How did early Automatic gear boxes on cars work?

Hardly a "rubber band". More like a heavy duty V belt.

I owned a modern Audi with a CVT (constantly variable transmission) auto gearbox, which used two hydraulically variable cone pulleys and a belt, and it was really good, although it required a different driving technique: Instead of setting an engine power with the throttle, you used the throttle to set a speed and the gearbox adjusted its ratio according to the road gradient to produce that speed. This was counter-intuitive to many drivers, but as an Airbus pilot, I was open to this type of automation, and got on with it very well.

Actually, the Daf had two V belts, one to each half of the rear axle, and this meant they relied on the two belts settling into the pulleys* more, or less, on corners, and so there was no need for a differential. Very nearly a good idea.

* pulleys with flanges that could move in or out, so altering the ratios and making proper gears unnecessary.

And while I am writing, remember the effect on driving, and engine design, resulting from crash geaboxes. It meant that anyone even slightly timid or nervous was discouraged from driving or owning a car, and designers relied on very flexible (but less efficient) engines to avoid gear changes wherever possible. It even affected motorcycles, with Brough Superior advertising '8 to 80 in top gear'.

Cheers, Tim

Edited By Tim Stevens on 07/06/2023 10:31:09

The post WW2 automatics were basically epicyclics where which brake band was operative was controlled by the manifold vacuum. hence the vacuum capsule. Road speed was sensed from the pressure produced by an oil pump within the transmission, and driven by the output shaft.

The Borg Warner 35 was relatively unsohisticated and in some applications could produce quite a rough ride!

Renauklt sophisticated this in the 70s, using electrical sensing of road speed and load by using a small generator, where the output was moderated by shading between stator and rotor, to snse throttle poisition (implying load )

A torque convertor was a development of the fluid dlywheel, wher a set of intermediate vanes produced torque multiplication.

Matching a torque convertor to a particular engine and installation could be quite a task. At Rolls - Royce, both the car and oil engine divisions employed specialists to calculate the best match. O E D used Twin Disc transmissions, made under licence at Crewe.

A torque convertor required fewer gear ratios. than a fluid flywheel, because it already provided torque multiplication

Unsynchronised gear boxes were used in commercial vehicles until the late 60s, although semi automatic transmissions were available. The Leyland "Moncontrol" was direct air control of the brake bands rather than the electromechanical system where the the tiny gear lever controlled solenoid valves which fed air to the approriate air cylinder to apply or release the required brake band.

The London Transport Routemaster used a more sophisticated electcal contol of the gear box, supercediung the fluid flywheel and epicyclic box prviously used on the RT and RTLs.

An unsynchromised box provided a lighter gear change than a synchromesh box, even if you double declutched any way!

Used cortrectly, a cluch brake (Clutch stop ) upward chnages could be made as fast as or faster than a syncromesh box!

Relaints used unsynchronished boxes into the 50s and 60s.

As Peugeot said of the unsynchronised gear box "C'est brusque; mais sa marche"!

Howard

In the late sixties my flat mate had a French car, I believe a Renault, which had an electrically operated automatic transmission. I believe it had a magnet particle clutch and a normal type gearbox but operated sequentially, up or down like a motorcycle gearbox, by electrical actuators.

I didn't take that much notice of it as it was a car and I was only interested in motorcycles.

I only had one ride in it as a passenger and it seemed to drive like a normal car. When stationary one would put it in drive and press the accelerator pedal and off you would go. At an appropriate speed the engine would throttle back slightly, irrespective of the accelerator pedal position, and the next gear would be engaged with the same sort of timings if done manually. If you took you foot off the accelerator pedal the car would slow and change down and I believe there was a link from the brake pedal to disengage the clutch to bring the car to a complete stop.

He did demonstrate that it could get confused sometimes if the accelerator was too on/off but otherwise it was reasonably reliable but I don't think he kept it long.

CS

Bruce,

Oh yes it was it was there to sense the reduced vacuum caused by the driver putting their foot down and would let the motor suck ATF if the diaphragm split.

