Design of MAZ-643008 clutch

Contents

CONTENTS

P

1 INTRODUCTION

2 OVERVIEW OF DIAGRAMS AND STRUCTURES OF THE DESIGNED ASSEMBLY

3 DESIGN DESIGN SELECTION AND JUSTIFICATION

4 DESCRIPTION OF OPERATION, ADJUSTMENTS AND TECHNICAL CHARACTERISTICS OF THE DESIGNED UNIT

5 CALCULATIONS OF THE DESIGNED PRODUCT AND ITS ELEMENTS

5.1 SELECTION OF MAIN CLUTCH PARAMETERS

5.2 CALCULATION OF CLUTCH LOADING

5.3 CALCULATION OF CLUTCH PARTS

5.3.1 Calculation of torsional damper springs

5.3.2 Calculation of splines of the hub of the driven disk

CONCLUSION

LIST OF LITERATURE USED

Coupling of diesel truck tractor

Introduction

The transmission of the car is a set of units and mechanisms that transmit engine power to the driving wheels of the car and change its parameters of torque, frequency and direction of rotation.

As a rule, transmission turns on the following units and mechanisms coupling, the transmission, cardan transfer, the main transfer, differential, waves of driving wheels.

The purpose of the clutch is to disconnect the engine and gearbox during gearshift and smoothly connect them again, preventing sharp application of load, as well as to ensure a smooth touching of the car from the place and its stopping without stopping the engine. In case of abrupt braking without clutch disengagement, it slips, protects the transmission from overloads with inertial torque. When on, the clutch must securely connect the engine to the transmission without slipping. The vast majority of clutches used on domestic cars relate to friction dry disc clutches, which use friction forces of dry surfaces.

Overview of diagrams and structures of the designed node

The whole variety of clutch structures used on modern cars can be classified by a number of features. So, by the nature of the work, constantly closed and constantly open clutches are distinguished.

Depending on the nature of the connection between the driving and driven elements of the clutch, it is divided into hydraulic (hydraulic clutch), electromagnetic (powder) and frictional. The latter, depending on the shape of the friction elements, are disk and special (cone, drum, tape, etc.).

According to the method of creating the pressure force, it is distinguished: spring (with one central or several peripheral springs), semi-centrifugal (with a spring and centrifugal weights), which are currently not used, centrifugal and electromagnetic .

By the type of clutch drive, they come with a mechanical, hydraulic and combined (electric vacuum, electromagnetic, etc.) drive.

According to the control method, non-automatic, semi-automatic and automatic clutches are distinguished.

The modern typical friction clutch consists of two parts: the clutch itself and its drive. First part consists of drive and driven elements transmitting engine torque and pressure device. The driving elements are most often the end part of the engine flywheel and the pressure disc assembled with the clutch casing fixed on the flywheel. Driven element is driven disk with torsional vibration damper installed on input shaft of gearbox. The pressure device most often has springs and a lever system for moving the pressure disk.

The design of the coupling with peripheral coil springs is shown in Figure 2.1. Such arrangement of springs ensures uniform compression of friction surfaces due to symmetrical arrangement of springs relative to each other. The coil springs used in such designs have a linear characteristic (Figure 2.2). This means that when friction pairs wear, the deformation of the springs and their pressing force will decrease.

The disadvantage of such clutches is also that at increased angular velocity centrifugal forces can distort the characteristic of the springs. Therefore, to center the springs and reduce their deformation under the action of centrifugal forces, cups, bosses or protrusions are used on the pressure disk and clutch housing (Figure 2.2).

The use of low stiffness pressure springs can help to maintain the pressure force within a predetermined range. However, in order to accommodate single springs of low stiffness, it is necessary to significantly increase the axial dimensions of the clutch. Therefore, double springs are used.

This type of clutch, which is switched on by the peripheral springs at their direct pressure on the pressure disc and is switched off by means of rigid levers, has the following advantages: when they are used, the necessary departure of the pressure disc is guaranteed when the clutch is turned off, the force is evenly distributed from the pressure disc to the driven one, it is possible to change the pressure force by changing the number of springs depending on the type and purpose of the clutch.

