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The exposed rubber at either end overlaps the flanged outer sleeve and there is an upper and lower plate bolted rigidly to the ends of the inner sleeve.. When the trailer is coupled to t

designed to be used with convergent `V' formation

engine suspension system where the blocks are

inclined on either side of the engine This

configura-tion enables the rubber to be loaded in both shear

and compression with the majority of engine

rota-tional flexibility being carried out in shear Vertical

deflection due to body pitch when accelerating or

braking is absorbed mostly in compression Vertical

elastic stiffness may be increased without greatly

effecting engine roll flexibility by having metal

spacer interleafs bonded into the rubber

Double inclined wedge with longitudinal control

mounting (Fig 1.18(d)) Where heavy vertical

loads and large rotational reactions are to be

absorbed, double inclined wedge mounts positioned

on either side of the power unit's bell housing

at principal axis level may be used Longitudinal movement is restricted by the double `V' formed between the inner and two outer members seen in

a plan view This `V' and wedge configuration pro-vides a combined shear and compressive strain to the rubber when there is a relative fore and aft move-ment between the engine and chassis, in addition to that created by the vertical loading of the mount This mounting's major application is for the rear mountings forming part of a four point suspension for heavy diesel engines

Metaxentric bush mounting (Fig 1.18(e)) When the bush is in the unloaded state, the steel inner sleeve is eccentric relative to the outer one so that Fig 1.18 contd

there is more rubber on one side of it than on the

other Precompression is applied to the rubber

expanding the inner sleeve The bush is set so that

the greatest thickness of rubber is in compression

in the laden condition A slot is incorporated in

the rubber on either side where the rubber is at its

minimum in such a position as to avoid stressing

any part of it in tension

When installed, its stiffness in the fore and aft

direction is greater than in the vertical direction, the

ratio being about 2.5 : 1 This type of bush provides

a large amount of vertical deflection with very little

fore and aft movement which makes it suitable for

rear gearbox mounts using three point power unit

suspension and leaf spring eye shackle pin bushes

Metacone sleeve mountings (Fig 1.18(f and g))

These mounts are formed from male and female

conical sleeves, the inner male member being

centrally positioned by rubber occupying the

space between both surfaces (Fig 1.18(f)) During

vertical vibrational deflection, the rubber between

the sleeves is subjected to a combined shear and

compression which progressively increases the

stiff-ness of the rubber as it moves towards full

distor-tion The exposed rubber at either end overlaps the

flanged outer sleeve and there is an upper and

lower plate bolted rigidly to the ends of the inner

sleeve These plates act as both overload (bump)

and rebound stops, so that when the inner member

deflects up or down towards the end of its

move-ment it rapidly stiffens due to the surplus rubber

being squeezed in between Mounts of this kind are

used where stiffness is needed in the horizontal

direction with comparative freedom of movement

for vertical deflection

An alternative version of the Metacone mount

uses a solid aluminium central cone with a flanged

pedestal conical outer steel sleeve which can be

bolted directly onto the chassis side member, see

Fig 1.18(g) An overload plate is clamped between

the inner cone and mount support arm, but no

rebound plate is considered necessary

These mountings are used for suspension

appli-cations such as engine to chassis, cab to chassis,

bus body and tanker tanks to chassis

Double inclined rectangular sandwich mounting

(Fig 1.18(h)) A pair of rectangular sandwich

rubber blocks are supported on the slopes of a

triangular pedestal A bridging plate merges the

resilience of the inclined rubber blocks so that

they provide a combined shear and compressive

distortion within the rubber Under small deflec-tion condideflec-tions the shear and compression is almost equal, but as the load and thus deflection increases, the proportion of compression over the shear loading predominates

These mounts provide very good lateral stability without impairing vertical deflection flexibility and progressive stiffness control When used for road wheel axle suspension mountings, they offer good insulation against road and other noises

Flanged sleeve bobbin mounting with rebound control (Fig 1.19(a and b)) These mountings have the rubber moulded partially around the outer flange sleeve and in between this sleeve and an inner tube A central bolt attaches the inner tube to the body structure while the outer member is bolted on two sides to the subframe

When loaded in the vertical downward direction, the rubber between the sleeve and tube walls will be

in shear and the rubber on the outside of the flanged sleeve will be in compression

There is very little relative sideway movement between the flanged sleeve and inner tube due to rubber distortion An overload plate limits the down-ward deflection and rebound is controlled by the lower plate and the amount and shape of rubber trapped between it and the underside of the flanged sleeve A reduction of rubber between the flanged sleeve and lower plate (Fig 1.19(a)) reduces the rebound, but an increase in depth of rubber increases rebound (Fig 1.19(b)) The load deflection charac-teristics are given for both mounts in Fig 1.19c These mountings are used extensively for body to subframe and cab to chassis mounting points

