pressure. From Eqs. (3) and (1) the value of F can be established then as:

F = S_m / S_r , (4) resulting in the linear response of the sensor: V_out(p) ~ (v_om + S_m x p)/ (v_om - S_m / S_r x v_or ) . (5)

Illustrated in FIG. 7 is a ceramic glow plug 6 having a central electrode 56 that extends through the metal sleeve 58 but is separated therefrom by a ceramic sleeve electrical insulator 60. The central electrode 56 is formed with an axial bore 62 or channel that broadens out to retain the sensing element 64, in turn sealed and laser welded into the electrode at 66. The laser welds 66 also retain the electrical conductor tube 68 to the central electrode 56. Radial holes 70 for combustion gases pass through both the metal sleeve 58 and the ceramic sleeve 60. Illustrated in FIGs. 8, 8A and 8B is a glow plug having a ceramic heater shell 110 with a resistance heater 112 therein. Supporting the ceramic heater shell 110 is a metal heater sleeve 114 in turn supported by the glow plug shell 116.

A plurality of radial pressure access holes 118 are formed in the metal heater sleeve 114 and communicate with a central axial passage or hole 120 through the metal heater sleeve. Separate axially directed holes are provided for the heater wires 122 and 124 leading to the resistance heater 112.

Located within the central axial hole 120 is a fiber optic pressure sensor 126 laser welded into the hole at 127 and having a sensor diaphragm 128.

Also located in the central axial hole 120 is a porous filter 130 of cylindrical shape. The porous filter 130 covers the radial pressure access holes 118 from the inside such that the sensor diaphragm 128 is only exposed to gases that have passed through the filter 130.

The porous filter 130 is preferably made of a high-temperature-resistant metal, such as high nickel stainless steel or refractory metal alloy, such as Inconel® or Hastelloy®. The metal mesh now commonly used for diesel exhaust particulate filters is suitable for the porous filter 130.

The heater wires 122 and 124 and fiber optic cable 132 lead to a socket 134 at the glow plug end opposite the ceramic heater shell.

Illustrated in FIGs. 9, 9A and 9B is a glow plug of an alternative embodiment having a ceramic heater shell 140 with a resistance heater 142 therein. The ceramic heater shell 140 is formed with a plurality of radial pressure access holes 148 in communication with a central axial hole 150 also formed in the ceramic heater shell. Located in the central axial hole 150 is a porous filter 160 of cylindrical shape. Supporting the ceramic heater shell 140 is a metal heater sleeve 144 having the central axial hole 150 extended there through. Also extending through the metal heater sleeve 144 is a pair of axially directed holes containing the heater wires 152 and 154 leading to the resistance heater 142. Located within the central axial hole 150 of the metal heater sleeve 144 is a fiber optic pressure sensor 156 laser welded into the hole at 157 and having a sensor diaphragm 158. The entire assembly is supported by the glow plug shell 146. As above, the heater wires 152 and 154 and fiber optic cable 162 lead to a socket 164 at the glow plug end opposite the ceramic heater shell 140.

Illustrated in FIGs. 10, 1OA and 1OB is a glow plug of another alternative embodiment having a metal sheath 170 enclosing a ceramic interior 172 and a coil 169 mounted on an electrode 168. The metal sheath 170 is mounted on a heater sleeve 174 in turn separated from the electrode 168 by a ceramic insert 166. The heater sleeve 174, electrode 168 and ceramic insert 166 are formed with a plurality of radial pressure access holes 178 in communication with a central axial hole 180 also formed in the electrode. Located in the central axial hole 180 is a porous filter 190 of cylindrical shape. Welded to the electrode 168 at 182 is an electrode tube 184, and located in the electrode tube and central axial hole 180 is a fiber optic pressure sensor 186 having a sensor diaphragm 188. The entire assembly is supported by the glow plug shell 176. The electrode tube 184 and fiber optic cable 192 lead to a socket 194 at the glow plug end opposite the metal sheath 170. FIGs. 11 and 12 illustrate further improvements in the glow plug integrated pressure sensors. In these embodiments, the opto-electronic interface is built into the glow plug thus providing a completely sealed environment for the critical optical components. The glow plug body 206 extends both inside and outside of a combustion chamber (not shown) as indicated by the threads 208. Extending from the body 206 is a heater shell 204. Within the body 206 is a concentric electrode extension 210 and electrode 212 leading to the ceramic heater 214 in FIG. 11 or the heater coil 216 enclosed in a heater shell sheath 218 in FIG. 12. The electric connection from the electrode 212 to the ceramic heater 214 or heater coil 216 is through a porous filter 220 of metal or other electrically conductive material. In FIG. 11, the porous filter 220 is bonded to the ceramic heater 214 with an electrode pin 222 and glass to wire mesh bond 224.

