Dynamic calculation of 4Ch7 VAZ engine. KP calculation of vase engine

Task

1. Brief description of the engine, selection of initial parameters to obtain an indicator diagram;

2. Construction of engine indicator diagram;

3. Calculation and plotting of change of forces of one cylinder acting on KSM:

- inertia forces;

- gas pressure forces;

- driving forces;

- lateral force;

- radial and tangent force;

is the total tangent force.

4. Analyses the design of a specified part that is used in the flywheel model.

6. Conclusions

Engine

On cars, 4-stroke piston carburetor internal combustion engines with an upper location of the camshaft are installed.

Cylinder blocks

The cylinder block is made by casting from special high-strength cast iron. Cylinder holes are spread directly in the block and no additional inserts (sleeves) are used in the cylinders. To obtain a high degree of accuracy and cleanliness of the surface, the cylinders are honing. By diameter, cylinders are divided into five classes after 0.01 mm, indicated by the Latin letters A, B, C, D and E. The class of each cylinder is marked on the lower plane of the cylinder block.

Holes for crankshaft crankshaft main bearings are stretched together with bearing covers. Therefore, they are not interchangeable either with each other or with the covers of other cylinder blocks, and in order not to confuse the covers, marking is made on them. Bearing covers are attached to the cylinder block by self-locking bolts, replacement of which with any other ones is unacceptable.

Roller (6) (refer to Figure 2) of auxiliary units drive is rotated in two bushings pressed into cylinder block. The front bushing is steel-aluminum, and the rear bushing is metal-ceramic. Bushings of nominal and repair sizes with a reduced 0.3 mm internal diameter are supplied to the spare parts.

Cylinder blocks of various engine models are not interchangeable. They can be distinguished by the model number cast on the left side of the cylinder block.

CONNECTING ROD-PISTON GROUP

Piston. Pistons 4 and 6 (Figure 3) of all engine models are cast from aluminum alloy. External surface of piston is covered with thin layer of tin to improve its working capacity to cylinder walls. To compensate for uneven thermal expansion, the piston skirt has a complex shape. It is conical in height, and oval in cross section. Therefore, it is necessary to measure the diameter of the piston only in the plane perpendicular to the piston pin and at a distance of 52.4 mm from the piston bottom.

According to the outer diameter, pistons (as well as cylinders) are divided into five classes after 0.01 mm, and according to the diameter of the hole for the piston pin 5 - into three categories 0.004 mm (see annex 2). The piston class (Latin letter) and category (digit) are marked on the piston bottom.

Class A, C, E pistons are supplied to spare parts, which are enough to select a piston for any cylinder, since pistons and cylinders are divided into classes with some overlapping dimensions.

Hole for piston pin is shifted from axis of symmetry by 5 mm to right side of engine. Therefore, the piston has a mark 11 in the form of a letter P for correctly orienting the piston in the cylinder. The mark, as well as the opening 10 on the oil outlet connecting rod, must face the front of the engine.

Piston rings. Two compression rings 2 and 3 and one oil collector 1 are installed on the piston. All of them are made of cast iron. Upper compression ring with barrel-shaped chrome outer surface. Lower compression ring of scraper type, phosphated.

Piston pin. All engine models have the same steel tubular piston pins 5 (see Figure 3). They are pressed into the upper head of the connecting rod 7 and freely rotate in the piston bosses. According to the outer diameter, the fingers are divided into three categories after 0.004 mm. The finger category is marked at its end with the corresponding color: 1st - blue, 2nd - green and 3rd - red.

Connecting rod. Steel, forged, the same for all engine models. The lower head of the connecting rod is detachable, connecting rod inserts 9 are installed in it. The connecting rod is processed together with the cover 8, and therefore they are not interchangeable with the covers of other connecting rods. In order not to confuse the connecting rod covers during assembly, on the connecting rod and its cover (side) there is a stamp of the number of cylinders in which they are installed. When assembling, the numbers on the connecting rod and cover must be on the same side.

Crankshaft and flywheel

Crankshaft. It is cast from high-strength cast iron and has five supporting (main) necks hardened with high-frequency currents to a depth of 2-3 mm. At the rear end of crankshaft 1 (Figure 4) there is a seat where the bearing of the gearbox drive shaft is inserted. Lubricating channels in crankshaft necks are closed with cap plugs, which are pressed in and cased in three points for reliability.

