Commercial car manufacturers and users are aware of the attendant results of high speeds and heavy loads over rough roads, so that at the present time this subject should be of considerable interest to those operating commercial cars.
The most practical means of obviating this excessive speed seems to be through the use of a governor, which should be sealed so that it cannot be tampered with.
This governor consists of a mechanical speed-measuring device so connected to the engine throttle as to cut off the intake when the speed exceeds a predetermined maximum. It was originally inherited from steam engine practice. However, lately, considerable improvements have been made in this device so as to make it more adaptable and efficient.
There are four methods of regulating the speed of the motor, as follows: (1) By holding the exhaust valve open or the intake closed, (2) by the spark, (3) by changing the quality of the mixture entering the cylinder, (4) by changing the quantity of the mixture entering the cylinder.
The method of regulating the motor speed through connecting the governor to the exhaust valves in such a way that these valves may be held open, and thereby retard the speed of the motors, or by connecting to the intake valves in such a way that they may be held closed, has been discarded long ago.
The Dedion Bouton method of regulating the motor speed through connecting the governor in such a way that it will open and close the electrical circuit, has also been discarded. This also applies to the method of changing the quality of the mixture entering the cylinders.
One method of governing the speed of the motor is by connecting the governor to a butterfly valve in the intake manifold, which reduces the quantity of the mixture entering the cylinder but does not in any way reduce the quality. The butterfly valve merely changes the volume of gas and allows the motor to get the proper mixture under any speed up to the setting of the governor.
The revolving ball, or more properly the centrifugal principle, is that generally employed. There are many variations of this construction and few that operate on different principles, but all are alike in fundamentals.
The hydraulic principle is also used by some. In this type, as the motor speed raises the pressure against a diaphragm connected with a plunger-head acting on the throttle spring. This action overcomes the resistance of the spring and closes the throttle. This type may either be built in a unit with the pump or connected to it.
There is also the automatic type which regulates the motor speed by governing the velocity of the incoming gases.
There are two methods of drive for the centrifugal type of governor. The usual method is direct from the engine, either through an auxiliary shaft, or by building the governor into the cam-shaft gear. With this method the speed of the governor is always proportioned to the speed of the motor.
Lately governors are being introduced which are driven from some part of the chassis and whose speed is proportioned to the speed of the vehicle instead of the motor.
In the former case the governor acts only on the motor and converts it into practically a constant speed motor. In changing speeds the allowed speed of the motor is in no wise altered.
The governor is generaly set at a maximum speed corresponding to the maximum car speed at which the car is to operate on high gear, and when it is running in second speed the effect of the governor on the motor does not change in any way. This second speed might correspond to 12 m.p.h., and the low speed to 0 m.p.h., thus limiting the motor speed on the lower gears, hence the power of the motor. This would be quite noticeable if the car was operated over a long stretch of bad road or in deep sand. The power output of the engine is dependent upon its speed and although it may be pulling hard on a wide open throttle, it is not developing its full power, for not enough power units are released from the fuel, owing to the limited speed. The maximum safe motor speed may be far above the speed permitted by governor for a given car speed.
These defects have caused engineers to investigate other methods of governor drives and has resulted in the introduction of a transmission jack shaft or front-wheel drive, on the theory that the speed of the motor should be governed by the speed of the car. In this way the truck can attain its maximum speed at a moderate engine speed, and with only a partly opened throttle. It also permits the motor to operate at a higher speed on the lower car speeds. In practice with the proper size motor for a certain car capacity, the gear ratio is generally such that the maximum safe motor speed is reached in second speed, so that the maximum power may be obtained when it is most necessary. The motor should not be permitted to develop its full power in high gear, as gear changes are provided to obtain increasing torque with decreasing car speed. Limiting the motor power in high speed is an advantage up to a certain point, for a truck should never be permitted to take a hill on high gear if it is necessary to retard the spark all the way.
There is also a governor on the market at the present time which controls both the motor speed and the ear speed, the object of this device being to obtain a letter fuel economy and to form an assistance to the driver in operating the vehicle.
While still another automatic governor in addition to controlling the speed also operates the throttle and spark and controls the motor under all speeds. The operator merely sets the governor as to the speed he wishes to make and the governor does the rest.
The writer is attempting to cover this subject in such a way as to present all types of governors now in use and those which may come into general use.