Top dead center measurement for reciprocating crank mechanism

A method or system for measuring the top dead center for a reciprocating crank mechanism, in which a reversible counter performs the additive counting operation from an amount H of shift of the piston of the reciprocating crank mechanism to another amount H of the shift of the piston in a reverse driving direction of the crankshaft of the reciprocating crank mechanism at both sides of a minimum shift of the piston, for each predetermined unit rotational angle deviation of the crankshaft. The reversible counter performs the subtractive counting operation from said another amount H of the shift of the piston in one driving direction of the crankshaft for each one half the predetermined unit rotational angle deviation of the crankshaft. A position of the piston is decided as the top dead center when the counting state of the reversible counter reached zero in said one driving direction of the crankshaft.

BACKGROUND OF THE INVENTION 
The present invention relates to top dead center measurement. 
It is well known in the art that it is necessary, in a final assembly step 
of an engine, to accurately determine an angle of a crankshaft to a 
connecting rod when the amount of shift of a piston into a cylinder is 
minimum. However, there has not yet been proposed suitable method or 
system in the art to accurately determine this angle. 
SUMMARY OF THE INVENTION 
An object of the invention is to provide a top center measurement control 
method or system for accurately determining a top dead center of a piston 
in a reciprocating slider crank mechanism for use in an internal 
combustion engine or the like of a motor vehicle. 
In accordance with the present invention, there is proposed a method or 
system for measuring the top dead center for a reciprocating crank 
mechanism, in which a reversible counter performs the additive counting 
operation from an amount H of shift of the piston of the reciprocating 
crank mechanism to another amount H of the shaft of the piston in a 
reverse driving direction of the crankshaft of the reciprocating crank 
mechanism, for each predetermined unit rotational angle deviation of the 
crankshaft. The reversible counter performs the subtractive counting 
operation from said another amount H of the shift of the piston in one 
driving direction of the crankshaft for each one half the predetermined 
unit rotational angle deviation of the crankshaft. A position of the 
piston is decided as the top dead center when the counting state of the 
reversible counter reached zero in said one driving direction of the 
crankshaft.

DETAILED DESCRIPTION 
FIG. 1 is a sectional view of an engine block. It is well known in the art 
that it is necessary, in a final assembling step of an engine, to 
accurately determine an angle .alpha. of a crankshaft 3 to a connecting 
rod 1 when the latter assumes such a vertical position as shown in FIG. 1, 
that is, when the amount of shift x of a piston 2 into a cylinder is 
minimum. It seems, however, that there has not been any available 
measuring equipment capable of determining the angle .alpha. with 
accuracy. In FIG. 1, reference numeral 4 indicates an engine block, and 
.alpha. represents an angle between a horizontal line passing through the 
axis 3a and a line joining the center of a big end portion 1a of the 
connecting rod 1 and the axis 3a of the crankshaft 3. 
The amount of shift x of the piston 2 increases with a decrease in the 
rotational angle .alpha. of the crankshaft 3. FIG. 2 is a diagram 
generally showing the rotation of the crankshaft 3 and the motion of the 
connecting rod 1 caused by a stroke of the piston 2. When the amount of 
shift x of the piston 2 is almost minimum as shown in FIG. 1A, the amount 
of change in the rotational angle .alpha. of the crankshaft 3 increases 
with respect to the amount of change in the amount of shift x. 
Accordingly, even if the rotational angle of the crankshaft 3 is measured 
when the amount of shift x is minimum, an error is very large. Another 
cause is as follows: A gap S.sub.1 between the connecting rod 1 and a 
crank pin 6 and a gap S.sub.2 between the connecting rod 1 and a piston 
pin 7 appear on opposite sides according to the direction of rotation 5 of 
the crankshaft 3, as shown in FIGS. 2A and 2B, so that if the resulting 
errors are added together, it will be inaccurate to determine the angle 
.alpha. if the crankshaft 3 when the amount of shift x of the piston 2 is 
minimum, that is, when the piston 2 lies at its top dead center. The 
present invention eliminates such an error. 