Hydroelastic engine mountings (Figs 1.20(a±c) and 1.21) A flanged steel pressing houses and sup-ports an upper and lower rubber spring diaphragm The space between both diaphragms is filled and sealed with fluid and is divided in two by a separator plate and small transfer holes interlink the fluid occupying these chambers (Fig 1.20(a and b)) Under vertical vibratory conditions the fluid will

be displaced from one chamber to the other through transfer holes During downward deflec-tion (Fig 1.20(b)), both rubber diaphragms are subjected to a combined shear and compressive action and some of the fluid in the upper chamber will be pushed into the lower and back again by way of the transfer holes when the rubber rebounds (Fig 1.20(a)) For low vertical vibratory frequencies,

the movement of fluid between the chambers is unrestricted, but as the vibratory frequencies increase, the transfer holes offer increasing resist-ance to the flow of fluid and so slow down the up and down motion of the engine support arm This damps and reduces the amplitude of mountings vertical vibratory movement over a number of cycles A comparison of conventional rubber and hydroelastic damping resistance over the normal operating frequency range for engine mountings is shown in Fig 1.20(c)

Instead of adopting a combined rubber mount with integral hydraulic damping, separate diagon-ally mounted telescopic dampers may be used in conjunction with inclined rubber mounts to reduce both vertical and horizontal vibration (Fig 1.21)

1.3 Fifth wheel coupling assembly (Fig 1.22(a and b))

The fifth wheel coupling attaches the semi-trailer to the tractor unit This coupling consists of a semi-circular table plate with a central hole and a vee section cut-out towards the rear (Fig 1.22(b)) Attached underneath this plate are a pair of pivot-ing couplpivot-ing jaws (Fig 1.22(a)) The semi-trailer has an upper fifth wheel plate welded or bolted to the underside of its chassis at the front and in the centre of this plate is bolted a kingpin which faces downwards (Fig 1.22(a))

When the trailer is coupled to the tractor unit, this upper plate rests and is supported on top of the tractor fifth wheel table plate with the two halves of the coupling jaws engaging the kingpin To permit Fig 1.19 (a±c) Flanged sleeve bobbin mounting with

rebound control

relative swivelling between the kingpin and jaws, the two interfaces of the tractor fifth wheel tables and trailer upper plate should be heavily greased Thus, although the trailer articulates about the kingpin, its load is carried by the tractor table

Flexible articulation between the tractor and semi-trailer in the horizontal plane is achieved by permitting the fifth wheel table to pivot on hori-zontal trunnion bearings that lie in the same vertical plane as the kingpin, but with their axes at right angles to that of the tractor's wheel base (Fig 1.22(b)) Rubber trunnion rubber bushes normally provide longitudinal oscillations of about 10 The fifth wheel table assembly is made from either a machined cast or forged steel sections, or from heavy section rolled steel fabrications, and the upper fifth wheel plate is generally hot rolled steel welded to the trailer chassis The coupling locking system consisting of the jaws, pawl, pivot pins and kingpin is produced from forged high carbon man-ganese steels and the pressure areas of these com-ponents are induction hardened to withstand shock loading and wear

1.3.1 Operation of twin jaw coupling (Fig 1.23(a±d))

With the trailer kingpin uncoupled, the jaws will be

in their closed position with the plunger withdrawn from the lock gap between the rear of the jaws, which are maintained in this position by the pawl contacting the hold-off stop (Fig 1.23(a)) When coupling the tractor to the trailer, the jaws of the Fig 1.20 (a±c) Hydroelastic engine mount

fifth wheel strike the kingpin of the trailer The

jaws are then forced open and the kingpin enters

the space between the jaws (Fig 1.23(b)) The

king-pin contacts the rear of the jaws which then

automatically pushes them together At the same

time, one of the coupler jaws causes the trip pin to

strike the pawl The pawl turns on its pivot against

the force of the spring, releasing the plunger,

allow-ing it to be forced into the jaws' lock gap by its

spring (Fig 1.23(c)) When the tractor is moving,

the drag of the kingpin increases the lateral force of

the jaws on the plunger

To disconnect the coupling, the release hand

lever is pulled fully back (Fig 1.23(d)) This

draws the plunger clear of the rear of the jaws

and, at the same time, allows the pawl to swing

round so that it engages a projection hold-off stop

situated at the upper end of the plunger, thus

jam-ming the plunger in the fully out position in

readi-ness for uncoupling

1.3.2 Operation of single jaw and pawl coupling

(Fig 1.24(a±d))

With the trailer kingpin uncoupled, the jaw will be

held open by the pawl in readiness for coupling

(Fig 1.24(a)) When coupling the tractor to the

trailer, the jaw of the fifth wheel strikes the kingpin

of the trailer and swivels the jaw about its pivot pin

against the return spring, slightly pushing out the

pawl (Fig 1.24(b)) Further rearward movement of

the tractor towards the trailer will swing the jaw

round until it traps and encloses the kingpin The

spring load notched pawl will then snap over the jaw projection to lock the kingpin in the coupling position (Fig 1.24(c)) The securing pin should then be inserted through the pull lever and table eye holes When the tractor is driving forward, the reaction on the kingpin increases the locking force between the jaw projection and the notched pawl

