Combustion pressure sensor

• US 4,586,018 A
• Filed: 05/03/1985
• Issued: 04/29/1986
• Est. Priority Date: 09/19/1983
• Status: Expired due to Fees

• Current Assignee: Ford Motor Company
• Original Assignee: Ford Motor Company
• Inventors: Bettman, Max
• Primary Examiner(s): Albritton, Clarence L.
• Assistant Examiner(s): LATEEF, MARVIN M
• Application Number:
  US06/730,250
• Time in Patent Office: 361 Days
• Field of Search: 338/42, 338/2, 338/4, 338/5, 338/36, 73/720, 73/721, 73/726, 73/727, 73/725, 73/115, 73/117.3, 73/706, 73/715, 73/716, 73/717, 310/338
• US Class Current: 338/42
• CPC Class Codes: G01L 19/0645 using isolation membranes, specially adapted for protection
• CPC Class Codes: G01L 19/0681 Protection against excessive heat
• CPC Class Codes: G01L 23/18 by resistance strain gauges

Abstract

A combustion pressure sensor has a first diaphragm adjacent a combustion region for deflecting in response to the magnitude of adjacent pressure. A second diaphragm is spaced from the first diaphragm and deflects as a function of the deflection of the first diaphragm. The second diaphragm is adapted to generate a signal indicative of the deflection of the second diaphragm. A force transmitting means between the first and second diaphragms transmits movement of the first diaphragm to the second diaphragm and reduces heat transfer from the first diaphragm to the second diaphragm.

Claims

1. A combustion pressure sensor means for mounting on an internal combustion engine so as to have access to the interior of a combustion cylinder, said sensor means having:

a first diaphragm means adjacent a combustion region for deflecting as a function of the magnitude of adjacent pressure in the combustion region, and for acting as a gas tight seal between the combustion region and an interior volume of said combustion pressure sensor means;

a second diaphragm means, spaced from said first diaphragm means, for deflecting as a function of the deflection of said first diaphragm and generating a signal indicative of the deflection of said second diaphragm means;

a force transmitting means located between said first diaphragm means and said second diaphragm means for transmitting movement from said first diaphragm means to said second diaphragm means, and for reducing the speed and amplitude of heat transmission from said first diaphragm means to said second diaphragm means; and

said second diaphragm including a steel member having a portion coated with an electrically insulating glass enamel, upon which is formed a thick film piezoresistor for use as a thick film resistive strain gauge and overlapping thick film conductor terminations for use as electrically conductive contacts, said thick film piezoresistor having a baseline resistance which can be temperature compensated by resistance measurement between successive combustion firings in the interior of the combustion cylinder.

2. A combustion pressure sensor means as recited in claim 1 wherein said second diaphragm includes type 316 stainless steel for forming a bond to said glass enamel.

3. A combustion pressure sensor means as recited in claim 1 wherein said second diaphragm includes decarburized silicon steel, which is adapted to be glass enamelled.

4. A combustion pressure sensor means as recited in claim 1 wherein said second diaphragm includes a ceramic plate onto which resistor and conductor pastes are screen-printed and fired for forming a strain sensitive piezoresistor with electrical connectors.

5. A combustion pressure sensor as recited in claim 1 wherein said first diaphragm means is a relatively thin, flat, steel alloy material having relatively good corrosion resistance and strength at high temperatures.

6. A combustion pressure sensor as recited in claim 5 wherein said first diaphragm includes concentric circular corrugations for added compliancy.

7. A combustion pressure sensor as recited in claim 1 wherein said force transmitting means is an elongated spindle extending between said first diaphragm means and said second diaphragm means.

8. A combustion pressure sensor as recited in claim 7 further comprising a radiation shield means positioned between said first and second diaphragm means for reducing the amount of radiant heat transfer between said first and second diaphragm means and for permitting axial movement of said elongated spindle.

9. A method of sensing combustion pressure in the interior of a combustion cylinder of an internal combustion engine with a combustion pressure sensor including the steps of:

sealing a gas flow passage between the interior of the combustion cylinder and an interior volume of the combustion pressure sensor using a first diaphragm;

deflecting the first diaphragm as a function of the magnitude of adjacent pressure in the interior of the combustion cylinder;

transmitting a force, generated by the combustion pressure, from the first diaphragm to a second diaphragm, spaced from the first diaphragm, providing some heat isolation of the second diaphragm from the first diaphragm so the magnitude of heat applied to the second diaphragm is reduced with respect to the magnitude of heat applied to the first diaphragm,

generating a signal indicative of the deflection of the second diaphragm means by sensing the resistance of a thick film piezoresistor formed on an electrically insulating glass enamel coating on a steel portion of the second diaphragm; and

calibrating the piezoresistor by repetitively measuring a baseline resistance between successive combustion firings in the cylinder when the cylinder pressure is known, the difference between the magnitude of the baseline resistance and the measured resistance during cylinder combustion pressure measurement being indicative of the cylinder combustion pressure.