copy of automotive transmission - 1.ppt

7/29/2019 Copy of AUTOMOTIVE TRANSMISSION - 1.ppt

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Automotive Transmission

Universal Joint

A universal joint is a form of connection between two shafts, whose axes intersect, whereby the rotation

of one shaft about its own axis results in the rotation of the other shaft about its axis.

There are several types of universal joint all working on the principle outlined above, but in motor cars

and lorries the joints are of two principal forms.

These may be called

(1) Cross type.

(2) Ring type.




Universal Joint – cross type

The yoke members A are secured to

the shafts

that are connected by the joint and

carry bushes B.

The keys D transmit the drive

The two yokes are coupled by the

cross member F




Universal Joint – cross type

Between the pins G and the bushes

B are needle bearings H.

The hole in the centre of the cross

member F is closed by two

pressings J and

forms a reservoir for lubricant which

reaches the bearings through holes

drilled in the pins G.




Universal Joint – Cross type




Universal Joint – ring type Fig. 30.3 shows a ring-type joint.

The member A is bolted to one shaftby its flange

and the fork B is secured to the other

shaft by splines.

The two members are coupled by the

ring C.

This ring is made of two steel

pressings each forming half the ringand being bolted together by the nuts.




Universal Joint – ring type

The pins of the fork member B fit in

two of the bushes and

the ends of the pin E, which is fixed in

member A, fit in the other two bushes.




Universal Joint – ring type

The nuts securing the ring are

locked by a pair of tab washers H.




Universal Joint - Ball

Another universal joint construction is

shown in Fig. 30.4.

It consists of a ball A having two

grooves formed round it at right

angles.

In these grooves the forked ends of the

shafts E and F fit.

the shaft E can slide round in its

groove, thus turning about the axis XX.

Similarly the shaft F can slide round in

its groove, thus turning about the axis

YY.




Constant Velocity Joint The Hooke’s type of universal joint

suffers from a disadvantage which is

obviated in some other types of joint.

It is that supposing one of the shafts

connected by a Hooke’s joint is

revolving at an absolutely constant

speed then the other shaft will not

revolve at a constant speed but with a

speed that is, during two parts of each

revolution, slightly greater and, during

the other two parts of the revolution,

slightly less than the constant speed

of the first shaft.

The magnitude of this fluctuation in speed depends on the angle between the axes of the two shafts, being

zero when that angle is zero but becoming considerable when the angle is large.




Constant Velocity Joint This disadvantage becomes of practical

importance in front wheel driven vehiclesand in the drives to independently sprung

wheels where the angle between the

shafts may be as large as 40°.

It can be obviated by using twoHooke’s

joints arranged as shown in Fig. 30.9(a)

and (b), the intermediate shaft being

arranged so that it makes equal angles

with the first and third shafts and the fork

pin axes of the intermediate shaft beingplaced parallel to each other.




Constant Velocity Joint The irregularity introduced by one joint is

then cancelled out by the equal andopposite irregularity introduced by the

second joint.

Examples of front wheel drives using this

arrangement are shown in Figs 30.16 and30.17.

A slightly different arrangement using the

same priniciple is given in Fig. 37.9.




Constant Velocity Joint

grooves is such that the balls lie always in a plane

making equal angles with the axes of the shafts

connected by the joint, this being a fundamental

condition that must be satisfied if the drive is to be a

constant-velocity drive.

This joint has the property that the shafts connected by

it may be moved apart axially slightly without affecting

the action of the joint and this axial motion is

accommodated by a rolling of the balls along the

grooves in the fingers of the joint members and so

takes place with the minimum of friction.

i i i




Constant Velocity Joint A third example is shown in Fig. 30.12. It is the Rzeppa

(pronounced Sheppa) and it consists of a cup member A

with a number of semi-circular grooves formed inside it

and a ball member B with similar grooves formed on the

outside.

Balls C fit half in the grooves A and half in B and provide

the driving connection. For true constant-velocity

operation the balls must be arranged to lie always in a

plane making equal angles with the axes of rotation of

the members A and B.

This is ensured by the control link D and the cage E. The

former has spherical ends one of which engages a

recess in the end of the member B while the other is free

to slide along a hole formed inside A; the link is kept in

place by the spring F.

A i T i i




Constant Velocity Joint The spherical enlargement G of the link engages a

hole formed in the cage E which has other holes inwhich the balls C fit.

When the shaft B swings through an angle relatively

to A the link D causes the cage E and the plane XX

of the balls C to swing through half that angle andthus the balls are caused to occupy the required

positions for the correct functioning of the joint.

In some designs of this joint, intended for use where

the angular deviation of the shafts is small, the

control link D is omitted.

A t ti T i i




Constant Velocity Joint

A joint developed by Birfield Transmissions Ltdwhich gives constant velocity ratio transmission and

allows for a plunging motion of one of the shafts

relative to the other is shown in Fig. 30.13.

The inner member is grooved to carry the balls that

transmit the motion and its outer surface is ground to

a sphere whose centre is at the point A.

The balls are housed in recesses in the cage and

this is ground on its inside to fit the outer surface of

the inner member while its outer surface is ground to

a sphere whose centre is at the point B.





Constant Velocity Joint The outer member has a cylindrical bore with

grooves formed in it to take the balls and the outer spherical surface of the cage fits the cylindrical

surface of the outer member.

The inner member can therefore move bodily

along the bore of the outer member thus giving the

plunging motion required in the drives to most

independently sprung wheels and which usually

has to be provided by sliding splines.

The off-setting of the centres of the spherical

surfaces of the cage keeps the plane of the balls at

all times in the plane bisecting the angle between

the shaft axes as is necessary for the maintenance

of a constant-velocity ratio

copy of automotive transmission - 1.ppt

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