Advanced Vehicle Technology Episode 1 Part 9 ppsx

The power drive is then directed though a Ravigneaux type dual planetary gear train which provides five forward gears and one reverse gear; it then passes to the output side via a second

5.9.3 Hydraulic control system (Fig 5.28)

The speed ratio setting control is achieved by a

spur type hydraulic pump and control unit which

supplies oil pressure to both primary and

second-ary sliding pulley servo cylinders (Fig 5.28) The

ratio settings are controlled by the pressure

exerted by the larger primary servo cylinder

which accordingly moves the sliding half pulley

axially inwards or outwards to reduce or increase

the output speed setting respectively This primary

cylinder pressure causes the secondary sliding

pulley and smaller secondary servo cylinder to

move proportionally in the opposite direction against the resistance of both the return spring and the secondary cylinder pressure, this being necessary to provide the correct clamping loads between the belt and pulleys' walls The cylinder pressure necessary to prevent slippage of the belt varies from around 22 bar for the pull away lowest ratio setting to approximately 8 bar for the highest overdrive setting

The speed ratio setting and belt clamping load control is achieved via a primary pulley position senser road assembly

Fig 5.26 Illustration of pulley and belt under- and overdrive speed ratios

Fig 5.27 Steel belt construction

152

However, engine and road speed signals are

pro-vided by a pair of pitot tubes which sense the rate of

fluid movement, this being a measure of speed, be it

either under the influence of fluid flow caused by

the engine's input or by the output drive relating to

vehicle speed

5.9.4 Epicyclic gear train construction and description (Figs 5.25 and 5.28)

Drive in both forward and reverse direction is obtained by a single epicyclic gear train controlled

by a forward multiplate clutch and a reverse multi-plate brake, both of which are of the wet type 153

(immersed in oil) (Fig 5.25) The forward clutch is

not only used for engagement of the drive but also

to provide an initial power take-up when driving

away from rest

The epicyclic gear train consists of an input

plan-etary carrier, which supports three sets of double

planetary gears, and the input forward clutch

plates Surrounding the planetary gears is an

internally toothed annulus gear which also

sup-ports the rotating reverse brake plates In the centre

of the planetary gears is a sun gear which is

attached to the primary pulley drive shaft

Neutral or park (N or P position) (Fig 5.28) When

neutral or park position is selected, both the

multi-ple clutch and brake are disengaged This means

that the annulus gear and the planetary gears driven

by the input planetary carrier are free to revolve

around the sun gear without transmitting any

power to the primary pulley shaft

The only additional feature when park position

is selected is that a locking pawl is made to engage

a ring gear on the secondary pulley shaft, thereby

preventing it from rotating and causing the car to

creep forward

Forward drive (D or L position) (Fig 5.28)

Select-ing D or L drive energizes the forward clutch so

that torque is transmitted from the input engine

drive to the right and left hand planetary carriers

and planet pins, through the forward clutch

clamped drive and driven multiplates Finally it is

transferred by the clutch outer casing to the

pri-mary pulley shaft The forward gear drive is a direct

drive causing the planetary gear set to revolve

bodily at engine speed with no relative rotational

movement of the gears themselves

Reverse drive (R position) (Fig 5.28) Selecting

reverse gear disengages the forward clutch and

energizes the reverse multiplate brake As a result,

the annular gear is held stationary and the input

from the engine rotates the planetary carrier (Fig

5.28)

The forward clockwise rotation of the carrier

causes the outer planet gears to rotate on their

own axes as they are compelled to roll round the

inside of internally toothed annular gear in an

anticlockwise direction

Motion is then transferred from the outer planet

gears to the sun gear via the inner planet gears

Because they are forced to rotate clockwise, the

meshing sun gear is directionally moved in the

opposite sense anticlockwise, that is in the reverse direction to the input drive from the engine 5.9.5 Performance characteristics (Fig 5.29) With D drive selected and the car at a standstill with the engine idling, the forward clutch is just sufficiently engaged to produce a small amount of transmission drag (point 1) This tends to make the car creep forwards which can be beneficial when on

a slight incline (Fig 5.29) Opening the throttle slightly fully engages the clutch, causing the car to move positively forwards (point 2) Depressing the accelerator pedal further sets the speed ratio accord-ing to the engine speed, road speed and the driver's requirements The wider the throttle is opened the lower the speed ratio setting will be and the higher the engine speed and vice versa With a light con-stant throttle opening at a minimum of about

1700 rev/min (point 3) the speed ratio moves up to the greatest possible ratio for a road speed of roughly 65 km/h which can be achieved on a level road If the throttle is opened still wider (point 4) the speed ratio setting will again change up, but at a higher engine speed Fully depressing the accelerator pedal will cause the engine speed to rise fairly rapidly (point 5) to about 4500 rev/min and will remain at this engine speed until a much higher road speed is attained If the engine speed still con-tinues to rise the pulley system will continue to change up until maximum road speed (point 6) has been reached somewhere near 5000 rev/min Partially reducing the throttle open then causes the pulley combination to move up well into the overdrive speed ratio setting, so that the engine speed decreases with only a small reduction in the car's cruising speed (point 7)

