The most important controls are the spark and throttle. The former may either be hand operated from the steering wheel, it may be so arranged as to cause ignition to occur at a predetermined point or it may be automatically controlled by the engine speed. The throttle may either be controlled by the driver or automatically. There are two means of manual control, by hand or foot. Automatic control was described in the chapter on governors.
The conventional type of control for cars with sliding gear transmissions, comprises two pedals located on opposite sides of the steering posts, the one at the left being the clutch pedal and the one at the right the brake pedal. The foot throttle or accelerator, if one is provided, is placed either between or to the right of these pedals for operation with the right foot. The mounting of these pedals depends upon the general construction of the vehicle. When a unit power plant is used they are generally mounted on the clutch housing; if the transmission is mounted amidships the common plan is to provide a tubular shaft extending partly or entirely across the frame, which is carried in brackets secured to the frame. Formerly the steering column was nearly always placed on the right side of the car, and the hand levers for operating the sliding gears and the emergency brake were located just outside of the driver's seat on the right. However, during the past years, quite a few makers have resorted to the left-side drive in which the steering column is located on the left side and the levers either on the left side or in the center.
On several makes of vehicles the clutch and service brake are operated by a single pedal. The f*irst motion of the pedal releases the clutch and a continued motion applies to service brake. The emergency brake may also be operated by a pedal; however, it must be provided with a ratchet lock. The brakes and clutch may also be connected through suitable linkage so that when either brake is applied the clutch will also be disengaged. The idea which led to this construction undoubtedly was that if the driver wants to stop quickly he should simultaneously disengage the clutch and apply the brake, so that the driving effort ceases and no braking effort need be expended in dissipating the energy stored in the flywheel.
In order to prevent shifting of the gears while the clutch is engaged, some designers have provided an interlock between the gear sliding and clutch mechanism. This is generally so arranged that the gears cannot be shifted unless the clutch is out, and the clutch cannot engage unless the gears are in full mesh.
The advantages and disadvantages of the two control positions may be divided into general and mechanical. The advantages of one are, moreover, usually the disadvantages and advantages of the other, so the question may be discussed for one only. The two essential features of the left side control are: first, greater ease in getting out of the vehicle on the right side, and second, the bringing of drivers meeting vehicles next to each other, lessening the dangers of collision.
The first is of importance only as regards convenience of both operator and helper. The second point is well worthy of consideration, as when two vehicles meet on narrow streets or roads, the distance between the two must be judged with great nicety in order to prevent scraping mud guards or bodies and locking wheels. The disadvantages are the difficutly of judging the distance from the curb, the distance of an overtaken vehicle and in some cases the difficulty in mounting the control levers.
The first claim seems to be a difference of opinion, as there are some who claim one is no more difficult than the other. However, if the distance is not judged properly the tires will suffer, not mentioning the strain imposed on the wheels, axles and steering knuckles in striking curbs.
In overtaking vehicles the driver is on the left side, and farthest from the overtaken vehicle, and this would seem to be offset by the advantage of bringing the operators of meeting vehicles next to each other, but a close study seems to point in favor of the right side control, for in the case of meeting vehicles two operators are watching and able to judge distance, while in overtaking vehicles there is only one who can judge the distance.
The mechanical points relate to details of design and apply to each type; however, the center control offers an advantage in that the gear lever can be mounted directly on the transmission, thus doing away with superfluous connections.