Fluidic oil viscometer

A fluidic oil viscometer for determining the degradation of machinery lubating oils compares the viscosity of the machinery oil with the viscosity of another fluid, such as air. Both the viscosity of the air and the viscosity of the oil are sensed, using capillary-orifice combination sensors, and the air viscosity reading is amplified using a series of laminar proportional amplifiers to equalize its change in viscosity with that of oil. The outputs of the capillary orifice combination sensors are applied to two different pressure gauges, the difference between these two pressure gauges represents the viscosity breakdown. This difference will be independent of temperature.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a means for determining the degradation of 
lubricating ability of an oil by detecting the change in viscosity of the 
oil. 
2. Description of the Prior Art 
There has long been a need to determine the degradation in the lubricating 
properties of an oil so that the oil may be changed before the lubricating 
properties deteriorate to an unacceptable degree. In the past, oil has 
been changed at regular mileage intervals, so that the lubricating 
properties may be kept at an acceptable quality. Changes in operating 
conditions, however, can cause a great difference in the quality of the 
lubrication ability of oils operated under different conditions. 
One known measuring technique is to extract a sample of the oil, and test 
it in a comercially available viscometer. This process has problems 
however, due to the fact that the oil must be removed from the vehicle, 
and tested in an expensive apparatus which is not easily movable. 
There exist prior art oil viscometers which test the oil viscosity using a 
built in capillary-orifice combination viscometer which tests the 
viscosity of the oil without removing the oil from its environment. 
However, these viscometers do not compensate for the variations in 
viscosity due to temperature, and therefore, they are not as accurate as 
the viscometer of the present invention. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a way to 
accurately determine the viscosity of oil without variations due to 
temperature. 
It is a further object of the invention to provide an oil viscometer which 
measures the change in oil viscosity without being affected by differences 
in the original viscosity of the oil used. 
It is still another object of the present invention to provide an oil 
viscometer which can measure the change in viscosity of the oil monitored 
without removal of a sample of the oil from the engine in which the oil is 
contained. 
It is a further object of the present invention to provide a simple oil 
viscometer which compares the viscosity of oil to standard, which is 
developed from the viscosity of air. 
These, and other objects of the invention are achieved by providing an oil 
viscometer which measures the viscosity of the oil and then the viscosity 
of air, which is modified to produce a model of the oil viscosity before 
use. This modification of the viscosity of air signal into an oil model 
viscosity signal is done by measuring the viscosity of the oil to be 
tested before use and amplifying the viscosity of air signal using laminar 
proportional amplifiers to produce the same viscosity change vs. 
temperature curve as the fresh oil to be tested. The oil model viscosity 
signal is then compared to the oil in use to determine the amount of 
degradation which has occurred to the oil in use. The comparison of these 
two output signals is done through the use of two separate pressure 
gauges. One pressure gauge is for measuring the viscosity of the fresh oil 
model and the other is for measuring the viscosity of the oil being 
monitored. When fresh oil is added to the engine the measurements of the 
two gauges are aligned so that they both read the same viscosity. Then, as 
the oil to be sensed degrades, the viscosity of that oil shown on one of 
the gauges changes from the viscosity shown on the other gauge, showing 
the operator that the oil has degraded. 
These and other characteristics of the present invention may be better 
understood in relation to the drawings and the detailed description to 
follow.

DETAILED DESCRIPTION OF THE INVENTION 
Referring in detail to FIG. 1 which shows a typical fluidic amplifier 10 
with control ports 11 representing the signal input ports to the fluidic 
amplifier, the outputs 12 representing the signal output ports of the 
amplifier. The vents 13 simply vent the excess fluid which is unable to 
exit from the output ports 12. In operation, the fluid supply 14 flows in 
a jet stream towards the splitter 15, symmetrically disposed with respect 
to outputs 12. If there is no difference in pressure at the control ports 
11, there should be no difference in pressure at the output ports 12. The 
splitter 15 acts as a means for splitting the jet stream equally in two 
directions in such a way as to create an equal pressure at both outputs. 
If there is a pressure differential at the control ports 11, then the jet 
stream will be affected in such a way that the splitter 15 will force a 
greater amount of flow through one output 12 than the other output 12. 