To extend the service life of the crankshaft, it is possible to switch the crankshaft necks in case of wear or damage to their surfaces. By grinding, the diameter of the necks decreases by 0.25; 0,5; 0.75 and 1.00 mm.

Axial displacement of crankshaft is limited by two thrust semi-rings 3 installed in cylinder block on both sides of rear main bearing. A steel aluminum semi-ring is installed on the front side of the bearing, and metal ceramic (yellow) is installed on the rear side. Semi-rings are made of normal thickness 2.31-2.36 mm and increased (repair) 2.437-2.487 mm. When assembling the engine, the semi-rings are selected in thickness so that the axial free stroke of the crankshaft is within the range of 0.06-0.26 mm.

Inserts of main and connecting rod bearings. All of them are thin-walled, bimetallic, steel-aluminum. Inserts 6 for 1, 2, 4 and 5 main bearings have a groove on the inner surface (since 1987, the lower inserts of these bearings have been installed without a groove). The insert 7 the central (3rd) core bearing differs from the other inserts by the absence of a groove on the inner surface and a larger width. All inserts 2 of connecting rod bearings without grooves are the same and interchangeable. Repair inserts are made of increased thickness for crankshaft journals, reduced by 0.25; 0,5; 0.75 and 1 mm.

Flywheel. It is cast from cast iron and has a steel pressed toothed rim for starting the engine with a starter. The flywheels 4 on all engine models are the same and interchangeable, since they are balanced separately from the crankshaft. Flywheel is centered with crankshaft by front bearing of gearbox drive shaft.

The flywheel is attached to the flange of the crankshaft by six self-locking bolts, under which one common washer 5 is laid. It is not allowed to replace these bolts with any other bolts. The flywheel must be installed so that the mark - cone-shaped hole A - is located against the connecting rod neck of the 4th cylinder. The label is used to determine in. M. t., in the 1st and 4th cylinders.

Cylinder heads and valve mechanism

Cylinder head. It is made of aluminium alloy and has wedge-shaped combustion chambers, pressed seats and guide bushings of valves. Valve seats are made of special cast iron to ensure high strength when exposed to impact loads. Working chamfers of seats are processed after pressing together with cylinder head 1 (Fig. 5) to ensure accurate alignment of chamfers with holes of guide bushings of valves.

Valve guide sleeves are also made of cast iron and pressed into the cylinder head with interference. On the outer surface of the guide bushings there is a groove where a locking ring is inserted. It ensures accuracy of bushings position when they are pressed into cylinder head and prevents bushings from possible falling out.

Holes in bushings are processed after pressing them into cylinder head. This provides a narrow tolerance for the diameter of the hole and the accuracy of its location with respect to the working chamfers of the seat and valve. In holes of guide bushings there are spiral grooves for lubrication. At bushings of inlet valves, grooves are cut to half the length of the hole and at bushings of outlet valves - along the entire length of the hole.

Oil reflective caps 3 made of heat-oil-resistant rubber with steel reinforcement ring are put on the guide bushings from above. The caps enclose the valve rod and serve to reduce oil penetration into the combustion chamber through the gaps between the guide sleeve and the valve rod.

Camshaft

Camshaft. Cast, cast iron, the same for all engine models. It rests on 5 necks and rotates in the aluminum bearing housing installed on the cylinder head. Driven sprocket is attached to front end of camshaft. Camshaft is retained from axial displacements by thrust flange placed in groove of front support journal of shaft.

Until April 1982, camshafts with cams and support necks with hardened high-frequency currents (i.e.) were installed on VAZ vehicles. Since April 1982, nitrided camshafts have been installed. Since 1984, the year of production has been marked on the shafts. Since 1985, camshafts with cam bleaching have been installed; these shafts have a distinctive hexagonal girdle between the 3rd and 4th cams.

