FIELD OF THE INVENTION AND RELATED ART STATEMENT
[0001] The present invention relates to an apparatus for suppressing torsional vibration
of a crank shaft of a diesel engine.
[0002] As shown in Fig. 8, a fuel injection apparatus 7 of a conventional diesel engine
is driven by a cam 6 and a roller 5 and is structured to inject fuel into each of
the cylinders at the same injection timing and period of time.
[0003] Suppression of resonance stress of torsional vibration in a crank shaft system of
a diesel engine equipped with a conventional injection apparatus is made by change
of a length and/or a diameter of the shaft system, addition of further mass or mounting
of a torsional vibration damper. For example, in the case of a diesel engine for a
ship having six cylinders, as shown in Fig. 4, a one-node six-order resonance point
16 of torsional vibration exists within an ordinary operation range. Accordingly,
a relatively wide operation avoidance area is established. Consequently, since an
operable range of rotational number is limited, steering is often inconvenient. Suppression
of the one-node six-order resonance stress is made by making the diameter of the shaft
extremely large to increase the resonant point to a high rotation side, by attaching
extremely large mass to a front end of an engine to reduce the resonant point to a
low rotation side, or by providing an expensive torsional vibration damper. Accordingly,
large modification of design and cost are required.
OBJECT AND SUMMARY OF THE INVENTION
[0004] It is an object of the present invention to provide a suppressing apparatus of torsional
vibration of a crank shaft of a diesel engine capable of suppressing the resonant
point stress only by adjustment of a fuel injection system.
[0005] In order to achieve the above object, the suppressing apparatus of torsional vibration
of the crank shaft of the diesel engine adjusts a fuel injection timing and a fuel
injection period (injection amount) for each cylinder in the vicinity of a resonant
point of torsional vibration properly and varies a characteristic curve of pressure
in the cylinder with respect to a crank angle to reduce the magnitude of harmonic
components 12 and 13 of resonance order of torque 11 added to each cylinder, or adjusts
phase differences 14 and 15 of the harmonic components 12 and 13 for each cylinder
and suppresses the resonant stress so as to cancel external force for the vibration
mode.
[0006] More particularly, the above problem in the prior art is solved by the following
apparatus:
A suppressing apparatus of torsional vibration of a crank shaft of a diesel engine
having a fuel injection mechanism capable of freely setting a fuel injection timing
and period comprises a detector of a rotational number of the engine, and a fuel injection
setting device for judging whether the detected value is within an area in the vicinity
of a resonant point of torsional vibration of a crank shaft system or not to vary
the fuel injection timing and period by a predetermined value if the detected value
is within the area.
[0007] A fundamental principle of the present invention is as follows:
The magnitude of stress in the resonant point of torsional vibration of the diesel
engine is proportional to the magnitude of a vector sum of the harmonic components
12 and 13 of the resonant order of the torque 11 added to each cylinder. Accordingly,
if the magnitude of the harmonic components 12 and 13 of the resonant order and the
magnitude of the vector sum are reduced in the resonance, the resonant stress can
be suppressed.
[0008] The fuel injection timing and period are properly varied to adjust the characteristic
curves 8 and 9 of pressure in the cylinder for each cylinder so that the harmonic
components of torque produced in each cylinder is decreased and the vector sum is
made small to reduce the resonance stress.
[0009] The effects of the present invention are as follows:
The present invention makes it possible to reduce the excitation torque component
in the vicinity of the resonant point of torsional vibration of the crank shaft by
modification of the fuel injection period in the diesel engine. Since the additional
stress by the resonance in the vicinity of the resonance point is reduced, the operation
avoidance area is made narrow and can be removed if circumstances require. Further,
suppression of resonance requiring the provision of the torsional vibration damper
can be effected by only adjustment of the fuel injection system.
[0010] Since the suppression of resonance by this method depends on reduction of the excitation
force, effect can be exhibited for not only one node but also every vibration mode
such as two nodes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011]
Fig. 1 is a block diagram of a suppressing apparatus of torsional vibration in a crank
shaft of a diesel engine according to the present invention;
Fig. 2(a) is a diagram showing a characteristic curve of a pressure in a cylinder
versus a crank angle;
Fig. 2(b) schematically illustrates a crank mechanism;
Fig. 3 shows harmonic component in variation of torque with respect to a crank angle;
Fig. 4 is a diagram showing a resonance curve of additional stress of torsional vibration
versus the rotational number of an engine;
Fig. 5 is a diagram showing one-node torsional amplitude mode;
Fig. 6 is a flow chart 1 of a suppressing apparatus of torsional vibration;
Fig. 7 is a flow chart 2 of a suppressing apparatus of torsional vibration; and
Fig. 8 is a schematic diagram illustrating a general fuel injection system.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0012] Embodiments of the present invention having six cylinders are now described in detail
with reference to Figs. 1 to 8.