A description will be given first of the principles of the present 
invention. A rotational angle detector (an encoder generating a pulse for 
each unit angle deviation, such as one minute) 8 for the crankshaft 3 and 
a sensor unit 9 for detecting the amount of x of the piston 2 are mounted 
on the engine block 4, as shown in FIGS. 4 to 6 (which will be described 
later), and the crankshaft 3 is turned first to the right (clockwise), as 
shown in FIG. 3A. When the position (=x) of the piston 2 has reached a 
height (H+A), the crankshaft 3 is stopped. Then the crankshaft 3 is turned 
to the left (counter-clockwise), as shown in FIG. 3B, and when the 
postition of the piston 2 has reached a height H, the content of a counter 
of the encoder 8 is made zero. The crankshaft 3 is further turned to the 
left, as shown in FIG. 3C, and when the position of the piston 2 has 
reached the height (H+A), the crankshaft 3 is stopped. Incidentally, it is 
desirable that the height H be selected at an angle position .alpha..sub.0 
such that the amount of change in the value of H is maximum with respect 
to the amount of change in the rotational angle, and the value of H can 
easily be obtained by computation. The value of A is optional. 
Next, the crankshaft 3 is turned again to the right, as shown in FIG. 3D, 
and when the position of the piston 2 has reached the height H (i.e. an 
angle position .alpha..sub.1), the number of amount-of-shift pulses for 
each unit angle deviation to the counter of the encoder 8 is doubled 
(described later with regard to FIG. 6). The crankshaft 3 is stopped when 
the content of the counter has become zero after further rightward 
rotation of the crankshaft 3, as shown in FIG. 3E. The position of the 
piston 2 at this time is its exact top dead center. Since the piston 2 has 
the height H in both cases where the crankpin 6 is at a point P.sub.1 in 
FIG. 3B and where the crankpin 6 is at a point P.sub.2 in FIG. 3D, a 
position corresponding to an angle equal to 1/2 of a rotational angle 
.alpha.T (FIG. 3D) from the point P.sub.1 to the point P.sub.2 is the top 
dead center. In an embodiment of the invention, with a view to simplifying 
a control circuit used, by performing a multiple subtraction when the 
crankshaft 3 has reached to point P.sub.2, the connecting rod 1 is stopped 
at the angle position equal to 1/2 of the angle .alpha.T. 
FIG. 4 illustrates the outline of an embodiment of the present invention as 
applied to the engine block (shown in section). The device of the present 
invention comprises a sensor unit 9 for sensing the amount of shift of the 
piston 2 and a driving unit 10, and their arrangements are such as shown 
in FIGS. 6 and 5, respectively. In FIG. 4, reference numerals 11 and 12 
designate wire ropes suspended, for instance, from the ceiling of a 
workroom, for facilitating a transfer of the driving unit 10 and the 
sensor unit 9 and their mounting on the engine block. Reference numeral 13 
identifies a flywheel, which is mounted on the shaft of the crankshaft 3, 
and 14 a truck for moving the engine block 4. 
The driving unit 10 has such a construction as shown in FIG. 5, in which 
the turning effort of a motor M, reduced by a reduction gear 15, is 
transmitted to the crankshaft 3 through a hook 17 attached to the tip of a 
shaft 16 and engaged with the axis of the crankshaft 3. On the other hand, 
magnets 19 and 20, as a unitary structure with a gear 18, mesh with an 
encoder pinion 22, transmitting the rotational angle (of the flywheel 
13.fwdarw. the crankshaft 3) to the encoder 8. The magnets 19 and 20 stick 
fast to the flywheel 13 firmly engaged with the crankshaft 3, and the 
magnet 21 sticks fast to the engine block body 4. Such an arrangement is 
made that the elements 18 to 22 are not engaged with the motor shaft 16 
through ball bearings 23. The reason for this is that the shaft 16 of the 
motor M and the shaft of the crankshaft 3 may engage with a little play, 
but it is required to accurately transmit to the encoder 8 the rotation of 
the flywheel 13 which accurately transmits the rotation of the crankshaft 
3. 