Figure 2.3 shows the typical design of a single-disc clutch with one central conical spring used on VAZ cars. Compressed conical spring 7 is located between support flange and movable bushing. Holder with balls of pressure elastic levers of plate type is fixed on the other end of bushing by means of locking ring. The holder consists of two washers. Up to 20 levers are installed in it, which are retained by balls placed in holes at the inner ends of the levers. Outer ends of levers rest on ring projections of support flange and pressure disk 2.

Spring 7 tends to move bushing together with holder to the right. As a result, the inner ends of the arms are also displaced to the right, compressing the friction surfaces of the clutch with the outer ends. When the clutch is switched off, the sleeve moves to the left and the resilient levers 3 cease to act on the pressure disc. Resilient levers provide uniform compression of friction surfaces and smooth engagement .

In addition to traditional friction clutches, other types of clutches (centrifugal, electromagnetic, etc.) have become somewhat common, which, due to their complexity and high cost, are rarely used.

Centrifugal coupling (Figure 2.4) is based on the principle of ensuring pressure on the pressure disc by centrifugal weights and is normally open.

This clutch is automatically switched on when touched and off when the car stops. However, when shifting gears, it must be forcibly turned off using a pedal. Sometimes such a clutch is used in combination with a friction clutch. The advantages of centrifugal clutches include the simplicity of their installation on the car, the best control of the moment of friction of the clutch when touching the car compared to other types of clutches. The disadvantage of such clutches is the possibility of a slip in the clutch when the car moves at low speed in higher gears.

Electromagnetic clutches can be without and with a ferro filler. These clutches are one type of clutch with automatic control.

Currently, gearboxes with a two-disc clutch are increasingly being used.

In fact, this design is two transmissions that are turned on and off in turn. Indirect gears and reverse gear are connected to one clutch, straight gears - to the second clutch. During acceleration, the nearest higher gear is automatically activated; when the gear shifts, one clutch is switched on at the same time, while the other clutch is turned off.

This clutch allows you to change gear without interrupting the power flow, which is convenient, first of all, in sports cars

Currently, two different concepts of two-disc adhesion are used: dry and "wet" (plate-shaped two-disc adhesion rotating in an oil bath). The dry version is suitable for small cars with low torque, this design is more compact. The "wet" plate clutch can transmit large torques, it is less sensitive to thermal loads, so it is suitable for cars with torque over 250 Nm. This option has been offered for the new Golf V since spring 2004 (Figure 2.6). In addition to the automatic module, which fully takes over the switching processes, there is also a Tiptronic module that allows manual switching. The control system also receives information on the speed of rotation of the wheels, which is output by the ABS so that the gearbox does not change gear during rotation.

This clutch is adapted for transmitting high torques - over 250 Nm, it is also less sensitive to thermal loads.

Gearboxes with a two-disc clutch (which are also called DSG or Direktschaltgetriebe - gearboxes with direct inclusion) are intended primarily for sports cars; their main advantage is that the gearshift process can occur without interrupting the power flow. Thus, the main argument in favor of a car equipped with a two-disc clutch is convenience. According to the fuel consumption, acceleration characteristic and maximum speed of the car, the gearbox with a two-disc clutch is at the same level as the manual gearbox.

The dual clutch transmission (DCT Dual Clutch Transmission), already used on the Audi TT 3.2 and Volkswagen Golf RS32, is becoming increasingly popular in Europe, according to a recently published Ricardo report (Figure 2.7).

The DCT transmission contains two clutches that allow you to simultaneously include two gears: one clutch is used when turning on the 1st, 3rd, 5th gear and reverse gear, the second when turning on the 2nd, 4th, 6th gears. During the switching process, there is some overlap of two clutches: when the first clutch transmitting torque is turned off, the second, previously open, is turned on. As a result of overlap during operation of two clutches, power flow rupture is eliminated. The switching process takes several tenths of a second without noticeable termination of traction forces.

