Dynamometer engine performance analyzer system

A dynamic engine performance analyzer system measures engine torque and power continuously from an absorption brake and produces a statistically corrected and deskewed value of torque and power for each of a number of RPM bands. Torque and power values are integrated during each N shaft revolutions as the engine is slowly accelerated through a range of interest. The data are accumulated such that for each 100 RPM wide band in the range, there is a statistical mean value produced of torque and of power. Each 100 RPM band element represents the mean or average of several separate data measurements. A deskewing operation compensates for the fact that the samples may not all be taken evenly throughout each 100 RPM average band during acceleration. The inertial effects of acceleration and deceleration are compensated by adjusting the torque and power values upwards during acceleration and downwards during deceleration. The engine analysis is quite rapid, and provides extremely reliable and accurate performance data which closely approaches the theoretical best possible according to statistical theory.

BACKGROUND OF THE INVENTION 
This invention relates to dynamometers, and is more particularly directed 
to a system for automatically measuring and recording engine torque and 
horsepower over a range of engine speed values, so that the performance 
characteristics of an engine can be determined. 
Existing dynamometer instrumentation systems operate according to a basic 
principle. An engine is brought to a predetermined engine speed and 
stabilized at a given RPM while holding a torsional load on the engine's 
rotary output shaft. The engine torque value and the RPM value are 
recorded, either manually (with pad and paper) or electronically. Then the 
engine is brought to another engine speed and stabilized, and the torque 
and engine speed values are recorded. This is a rather slow process, so 
usually there are no more than about 5 or 6 data points taken. This 
usually means recording only a single torque value for every 500 RPM over 
a very narrow speed band. 
Computer controlled instrumentation has been employed in connection with 
this general method. Unfortunately, the method still involves taking a 
very limited number of data samples, and then over widely separated RPM 
values. This yields simple point value readings, as before. This method is 
subject to wide variances from one test run to another, and this is 
largely due to statistical fluctuations of the measured data. The previous 
method more or less assumes an engine that delivers smooth, steady power 
during every aspect of a power cycle. In a real internal combustion 
engine, however, the power is produced in pulses (during the power 
strokes) with each cylinder contributing zero or negative values of torque 
being applied during intake, exhaust and compression strokes. Each engine 
stroke will be inconsistent from cycle to cycle, producing natural 
fluctuations in the torque impulses. As should be understood from this, 
the torque, power, and RPM delivered from the engine shaft vary even 
during steady state conditions. Consequently there is a rather large 
uncertainty factor in the prior art method readings. This uncertainty can 
be on the order of about 1% reading. 
Attempts to measure torque (and power) during engine acceleration have not 
presented reliable and consistent results. The reasons for this have not 
been appreciated, even though in hindsight it might seem obvious. The 
engine and the dynamometer have rotational inertia, and this absorbs some 
of the engine torque when acceleration takes place. The rotational inertia 
releases power and torque when the engine is decelerated. Consequently, 
torque and power readings are below the true values during acceleration, 
but above them during deceleration. This variation is a simple first order 
relationship, the torque loss owing to acceleration being directly 
proportional to the amount of acceleration. There is one other factor 
limiting the reliability and accuracy of the results during an 
acceleration test run. Conventional instrumentation techniques obtain data 
by taking quick "samples" of the signal and rely on having this signal 
being filtered to smooth out the torque pulses and other fluctuations. 
However, this filtering also causes the signal to lag behind during 
changes and engine accelerations thus creating a false and misleading 
result. 
OBJECTS AND SUMMARY OF THE INVENTION 
It is an object of this invention to provide a dynamometer system which 
overcomes the drawbacks of the prior art. 
It is a more specific object of this invention to provide a dynamometer 
system which produces a statistical torque and/or power measurement which 
is highly repeatable and is significantly more accurate and reliable and 
much more representative of actual engine performance than the prior art 
techniques. 
It is a further object of the invention to provide a dynamometer system in 
which the measurements of torque and/or power are taken while the engine 
is undergoing acceleration or deceleration as well as during steady state 
conditions. 
It is a still further object of the invention to provide a dynamometer 
system in which the values of torque and power can be found and listed 
with accuracy over a rather wide range of engine speeds. 
It is a still further object of this invention to provide a dynamometer 
system in which the values of engine speed, when torque or power is 
measured, are known to rather high accuracy, preferably on the order of 
about .+-.1 RPM. 
It is a yet further object of the invention to be able to adjust the 
statistical average values of torque or power to account for the average 
engine speed being above or below the center of a listed RPM band to 
effectively cancel the inconsistencies of manual dyno control. 
