English: US Patent 598,314 (1898). Page 4 of patent document, altered to highlight the centrifugal clutch. Of note, this is an electric car. The clutch was considered necessary due to the low starting torque of electric motors available at that time.
Excerpt from the patent document follows (page 9, lines 60-116)
It is well known that in starting an electric motor from rest the armature has practically little power until a speed sufficient to generate a counter electromotive force has been attained, and for this reason an electromotor requires many times more its normal amount of current in order to start a load from rest. To overcome this serious objection, I have made an armature-shaft, as above indicated, in several parts, one that contains and supports the armature and two independent extensions that carry the driving-pinions.
These several shafts are adapted to be connected together by means of an automatically-actuated centrifugal friction-clutch, as hereinafter fully described, and which is designed so as not to be actuated until the armature of the motor has attained a given speed or a predetermined number of revolutions per minute.
To accomplish this result and construct a clutch, I provide a circular friction-cup H, which is rigidly secured, as shown in Fig. 5, to the pinion-shaft, with its cup-shaped portion extending toward the armature. To the outer end of the armature-shaft I rigidly secure an eccentric block or disk H' and on it mount a ring, which I term, for convenience, a "circular strap" portion h, which is held thereon firmly and rotatable by means of the flange-disk h', Which is secured thereto by screws h3 or in any other desired manner. To this ring or strap portion I rigidly secure a split circular spring H2, which is provided with a shoe portion H3, adapted to engage with the inner surface of the friction-cup. This shoe portion is connected with the eccentric portion by means of a helically-coiled spring h3, of any desired tension, which acts to hold the shoe and friction-cup in normal disengagement, as. shown in Fig. 6.
When the motor is supplied with current and its shaft rotated, the shoe and eccentric begin to lag behind on account of the tangential pull until sufficient speed is reached to overcome the tension of the helical spring, which action forces the shoe into engagement with the inner surface of the friction-cup, as shown in Fig. 7. The moment the shoe comes into frictional engagement with the inner surface of the cup the lagging pull in increased by the amount of friction between the surfaces of the shoe and cup, which causes further lagging on the part of the shoe and acts to exert force on the circular spring, thus giving the shoe additional contact-pressure against the cup in proportion to the pull exerted by the motor.