As above, a radial pressure hole 226 leads from the combustion chamber through the porous filter 220 to a diaphragm sensor 228 within the electrode extension 210. From the sensor 228 a plurality of optical fibers 230 connect with one or more self-aligning photo-diodes 232 and one or more light emitting diodes 234 mounted on a printed circuit board 236 and encapsulated in silicone 238. Under the printed circuit board is an integrated circuit 240 connected to the photo-diodes 232 and light emitting diodes 234 and, in turn, connected to the sensor electrical contacts 242. The opto-electronic interface lies within the electrode extension 210 and extended body 244 with a hex head 246. One or more high current contacts 248 for the ceramic heater 214 or heater coil 216 lie within the extended body 244. The integrated glow plug and pressure sensor units of FIGs. 11 and 12 are completely self-contained, needing only electrical connections.

Claims

1. An internal combustion engine glow plug comprising a heater shell, a heater enclosed within the shell and a glow plug body for supporting the heater and heater shell in an engine, an axial bore channel within the glow plug and at least one radial hole communicating at one end with the axial bore channel and so located as to communicate at the other end directly with an engine combustion chamber, a pressure sensor located in the glow plug and having a diaphragm thereon, said diaphragm being exposable to combustion gases entering the radial hole and axial bore channel, a heater sleeve attaching the heater shell to the glow plug body, said axial bore channel being formed in the heater and said radial hole being at least partially formed in the heater and passing through the heater sleeve, and a ceramic sleeve located between the heater and the heater sleeve.

2. An internal combustion engine glow plug comprising a heater shell, a heater enclosed within the shell and a glow plug body for supporting the heater and heater shell in an engine, an axial bore channel within the glow plug and at least one radial hole communicating at one end with the axial bore channel and so located as to communicate at the other end directly with an engine combustion chamber, a pressure sensor located in the glow plug and having a diaphragm thereon, said diaphragm being exposable to combustion gases entering the radial hole and axial bore channel, said pressure sensor being an absolute pressure sensor, the output of the absolute pressure sensor comprising a measurement signal and a reference signal, and wherein the absolute pressure sensor includes three optical fibers terminating with ends in a ferrule, the optical fiber ends being spaced from the diaphragm.

3. The engine glow plug of claim 2 wherein the distance between the ends of the first and second optical fibers differs significantly from the distance between the ends of the first and third optical fibers.

4. The engine glow plug of claim 3 wherein the pressure response of the absolute pressure sensor may be substantially represented by the expression:

V_Out(p) ~ (V_om + S_m X p)/ (V_om - S_n, / S_r X V_or ) .

5. An internal combustion engine of glow plug comprising a heater shell, a heater enclosed within the shell and a glow plug body for supporting the heater and heater shell in an engine, an axial bore channel within the glow plug and at least one radial hole communicating at one end with the axial bore channel and so located as to communicate at the other end directly with an engine combustion chamber, a pressure sensor located in the glow plug and having a diaphragm thereon, said diaphragm being exposable to combustion gases entering the radial hole and axial bore channel, said pressure sensor being an absolute pressure sensor, the output of the absolute pressure sensor comprising a measurement signal and a reference signal, and wherein the pressure response of the absolute pressure sensor may be substantially represented by the expression:

V_out(p) ~ (V_om + S_n, X p)/ (V_θm - S_m / S_r X V_or ) .