According to an important aspect of the present invention, an engine 
dynamometer instrumentation and engine performance analyzer system has 
been designed to be practical, accurate, and simple to use. The system 
carries out at least five functions which have not previously been 
incorporated into any prior dynamometer systems: 
For purposes of this specification, we may define "SAMPLE" to mean the data 
value obtained by a pure mathematical integration of the data signal over 
a period that corresponds to a whole number N of engine cycles. That is, 
if N=4, there will be four complete cycles or pulses of power for each 
cylinder, and the sample will have a value that corresponds to the mean or 
integrated average. The variance from one sample to the next will be 
smaller than that from one engine cycle to the next, and certainly less 
than from one point value to another point value. 
(a) This system continuously samples the values of torque, RPM, and other 
data while the tested engine is accelerated, decelerated or in steady 
state and the values within each given RPM band are statistically 
averaged. Power is calculated after measurements of torque and RPM. The 
resulting value is more accurate than the previous technique by the square 
root of the number of samples in that range. 
(b) To account for the "noise" or power pulses of the engine, the samples 
are each taken over an even integral number of complete revolutions 
continuously. Each sample represents exactly the same number of power 
strokes. The time is measured over this interval and the engine speed is 
derived with extreme accuracy, on the order of .+-.1 RPM. 
(c) A deskewing process is carried out for each engine speed band. This 
accounts for the fact that not all of the torque samples are evenly 
distributed within the band. The average RPM speed for each band is stored 
together with the total number of samples in the band and the statistical 
average torque and/or power value. The slope, or the change of torque per 
RPM is found from comparing the values in the previous and next RPM band. 
This is multiplied by the difference between the band average engine speed 
and the band center speed, yielding a deskewing adjustment to be added to 
the previously mentioned statistical average torque or power value. This 
yields a corrected or deskewed value of high accuracy and reliability. 
(d) An inertia factor is empirically derived and is used to account for 
errors in torque and/or power due to acceleration and deceleration of the 
engine. During the test, the engine speed derived in (b) above is compared 
with the engine speed for the next previous sample. The difference in 
engine speed which represents acceleration or deceleration is multiplied 
by the above factor and the product is added to the measured torque and/or 
power. The factor is the same for deceleration, which is simply 
acceleration at a negative rate. 
(e) This system finally lists the resulting averages of the data over a 
wide band of engine speeds, determined by the test, which is usually 
conducted over the speed range used in the final application. This final 
data average is very representative of the performance expected of the 
engine in the end application. 
The results of the above are automatically listed, either by a computer 
printer, on a screen, on a plotter, or with a similar device, so that the 
engine characteristics can be known and compared. The usual adjustments 
are made for temperature, pressure, and absolute humidity, and a record is 
also made of exhaust temperature, engine temperature, and fuel consumption 
rate, so that the engine test conditions can be repeated as exactly as 
possible. 
The high accuracy of the torque and power measurements, and the use of 
narrow RPM bands (e.g. 100 RPM or 250 RPM wide) is extremely important for 
racing engines, for example, where small differences in performance 
characteristics can be critical. Also, for adjusting the fuel injectors of 
diesel engines, it is desirable to know the torque/RPM and power/RPM 
curves as exactly as possible as well as the (brake specific fuel 
consumption (BSFC). 
The equipment for carrying out this technique is relatively inexpensive and 
uncomplicated, and can be used by technicians with only ordinary 
dynamometer expertise. 
The above and many other objects, features, and advantages of this 
invention will be more fully understood from the following description of 
a preferred embodiment, when considered in connection with the 
accompanying drawing.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
With reference to the drawing, and initially to FIGS. 1 and 2 thereof, the 
equipment for this apparatus includes a processor/display unit 10, an 
80-column dot matrix printer 12, and an electric tachometer indicator 16, 
here with a four-inch diameter scale. The unit has a front panel 13 (FIG. 
1) and a rear panel 14 (FIG. 2). A tachometer sensor input 18 connects the 
processor display unit 10 to a tachometer sensor 18s, (see FIG. 3) that 
replaces the more conventional mechanical tach drive adaptor. Here a 
magnetic or optical sensor produces a predetermined number of pulses for 
each complete shaft rotation, to detect when an engine shaft has rotated 
360 degrees to a home position. 
