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2.1.3. Acceleration of The Piston: 2.2. Structure Dynamics of Crankshaft - Connecting ROD

The document discusses the acceleration of the piston in an engine and summarizes the piston acceleration formula. It then discusses the structure dynamics of a crankshaft-connecting rod mechanism. Key forces acting on it include gas pressure forces, inertial forces of moving components, and the total force acting on the piston pin which is the sum of gas pressure and translational inertial forces. Equations are provided for total moment on the crankshaft and forces acting on crankpins.

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Bùi Quốc Vinh
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93 views3 pages

2.1.3. Acceleration of The Piston: 2.2. Structure Dynamics of Crankshaft - Connecting ROD

The document discusses the acceleration of the piston in an engine and summarizes the piston acceleration formula. It then discusses the structure dynamics of a crankshaft-connecting rod mechanism. Key forces acting on it include gas pressure forces, inertial forces of moving components, and the total force acting on the piston pin which is the sum of gas pressure and translational inertial forces. Equations are provided for total moment on the crankshaft and forces acting on crankpins.

Uploaded by

Bùi Quốc Vinh
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as DOCX, PDF, TXT or read online on Scribd
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2.1.3.

Acceleration of the piston


- Taking the derivative V over time, we have the piston acceleration formula:
J = R.ω 2.(cosα + λ.cos2α)

- The acceleration of the piston is the sum of two harmonic functions of class I
and class II:
J = J + J = R.ω 2.cosα + R.ω 2 .λcos2α =
I I

2.2. STRUCTURE DYNAMICS OF CRANKSHAFT – CONNECTING


ROD
2.2.1 Gas pressure forces Pkt
- Gas pressure force is a quantity that varies with the angle of rotation of the
crankshaft, defined as obtained from gas pressure P at the thermal calculation of
the engine.
Pkt = (pkt – po)
Where:
pkt– gas pressure in the cylinder
p0 = 0,1 MN/m2 – atmospheric pressure
- Intake process: Pkt = Pa – Po
- Compression process: Pkt = Pa.in 1 – Po, with i from 1 (1800) to ε (3600 – θs)
Pz
- Expansion process: Pkt = −¿ Po
ɛn 2

- Expansion process: Pkt = Pr – Po


2.2.2 Inertial forces of moving details
- Translational inertial force:
Pj = −¿mt.J = −¿mt. Rω2(cosα + λcos2α)
- Centrifugal inertial force:
PK = −¿mr. Rω2 = const With: mt = mnp + mA
mr = mK + mB mA = (0,275 ÷ 0,35)mtt
mB = (0,725 ÷ 0,65)mtt
Where:
Pj – translational inertial force
PK – centrifugal inertial force
mt – the mass of translational motion details
mr – the mass of rotational movement details
mtt – the mass of connecting rod
mnp – the mass of piston group mK – the mass of the crankshaft
mA – the mass of connecting rod small end
mB – the mass of connecting rod big end
2.2.3 The force system acting on the crankshaft – connecting mechanism
- Total force acting on the piston pin
Is the synergy of the gas pressure force Pkt and the translational inertial force Pj,
valid equal to the algebraic sum of these two forces:
P1 = Pkt + Pj
- Vertical force acting on the connecting rod
P∑
Ptt = cos β with β = sin−1(λ. sinα)

- Thrust force N
N = Ptt.tgβ
- Tangential force T
sin(α + β)
T = Ptt. sin(α + β) = P∑ .
cos β

- Normal force Z:
cos(α + β )
Z = Ptt. cos(α + β) = P∑ .
cos β

2.2.4 Rotation moment M of the engine


- Calculation of the working deflection angle of the engine: δK = 180o
Select the working order of the engine: 1 – 3 – 4 – 2
Determination of the working phase of each cylinder:
+ Cylinder 1: α
+ Cylinder 2: α + 180
+ Cylinder 3: α + 540
+ Cylinder 4: α + 360
- Total moment ∑ Mi defined by the relation:
i

∑Mi = R.∑ Ti
i=1

Where:
∑ Mi: total moment
∑ Ti – total tangential force

2.2.5 Forces acting on crankpins


At the crankpin there is the following force: tangential force T, normal force Z,
centrifugal force PKO. The force acting on the crankpin is the force vector ⃗
Q
defined by force balance equation:
⃗
Q =T⃗ + ⃗
Z +⃗
P KO with PKO = −mB. R. ω2

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