Mini-1100 AP Automatic
Transmission
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Information on the
following article was sourced from an Automotive Products (AP)
publication in 1967. AP was possible best known for its Lockheed
brakes and Borg & Beck clutches etc. So when in 1965 at the
Earls Court Motor Show, this ingenious system was announced, it
caused quite a stir throughout the motoring world.
Considered by many to be
the most outstanding technical development in the 70 year history
of the British motor industry, this remarkable AP automatic
transmission for small cars is not merely an enviable achievement
for design and development engineer but is a complete break-through
in volume production engineering and assembly techniques.
Development
and Prototypes
It
took 10
years of painstaking design and development work before the simple
two-speed self-changing gear unit became the unique four-speed AP
automatic transmission for small cars. This was a major advanced in
producing a four-speed automotive gearbox that could be operated
like a manual box. It must be remembered that this was nearly sixty
years ago, and was unique because it operated in a very small space
using standard engine oil. To reach this goal, involved much detail
design work, long-term development, and teamwork from the start
between designer and service engineer.
It all started in the early
1950s when the Company announced the 'Manumatic' transmission
system. This was a semi-automatic two pedal system using a standard
synchromesh gearbox in conjunction with an electro-pneumatically
controlled centrifugal clutch. The 'Manumatic' system enabled the
driver to change gear merely by selecting the gear he wanted
without using a clutch pedal. Various car manufactures included it
as an option with Austin fitting it on the A40-50 Cambridge. It did
not catch on mainly because it was neither a manual or an auto,
there were also some service problems.
A
lot of knowledge was gained for this first product, and on the back
of this, AP Group decided they would develop a fully automatic box
for British and European manufactures. It was from 1955 onwards
that AP started its highly secret investigation which they were
confident would eventually lead to a fully automatic gearbox at
that stage of an unspecified type. Early studies at Leamington Spa
centred around spur gear layshaft boxes with multiple clutches
providing power shifts between ratios. Inevitably a torque
convertor had to be designed as this provides the only practicable
means of coupling an automatic gearbox to the power unit. As it
turned out the torque convertor was the only item which reached
fruition at this stage for in 1956 an independent Belfast engineer,
Mr Hugh Reid, approached the Company with a bevel gear device which
he had designed as an overdrive unit; he suggested that the same
device might form the basis for an automatic gearbox.
2 Speed version installed
in a Humber Mark
The Reid system involved various cluster of bevel gears arranged as
a planetary system. But the main drawback was that this basic
system gave only two ratios, low and direct. It was only possible
to change from direct to indirect drive by taking your foot of the
accelerator. A decision was taken to married one of the Reid
two-speed unit to the latest AP torque converter. The complete unit
was then installed in a Humber Hawk which successfully completed
close on 20,000 miles of development testing, although it was
without any reverse gear! (must have made it
interesting).
Two-speed
transmission on test
A50 Cambridge on
Test
The next major development
came in 1957 when, still within the Reid patent, two complete
two-speed units were manufactured for test and installed in
1.5-litre Austin A50 Cambridge. These units, while retaining the
weight control system (because of the patent), had the added
refinements of a reverse gear and a system of dogs for connecting
the drive to the output. The sheer simplicity of this early
arrangement had much to recommend it. It had no complicated
hydraulic system, and a centrally mounted selector lever made for
very efficient dog engagement particularly when it was depressed,
to brake the torque convertor turbine before engaging the dog
drive. This level of simplicity ended abruptly, however when it was
decided to build a three speeds version.
Two-Speed version installed
in a A50 Cambridge
The two A50 Cambridge
saloons eventually covered a total of 100,000 miles of severe
testing. Over this distance not only did they prove the
satisfactory operation with both the two and three-speed AP
transmission units. It was decided to convert one so that engine
oil could be circulated through the gearbox and pumped back into
the sump. This gave the Group valuable advance information on the
behaviour of automatics running in lubricating oil which was
contaminated by products of combustion and other foreign matter. It
was at the height of the A50 Cambridge testing programme that the
BMC Mini was announced and its combination of a low capacity,
modestly powered engine with a very compact transmission system
offered a challenge which AP designers could not ignore. By
December 1959 design work commenced on a fully automatic
three-speed transmission system for the Mini based on the
successful three-speed Cambridge unit.