A remote inlet air temperature probe coupling 20 connects to a temperature 
probe (not shown) and provides the system with air temperature information 
for computing an SAE correction factor. A torque sensor 22s, attached to 
the torque arm of an absorption brake, of either water or electric type, 
connects to a torque sensor input coupling 22. The exhaust temperature 
probes 24s, attached to the engine exhaust manifold, connects to an 
exhaust temperature input coupling 24. An engine fuel flow sensor 26s 
sends fuel flow information to a coupling 26 of the device. An auxiliary 
input 28 allows additional information to be supplied automatically to the 
processor display unit 10. This input 28 can be connected, for example, to 
an air flow sensor connected to the carburetor or to the intake manifold 
of the engine. 
An inertia factor adjustment 30 allows empirical adjustment to be made to 
compensate for the effects of acceleration or deceleration of a given 
engine. A fuel specific gravity adjustment 32 is located just above the 
inertia factor adjustment 30. Torque zero setting and scale adjustments 34 
are also disposed on the processor/display unit rear panel 14. An arm 
select switch 36 can be set for either a short or long torque arm of one 
particular style of brake. An on/off switch 38 is disposed on the front 
panel 13 of the processor/display unit 10, and relative humidity and 
barometric pressure adjust setting knobs 40 and 42 allow the torque and 
power adjustments to be SAE adjusted for pressure and relative humidity 
conditions. 
A result test switch plugs into a switch jack 44. This switch can be 
actuated to commence a test run, and released to end the test run. A band 
select switch 46 allows the RPM bands or intervals to be printed on at 100 
RPM or 250 RPM. A tachometer test source switch 45 provides a precise 
signal that corresponds to an engine speed of 7680 RPM. This is used for 
calibrating the tachometer using a control 48 to set the tach reading to 
the calibration mark. 
On the front panel 13 of the processor/display unit 10 there are a digital 
torque display 50, an SAE corrected power display 52, and an auxiliary 
display 54. 
As shown schematically on FIG. 3, an engine 56 to be tested has its drive 
shaft 60 coupled to an absorption brake which is attached to the torque 
sensor 22s and the tachometer 18s, which provide torque and rotation speed 
information to a data integrator circuit 60 that is situated in the 
processor/display unit 10. A microcomputer memory and processor unit 62 is 
also located within unit 10, and is coupled to the data integrator circuit 
60 as well as to the controls in the front panel 13 of the 
processor/display unit 10. The memory and processor unit 62 is also 
coupled to the displays 50, 52, 54, and to the printer 12. As shown in 
FIG. 1, a power outlet 64 is provided for printer power, and an input 
filtered outlet 66 is provided to mate with standard power cords. A 
display select switch 68 sets the display 54 to indicate any of several 
engine conditions, and a test/copy switch 70 allows an operator to start 
and stop a test operation directly at the control panel as well as print a 
copy of the most recent test. 
The system has been designed to be practical, accurate, and easy to use. An 
operator by using either a remote switch coupled to the jack 44 or the 
test switch 70, can operate all of the test functions possible, from a 
single line printout of power and torque at a given RPM to a complete data 
documentation over a wide range of engine speeds. The system employs a 
technique for securing statistically accurate and repeatable dynamometer 
results. 
The system can accept and process up to six additional sensor inputs, and 
can communicate with other computers for further data processing and 
analyses, if desired. Also, the system in this embodiment is designed to 
operate over an engine speed range of 1,000 to 12,000 revolutions per 
minute. 
To achieve the most accurate and repeatable results from a test, the normal 
precautions are taken to control the conditions that might affect the 
final results. Maintaining a consistent supply of inlet air to the engine 
and controlling the engine coolant and oil temperatures are essential for 
optimum test repeatability. 
The controls on the front panel 13 function as follows. The power switch 38 
controls the main power and also controls power to the printer outlet 64. 
Turning the power switch off and back on initializes the computer 
processor 62. The processor 63 remembers the last test run data and the 
last test number when the switch 38 is turned off. 
When the test switch 70 is in its normal or "standby" position, the 
processor scans and displays data only. If the switch 70 is switched up 
for a test (which is the same as depressing a remote test button connected 
to the jack 44) the processor 62 begins to statistically accumulate data 
into its memory for printout when the switch 70 is returned to standby. 
Another test run can be started immediately after completing a previous 
test run, without waiting for the printer 12 to finish. The copy position 
of the switch 70 initiates the printer 12 to print another copy of the 
previous test run. 
The torque display 50 displays the actual uncorrected torque as determined 
from the sensor 22s. This is needed for setting the zero offset, achieved 
by the controls 34, and for checking the dead-weight calibration setting. 