Oddly the Ford cruise-o-matic box normally only used 2nd and top, 1st was only engaged when you flood the loud pedal.

While a student I moonlighted at a number of small backstreet garages, including one where the TV and electronics engineer partner (don't ask) also did trade repairs on autoboxes, often BW DG or Model 35 and 13J

His own van was converted to auto with a BW35 but it was fitted with a rear pump in addition to the normal front one which was used by the engine input to pressurise the system so if you rolled it down hill fast enough (30 - 40 mph!!) the rear pump would act in place of the front one and enable the brake bands to operate and the torque convertor would bump start the engine - sometimes! The rear pump was only used on some Triumph and Rover cars and then no for long, but all of the casings could accommodate one if you had one spare lying around.

Another memory is taking the metal plates out of a worn multiplate clutch in a BW box and being warned to take care as they were sharp. Even though not causing a problem the plates had worn down from approx 2mm thick to the point where they would cut a sheet of paper!

Perhaps not as efficient as has already been suggested, but they were incredibly engineered for a mass produced item!

PS:- The AP auto gearbox fitted to the BMC minis an 11/1300s were produced in a factory just round the corner from where I am typing this, on the Pershore Road, Stirchley in Birmingham.

Edited By Nick Clarke 3 on 07/06/2023 15:26:47

The Borg Warner DG (used on older Jaguars) had a rear pump as well. I had a Jaguar Mk10 which needed to be rolling at 25 - 30 mph to engage the gears and allow a bump start - not a procedure for the faint-hearted since with no power assistance the brakes were basically inoperative (not that they were that great even with the engine running).

Iveco fit a thing they call an automated gearbox to some of their smaller lorries - a conventional manual gearbox and clutch, but with various servos to shift the gears and operate the clutch. I think they're absolutely horrible to drive because there's quite a lengthy pause between pressing the accelerator and the gearbox deciding its time to engage a gear and let the clutch in. This is not what you want when trying to pull out into a gap on a busy roundabout.

CVT transmission used by Fiat and others was a development of the DAF system, the belts seemed to last well, or perhaps it was a service item. Father in law had one in a Punto, probably the only thing that didn't give trouble.

"Extremely" is a bit extreme.

My late father (born 1920) used to start in 2nd because he was brought up with limited synchromesh. By the time that he could afford a car, the gearbox probably had it on 3rd and 4th.

I have one car (TR2) with limited synchromesh and a couple of pre-war cars with none. They are not that difficult to drive!

These days they would be considered "impossible" to drive. A policemen told my my car is unlikely to get stolen because the youngsters who do such things do not know how to drive a manual car.

And apparently manual cars are harder to sell secondhand for the same reason. Many youngsters here get their license in an automatic and never get the endorsement now required to drive a manual.

Changing gears? Physical effort? Isn't there an app for that?

For years I recommended anyone learning to drive to learn and pass their test in a manual car because that left all their options open but nowadays it is far less important as the next new car someone drives is likely to be electric or hybrid, both of which count as automatics.

It used to be that, in UK, to pass the PSV or HGV driving test one had to be able to bring the vehicle (With an unsynchronised - "crash" box) to rest usingbthe gears and the handbrake.

A friend had a preserved Austin K2 A T V, which had a knob rather than akey to moperate the ignition switch,

The gearbox was unsynchronised, and rather like the Bedford O lorries and OB buses and coaches made lovely "vintage" noises . The gear change was light, BUT you HAD to get nthe rvs right, or else the whole world knew about it.

He used yo leave it boutside his house, saying if anyon took it, "They probably wouldn't get past the end of the road, being unable to get into second gear".

With such a gearbox and less efficient brakes than today, it certainly taught you to look ahead and anticipate!

On the Bristol buses (LDs and FLFs )used by Brighton Hove and District, with a skilled driver, and a properly adjusted clutch stop, upward changes could be made quickewr than on a syncromesh box.

