Encoders take position on diesel engine tests

Edited by the Engineeringtalk editorial team Jun 19, 2006

To undertake accurate performance tests on new diesel engines, Cummins Engine Company has to track the position of pistons in the cylinders.

To undertake accurate performance tests on new diesel engines, Cummins Engine Company has to track the position of pistons in the cylinders.

The new Sick DRS60 encoder makes the process much simpler with more accurate tests, providing cost and time savings.

Cummins Engine Company is the world's largest independent designer and manufacturer of diesel engines in the 30 to 3500bhp range.

Cummins Daventry plant produced 3000 12-, 16- and 18-cylinder engines in 2005 for generator sets, locomotive traction, dumper trucks and marine use.

During the design and development stage, new engines are extensively tested using three in-house cells.

As part of Cummins focus to continually improve its processes, the three main components of the test cells, the encoders, couplings and support brackets, were reviewed for possible upgrading.

In the company's search for products that would further enhance its test cells, the engineers at Cummins discovered the DRS60 encoder from Sick (UK).

One of the more important tests is to measure the peak cylinder pressure at the point of combustion.

In making this test, it is vital for the technicians to know the position of the piston in the cylinder and this is achieved with the help of a once-per-revolution pulse from an incremental encoder.

This pulse has to align with top dead centre (TDC) on the cylinder and becomes the reference point for all other measurements.

With the previous system, the once-per-revolution pulse had to be aligned with TDC by hand.

This meant turning the engine to TDC then turning the encoder until the pulse was found.

The technician then had to try and fit the encoder without any rotation of the shaft, which was an extremely time consuming and difficult task.

The Sick DRS60 encoder has, as a standard feature, electronic adjustment of the position of the once per revolution pulse via a button located under a cap on the rear of the encoder.

When this button is pressed, the position where the zero-pulse occurs is instantly shifted to the current shaft position.

Therefore, it is no longer necessary for the commissioning engineer to manually move the encoder shaft prior to mounting.

The DRS60 is simply mounted and the button pressed.

With conventional encoder designs the time taken to align once-per-revolution pulse with the machine mechanics can be in excess of 20-30 minutes.

Due to its unique electronic adjustment, alignment can be performed with the DRS60 in a matter of seconds.

The DRS60 is available in solid- and hollow-shaft designs, with cable or connector exit and a choice of output circuits including RS422 (TTL) and push-pull (HTL).

It is also available as a self-programmable unit, the DRS61, where the user can programme the ppr the encoder produces using a USB programming tool.

So, with one of these encoders installed, all the technician has to do it turn the engine to TDC, mount the encoder and press a button to align the once per revolution pulse with the shaft position.

The resulting accuracy and the smile on the technician's faces, has to be seen to be believed.