The power display 52 shows SAE corrected engine brake horsepower. The 
auxiliary display 54, in connection with the associated display select 
switch 68, displays any of the following data: Brake specific fuel 
consumption (BSFC), i.e., pounds per hour per brake horsepower, while the 
engine is running, but displaying the value of the fuel specific gravity 
when the engine has stopped; the fuel flow, that is the actual fuel 
consumption of the engine in terms of pounds per hour; the SAE correction 
factor, as derived from the barometric and humidity settings 40, 42 and 
from the air temperature input; and the exhaust temperature, in degrees F, 
when the engine is running, with the inertia factor (from the setting of 
the knob 30) being displayed when the engine is off. The tachometer scale 
calibration setting 48 adjusts for fine trimming of the tachometer scale 
calibration, and is used in connection with the test RPM switch 45. 
Of the torque scale adjustments 34, the zero offset adjustment corrects for 
imbalance to the torque zero scale caused by hanging water hoses and by 
the torque arm weight. The torque scale adjustment is made after the zero 
offset has been checked. The fuel specific gravity adjustment 32 inputs 
the specific gravity (SG) of the fuel that is being used, so that the BSFC 
and fuel flow indications are correct for that test run. The SG factor is 
displayed on the auxiliary display 54 when the engine is stopped. 
The inertia factor adjustment 30 allows for corrections to the torque and 
power results owing to the effect of rotational inertia of the engine and 
dynamometer system on readings taken during engine accelerations and 
decelerations. During positive RPM changes, the system inertia will absorb 
torque, and during negative RPM changes, the system inertia will release 
torque. This affects the resulting measured torque. The optimum setting of 
the inertia factor is determined experimentally by making two test runs 
over the same RPM band, accelerating and then decelerating at 
approximately the same rate, e.g. 200 RPM per second. The average torque 
results will be the same for both increasing and decreasing engine speed 
runs if the inertia correction factor is optimal. The front panel 
auxiliary display 54 will show a relative number between "0" and "250" for 
this inertia factor when the engine is stopped. 
On the rear panel, the switch 46 selects whether the final printout will 
show the results at "100 RPM" or "250 RPM" intervals. The 250 position is 
used to compact the results without affecting the average results. Should 
a more detailed printout be required after the test has been printed at 
"250", the switch 46 can be set to "100" and the switch 70 depressed to 
the "copy" position for an expanded 100 RPM band printout. 
The torque arm switch 36 is needed for Stuska Engineering dynamometers, and 
supplies the processor 62 with information as to which torque arm length 
is needed, "long" being 12.6 inches and "short" being 6.3 inches. 
The system has the following operating characteristics: the RPM speed 
range, as exhibited on a page product from the printer 12, extends from 
about 1,100 to 12,000 RPM, at either 100 or 250 RPM intervals. The torque 
range depends on the sensor employed, and can be up to 2,000 foot pounds. 
The fuel flow sensor range is from 0 to 1,500 pounds per hour, at a 
specific gravity of 0.73, the fuel specific gravity range being from 0.60 
to 1.05. The exhaust temperature range is from room temperature up to 
1,700.degree. F. 
The engine analysis system of this invention can be used either in the 
traditional single point RPM mode or in the preferred sweeping 
acceleration mode. 
In the traditional mode, the operator attempts to hold the engine 56 stable 
at a specific engine speed, and then momentarily moves the switch 70 to 
the test position. The printed resolution in this mode is 10 RPM. When the 
test switch is released, a single line of data is printed by the printer 
12, showing the RPM SAE torque, SAE brake horsepower, BSFC, exhaust 
temperature, and a sample number which indicates the total number of 
measurements that form the printed results. The longer the test switch is 
held, the more separate data measurements there are that are taken and 
averaged into that single one-line data printout. 
In the sweeping or accelerating mode, a full use of the statistical and 
computational power of the computer processor 62 is employed. This method 
provides much more accurate and detailed information about the engine 
being tested in a much shorter time than does the traditional method. The 
procedure involves first selecting an RPM test band, such as about 5,000 
to 7,000 RPM, and then fully loading the engine 56 below that test band, 
e.g. about 4,800 RPM. Then the load on the engine 56 is slowly reduced 
while the test switch 70 is in the test position, allowing the engine 56 
to slowly increase speed over this band. Alternatively, the test can be 
initiated when the engine 56 is running faster than the test band, and 
decelerating the engine from a higher RPM to a lower RPM. The objective is 
to have the engine 56 accelerate or decelerate smoothly at about 100 RPM 
per second, and it is also important that the load change smoothly. The 
test switch 70 is released when the engine is brought through the desired 
RPM range, and before the engine is shut down. As soon as the test switch 
70 is released, the printer begins to document all of the data accumulated 
into the 100 RPM (or 250 RPM) bands or intervals. Also provided are a 
formal heading, a test number, average correction factor, fuel specific 
gravity, and other data. Also, all of the data are averaged over the test 
band, and the averages are printed on a separate line. If several 
temperature inputs were used, these would be automatically printed in a 
following paragraph. The test number is automatically incremented. 
