The Thomas Transmission System.
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For the past three or four years, J. U. 1:". Thomas has been developing his interesting petrol-electrical transmission system,and, during that time, he has accumulated a
vast amount of experience with the system as applied to the Leyland four-tonner, which we described in our issue of 17th June, 19C9. That vehicle has been in experimental service for over two years, and for a period of four months it was operated as a motorbus at Bournemouth, The same vehicle, with an improved electrical equipment, commenced a 2,000 miles test under A.A.C. observation on Monday, the 24th ult., the test taking place be • tween Bromley Common and Crowborough, between which two places the vehicle was to continue to run, to and fro, night and day, until the 2,000 miles were completed. So far as we are aware, the teial progressed without mechanical or electrical trouble. The vehicle was delayed one night for about five hours, due to the road's giving way and letting one of the back wheels into the ditch. It is expected that the rate of petrol consumption will prove to be extremely low, but we cannot, of course, divulge any figures yet awhile. All who are interested, however, may rely upon our giving the official figures at an early date.
The accompanying diagram will assist our readers to understand the functions of the various parts of this interesting system. It consists of : two electrical machines (B2 and 02), which may be run either as dynamos or as motors ; two positive couplings (133 and 03) ; and a drum (A), which forms the flywheel that encloses a simple epicyclic gear. There are thus two methods of driving flie ear in a forward direction : (1) partly electrical and partly mechanical ; and (2) entirely mechanical by direct drive. Commencing with the epicyclic gear, it should he noted that the planetary pinions P P and P1 P1) are carried by the ill 'ME (A). The sun pinion B is permanently fixed to one end of the shaft 131, whilst, to the other end the armature of the dynamotor B2 is coupled. Riding freely on the shaft IL is a sleeve (01) on one end of which the armature of the elecHeal machine 02 is permanently
taehed, and fixed on its other end
is sun pinion C. The two electrical machines are cennectoel in series. Commencing with the controlling lever in neutral position, the engine may be started and the vehicle brought up to its top gear as follows: the drum (A) is rotated by the engine at constant speed, and, as in neutral position there is no electrical connection between the two dynamotors and the coupling 03 is disconnected, it follows that the sun pinion C and the parts attached to it (Cl and the armature of C2) will be rotated in an anti-clockwise direction, because the sun pinion B will remain stationary, due to the resistance of the rear wheels upon the ground. So long as there is no electrical connection between the two dynamotors, the parts will continue to ran as stated.
When the two dynamotors are connected in series, C2 will act as a
dynamo, and B2 as a motor ; the electrical load which is then thrown upon the dynamo 02 tends to decrease its speed, and, consequently, the speed of the sleeve Cl and the sun pinion C. The current entering the motor 132, however, tends to set up rotary motion in a clockwise direction within that machine, and this motion is transmitted through the shaft 131 to the back axle. The engine power is thus transmitted to the back partly electrically, and partly through the epicyclic gear. As the speed of C2 is gradually decreased, the speed of 132 gradually increases, until C2 and its sun pinion (C) practically come to rest ; in other words, the dynamotor C2 acts as an electric brake upon one. member of the epicyclic gear. When C2 conies to rest, it ceases to act as a dynamo, and B2 as a motor, and their functions become reversed. The current from B2 now drives the armature of 02 in the same direction as theengine, and in this way the speed of the driven
shaft B1 is gradually inci eased until it is equal to that of the drum (A). The coupling C:3 may then be engaged, and the electrical machinery rendered inoperative. A maximum of efficiency is thus obtained for the greater part of the vehicle's running.
For propelling the vehicle in a reverse direction, not very frequently or for any great length of time, the drive is entirely electrical. The dynamotor C2 is caused to act as a dynamo and B2 as a motor, the coupling B3 meanwhile being disconnected.
A small battery of six cells is carried on the machine, and these may be charged from the dynamo ( while the vehicle is running on the level or down hill on direct drive, The current thus stored may used for lighting purposes, or, as the dynamotors are low-voltage machines, current may he fed to 02 from the battery, and, by this means, the engine may be started by the mere turning on of a switch.
Among the advantages claimed for the Thomas system of transmission are the following: (I) a large proportion of the power is transmitted mechanically ; (2) only a small portion of the power is transmitted electrically, and, therefore, the dynamotors may be made very small and relatively inexpensive ; (3) the controller provides for a large number of running speeds, thus allowing the full engine power to be utilized at all times ; (4) there is no break in the transmission during the periods of changing speed ; (5) the rate of acceleration is very hih and perfectly smooth ; (6) the drive on top speed is direct : (7)
there is complete freedom from mechanical noise and shock. In addition, there are the two advantages which we have already named. viz., the sel f-contained lighting set, and a facility for starting the engine.
One of our representatives travelled down to Sevenoaks, on Thursday last, and, after driving out from Tubs Hill Station with Mr. Thomas, in his Thomas-transmission, 12-16 h.p. Delahaye car, to meet the test wagon, joined the latter vehicle just south of Tonbridge, and travelled back upon the wagon as far as Sevenoaks. The climb up River Hill, notwithstanding the heavy nature of the road, owing to recent tarring and heavy showers, was taken at a higher speed than is usually made by vehicles which are fitted with petrol-electric systems. The test-load was of sand, partly in boxes and partly in bags, and. although its original weight was stated to be three tons, it is more than probable that, at the time of our representative's run on the machine, the load was considerably augmented by the absorbnon, by the sand, of a considerable amount of rain water.