Three Speed Version
Three-Speed Version (Early
Mini)
This three-speed unit was a complex little box, which retained the
bulky double cone clutch assembly. With sucessful development
testing, it was decided to demonstrate this to BMCs Technical
Director Alex Issigonis. He was so impressed, that he immediately
ordered a number of prototypes for test purposes. Soon after the
four-speed version came along, this proved a winner with BMC as it
utilised the full performance of the 850cc Mini yet gave the car
the same performance as the conventional 4-speed manual gearbox
while occupying the same amount of space beneath the engine.
Four
Speed Version
The new four-speed prototype transmission unit, after more
development soon became the basis for the production version of the
unit which was adopted by BMC for their million-selling Mini and
1100 models. Before this went into production, however, a number of
significant changes had to taken place. In the first instance the
four-speed unit retained the double cone clutch but it was found
that using this device in a small car with short, stiff drive
shafts and no lengthy transmission shaft to absorb the torsional
stresses proved to be a great problem so it was necessary to
redesigned the unit, to incorporate hydraulically operated
multi-plate clutches.
Another problem arose with the standard crankshaft, as at the point
where the torque convertor is attached it was prone to fracture.
Because of this it was necessary to complete re-design the torque
convertor around an extended crankshaft. The two and three versions
had a free wheel unit which was complemented by additional clutches
for overrun braking. With the newer four speed version there was
now not enough room for the free wheel unit, so in the end, the
free wheel was abandoned and the transmission now included overrun
braking on all ratios.
The prototype four-speed AP
automatic transmission first appeared in an 850 cc Mini in 1962.
All the units produced up to this stage had been built in a
relatively small department at the Group's Leamington Spa
headquarters. With BMC's decision to place a large order, meant
that a large manufacturing facility had to be set up at Leamington
for full-scale production work. Rather than build new factory
premises AP decided that it would be more economical to transfer
their self-contained Purolator filter division to premises in
Bolton, Lancashire. So with the vacant factory space it was time to
place orders for all the equipment needed to set up the new
Automatic Gearbox Division. BMC would be suppling the following,
the main sump and differential casings, and the bevel gear train,
main shaft and intermediate gearing and main oil pump. All the
various sub-assemblies and components for the transmission to be
manufactured at Leamington.
It was estimated that to setup a machine shop to produce the
components to support the orders placed by BMC would cost
£1million. From day one it was decided to buy machinery from the
very best available sources, regardless of their country of
origin.
The production shop layout is planned almost exclusively on a
component group basis so that all machines, heat treatment plant,
inspection facilities and test plant appertaining to one particular
component are adjacent to each other. All groups are equipped with
their own air or electrical measuring and gauging instruments and
manual operations have been reduced to an absolute minimum. Ninety
per cent of the machines require only manual loading and unloading
and the machine cycle is then automatically controlled, often with
plugboard or similar pre-set sequencing control methods. To reduce
working capital the department's inventory is closely controlled to
a weekly intake of materials and bought-out parts. As a result of
adopting the best and very latest of modern production methods and
techniques the department's output has steadily risen from 75 sets
of components per week in September 1965 to 1200 sets a week less
than two years later in step with BMC's ever-increasing production.
The production could be quickly expand to over 2000 units per week
which would be the optima capacity of the present plant
layout.
Longbridge gears up for production
(Kings Norton)
It was decided at the time that no
building on the Longbridge plant was suitable for the assembly of
the automatic transmission, but it did have a unit on the Kings
Norton Factory Centre on the Pershore Road. This had been used in
WWII to assemble Jerrycans, and since then as a surplus machine
store.
So plans were put in place to convert this rather dismal store into
an ultra-clean factory using the very latest production techniques
and machinery.