The DCT transmission can operate both automatically and with the driver shifting gears by means of an appropriate control. Drivers using the sports style of driving note the high ease of switching. The control unit, which receives signals about wheel speed from the anti-lock brake system, eliminates undesirable gear shifts when turning the car.

A wet multi-disc double clutch operating in oil is preferred for use in middle class to sports cars with engines having a maximum torque of more than 250 Nm. Such a unit has a high heat capacity, has a low moment of inertia and during its operation small centrifugal forces arise. High compact design facilitates integration into transmissions.

Significant values of the transmitted torque, low moment of inertia and fast switching without breaking the power flow cause excellent dynamic properties comparable to systems using moment transformers.

The main advantages of the DCT transmission are low cost and light weight compared to automatic transmissions. At the same time, the value of power losses is similar to mechanical transmissions, and comfort in switching is comparable to automatic transmissions. The use of an automatic control system improves fuel and economic performance and environmental properties.

The main task in mastering the production of DCT is the maximum possible use of existing technologies for the manufacture of mechanical transmissions. The increase in the cost of production and the cost of the control system can correspond to an improvement in consumer properties and operational performance .

Design Design Selection and Justification

Based on the design review and initial data (total vehicle weight 26150 kg, maximum engine torque 1715 Nm), we accept the design of a dry friction permanently closed clutch.

The clutch mechanism is two-disc with a central poppet spring, since it has the most favorable characteristic, compared to a conical or cylindrical one. Its force in the operating range varies slightly when the clutch is turned off, and this compensates for the wear of the straps.

Description of operation, adjustments and technical characteristics of the designed unit

When operating the car, most often you have to adjust the free stroke of the clutch pedal.

Adjustment of clutch pedal free stroke, which must be within 35-45 mm, is performed at absence of air in pneumatic system.

Before starting adjustment of pedal free travel it is necessary to check alignment of pin (3) (Figure 4.1) of lever (4) with cockpit throwing axle, which is achieved by adjustment of rod (1) length.

Adjust the pedal free travel in the following sequence:

• disconnect the plug (15) of the valve rod and plug (12) of the cylinder rod from the bell-crank (11);

• pull the lever 11 back behind the lower arm (in the direction of the car) until stop, at that misalignment of hole of upper arm of lever 11 and hole of cylinder rod fork must be 8 - 10 mm (not more than the diameter of the pin hole) at the extreme lower position of the cylinder piston, and the misalignment of the hole of the lower arm of the lever with the hole of the valve plug should be 5-6 mm (by half of the hole) while maintaining clearance A.

Adjust rod and rod length by moving forks (12), (15) and fork (8) of valve rod.

After adjustment check the pedal free stroke value, which must be within 35-45 mm at lowered cockpit and absence of air in pneumatic system.

Calculations of the designed product and its elements

5.1 SELECTION OF MAIN CLUTCH PARAMETERS

As a prototype, we choose the truck tractor MAZ643008030010. Technical characteristics of this vehicle are given in Table 5.1.

In accordance with the recommendations of [1], we choose the grip margin factor β = 1.5... 2.0 for trucks and buses.

We take β = 1.7.

Find the moment of adhesion:

Based on maximum engine torque and maximum RPM, we select the following linings as per GOST 1223876:

Outer diameter: D = 400 mm.

The inside diameter of the straps d is determined by the formula

According to Table [1], the inner diameter d = 240 mm and the thickness of the straps δ = 5 mm are assumed.

We determine the pressure force :

i is the number of friction surfaces, i = 4, since the adhesion is two-disk,

[mu] is friction coefficient, according to recommendation [1] [mu] = 0.3.

Check specific pressure on friction lining

According to recommendations [1], the value of q should not exceed 0.21 MPa, and for trucks and buses it is in the interval of 0.14... 0.21 MPa .

The condition is met.

5.2 CALCULATION OF CLUTCH LOADING

Calculation of adhesion for specific operation of slip and heating.

