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A NEW PETROL-ELECTRIC CHASSIS.

3rd October 1922, Page 10
3rd October 1922
Page 10
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Page 10, 3rd October 1922 — A NEW PETROL-ELECTRIC CHASSIS.
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Mr. Percy Frost Smith Produces a New Chassis which Embraces in its Design Many Points Making for Safety, Ease of Control and Economy.

THE.ENTRY of Mr. Percy Frost "Smith into the realms of chassis manufacture is a notable . event, because he has devoted his talents, his thoughts, and attentions. for the past 12 years to the perfecting of the petrol-electric vehicle, and since the severance of his connection with Tilling-Stevens, Ltd, of Maidstone, he has worked hard, in association with Mr. Phillip V: Powell, to design and produce a, vehicle of the type which shall possess points of merit 'at every turn, and be free .from the troubles and weaknesses that long experience would lead one

to expect. . Starting afresh, and unfettered by any consideration but the desire to produce a perfect chassis, Mr. Frost Smith and Mr. Powell have paid heed to every criticism that has ever reached their ears in the past, and, aé the use of the chassis for motorbus work is generally in contemplation, Scotland Yard's regulations have been kept in view throughout the Whole period of design and manufacture.

We have had the pleasure of following the Frost Smith design through its various stages, and of inspecting the chassis now in course of construction, and have been impressed with the general excellence of the design and workmanship. The main points aimed at by the designer are safety, economy, and perfect control, and with the new combination control gear, which is the subject of. letters patent, these aims should he attained, for the control of a petrol-electric vehicl,c is something that

has to be observed to be appreciated. There are no gear changes to miss and no gears to be stripped. Economy can be obtained, on various counts, not the least in brake maintenance, whilst the electric braking system tends to the perfection of safety in all circumstances.

We propose only briefly to go over the details of the chassis, and the first good feature that catches the eye is the depth of the frame members. These are of pressed steel, tapering towards both ends,

from ins.—the greatest depth which extends for about 6 ft. in the centre portion of the members. The chassis can be as long as 25 ft. 6 ins. overall On a 15-ft. 6-in, wheelbase, but in the case of buses that have to pass Scotland Yard this length will be slightly reduced. The frame is amply stiffened, by cross-members, tubular or pressed steel. To give a few further important dimensions the frame width is 3 ft. 243ins, the wheel track of the rear *heels (centre to. centre oftyres) is 6 ft. SI ins., and of the front wheels 6 ft., whilst the width over rear-axle caps is 7 ft... 1/ ins. The rear springs are 5 ft. long, made up of 11 leaves, each :31ins, wide, the top leaf being I in. thick ; the front springs are 3 ft. 6 ins. long, made up of nine leaves, each 2i ins, wide, the top leaf being in. thick. The wheels are of equal size all round. being shod with single tyres on the front and twin tyres on the rear, of 1,030 TM, diameter by 120 mm. in section, fitting on to 881 mm. rims.

. The engine is a 45 h.p. White and Poppe foureylindered, with the cylinders cast In pairs, cylin der dimensiens being 115 mm. bore and 150 mm. stroke. It has a Scintilla magneto and a Solex carburetter, the former being a particularly interesting component because of its Simplicity and superiority. In turning a magneto shaft by hand we could detect Very little magnetic drag on the armature.

The drive is taken to the dynamo through a threepoint: spring coupling.. On the flywheel rim are fixed, at equal distance, three pins, on each of which is carried a roller, which is embraced by the loop of a spring blade, the blade being disposed tangentially, and its inner end being hookedinto a recess in the boss of the flywheel, to which it. is secured by setscrews, the latter, however, not taking any Part of the load. This coupling gives a flexible drive, and effectively damps down periodic vibrations. The electrical equipment consists of a dYnamo, a motor and the electrical control gear. The dynamo is coupled to the engine and the motor to the forward end of the propeller shaft. The dynamo is ef the shunt, conwound, inter-polar type, the compound winding being introduced on two poles only, which is rather a departure from general practice, making for safety and a greater air space between the winding of the dynamo and the casing, thus tending to greater efficiency because of the greater cooling.

The brush gear is of standard practice, although it has been specially designed for petrol-electric vehicle work. The machine is cooled by an internal fan.

