DESIGNING the
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DRIVER'S CAB
for maximum efficiency
Building Cabs for Goods Vehicles with a View to Giving Ample Comfort for the Driver and Providing the Minimum of Obstruction to Awkward Loads
THE driver's cab should have a comfortable seat, a good outlook and efficient ventilation. The seat has to withstand prolonged usage, therefore it should be strongly niade of good materials. The quality of the upholstery may seem of little importance, but when regarded in this light, the driver's seat is often the only shabby part of an otherwise well-kept vehicle.
If no adjustment be provided, the back of the seat or squab should be 15 ins, from the back of the steering wheel and the measurement under the wheel to the top of the cushion about 8 ins., with a length of cushion from front to back of 16 ins., and 18 ins, for the hei'ght of the squab.
The introduction of wider doors has improved the driver's outlook, the sloping windscreen brings the glass nearer to the steering wheel and the reduction of the amount of projection of the roof above the screen has enhanced the natural lighting.
Roof Finishes and Types of Windscreen.
Many cabs now have flush-type roofs, which give the maximum of natural lighting. The overhanging roof canopy, however, acts, to a certain extent, as a sun visor. With the flush-type roof, the visor may be added, but in order to preserve the flush appearance of the front of the cab, the visor may be fitted inside, where it is easily accessible when any adjustment may become necessary.
For the small van, the private-car type of windscreen is fitted. This has a single panel which is hinged from the top. There is no division between upper and lower panels, which may obstruct the sight line. Larger vans have the two-panel screen with an adjustable• upper half, or the three-panel variety with B30 the moving pane confined to the off side.
The four-piece screen has an independently adynstable upper section on each side. It is considered that there is scope for the introduction of a two-panel screen with each half to open for the full height and without any fixed glass below.
The modern cab is well ventilated. This aspect of design has received much attention, Owing to the increasing number of forwardcontrol vehicles in service. • The cab is usually a full-width one with a seat on each side of the engine casing. In order to maintain a supply of fresh air, without opening the windscreen, there should be, a louvre panel on each side of the radiator in the front dash plate, a narrow opening above the screen and one or more air ejectors or ventilators in the roof, placed towards. the rear. if the shape of the roof permits, louvres may be inserted in a cant-rail panel above the doors.
Heated air tends to rise and collects under the roof, particularly at the rear. Here it may escape readily through a roof ventilator, the actfon of which is promoted by the stream of air flowing over the roof. A roof ventilated in this way also prevents down-draught at the seat-hack.
Good ventilation is also dependent on adequate headroom. With the older type of van, with its builtAn cab, headroom was sometimes excessive, because the roof line of the loading portion decided that of the cab. Nowadays the cab is usually a separately designed unit, even in the case of many light delivery vans, with the result that headroom may, in some instances, be curtailed. From the centre of the cushion the _measurement to a point just under the roof framework should not be less than 3 ft, 4 ins, Window Types and Provision
for Signalling.
As a rule, there is a horizontally sliding window on the off side, because it is suitable for hand signalling. This variety of window is adaptable also to any degree of sloping front, whereas, with a drop window, a gap is made when the window is lowered. It is possible that more winding windows will be used now that mechanical signalling devices are so frequently fitted.
Ease of access to the forwardcontrol cab depends chiefly on the position of the front axle. When the front of the wheel and radiator are approximately in line, a rear door shutting on the hind corner pillar is most convenient in conjunction with a binged seat. With a wellrecessed front axle, the door may be in front and open immediately behind the screen.
Often, the cab roof is utilized to carry a portion of the load, and when it is narrower than the main portion of the body, the cab may have a tray built on it, which projects on each side. The full development of the cab roof for loading purposes is to be seen in the Luton-type van, a pattern which continues to find favour for the transport of a wide range of commodities.
Designing to Deal with Unusually Long Loads.
For a lengthy load, such as timber, constructional ironwork, metal bar, channel and piping, the problem is to load the vehicle without an excessive rear overhang. To prevent this the length of the vehicle which is occupied by the cab and, perhaps, the bonnet as well is used. The simplest method is to have a gantry, so that the load is slanted and projects above the cab roof.
Another method of carrying such a load is to restrict the width of the cab in order that the piping or other material may project on each side of it. Tilt front boarding of the loading portion is only as wide as the cab, or the overhanging side portions are "hinged. Supporting trays are mounted at the side of the cab, and form an extension of the floor. If a hinged tray be used, It may extend across the doorway, which will be temporarily obstructed.
(Left) Two, three and four. panel wind-screens, as used on different types of commercial vehicle.
Loads Extending by the Cabdoor Sides.
Although the load may be carried in a similar manner on each side of the cab, the disadvantage of obstructing both doors may be obviated by carrying part of the load at the slope. Assuming that the load requires more support than is provided by the cross-bar of a gantry, the cab roof has a sloping tray mounted on it at the angle suiting the length of the body.
There is a similar means for support in the centre of the lorry. The back end of the load rests on the tailboard, which is opened at an angle corresponding with the slope of the front and centre supports. On the near side, the lorry is designed to carry the load horizontally. Part of the front hinges forwards to form an extension of the floor, whilst at the rear the tailboard 'has a wedged-shaped platform so that it may carry a load arranged partly horizontal and partly at the slope.