The Control of the Machine.
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Some Observations on the General Arrangement of Control Gear on Petrol-Driven Commercial Vehicles.
Considered from the crucial points of view of simplicity and ease of manipulation, combined with the invariably good results that are attained thereby, the arrangement and disposition of the control gear on commercial vehicles are subjects upon which a great deal can well be written. In this presem article, it is our intention, however, to deal with the matter only so far a-s to consider what, in our opinion, are the more desirable features and the more satisfactory arrangements of the control details, having regard to the comfort and efficiency of the driver ; we shall therefore briefly make suggestions concerning the steer i n g wheel, the various handoperated levers, and the pedals, in relation to the driver's seat, the footboard, and the dash.
We have, on the present occasion, confined ourselves to petrol-vehicle control only. We shall probably consider the disposition of steam-wagon control, and its special problems, at some future date. As a useful form of reference we have included a number of reproductions of photographs of the control-gear arrangements on some of the well-known types of petrol chassis. All these pictures have been specially taken for this article ; we also include certain line drawings illustrative of special points. There are sometimes undesirable features in regard to control gear which may tend to interfere with the efficient driving of amachine ; these are considered, therefore, from that aspect. We fear that control gear proper does not always receive such de tailed attention in its design stage as usually falls to the lot of the engine and to other important parts of the chassis. Control is often the last chassis detail to be considered by the designer, and therefore is not infrequently hurried. The evolution of a perfectly-suitable arrangethent has, in consequence, not been so rapidly attained as have other details of modern standard machines. It must be admitted. however, that control mechanism, as fitted at the present aay. is relatively perfect, when compared with the usually scranpy "afterthoughts " of so-called design which frequently obtained, say, six years ago. For the sake of general convenience, we will consider the control gear in detail.
The Steering Wheel, its Size and Position. Particularly conducive to the easy manceuvring of a machine, is the fitting of a steering wheel of ample diameter. Nothing, in this respect, is more laborious for a driver, than his having to negotiate narrow turnings, or to endeavour to manceuvre through congested traffic, by struggling with a small
wheel of perhaps no more than 12 in. in diameter and with four turns to the lock. The modern steering wheel should be at least 15 in. across, and when ithas, at the very most, throe turns to each lock, the driver will feel that he has his machine well under control, however tight the corner in which he may find himself, Moreover, when it is the practice of builders to fit the throttle and ignition-control levers on top of the steering wheel, if the latter lie of an ample diameter, ample-sized quadrant and finger levers can be fitted.
Concerning the position of the wheel, and the rake of the steering column, many ruling factors enter into consideration. At any time makers are restricted as to the inclination of the column on their various types of machines, as users quite naturally demand the maximum platform area and body space on any vehicle of a given wheelbase.
If the inclination of the column from the vertical be 40 degrees, then a very convenient plane of the haeldwheel, and linger levers is presented to the driver. Such a rake, however, is /lot always possible for the reason that, when the carburetter, or magneto is fitted on the offside of the engine, or when largesized crank-chamber doors are fitted and are intended to be easily detachable, then the steering sectorand-worm box, with its anchorage bracket, generally has to be fitted immediately behind the engine. Considering the position of the driver's seat, this automatically decreases the rake to a considerable extent, and on many well-known makes of chassis, the steering column is inclined at not more than 20 degrees from the vertical. Under these conditions, the higher. the handwheel in relation to the seat, the more awkward to the driver is the steering, and finger-lever control.
Best Position for Levers.
When it is the practice of manufacturers to fit a hand lever, in addition to a pedal lever for operating the throttle, undoubtedly the best arrangement, when considered with the ignition control, is for the throttle lever and quadrant to be fitted on the steering wheel, and the ignition lever to be placed on the dash at aconvenient height for the driver to reach. The sketch shows what the writer considers to be a satisfactory position for the hand lever and quadrant on the steering wheel. Placed thus, they are clear of the driver's coat sleeve, besides being in a good positon to encourage careful and economical driving.
