Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to a device for measuring
pressure, and in particular to a device fox measuring the max-
imum pressure in a cylinder of an internal combustion engine.
The maximum pressure in a cylinder of an internal
combustion engine is typically measured by somewhat complicated
mechanical or electomechanical devices. Typical of such devices
are those disclosed by United Staltes Patents Nos. 2,202,900,
issued to C.S. Draper on June 4, 1940; 2,355,088, issued to
S.D. Lavoie on August 8, 1944; 3,216,244, issued to G.W. Borchers
on November 5, 1965; 3,633,410, issued to A.A. Isaev on January
11, 1972; 3,943,759, issued to T. Kato et al on March 16, 1976;
and 3,983,748, issued to A.A. Isaev on October 5, 1976. Some
of the devices, for example the Draper and Lavoie apparatus, rely
on the movement of a rigid diaphragm which is translated into
an electromagnetic signal indicative of the rate of change of
pressure within a cylinder. Others, including the Borchers
device, use spring or valve movement as a means of measuring
pressure.
In any event, it is readily apparent from a review of
the prior art that a need exists for a simple, accurate device
for measuring the maximum pressure in a cylinder of an internal
combustion engine.
The object of the present invention is to attempt to
meet such need by providing a relatively simple device for
accurately measuring the maximum pressure in a cylinder of an
internal combustio~ engine.
Accordingly, the present invention relates to a device
for measuring the pressure in a cylinder of an internal combus-
tion engine comprising a tubular body; inlet means in said
body; connector means on said body for connecting said inlet
,
'. . -
means to an indicator cock on an internal combustion engine to
place the body in fluid communication with a cylinder of the
engine; pressure transducer means in said body for producing
an electrical signal dependent on the pressure in said cylinder;
cooling means integral with said body for cooling the body;
and means for connecting said transducer means to an indicator
circuit for receiving said elctrical signal and providing a
visual indication of cylinder pressure.
The particular cooling means referred to above is a
finned exterior on the transducer casing which is surrounded
by a water reservoir, i.e. the pressureprobe defined by the
casing has a self-contained or integral water cooling system.
Accordingly, the device can operate without air or water cooling
hoses attached thereto. The water cooling system functions
even when the water is boiling, the boiling water still providing
adequate cooling.
The use of the device of the present invention permits
one person to balance rapidly the load required among the
cylinders of internal combustion engines. By observing the
fluctuation of peak firing pressures from cycle to cycle, the
suitability of a given air/fuel ratio can be determined, and
the necessary corrections can be made to produce regular combus-
tion from cycle to cycle. Detonation spikes caused by a rich
air-fuel mixture can be detected. By temporiarily removing
spark ignition or fuel, the running compression pressures are
taken to provide a rapid evaluation of the condition of the
cylinder walls, piston rings and valves.
The invention will now be described in greater detail
~ with reference to the accompanying drawings, w~$h illustrate
a preferred embodiment of the invention, and wherein:
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Figure 1 is an elevation view of a pressure measuring
device in accordance with the present invention;
Figure 2 is a longitudinal sectional view of the
measuring device of Figure l;
Figure 3 is a plan view of the measuring device of
Figures 1 and 2 with parts removed; and
Figure 4 is circuit diagram of the electronic circuit
employed with the device of Figures 1 to 3.
With reference to Figures 1 to 3, the pressure measuring
device of the present invention includes an elongated tubular
body 1 with a handle 2 at one end thereof and a connector 3 at
the other end thereof for connecting the body 1 to an indicator
cock (not shown) on an internal combustion engine. The area
of the body 1 between the hand~e 2 and the connector 3 is
surrounded by a coolant container defined by a cup-shaped base
4 and a bottle-shaped top 5.
Referring specifically to Figures 2 and 3, the body 1
is generally cylindrical with a longitudinally extending central
~ passage 6. The passage ~ is stepped at one end and internally
threaded for receiving a pressure transducer 7 and one exter-
nally threaded end 8 of the handle 2. Inlet end 9 of the body
recP ;ve
1 r~cciYed the connector 3. The nut-shaped connector 3 is
rotatably mounted on the body 1 and is internally threaded at
10 for mounting on the indicator cock. Annular fins 11 are
provided on the portion of the body 1 within the base 4 of the
coolant container for ensuring efficient cooling of the body 1.
The base 4 of the coolant container includes an intern-
ally threaded, open top end 12 for receiving externally threaded
neck 13 of the plastic top 5~ An O-ring 14 between shoulder
15 of the top 5 and the top end 12 of the base 4 provides for
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a fluid-tight seal. A vent tube 16 extends upwardly through
bottom wall 17 of the base 4 to closed top 18 of the plastic
top 5.