Cooling system

Liquid cooling system, closed type, with forced circulation (Fig. 6), The system is filled with cooling liquid Tosol A40, which is an aqueous solution of Tosol A antifreeze (concentrated ethylene glycol with anticorrosive and anti-foaming additives). Coolant density Tosol A40 is 1.078 - 1.085 g/cm. The capacity of the cooling system is 9.85 liters. For liquid drain, there are two drain holes closed by plugs: one hole in the lower tank of the radiator, the second in the cylinder block on the left side

LUBRICATION SYSTEM

Combined lubrication system - under pressure and spraying. Crankshaft main and connecting rod bearings, camshaft and auxiliary unit drive shaft supports, camshaft cams and oil pump drive gear sleeve are lubricated under pressure. Cylinder walls, pistons with piston rings, piston pins in bosses, chain of distribution mechanism drive are lubricated with oil flowing out of clearances and sprayed with moving parts.

Calculation and construction of theoretical

indicator chart

The calculated indicator diagram is built based on the calculation data of the working cycle. In the future, this diagram is the starting material for dynamic and strength calculations of the engine. Chart construction is done analytically because graphical construction methods produce large errors.

Ordinates of points of compression and expansion polytrope are calculated by the following formulas:

- for compression process

- for expansion process

Using the V/Vc ratio as a variable allows you to simplify the calculations, since the numerical values ​ ​ of V/Vc necessary for calculating the ordinates of the compression and expansion polytrop are mainly integers (from 1.0 to g for the compression polytrop, from p to e for the expansion polytrop). It is also convenient to set the same values of V/Vc to calculate the ordinate of the compression and expansion polytrop. At the same time, two ordinates of compression and expansion polytropes correspond to one abscissa, which greatly simplifies their construction.

The theoretical indicator diagram of the working cycle in this case is represented in the coordinate system p - V/Vc dimensionless in the direction of the axis of volumes. Absolute volumes corresponding to the V/Vc ratio values are easily found by multiplying the V/Vc ratio by the constant compression chamber volume Vc:

- for four-stroke ICE

Calculation of ordinates of points of compression and expansion polytropes is conveniently carried out in tabular form and in certain order

The values of ps, pa, pz and pp are control values and must correspond to those obtained in the calculation of the cycle.

Source Data for Indicator Chart Construction

PS = 0.1013 MPa;

PA = 0.091 MPa;

Pz = 6.485 MPa;

Rs = 1.733 MPas;

= 8.5;

= 1;

n1 = 1.376;

n2 = 1,228.

Building an Indicator Chart

Dynamic calculation of the engine

Inertia Forces

Force of inertia of translational moving masses is applied in center of piston pin acts along cylinder axis and is equal to:

We choose from average statistics for VOD ms = 0.0025 MPa

r is the radius of the hoist;

0 is the average angular speed of rotation of the shaft;

0 = ⋅n/30=3,14⋅5600/30=586,1с-1

= 0.3 - ratio of hoist radius to connecting rod length;

is the angle of rotation of the crankshaft from the position of the hoist

top dead point toward shaft rotation.

Gas pressure forces

The piston on the side of the combustion chamber is influenced by the pressure of gases in the cylinder of the engine Rg (Fig.8.). It is applied in the center of the piston pin and acts along the axis of the cylinder.

The gas pressure forces acting on the piston Rg and on the cylinder cover Rg are mutually balanced inside the engine and are not transmitted to its supports. Outside the engine, the pressure forces of the gases are manifested in the form of the rotating MIR and the overturning moments of the MOTAPM. The relative value of the pressure force of gases depending on the angle of rotation of the crank Pg = f (¼) is determined analytically or graphically from the calculated or actual indicator diagram.

It is more advantageous to analytically determine the working fluid pressures for the calculated crank positions. In this case, the following data should be available:

and e is the conditional and actual compression ratio;

and - the degree of preliminary expansion and the degree of subsequent expansion;

Pz and Pa - cylinder pressures - maximum and at the beginning of compression;

n1 and n2 - indices of compression and expansion polytropes;

The calculated positions of the mechanism and their corresponding values ​ ​ will be marked with index i; S * and s * without indices are used to indicate the full stroke of the piston.

The current compression ratio i is the ratio of the volume of the cylinder at the moment of the beginning of compression to its current volume, equal to the ratio of the pistons corresponding to these volumes:

For four-stroke diesel when S = 0,

The current compression ratio may vary between one and the actual compression ratio.

