Minki I and Minki II
1992
The thinking behind the
replacement for the Mini started back in about 1992, while under
the ownership of British Aerospace and called at that time The
Rover Group.
So how was the name MINKI arrived at, simple, put a ‘K’ series
engine into a Mini and you have MINKI.
At the time the general
feeling was that because the design was then thirty three years
old, technology had moved on so much, and with new legislation on
emissions and crash testing etc., that it was best to start with a
clean sheet.
The first part of the
concept stage was to do an appraisal of the current Mini and see
how improvements could be made.
1) Improve the powerunit, by installing the ‘K’ series engine with
a 5-speed gearbox
2) Improve the suspension, by installing hydragas suspension.
3) Improve the driving position, by installing better seats,
altering the rack of the steering column, and along with the fascia
/ controls
4) Improve its overall luggage capacity, by making it into a
hatchback and altering the rear end package.
It must be remembered that
some times projects are started on, even no formal programme budget
has been agreed. This can actually work quite well as it means that
on a ‘zero-cost’ bases by using scrapped components and with no
design resource it gives the Project Manager and the skilled
fitters the flexibility to change the design as the work
progresses. This work would be carried out in the Flight Shed
Chassis workshop, were a small team who were used to working this
way “in the good old days”.
A decision was made that
the work would be divided into three parallel
activities:-
1) A running vehicle modified to take the hydragas suspension and
‘K’ series engine / 5-speed gearbox
2) A scrap bodyshell
modified at the rear end to demonstrate the improved rear package
and hatchback.
3) Another scrap bodyshell to develop the driver environment, with
a ‘clayed up’ fascia, revised steering column arrangement,
etc.
The above information, along with a brochure and slide show were
used to make a presentation to senior management in October
1992.
Running
Vehicle
It was now time to look at
making a running vehicle, so Tony Spillane used his previous
chassis experience to collect together various drawings and slide
them over each other to develop ideas for the running vehicle. This
allowed the following modifications to be made:-
The hydragas suspension required the geometry of the Rover 100
front suspension, which in turn required the front subframe to hold
it all together. This could be grafted into the Mini as long as it
was narrowed across the car to get back to Mini front track, and
the hydragas units were ‘split’, so that the gas egg was remote.
This allowed the suspension tower of the Rover 100 front subframe
to have a plate welded on, so that it could then bolt up to the
Mini bodyshell using the standard Mini ‘big bolt’ that goes through
the body cross beam into the subframe tower. The front cross beam
of the Rover 100 subframe also had to be replaced to stop it
appearing in fresh air in front of the Mini’s front
bumper!
It was relatively easy,
using prototype dismantlable hydragas units to fit the ‘displacer’
part in the subframe tower, and the ‘gas egg’ in the front wing,
using the redundant damper top mounts. Finally, the modified front
subframe was dangled into position, and ‘persuaded’ to fit by
attention to the bulkhead, inner wings, etc, as well as shortening
a Rover 100 steering rack to fit.
The big issue now was that the subframe was around four inches too
narrow to take the ‘K’ series engine and gearbox. However, on the
‘K’ series engine each cylinder is around four inches, so the
obvious thing was to make a three cylinder version! No problem, as
a three cylinder engine cylinder head was available, from the KV6
engine. The crankcase was made by chopping down a four cylinder
casting pattern to cast a three cylinder crankcase, that could then
have each end machined as normal. This allowed us to complete the
powertrain installation, and it all went in perfectly, with the
five speed gearbox and front mounted radiator. The only thing we
needed was a proper three cylinder crankshaft, with its 120 degree
crankpin layout. Unfortunately, this was going to cost
money.
Minki
Suspension
We had proved the front end
layout, but now wanted to drive the vehicle to develop the hydragas
suspension.
Front
Suspension
Rear
Suspension
We had converted the
standard Mini rear suspension and subframe to take a hydragas unit
very easily. There was nothing for it but to re-install the good
old ‘A’ series engine and underslung gearbox to get it all mobile.
This meant new engine mounts to get back to the Rover 100 subframe.
We did look at whether we could have used the Maestro ‘A’ series
engine and end-on gearbox, but it was too tight – the ‘A’ four
cylinder engine was roughly equivalent to a ‘K’ three and a half
cylinder engine in length!
'A' Series
Power Unit
Once the vehicle was
running, it soon became apparent that the ride was awful! This was
found to be due to the short connecting pipe from the displacer to
the gas egg, that was too restrictive. A larger smoother flow pipe
solved the problem.
