structural kinematic and dynamic analysis of internal combustion engine

Contents

INTRODUCTION

Chapter 1 Description of the type of internal combustion engine under investigation

1.1 Description of V-motor design

1.2 Main parameters of internal combustion engine

Chapter 2 Structural analysis of crank mechanism of internal combustion engine

2.1 Determining the composition of the mechanism

2.2 Drawing up a plan of the provisions of the mechanism

Chapter 3 Kinematic analysis of crank mechanism of internal combustion engine

3.1 Construction of the mechanism speed plan

3.2 Construction of the acceleration plan of the mechanism

Chapter 4 Dynamic analysis of crank mechanism of internal combustion engine

4.1 Calculation of external forces acting on the mechanism

4.2 Calculation of structural group 2-

4.3 Calculation of structural group 4-

4.4 Calculation of the leading link

Chapter 5 Description of cam gears

5.1 Main parameters of cam gear

5.2 Synthesis of cam mechanism

CONCLUSION

LIST OF INFORMATION SOURCES

APPLICATIONS

Introduction

Course work on the theory of mechanisms and machines provides for the solution of the following problems:

structural and kinematic analysis - determination of positions, speeds and accelerations of all points of the mechanism when changing the position of the input link - crank;

dynamic analysis - determination of reactions in kinematic pairs and determination of balancing moment by two methods;

1.2 Main parameters of internal combustion engine

The diameter of the cylinder is the size of the hole in the cylinder block (cylinder liner) in which the piston translates. This is a structural parameter of the cylinder block that affects the displacement of the engine. In addition the general dimensional width depends on diameter of a cylinder and it is long the engine. The size is usually specified in millimeters or inches with an accuracy of one hundredths. The size of the nominal cylinder diameter is indicated at room temperature (20 degrees Celsius). Measurements are made by a nutrometer or a tool similar in accuracy.

The stroke of the piston is the distance between the position of any center of the piston in the upper dead center (V.M.T.) and the position of the piston in the lower dead center (N.M.T.). This is a structural parameter of the crankshaft that affects the working volume of the engine. The size is usually specified in millimeters or inches with an accuracy of one hundredths. Measurements are made by a stangelcircle or a tool similar in accuracy. As a rule, measurements are made directly on the crankshaft. The overall height of the engine depends on the size and stroke of the piston.

The number of cylinders is the most important design characteristic of the engine. Depending on the number of cylinders, the engine cooling system is calculated and designed. The number of cylinders most directly affects the overall overall dimensions and weight of the car. For example: with an increase in the number of cylinders with the same engine liter, the size of its cylinders decreases. This decrease due to an increase in the ratio of the inner surface of the cylinder to its volume is accompanied by an increase in engine cooling. Reducing the diameter of the cylinder allows a combustion chamber of an improved shape and, together with the circumstance of increasing cooling, allows the manufacturer to create more economical engines. But there is also the reverse side, an increase in the number of cylinders leads to a general increase in the cost of the power unit. In modern automotive engine building, 2x, 3x, 4x, 5-i, 6-i, 8-i, 10i, 12i, 16-and cylinder engines have become widespread.

The working volume of the engine (VH) (engine liter) is composed of the working volumes of all cylinders. That is, the product of the working volume of one cylinder Vp by the number of cylinders Z.

The working volume of the cylinder (Vp) is the space that releases the piston when moving from the upper dead center (VMT) to the lower dead center (NMT).

The total volume of the cylinder (Vo) is the sum of the working volume of one cylinder Vp and the volume of one combustion chamber in the head of the unit Vk.

The volume of the combustion chamber (Vk) is the volume of the cylinder cavity and the combustion chamber in the head of the cylinder block above the piston located in the upper dead center (VMT) - i.e. in the extreme position and at the longest distance from the crankshaft. A parameter that directly affects the compression ratio of the engine. Under garage conditions, the combustion chamber is measured by measuring the volume of liquid filling the chamber.

In modern automotive industry, engines with a multi-valve gas distribution mechanism are increasingly used. Increasing the number of valves is an important parameter that allows you to obtain more power at the same engine volume by increasing the volume of mixture or air entering the cylinders at the intake stroke. Increasing the number of valves makes it possible to obtain a better filling of cylinders with a fresh working mixture and to quickly free the combustion chamber from exhaust gases.