On the Southdown Bristol REs,with the manual box, the synchro on second was so poor, almost non existent, and there was none on fifth gear, so safest was to double declutch every gearchange.

A "crash" box was usually lighter and sometimes quicker than oine with balky synchromesh.

If the clutch operating system failed, (Fluid leak or broken cable ) by driving as if unsynchronised, it was possible to drive. (onbce across town in the evening rush hour, and once the 55 miles to home.

Our daughter brought her car home to Peterborouygh from the Hague when the clutch cable broke!

On vehicles with heavy clutches, such as the Scammel Pioneer, it was quite usual only to use the clutch when starting or stopping.

Howard

I had a Fiat500 old model with constant mesh, at least on some of the gears. I learned to double declutch quite quickly after a while found that I was depressing the clutch less and less so decided to stop using it except when starting off as an experiment, it worked very well. But it was a horrible car, shed all the teeth on the sprocket driving the camshaft after not many miles, apparently a standard fault.

During my time in the Air Force at one station I used to drive an ancient Bedford Tanker which was filled with hot de icing fluid which we used for hot de icing of large transport aircraft. The tanker was quite large and I am sure that there was no syncro in the gearbox but the worst aspect of driving it was that it did not have power steering, it was a real brute to manoeuvre round corners with god knows how many thousand gallons on board in the tank, driving it was better than a workout in the gym. Dave W

I have a 1979 Ford F100 truck with a 302cu in v8. It has an autobox as they were cheaper to produce than a manual box that would take the power of the engine.

Modern CVT 'boxes use metallic link belts not an elastomeric ones like the old DAF 33. My Outlander plug-in hybrid has one CVT 'box plus two motors and a generator. It can run pure electric on one or two motors, IC only, IC + 1 motor in parallel, IC + one or two motors in series / parallel. The software tries to keep the IC engine on a optimum operating point and changes mode automatically depending on demand and battery state of charge.

Robert.

When I was a development engineer on hydraulic auto gearboxes, the two significant problems were starting from rest, and getting a smooth gear change without flare or tying up (for all oil temperatures and throttle openings). The first was typically solved with torque converter, maybe also fitted with lock-up clutch for the last 5-7% of slip. The latter was addressed by ever more complex valve blocks, but by the early 80's we saw the early use of electronic position control for a manual type clutch, and electronic maps to account for the shift variables.

Our prototype DSG on a Ford Fiesta never reached production, but VW did make a big success of it a few years later.

I have a modern hydraulic 8 speed auto, and am very impressed with the shift quality under all conditions. It's very difficult to catch out the logic, and the packaging is very impressive.

It certainly is very impressive. And with electronic control, they have solved the clutch activation - my Audi DSG gearbox feels as it if had a fluid torque convertor, (without the losses), but it has two conventional friction clutches, actuated automatically by servos. They have got the logic of the clutch engagement just right, and pulling away from rest is absolutely smooth and seamless. Very clever.

All this and 7 gears + reverse in a front wheel drive gearbox housing

Edited By John Doe 2 on 09/06/2023 10:05:37

The beauty of DSG is(was) that 95% of the gearbox is identical to a manual. All that is needed is a quill shaft through the mainshaft cluster and a small wet clutch at the opposite end to the main clutch. So it fitted in the same space as a manual and coukd have the same number of ratios, but of course manuals are no longer required by most users.

DSG itself is a very old idea -used by Citroen and others more than 100 years ago. It can give a power on shift - very useful for tractors

Edited By john halfpenny on 09/06/2023 11:13:33

Though manuals are in decline, they're still the most popular single type of transmission as this graph from Statista shows:

Quite interesting to see what manual gearboxes are losing out to - it's not plain automatics, sales of which are also dropping. Winners: AMT, rare but growing slowly; with CVT and DCT both big players.

There's a mystery! The graph shows the fastest growing transmission type is 'others', predicted to have 9% of market share by 2025. I guess these could be the incoming electric transmission systems, does anyone know? Or are there other types, perhaps driving hydraulic motors on each wheel?

Dave