On 29 January 1975, Associated Engineering Ltd of Leamington Spa was granted a UK Patent for a revolutionary means of controlling automatic gearboxes. The two inventors cited in the patent were Norman Hunt and John Noddings, both employed by the company.
Why are we posting this News item now, over 50 years later? Because, despite the dramatic improvement made by this invention upon the ease and effectiveness of controlling automatic gearboxes, it has, until now, received virtually no publicity. That omission needs to be corrected. There is ample, solid evidence that this invention is now used in virtually every automatic gearbox in the world.
In the words of Norman Hunt, only a few weeks ago:
“The system described in UK patent 1382331 was a world-first British achievement, back in 1972 (before the abbreviation PWM was in common use), with fully working applications on both a VW Golf (1972) and a BMW 3.0S (1973), and I do find it disappointing that it is has not been recognised anywhere as such.”
What is so special about PWM? To quote from an article in Autocar in August 1973:
“NEW TRANSMISSION
“ASSOCIATED Engineering Developments Ltd. at Rugby have come up with a new automatic transmission which is exciting a great deal of interest in the industry. Already Volkswagen have been granted an option to license the new transmission for their cars. BMW are also interested and have a 3.0S saloon fitted with the transmission on test at this time.
“Basically, the AED scheme replaces the familiar but complex hydraulic labyrinth of oilways and valves in the traditional transmission with an electronic package and simple valves. It requires no mechanical governor nor does it need throttle linkage inputs as these are fed in electronically. The selector is no longer linked mechanically to the box, so the transmission control can be placed wherever the designer wishes inside the car. Failsafe facilities including electronic interlocks to prevent changes at excessive speeds are built in. They fail to top gear in the event of electrical faults. This means the electronic control can be unplugged if it malfunctions and the car can be driven home in top gear. A conventional car with a major fault is normally immobilized. The electronic brain controlling the transmission also makes it easy to provide a means of rapid diagnostic testing for the complete installation, thus reducing servicing costs.”
On 25 July 1973, the Financial Times told the same story but went a little further:
“Electronic gear change system
“Advanced design features of Associated Engineering Development’s electronically controlled automatic transmission for cars are arousing considerable interest, particularly in Germany.
“An option to Volkswagen to license the new transmission control system for cars covers a specific test programme under which the suitability of the electronic control equipment for use in Volkswagen vehicles will be examined.
“BMW is also evaluating one of its 3.0S saloons that has been modified at AED’s centre at Cawston, Warwicks, to accept this new form of control.
“Considerable development has gone into the system which replaces the complex hydraulic labyrinth of oilways and valves with an electronic package and simple hydraulic valves. It requires no mechanical governor or throttle linkage inputs as these are derived electronically to save space and weight.
“It is extremely flexible in terms of the gear change programs available to the user and the quality of the change is optimised at all times by precise control of the main hydraulic feed pressure within the gearbox. This technique eliminates “hard” gear shifts and engine speed run-up during shifts, so prolonging the normal life of gearbox components.
“Modular “plug-in” interchangeable cards will satisfy all foreseeable customer or vehicle requirements. They also provide a means of rapid diagnostic testing for the complete installation, thus reducing servicing costs.
“The electronic package can be easily produced by large scale integrated circuit methods for high-volume, low-cost assembly.
“Mechanical coupling of the transmission selector lever to the gearbox is no longer necessary, since transmission mode selection is initiated entirely by electrical switching. This feature makes the new system very attractive to the car interior designer, insofar as transmission selection can be of conventional “T” bar form or, more conveniently, consist of a row of illuminated push-buttons, TV type “touch-plates” or even a single rotary switch. The location of this control does not have to be on the steering column or transmission tunnel. It can be situated anywhere within easy reach of the driver to give effortless, ergonomic selection.
“Several fail-safe facilities are incorporated, including electronic interlocks to prevent forced changes at excessive speed. They fail to top gear in the event of electrical faults. This means in practice, in the unlikely event of the electronic package malfunctioning, it can simply be unplugged, thus permitting the vehicle to be safely driven home in top gear, whereas a major fault condition on a conventional automatic normally immobilises the vehicle until it has been rectified by a specialist service engineer.”
What is Pulse-Width Modulation?
Norman Hunt is no longer a young man, but the mark of a truly gifted engineer is that he keeps up with the latest technology at any age. Norman has sent us an AI-generated analysis, which does explain very well what is going on. We publish here some key extracts:
“A full review of UK Patent 1,382,331, filed by Norman Hunt and John Noddings in January 1972, describes a system that varies the width of pulses at a constant frequency to control solenoids, which then operate spool valves. This is the very definition of Pulse-Width Modulation (PWM) technology, even though the patent does not use the specific term “PWM”.
“The patent details how the spool valves, controlled by the solenoids, can adjust the flow and pressure of the transmission fluid. This variable control over the fluid pressure is what allows for the precise regulation of shift quality, making shifts smoother or firmer as desired.
“This patent evidence suggests that Norman Hunt and Associated Engineering were indeed pioneers in applying this principle to automatic transmission control in the early 1970s.
“The term “PWM” may not have been standardised in this specific application at the time, but the described mechanism of controlling valve movement by varying pulse width at a constant frequency is functionally identical to modern PWM systems.
“While this patent represents an early invention, the widespread commercial adoption of electronic transmission controls with PWM solenoids for regulating shift pressure did not occur until the 1980s and beyond. The delay between invention and widespread commercial use is common in the automotive industry due to technological, manufacturing, and cost factors.”
Figure 1 – Pictures showing the valve block, PWM traces and BMW
3.0S assessment vehicle.
Figure 2 – Volkswagen Golf gearbox with
AED valve block installed
We hope that our publication of this story will enable future internet researchers to find the true origin of this vital automotive invention: the two engineers Norman Hunt and John Noddings.
A masterfully encompassed article.Many thanks.