By type of fuel, engines are divided into the following groups:

Petrol engines - have positive ignition of the fuel-air mixture with spark candles. Fundamentally different by type of power system:

In carburetor power systems, mixing of gasoline with air begins in the carburetor and continues in the inlet pipeline. Currently, the production of such engines is almost discontinued due to high fuel consumption and non-compliance with modern environmental requirements.

In injection engines, the fuel may be sprayed by a single injector into a common inlet conduit (central, monovrush) or by several injectors upstream of the inlet valves of each cylinder of the engine (distributed injection). In these engines, there may be a slight increase in maximum power and a decrease in fuel consumption and a decrease in exhaust toxicity due to the calculated fuel dosage by the electronic engine control unit;

Engines with direct injection of gasoline into the combustion chamber, which is supplied to the cylinder in several portions, which optimizes the combustion process, allows the engine to operate on depleted mixtures, accordingly, the consumption of gasoline and the release of harmful substances into the atmosphere are maximized.

Diesel engines are piston internal combustion engines with internal mixing, in which the ignition of the mixture of diesel fuel and air occurs from an increase in its temperature during compression. Compared to gasoline, diesel engines have better economy (by about 1520%) due to more than twice the compression ratio, which significantly improves the combustion processes of the fuel - air mixture. The undeniable advantage of diesel engines is the structural absence of a throttle valve, which creates resistance to air movement at the inlet and therefore increases fuel consumption. The maximum torque of the diesel engine develops at a lower crankshaft speed.

Hybrid engines - engines combining the characteristics of a diesel engine and a spark-ignition engine.

Compression ratio (a) is the ratio of the total volume of the engine cylinder to the volume of the combustion chamber. This parameter indicates how many times the total volume of the cylinder decreases as the piston moves from the bottom dead center to the top dead point. For gasoline engines, the compression ratio determines the octane number of the fuel used. For petrol engines, the compression ratio is defined between 8:1 and 12:1 and for diesel engines between 16:1 and 23:1. The general global trend in engine construction is an increase in the compression ratio of both gasoline and diesel engines, caused by toughening environmental standards.

Compression (pressure in the cylinder at the end of the compression stroke) (p c) is one of the indicators of the technical condition (wear) of the cylinder-piston group and valves. Engines with serious mileage, as a rule, already have uneven wear of the cylinder liner and piston rings, and therefore the piston ring does not fit tightly to the surface of the cylinder. The valve mechanism, or rather the valve rod and the valve guide sleeve, is also worn out. Due to the above reasons, loss of tightness of the combustion chamber occurs.

Power is a physical quantity equal to the ratio of the work performed or the energy change that occurred to the time period during which the work was performed or the energy change occurred. Typically, power is measured in Horse Power. Value 1 hp (HP) = 0.735 kW) or in Kilowattah (1 kV) = 1.36 hp (HP). Maximum power and maximum torque are achieved at different engine speeds [4].

Description of cam gears

5.1 Main parameters of cam gear

A cam is a part of a cam mechanism with a shaped sliding surface in order to transfer movement to a mating part (pusher or rod) with a given law of speed change during its rotational movement. The geometric shape of the cams can be different: flat, cylindrical, conical, spherical and more complex.

Cam mechanisms are transformative mechanisms that change the nature of movement. In mechanical engineering, cam mechanisms are widespread that convert rotational motion into reciprocating and reciprocating. Cam mechanisms, like other types of mechanisms, are divided into flat and spatial.

Cam mechanisms are used to perform various operations in the cycle control systems of process machines, machine tools, engines, etc. The main element of the gas distribution system of the internal combustion engine is the simplest cam mechanism. The mechanism consists of a cam, a rod connected to the working element, and a post supporting the mechanism links in space and providing each link with appropriate degrees of freedom. The roller, installed in some cases at the end of the rod, does not affect the law of movement of the links of the mechanism. The bar performing the translational movement is called the pusher, and the rotary rod is called the rocker. In case of continuous movement of cam pusher makes intermittent translational motion, and rocker makes intermittent rotational motion.

Constant contact of the rod and cam (closing of the mechanism) is a prerequisite for normal operation of the cam mechanism. The closure of the mechanism can be power and geometric. In the first case, the closure is usually provided by a spring pressing the rod against the cam, in the second - by the design of the pusher, especially its working surface. For example, a pusher with a flat surface touches the cam with different points, so it is used only in the case of transmission of small forces.

