Method for determining camshaft and crankshaft timing diagnostics

In an engine, associated control system, and method the engine including at least one camshaft having an angular position at a given point in time, and a crankshaft having an angular position at a given point in time. The method comprising the steps of measuring a first window of time using at least one crankshaft angular position pulse as a reference point in time and measuring a second window of time using at least one camshaft angular position pulse as a reference point in time. The method also ascertains an angular position difference between at least one camshaft and crankshaft equal to the second window of time divided by the first window of time and determines whether a misalignment between the at least one camshaft and the crankshaft exists by comparing the angular position difference between the at least one camshaft and crankshaft to a predetermined value.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to timing diagnostics and, more 
particularly, to a method of measuring angular degree relationship between 
the camshaft and crankshaft of an engine. 
2. Description of the Related Art 
Increasingly stringent hydrocarbon, nitrous oxide, and carbon monoxide 
emission standards are being placed on the industry through government 
regulation. Unwanted emissions can be caused when a timing deficiency 
between the camshaft and crankshaft exists. Currently, to determine 
whether a deficiency has occurred, service technicians must disassemble 
the front of the engine to inspect visually, or use a timing tool. A 
technique using a two-channel oscilloscope is available. But the 
oscilloscope readings are subject to operator interpretation. Moreover, 
oscilloscopes are not readily available to all automobile service 
technicians. Physical inspection of camshaft and crankshaft timing is 
especially difficult when two camshaft gears exist and is virtually 
impossible without mechanical disassembly or "degree marking" of the 
engine. 
It is also known in the art that in belt, chain, or gear driven camshaft 
engine designs, timing belt, timing chain, or gear slippage can occur. 
Excessive wear or stretching can also cause the timing apparatus to slip. 
If such slippage does occur, misalignment between the camshaft and 
crankshaft will result. The cause of timing belt, chain, or gear slippage 
is commonly the result of low belt, chain, or gear tension. Such slippage 
can also be attributed to debris entering the timing cover or wear on the 
timing apparatus due to high engine mileage. Timing belt, chain, or gear 
slippage may lead to such undesirable conditions as excessive emissions, 
poor engine performance, bent valves, or an aperture being punched in the 
cylinder head or piston damage. 
It is therefore desirable in the art of vehicles to have a timing 
diagnostics method which internally determines the camshaft and crankshaft 
timing relation for easy retrieval by a service technician and further 
denotes timing apparatus slippage. 
SUMMARY OF THE INVENTION 
In light of such desirable characteristics, the present invention provides 
a timing diagnostics method which internally determines the camshaft and 
crankshaft timing relation for easy retrieval by a service technician. 
The present invention relates to an engine, associated control system, and 
method. The engine includes at least one camshaft having an angular 
position at a given point in time, a crankshaft having an angular position 
at a given point in time, and an ECU with corresponding memory and at 
least one bus line. 
In an engine, associated control system, and method the engine including at 
least one camshaft having an angular position at a given point in time, 
and a crankshaft having an angular position at a given point in time. The 
method comprising the steps of measuring a first window of time using at 
least one crankshaft angular position pulse as a reference point in time 
and measuring a second window of time using at least one camshaft angular 
position pulse as a reference point in time. The method also ascertains an 
angular position difference between at least one camshaft and crankshaft 
equal to the second window of time divided by the first window of time and 
determines whether a misalignment between the at least one camshaft and 
the crankshaft exists by comparing the angular position difference between 
the at least one camshaft and crankshaft to a predetermined value. The 
method can determine whether a misalignment between the camshaft and the 
crankshaft exists by comparing the angular position difference between the 
camshaft and crankshaft to a predetermined value. If camshaft and 
crankshaft misalignment has occurred, the method can implement a 
dosed-loop operation of various engine fuel components. 
One advantage of the present invention is that a reduction in service 
diagnostics will be created as a result of mechanical timing being able to 
be checked without disassembly of the engine or the need for extra timing 
diagnostic equipment by polling the information stored in the ECU. 
A further advantage is that by continuously calculating the relationship 
between the camshaft and crankshaft, the engine controller or service 
technician can calculate the degree of wear on the vehicles timing 
apparatus and sensor misalignment. 
Another advantage of the present invention is that a skipped tooth, chain 
link, or gear tooth can be detected and stored in the engine timing 
system. The method can fully operate along any points along the crankshaft 
and camshaft pulse trains. 
