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Step-By-Step Lubrication

01 May 2003

Martin Hyde describes a custom-designed system, comprising a stepper
motor and control electronics, that provides instant vehicle lubrication,
whatever the conditions

Interlube Systems based in Plymouth, manufactures a range of centralised
lubrication systems for commercial chassis lubrication that primes and
maintains a vehicle's lubrication quickly and effectively. Suitable for
use in all climates, including the climatically extreme North America,
Russia and the Far Eastern markets, it can distribute lubricants in
ambient temperatures varying from +40°C to as low as -25°C.

When Interlube was looking for an electronic pump solution for these
systems, its engineers worked closely with automation and control
component manufacturer Crouzet, to find the right products. Crouzet used
its experience and application knowledge to supply a stepper motor and
gearbox together with a specially developed electronic control board.

The new design offers an alternative to conventional pneumatic or
electro-pneumatic systems that use the vehicle's engine and air supply as
their power source. The drawback with these types of systems is that
whilst in use, the vehicle is immobilised and this delay can be
inconvenient, particularly during commissioning, which can take up to a

Called the AC3, the new pump has a capacity of three litres and is
designed to feed up to 108 lubrication points on a vehicle. Interlube's
specifications called for a motor that would not only create the torque
necessary to replace pumping pressure from a vehicle's pneumatic system,
but could do so at variable speeds and lengths of time. They also wanted
the pump to be equipped with a memory to avoid needless lubrication.

Initial trials on a synchronous ac motor and gearbox solution showed that
this arrangement produced insufficient torque. This was because
converting the vehicle's dc supply to ac with a pure sinusoidal waveform
was proving difficult. This resulted in the motor running at the correct
speed but with reduced torque. Crouzet recommended a dc permanent magnet
stepper motor from its geared range and this was combined with a
specially customised electronic control board to add functionality and
improve performance.

Stepper motors are ideal for applications where speed, direction and
positioning are required at low cost. They are simple to control using a
microprocessor based control unit, which energises the motor coils in
sequence to provide the desired result. Speed control is achieved by
varying the switching frequency and simply reversing the sequence of
energisation changes the direction of rotation. The control board always
knows the position of the rotor and therefore a feedback loop is not
required. This avoids the need - and therefore the cost - of an encoder
and feedback electronics.

The Crouzet stepper motor is coupled to a gearbox and the integrated unit
provides over 7Nm of torque at an output shaft speed of 1rpm. The motor
and gearbox assembly is itself lubricated to ensure faultless operation
at extreme temperatures. Extensive testing in an environmental chamber by
Interlube's technical director, Pat Read and engineer, Doug Birnie,
verified the motor's viability down to -30°C.

The improved drive board also enabled Interlube and Crouzet to add extra
control electronics in the system. These include dual speed, which
provides a slow speed for normal use and a fast speed for reducing
priming times, manual override, and a memory circuit to ensure correct
lubrication throughout ignition on/off cycles, loss of power or operation
of the manual override.

Interlube's AC3 system has been specifically designed to provide reliable
and virtually maintenance free service. It comprises of the main unit,
which connects to each of the vehicle's lubrication points via a loom
made up of individual supply tubes. The 3 litre reservoir houses the
electronic cont

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