A third mode can also be selected, in which groups of 100 RPM band lines 
are printed out, similar to the traditional or single line mode, but 
without incrementing the test number and without printing a complete 
heading and format. 
In any of the above modes of operation, the system is immediately available 
for another test after a previous test is completed, even while the 
previous test data are being printed out. 
This means that after a test run is made in the sweeping or continuous 
mode, a series of back-up test runs can be made in the traditional mode, 
more or less to verify the results. The system stores the data in memory, 
even if the printer 12 should run out of paper. This allows test runs to 
be made continuously, even while the printer 12 is being reloaded. 
Other features which are not shown in detail include an interchangeable 
PROM or program chip which configures the system to the particular type of 
dynamometer being used i.e., Stuska, Clayton, Go-Power, etc. A battery 
backup permits the memory to store or recall the last test number and the 
associated data from the previous test run, even after the power switch 38 
has been turned off. 
A torque sensor, which can be either a strain gauge load cell or pressure 
transducer, is factory calibrated to provide torque readings of .+-.0.1%, 
and is furnished with the system as the torque sensor 22s. The fuel flow 
sensor 26s is one of four available sensors which cover a range of zero to 
1500 pounds per hour at a specific gravity of 0.73. As for the tachometer 
sensor 18s, the system will accept engine speed inputs from several 
different sources, depending on the type of dynamometer used. The standard 
tach sensor 18s attaches directly to the SAE tach drive fitting mounted on 
the back of the standard absorption brake. As aforementioned, this 
provides a predetermined number of pulses for each rotation of the shaft, 
and it is possible simply by counting pulses to know when the shaft has 
rotated 360 degrees back to its home position. 
The principle of operation of this system departs from the traditional 
concept of associating points of dynamometer data with predetermined 
engine RPMs. Instead, the system provides performance data, such as power 
and torque readings, which are statistically averaged over their 
associated RPM bands, such as a 100 RPM width band, and the printout 
provided by the printer 12 represents the statistical aggregate of all 
measurements taken within that band. This average data printed for each 
speed band is much more accurate and representative of engine performance 
than any single point measurement. Also, because the measurements are 
taken continuously, the entire range of engine speeds is covered in about 
the same time it takes to obtain one or two data points using the 
traditional method. This allows the operator to develop an accurate feel 
for actual engine performance, which relates more closely to racetrack 
performance. Readings from this system are highly repeatable with manually 
controlled dynamometers, whereas with the previous system it was rare to 
have two test runs yield the same results. The system automatically 
screens all of the incoming data and compensates for speed changes during 
acceleration or deceleration, and rejects data if the engine speed 
acceleration is faster than a predetermined amount, for example, .+-.350 
RPM per second. 
The technique of this invention involves sweeping or accelerating the 
engine smoothly through the desired range of RPMs of interest, while the 
system accumulates data continuously on actual performance of the engine 
at a rate of about ten samples per second. A typical test over a range of 
about 3,000 RPM, e.g., from 5,000 to 8,600 RPM (takes about 30 seconds) 
and makes 300 separate and accurate readings. The system analyzes these 
data and then prints the performance results in a standard format, as 
shown in Appendix A. Test runs can be as narrow as about 300 RPM and still 
take full advantage of the powerful processing techniques employed with 
this invention. On the other hand, there is no maximum limit on the amount 
of data that can be accumulated, and the longer the test switch 70 is held 
in the "test" position, the more data that will be accumulated, and the 
closer the average will be to the actual engine performance 
characteristics. 
Other features can easily be added to this system, such as a turbocharging 
monitor, a mass air flow sensor for measuring air consumption, a personal 
computer interface, which can include a fiber optic cable or current loop 
that plugs into an RS-232 port on the back panel 14 of the unit 10 and to 
a standard port on the personal computer, or other custom hardware/program 
enhancement to service almost any conceivable engine testing application. 
In practice, an optimum sweeping rate has been established to be about 100 
RPM per second. In this way, as aforementioned, a 3,000 RPM sweep band 
would consume about thirty seconds of time. Any longer test sweep will not 
significantly improve the overall accuracy of the test or improve the data 
performance. However, if the sweep is made faster than this, there is a 
risk that some of the test bands will have fewer than ten data samples. 