By having such information, the ECU can compensate for fuel and spark 
characteristics, by controlling various fuel components, thereby reducing 
engine timing variance effects on emissions and power. Moreover, a service 
technician, by having this information, will be able to diagnose timing 
belt, chain, or gear wear by polling information already stored in the ECU 
.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
Vehicles having internal combustion engines, commonly have at least one 
camshaft with one or more cams attached for opening and closing valves. 
The camshafts have camshaft sprockets attached to at least one end. In 
addition, such vehicles also have a crankshaft with one or more crank 
journals attached thereto for imparting motion to a transmission. Current 
vehicles may employ the use of camshaft and crankshaft sensors. These 
sensors generate electrical pulses through the detection of notches or 
gaps in a gear or metal ring through the use of electromagnetics. 
Referring now to FIG. 1, a camshaft sprocket 15 is shown. The camshaft 
sprocket 15 has a first circular level 16 which is integrally formed with 
a second circular level 17. Disposed within the first circular level 16 
are a plurality of chain notches 18 for holding a chain link disposed 
therein. The sprocket 15 also contains a sprocket-to-camshaft connection 
aperture 19 disposed therein. Referring to FIG. 2, a top view of the 
camshaft sprocket 15 is shown. Within the second circular level 17, a 
plurality of cylinder timing notches are formed. The second level 17 has a 
notch 21 for the second cylinder, a set of notches 22 for the third 
cylinder, a notch 23 denoting a fourth cylinder, a notch 24 denoting fifth 
cylinder, and a set of notches 25 for the sixth cylinder. The first 
cylinder is represented by a first cylinder rim 20 on the second level 17 
of the camshaft sprocket 15. It is to be understood, however, that the 
present invention is also applicable to any number of cylinders depending 
on the type of engine. 
Turning now to FIG. 3, a perspective view of a camshaft sprocket 27 for a 
belt driven timing system is shown. The sprocket 27 has a first circular 
disc 28 and a second circular disc 29 integrally formed or assembled 
together. The first circular disc 28 has a plurality of grooves 30 for 
frictionally receiving a timing belt. The second disc 29 contains cylinder 
timing windows. The sprocket 27 further contains a sprocket to camshaft 
connector aperture 31. FIG. 4 shows a top view of the belt driven camshaft 
sprocket 27. The second disc 29 has a fifth cylinder window 35 shown in 
FIG. 9. Windows 36, denoting a sixth cylinder, are shown in FIG. 8 and a 
second cylinder window 37 is shown in FIG. 7. Third cylinder windows 38 
are shown in FIG. 6 and fourth cylinder windows 39 are shown in FIG. 5. 
The first cylinder is denoted on the second disc 29 of FIG. 3. It is 
appreciated that the present invention is equally functional on a vehicle 
with any number of cylinders and is not limited to the present embodiment 
of six cylinders. A crankshaft sprocket (not shown), having a plurality of 
timing notches or windows is also employed and is commonly know in the 
art. In the embodiment shown in FIG. 12 of this invention, four timing 
notches or windows are used to produce the four angular signal pulses per 
cylinder. Any number of timing notches or windows could be used with the 
present method depending on the type of crankshaft sprocket used. 
Turning now to FIG. 10.A, a method is disclosed for execution by an 
Electronic Control Unit (ECU) during a crankshaft pulse. The method begins 
or starts at bubble 50 upon interrupt or ECU command calling for 
diagnostics to be performed. The method then falls to decision block 56 
where it is determined whether a measurable cylinder is currently 
functioning. A measurable cylinder is denoted in the present method by the 
detection of a single angular position pulse generated by the camshaft, 
denoted as sync pickup in FIG. 12. In the present method cylinders 2 and 5 
are designated as the operable cylinders and produce a singular camshaft 
angular position pulse in accordance with the timing notches or windows of 
the camshaft sprocket of the timing apparatus. The method could also 
perform equally well by using any other cylinder as the measurable 
cylinder and is not limited to the number of camshaft or crankshaft 
angular position pulses generated per cylinder. 
If the answer is in the negative in block 56, the method ends at bubble 86. 
