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Tuesday, 22 January 2013

Governors on Diesel Locomotive Engines




Governors on Diesel Locomotive Engines
 


Speed control governors on the prime movers of diesel locomotives

By
Gyan Fernando

Introduction
A vital component of all diesel engines is a mechanical or electronic governor which regulates the idling speed and maximum speed of the engine by controlling the fuel supply.

Governors
The major function of the governor is determined by the application of the engine.
In an engine that is required to get up to and run at only a single speed regardless of load, the governor is called a constant-speed type governor.

If the engine is manually controlled, or controlled by an outside device with engine speed being controlled over a range, the governor is called a variable-speed type governor.
If the engine governor is designed to keep the engine speed above a minimum and below a maximum, then the governor is a speed-limiting type.

The last category of governor is the load limiting type. This type of governor limits the fuel supply to ensure that the engine is not loaded above a specified limit.
In practical terms, many governors act to perform several of these functions simultaneously.

How Governors Work
How engine governors work
In its simplest form, a governor is a simple mechanical device which first appeared on static steam engines.


Between the years 1775 and 1800, James Watt, in partnership with industrialist Matthew Boulton, produced some 500 rotative beam engines.

At the heart of these engines was Watt’s self-designed "conical pendulum" governor: A set of revolving steel balls attached to a vertical spindle by link arms, where the controlling force consists of the weight of the balls.
It operates as shown in the diagram above.

The governor consists of a rotating shaft, which is driven by the engine.  A pair of flyweights is linked to the shaft and they rotate as the shaft rotates.  The centrifugal force caused by the rotation causes the weights to be thrown outwards as the speed of the shaft rises.  If the speed falls the weights move inwards.

As the speed increases, the balls fly outwards and the linkage closes the steam valve.  
In James Watt's days, there were a number of disastrous flywheel break-ups on uncontrolled static steam engines.

Governor on model steam engine
A Stuart Models steam engine


In the Stuart Modelstm model steam engine (left) the governor can be seen in the middle and identified by the flyweights. The picture above shows detail.

The governor shaft is connected by a belt to the flywheel. The governor linkage, a grey lever., is attached to the steam inlet valve.

How governors work
The flyweights are linked to a collar fitted around the shaft by a pair of arms.  As the weights move out, so the collar rises on the shaft.  If the weights move inwards, the collar moves down the shaft.

In a Diesel engine, the movement of the collar is used to operate the fuel rack lever controlling the amount of fuel supplied to the engine by the injectors.

Unlike in the model steam engine shown above, on Diesel engines some form of a servo mechanism is needed to transmit the movement of the collar to the fuel rack lever. 
This is achieved by a hydraulic or pneumatic system. 
The hydraulic or the pneumatic system, may in turn be operated by an electrical solenoid system.
 

Woodward Governors
Woodward is a major manufacturer of governors and Woodward governors are fitted to the prime movers of Sri Lankan locomotives.

Woodward is an American company described as: “the world's oldest and largest independent designer, manufacturer, and service provider of energy control solutions for aircraft engines, industrial engines and turbines, power generation and mobile industrial equipment” (Wikipedia).

Woodward trace their beginning to 1870: “In 1870 our founder, Amos Woodward, invented a responsive, non-compensating governor for water wheels.”
Today, approximately 75 % of all propeller-driven aircraft use Woodward AES controls.




 Woodward governors, as fitted to Sri Lankan locomotives, are of the electro-hydraulic type.


It is easier to understand how they work if you first study how hydro-mechanical governors work. Above left, is a schematic diagram shows how these work. The flyweight mechanism operates a hydraulic valve, which in turn allows oil into a hydraulic cylinder. The piston of this cylinder, is linked to the fuel rack lever.
 
In the electro-hydraulic type, the flyweights actuate solenoids. The solenoids in turn operate the hydraulic valves. Finally, the hydraulic system actuates the fuel rack lever



 On Sri Lankan Locomotives

Woodward governors are fitted to Sri Lankan locomotives. 
 They are of the electro hydraulic type. 


 Woodward governors, as fitted to Sri Lankan locomotives, are of the electro-hydraulic type.


It is easier to understand how they work if you first study how hydro-mechanical governors work. Above left, is a schematic diagram shows how these work. The flyweight mechanism operates a hydraulic valve, which in turn allows oil into a hydraulic cylinder. The piston of this cylinder, is linked to the fuel rack lever.

In the electro-hydraulic type, the flyweights actuate solenoids. The solenoids in turn operate the hydraulic valves. Finally, the hydraulic system actuates the fuel rack lever



 On Sri Lankan Locomotives

Woodward governors are fitted to Sri Lankan locomotives. 
 They are of the electro hydraulic type. The following photographs show the governor on the EMD engine of Class M2c No 626 "Montreal" and on a Caterpillar engine on a Class W locomotive.On the EMD engine, the governor is mounted vertically whereas on the Caterpillar engine it is mounted horizontally. The
electrical and hydraulic lines can clearly be seen.


Governor and linkage on No 626 Montreal


Governor on Class W loco Caterpillar engine

Governor on Class W loco Caterpillar engine




Governor on Class W loco Caterpillar engine


Rating plate on Class M2c loco governor

Picture credits:
The photographs of the engines of Sri Lankan locomotives belong to the author. Some of the other illustrations are copyright free. The simplified diagram of a Diesel engine governor is copyright (Railway Technical Pages) and is used here with permission.
The schematic diagrams of electro-mechanical and electro-hydraulic governors are from the EMD 567 Operators Manual available copyright free on the web (see references)

References
1 A United States Navy black and white instructional film (1942). Probably the best explanation of how governors work: diesel engine speed governor explained

2 A good site explaining the basics: Railway Technical Web Pages

3 Woodward, Inc. - Wikipedia, the free encyclopedia: Link to Wikipedia on Woodward


 

4 comments:

  1. Your blog posts are simply great! please continue - hoping to see more in the near future! cheers!

    ReplyDelete
  2. Wow! this informative post! I got more great ideas. Also, the implementation of the Digital governors is an effective way to control disturbances and make it easier to detect possible problems and failures.

    ReplyDelete