Displacement sensors for automotive applications

Miniature precision displacement sensors

UK auto industry uses a range of displacement sensors for turbocharger speed and coolant pump testing as well as measuring valve lift displacement.

Non-contact, high performance displacement measurement sensors from Micro-Epsilon are solving measurement applications for a number of key UK-based powertrain developments, including the testing of vehicle turbochargers, engine coolant pumps and hydraulic valve systems. These robust sensors are providing reliable measurements that were not previously possible using other types of sensor.

Turbocharger speed testing

Over the last decade, a number of UK customer projects have been undertaken, which have relied heavily on the use of Micro-Epsilon sensors. One of these includes the use of the turboSPEED DZ140 from Micro-Epsilon, a turbocharger speed and temperature sensor system that automotive suppliers are using in a wide variety of applications, including for general test bed development work, on-vehicle fleet testing, vehicle turbocharger calibration, and for monitoring compressor speed and temperatures.

Chris Jones, Managing Director at Micro-Epsilon UK comments: “10 to 15 years ago, some of our UK customers were producing their own sensors in-house for all their turbocharger speed testing. However, over the last decade or so, our range of turbocharger speed sensors have proven themselves in terms of their performance, reliability and ease-of-use. Almost all of our UK customers have stopped making their own speed sensors and now use the latest DZ140 sensor.”

With a robust miniaturised controller and the ability to measure both aluminium and titanium blades, the DZ140 offers a variety of useful features and technical advantages. The speed and temperature sensor system operates on the eddy current non-contact measuring principle and so is resistant to oil and dirt – a major advantage over optical speed measurement systems. The system is robust, durable and compact, with a 3mm diameter sensor and a lightweight controller that measures 83 x 41 x 33mm. One customer explained how this allows them to install the sensor and controller in areas where space is tight such as on vehicle engine compartments and the smallest of turbochargers.

The turboSPEED DZ140 is a turbocharger rotation speed (and temperature) sensor and controller. As well as being able to measure the rotational speed of a turbocharger, the DZ140 also enables the user to measure the temperature of the sensor head/tip. This feature is particularly useful as it allows the user to monitor the temperature inside the turbocharger without having to fit a separate thermocouple. The DZ140 enables measurements on blades with spacing of up to 2.2mm, at speeds of 200rpm up to 400,000rpm. The sensors offer a high ambient operating temperature of up to 285C.

Engine coolant pump testing

In another recent application, Micro-Epsilon sensors helped solve a complex problem for a UK customer. The application involved an engine coolant pump on a high performance sports car, which kept failing in service after only a couple of months. After further investigations, it was discovered that the carbon seal on the pump was leaking, but the actual seal failures were varying quite dramatically, which made diagnosis even more challenging. After initial investigations, it was discovered that the spring-loaded carbon ring seal was dynamically unstable under some conditions in service, allowing coolant to pass through.

After speaking to application engineers at Micro-Epsilon, a suitable sensor was provided, which was capable of measuring the movement and alignment of the carbon seal. As the space available for mounting a sensor was very confined, Micro-Epsilon recommended its eddyNCDT 3300 range of miniature, non-contact eddy current displacement sensors.

With very limited space to measure the static seal, two 2mm diameter EU-05 eddy current displacement sensors were mounted at 90 degrees to one another, which enabled the customer to get close to the static seal to measure its radial displacement. This enabled the customer to see exactly when the amplitude of the oscillations was highest. The ES-08 eddy current sensor from Micro-Epsilon was also used to measure the radial and axial displacement of the pump shaft pulley.

Measuring valve lift for more than 20 years

Non-contact laser displacement and inductive sensors from Micro-Epsilon are being used to measure valve lift movement on a variety of engines, from standard push rod engines to more complex high performance motorsport engines. On a particular UK customer’s valve lift test rig, four Micro-Epsilon optoNCDT sensors have been performing reliably for more than 20 years! During this time, the sensors have reliably measured valve lift, bounce and ripple, at resolutions down to 0.05µm.

In a typical test rig arrangement, a push rod with a target on the top is attached to the spring retainer of the valve. As the valve moves up and down, the push rod passes up through the top cover, where the optoNCDT laser sensors are positioned to take measurements. The sensors are typically mounted above the valve train on the cylinder head.

The UK customer stated: “It’s incredible that we’ve never had to replace any of these original four sensors – we’re still using the same ones that we purchased 20 years ago.”

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