The Kings Norton
Factory
In the record time of
twelve months BMC transformed the unit into a modern, high output
factory for the production of complete Mini and 1100
engine/automatic transmission units. To do this BMC have had to
spend £750,000 in redesigning the interior of the building,
reflooring most of its 21,600sq ft, and installing all the assembly
plant, test equipment and offices associated with the most modern
present-day factory production techniques. The interior of the
building is bright and airy with a degree of cleanliness not
normally encountered in a factory, but which is essential for the
assembly of the precision-made AP automatic transmission system.
This cleanliness is maintained by an air conditioning system which
feeds the main assembly area with a complete change of pressurised
and filtered air 15 times every hour; also a complete ban on
smoking in the area preserves this dirt-free atmosphere. Similarly,
an interesting overhead conveyor system, with the units suspended
on pendant arms, enables the floor to be kept in a clean,
uncluttered condition. The new Kings Norton factory (designated
Austin No 2 Factory) is arranged so that the transverse (or
'east-west') power unit is assembled on a moving track in the main
assembly area while the transmission system is built in another
area of the building. After inspection and test, the transmission
enters the power unit assembly track where the two components are
joined together and the whole engine/transmission unit moves on to
inspection, test and despatch.
Engine
assembly Process
Engine assembly starts with
the introduction of the washed cast-iron cylinder block onto the
assembly track, where it is secured to one of the overhead conveyor
pendant arms. After a delivery and pressure test in a cabinet
alongside the track the main oil pump is attached to the block and
the unit moves on for the attachment of the crankshaft and its
associated gearing. Between this point and the next assembly stage
the pendant arm carrying the cylinder block is equipped with wire
baskets. Whilst this is going on the cylinder head is built
up.
Final stage in the assembly
of the cylinder head
Cylinder heads are
constructed in an overhead section of the shop on a flow-line basis
wherein the washed head casting, ready machined, enters the line at
one end and in four stages the valves, springs and collets are
assembled, the various side studs and head studs are screwed in and
then the camshaft and rockers are secured to complete the assembly.
Each cylinder head is given a leak check (to prove the valve
seating) on a rig in the department and a special vibrator rig is
also used to give the valves an initial 'running-in' period and
thus reduce tappet setting drift at the engine test stage.
A set of engine block components are passed through a automatic
degreasing plant; these items include connecting rods, timing
gears, manifolds, end-plates and the like. The other basket
contains non-washable items such as the starter, dynamo, coil and
similar components. The final assembly phases include fitting the
calibrated carburettor and its manifold, the rocker cover and the
transmission 'kick-down' linkage. After introduction of the
subsidiary components the whole central portion of the power unit
is built up in stages along the assembly track until it is ready to
receive the transmission assembly.
The
transmission test department at Kings Norton contains four test
rigs (three for production test and one for inspection
rectification) specially developed to give the automatic
transmission system a complete functional test in as little as six
minutes.
The rigs are driven by electric motors and incorporate a
dynamometer and an auto/manual control system which controls the
following test sequence. With the gear selector in neutral, oil
pump delivery, flow and pressure is checked right through the unit
including the valve block operation and delivery to the engine. In
'drive', gear-changing and load are checked in all gears at a light
throttle setting; the motor input is varied by a rheostat. A
similar check is then carried out under full throttle in each gear.
A fourth test in 'drive' checks for slip in all gears by holding
the output with a disc brake. Finally a tow-start test checks the
auxiliary pump and its associated valves and sequencing ; this test
is carried out by spinning the differential at 20 mph with the gear
selector in third gear. Any failures during this rigorous test
procedure are recorded and the unit is diverted to the
rectification bay where it is stripped, examined and rebuilt so
that it can pass the specified test on a similar test machine.
Those which pass the test are loaded on an overhead conveyor and,
identified by a Mini or 1100 'flag', are despatched to the engine
assembly line.
The transmission units join the assembly line from a lift which
lowers the units off the overhead conveyor and down to bench level.
At this point they are removed and secured to the power unit while
the empty gearbox carrier returns to the transmission test house
for another load. With the gearbox secured, the engine assembly
moves on to receive the torque converter and various engine
components before the ready-made cylinder head is secured.
View of the pendent
conveyor system on final engine/transmission
assembly.