Is Single-lever Engine Control Desirable ?
An economical form of engine control is generally associated with the fitting of both hand and footoperated throttle as well as a single lever for controlling the ignition. When engine throttle, operated by pedal alone, is provided, it is, of course, only effective whilst the pedal is being depressed, or when some form of adjustment is attached to facilitate starting ep. If, however, both means for operating the throttle are provided, the foot accelerator is particularly useful for town work and in congested traffic, whilst for long journeys, when prolonged holding down of the pedal would be a very tiring proposition, the hand lever controlling the throttle may be readily set in the best position for economical running, and the foot lever need then only be used should any varying effect be instantly desired.
Concerning the ignition lever, attempts have been made to eliminate it by fitting some form of mechanism near to the magneto, with which to synchronize the ignition range with engine speeds. But at the present time, a hand-operated lever, placed conveniently near the driver, still holds high favour. Speaking generally then, singlelever engine control, however attractive as a scheme, would lead to rather expensive complication, with probable restrictions in the direction of economy under the different. working conditions of a machine.
Arrangement and Form of Pedals.
When we consider the present few standard methods adopted for transmitting and controlling the power of the engine on petrol vehicles, there does not appear to be any immediate prospect of designers being able to eliminate any one of the pedals, operating the accelerator, the clutch or the brake. This being the case, and noticing
the unsatisfactory shape and arrangement of pedals on some mouern commercial vehicles, we certainly consider that there is room tor improvement in this direction. A little co-operation on the part of the chassis designer and the hody builder would undoubtedly improve matters. Broadly speaking, the pedals are often fitted to a chassis last of all, with little idea as to the position of the footboards. and the body builder has to cut and fit round them as best he can, taking care not to impede their travel. Consequently the pedals are very often "much in mid-air" ; the result is thata driver on a machine for eight or ten hours a day is tempted to rest each foot in turn on the footboard., especially when the clutch spring and the one which pulls back the brake pedal are rather sensitive. aloreover, the foot throttle
under these conditions, often kept fully open longer than need be for economical running. More suitable footboard construction should obviate much of such trouble.
With regard to the arrangement of the fool. levers, the direction of
their travel, and as to what particular shape of pedal-plate vvill present to the driver the most convenient form of foot control, our last illustration will convey our suggestione in the matter. The push-forward types of levers are shown, as not only allowing a normal position for the driver when seated hut as also enabling him to secure better n purchase" if their direction of travel be vertically downwards, the. pedal plates usually have a tendency to creep under the driver's hoot.
Gate and Straight-through Gear Control Compared.
Mention of either the gate or the straight-through type of speed-. change control at once conveys which particular type of gearbox is fitted. As a eommercial proposition, both the gate and runthrough sector-controlled box has each its own particular advantage. The latter form is in comparison cheaper to make than the gate type, embodying, as it does, fewer moving parts which necessitate costly machining. Moreover, when
the transmission is shaft-to-shaft drive throughout, as is so often the case in rim-through boxes, it is more efficient, to the extent of 10 to 20 per cent., than the gate design, except on the direct drive of the latter type. there being a pair
of gears less in mesh for each speed. This form of box is somewhat bulky, but that should not be a drawback to its being fitted to a commercial chassis. The one great disadvantage, however, against, its more general adoption is that, in practice, its control calls for caret ul handling, as it is not difficult, with it, to miss gears. This is bad treatment, and not only causes extra wear and tear on the sliding member, but there is the danger of stripping the teeth, and: be it remembered, all petrol vehicle drivers are not trained mechanics. This is where the gate-change possesses the undoubted advantage. in that it is practically proof against indifferent handling. The balance of favour is on its side, and makers now usually adopt this form of transmission and speed control. in spite of its increased cost.
The Best Form of Handle.
There is not much room for improvement in the usual form of handles which are now fitted to control levers. We. however, shall make a few suggestions thereanent_ concluding this article next week.