Some ride development work
was done, including the fitting of old hydrolastic rear helper
springs to get the necessary preloads into the system. This was
overseen by engineer Spike Hawthorn, who loved to create pages of
mathematical formulae. However, some numbers would always drop out
at the end, and when the suspension parameters were set up to
Spike’s predictions, we got a tremendous vehicle ‘straight out of
the box’! The vehicle exhibited a much better ride than standard,
whilst retaining its ‘Mini-ness’ to drive, and was assessed by many
Rover Group engineers, managers and directors.
The Rear
Package
Some
sketches soon showed that a traditional one-piece full length
hatchback on a Mini didn’t look right, and got in the way when
trying to load / unload the vehicle. A split tailgate, like the
Austin A40 (and subsequently copied on the Range-Rover) suited much
better. This was mocked up on a scrap bodyshell in the Tinsmiths
department at Canley. Getting a suitable hinge arrangement for the
upper section was difficult with the roof curvature and drain
channel, as we didn’t want to change the roof panel or
style.
Luggage space was increased
(more than doubled, in fact) by re-sighting the fuel tank into that
‘wasted’ space under the front edge of the rear seat, and by
changing the rear subframe rear crossmember, so that the battery,
spare wheel and whole boot floor could be lowered. We achieved
nearly Rover 100 levels of boot space, amazing in a
Mini!
The rear bulkhead was
removed and replaced by a frame, that allowed for a split folding
rear seat, based on modified Rover 100 components. A very practical
arrangement, particularly as the rear of a standard Mini becomes
almost impenetrable with larger than standard front
seats!
The Drivers
Ergonomics
Here, I was fortunate
enough to have the assistance of Wyn Thomas (interior designer for
Rover 200, Rover 75, etc). A pair of special front seats were made,
using mainly Rover 100 components, and the jointed steering column
was installed, again derived from Rover 100. This gave a much more
normal driving position, but meant that the switches and minor
controls were further away from the driver.
The above components were
fitted into a scrap bodyshell, together with a new instrument pack
(from a Honda Beat, looking more like a motorcycle instrument
pack). A new interior design using Wyn’s sketches translated into a
full-sized clay interior model, constructed inside the scrap
bodyshell. A fiberglass ‘negative’ mould was taken off the clay,
from which a ‘positive’ fiberglass fascia was made. This was
trimmed and installed to give a complete interior
buck.
Clay Stage
1
Clay Stage
2
Clay Stage
3
Final Clay
Stage
Fibre glass
version of the clay
Final Version
Painted
Final
Car
Management
Presentation
A senior management
presentation was set up in the showroom at Canley. Exhibits were
shown, along with a slideshow presentation showing their
construction, the product strategy, test results, etc. Wyn created
some lovely vehicle sketches and cartoons to illustrate the handout
brochure.
The conclusion reached was
that although the technical changes made gave a dramatic
improvement and up-dating the product, it was effectively too late.
The cost of engineering the changes, and the significant
homologation difficulties that would have to be overcome (the
original car pre-date much of this, such as crash testing), was all
too much for the production volumes that Mini could now
achieve.
The Minki-I exhibits were eventually scrapped.
___________________
Minki-II
1995
arrived, and so did BMW! They were surprised that we had such a
strong brand of Mini, but no plans to do anything with it. Plans
for a new Mini were required, and a ‘competition’ was set up, for
later on in 1995, to decide on the route forward.
It was decided that a part of that event should be a vehicle that
represented what current Mini could have become if investment and
development had been put into the Mini over many years. This
vehicle would then act as a better benchmark than a standard
current Mini for judging what the new Mini needed to beat.
Fortunately, all of the old Minki-I stuff had just been scrapped
off, so a Minki-II was hastily required! I say fortunately, because
in comparison, the Minki-II project was a very grand affair! By
this time, our senior management had seen BMW in operation, and
were impressed by the way that they did everything properly, with
very high quality prototype vehicles, excellent engineering, etc.
Minki-II had to live up to this standard. Great! It was a proper
project, with designers and even a few bought-out parts!
I was seconded into Mike Pendry’s Experimental Vehicles dept, who
did the design and build work, under my guidance. We used the
Minki-I learning, together with a re-appraisal of the current
Mini’s strengths and weaknesses.
As before, the engine was
going to be a key issue, as there was not sufficient time (approx
six months) to develop a running three cylinder ‘K’ series engine.
It was decided instead to widen the vehicle just enough to get the
standard ‘K’ series four cylinder engine in. This would also give a
better driving environment, and whilst we were chopping the shell,
we might as well lengthen it slightly as well, as we knew from
Minki-I experience that we were going to end up with the front
seats further back to suit the jointed steering column. It was
important that the car still looked like a Mini, so a painted Mini
bodyshell was sawn down the middle, and the two halves slid apart
the calculated amount necessary to see if it still looked
acceptable. The required extra width was 50mm, and the extra length
was also 50mm. The look was acceptable in width, and also in length
as long as the increase was in the doors.