[0013] A configuration of a first embodiment is now described. Stress produced in a crank
shaft in operation in a resonance of torsional vibration or in the vicinity thereof
is proportional to a magnitude of a harmonic component of the resonant order of a
composite torque of an engine producing vibrating force. In the present invention,
the harmonic component of the composite torque is decreased by reducing the harmonic
component of the resonance order of torque by each cylinder so that the stress in
the resonance of the crank shaft or in the vicinity thereof is reduced to avoid the
resonance.
[0014] In Fig. 1, numeral 26 denotes a detector coupled to a crank shaft of an engine to
detect a rotational angle of an engine. Numeral 24 denotes a fuel injection timing
setting device which is connected to the detector 26. Numeral 25 denotes a memory
which is connected to the fuel injection timing setting device 24. Numerals 23₁ to
23₆ denote actuators each corresponding to each of the cylinders and connected to
the fuel injection timing setting device 24. Numerals 22₁ to 22₆ denote control valves
each connected to each of the actuators 23₁ to 23₆. Numeral 4 denotes a fuel pump,
3 an accumulator to which the fuel pump 4 is connected. The accumulator and the control
valves 22₁ to 22₆ are connected in parallel with each other.
[0015] Numerals 1₁ to 1₆ denote fuel injection valves each disposed in each of cylinder
heads and opened in a fuel chamber and connected to each of the control valves 22₁
to 22₆.
[0016] Operation of the first embodiment is now described.
[0017] The detector 26 detects a rotational angle of a crank shaft and a time with the top
dead point of a first cylinder as the origin to produce the detected signal. The fuel
injection timing setting device 24 receives the signal of the detector 26 and calculates
a rotational speed of engine in accordance with the flow chart 1 of the torsional
vibration suppressing apparatus of Fig. 6. Whether the rotational speed is within
the resonance area of torsional vibration or not is judged on the basis of the contents
stored in the memory 25 connected thereto. When it is not within the area, the fuel
injection process of normal operation is set for each cylinder and the signal is sent
to each of the actuators 23₁ to 23₆. Thus, the actuator 23₁ to 23₆ are operated to
actuate the control valves 22₁ to 22₆ so that the fuel injection valves 1₁ to 1₆ normally
injects the pressurized fuel stored in the accumulator 3 into combustion chambers
of the cylinders.
[0018] When the fuel injection timing setting device 24 determines that the rotational speed
of the crank shaft is within the resonance range of torsional vibration, the setting
device 24 sets an injection timing delay amount common to the cylinders and an injection
period extension amount for preventing deterioration of the thermal efficiency and
much fuel consumption on the basis of the memory contents of the memory 25 to send
signals to the actuators 23₁ to 23₆. Thus, the actuators 23₁ to 23₆ are operated to
actuate the control valves 22₁ to 22₆ so that the fuel injection valves 1₁ to 1₆ make
uniformly modified fuel injection. The above operations are repeated.
[0019] When the rotational speed of engine escapes from the resonance range of torsional
vibration, the fuel injection timing setting device 24 can determine that it is not
within the resonance range of torsional vibration and accordingly returns to set the
normal injection as described above.
[0020] A structure of a second embodiment is different only in the contents of the memory
from the first embodiment and accordingly description of the structure is omitted.
[0021] Operation of the second embodiment is now described.
[0022] The six-order harmonic component of torsional vibration of a crank shaft of a series
6-cylinder engine resonates with one-node vibration within the operation range. The
resonant state is shown by 16 of the resonance curve of Fig. 4. In Fig. 4, numeral
18 represents an operation avoidance area.
[0023] A reason of resonance is as follows:
In the normal operation state, the fuel injection process of the cylinders is relatively
identical. Accordingly, the characteristic curve of pressure in the cylinder with
respect to the crank angle of the cylinders, the harmonic component of torque of the
crank shaft by the cylinders, and the phase from the top dead point of the cylinders
are identical. In a harmonic component diagram of Fig. 3, numeral 12 represents the
six-order harmonic component of torque of the crank shaft by one cylinder in the normal
operation, and numeral 14 represents a phase from the top dead point. Since ignition
is at regular intervals in the series six-cylinder engine, the phase of six-order
harmonic component of torque of the crank shaft by the cylinders is just identical.
