Advanced Vehicle Technology Episode 1 Part 5 pot

3.4 Remote controlled gear selection and engagement mechanisms Gear selection and engagement is achieved by two distinct movements: 1 The selection of the required gear shift gate and th

Fig 3.9 (a±d) Split baulk ring synchromesh unit

The axial thrust applied by the gear stick to the

sliding sleeve will now be sufficient to compress the

split synchronizing ring and subsequently permits

the sleeve to slide over the gear wheel dog teeth for

full engagement (Fig 3.9(d))

3.4 Remote controlled gear selection and

engagement mechanisms

Gear selection and engagement is achieved by two

distinct movements:

1 The selection of the required gear shift gate and

the positioning of the engagement gate lever

2 The shifting of the chosen selector gate rod into

the engagement gear position

These two operations are generally performed

through the media of the gear shift lever and the

remote control tube/rod Any transverse

move-ment of the gear shift lever by the driver selects

the gear shift gate and the engagement of the gate

is obtained by longitudinal movement of the gear

shift lever

Movement of the gear shift lever is conveyed to

the selection mechanism via the remote control

tube Initially the tube is twisted to select the

gate shift gate, followed by either a push or pull

movement of the tube to engage the appropriate

gear

For the gear shift control to be effective it must

have some sort of flexible linkage between the gear

shift lever supported on the floor of the driver's

compartment and the engine and transmission

inte-gral unit which is suspended on rubber mountings

This is essential to prevent engine and transmission

vibrations being transmitted back to the body and

floor pan and subsequently causing discomfort to

the driver and passengers

3.4.1 Remote controlled double rod and bell

cranked lever gear shift mechanism, suitable for

both four and five speed transverse mounted

gearbox (Talbot) (Fig 3.10)

Twisting the remote control tube transfers

move-ment to the first selector link rod This motion is

then redirected at right angles to the transverse

gate selector/engagement shaft via the selector

relay lever (bell crank) to position the required

gear gate (Fig 3.10) A forward or backward

movement of the remote control tube now conveys

motion via the first engagement relay lever (bell

crank), engagement link rod and second relay

lever to rotate the transverse gate

selector/engage-ment shaft Consequently, this shifts the transverse selector/engagement shaft so that it pushes the synchronizing sliding sleeve into engagement with the selected gear dog teeth

3.4.2 Remote controlled bell cranked lever gear shift mechanism for a four speed transverse mounted gearbox (Ford) (Fig 3.11) Gear selection and engagement movement is conveyed from the gear shift lever pivot action to the remote control rod universal joint and to the control shift and relay lever guide (Fig 3.11) Rocking the gear shift lever transversely rotates the control shaft and relay guide This tilts the selector relay lever and subsequently the selec-tion relay lever guide and shaft until the striker finger aligns with the chosen selector gate A fur-ther push or pull movement to the gear shift lever

by the driver then transfers a forward or backward motion via the remote control rod, con-trol shaft and relay lever guide to the engagement relay lever Movement is then redirected at right angles to the selector relay guide and shaft Engagement of the gear required is finally obtained

by the selector/engagement shaft forcing the strik-ing fstrik-inger to shift the gate and selector fork along the single selector rod so that the synchron-izing sleeve meshes with the appropriate gear wheel dog clutch

Fig 3.10 Remote controlled double rod and bell crank lever gearshift mechanism suitable for both four and five speed transversely mounted gearbox

3.4.3 Remote controlled sliding ball joint gear

shift mechanism suitable for both four and five

speed longitudinal or transverse mounted gearbox

(VW) (Fig 3.12)

Selection and engagement of the different gear

ratios is achieved with a swivel ball end pivot gear

shift lever actuating through a sliding ball relay

lever a single remote control rod (Fig 3.12) The

remote control rod transfers both rotary and

push-pull movement to the gate selector and engagement

shaft This rod is also restrained in bushes between

the gear shift lever mounting and the bulkhead

It thus permits the remote control rod to transfer

both rotary (gate selection) and push-pull (select rod

engagement shift) movement to the gate selector and

engagement shaft Relative movement between the

suspended engine and transmission unit and the car

body is compensated by the second sliding ball

relay lever As a result the gate engagement striking

finger is able to select and shift into engagement the

appropriate selector rod fork

This single rod sliding ball remote control

linkage can be used with either longitudinally or

transversely mounted gearboxes, but with the latter

an additional relay lever mechanism (not shown) is needed to convey the two distinct movements of selection and engagement through a right angle