The vehicle would have to
be driven by the BMW hierarchy, and exhibit excellent levels of
refinement. For this reason, the rear end changes (hatchback) were
not made, as the body stiffness and water sealing issues would be
too risky, anyway we still had the Minki-I
photos.
Much of the Minki-II
followed the Minki-I spec, especially the installation of the Rover
100 hydragas suspension, the ‘K’ series engine and 5 speed gearbox
(although now wider and a four cylinder engine). The Minki-I fascia
unfortunately had gone, and there was not time to recreate it, so a
modified Rover 100 fascia, instrument pack and heater controls were
installed, along with the Rover 100 jointed steering column and
seats.
The bodyshell was expertly
made by the Canley tinsmiths (who ended up as Gaydon tinsmiths,
moving during this time). They used a production Mini bodyshell,
taken off the production line before its roof was fitted (as per
the convertible Mini’s), and “hot cross bunned” (chopped into four
quarters!). New longer sills, cross-members, etc were made up to
get back to one entity. Longer doors were made, wider bonnet and
boot lid, and a special new wider and longer roof. This was made
using an ‘egg crate’, which was a set of wooden formers,
longitudinal and lateral, that gave the curvature of the roof. This
was than opened up 50mm in each direction, blended in, and then
used to mate together four oversized roof quarters into a new roof
panel. The final bodyshell, painted in bright ‘flame red,’ was
immaculate.
Suppliers made up oversized front grille, bumpers, seals and trim
strips, glass panels, window winder mechanisms, etc. The fascia was
cut and modified in-house, as was a new wiring loom. New inlet and
exhaust manifolds were fabricated, this was needed as the engine
had to be re-orientated, as normally the ‘K’ series engine leans
forward by 15 degrees, in the Minki it had to be upright. This
required new bolting arrangement at the bell-housing, also changes
to the bulkhead cross-member to clear the new inlet manifold. It
was for this reason that we chose to use the (then) top of the
range ‘K’ series engine – the 1.4 litre MPi engine, on the basis
that we wanted to start off with as much power as possible as we
feared the new tighter packaged manifold system would lose some
power (in the end, it didn’t), and also the power would be useful
to fully exploit the new chassis. The alternator had to be
re-sighted to clear the suspension tower, and the brake servo
system ‘reversed’, so that it could be mounted on the left hand
side under the bonnet. The distributor had to be driven by the
front camshaft, rather than the rear camshaft.
The vehicle was running a few weeks prior to the big ‘Mini Event’
run by Dr Reitzle, the BMW board member responsible for all product
engineering, taking over the Gaydon Heritage Musuem,. It was
arranged for Dr Reitzle to have a test drive of the Minki-II prior
to the Mini Event at Gaydon. He was very complimentary of the
vehicle, and the work that had been put in to achieving
it.
The Mini Event at
Gaydon
18th October 1995
At
this very significant event, there were many exhibits and
presentations. From the UK, there was the Minki-II, representing
what the current Mini could have become. There was also the R59,
Rover’s design for the new Mini, which included one with Hydragas
and the other with conventional coil springs version. There was
also the ‘Spiritual Mini’, and its bigger brother ‘Spiritual Too’.
Whilst the main exhibits were fairly conventional arrangements,
Spiritual was attempting to recreate the radical step made in 1959,
and make something truly innovative. BMW presented a number of
styling themes, using relatively conventional engineering. Their
dynamic vehicles were based on Fiat Punto running gear.
Alex Moulton made a speech, able as he was to talk from first hand
experience of working with Alec Issigonis on the original Mini, and
the issues that were uppermost at the time.
At the end of the event, Dr Reitzle determined the route for the
new Mini. Whereas Minki-II was too late (it should have been in
production years ago), Spiritual was judged to be too early. BMW
decided it needed something ‘now’, ready prior to the new
millennium. It therefore had to be relatively conventional in
engineering, with a striking but recognizably Mini appearance. It
was to be a development of the BMW style, over the Rover developed
package. Both hydragas and conventional suspensions were to be
pursued in parallel, for around six months as it happens, until a
clear decision could be made.
Minki-II Hydragas
Development.
There
now followed an intense amount of hydragas development, with the
valuable assistance of Phil Turner, who was in charge of the
chassis for MGF and MG TF, to prove whether the dynamics could be
improved to current day standards.
Just like current Mini, hydragas had suffered from no real
development for years, and was beginning to show its age. BMW had a
poor perception of hydragas, mainly through their perception of
Rover 100, which for them seemed biased towards ride rather than
handling. As the interface to BMW on Chassis Concepts, it was my
job to show whether hydragas could compare favorably with
conventional spring / damper systems. This was done using
measurements of ‘vertical dynamics’, ie measuring the stiffness and
damping versus frequency for the complete vertical control
system.