With this system, repeatability is better than .+-.0.11%, from each run to 
the next, so that any changes in data that are greater than this represent 
actual small changes in engine performance. 
The statistical accumulating and averaging and deskewing of the engine 
performance data, that is, of the torque and power, are explained with 
reference to FIGS. 4A and 4B. 
When the power switch 38 is turned on, the processor 62 initializes and 
monitors the test switch 70 to determine whether it has been actuated to 
its test position, as in block [1]. If not, the processor 62 proceeds with 
standard housekeeping routines (block [2]), but if so, the processor 
zeroizes or clears the data memory and registers, as in block [3]and waits 
for the occurrence of a pulse signifying the Nth revolution (block [4]). 
The processor 62 then commences counting precise clock pulses until the 
next pulse indicating another N revolutions have occurred. At that time, 
the clock count is held, and the torque average reading and other 
parameters are read into a temporary storage memory (block [5]), and the 
registers are reset (block [6]) to count clock pulses for the next 
interval and to measure the torque value for that interval. The clock 
information is processed to produce an engine speed (block [7]), which has 
an accuracy of .+-.1 RPM. This is significantly better than the engine 
speed that could be measured in the traditional fashion, that is, by 
measuring the number of revolutions over a fixed period of time. For a 
four-stroke gasoline or diesel engine, N should be an even integer (2, 4, 
. . . ) and in the preferred mode, N equals ten. For a low speed diesel 
engine N would be 4 or 6, and the program would work over a lower speed 
range, perhaps with narrower RPM bands. For a two-stroke engine, i.e., a 
high-performance outboard motor marine engine, N could be either odd or 
even. The object is to have an integral number of power strokes in each 
sample period. 
This information is validated for excessive acceleration or deceleration, 
by comparing the RPM value with that from a next previous N revolutions, 
and if the resulting difference RPM is over 350 RPM (block [8]), the 
results are cancelled from memory. The results are next checked to see if 
they are in the target RPM range 1,000-12,000 RPM, as in block [9]. If the 
data are valid, the results are fed to the temporary storage memory. The 
speed change .DELTA.RPM is multiplied by the inertia factor IF to find the 
correction factor (block [10]). While not specifically shown here, the 
inertial acceleration adjustment factor IF is now multiplied by the speed 
difference value a RPM and the product IF .times..DELTA.RPM is added to 
the sample torque value to compensate for the inertial effects of 
acceleration or deceleration. Power is computed from RPM and torque (block 
[11]). The particular RPM band associated with these data samples is 
identified, as in block [12]. In this invention, the term sample means the 
mathematical integration of the data signal over the time interval of N 
revolutions. It should be considered as the pure mathematical average of 
the signal over this time period. 
During the continuous mode test run, the adjusted sampled torque value is 
combined with previously stored values for the same RPM band to develop 
RPM band running mean or average values of torque and calculated power, as 
in block [13]. The sampled torque and sampled RPM are multiplied to form 
the sampled power which is accumulated into running band averages just as 
with the torque results. Each sampled RPM value is also used in connection 
with previous sample RPM values to calculate and store an average RPM 
value for each of the 100-RPM bands (Block [14]). The number of samples 
for each 100-RPM band is counted and the accumulated number is stored, as 
in block [15]. After each operation, the test switch 70 is interrogated 
(block [16]), and if it remains actuated, the cycle is repeated; if not, a 
post-processing operation (block [17]) is carried out on the continuously 
accumulated torque and power values, after which the results are printed 
(block [18]). This is described in more detail with reference to FIG. 4B. 
The "post processing" procedures generally commence by scanning the RPM 
range beginning with the lowest RPM band (block 18). The band is checked 
to see if there are more than two samples (block [19]) and if not the band 
number is incremented (block [20]), but if so the band number is stored as 
a lower limit (block [2]). Then the post-processing goes to the highest 
RPM band (block [22]), and checks to see there are over two samples in 
that band (block [23]). If not, the band number is decremented to go to 
the next band lower (block [24]) but if there are sufficient samples, the 
band number is stored (block 25]). These data provide the upper and lower 
limits of valid statistical data for the test run. 
At this point the processor 62 checks to see if a one-line print mode has 
been selected, as in block [26], and if so proceeds to print the single 
line of results, as in block [27], after which the program returns to its 
housekeeping routine. If the single-line mode was not selected, the 
post-processing proceeds with a deskewing operation (block [28]), which is 
detailed in FIG. 4C. 