Fig 3.11 Remote controlled bell crank level gear shift mechanism for a four speed transversely mounted gearbox

Fig 3.12 Remote controlled sliding ball joint gear shift mechanism suitable for both four and five speed longitudinally or transversely mounted gearbox

3.4.4 Remote controlled double rod and hinged

relay joint gear shift mechanism suitable for both

four and five speed longitudinal mounted gearbox

(VW) (Fig 3.13)

With this layout the remote control is provided by

a pair of remote control rods, one twists and selects

the gear gate when the gear shift lever is given a

transverse movement, while the other pushes or

pulls when the gear shift lever is moved

longitudin-ally (Fig 3.13) Twisting movement is thus

con-veyed to the engagement relay lever which makes

the engagement striking finger push the aligned

selector gate and rod Subsequently, the

synchro-nizing sleeve splines mesh with the corresponding

dog clutch teeth of the selected gear wheel Relative

movement between the gear shift lever swivel

sup-port and rubber mounted gearbox is absorbed by

the hinged relay joint and the ball joints at either

end of the remote control engagement rod

3.4.5 Remote controlled single rod with self

aligning bearing gear shift mechanism suitable for

both five and six speed longitudinal mounted

gearbox (Ford) (Fig 3.14)

A simple and effective method of selecting and

engaging the various gear ratios suitable for

commercial vehicles where the driver cab is

for-ward of the gearbox is shown in Fig 3.14 transverse and longitudinal directions providesMovement of the gear shift lever in the usual

both rotation and a push-pull action to the remote control tube Twisting the remote control tube transversely tilts the relay gear shift lever about its ball joint so that the striking finger at its lower end matches up with the selected gear gate Gear engagement is then completed by the driver tilting the gear shift lever away or towards himself This permits the remote control tube to move axially through the mounted self-aligning bearing As a result, a similar motion will be experienced by the relay gear shift lever, which then pushes the striking finger, selector gate and selector fork into the gear engaged position It should be observed that the self-aligning bearing allows the remote control tube

to slide to and fro At the same time it permits the inner race member to tilt if any relative movement between the gearbox and chassis takes place 3.4.6 Remote controlled single rod with swing arm support gear shift mechanism suitable for five and six speed longitudinally mounted gearbox (ZF) (Fig 3.15)

This arrangement which is used extensively on commercial vehicles employs a universal cross-pin joint to transfer both the gear selection and

Fig 3.13 Remote controlled double rod and hinged

relay joint gear shift mechanism suitable for both four and

five speed longitudinally mounted gearbox

Fig 3.14 Remote controlled single rod with self-aligning bearing gear shift mechanism suitable for both five and six speed longitudinally mounted gearbox

engagement motion to the remote control tube

(Fig 3.15) Twisting this remote control tube by

giving the gear shift lever a transverse movement

pivots the suspended selector gate relay lever so that the transverse gate selector/engagement shift moves across the selector gates until it aligns with the selected gate The gear shift lever is then given a

to or fro movement This causes the transverse selector/engagement shaft to rotate, thereby for-cing the striking finger to move the selector rod and fork The synchronizing sleeve will now be able to engage the dog clutch of the appropriate gear wheel Any misalignment between the gear shift lever support mounting and the gear shift mechanism forming part of the gearbox (caused

by engine shake or rock) is thus compensated by the swing rod which provides a degree of float for the selector gate relay lever pivot point

3.5 Splitter and range change gearboxes Ideally the tractive effect produced by an engine and transmission system developing a constant power output from rest to its maximum road speed would vary inversely with its speed This characteristic can

be shown as a smooth declining tractive effect curve with rising road speed (Fig 3.16)

In practice, the transmission has a fixed number

of gear ratios so that the ideal smooth tractive effect curve would be interrupted to allow for loss

Fig 3.15 Remote controlled single rod with swing arm

support gear shift mechanism suitable for five and six

speed longitudinally mounted gearbox

Fig 3.16 Ideal and actual tractive effort-speed characteristics of a vehicle

of engine speed and power between each gear

change (see the thick lines of Fig 3.16)