Alex Moulton organized many meetings at Dunlop, Coventry, where we
all got together to discuss our findings, and decide on the next
course of action. Dunlop measured the systems on their
electro-hydraulic test rigs, BMW supplied samples of their current
3-series front suspension struts for comparison, we provided Rover
200 front struts, and through Alex we got new prototype hydragas
parts made.
From these results we found that the BMW struts were not as good as
they claimed, with much more frequency dependence of the out of
phase damping component than they expected, whilst the hydragas
units had insufficient low speed damping.
So from the technical data
from the rig testing, a number of changes to the hydragas unit were
made, which turned out to give dramatic improvements:-
1) Kevlar diaphragm. This gave a large increase in hydraulic bulk
stiffness (ie, stopped it ‘ballooning’ under pressure) as well as a
massive reduction in flexural stiffness (ie less hysteresis under
suspension movement)
2) Disc type damper valve.
This replaced the old fashioned petal valves, and resulted in
better damper control
3) Damper pack decoupler.
With the greater diaphragm effectiveness, and the better damper
pack, there was now too much high frequency damping. A conventional
system uses rubber mounts at the end of the damper to give some
high frequency small amplitude isolation. There now needed to be a
similar feature in the hydragas unit. This was achieved by
internally mounting the damper pack via rubber ‘O’ rings, with a
carefully controlled pre-load.
4) Larger bore front to rear interconnection pipes, to allow
greater peak flow requirements, but with a blow-off valve, to
control low frequency vehicle pitch.
5) As with Minki-I, a good large bore pipe was required from
displacer to front gas egg, as this has to cope with full
suspension flow requirements.
6) Adjustable gas sphere
pressures, system pressures, damper pack shimming and displacer
pushrod lengths all allowed ‘system
tuning’.
Many permutations were
tested, both on rig-test and on the Minki-II vehicle. By this
stage, we had got to a good stage of vehicle development, and
needed to make a more extensive appraisal of the vehicle.
With BMW’s assistance, we took Minki-II down to the BMW test track
at Miramas, southern France, and then on to Munich. In Miramas, we
inadvertently got caught up with Reitzle and his first line
assessing all the new BMW products, as they do each year with a
string of armed guards on motorbikes. Fortunately, they soon
realized that we were ‘the mad Englishmen’, and waved us out of
their way.
Next, it was up to Munich, skirting around Switzerland. Being able
to cruise at 100mph on the autobahns, without using full throttle,
and still being able to speak easily was a unique experience in a
Mini, as was the surprised looks on the Porsche
drivers!
We
drove the Minki-II into the BMW engineering Fiz building, where it
was kitted out with a radio communication system. Then off to the
local BMW test track with the BMW chassis engineers, for some
handling assessments and violent lane-change manoeuvres. Most of
the BMW engineers admitted it was hard for them to assess such a
vehicle, as they were so tuned into BMW brand values and sizes of
vehicles, and ‘Mini-ness’ was something alien to them!
Next day, we went on the autobahns out towards the Czech border,
and used some of the quiet local roads there to make assessments.
However, all the German roads are so smooth and well maintained
compared to UK roads, and generally built with constant radius
bends. They were in for a shock with the UK roads!
Next stage was to assess Minki-II, and a number of other Minis,
back in the UK. A number of the BMW engineers joined us for a trip
to Wales. Here, the Minis were even more in their environment, with
the roller-coaster roads twisting and winding all the way. The BMW
chassis development engineer rather disparagingly dismissed them as
‘Mickey Mouse roads’, but then started to understand why the cars
were as they were. (He subsequently brought his family across for a
holiday in Wales, as did other BMW engineers!).
I think it’s fair to say that the general conclusion of all of this
vehicle assessment work was that the Minki-II was a more ‘grown-up’
Mini, in every sense of the word. There was more space inside the
car, the driving position was more accommodating and comfortable,
the car had much better performance and refinement, the ride was
much more accomplished, mainly because it had got rid of those
sudden vertical jolts of the standard Mini. The car was able to
steer and handle without drama at higher speeds than a standard
Mini, and yet overall still having a very clear ‘immediacy of
response’ that characterizes Mini driving.
Eventually a decision had to be made as to whether the new Mini was
going to use hydragas or conventional suspension. The BMW chassis
guys were appreciative of the developments we had made, but gently
allowed us to come to the realization that the durability proving
and productionisation of the new hydragas developments would take
it beyond the timescale of the vehicle programme.
The Minki-II vehicle then earned a well-deserved rest, going on
display in the Heritage Museum at Gaydon, and the hydragas
developments we had made looked for a new potential
application.
THE END
My
thanks to
Tony Spillane for supplying all the information and
pictures.