In the deskewing process, the processor returns to the lowest RPM band, as 
in block [29]. The system checks to make sure there are valid data in that 
band, in the previous RPM band, and in the next RPM band, as shown in 
blocks [30a], [30b], and [30c]. If not, it automatically goes to the next 
RPM band as in block [31]and repeats the process. Because the deskewing 
requires three successive RPM bands, the deskewing is not carried out on 
the highest and lowest RPM bands. Because of this, the test should be 
started at least 100 RPM below the desired end of the range and should 
continue up at least 100 RPM above the top end of the target range. 
The deskewing takes advantage of the fact that for small changes in engine 
speed, the changes in torque and power are almost linear, that is, they 
change smoothly and can be accurately represented as having a straight 
line slope. This would not necessarily be true if the separation between 
bands were wider, e.g., 500 RPM, but it is valid for RPM bands of 100 RPM. 
The object of the deskewing process is to correct the data to account for 
any changes in acceleration of the engine as it sweeps through the speed 
band. If the acceleration is constant, there is no skew as the number of 
data samples are distributed evenly throughout the band and the average of 
all the data can be considered to be centered in the band. But if, for 
example, the engine is increasing acceleration when sweeping through the 
band there will be more data samples below the midpoint than above, and 
therefore the data averages will be skewed downward along the slope of the 
data curve. The deskewing process effectively eliminates this common 
inconsistency of manual dyno operation eliminating the need for precise 
automatic control of the engine speed for accurate results. A factor is 
calculated and is used to shift the statistical average sample value of 
torque and calculated power to the value it would be expected to have if 
the engine acceleration was constant throughout this speed band interval. 
The torque deskewing is carried out as shown in blocks [32]through [34]. 
First, the slope T' is found from the difference between the statistical 
mean torque value for the band just above Tn+1 and the band just below 
Tn-1 the RPM band of interest (block [32]). Then the difference value 
.DELTA. R is calculated between the band average RPM value RPM and the 
center value BAND of the RPM band (block [33]). For example, for the 
engine speed band from 7250 to 7349 RPMs, the center value BAND would be 
7300 RPM. 
After this, a deskewing operation is carried out in step [34]and a deskewed 
value T* is obtained by adding the "raw" statistical average torque value 
T to the product of the RPM difference value .DELTA.R times the slope in 
torque T' as determined in block [32]. 
The values of power P are also deskewed, first of all as in block [35]by 
finding the slope P' of the power function by taking the difference 
between the power of the next successive RPM band Pn+1 and the previous 
RPM band Pn-1, and calculating a deskewed power value P* as the sum of the 
raw statistical average power P and the product of the RPM difference 
value R times the slope P' as in block [36]. 
After the deskewed values of torque T* and power P* are calculated and 
stored, the system automatically goes to the next higher RPM band as in 
block [31]. The process is continued as long as there is at least one more 
RPM band to be considered, as in block [37]. When the data have been 
deskewed for all of the RPM bands (except the very bottom and top), the 
system continues with post processing (FIG. 4B) and the results are 
eventually printed. 
The normal printout of data is in 100 RPM wide bands, which effectively 
represents the average or area of the data curves within this band. If the 
printout is in the 250 RPM band position, the program averages several 100 
RPM bands to form wider band averages, for no loss of information. The 
results can either be printed a second time if the switch 70 is actuated 
to the "copy" position, or another test run can be carried out if the 
switch 70 is actuated to its "test" position. 
After the deskewing is completed as in block [28], if there are more than a 
predetermined number of 100 RPM bands (block [38]), the test run number is 
incremented, and the system prints out appropriate headings, correction 
factor, fuel specific gravity (block [39]). Then, as in block [40], 
regardless of the number of 100 RPM bands, the system will then print a 
line of data for each 100 RPM band, from the lower limit to the upper 
limit, the data including the deskewed torque and power, BSFC, exhaust 
temperature, oil or water temperature, and the results of the auxiliary 
channel (here the airflow per cycle), followed by the number of sample 
values taken for that RPM band. The system then prints the mean values of 
power, torque, and other parameters as averaged over the main part of the 
test run, e.g., from 7,000 to 9,000 RPM, as in block [41]. Thereafter, the 
system interrogates (block [42]) whether there are data being supplied 
from a remote exhaust gas temperature box (not shown) which can 
accommodate up to eight ungrounded thermocouple probes. If so, the system 
will then print out the individual values of the temperature from the 
several probes (block [43]), print out the average temperature (block 
[44]), and then (block [45]) will return to the housekeeping routines 
(block [2]). 