The engine test bay is a triumph in sound-proofing, for despite the
fact that its ten booths are open at the sides and the whole bay is
doorless, the noise level inside and out is negligible. Inside each
booth a completed power unit is connected to a dynamometer via its
final drive couplings and with fuel, oil and water connected (the
latter being preheated to working temperature) and electrical
connections made, the unit is subjected to a full, simulated road
test lasting 15 minutes. The test is governed by a punched-tape
programme, housed in a console above the power unit, and this
varies the load on the engine whilst the operator governs the
throttle setting by hand. Dials and indicator lights record the
engine's performance and among these are two sets of lights, one
signifying 'rich' or 'lean' carburettor setting, the other
recording torque output and converter slip.
Should any of these lights indicate a fault the power unit, after
disconnection, is automatically routed to a rectification bay
outside the test area where the fault is diagnosed and corrected
before it is re-directed back into the test bay.
The final production stage takes the power unit from the test bay
to a rotary carrier - the 'carousel' - where the units are painted.
Even this process is as advanced as the rest of the Kings Norton
methods, for it is done electrostatically. As the paint spray
leaves the operator's gun it is electrically charged so that the
attraction between the paint and the engine mass ensures a uniform
and semi-permanent covering on the unit. After painting it only
remains for the units to be secured to transport cradles-for the
short journey by road to the vehicle final assembly track at
Longbridge, headquarters of the British Motor Corporation.
The Power Units are then transported to Longbridge for the Mini
version assembled in CAB1 and the 1100/1300 models to CAB2, with
some going down to Cowley.
____________________
How
does this automatic transmission work?
In place of the normal
clutch a torque converter is bolted to the end of the crankshaft.
Drive is transmitted by primary gears to the main bevel gear train
in the transmission case. This is best described as a differential
within a differential, and by holding different parts of the
assembly through servo-operated brake bands the different gear
ratios are obtained. Two clutches are used to complete the power
transmission; one of these is used for all forward gears,
supplemented by the second one when top gear comes into use; this
second clutch also transmits reverse. The clutches drive onto the
differential, whence conventional drive-shafts take power to the
road wheels.
An oil pressure system operates the brake bands and clutches which
are controlled by valves operated by cable from the
quadrant-control in the car and by a governor driven from the
auxiliary oil pump that rotates in proportion to road speed. The
main oil pump runs with the engine, circulating oil to the torque
converter and valve block as well as to the power unit. As one
'fill' of oil circulates in the whole unit, the need for regular
oil are necessary along with a oil filter which has a larger
capacity that the manual version. An extension of the throttle
linkage provides additional bias for the governor and gives extra
speed in the gears for accelerating, as well as the kick-down
change facility.
The auxiliary pump pressurizes the circuit once the car is on the
move even without the engine running, thus enabling the vehicle to
be tow-started. The unit is astonishingly compact, taking up little
more room than the normal manual transmission. The slightly more
powerful engine (55 instead of 50 bhp on the 1100) is mounted a
fraction higher in its compartment in a stronger, redesigned front
sub-frame, with the result that an annular air cleaner surrounds
the carburetter vacuum chamber in place of the normal overhead
unit. The main advantage of any auto transmission system is that
anyone can jump straight into the car and drive it properly,
smoothly and safely from the word 'go'. Start the engine, pull the
selector lever all the way back through its neat quadrant to the
'D' position, press the accelerator, steer and hey presto, you are
off ! But there is much more to it than that, once the driver has
settled down to the job, or rather enjoyment of exploiting the
system to the full, in particular the unusual fully automatic/fully
manual facility of this tiny AP 'magic' box.
____________________
Design for easy servicing
Servicing was one of the things foremost in the designers' minds
when the production version of the AP automatic transmission was
finalised. This accounts, in part, for the neat packaging of the
system into self-contained units and for the comparative ease with
which these units can be removed and replaced in the transmission
case. Indeed so aware were the designers of the need for rapid and
economical servicing that AP's experts from their Banbury Service
and Spares Division were introduced to the system at the early
production prototype stage. It was in these early days that the
overall servicing policy was visualised when, together with their
counterparts from BMC, AP's servicing organisation decided that it
would best be maintained on an exchange unit basis. With some
exceptions this is still the policy today, so that any damaged unit
in the transmission system is removed from the vehicle and replaced
by a new unit. The customer, of course, is given an allowance on
the damaged part and the whole repair is performed with the minimum
of delay and expense. At first it was thought that any unit in the
transmission system which failed would need to be completely
replaced. However, after careful examination at AP's Banbury
factory it was found that many of the various units could be
repaired using a kit of spare parts.