The moment of resistance to the movement of the car brought to the primary shaft of the gearbox is determined by the formula

Reduced moment of inertia of the car

where δ "is the accounting factor of the rotating masses of the car, δ" = 1.05.

Design speed of engine crankshaft

Slip operation

Friction surface area is determined by formula

where An is the area of ​ ​ the overlay,

z is the number of friction surfaces (z = 4).

Specific work of skidding

Increase in the average temperature of the pressure disc when touching the car from the place:

where γ is the fraction of heat perceived by the pressure disk (for a two-disc adhesion γ = 0.25),

mn is the mass of the disk,

С - specific heat capacity of cast iron (С = 481.5 J/( kg • ° С).

Check for specific operation of slip and heating is performed for three modes:

1. Touching on the first gear at A = 0.02.

2. Touching on the first gear at A = 0.16.

3. Start-off on the second transfer at ψ = 0.02.

For three cases, we calculate the moment of resistance

Specific operation of slip is determined by formula

On the recommendation of [1], the specific work of the slip should be Nm/m2.

The condition is met.

The increase in the average temperature of the pressure disk when touching the car is determined by the formula

According to recommendation [1], the increase in the average temperature of the pressure disc should not exceed 100С .

The condition is met.

5.3 CALCULATION OF CLUTCH PARTS

5.3.1 Calculation of torsional damper springs

The main parameters of the torsional damper are selected based on the recommendations of the literature [1].

Friction moment

The closing angle of the dampener has to be.... g = 20 30... " 30 40’

We accept ¼ g = 30, the number of springs is 6.

Springs are installed in a circle with a diameter of 80... 120 mm in windows with a length of 25... 27 mm. We take a diameter of 120 mm, a window 27 mm long.

Wire diameter dpr = 6 mm.

The average diameter of the turn Db = 16 mm.

Maximum force compressing one damper spring

where rp.d is the radius of application of force to the spring,

zpg - number of damper springs.

Calculate spring stress

The condition is met.

5.3.2 Calculation of splines of the hub of the driven disk

Calculation of splines is performed by crushing stresses and bending stresses.

Crumbling stress

The condition is met.

According to CT CMEA 188, straight splines of the heavy series were chosen. Basic dimensions (z x d x D) 16x56x64.

Conclusion

As a result of the course work, a review of the schemes and designs of clutches of foreign and domestic cars was carried out.

The design of the designed clutch with the justification of this design is chosen. As a result, preference was given to the design of a dry friction permanently closed clutch, the mechanism of which is two-disc with a poppet pressure spring.

A brief description of the operation, adjustments and technical characteristics of the clutch of the car MAZ643008030010 is given.

Clutch and its elements were calculated:

a) Main clutch parameters selected

• Outer diameter of friction straps 400 mm,

• Internal diameter of friction linings 240 mm,

• Lining thickness δ = 5 mm.

• The specific pressure of the friction lining was checked, as a result of which it was concluded that the lining was consistent with this parameter.

b) Calculation of clutch load

• The specific work of slippage on the first and second gears is calculated, the values of which correspond to regulatory requirements,

• An increase in the average temperature of the pressure disc when touching the car is calculated. The values obtained do not exceed the maximum permissible values.

c) Calculation of clutch parts

• Torsional vibration damper springs were calculated, as a result of which it was concluded that the stresses in the springs do not exceed the maximum permissible values.

• Calculation of splines of the hub of the driven disk by crushing stresses and bending stresses was made. Values meet regulatory requirements.

List of literature used

1. Cars: Design, design and calculation. Transmission: Training manual for specialists. "Cars and tractors "/A.I. Grishkevich, V.A. Vavulo, A.V. Karpov and others. Ed. A.I. Grishkevich. - Mn.: Vysh. Shk., 1985. - 240 s., Il.

2. Design of car transmissions: reference book/Under the general edition of A.I. Grishkevich. - M.: Engineering, 1984. – 272 pages.

3. Trucks: Design and Basis of Design/M.S. Vysotsky, L.H. Gileles et al. - M.: Mechanical Engineering, 1995. – 256