Elevator Wiki

A bi-directional overspeed governor installed on a Kone MonoSpace elevator.

An overspeed governor is an elevator device which acts as a stopping mechanism in case the elevator runs beyond its rated speed. This device must be installed in traction elevators and roped hydraulic elevators. This device was first patented by Warner Elevator Mfg Company (Patent no.: US1549736[1]) and then Otis (Patent no.: US3327811[2]).

Background and Overview

Conventional elevator safety equipment includes an overspeed governor for restricting elevator car movement when a predetermined speed is exceeded. Overspeed governors include a switch that opens when the elevator reaches a predetermined velocity such as 110% of rated speed [3]. When the switch opens, power is removed from the machine motor and brake. A braking mechanism, actuated in response to movement of the elevator car by motion transmission means, then impedes the motion of the elevator car. The switch remains open, and the elevator remains inoperable until the switch is manually reset.

Typical governor designs include a sheave coupled to a rope attached to the elevator car. The sheave moves in response to rope movement in tandem with the movement of the elevator car. The sheave drives a shaft or spindle coupled to an actuation mechanism. The actuation mechanism may be a set of flyballs or flyweights adapted to extend radially when a predetermined level of centrifugal force is applied to them. Radial extension of the flyballs or flyweights causes them to contact an overspeed switch. When the overspeed switch is actuated, the power to the motor and motor brake is cut, thereby causing the motor brake to apply a braking force on the motor shaft. If the elevator car continues to increase in speed, a tripping assembly is triggered by the flyweights. The tripping assembly actuates a mechanism to stop the governor rope. Braking of the governor rope causes the safeties to be engaged and thereby stop the car.

Because the overspeed switch remains open until it is manually re-set, the elevator machine and brake power are not restored and the elevator system remains inoperable. In conventional elevator systems having machine rooms the switch to be re-set is conveniently accessible in the machine room by a technician. Typically, the governor is located in an overhead machine room.

In more recently developed "machine room-less" elevator systems, where the conventional machine room is eliminated, the governor and various other components are located in the hoistway. With the governor in the hoistway, the task of accessing and resetting a governor overspeed switch is time-consuming, complicated, and costly. Although a solution may be to provide a special door or hatch to access a governor in a hoistway, such a solution adds cost and space requirements. However, some MRLs may instead provide a switch in the cabinet to reset the governor automatically.

It is an object of the present invention to provide an overspeed switching system that operates safely and reliably while reducing the time and cost of restoring an elevator to operation after the overspeed switch has been tripped.

The present invention is directed to an overspeed switch system for an elevator where a first switch located in the governor is tripped in response to detected overspeed, and the tripping of the first switch causes a second, remotely located switch to be tripped, whereby when either or both switches are open, power to the elevator system is shut down. The first switch is provided with automatic re-set means, while the second switch is manually re-set in an easily accessible, remote location such as a control panel in a landing.

Ascending Car Overspeed Protection also can be done by the overspeed governor, while install the other set of overspeed governor on the counterweight (also can be used when the building facilitates implemented under the shaftway), or replace the existing overspeed governor and safeties to the bi-directional once[4][5][6][7][8].

How it Works

The system includes a governor that is responsive to elevator car speed through conventional coupling means such as a governor sheave coupled to a rope that is attached to an elevator car, whereby the rope transmits elevator car speed to the governor. When a predetermined speed is exceeded conventional actuation means, such as centrifugal flyweights, trigger a first set of switches and, if the car speed continues to increase, cause actuation of conventional mechanical means to impede elevator car movement. The first set of switches  may comprise one switch or any other number of switches, depending on various factors such as the degree of safety redundancy desired or the number of different components dependent upon overspeed conditions. For example, a "safety chain" electrically linking various components and associated switches may be implemented, whereby the opening of one switch renders the system inoperable. The first switch  of the first set, for example, may be for the purpose of tripping the remote overspeed switch while the second switch  of the first set may be directly in the safety chain.

The tripping of the first set of switches  causes them to open and, as a result, the power to the elevator machine and brake is cut, and mechanical braking means in the elevator machine impede elevator car movement. It is preferable that the first switch set comprises two monostable contacts located in the governor. The monostable contacts are configured to maintain contact, in a closed position, during normal operation. Implementing them in this way, as opposed to setting them in an open position during normal operation, reduces the possibility of a malfunction in overspeed mode due to, for example, corrosion or contaminant build-up on exposed contacts.

When the first set of switches  are tripped, they cause tripping of a second set of switches. The first set of switches  may, for example, trip the second set of switches by causing power loss when a contact is broken in response to first switch tripping. The second set of switches  is remotely located, preferably in a convenient and easily accessible location such as a control panel in an elevator landing or in a building managers office or a security office.