6. An internal combustion engine glow plug comprising a heater shell, a heater enclosed within the shell and a glow plug body for supporting the heater and heater shell in an engine, an axial bore channel within the glow plug and at least one radial hole communicating at one end with the axial bore channel and so located as to communicate at the other end directly with an engine combustion chamber, an absolute pressure sensor located in the axial bore channel and having a diaphragm thereon exposable to combustion gases entering the radial hole and axial bore channel, and a ferrule in the absolute pressure sensor having at least three optical fibers terminating with ends spaced from the diaphragm.

7. The engine glow plug of claim 6 wherein the output of the absolute pressure sensor comprises a measurement signal and a reference signal.

8. A method of sensing combustion chamber fluid pressure in an engine comprising sensing pressure with a diaphragm sensor located in a bore communicating through a glow plug with the combustion chamber, producing a measurement signal and a reference signal within the diaphragm sensor in response to the instantaneous combustion chamber fluid pressure and in response to the measurement signal and reference signal computing an absolute pressure wherein the absolute pressure is calculated from the measurement signal and the reference signal with the expression:

Vout(p) ~ (Vom + S_m X p)/ (V_om - S_n, / S_r X V₀₁-).

9. In an integrated glow plug and pressure sensor having a passage leading to the pressure sensor, the improvement comprising a porous filter in the passage.

10. The integrated glow plug of claim 9, including a ceramic heater shell and a metal heater sleeve, the metal heater sleeve supporting the ceramic heater shell.

11. The integrated glow plug of claim 10 wherein at least a portion of the passage is located in the metal heater sleeve.

12. The integrated glow plug of claim 10 wherein at least a portion of the passage is located in the ceramic heater shell.

13. The integrated glow plug of claim 9 wherein the porous filter comprises a wire mesh.

14. The integrated glow plug of claim 9 wherein the porous filter comprises a porous ceramic.

15. In an integrated glow plug and pressure sensor having a passage leading to the pressure sensor, the improvement comprising means in the passage to trap combustion deposits.

16. The integrated glow plug of claim 15 wherein the means in the passage burns trapped combustion products in response to heating of the glow plug.

17. The integrated glow plug of claim 15 wherein the means in the passage acts as a heat shield for the pressure sensor.

18. The integrated glow plug of claim 15 wherein the means in the passage damps acoustic high frequency ringing in the passage.

19. In an integrated glow plug and pressure sensor having a passage leading to the pressure sensor, the improvement comprising at least one non-axial pressure access hole communicating with the passage and a porous filter positioned to intercept gases entering the passage from the access hole.

20. The integrated glow plug of claim 19, including a ceramic heater shell supported on a metal heater sleeve and wherein the access hole is formed in the metal heater sleeve.

21. The integrated glow plug of claim 19, including a ceramic heater shell supported on a metal heater sleeve and wherein the access hole is formed in the ceramic heater shell.

22. The integrated glow plug of claim 19, including a metal sheath enclosing an electrode, the metal sheath being supported on a heater sleeve and a ceramic insert separating the electrode from the heater sleeve, and wherein the access hole penetrates the heater sleeve, ceramic insert and electrode.

23. The integrated glow plug of claim 19 wherein the passage is axially located in the glow plug and the pressure sensor is axially located in the passage.

24. The integrated glow plug of claim 23 wherein the access hole comprises a plurality of holes radially intercepting the passage.

25. An internal combustion engine glow plug comprising a heater shell, a heater at least partially enclosed within the heater shell and a glow plug body for supporting the heater and heater shell in an engine, an axial bore channel within the glow plug and at least one radial hole communicating at one end with the axial bore channel and so located as to communicate at the other end directly with an engine combustion chamber, a pressure sensor located in the glow plug and having a diaphragm thereon, said diaphragm being exposable to combustion gases entering the radial hole and axial bore channel, a plurality of optical fibers connecting the pressure sensor to at least one light emitting diode and at least one photo-diode, said diodes being connected to an electrical integrated circuit within the glow plug body, and means on the glow plug body for external electrical connection of the heater and of the integrated circuit.

26. The engine glow plug of claim 25 including a porous filter located in the axial bore channel.

27. The engine glow plug of claim 25 wherein the diodes and integrated circuit are located within an extension of the glow plug body.