It is necessary to get various special service tools made to supply
the agents. So a team comprised a service advisor from AP, one from
BMC, and an expert from V. L. Churchill Limited, the company which
manufactures servicing tools for BMC. This team spent some time at
Banbury stripping and rebuilding the transmission system and
performing every foreseeable maintenance job on the system before
they finally arrived at a set of tools that could form the basic
kit. The first tools to be decided upon were those which permitted
easy removal of units from the transmission and those which ensured
rapid and correct replacement of units. After this various tools
were designed which would enable the mechanic to service selected
units using an approved repair kit. The policy during this period
was that the tools should be designed jointly by AP, BMC and
Churchill, that the design must be accepted by BMC, and that the
manufacture was the responsibility of Churchill. Naturally special
tools are only one aspect of servicing which must be decided at an
early date, another important item to be progressed as early as
possible being the various technical publications. AP's
Publications Department at Banbury had to familiarise themselves
with the unit as quickly as possible so that eventually they were
able to supply information to BMC for the Automatic Mini and 1100
owner's handbook and the BMC service and spare parts manual. In
addition, the writers had to complete AP's own service diagnosis
manual. People such as packaging specialists had to be shown the
transmission in order that they could decide the most effective and
efficient ways of packing and storing spare parts and of ensuring
that the spares, whilst in store, remained in mint condition.
All this organisation has evolved into a regular routine wherein
spares for the AP transmission components are packed and despatched
from Banbury and distributed through BMC to their various retail
outlets. Similarly any modifications to the AP components are
covered by the Publications Department at Banbury who issue
modification leaflets informing interested parties of the changes
to the transmission system. Eventually AP's Banbury factory will
undertake the servicing of all the transmission units of AP
manufacture which are returned on an exchange basis. A vitally
important facet of any service organization's work is the
instruction of personnel who will have to work on the Company
product. This is true, of course, whether the product is new and
revolutionary (as in the case of the AP transmission) or a well
established and familiar line (such as Lockheed brakes, Borg &
Beck clutches and the like). Thus, following the lead from BMC, the
Service School at Banbury sent out letters detailing a three-day
instruction course for mechanics on the principle, operation and
maintenance of the unique AP transmission. These letters went to
selected BMC service centres (other than direct BMC franchise
holders, who are instructed by BMC themselves) and asked for names
to be put forward for entry to the course. The response to the
invitations was so overwhelming that within one month the year's
course list was full. The courses opened during the first week in
January 1967 and are held for three days every week. Although it
was originally planned to have only six people on a course at one
time, so that the instructor could give individual attention to
each student, the classes have averaged nine students at a time.
The course makes extensive use of coloured slides for instruction
purposes and is divided up as follows: on the first day students
are instructed in the principle and operation of the transmission.
Day Two is allocated to the operation and servicing of the
individual units, and Day Three is taken up with practical
instruction in stripping, rebuilding, adjustment and fault
diagnosis on the unit. During the course (which lasts for seven
hours every day) all the students are given the opportunity of
doing every job on the gearbox which is likely to be encountered in
the garage. Unlike many similar kinds of courses there is no
examination or certificate at its completion for, as the Chief
Instructor says, "the valuable time taken in examining students can
be better employed in further instruction".