The system is configured so that when both sets or either set of switches are open, the elevator is inoperable. Thus, the first set of switches may be provided with automatic re-setting means and configured to remain open long enough to cause tripping of the second set of switches The automatic re-setting means  may comprise, for example, a spring-loaded mechanism and/or a timing control.

While the second set of switches  may comprise any number or variety of switches, it is preferable that the second switches  are bistable switches. Bistable switches, as opposed to differential circuit breakers, reduce the possibility of problems associated with mixing of different types of signals, such as alternative and/or continuous while providing a fast and reliable signal response. As discussed with regard to the first set of switches, one of the second set of switches  may be a safety chain switch while the other one is part of the overspeed control. The second set of switches remain in an untripped, closed position during normal operation of the elevator system.

By configuring the system so that the second set of switches remain open until manually re-set, and so that the first set of switches  automatically close after tripping the second set of switches, all that is required to re-start the elevator system is to close, or re-set, the second set of switches. By locating the second set of switches  in a conveniently accessible panel, the system  can be quickly and conveniently re-set. In some instances, where the services of a skilled service technician are not otherwise required, the system  can be re-set without the need for a skilled technician.

Power to trip the second set of switches  can be supplied from a main controller  during normal operation, and from the brake power supply during rescue operations.

If desired, a software-based switch may be implemented that is triggered by the overspaced switch on the governor and remains latched until a service technician resets them.

Notable Governor Series

  • Schindler GBP
  • Wittur OL35
  • Wittur OL100


See also

Notes and references

  1. US 3327811: Governor for elevators and the like (Archived by Google Patent)
  2. US 3327811: Governor (Archived by Google Patent)
  3. The Secret Life of the Lift by Tim Hunkin
  4. Guidelines for Modernising Existing Lifts (Chinese version) (Electrical and Mechanical Services Department, Hong Kong)
  5. 限速器及安全鉗為升降機安全的重要元件。傳統限速器及安全鉗都是防止升降機向下超速;隨著升降機安全要求日益提升,限速器設計開始加上「上行超速」電氣掣,及後也漸漸演變出「雙向限速器」配合上行安全鉗(設於機箱框架上方)或雙向安全鉗使用,防止向上超速意外發生。, Facebook page: hkelev.com.
  6. 上回提到加裝上行安全鉗或更換為雙向安全鉗,配合雙向限速器,都可做到「防止上行超速保護(ACOP)」功能。而另一個業界近年關注的「防止不正常移動保護(UCMP)」(或稱「防止非預定移動保護」),原來也可透過同樣方法達成,不同的是,機房限速器的設計稍有不同。一般限速器只在超速時透過離心力,使其機械動作生效;備有UCMP功能的限速器,加上了電磁鐵,一般情況下長期接通電源,在電梯控制櫃偵測到開門行機時會立即斷電,電磁鐵跌出並透過一連串機械動作,使限速器停止,帶動機廂安全鉗生效,從而防止機廂繼續移動。本港市面仍較少使用這種保護,主要因為舊機普遍透過加裝夾纜器;新機多數為無齒輪機器,並透過曳引輪制動器(每邊制動器都可獨立固定125%載重的機廂)達成。只有少量採用齒輪機器的新機方有使用。, Facebook page: hkelev.com.
  7. Lift misconceptions 1 - The lift could plummet down the shaft
  8. Detailed look at a modern governor
Drive systems: Traction • Winding Drum • Hydraulic

Types of elevators: Double DeckDumbwaiterFireman'sFreightIncline • PassengerResidentialWheelchair lift

Concept: CapacityDestination dispatchElevator algorithm • Elevator control systemElevator machine room • Elevator maintenance • Elevator monitoring systemElevator modernizationACOP & UCMPMachine room less elevatorMajor alterationsRated speed

Elevator systems, controllers and equipments: Elevator emergency automatic rescue device • Elevator fixtures • Elevator keys • Elevator special modesElevator doorsDoor camDoor interlocks (Interlock wiring communication system) • Door restrictorElevator Inspection CertificateEmergency stop buttonFloor designatorsGate switch • Old Deadman controls • Overspeed governorMotor-generator set & Silicon-controlled rectifier (for DC-powered elevators) • Insulated-gate bipolar transistor (for AC-VVVF-powered elevators) • SelectorTape headRegenerative converter (for AC-VVVF-powered elevators)

See also: List of elevator fixtures guide • List of elevator and escalator companies • Elevator door sill guide (Non-proprietary elevator component door sill guide) • Floor numbering (Unlucky floor numbers) • Elevator incidents and accidents