Even more throttle reduction at this road speed causes the pulley combination speed ratio setting to

go into what is known as a backout upshift (point 8), where the overdrive speed ratio reaches its maxi-mum limit Opening the throttle wide again brings about a kickdown downshift (point 9) so that there

is a surplus of power for acceleration A further feature which provides engine braking when driving fast on winding and hilly slopes is through the selection of L range; this changes the form of driving by preventing an upshift when the throttle

is eased and in fact causes the pulley combination

to move the speed ratio towards an underdrive situation (point 10), where the engine operates between 3000 and 4000 rev/min over an extensive road speed range

The output torque developed by this continu-ously variable transmission approaches the ideal 154

constant power curve (Fig 5.29) in which the

torque produced is inversely proportional to the

car's road speed

5.10 Five speed automatic transmission with

electronic-hydraulic control

5.10.1 Automatic transmission gear train system

(Fig 5.30)

This five speed automatic transmission system is

broadly based on a ZF design Power is supplied

though a hydrodynamic three element torque

con-verter incorporating an integral disc type lock-up

clutch The power drive is then directed though

a Ravigneaux type dual planetary gear train which

provides five forward gears and one reverse gear; it

then passes to the output side via a second stage

single planetary gear train The Ravigneaux

plan-etary gear train has both large and small input sun

gears, the large sun gears mesh with three long

planet gears whereas the small sun gears mesh

with three short planet gears; both the long and

the short planet gears are supported on a single

gear carrier A single ring-gear meshing with the

short planet gear forms the output side of the

plan-etary gear train Individual gear ratios are selected

by applying the input torque to either the pinion

carrier or one of the sun gears and holding various

other members stationary

5.10.2 Gear train power flow for individual gear ratios

D drive range Ð first gear (Fig 5.31) With the position selector lever in D drive range, the one way clutch (OWC) holds the front planet carrier while multiplate clutch (B) and the multiplate brake (G) are applied Power flows from the engine to the torque converter pump wheel, via the fluid media

to the output turbine wheel It is then directed by way of the input shaft and the applied multiplate clutch (B) to the front planetary large sun gear (SL) With the front planet carrier (CF) held stationary

by the locked one way clutch (OWC), power passes from the large sun gear (SL) to the long planet gears (PL) in an anticlockwise direction The long planet gear (PL) therefore drives the short planet gears (PS) in a clockwise direction thus compelling the front annular ring gear (AF) to move in a clockwise direction Power thus flows from the front annular ring gear (AF) though the rear intermediate shaft

to the rear planetary gear annular ring gear (AR) in

a clockwise direction With the rear sun gear (SR) held stationary by the applied multiplate brake (G), the rear planet gears (PR) are forced to roll around the fixed sun gear in a clockwise direction, this in turn compels the rear planet carrier (CR) and the output shaft also to rotate in a clockwise direc-tion at a much reduced speed Thus a two stage speed reduction produces an overall underdrive 155

Crown wheel

Bevel pinion

Final drive

Front planetary gear train

Parking cog

Pawl

Transfer shaft

Rear planetary gear train CLC

(2+3+5)B E

S

RC A

DC B A

C F

(4+5)C C

OWC Input

from

engine

Input shaft

Front intermediate shaft

Rear intermediate shaft

Output shaft

A F

P L

S S

S L

F

OWC

F RB

A R

P R

C R

SR

Transfer gears

P S

Brakes

A B C D E F G

HC

Fig 5.30 Five speed and reverse automatic transmission (transaxle/longitudinal) layout

Brake G applied

Rear planetary gears (RPG)

gear train

Input

Output

Input

Output

Rear planetary gear train

Output gear

Output shaft Rear

intermediate shaft OWC

locked

Front intermediate shaft

Input shaft Input

from

engine

OWC

S

P

B

C

C F

A F

S S

SL

PL

OWC

G

D

A R

P R

CR S R

F CLC

Clutch A applied

Front planetary gears (FPG)

C R

A R S R

P R

S L

A R

P S PL

CF

S S

Fig 5.31 Five speed and reverse automatic transmission power flow first gear

first gear If the `2' first gear is selected multiplate

brake (F) is applied in addition to the multiplate

clutch (B) and multiplate brake (G) As a result

instead of the one way clutch (OWC) allowing

the vehicle to freewheel on overrun, the

multi-plate brake (F) locks the front planetary carrier

(CF) to the casing Consequently a positive drive

exists between the engine and transmission on

both drive and overrun: it thus enables engine

braking to be applied to the transmission when

the transmission is overrunning the engine

D drive range Ð second gear (Fig 5.32) With the

position selector lever in D drive range, multiplate

clutch (C) and multiplate brakes (B) and (G) are

applied

Power flows from the engine via the torque

con-verter to the input shaft, it then passes via the

multiplate clutch (B) to the first planetary large

sun gear (SL) With the multiplate brake (E)

applied, the front planetary small sun gear (SS) is

held stationary Consequently the large sun gear

(SL) drives the long plant gears (PL) anticlockwise

and the short planet gears (PS) clockwise, and at

the same time, the short planet gears (PS) are

com-pelled to roll in a clockwise direction around the

stationary small sun gear (SS)