The sensor unit 9 has such a construction as shown in FIG. 6, in which a 
contactor 26 is mounted on the top of a sensor 24, which makes contact 
with the head of the piston 2. The contactor 26 is pushed up by the spring 
force of a spring 25 into contact with the piston 2 at a proper pressure. 
Reference numeral 27 denotes a block which supports the sensor 24 and a 
magnet 28 and sticks fast to the outside of the engine block by virtue of 
the magnet 28, securing the sendor body. As the sensor unit 9, a known 
displacement sensor is used for detecting the amount of shift of the 
piston 2. 
FIG. 7 is an electrical circuit connection diagram for top dead center 
measurement control showing motor driving by the sensor unit 9 and the 
driving unit 10. In FIG. 7, a reversible counter 31 is designed to perform 
an adding operation and a subtracting operation during counterclockwise 
and clockwise rotations of the crankshaft 3, respectively. At first, an 
output is provided from a control logic 30 to a motor driving circuit 32 
to turn the motor M clockwise. At this time, the sensor 24 always detects 
a movement of the piston 2 and generates pulses having the number 
corresponding to the amount of movement, and a counter 29 counts the 
number of pulses corresponding to the height of the piston 2. (For the 
following description, refer to FIG. 3.) 
(1) When the height of the piston 2 has reached a value (H+A), a comparator 
(A) 37 generates an A-signal output on the basis of coincidence with an 
(H+A) output from a position setter 38, causing the control logic 30 to 
deliver a signal for driving the motor M counterclockwise. 
(2) When the height of the piston 2 has lowered to a value H as a result of 
the counterclockwise rotation of the motor M, as shown in FIG. 3B, a 
comparator (B) 35 provides a B-signal to the control logic 30 on the basis 
of coincidence between an H output from a position setter 36 and the H 
output from the counter. The control logic 30 performs a sequence 
operation, and hence does not respond to the output from the comparator 
(B) based on the passage of the piston through the height H in the case of 
(1). Upon reception of the output from the control logic 30, the 
reversible counter 31 resets its added value (during counterclockwise 
rotation of the crankshaft 3) to zero. 
Now, a description will be given of an output circuit of the encoder 8 in 
FIG. 7. The encoder 8 generates, in succession, rectangular waves having 
the number corresponding to the rotational angle of the crankshaft 3, as 
described previously, and a pulse generator (A) 33 and a pulse generator 
(B) generate, at different time points, A-pulses by the front edge timings 
of the encoder output pulses and B-pulses by their rear edge timings, 
respectively, for input into an OR gate G.sub.2 and AND gate G.sub.1. 
Since the gate G.sub.1 is normally closed, only the A-pulses from the 
circuit (A) are counted by the reversible counter 31. 
(3) The motor M is further rotated counterclockwise and an addition 
operation is carried out correspondingly after resetting of the counter 
31, and when the piston 2 rises to the height (H+A), as shown in FIG. 3C, 
the control logic 30 is activated by the output signal from the comparator 
(A) 37 to carry out a third operation, rotating the motor M clockwise. In 
this case, the B-output is also provided when the piston 2 is at the 
height H, but the control logic 30 does not respond thereto. 
(4) When a subtraction operation is effected and the piston 2 lowers to the 
height H, as shown in FIG. 3D, the control logic 30 is activated by the 
output from the comparator (B) 35 to perform a fourth operation, opening 
the AND gate G.sub.1. Upon application of both of the A- and B-pulses, the 
counter 31 starts a twice-fast subtraction (a multiple subtraction) in 
comparison with a case where only the input from the pulse generator (A) 
33 is applied to the counter 31. 
(5) The clockwise rotation of the motor M is further continued and when the 
count value of the reversible counter 31 becomes zero, the control logic 
30 performs a fifth operation, suddenly stopping the motor M and 
consequently the piston 2. This position of the piston 2 is the top dead 
center shown in FIG. 3E. In this way, the top dead center is automatically 
determined with high accuracy. 
As will be appreciated from the foregoing description, the present 
invention permits an accurate determination of the top dead center, 
through the use of a relatively simple device, and produces an excellent 
effect.