Mechanical Systems and Power Transmission
1. Machine or Technical System
A machine or technical system is a combination of mechanisms or devices, grouped properly, that use a default power to transform and produce a final effect.
2. Drive Elements
Movers: These engines rarely provide power directly to the machine. They transform it into electrical energy, generally for use by a secondary engine.
Side-motors: These directly drive the machines. The energies used in secondary engines are:
a) Energy Muscles (from animals or people): Increasingly less used.
b) Thermal Energy: Obtained by burning fuel. Depending on whether combustion occurs inside or outside a cylinder, we have:
External Combustion Engines: The best known is the steam locomotive. It produces high-pressure steam to move a piston, converting heat into mechanical energy.
Internal Combustion Engines: Combustion occurs inside a cylinder. The operating principle and fuel used classify them as gasoline engines, diesel, and gas turbine or turbojet.
c) Electricity: Secondary electric motors are well-known.
3. Machine Parts
These are the individual components. The term mechanism is usually assigned to machine elements with mobility.
4. Shaft
A shaft is a revolution that allows power or energy transmission. An axis is a machine element, usually cylindrical, that supports rotating parts but does not transmit power and is not subject to torsion.
Rigid Coupling: Trees are placed along the same geometric axis and do not change position during rotation.
By Flanges: Two half flanges are placed at the ends of the trees, and screws are tightened to secure them.
Cymbals: Conical pressing pieces compress a conical piece against the two trees, allowing one tree to drag the other.
Mobile Link:
Gasket: A coupling, generally rubber or neoprene rubber, absorbs irregularities and allows up to 15° of misalignment between shafts.
Hook Universal Joint or Gasket: Transmits motion between non-aligned trees. Forks at the shaft ends are joined by a cross or spreader with bearings.
CVJs: Fulfill the same mission as universal joints but without oscillations, used mainly in the automotive industry.
Board Oldham: Discs are placed on trees, and another disc transmits motion between them, used for side trees separated by a small distance.
Sliding-Spline Shaft: Allows the tree to vary its length, also known as a sliding sleeve.
5. Transmission Through Pulleys and Belts
Keystone: Most commonly used for industrial applications.
Flat/Rectangular: Used for small powers or non-parallel shafts. The curved pulley prevents output during turns.
Round: Used in machines with low RPM or non-parallel axes.
6. Transmission Gears
Used for transmitting large effort or maintaining a constant gear ratio.
- Transmission Between Parallel Axes
Straight Teeth Gears: Used when power and revolutions are not high. Features include primitive circumference, module (m), and gear ratio.
Addendum H1 = height = 1 * m
H2 = height dedendum = 1.25 * m
H = height of tooth = h1 + h2 = 2.25 * m
B = length of the tooth = 10 * m
S = thickness of tooth = (19/10) · p
W = hollow tooth = (21/40) · p
Step = p = ? * m = w + s
Diameter | For wheel | For the pinion |
Primitivo | Dp = m · Zr | Dp = m · Zp |
Outside | De = m · (Zr +2) | De = m · (Zp +2) |
Inside | Di = m · (Zr-2.5) | Di = m · (Zp-2.5) |
* Helical gears teeth: are characterized by their teeth about its axis inclined. The teeth mesh several at once, this leads to the bending stress is dealt with during transmission. The only drawback is that they are more expensive.
* Gears of teeth in V: in order to compensate the axial forces, using two gears whose teeth form a complementary angle, which join together to form a V-Gear
* Epicyclic gear: consists of a ring gear inside, a central pinion gears and three smaller (satellite).
7.0 Kinematic Chains
A kinematic chain is a set of two or more pairs of gears, which mesh with each other, and that aim to change the number of revolutions of the last axle.
The gear ratio between two or more trees or axes is the product of the teeth of the sprocket (wheels lines) divided by the product of the teeth of the wheels (driving).
8.0 Relationship between power and torque: a couple or moment (M) is the product of force by a distance.
9.0 Transmitters and chain timing belt
Chain-> Ideal for dusty areas in which high availability requires the submission. They have the disadvantage of being a bit noisy. It should be lubricated.
Timing belt-> It’s very simple and requires no lubrication. A drawback of deteriorating periodically, which requires to be changed.