Balancing the inline engine

Contents

Summary

Introduction

1. General positions for engine balancing

2. Balancing the inline engine

3. Balancing V-motor

List of literature used

Introduction.

The dynamics of piston ICE studies the laws of movement of engine parts, its balancing, ensuring the necessary uniformity of travel, etc.

The modern reliable engine can be created only on the basis of a detailed study of the kinematics and dynamics of the moving parts of the internal combustion engine, taking into account the operating conditions and the nature of the change in the forces loading the engine.

During ICE operation, the forces arising in it can be divided into two types: balanced and unbalanced.

Equilibrium forces are those forces that are equal to zero, and which, when summed, do not give free moment, i.e. the moments from them are also equal to zero. Balanced include the pressure forces of the gases in the cylinder and the friction forces.

Unbalanced forces include the forces transmitted to the engine supports, namely:

1. Inertia forces of reciprocating masses (PDM) of the engine Pj. Engine PDM includes:

- piston with piston rings, piston pin and upper part of ball

tuna - for throne engines;

- piston with piston rings, piston rod, crosshead and upper

part of the connecting rod - for cruising ship ICE.

The inertia forces Pj are represented as the sum of the inertia forces of the first, second and higher orders. The inertia forces of the higher orders are small, so they are not taken into account in the calculation.

The inertia forces P, 1 and Pj11 act along the axis of the cylinder, i.e. constant in direction, but variable in magnitude and depend on the crank angle of the crankshaft a.

.

2. Centrifugal forces of unbalanced masses of engine Rg. They create

unbalanced torque Mvr. To the rotating masses of the motor,

the creating Mvr include:

- crank mass and lower part of connecting rod, which is assigned to connecting rod journal. Force Rg is constant in magnitude, but changes its direction along with crank rotation.

3. Jet (or tilting) moment of MR engine at any

crank position is equal to engine torque, but opposite in direction. MR, unlike torque, is never balanced.

4. Tangent inertia forces of rotating masses arising at non-

constant angular speed of engine crankshaft rotation.

5. Engine weight.

6. Fan thrust force.

7. Reaction forces of exhaust gases and moving liquids.

It should be noted that the forces (paras. 4-7) have little effect on the engine imbalance, so they are not taken into account in the calculation. Let us limit ourselves to considering only the inertia forces of the first and second orders and the centrifugal inertia forces.

These periodically changing forces are transmitted to the engine frame and the sub-engine frame, as a result of which these structures will begin to oscillate, which can lead to the destruction of the entire plant.

The engine is considered fully balanced if the resulting forces Pj, "P, p, Pg and moments from them are zero.

As measures to reduce inertia forces and their moments (or to reduce them to permissible values), the following are used:

1. Selection of optimal angles between cranks of engine crankshaft.

2. Optimal choice of number and operation order of cylinders.

3. Installation of additional rotating masses on the engine (Lanchester mechanism).

4. High uniformity of torque over crankshaft turn angle.

The provision of item 4 is achieved by performing a number of design and technological measures, namely:

1. Equality of scales of piston group by cylinders.

2. Equal weights and equal position of center of gravity of connecting rods.

3. Static and dynamic balance of the crankshaft that

it is achieved by balancing it.

4. Uniformity of working process in cylinders, which is ensured due to the same filling of cylinders, the same compression ratio and

the shape of the combustion chamber, the same moments of fuel injection along the cylinders,

the same value of the cycle fuel supply, etc.

1. General positions for engine balancing

Engine vibration is caused mainly by inertia forces of progressively moving and unbalanced parts of engine.

1. The inertia forces of one group can result in one force and one

moment. To do this, you need to transfer the force vectors to one point - the center of the drive.

In this case, moments arise that are depicted by the vector in the diagram. Geometric summation of force and moment vectors allows you to determine the total force and moment and is performed separately for each group of forces and moments.

2. Vectors of centrifugal inertia forces, first and second order inertia forces and their moments represent actual forces and moments acting in

engine.

3. Total force or total moment is determined from the construction

vector diagram. The value of the sum vector is represented in the received

scale magnitude of force or moment. Direction of the resulting op- vector

determines the direction of force or moment in accordance with the accepted conditions:

- if centrifugal (c/b) forces act up the diagram, then both the vector

the force is directed upward;

- if moments from c/b forces act in vertical plane and tend

turn the motor clockwise, then the torque vector in the diagram is directed

up..

4. If the total force of this group is zero, as is often the case, then

the center of the drive may be selected arbitrarily, for example in the middle of the crankshaft. In this case, the forces behind the center of bringing will be created -

enter a moment with a negative sign.

5. For ease of constructing vector diagrams of forces or moments, first

their values are determined, then phase diagrams are built, and based on them they are built

vector charts.

6. Balance the total moments or forces for each group separately.

7. In the V-shaped engine, the inertia forces of the 1st and 2nd orders act in

vertical and horizontal planes. The total force or moment is determined in each plane separately.

For vertical forces and moments, the above conditions are taken when the forces or moments reach the maximum value (the vector in the graph is directed upward). When the crankshaft rotates at the desired angle, the force or torque vector rotates at the same angle in the same direction.

Phase diagrams for forces and moments in vertical and horizontal planes correspond to each other.