The printed results of a typical test run are shown in Appendix A. Here, 
the attached sample data printout was obtained by sweeping the engine 56 
over a range of engine speeds from 6700 to 9100 RPMs. The test consumed 
about thirty seconds. The printout started as soon as the test switch 70 
was released. The data printed out on the Attachment A are more or less 
self-explanatory. Each test run has a unique test sequence number; in this 
case the test number is 27. The average SAE correction factor was 1.023 
and the fuel specific gravity was 0.728. The correction factor was 
computed based on the temperature, pressure, and absolute humidity and 
used to determine the SAE corrected torque and brake horsepower. The 
specific gravity SG was used to determine the fuel flow in terms of pounds 
per hour as well as to determine the brake specific fuel consumption 
(BSFC). For each RPM band printed, the number # of samples is recorded. 
This provides a measure of the reliability of the data. The operator 
should try to obtain ten or more readings in each RPM band to keep the 
statistical error as low as possible. In this example, AUX 1 which 
identifies the number one auxiliary channel, represents the relative 
amount of air flow per cycle. 
The overall run average torque, power, brake specific fuel consumption, 
exhaust temperature, and air flow over the main part of the test run are 
printed out at the bottom of the page as a single line summary. This line 
is considered the primary readout on engine performance, and assumes the 
test was made over an RPM band which would be used, for example, at a 
racetrack. Very small changes in performance can be seen here and these 
figures will generally indicate how well the engine will perform at a race 
track, and whether it is maximizing the torque or power over a given band. 
The average printout of BSFC, exhaust temperature, and the auxiliary 
channel (here, the air consumption) will indicate the effects of changes 
made during a test program. The overall span (to the nearest 500 RPM) is 
determined by the engine RPMs at the top and bottom of the test runs. For 
example, of a band between 7500 and 9000 RPM were required, the engine 
would be accelerated from about 7300 to about 9100 RPM before releasing 
the test switch. 
The results of the data obtained with this invention can be explained 
graphically with reference to FIGS. 5A to 5C. 
The curve of FIG. 5A shows the traditional "point" method of taking 
dynamometer readings. There are discrete readings of data at separate 500 
RPM points. There is much information missing. Also, the individual 
readings are not as accurate as can be obtained under this invention, 
because the RPM reading may not be exact and the torque or power readings 
whether visual or electronic, will contain normal statistical 
fluctuations. The errors involved here, systematic and statistical, limit 
the repeatability. Engines that are tuned based on this "point test" data 
may seem to improve performance at the 500 RPM points, but may actually be 
losing performance between the points. For any serious engine development, 
one needs to see positively all small performance changes, but the 
dynamometer test can be tedious and frustrating if the point test method 
is used. 
Curves that show data taken according to the technique of this invention 
are shown in FIGS. 5B and 5C. This invention deals with integration of 
readings, and thus area under curves. Consequently, this technique 
provides the most complete information on real engine performance, because 
real-world engines accelerate smoothly across bands of engine speeds, and 
do not remain set on some multiple of 500 RPM. In a 100 RPM band line 
printout mode (FIG. 5B) the area under the curve is split into 100 RPM 
strips. This gives optimum RPM resolution and data accuracy. The data on 
this curve represent the average of the data over respective 100 RPM bands 
centered on the printed engine speed value. The band-centered data are 
much more representative of acceleration through this range of RPM in 
competition. 
The curve of FIG. 5C illustrates the data averages contained in a 250 RPM 
line printout. Even though the printout is compacted into fewer bands 
(i.e., fewer lines), each represents a wider averaging band, so no 
information is lost. The printed data in this mode are not necessarily 
comparable with the data in the 100 RPM line mode. An advantage of the 250 
RPM line mode is that the test can be swept at a faster rate because of 
the wider bands. The engine can be accelerated as fast as 350 RPM/sec. and 
will still provide sufficient samples, albeit in wider bands, for an 
accurate printout. 
In both the 100 and 250 RPM band modes, the data will clearly indicate if a 
change will help or hurt engine performance. The mean/average printouts, 
showing a sweep over a number of 100 RPM bands, will indicate race track 
performance, whether the object is to maximize average torque or average 
power. These data can be further analyzed to find optimum gear ratios and 
shift points for winning performance. 
While the invention has been described in detail with reference to a 
specific embodiment, it should be understood that the invention is not 
limited to that specific embodiment, but that many modifications and 
variations would present themselves to those of skill in the art without 
departing from the scope and spirit of this invention.