Speed governor

The invention of the elevator as a means of vertical transport immediately needed speed governor systems. The first elevators controlled by a “liftman” had a range of speeds within which to operate; these speeds were controlled by a rope that operated valves in the hydraulic systems and then by a rheostat with the drum systems operated by an electric motor. The ”liftman”, however, could get distracted and the system could thus reach dangerous speeds.

In all those cases in which, either due to breakdowns or distractions, the system reached excessive speeds, some emergency system was needed to activate the safety devices of the cabin called safety gears or even parachutes.

It seems that the term parachute was linked to some particular safety devices that were also equipped with a canvas placed under the cabin and kept taut. In case of excessive speed, or in case of impact with objects (for example stairs) not belonging to the elevator that were present in the shaft, the safety devices were activated. When the canvas swelled, it took the form of a parachute and perhaps it was also made with the same fabric used for parachutes.

The introduction of the steam engine in the late 1700s made it necessary to think about methods to manage / adjust the energy produced. Watt himself created the first device to adjust the steam flow by two masses set in rotation by a rotating shaft which, due to the effect of the centrifugal force, tend to move away from the axis itself. Their spacing is opposed by a system of springs and / or by the force of gravity through an articulated system of arms and levers. The spacing of the masses therefore allows to adjust the opening of the valves, or as it will happen later for the lifts, it allows preloaded systems to snap and lock, in different ways, the rope that will be connected to the safety devices. The watt regulator is one of the earliest examples of a negative feedback control system.

The exploitation of the centrifugal force, in the most varied forms, is the principle that up to the present day has made the foundation for the speed governors.

The Watt governor is found in practically all the very first hydraulic lifts to regulate the maximum speed by acting directly on the valve that allowed the piston to be filled and emptied. In parallel, the same principle is used as an overspeed governor even in case of ropes breaking combined with a safety device which stopped the car by means of jaws or devices of various types, activated by the speed governor by means of a rope.

Below are reported a series of patents, taken from the archive made available by Google Patents, in which a speed governor is reported. As it could be seen, in its various forms, the operating principle is practically always the same. In fact it is possible to find since the end of the 1800s, governor models that are still used today, even if with different activation methods and materials.

The first patent here reported is dated 1878 and issued by by R. H. Hill. It is made by a watt regulator set in motion by a rack and pinion system integral with the wooden guides. Once the activation speed has been reached, the governor, by means of a lever articulated on its masses, releases a hook which holds a spring that pushes wedges towards the studs, making the cab lock on the guides.

 It could be found a similar patent in 1883 by P. J. Singer.  In this case the  governor is set in motion by a rope; the patent does not explain how; probably a rope starting from a fixed attachment in the headroom has been used which, after having turned around the pulley of the governor, returns to the headroom to pass through a return pulley and  reach the counterweight. This time, however, the wooden guides do not have  pawls but are smooth, the parachute acts with clawed eccentrics that tend to ”bite” the guides and stop the cabin.

In the following patent of 1884 by C. P. Adams the speed  governor is set in motion by a series of gears  that engage in the rack  carved in the wooden guides. Once the  activation speed has been reached, the  governor releases a lever which causes  that belts  are pulled onto the discs, slowing the cabin until it stops. Practically, the  governor triggers a friction brake.

In the invention of 1888 by a. C. Ellithorpe it is found the governor with inner centrifugal masses which was widely used over the time by the way, the same principle is still applied today.
In practice, two weights rotate together with the pulley, connected to an eccentric and a spring. As the speed increases, the weights, due to the centrifugal force, tend to counteract the force of the spring and extend until they impact on a wedgefixed.
At this point, due to friction, the rope push the governor to rotate on its anchor point t; in this way a series of levers connected to a drum brake continue to hold the governor in place . Due to the friction on the pulley, the rope opposes the movement of the cabin, allowing a drum to rotate which in turn engages the jaws that tighten on the guides. We note that the governor also acts as a tensioner of itself aided by a weight. The system has an open rope with a counterweight placed on the opposite side of the cabin. The parachute used in this case is of the progressive grip type.

It does not take long, until in 1893, by W. H. Hultgren file a patent with the governor supplied with rope and tensioner in the pit as it is in use still today. The governor always exploits the centrifugal force and like today’s governors. The pulley blocks when the movable weight, integral with it, overcoming the force of a spring that opposes the centrifugal force, manages to impact on fixed blocks that stop the pulley. The rope then tends to stop due to friction.

Similar patents but with watt regulator we find them then in 1901 by G. John and C. R. Pratt and in 1906 by N. P. Otis

A first speed limiter with harpoons is found in 1904 by M. Hanford. This speed limiter is bidirectional and, thanks to a worm screw, also acts as a limit switch on the extreme floors.

In 1916 we find a centrifugal limiter with the kinematics connected to the two inverted weights. when this limiter intervenes, it blocks the rope both by its friction with the pulley groove and by two jaws.

A similar speed governor is that of Schindler put on the market since 1920 and of which we have disassembled and analyzed a specimen donated by Nova Elex and which you can find on the page dedicated to the KRK15 speed governor

A speed governor used on several systems and still in use in some countries is the centrifugal one made by Otis and of which we report below the photos granted by Nova elevators.


In 1919, thanks to the inventiveness of D. L. Lindquist, it is found the first governor with eccentric and jack. We always have concentric masses which, due to the centrifugal force, tend to move to the periphery of the pulley, plus on one of the two masses there is a wheel that tends to slide on an eccentric; at each rotation when the wheel is on the most extended part of the eccentric, due to the force of inertia, the masses tend to continue their trajectory towards the outside. By increasing the speed, the trajectory becomes more and more eccentric until the weight to which the wheel is attached hits a stop on which an arm that rotates on its axis is placed in position (point 20 in the figure). This arm, after having impacted with the mass and having lost its rest position, tends to squeeze the rope while it is dragged by it. Furthermore, a shoe is mounted on the arm pushed towards the pulley by a spring which, being no longer blocked, pushes the shoe towards the center of the pulley, increasing the friction with the rope until its motion stops.

The technology used nowadays is still similar to that used in the first governors with jumping mass: there is a mass that is moving on a cam profile , when the maximum speed is reached, blocks the rotation of the pulley which, through a groove, block the rope that activates the parachute. Over the years the technology has evolved in every direction, allowing to reduce the masses, increase the friction on the rope, reduce the noise and make the activation speed more and more precise. In Italy and in other countries the legislation had then imposed for years the use of a second groove on the pulley to allow checking the operation of the limiter at reduced speeds by simulating its activation at rated speed.

Thanks to the technology based on absolute encoders with redundant channels and special safety circuits, that directly calculate the speed of the car, and allow the springs that activate the parachutes to put them in the car stop position, the classic mechanical governor will be progressively replaced by electronic systems.

All patent images were taken from documents archived by Google patents; unfortunately in this archive, from the years between 1800 and 1900, we find only patents made in USA.