In light industry machines, spatial cam mechanisms are used to provide very complex interconnected movement of parts, along with the simplest flat ones. In the spatial cam mechanism, you can see a typical example of geometric closure - a cylindrical cam with a profile in the form of a slot into which the pusher roller enters.

When choosing the type of cam mechanism, they try to stop using flat mechanisms that have a significantly lower cost compared to spatial ones, and in all cases, where possible, they use a rod of a swinging structure, since the rod (rocker arm) is conveniently installed on the support using rolling bearings. Furthermore, in this case, the overall dimensions of the cam and the entire mechanism may be smaller.

Cam mechanisms: A cam is a three-link mechanism with a higher kinematic pair whose input link is called a cam, and the output link is called a pusher (or rocker). Often, to replace the sliding friction in the highest pair with rolling friction and reduce wear, both of the cam and the pusher, an additional link - roller and a rotary kinematic pair are included in the mechanism circuit. Mobility in this kinematic pair does not change the transfer functions of the mechanism and is local mobility.

Purpose and Scope: Cam mechanisms are designed to convert the rotational or translational motion of the cam into the reciprocating or reciprocating motion of the pusher. At the same time, in a mechanism with two movable links, the transformation of motion according to a complex law can be realized. An important advantage of the cam mechanisms is the ability to ensure accurate height of the output link. This advantage was determined by their wide use in the simplest devices of cycle automation and in mechanical counting and solving devices (arithmometers, calendar mechanisms). Cam mechanisms can be divided into two groups. The mechanisms of the first provide movement of the pusher according to the specified law of motion. The mechanisms of the second group provide only the specified maximum movement of the output link - the pusher stroke. At the same time, the law by which this movement is carried out is selected from a set of typical laws of movement depending on the operating conditions and manufacturing technology.

by location of links in space: spatial, flat

by cam motion, rotational, translational, screw

on movement of output link reciprocating (with pusher), reciprocating (with rocker)

by presence of roller with roller, without roller

by cam type disc (flat), cylindrical, conoid (complex spatial)

by the shape of the working surface of the output link: flat, pointed, cylindrical, spherical, involute

according to the method of closing elements of the highest pair: force, geometric.

In case of power closure, pusher is removed by action of cam contact surface on pusher (driving link - cam, driven link - pusher). Movement of the pusher at approach is carried out due to force of spring elasticity or force of pusher weight, at that the cam is not a driving link. At geometric closure, pusher motion at removal is performed by action of external working surface of cam on pusher, at approach - by action of internal working surface of cam on pusher. At both phases of movement cam is driving link, pusher - driven link [8].

5.2 Synthesis of cam mechanism

In the synthesis of the cam mechanism, as in the synthesis of any mechanism, a number of tasks are solved, of which two are considered in the TMM course:

selection of structural diagram;

Defines the basic dimensions of the mechanism links (including the cam profile).

The first stage of synthesis is structural. The block diagram determines the number of links of the mechanism; number, type and mobility of kinematic pairs; the number of redundant links and local mobility. In structural synthesis, it is necessary to justify the introduction of each redundant communication mechanism and local mobility into the scheme. The determining conditions when selecting a structural diagram are: the specified type of motion conversion, the location of the axes of the input and output links. The input motion in the mechanism is converted into an output motion, for example, rotational to rotational, rotational to translational, etc. If the axes are parallel, then the planar circuit of the mechanism is selected. For intersecting or intersecting axes, you must use a spatial scheme. In kinematic mechanisms, the loads are small, so pushers with a pointed tip can be used. In power mechanisms to increase durability and reduce wear, roller is inserted into mechanism circuit or reduced radius of curvature of contact surfaces of higher pair is increased.

The second stage of synthesis is metric. At this stage, the basic dimensions of the mechanism links are determined, which provide a given law of motion conversion in the mechanism or a given transfer function. As noted above, the transfer function is a purely geometric characteristic of the mechanism, and therefore the metric synthesis problem is a purely geometric problem, independent of time or speed. The main criteria that guide the designer in solving the problems of metric synthesis: minimization of dimensions, and, therefore, mass; minimizing the pressure angle in the top pair; obtaining a process shape of a cam profile [8].

Conclusion

During the course work on the theory of mechanisms and machines, the following main problems were solved:

structural and kinematic analysis of the crank mechanism was carried out - positions, speeds and accelerations of all points of the mechanism depending on the position of the input crank were determined;

dynamic analysis was carried out - reactions in kinematic pairs were determined, balancing moment at the crank was determined;