The mode of one-node torsional vibration is as shown by 20 of one-node torsional vibration
mode diagram of Fig. 5 and since specific amplitudes 21 in positions of the cylinders
have the same direction, the torque component of the same six-order phase excites
the vibration strongly.
[0024] In the present invention, the fuel injection process of three cylinders of six cylinders
is changed and curve 8 in the normal fuel injection shown by the characteristic curve
of Fig. 2 is changed to curve 9 shown by broken line of Fig. 2. Thus, the six-order
harmonic component of the crank shaft torque is changed as shown by 13 of the harmonic
component diagram of Fig. 3 and as shown in Fig. 3 the phase for the top dead point
is delayed by about 30° as compared with that shown by 14 of Fig. 3 to reverse the
phase as shown by 15 of Fig. 3. Consequently, the torque of the crank shaft by the
six cylinders for the one-node torsional vibration mode can be canceled each other
to reduce amplitude in the resonance. This is shown by 17 of the resonant curve diagram
of Fig. 4. In Fig. 4, numeral 19 denotes an area in which operation must be avoided
in the embodiment, while the area is very narrower as compared with the prior art.
[0025] Actually, the phase is controlled as follows.
[0026] The detector 26 detects the rotational angle and time with the top dead point of
the first cylinder of the crank shaft as the origin to produce the signal. The fuel
injection timing detector 24 calculates the rotational speed of the crank shaft as
shown in the flow chart 2 showing operation of the torsional vibration suppressing
apparatus of Fig. 7. Then, it is judged whether the rotational speed of the crank
shaft calculated on the basis of the contents of the memory 25 is within the resonant
area of torsional vibration or not. When it is determined that it is not within the
area, the operation is the same as that of the first embodiment. When it is determined
that it is within the area, three cylinders of the six cylinders remain normal while
the injection period of three remaining cylinders are set to be delayed by about 30°
in common to the three cylinders on the basis of the memory 25 and signals are sent
to the actuators 23 corresponding to the three cylinders. Thus, the actuators 23 are
operated to actuate the control valves 22 so that the injection valves perform the
modified fuel injection. The above process is repeated.
[0027] When the rotational speed of the engine escapes from the resonance range of torsional
vibration, the fuel injection timing setting device 24 judges it and returns the operation
to the normal injection process.
1. An apparatus for suppressing torsional vibration of a crank shaft of a diesel engine,
comprising:
a detector for detecting a rotational angle of an engine;
a memory for storing a fuel injection timing in a normal operation and a fuel injection
timing in the vicinity of a resonance of torsional vibration; and
a fuel injection timing setting device supplied with the rotational angle of the
engine from said rotational angle detector to calculate a rotational number of the
engine and for judging whether the rotational number is within a resonance area of
torsional vibration or not so that when the rotational number is within the resonance
area of torsional vibration, the fuel injection timing in the resonance of torsional
vibration is read out from said memory to inject fuel at the fuel injection timing.
2. An apparatus for suppressing torsional vibration of a crank shaft of a diesel engine,
comprising:
a detector for detecting a rotational angle of an engine;
a memory for storing a fuel injection timing in a normal operation; and
a fuel injection timing setting device supplied with the rotational angle of the
engine from said rotational angle detector to calculate a rotational number of the
engine and for judging whether the rotational number is within a resonance area of
torsional vibration or not so that when the rotational number is outside of the resonance
area of torsional vibration, the fuel injection timing in the normal operation is
set while when the rotational number is within the resonance area of torsional vibration,
an injection timing of a half of cylinders is delayed to reduce starting torque in
a mode where resonance occurs in torsional vibration so that a phase of the starting
torque in the mode by the cylinders is reversed to a phase of starting torque in the
mode of remaining cylinders.
3. An apparatus for suppressing torsional vibration of a crank shaft of a diesel engine,
according to Claim 2, wherein the number of cylinders is six and the mode where resonance
occurs in one-node torsional vibration is a six-order harmonic vibration, and when
the rotational number is within the resonance area of torsional vibration, the injection
timing for three cylinders is delayed by about 30°.