Training service technicians
In addition to actual
course instruction, knowledge of the gearbox and its operation can
be spread in other ways, one of the most popular being from the
lecture platform. Ever since the AP transmission first appeared the
AP Group has been inundated with requests from professional bodies,
technical colleges and motoring organizations for lectures on the
'magic' gearbox. To date Company representatives have presented
lectures twice a month all over the country so that with a regular
audience of 120 appreciation of the technical aspects of the
transmission is growing rapidly.An important part of AP automatic
transmission service, as with all other AP products, is field
service wherein a trained factory engineer can be made available
immediately to offer advice and practical assistance on the
customer's own premises. Even though there are an estimated 40,000
Automatic Minis and 1100's in service in the UK this duty at
present requires only one specialist who, along with other service
engineers, is on call to any part of the British Isles. Normally
requests for service advice go direct to BMC Service Limited at
Oxford who deal with the matter either themselves or, if they feel
the need, in conjunction with the AP service engineer. Calls which
come direct to AP are dealt with by our own service engineer but
always in consultation with the BMC Service Department. Similarly
all automatic transmission service personnel keep in regular
contact with the AP Leamington and BMC Kings Norton production
plants to ensure a continuity of development in the overall
servicing policy.
Pictures showing the various components made by AP.
The auxiliary oil pump
gears are sintered and only require grinding for thickness before
assembly. With the gears positioned in the pump housing their
height is checked with a dial indicator.
This test rig automatically
checks auxiliary pump output and flow while measuring movement of
the governor at various speeds.
This balancing machine is connected to an electronic control
circuit and panel which automatically measures and records the
amount - and angle – of unbalance in the convertor stator
assembly.
This automatic induction
heater is used to harden collars and sleeves on torque convertor
components. The sleeve is heated to a predetermined temperature;
then the assembly is dropped into a cold quenching bath to complete
the hardening process.
Every torque convertor is
given a complete leak test and functional check under full stall
conditions on this fully automatic test console. The hydraulic
clamp Is lowering after completion of a test
sequence.
The
automatic transmission clutches been assembled by hand.
____________________
Showing the lubrication system and 'power flow'
1.
Main oil strainer. 2. Oil pump 3. Oil filter assembly. 4. Valve
block. 5. Engine oil feed 6. Converter feed pipe.
7. Converter to low pressure valve feed. 8. Low pressure valve 9.
Gear train. 10. Top and reverse clutch.
11. Governor. 12. Forward clutch. 13 Servo unit. 14 Auxiliary pump
oil strainer. 15. Auxiliary.
Mechanical Flow Diagrams
1.
Crankshaft. 2. Converter output. 3. Idler gear. 4. Input gear. 5.
One-way clutch. 6 Gear carrier.
7. Reverse band. 8. Third gear band. 9. Second gear band. 10. Top
and reverse clutch. 11. Forward clutch.
12. Final drive pinion. 13. Final drive gear.
When in neutral all the bands and clutches are disengaged,
therefore there is no drive to the final drive pinion.
First
Speed: In this ratio
the forward clutch is applied and the one-way clutch is operative.
The carrier is stationary, its reaction being controlled by the
one-way clutch. The input bevel drives the planet wheels and the
planet pinions drive the forward output pinion and shaft. Thus
power is transferred through the planet assemblies to the
mainshaft, forward clutch, and the output gear providing a ratio of
2.69 : 1
Second
Speed: As for all
forward gears the forward clutch remain engaged, and in addition
the second speed brake band applied. This controls the reaction
which is imposed on the reverse drive bevel when in this ratio.
With the planet cluster orbiting around the reverse drive bevel
power is transmitted from the input bevel through the planets to
the mainshaft and provides a ratio of 1.845 : 1.
Third
Speed: For this ratio
the third speed bevel wheel is held by its appropriate drum and
brake band, and in this case the planet clusters orbit around this
gear. Like second speed, power is transmitted from the input bevel
through the planets to the mainshaft and in this provides a ratio
of 1.46 : 1
Top
Speed: In addition to
the forward clutch, the top and reverse clutch is engaged. This in
effect locks up the bevel gears and the reduction gear assembly
then rotates as one unit to provide direct drive.
Reverse:
In this ratio the carrier is
held by the reverse band -- (the one-way clutch being inoperative
because the reaction is in the opposite direction to first speed)
In addition the top and reverse clutch is engaged,. The input bevel
wheel drives the planet wheel and the planet pinion drives the
reverse drive gear. Thus power is transmitted through the planet
assemblies to the top and reverse clutch and thence to the final
drive pinion to provide a ratio of 2.69 : 1.