Analyzing exhaust gases of vehicle internal combustion engines

When analyzing exhaust gases from vehicle internal combustion engines according to the simplified method, where the inertia and the internal losses of the engine are used as braking factors and the engine, during a given period of time, is subjected to a series of short incidents of fuel supply increases above idling speed level, it is important to ensure that all play is eliminated in the transmission path between the monitoring unit determining the fuel increase incidents and the fuel supply means. The fuel supply increase incidents should furthermore be selected so with respect to resulting changes in effective mean pressure (PME) and speed (RPM), that the fuel supply means, during each incident, will be displaced in a positive direction only, until the engine returns to the idling speed level.

BACKGROUND OF THE INVENTION 
In order to establish the content of undesirable emissions in the exhaust 
gases from a vehicle internal combustion engine, the engine is, during a 
given period of time, run according to a so called test cycle. This is 
intended to simulate a certain traffic sequence, and it will usually take 
about 30 minutes to run such a test. The vehicle will then have to be 
mounted upon a chassis dynamometer providing the necessary braking load. 
Such testing necessitates the use of expensive equipment, and will 
furthermore waste a lot of time, as it not only is a question of passing 
through the cycle--the vehicle must be mounted upon and dismounted from 
the chassis dynamometer. 
The inventor has already proposed a method and means suitable for use when 
analysing the exhaust gases from internal combustion engines, where a 
noticeable reduction in time is obtainable by using the inertia of the 
engine and its internal losses as the braking factor. This presupposes 
that the test cycle is composed of short acceleration and retardation 
incidents. 
SUMMARY OF THE INVENTION 
The present invention refers to a method which makes it possible to compare 
results obtained with equipment of the last mentioned type with any known 
test cycle. It will however be necessary to reduce the time scale in a 
representative manner. 
An essential feature will then be to override any possible play in the 
transmission between the primary fuel control means and the member finally 
determining the amount of fuel, for instance the throttle valve of a 
carburettor. 
The invention is characterized in that the fuel supply control means, 
before the first occasion of increased fuel supply, is adjusted to a zero 
position where all play is eliminated, and that the values of PME/RPM for 
each fuel increase incident are so selected, that the fuel supply control 
means, until it returns to the idling condition will be displaced in a 
positive direction only. 
The reduction of the time scale is according to the invention obtained by 
drawing up, in a diagram, the changes in effective mean pressure (PME) in 
relation to speed (RPM) to which the engine is subjected when running 
through the selected cycle, statistically simplifying this diagram, so 
only a few, for instance six, mean value curves are obtained in which the 
extension in time for each RPM- and PME-level is used as a weighing 
factor, recalculating, based upon the knowledge of the moment 
characteristics of the actual engine at different speeds, the PME/RPM 
diagram to a fuel control means/time diagram, and making up a program for 
operating a monitoring unit actuating the fuel supply control means based 
upon last mentioned diagram.