For a vehicle such as a saloon car or light van

which only weighs about one tonne and has a large

power to weight ratio, a four or five speed gearbox

is adequate to maintain tractive effect without too

much loss in engine speed and vehicle performance

between gear changes

Unfortunately, this is not the situation for heavy

goods vehicles where large loads are being hauled

so that the power to weight ratio is usually very

low Under such operating conditions if the gear

ratio steps are too large the engine speed will drop

to such an extent during gear changes that the

engine torque recovery will be very sluggish

(Fig 3.17) Therefore, to minimize engine speed

fall-off whilst changing gears, smaller gear ratio

steps are required, that is, more gear ratios are

necessary to respond to the slightest change in

vehicle load, road conditions and the driver's

requirements Figs 3.2 and 3.18 show that by

dou-bling the number of gear ratios, the fall in engine

speed between gear shifts is much smaller To cope

with moderate payloads, conventional double

stage compound gearboxes with up to six forward

speeds are manufactured, but these boxes tend to be

large and heavy Therefore, if more gear ratios are

essential for very heavy payloads, a far better way of

extending the number of gear ratios is to utilize a two

speed auxiliary gearbox in series with a three, four,

five or six speed conventional compound gearbox

The function of this auxiliary box is to double the

number of gear ratios of the conventional gearbox

With a three, four, five or six speed gearbox, the

gear ratios are increased to six, eight, ten or twelve

respectively (Figs 3.2 and 3.18) For very special

applications, a three speed auxiliary gearbox can be incorporated so that the gear ratios are trebled Usually one of these auxiliary gear ratios provides a range of very low gear ratios known as crawlers or deep gears The auxiliary gearbox may be situated either in front or to the rear of the conventional compound gearbox

The combination of the auxiliary gearbox and the main gearbox can be designed to be used either

as a splitter gear change or as a range gear change

in the following way

3.5.1 Splitter gear change (Figs 3.19 and 3.20) With the splitter arrangement, the main gearbox gear ratios are spread out wide between adjacent gears whilst the two speed auxiliary gearbox has one direct gear ratio and a second gear which is either a step up or down ratio (Fig 3.19) The auxiliary second gear ratio is chosen so that it splits the main gearbox ratio steps in half, hence the name splitter gear change The splitter indirect gear ratio nor-mally is set between 1.2 and 1.4:1 A typical ratio would be 1.25:1

A normal upchange sequence for an eight speed gearbox (Fig 3.20), consisting of a main gearbox with four forward gear ratios and one reverse and a two speed auxiliary splitter stage, would be as follows:

Auxiliary splitter low ratio and main gearbox first gear selected results in `first gear low' (1L); auxiliary splitter switched to high ratio but with the main gear-box still in first gear results in `first gear high' (1H);

Fig 3.17 Engine speed ratio chart for a vehicle

employing a five speed gearbox

Fig 3.18 Engine speed ratio chart for a vehicle employing either a ten speed range change or a splitter change gearbox

splitter switched again to low ratio and main

gear-box second gear selected results in 2L; splitter

switched to high ratio, main gearbox gear remaining

in second gives 2H; splitter switched to low ratio

main gearbox third gear selected gives 3L; splitter

switched to high ratio main gearbox still in third

gives 3 H This procedure continues throughout

the upshift from bottom to top gear ratio Thus the

overall upshift gear ratio change pattern would be:

Gear ratio 1 2 3 4 5 6 7 8 Reverse

Upshift

sequence 1L 1H 2L 2H 3L 3H 4L 4H RL RH

It can therefore be predicted that alternate

changes involve a simultaneous upchange in the

Fig 3.19 Eight speed constant mesh gearbox with two speed front mounted splitter change

Fig 3.20 Splitter change gear ratio±speed chart

main gearbox and downchange in the splitter stage,

or vice versa

Referring to the thick lines in Figs 3.2, 3.17 and

3.18, these represent the recommended operating

speed range for the engine for best fuel economy,

but the broken lines in Fig 3.17 represent the gear

shift technique if maximum road speed is the

criteria and fuel consumption, engine wear and

noise become secondary considerations

3.5.2 Range gear change (Figs 3.21 and 3.22)

In contrast to the splitter gear change, the range

gear change arrangement (Fig 3.21) has the gear

ratios between adjacent gear ratio steps set close

together The auxiliary two speed gearbox will have

one ratio direct drive and the other one normally

equal to just over half the gear ratio spread from

bottom to top This is slightly larger than the main

gearbox gear ratio spread

To change from one gear ratio to the next with,

for example, an eight speed gearbox comprising

four normal forward gears and one reverse and a

two speed auxiliary range change, the pattern of

gear change would be as shown in Fig 3.22

Through the gear ratios from bottom to top

`low gear range' is initially selected, the main gear-box order of upchanges are first, second, third and fourth gears At this point the range change is moved to `high gear range' and the sequence of gear upchanges again becomes first, second, third and fourth Therefore the total number of gear ratios is the sum of both low and high ranges, that is, eight A tabulated summary of the upshift gear change pattern will be:

Gear ratio 1 2 3 4 5 6 7 8 Reverse Upshift

sequence 1L 2L 3L 4L 1H 2H 3H 4H RL RH

3.5.3 Sixteen speed synchromesh gearbox with range change and integral splitter gears (Fig 3.23)

This heavy duty commercial gearbox utilizes both a two speed range change and a two speed splitter gear change to enable the four speed gearbox to

Fig 3.21 Eight speed constant mesh gearbox with two speed rear mounted range change

extend the gear ratio into eight steps and, when

required, to sixteen split (narrow) gear ratio

intervals

The complete gearbox unit can be considered to

be divided into three sections; the middle section

(which is basically a conventional double stage four

speed gearbox), and the first two pairs of gears at

the front end which make up the two speed splitter

gearbox Mounted at the rear is an epicyclic gear

train providing a two speed low and high range

change (Fig 3.23)

The epicyclic gear train at the rear doubles the

ratios of the four speed gearbox permitting the

driver to initially select the low (L) gear range

driving through this range 1, 2, 3 and 4 then

select-ing the high (H) gear range The gear change

sequence is again repeated but the gear ratios now

become 5, 6, 7 and 8

If heavy loads are being carried, or if maximum

torque is needed when overtaking on hills, much

closer gear ratio intervals are desirable This is

provided by splitting the gear steps in half with

the two speed splitter gears; the gear shift pattern

of 1st low, 1st high, 2nd low, 2nd high, 3rd low and

so on is adopted

Front end splitter two speed gearbox power flow

(Fig 3.23) Input power to the gearbox is supplied

to the first motion shaft When the splitter

synchro-nizing sliding sleeve is in neutral, both the splitter

low and high input gear wheels revolve on their

needle bearings independently of their supporting

first motion shaft and mainshaft respectively

When low or high splitter gears are engaged, the first motion shaft drive hub conveys power to the first or second pair of splitter gear wheels and hence to the layshaft gear cluster

Mid-four speed gearbox power flow (Fig 3.23) Power from the first motion shaft at a reduced speed is transferred to the layshaft cluster of gears and subsequently provides the motion to all the other mainshaft gear wheels which are free to revolve on the mainshaft, but at relatively different speeds when in the neutral gear position

Engagement of one mid-gearbox gear ratio dog clutch locks the corresponding mainshaft drive hub

to the chosen gear so that power is now able to pass from the layshaft to the mainshaft through the selected pair of gear wheels

Reverse gear is provided via an idler gear which, when meshed between the layshaft and mainshaft, alters the direction of rotation of the mainshaft in the usual manner

Rear end range two speed gearbox power flow (Fig 3.23) When the range change is in the neu-tral position, power passes from the mainshaft and sun gear to the planet gears which then revolve on the output shaft's carrier pin axes and in turn spin round the annular gear and synchronizing drive hub

Engaging the low range gear locks the synchron-izing drive hub to the gearbox casing This forces the planet gears to revolve and walk round the inside of the annular gear Consequently, the carrier and output shafts which support the planet gear axes will also be made to rotate but at a speed lower than that of the input shaft

Changing to high range locks the annular gear and drive hub to the output shaft so that power flow from the planet gears is then divided between the carrier and annular, but since they need to rotate at differing speeds, the power flow forms a closed loop and jams the gearing As a result, there

is no gear reduction but just a straight through drive to the output shaft

3.5.4 Twin counter shaft ten speed constant mesh gearbox with synchromesh two speed rear mounted range change (Fig 3.24) With the quest for larger torque carrying capacity, closer steps between gear ratio changes, reduced gearbox length and weight, a unique approach

to fulfil these requirements has been developed Fig 3.22 Range change gear ratio±speed chart

Fig 3.23 Sixteen speed synchromesh with range change and integral splitter gears