It should be noted that the vertical and horizontal inertia forces reach a maximum when the cylinder pistons are in the TDC. Vertical forces for cylinders of right and left blocks have the same sign. Therefore, for the right block, force and moment vectors are deposited in the directions indicated in the phase diagrams, and for the left block in the opposite direction.

Horizontal moments can be balanced by 4 counterweights mounted on two shafts.

Counterweights are installed not only for "external," but also for "internal" balancing:

- to reduce internal bending moments;

- for main bearings unloading.

The internal bending moment is usually determined for the middle of the engine. The magnitude of the internal bending moment depends on the acting forces in one half and the reaction forces in the same half. If for the whole engine the force and moment are zero, then the reactive forces are zero, and the internal

bending moment is equal to total torque acting in nose half of engine. This is true for Pj, P, p and for the c/b inertia forces of the counterweights.

The internal bending moment in the horizontal plane in the in-line engine is geometrically composed of the moment from c/b inertia forces in the nose compartment and half of the external unbalanced moment. Taking into account counterweights, the moment from the c/b forces of inertia of the counterweights in the nose compartment is geometrically added plus half of the external unbalanced moment from the counterweights taken with the reverse sign.

The internal bending moment in the vertical plane is obtained by summing the moment from the inertia forces of the 1st order in the nose compartment with half of the external unbalanced moment of the 1st order taken with the reverse sign.

3. Balancing V-shaped engine.

TASK: balance the V-shaped 6-cylinder engine with the camber angle of the blocks 60 ° with the operating order of the cylinders 12/3-4/5-6/and the wedge angle KB 135 °.

We determine the result of centrifugal inertia forces of unbalanced rotating parts. They are constant in size, act on their crank and are directed from the center of rotation. The centrifugal inertia forces generated in the 6 cylinder V-shaped engine in question are shown on sheet 2. We select the center of the cast at the point "O."

The magnitude and direction of all centrifugal inertia forces can be determined by a crank pattern. We obtain a first order vector diagram for centrifugal inertia forces PR on the scale L = PR, where L is the radius of the circle of the vector diagram.

Centrifugal inertia forces are applied at different points along length of crankshaft and are directed according to diagram on sheet 2. They form a spatial system of forces that must be brought to one force (main vector) and to one moment (main moment).

To determine the resultant (or total force), transfer PR from all cylinders parallel to itself to the plane passing through the center of the drive (0), directing PR along its cranks. Remember that the PR of each cylinder gives rise to moments (relative to the center of the drive), which must be taken into account when balancing the engine.

The resulting system of forces will be in one plane passing through the center of drive (0). The addition of PR forces is done geometrically according to the rule of the polygon of forces. The resulting force sought is denoted by ∑ PR ~ (total). In this calculation, the resulting ∑PR is 0.

3.2. Determine the resulting inertia forces of the first and second

order and their moments.

First, we examine the effect of the first order inertia forces, the value of which is equal.

where φ - an angle of rotation of a crank of each cylinder.

It is known that the first order inertia forces are different for all cylinders, but always the direction along the axis of its cylinder. When determining the resulting these forces graphically, it is convenient to take advantage of the fact that the forces Pj are a projection on the cylinder axis of the radial vector Pg, rotating as a vector of the centrifugal force of inertia, but having a value

P) 1= RG =mtsam ω2 r

Vector Rg represents centrifugal force of inertia of unbalanced rotating mass (t ^), weight of which is equal to weight of translational moving masses.

Therefore, instead of adding parallel vectors Pjl, it is easier to geometrically add constants in magnitude, but directed along the axes of the cranks in the same way as vectors Pg, i.e., vectors of inertia forces, and then design them on the cylinder axis.

To create a phase diagram of the inertia force of the left row (block), rotate each vector by an angle A = A/2 (half of the angle of the cylinder collapse) relative to its crank against rotation for the left block, and for the right block rotate relative to its crank by the same angle along the rotation.

Then, in the phase diagram, we direct Pj! and closing the polygon of forces. In this case, polygons are built for vertical and horizontal planes; in the horizontal plane we change the directions of the vectors for

left block by opposite ones. The resulting 1st order inertia forces for vertical and horizontal planes are 0, sheet 2.

3.3. To Create a Resultant Moment from Inertia Forces

first order.

Since the moment vectors of the first-order inertia forces are projections of the moments of the centrifugal inertia forces on the cylinder axis, it is possible to obtain the following expression for the resulting moment of the first-order IDM inertia forces with respect to the center of motion for the moments.

М1= m ω2 r l cosφ

This moment, being variable in magnitude, depending on the position of the first crank and acting in a plane passing through the axes of the cylinders, will tend to rotate the engine in its plane in both directions around the center of gravity once per revolution of the crankshaft.

Analyzing the above reasoning, it can be concluded that if the centrifugal inertia forces and their moments are balanced, the first-order inertia forces and their moments will also be balanced.

This is achieved by mutual arrangement of cranks, and not by installation of counterweights on cheeks.

In this calculation, the moment vector from Pj! guide the respective cylinders, and the torque is M1 = Pjl 1, where 1 is the distance from the center of drive to the axis of the respective cylinder. The resulting moment is shown on sheet 2.

The resulting (total) moment in the vertical plane is denoted by ∑ MP