The handle 2 includes a knurled exterior surface 19,
and a longitudinally extending central passage 20 through which
leads 21 from the transducer 7 extend~ The transducer leads 21
pass through a plastic grommet 22 in the outer end of the handle
2 to the electronic circuit illustrated in Figure 4.
OPERATION
The operation of the device will now be described
primarlily with reference to Figure 4.
In operation, the connector 3 is connected to the
indicator coc~ of an engine. The body 1, being formed of mild
steel wi h fins 11, is designed to provide maximum surface area
for effective heat transmission. The mild steel cup defining
the base ~ defines a portion of a water container, which
includes the top portion 5 defined by an inverted plastic
bottle. The vent tube 16 prevents pressure build up in the
coolant container. The plastic top 5 is a safety feature,
because the plastic will melt if the temperature of the steel
base rises above 150C. The transducer 7 in body 1 and the
leads 21 form part of the electronic circuit of Figure 4. The
pressure transducer 7, which is of the piezo-electric type
having a built in amplifier providing a high level low impedance
output, is a standard product of the type made by PCB
Piezontronics, Buffalo, N.Y. The signal from the transducer
7 is fed into a signal conditioning and amplifying device 23O
The signal consists of an A.C. component and a D.C. component~
In the device 23, the D.C. component of the signal is removed
and the A.C. component is clamped above zero volts, i.e.
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raised above zero volts with the lowest level of the A.C.
signal corresponding to zero volts. The signal i9 then ampli-
fied, with a variable adjustment, to a fixed sensitivity
(psi or kPa per volt~ level. The adjustable amplification is
required because of the variable sensitivities of transducers.
The device 23 is followed by a peak detector 24 which stores
the highest voltage level reached by the signal since the last
time the peak detector was reset, such level corresponding to
the peak firing pressure.
A comparator 25 and an eight bit D/A 26 define an
analog to digital converter. The voltage level stored by the
peak detector is converted to numerical form by the converter.
The converter is a successive approximation type, conversion
logic being implemented by the software program of a micro-
processor 27.
Control and operation of the system is effected by
the microprocessor 27. The microprocessor uses the relation-
ship of the signal level to a predetermined threshold level to
derive power cylinder cycle timing information with which to
perform an "average" or "consecutive" operation. The informa-
tion is provided to the microprocessor 27 by threshold level
and comparator devices 28 and 29, respectively. Thus, when
either "average" or "consecutive" functions are requested,
the microprocessor 27 measures the peak signal levels as framed
by the timing information, i.e. controls the peak detector 24
through a reset: line 30, converts the levels into numerical
form and displays the results on light emitting diode (LED)
display device 31. Upon receiving a "display refresh" request,
the microprocessor re-displays the last message or result.
The circuit is completed by a power supply 32 and
a battery check block 33. The microprocessor 27 also checks
the level or charge of the batteries or power supply using
the bat-tery check block 33 and displays an appropriate message
when the battery level i5 1QW.
PR~CTICAL-AND-THEORETICAL CONSIDERATIONS
The device described hereinbefore has been tested on
engines at speeds ranging from 250 rpm to 630 rpm with good
results. Theoretically, the device will work from 15 -to
20,000 rpm. The pressures measurable are determined by the
sensitivity of the transducer. Normally, a transducer pro-
viding maximum pressure of 1,000 psi (7,000 kPa) and capable
of detecting compression pressures as low as 80 psi (560 kPa)
would be used in the device. These limits are readily adjust-
able by changing software in the case of the upper limit, and
by changing a resistor in the case of the lower limit. The
ability of the system to read high pressures, i.e. above 999
psi (7,000 kPa~ is limited by the transducer (maximum linear
range of 1,000 psi) and by the 3 digit display. In order to
obtain 3 digit resolution below 999 psi, numbers over 999 could
not be displayed. -Of course, a higher pressure transducer,
e.g. 5,000 psi maximum and a 4 digit display could be used.
The minimum readable pressure is determined by the threshold
level device, ~hich prevents the digital to analog converter
from accepting signals below the threshold level. Thus, the
system is prevented from detecting peaks due to spurious low
level electrical noise rather than a peak due to pressure rise.
The amplitude of the spurious low level electrical noise is
variable from engine to engine, and originates primarily ~rom
the ignition system. The threshold level can readily be set
below any known compression pressures so that maximum protection
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from noise is achieved ~hile compression pressures of any known
engine can be obtained.
