Over the past decade the use of ceramic in automotive design and manufacture has become increasingly common. Its powerful physical, thermal and electrical properties make it a reliable, highly durable and cost-effective alternative to metal. As the industry faces continued pressure to deliver innovative design, improved safety features and environment-friendly vehicles (while also reducing production costs), use of this material looks set to grow.
Keith Parker, Marketing Director, Morgan Technical Ceramics, looks at some of the applications where the company is supplying ceramic and the resulting benefits.
Transducers and Sensors
The piezo-electric properties of PZT ceramic make it an ideal material for transducers and sensors, it can already be found in numerous automotive applications such as parking aids, alarm systems, wheel balancing, engine knock sensors and ignition systems. Using a piezoceramic has several key advantages. It is proven to be robust, having been used in industrial applications for more than 50 years and is a compact, solid-state transducer with no moving parts. As a result it offers long-term reliability, even in harsh environments.
Fuel Tank Ultrasonic Level Sensor
One innovative new design incorporating piezoceramic material is the fuel tank in the 2004 Ford GT. Using ‘Ship In A Bottle’ technology, TI Automotive created a blow-moulded plastic tank that encloses the fuel pumps, level sensors and other components. This first-of-a-kind solution reduces the number of openings, minimizing evaporative emissions and providing additional space for a larger amount of fuel. The traditional float gauges have been replaced with an ultrasonic level sensor with PZT ceramic for greater accuracy.
The sensor is installed at the bottom of the interior of the tank and an electric current is sent to the material, which responds by oscillating. This then sends a sound wave into the liquid that rebounds off the surface and returns to the transducer, registering the current fuel level based on a ‘time of flight’ measurement. The piezoceramic’s proven robustness in harsh fuel environments ensures consistent, reliable operation.
Piezo Bimorphs in Automotive Seating
Another interesting use of piezoceramic is in comfort systems of car seats that are now found in several luxury brand cars. These systems use piezo bimorphs (benders) embedded in the seat to drive valves that inflate/deflate strategically positioned aircushions, creating a massaging effect. A personalized level of comfort can be set and memorized to perform varying functions, for example lower back massage or temporarily increased side support. The bimorph consists of two active piezo plates separated by a carbon fibre inactive inner layer. One of the two piezo plates is electrically driven so it expands and the whole component bends, opening a valve. Using piezoceramic coupled with carbon fibre instead of traditional metal enables 20-30% greater deflection and therefore more flexibility of movement. The designer can create a more intricate product with lower weight.
Ceramics in Tyre Pressure Monitoring Systems
Ceramic is also being used in the development of tyre pressure monitoring systems (TPMS) which are set to become a legal safety standard in the US in November 2006.
Tyre pressure is an important factor for road safety and underinflation can lead to increased tyre wear resulting in longer stopping distances, reduced handling, and sudden tyre failure. A study carried out by the National Highway Traffic Safety Administration in February 2001 revealed that just under 56% of passenger cars had at least one tyre which was under inflated.
TMPS have been designed to warn the driver if there is any decrease in tyre pressure or if its is incorrectly inflated. Piezo ceramic’s unique ability to convert mechanical energy to electrical energy and vice versa, means it is ideal for this application. To provide the most accurate feedback of exact tyre pressure, the sensing device is located in the tyre. Each time the mechanical force of the tyre moving over ground is exerted on the ceramic it generates an electrical output providing enough power for the TMPS. The system then sends a pressure measurement to the driver using an RF transmitter.
Seals, Bearings and Valves
Technical ceramics, such as Alumina and Zirconia offer very high mechanical strength, the ability to retain dimensional stability in high temperatures and excellent chemical resistance. As a result of this strength and resilience, ceramic makes an ideal material from which to manufacture mechanical components, especially in aggressive environments, such as the seals used in injector units, pump bearings and valve plates.
During the compression stroke of a diesel engine cycle the air can reach in excess of 800°C and the injector pump delivers diesel fuel at a pressure of 2000 bar. The seal needs to be robust to withstand up to 8000 cycles per minute and reliable for the engine to run at maximum efficiency. The diamond-like hardness of Alumina makes it a reliable, cost effective alternative to traditional metal seals, which were prone to wear and often required replacing.
The heat produced in water-cooled engines is removed by circulating water through the engine. To prevent over-heating it is essential that the bearings in the water pump are reliable, as they are critical to its performance. Traditionally, steel-shaft carbon bearings have been used but these are not as resistant as ceramic to the particles found in the water and often create noise as they wear. Ceramic’s resistance to abrasive wear means improved reliability and longer life.
To account for the load trailer in heavy trucks, alumina plates can be used in valves controlling the compressed air for adjusting suspension levels of the cabin, chassis, or seat. The key advantages of using alumina plates in such assemblies are that the valves are typically used for more than 20 million cycles. The mechanical hardness of the alumina minimizes abrasion and leakage enabling the valves to be totally maintenance free for the service life of the valve.
Ceramic is already used in more than 50 different automotive applications (see image 1) and the list continues to grow. Its electrical properties and mechanical strength make it an increasingly attractive option. Morgan Technical Ceramics works with designers looking to improve reliability while also developing new features. This materials revolution is not just confined to the automotive industry – manufacturers in aerospace, defence, medical and telecommunications companies are also increasingly using ceramic alternatives. Ceramic is fast becoming known less for its use in earthenware and pottery and more for the opportunities it creates in the manufacture of items essential to our every day lives.