To disconnect the coupling, lift out the securing pin and pull the release hand lever fully out (Fig 1.24(d)) With both the tractor and trailer stationary, the majority of the locking force applied to notched pawl will be removed so that with very little effort, the pawl is able to swing clear

of the jaw in readiness for uncoupling, that is, by just driving the tractor away from the trailer Thus the jaw will simply swivel allowing the kingpin to pull out and away from the jaw

1.4 Trailer and caravan drawbar couplings 1.4.1 Eye and bolt drawbar coupling for heavy goods trailers (Figs 1.25 and 1.26)

Drawbar trailers are normally hitched to the truck

by means of an `A' frame drawbar which is coupled

by means of a towing eye formed on the end of the drawbar (Fig 1.25) When coupled, the towing eye hole is aligned with the vertical holes in the upper and lower jaws of the truck coupling and an eye bolt passes through both coupling jaws and draw-bar eye to complete the attachment (Fig 1.26) Lateral drawbar swing is permitted owing to the eye bolt pivoting action and the slots between the Fig 1.21 Diagonally mounted hydraulic dampers suppress both vertical and horizontal vibrations

jaws on either side Aligning the towing eye to the

jaws is made easier by the converging upper and

lower lips of the jaws which guide the towing eye as

the truck is reversed and the jaws approach the

drawbar Isolating the coupling jaws from the

truck draw beam are two rubber blocks which act

as a damping media between the towing vehicle and trailer These rubber blocks also permit additional deflection of the coupling jaw shaft relative to the draw beam under rough abnormal operating con-ditions, thus preventing over-straining the drawbar and chassis system

Fig 1.22 (a and b) Fifth wheel coupling assembly

Fig 1.23 (a±d) Fifth wheel coupling with twin jaws plunger and pawl

Fig 1.24 (a±d) Fifth wheel coupling with single jaw and pawl

The coupling jaws, eye bolt and towing eye are

generally made from forged manganese steel with

induction hardened pressure areas to increase the

wear resistance

Operation of the automatic drawbar coupling

(Fig 1.26) In the uncoupled position the eyebolt

is held in the open position ready for coupling

(Fig 1.26(a)) When the truck is reversed, the jaws

of the coupling slip over the towing eye and in the

process strike the conical lower end of the eye bolt

(Fig 1.26(b)) Subsequently, the eye bolt will lift This

trips the spring-loaded wedge lever which now rotates

clockwise so that it bears down on the eye bolt

Further inward movement of the eye bolt between

the coupling jaws aligns the towing eye with the eye

bolt The spring pressure now acts through the wedge

lever to push the eye bolt through the towing eye and

the lower coupling jaw (Fig 1.26(c)) When the eye

bolt stop-plate has been fully lowered by the spring

tension, the wedge lever will slot into its groove

formed in the centre of the eye bolt so that it locks

the eye bolt in the coupled position

To uncouple the drawbar, the handle is pulled

upwards against the tension of the coil spring

mounted on the wedge level operating shaft

(Fig 1.26(d)) This unlocks the wedge, freeing the

eyebolt and then raises the eye bolt to the

uncoupled position where the wedge lever jams it

in the open position (Fig 1.26(a))

1.4.2 Ball and socket towing bar coupling for light caravan/trailers (Fig 1.27)

Light trailers or caravans are usually attached to the rear of the towing car by means of a ball and socket type coupling The ball part of the attach-ment is bolted onto a bracing bracket fitted directly

to the boot pan or the towing load may be shared out between two side brackets attached to the rear longitudinal box-section members of the body

A single channel section or pair of triangularly arranged angle-section arms may be used to form the towbar which both supports and draws the trailer

Attached to the end of the towbar is the socket housing with an internally formed spherical cavity This fits over the ball member of the coupling so that it forms a pivot joint which can operate in both the horizontal and vertical plane (Fig 1.27)

To secure the socket over the ball, a lock device must be incorporated which enables the coupling to

be readily connected or disconnected This lock may take the form of a spring-loaded horizontally positioned wedge with a groove formed across its top face which slips underneath and against the ball The wedge is held in the closed engaged pos-ition by a spring-loaded vertical plunger which has

a horizontal groove cut on one side An uncoupling lever engages the plunger's groove so that when the coupling is disconnected the lever is squeezed to lift and release the plunger from the wedge At the same time the whole towbar is raised by the handle

to clear the socket and from the ball member Coupling the tow bar to the car simply reverses the process, the uncoupling lever is again squeezed against the handle to withdraw the plunger and the socket housing is pushed down over the ball mem-ber The wedge moves outwards and allows the ball

to enter the socket and immediately the wedge springs back into the engaged position Releasing the lever and handle completes the coupling by permitting the plunger to enter the wedge lock groove

Sometimes a strong compression spring is inter-posed between the socket housing member and the towing (draw) bar to cushion the shock load when the car/trailer combination is initially driven away from a standstill

1.5 Semi-trailer landing gear (Fig 1.28) Landing legs are used to support the front of the semi-trailer when the tractor unit is uncoupled Extendable landing legs are bolted vertically to each chassis side-member behind the rear wheels of Fig 1.25 Drawbar trailer

Fig 1.26 (a±e) Automatic drawbar coupling