The motor is of the series wound, inter-polar type, the inter-poles being strip wound (the same may be said of the dynamo winding). The armature conductors are fastened to the commutator by the closedlug system, -which makes for greater reliability.

Special attention has been paid to every point in connection withboth the dynamo and the motor, where wide experience has shown that there is a need to avoid liability to weakness. The dynamo and the motor are each supported direct from the main frame by means of two cast-steel boxes, to each of which the unit is keyed by a steel key ; thus,the bolts holding the dynamo and the motor do not have to carry the weight of either component. On removing the bolts and the keys, the dynamo–,-or the motor, as the ease may be—can be dropped down clear of the chassis. This ease of removing the unit is a great point in the matter of economical maintenance. .

The drive is taken from the -motor through a propeller shaft of 2 ins. diameter and made of 60-ton steel, splined at each end with 12 equidistant splines, the end nearest the motor being. free to slide on the splining. There is a universal Joint at each end of the propeller shaft, and these joints have been sped

ally designed, the trunnion centres being kept extremely short.

The back axle is a Kirkstall steel forging, with the .spring and brake brackets dogged and shrunk into position.

David Brown and Sons, Ltd., of Huddersfield, have, at Mr. Frost Smith's instructions, designed and manufactured the back axle (except the casing), .propeller shaft, universal joints and steering eoluinn.

The two expanding brakes work -on independent drums,. the brake shoes being lined with Ferodo and being interchangeable. This makes for economy in the number of spare parts that have to be stocked. The brake-operating gear, both in the case of the hand brake and the foot brake, is adjustable by means of brass hand wheels placed on the outside of the frame.

The rear wheels both run in floating bushes on hardened and ground steel sleeves, so that no wear is able to fall upon the axle easing. The wheels are of cast-steel, each having six spokes branching out into a Y shape at the rims, and eac,h spolt being cruciform in section ; thus, the whole wheel is amply webbed and flanged, and looks to be extremely strong and yet light.

The steering column is designed so that it can be mounted on the outside of the frame, and therefore can be placed right forward just behind the radiator, or in the normal position just behind the level of the dashboard. In the chassis which we inspected the steering column is in the latter position.

The patented form of control gear is a combination of four elements contained in a box which is bolted to the dashboard slightly to the left of the line of the steering column and immediately in front of the driver. It gives in its combination the four positions : " forwards," " neutral," " electric brake," and "reverse," operated directly without the needfor any intermediate rods.

The hand lever is immediately to the hand of the driver, and the indicator plate, just below it, is right under his view. This , unit is extremely light in weight as compared with earlier types of controllers, and the introduction of the electric brake is an extremely good feature, because the brake can be applied when the vehiele is travelling at its maximum speed, and yet give a. very smooth and gradual retardation entirely at the will of the driver. The brake has been tried and proved on some of the worst

hills in Scotland and in North and South Devonshire, by Pick-fords, Ltd., or their motor coaches, and has been found to be most-effective. Of course, it is not intended to be used for constant traffic work, because its action would probably not be so quick as that of a mechanically operated foot brake. The braking effect is regenerative from the motor, and has no connection with the dynamo. The use of this brake means a very great saving in the wear of the brake linings acting on. the drums of the rear wheels.

A further point of interest about the control gear is that a magnetic. stop has been introduced providing a positive means of preventing the driver moving from a forward position into a reverse position, or vice versa, while the current is flowing through the circuit.

By means of a new combination cut-out and pole changer, which has been patented, current is taken from the dynamo to charge a 12-volt battery, the current from which is taken through lead-cased Wires , and is used for lighting the side lamps and tail lamp, and also for the whole of the interior lights of the vehicle. This patented cut-out is mounted on the dashboard, and. has, combined in the one 'unit, the volt meter switch, volt meter, ampere meter, and lighting and charging switches.

Should the dynamo excite its-elf in opposite polarity the cut-out automatically changes the direction of the current to enable the battery always to be charged in correct relation to the polarity. This reversal of polarity, of course, does not saffect the driving Motor, but it would affect the battery charging.

Si ir of the Frost Smith petrol-electric vehicles will shortly be seen on the streets of London as omnibuses.


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