If a measurable cylinder is present, the method falls to block 62. In task 
block 62 a ratio calculation is made to determine the angular position 
difference between the camshaft angular signal pulse or pulses occurring 
during the measurable cylinder event and the angular position pulse B of 
the crankshaft. This is accomplished by determining a first window of time 
equal to a camshaft time, captured on the previous camshaft angular 
position pulse falling edge C as shown in FIG. 12, subtracted from a 
reference crankshaft time captured on the crankshaft angular position 
pulse falling edge B. The result is divided by a second window of time 
equalling the reference crankshaft time, captured at the crankshaft 
angular position pulse falling edge B, less the base crankshaft time, 
captured at the crankshaft angular position pulse falling edge A. The 
result is then multiplied by a fixed angular value to obtain an angular 
difference between the camshaft angular position pulse C and the 
crankshaft angular position pulse B. 
Signal pulse trains representing the angular positions of the crankshaft 
and camshaft for a six cylinder engine are shown in FIG. 12. It is to be 
expressly understood, however, that the present methodology is equally 
applicable to any number of cylinders that a given engine may ;have. It is 
also appreciated that the falling edge angular position pulse 
representations A, B, C, and D shown in FIG. 12 can be based on falling, 
rising edges, or a combination of both anywhere along the camshaft and 
crankshaft angular signal pulse trains, and the method will operate the 
same. In particular, both the A and B crankshaft angular signals can be 
calculated within one cylinder pulse train. The phantom camshaft angular 
position pulse E in FIG. 12 represents the optimal or ideal camshaft 
angular position pulse. 
After block 62, the method falls to task block 64. In this block, the 
nominal crankshaft angular position, equal to the camshaft angular 
position pulse D less the crankshaft angular position pulse B, is 
subtracted from the current crankshaft angular position obtained in block 
62 which is equal to the angular difference between the camshaft angular 
position pulse C and the crankshaft angular position pulse B. This 
difference is stored in memory of the ECU. 
The method then falls to decision block 66 shown in FIG. 10.A. In block 66 
it is determined whether an initial or original build error between the 
angular differences of the camshaft and crankshaft has been calculated and 
stored in ECU memory. If the answer is in the affirmative, the method 
falls to block 68 where the original build error is subtracted from the 
result obtained in block 64. The result is obtained by subtracting a 
difference between the original camshaft angular position and optimal 
camshaft angular position pulse D from the present camshaft angular 
position and optimal camshaft angular position pulse D result obtained in 
block 64. The method then falls to decision block 76. If it is determined, 
in block 66, that the original build value has not been computed and 
stored in ECU memory, this indicates an initial start of the engine after 
manufacture. The method will then advance to decision block 76. In block 
76 the number of skipped belt teeth, chain links, or gear teeth is 
determined and depends on the type of timing apparatus employed in the 
engine. The method divides the angular difference between the camshaft and 
crankshaft by the number of crankshaft angle degrees per belt tooth, chain 
link, or gear tooth. Such a division will result in a real number that can 
be used to obtain the number of teeth or links skipped. After block 76 the 
method falls to block 78 whereby the number of teeth or links skipped is 
stored in ECU memory for subsequent retrieval by a service operator. The 
method then falls to decision block 80. 
In block 80 it is determined whether an initial build error between a 
falling edge of the camshaft and the designed camshaft position has been 
calculated and stored. If the answer is in the affirmative, the method 
falls to block 85 whereby an engine fuel component is adjusted. If, 
however, the original build value error has not been learned, the method 
falls to task block 84. In this block the number of angular degrees error 
between the camshaft and crankshaft at build time is stored in ECU memory. 
The method then continues to block 85. In this block at least one engine 
fuel component is adjusted to compensate engine performance degradation 
resulting from the camshaft and crankshaft misalignment. Such engine fuel 
components can include, but are not limited to, fuel injectors, spark 
advance, piston valves, and other fuel related engine parameters that are 
commonly known in the art to be controlled via an ECU. 
Referring now to FIG. 11 a camshaft interrupt processing system 110 and 
method is shown. The method begins or starts in bubble 90. The method then 
falls to block 92. In this block the updated or current time that the 
camshaft angular position pulse C occurs is stored in the ECU memory 
register holding the camshaft time value. The method then falls to bubble 
94 whereby the method ends. 
While the invention has been described in detail, it is to be expressly 
understood that it will be apparent to persons skilled in the relevant art 
that the invention may be modified without departing from the spirit of 
the invention. Various changes of form, design or arrangement may be made 
to the invention without departing from the spirit and scope of the 
invention. Therefore, the above mentioned description is to be considered 
exemplary, rather than limiting, and the true scope of the invention is 
that defined in the following claims.