'Easidrive' was an automatic transmission system designed by Smiths, and available as an option on the Series IIIA, Series IIIB and Series IIIC Minx saloon, convertible and estate.
It was received with some enthusiasm by the motoring press. For example, Autocar, September 4th, 1959 began their review of the Series IIIA thus:
"First British production car in the 1 1/2 litre range to have fully automatic transmission is the Hillman Minx Series IIIA. This is a development long awaited by motorists all over the world, and the distinction of achieving it is a matter for congratulation to both the Rootes Group and to Smiths Motor Accessories."
and Country Life, December 31st, 1959, added:
"One advantage of two-pedal control that was immediately apparant on starting to drive is the greater amount of room available for the driver's feet around the pedals, and the greater amount of space provided between the accelerator and the extra-wide brake pedal. The car moves away from rest remarkably smoothly, once one has become accustomed to some free movement on the accelerator pedal. There is no appreciable difference between the acceleration of the version fitted with Easydrive and that with a normal gearbox, if both examples are driven to the limit by an experienced driver, but most drivers will find the acceleration better and more effortless with Easydrive."
Full details of the construction and operation of the Easidrive unit were explained to its readers by Autocar:
"Basic operating principle depends on the use of magnetic powder couplings. In these, driving and driven members are separated by a small air gap partly filled with small particles of ferrous metal. Creation of a magnetic field in these particles causes them to offer frictional resistance to relative movement between the separate members, this resistance increasing with the strength of the field until the coupling becomes virtually solid.
"'Easidrive' has two features in common with other forms of automatic transmission. The normal precaution is taken of wiring the starter circuit so that the engine will start only when neutral is engaged; and the driver has a certain amount of overall control in that changes are not only dependant on road speed but on throttle opening also.
"Seven main units comprise the complete transmission. First there is the coupling unit driven by the crankshaft, next a three-speed and reverse gearbox of the counter shaft type, and thirdly an intermediate gear shift solenoid. Beneath the bonnet are a governor which controls the engagement of each forward speed and which is cable-driven from the back of the gearbox; a throttle solenoid which speeds up the engine when intermediate is engaged from drive; a selector switch connected to the lever on the steering column; and finally a control unit containing eight relays, a thermal switch, a rectifier and resistances used in the control circuit.
"Connections between the various units are made by a wiring harness which is completely separate from that of the car lighting circuit. Multi-pin plug connectors are used except for the intermediate gear solenoid, which has a larger capacity cable and bolt-on terminals.
"Overall the transmission unit occupies little more space than the conventional clutch and four-speed gearbox. A standard length propellor-shaft connects the gearbox to the differential. The alloy casing containing the stator and magnetic couplings is slightly longer than the usual clutch bell housing, but foot room for occupants of the front seat is not impaired.
"Power is transmitted from the engine to the gearbox by two separate magnetic couplings. A stationary field piece contains the two energizing coils and this is spigoted and bolted to the alloy bell housing. Secured to the crankshaft flange is a flexible steel plate which eliminates the effects of any minor misalignment between engine and gearbox. A spigot ring, carrying a toothed starter ring, is bolted to the steel plate and the same bolts carry the rotataing intermediate field piece. This is supported at each end of its inner diameter by a ball bearing. There is a small air gap between the stationary and rotating field pieces.
"Splined on the front end of the main shaft is the direct drive coupling, or driven member. Behind it, and housed in a separate compartment is the rear driven member. This drives through a countershaft the intermediate and low gears. Each driven member contains a series of short, strong coil-springs, resembling those of the centre plate of a conventional friction clutch, to provide a cushion drive.
"In each driven member compartment there is a small quantity - approximately an egg-cup full - of chrome iron magnetic powder which, as soon as the engine is running, fills the space between the periphery of each driven member and the rotating field-piece. Baffles formed by pressed steel rings prevent any powder from reaching the sealed bearings in the centre of the unit. The surfaces of the driven members and the rotating field-pieces, which are all turned from carbon steel, are chrome plated.
"Starting from rest with the selector lever in Drive, the action of depressing the accelerator pedal energizes the rear coupling to drive first gear through the low gear train and a roller type free wheel. An arrangement is made whereby the current build-up in the coil is gradual and therefore the coupling drive does not become solid until the engine speed reaches approximately 1800 rpm. This obviates any possibility of a laden car stalling when starting on a gradient.
"As soon as road speed and load conditions determine, a signal is passed by the governor to the control unit, and a solenoid is energized to engage second gear by means of a dog clutch. In order that the dog clutch may engage freely, synchronization is achieved by means of the control unit and the operation of a baulk ring mechanism which is carried on a spigot forming part of the intermediate gear. The free wheel allows first gear to be overrun when second is engaged.
"As the road speed builds up, a signal is again passed by the governor through the control unit; the rear coupling and solenoid are de-energized, a withdrawal spring disengages the dog clutch, the front coupling is disengaged and there is direct drive through the mainshaft.
"Extra acceleration can be obtained in 'Drive' by means of 'kickdown' when either top or intermediate are engaged, and providing the speed in these ratios does not exceed 40 or 18 mph respectively. With the control lever in the 'Hold Second' position a maximum speed of 50 mph is available, together with engine braking for descending steep hills or driving on ice-bound roads. A throttle solenoid ensures that the correct engine speed is obtained when the selctor lever is moved from 'D' to '2'.
"As it is not possible for the mechanism to engage low gear with '2' selected, all restarts should be made with the lever in 'Drive' position. Reverse gear is engaged by moving the selector lever into the indicated position, and the car must be stationary when this is done. The action of moving the lever into reverse also selects the rear magnetic coupling to complete the drive, when the throttle is opened, through the countershaft and reverse gear train.
In emergencies, providing there is sufficient power in the battery (or passing through it) to operate the ignition system, the transmission will function. If the generator or any of the control units are suspect, the system may be by-passed by reversing one of the multi-pin connectors on the selector switch. When its position is changed, the magnetic couplings are operated direct from the batttery."
As a final word on the subject, though, in 1959 The Motor had this to say:
"It is easy when describing a complicated mechanism to give a false impression that complicated tactics are needed to control it, which is the opposite of the truth. For nine people out of ten 'Drive' is the only position of the lever which will be used for everyday journeys, and apart from a slowish change up from the bottom gear the workings of the transmission will be ignored."
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