This causes the input pressure differential to be amplified so that the 
output pressure differential is greater than the input pressure 
differential. 
In the present invention, two fluidic viscosity sensors at the same 
temperature and location are used, generally indicated in FIG. 2 as 18, 
19. A first air viscosity sensor generally indicated as 18, is 
representative of capillary-orifice combination fluidic sensors. This air 
viscosity sensor includes a variable orifice 21, and a capillary sensor 
22. When the air pressure is applied to input P.sub.air 20 then any change 
in viscosity of the air results in a change in the differential pressure 
at the inputs 28,29 of laminar proportional amplifier 25. The change in 
differential pressure at the inputs 28, 29 of amplifier 25 is proportional 
to the change in viscosity of the air. The differential output pressure of 
this viscosity sensor is input to control terminals 28 and 29 of a laminar 
proportional amplifier 25. A constant input air pressure Pair is applied 
to supply terminal 30 of this amplifier, and the pressure differential 
applied at terminals 28 and 29 is amplifier at terminals 31 and 32. This 
amplifier pressure differential at 31 and 32 is again applied to the input 
of a second laminar proportional amplifier 26 and the resulting pressure 
differential is again amplified at output 36, 37. This process is again 
repeated in a third amplifier 27 to obtain a resulting output pressure 
differential across the output terminals 41, 42. Excess air is vented from 
the amplifiers 25, 26, 27 by the use of vents 52 which return this air to 
the engine manifold or outside by lines 24. 
The oil viscosity sensor 19 is also a capillary-orifice combination sensor 
and functions in the same manner as air viscosity sensor 18. The viscosity 
of the oil is monitored using viscosity sensor 19 including variable 
orifice 45 and capillary sensor 44 whose output is applied to the input 
terminals of ports 48, 49 of laminar proportional amplifier 46. Excess oil 
is vented from the amplifier 46 by use of vents 52 to the crankcase sump. 
The output of this amplifier is indicative of the viscosity of the oil to 
be measured. The pressure differentials of air viscosity amplifier and of 
the oil viscosity amplifier are each connected to a separate pressure 
gauge which reads the viscosity in response to the differential pressure 
applied across it. Since viscosity of a gas increases with increasing 
temperature and the viscosity of a liquid decreases as a function of 
increasing temperature, it is necessary to reverse the differential output 
polarity of the air viscosity amplifier output. 
The variable orifices of the air and oil sensors can be adjusted to allow 
the matching of the two sensors when different weights of oil and/or fresh 
oil is added. This adjustment is done to align the viscosity values of the 
two gauges when the oil to be monitored is fresh. Because of the 
differences between the change in the viscosity vs. the change in the 
temperature of air and oil, more gain is necessary in the air sensor to 
equalize these changes. This is necessary because a change in temperature 
will change the viscosity of air. For a 0.degree.-200.degree. F. change in 
temperature, the change in viscosity of oil over the change in viscosity 
in air is approximately equal to 230, thus requiring that the air powered 
unit reflect this ratio in additional gain. This gain of 230 is obtainable 
using the three stages of amplification provided by amplifiers 25, 26, 27. 
Once properly matched, the viscosity versus temperature for the fresh oil 
and the air standard will be equivalent for the same batch of oil. 
FIG. 3 shows the viscosity of oil versus engine oil temperature when fresh 
engine oil is matched to the viscosity of the output of the air standard. 
In this case, when the oil has degraded, the viscosity of the oil 
increases, decreasing the pressure differential and the resultant 
differential pressure output of the laminar proportional amplifier 46 that 
has the oil input applied. This is shown in curve 54. The distance between 
the two curves is proportional to the viscosity change at a given 
temperature. 
The pressure transducers used for indicating the viscosity of the oil can 
easily be engine mounted, or mounted on the dashboard thus eliminating the 
need for motor pool inspection or sampling of the oil in the crankcase. 
It is noted that various modifications may be made to this invention, these 
modifications limited only by the necessity for matching the viscosity of 
air with the viscosity of fresh oil. 
We wish it to be understood that we do not desire to be limited to the 
exact detail of construction shown and described for obvious modifications 
can be made by persons skilled in the art.