The current degree of subsequent expansion i is the ratio of the volume of the cylinder at the moment of the end of the preliminary expansion. Regardless of engine speed

The pressure of gases per 1 cm2 of the area of ​ ​ the piston rG is determined by thermodynamic formulas:

Since d = 8.5; = 1; Pa = 0.091 MPa; Pz = 6.485 MPa; n1 = 1,376; n2 = 1.228 can find gas pressure values at the moment of crankshaft rotation

hc = 0.2667; Nf = 2.2667

Absolute value of gas pressure force on piston Rg = pgFn, MN, and relative value Rg = p, MPa.

Driving force

The driving force is the resultant of all the forces acting on the piston - the pressure force of the gases in the cylinder Rg, the air pressure force in the sub-piston cavity Rp, the inertia force of the PDM Pj, the gravity force and the PDM Rt and is equal to their algebraic sum, MPa,

Figure 8 shows the driving force in KSM. It is applied in the center of the piston pin and acts along the axis of the cylinder. Force Pdv is spread out into components: normal force acting perpendicular to the cylinder axis and pressing the piston to the bushing N = Pdvtg, and force acting along the connecting rod axis, Q = Pdv/cos.

The force Q is transferred along its line of action to the center of the connecting rod neck and is laid out into two components: the radial force acting on the crank, Z = Q cos (¼ +) = Pdb cos (¼ + )/cos and the tangential force T = Q sin (¼ +) = Pdb sin (¼ + )/cos.

The forces acting on the CMM are variable in magnitude and direction, therefore, for ease of analysis, they are represented in the form of graphical dependencies showing the change in forces along the angle of rotation of the crank. Periodic curves, with a period of 360 ° in two-stroke engines and 720 ° in four-stroke engines. The forces are considered positive when Rdv, Pj and Z are directed to the center of rotation of the crankshaft, T is directed to the side of rotation of the crankshaft, and N is directed to the side opposite to rotation. The angle is positive when the connecting rod is deflected towards the crankshaft rotation.

Total tangent forces in

multi-cylinder engine

The total tangent forces in multi-cylinder engines must be known in order to determine the torque and calculate the crankshaft for strength.

The diagram of the total tangent forces T of the multi-cylinder engine is constructed by sequentially summing the tangent force curves of each of the cylinders shifted in phase by the angle of the wedge of the cranks. Summation can be done graphically or in tabular form. Builds T.

The values of T are obtained by summing ordinates within each row. Values of Tz = T0, as T - periodic function with the period ϕз. According to the obtained data, we build a dependence T = f (¼).

According to the table, we plot the total tangent forces.

To construct Tsr, we find the area under the curve T and divide it by the length of the segment 0180. Then we get Tsr ≈ 0.721 MPa.

The total tangent force is applied to the flange of the crankshaft at radius r and determines the total torque, MN⋅m.

Mvr = T⋅r⋅Fp

Average torque value, MN⋅m

Mfr.sr = Tsr⋅r⋅Fp

For 4H engine 7.6/6.6 Mfr.sr = Tsr⋅r⋅Fp = 0.721⋅0,033⋅3,14⋅0,0762/4=0,1078 kN⋅m.

Flywheel Calculation

If our engine runs on vehicles, then we accept the unevenness of rotation n = 1/100.

Assuming that the entire moment of inertia required to ensure a given degree of non-uniformity should be created by the flywheel, we will find the weight of the flywheel, kg:

Excessive torque operation

fizb - the area of the largest excess area, if during the period of change Mvr there are two excess areas, mm2;

At = 7800 kg/m3 we will find the width of the flywheel.

Conclusions

In this work I constructed the indicator chart for engine 4Ch 7,6/6,6 that allowed to find also pressure forces of gases, inertia force, driving forces, radial, side and tangent forces. These forces determine the design and, accordingly, the weight and size of the diesel engine. Finding tangent forces made it possible to find a change in torque on the flange of the engine. Since this is a transport engine, by setting the degree of non-uniformity of rotation we can find the geometric dimensions of the flywheel using the dependence of the change in the total tangent force on the angle of rotation of the crankshaft

List of literature used

1. Istomin P.A. Dynamics of ship ICE. L. Shipbuilding, 1964.

2. Fomin Yu.A. and others. Ship ICE. L., Shipbuilding, 1989.

3. Gogin A.F. and others. Ship diesel engines, M., Transport, 1988.

4. Khandov Z.A. Ship ICE, M., Transport, 1968.

5. Vansheidt V.A. Ship ICE, Shipbuilding, 1962