DESCRIPTION OF A PREFERRED EMBODIMENT 
When performing exhaust gas tests at a vehicle engine, an equipment of the 
type schematically shown in FIG. 1 may be used. The vehicle is indicated 
by its front portion only, where the engine 10 is located. The supply of 
fuel is in a conventional manner determined by means of a gas pedal 11. 
The exhaust gases are conducted away by an exhaust pipe 12, including a 
silencer (not shown). 
For the simplified test procedure, actual here, it will not be necessary to 
mount the vehicle upon a chassis dynamometer. The engine is run at idling 
speed, disengaged from the driving transmission. During a short period of 
time from, say, one half of a minute, up to a minute, which should be 
compared with thirty minutes usually required to run an established test 
cycle, the engine is subjected to a series of short incidents of 
variations in the fuel supply. 
Each such incident has such a short duration that the engine, which, as 
mentioned above, is not subjected to any external load, will not attain 
any equilibrium condition at constant speed, but will be essentially 
accelerated and retarded only. 
The gas pedal will, during the test, be operated by a motor 13, which is 
connected to the pedal by a linkage 14, and will provide a number of 
depressions of predetermined magnitude, spaced apart by intervals 
permitting the engine to return to the idling speed. 
The motor is governed by a monitoring unit 15, and the programming thereof 
forms the background for the present invention. 
On occasions it may be desirable to simulate also the conditions during 
cold starting. The testing sequence may therefore be selected so as to 
include pre-selected instances during the heating-up of the engine. 
During the test a gas volume divider 16 is attached to the exhaust pipe 12, 
and a known portion of the total volume of gas is conducted to an 
analysing apparatus 17. The latter may be of any known type, and as it, by 
itself, does not have any influence upon the method according to the 
present invention, it is shown as a dotted line box only. In the conduit 
between gas distributor 16 and analysing apparatus 17, a valve 18 is 
provided, which is governed by monitoring unit 15 to open during the test 
only. 
The equipment shown in FIG. 1 is an example only of the basic means 
necessary for performing the testing of exhaust gases from a disengaged 
vehicle engine, i.e. an engine operated without any external load. 
In order to obtain an evaluation basis comparable with a desired, 
established test cycle it is necessary to reduce the time scale from about 
30 minutes to less than one minute, while maintaining a corresponding, 
representative load upon the engine. It is evident that it will be 
necessary to produce, during a short moment of acceleration a composition 
of the exhaust gases, which corresponds with what is obtained during 
driving under load upon a chassis dynamometer. 
FIG. 2 shows a portion of a typical test cycle diagram, which includes a 
number of "humps" 30 representing variations in the engine load during 
various moments of time. The theory behind such a test cycle is that it 
shall simulate a series of situations in the traffic, where the vehicle 
for instance is driven from a suburb into a big city, and is subjected to 
repeated accelerations and retardations, as well as varying up-grades and 
down-grades. 
FIG. 3 shows how a test cycle diagram according to FIG. 2 by 
computerization has been recalculated to represent changes in effective 
mean pressure (PME) in relation to engine speed (RPM). It should, however, 
be noted, that each "hump" in the diagram according to FIG. 2 may include 
one or more occasions of gear-shifting. The discontinuties during 
gear-shifting means that the engine speed does not necessarily increase 
all the time when the engine passes through a "hump", but may be reduced 
while the PME increases, and also that it may increase while the PME 
remains constant. Diverse load zones may be represented by spaced peaks 
along the speed scale. 
The jumble of lines 31 obtainable in this manner and shown in FIG. 3 cannot 
be used directly for practical purposes. FIG. 4 shows how the diagram is 
statistically reduced to a few mean pressure curves 32, where the 
extension of time for each level of speed and PME is used as weighing 
factor. 
When combining curves 32 it will be necessary to take into account the 
negative influence of the idling speed braking, which in FIG. 4 is shown 
by area 33. 
When the moment characteristics at different speeds and fuel supply are 
known for a given engine it is possible to transfer the mean value diagram 
according to FIG. 4 into a fuel supply/speed diagram. In order to obtain a 
satisfactory reiteration positive movements only will be permitted at the 
fuel control means, whereby the influence of play as well as of friction 
and inertia in links and joints will be eliminated. 
This is shown in FIG. 5, which is a simplified diagram, illustrating 
variations in PME, which may occur during one fuel supply incident. 
Curve 40 shows a first peak 41 and a second peak 42, spaced apart by a 
valley. If the play and the friction in the transmission mechanism between 
the gas pedal and the member finally determining the amount of fuel supply 
has a magnitude corresponding to 43, it is impossible to control the upper 
portion of peak 41 properly, and the desired change at the engine may not 
be attained. If the play and the friction amount to what is indicated at 
44 no change at peak 41 will be noticed. 
It therefore is important that the fuel control supply means, before the 
first load incident in the test series, is adjusted to a zero position, 
where all play etc. is eliminated and that furthermore the means, during 
each following actuation incident, up to the point where it returns to 
idle running position, will be displaced in a positive direction only. 
The actual testing method, which is based upon the engine being braked 
mainly by its own inertia, is time-based and it will therefore be 
necessary to perform one further recalculation in order to provide a fuel 
supply means position/time diagram according to FIG. 6. This is simply 
established by the relation 
EQU W=1/2I.OMEGA..sup.2, where 
W is the work supplied as recorded in the PME/RPM diagram, 
I is the inertia of the engine, and 
.OMEGA. is a linear function of the speed (radians/second). 
The running of a test cycle according to FIG. 2 implies several tens of 
thousands of ignitions in the engine, while an operating according to a 
diagram according to FIG. 6 will mean some thousands of ignitions only. 
It should be noted that curves 45 according to FIG. 6 clearly indicate that 
the fuel control means, during each load incident, will be moved in a 
positive direction only, up to the point where the incident is terminated. 
The fuel control means may be kept stationary during parts of the 
incident, but this will not offer any possibility for the play to 
influence the supply. 
The method of running the engine against its own inertia and internal 
losses during an exhaust gas test means a considerable reduction in time. 
It is further evident that the present invention makes it possible to 
establish programs for the actuation of the fuel supply system of an 
engine, which ensures that the amount of gas collected for analysing 
during the simplified test procedure will be fully representative of any 
desired test cycle of established type. PG,8