The drive then passes from the front planetary

annular ring gear (AF) to the rear planetary

annu-lar ring gear (AR) via the rear intermediate shaft

With the rear sun gear (SR) held stationary by the

applied multiplate brake (G) the clockwise

rota-tion of the rear annular ring gear (AR) compels

the rear planet gears (PR) to roll around the held

rear sun gear (SR) in a clockwise direction taking

with it the rear carrier (CR) and the output shaft

at a reduced speed Thus the overall gear

reduc-tion takes place in both front and rear planetary

gear trains

D drive range Ð third gear (Fig 5.33) With the

position selector lever in D drive range, multiplate

clutches (B) and (D), and multiplate brake (E) are

applied

Power flows from the engine via the torque

con-verter to the input shaft, it then passes via the

multiplate clutch (B) to the front planetary large

sun gear (SL) With the multiplate brake (E)

applied, the front planetary small sun gear (SS) is

held stationary This results in the large sun gear

(SL) driving the long planet gears (PL)

anticlock-wise and the short planet gears (PS) clockwise, and

simultaneously, the short planet gears (PS) are

compelled to roll in a clockwise direction around

the stationary small sun gear (SS) Consequently, the annular ring gear (AF) is also forced to rotate in

a clockwise direction but at a reduced speed to that

of the input large sun gear (SL) The drive is then transferred from the front planetary annular ring gear (AF) to the rear planetary annular ring gear (AR) via the rear intermediate shaft With the mul-tiplate clutch (D) applied the rear planetary sun gear (SR) and rear annular ring gear (AR) are locked together, thus preventing the rear planet gears from rotating independently on their axes The drive therefore passes directly from the rear annular ring gear (AR) to the rear carrier (CR) and output shaft via the jammed rear planet gears Thus it can be seen that the overall gear reduction

is obtained in the front planetary gear train, whereas the rear planetary gear train only provides

a one-to-one through drive

D drive range Ð fourth gear (Fig 5.34) With the positive selector lever in D drive range, multiplate clutches (B), (C) and (D) are applied Power flows from the engine via the torque converter to the input shaft, it then passes via the multiplate clutch (B) to the front planetary large sun gear (SL) and via the multiplate clutch (C) to the front planetary planet-gear carrier (CF) Consequently both the large sun gear and the planet carrier rotate at the same speed thereby preventing any relative plane-tary gear motion, that is, the gears are jammed Hence the output drive speed via the annular ring gear (AF) and the rear intermediate shaft is the same as that of the input shaft speed Power is then transferred to the rear planetary gear train by way

of the front annular ring gear (AF) and rear inter-mediate shaft to the rear planetary annular ring gear (AR) and rear intermediate shaft to the rear planetary annular ring gear (AR) However, with the multiplate clutch (D) applied, the rear annular ring gear (AR) becomes locked to the rear sun gear (SR); the drive therefore flows directly from the rear annular ring gear to the rear planet carrier (CR) and output shaft via the jammed planet gears Thus there is no gear reduction in both front and rear planetary gear trains, hence the input and output rotary speeds are similar

D drive range Ð fifth gear (Fig 5.35) With the position selector lever in D drive range, multiplate clutches (C) and (D) and multiplate brake (E) are applied Power flows from the engine via the torque converter to the input shaft, it then passes via the multiplate clutch (C) to the front planetary planet 158

Brake G applied

Rear planetary gears (RPG)

gear train

Input

Output

Input

Output

Rear planetary gear train

Output gear

Output shaft Rear

intermediate shaft

Front intermediate shaft

Input shaft Input

from

engine

OWC

S

P T

E

A

B

C

C F

A F

S S

S L

PL

OWC

G D

A R

P R

C R S R

F CLC

Clutch A applied

Front planetary gears (FPG)

C R

AR SR

P R

S L

A F

P S P L

C F

SS

Brake C applied

Fig 5.32 Second gear

Clutch F applied

Rear planetary gears (RPG)

planetary gear train

Input

Output

Input

Output

Rear planetary gear train

Output gear

Output shaft Rear

intermediate shaft

Front intermediate shaft

Input shaft

OWC

S

P T

E

A

B

C

C F

A F

S S

SL

P L

OWC

A R

P R

C R SR

F CLC

Clutch A applied

Front planetary gears (FPG)

C R

A R

S R

P R

S L

A F

P S P L

C F

SS

Brake C applied

Fig 5.33 Third gear

gear train

Input Output

Input

Output

Rear planetary gear train

Output gear

Output shaft Rear

intermediate shaft

Front intermediate shaft

Input shaft Input

from

engine

OWC

S

P T

B

C

C F

AF

S S

S L

P L

OWC

A R

P R

C R S R

F CLC

C R

A R S R

PR

S L

PS P L

C F

S S

Fig 5.34 Fourth gear