Capacitec - PRODUCT NEWS


Advances in Non-contact displacement sensors bring new levels of quality and efficiency to vehicle manufacturers.
By Bryan Manning and Robert Foster - Capacitec

Over the past decade continued breakthroughs in sensor technology has improved the automobile both inside and out. Most consumers are aware of the benefits that sensors have contributed to automotive subsystem improvements such as air bags, automatic braking systems (ABS) and load leveling systems. Less obvious is the role sensors have taken in the dramatic improvements in today's automobiles that are a result of improved R & D, Quality Control and manufacturing methods.

A major trend in the Automotive market that is driving the requirement for improved sensing is the fact that vehicle manufacturers are outsourcing major subassemblies to so called Tier 1 suppliers. Today Tier 1 suppliers such as Robert Bosch, Delphi, Visteon and Continental Teves are being given full design and manufacturing responsibility for large subassemblies of the automobile. They now supply major components such as complete suspensions, wheels/brakes or transmissions to Toyota, DaimlerChrysler, GM, Ford, Volkswagen and other global vehicle manufacturers. The role of the vehicle makers has also changed over the years from one of a vertically integrated manufacturer to the role they have today as major assembly houses.

This change at the top has driven down to Tier 1 suppliers a more intense requirement for R & D, Quality, and efficient manufacturing. This shift in turn has dramatically increased the need for improved sensor technology to meet the ever-increasing demands of these highly specialized Tier 1 suppliers. They are now developing very specialized state-of-the-art braking, drivetrain or suspension systems and need specialized sensors to help in their research, design and quality/efficient production processes. They are also subjected to the very stringent quality system requirements such as Q1 and QA9000 placing constant emphasis on building quality parts the first time, every time.

Capacitive non contact displacement and thin gap sensors are good examples of the type of sensors that have made significant contributions to improving R & D, quality and manufacturing efficiencies for vehicle manufacturers around the globe. The types of vehicles that have been improved include automobiles, sports utility vehicles (SUVs), light and heavy trucks as well as off-road vehicles.

As new Quality Control methods such as In-process and 100% parts inspection become more commonplace, displacement sensors are being used in a greater number of locations throughout the automotive manufacturing process. Non contact displacement sensors, in particular, are more often the optimum choice in displacement sensors. This is due to their many advantages such as the ability to handle 1000°C, accuracy in the micron range, and small size. Additional benefits will be outlined further in this article. Although there are many determinants driving the increased demand for these sensors, the benefits fall into the two major categories of improving quality/performance and reducing cost.

Brought on by global competition and more demanding end user customers, improved quality continues to be a major theme for vehicle manufacturers around the world. Manufacturers such as DaimlerChrysler, Ford and Honda promote in their advertising that one of the best long-term values that they can offer their customers is a consistent high quality product. As technology progresses so too do the quality methods employed. Older quality methods such as AQL are now consistently being replaced with preferred methods such as 100% inspection and zero defects. This change in philosophy requires displacement sensor technology capable of measuring a new array of difficult targets, locations and configurations.

The requirement of increased precision measurement is another major factor in today's quality control environment. Component and subassembly dimensions are getting more and more precise. This is in turn driving the need for increased precision in the measurement systems controlling them. In many cases the components themselves are becoming smaller requiring smaller and often more precise displacement sensors. Automotive engineers now require sensors that can be fit into locations with diameters of less than 1 mm. They also need to measure gaps as small as 0.009" (0.23mm). Today engineers are looking for displacement measurement systems that can measure in millionths instead of tenths or measure 100 nanometers instead of a micron.

In the R & D departments of Vehicle Manufacturers and Tier 1 and Tier 2 suppliers, engineers are being forced by the marketplace to create higher quality, longer mean time between failure (MTBF), better performing, easier to manufacture components. Those involved with engine components are also required to meet ever more stringent government driven fuel efficiency and emissions requirements such as the new Diesel Fuel Efficiency requirements enacted in the United States in the year 2000.

The combined growing demands from R & D, Quality and manufacturing methods engineers has resulted in significant improvements in non contact capacitive displacement technology at Capacitec over the past decade.

Figure 1
From engine piston and valve design to braking and suspension system testing non-contact displacement and gap measurements systems help engineers design better cars and trucks.

Here are some examples:

Increased temperatures up to 1832°F (1000°C)
Sensor overall diameter reduced to 0.004" (100 microns),
thin gaps as small as 0.009" (0.23mm)
Accuracy as precise as 8 microinches (0.2 microns)
Immunity to magnetic fields
Faster response (up to 200kHz)
On-vehicle DC modular electronics

These improvements have allowed sensors to play a greater role in the labs and factory floors of automotive manufactures from Porsche and BMW to Ford, General Motors and Honda. Here are some specific examples of where these technology breakthroughs have yielded the most added benefits to vehicle makers:

1. Braking Systems (Disc and Drum)

Beginning in the early 1990's Capacitec has developed a new line of Disc Brake Wear Analysis Sensors. The new sensor system is capable of taking high temperature 932°F (500°C) dynamic brake system measurements both in the lab using dynamometers and on-vehicle using rugged modular electronics. By measuring displacement variables on a brake rotor in motion, data can be collected and analyzed to show several characteristics such as:

Rotor run-out (TIR) Rotor thickness variation (RTV) Rotor coning
Thermal expansion Plate-to-plate orientation (V-ing, barreling) Wobble

Working with OEMs such as Ford, Honda and Renault and
Brake suppliers such as Akebono, Allied Signal, Bosch and Federal Mogul along with Brake Testing Houses such as Link Engineering, we have continued to expand and enhance our capabilities.

Disc Brake Wear Analysis Sensors

Figure 2
Displacement sensors can be placed in pairs on either side of an automotive brake disc to dynamically monitor an assortment of performance parameters.

The increased demand for closer tolerances and rapid prototype designs has forced automotive brake system and testing engineers to look for new ways to verify engineering predictions and/or explain the dynamic physical characteristics of braking system components.

Driven by Automotive Manufacturers such as Ford, GM, Renault, Jaguar and Mitsubishi along with Disc Braking Systems Suppliers such as Robert Bosch, LUK, Akebono, Ferrodo, Teves and Federal Mogul as well as Testing Laboratories in the US, Europe and Asia, Capacitec has developed a new line of specialized non contact capacitive sensors. The new model HPC-150-E-H sensor assembly combines the benefits of small size and a high temperature 932°F (500°C) operation.

Another major advantage of the new configuration is lower sensor replacement cost. The redesigned sensor surface provides enhanced impact survivability. In addition, an innovative new integral connector, located behind the sensing surface, allows easy replacement of coaxial extension cables without the added cost of replacing the sensors themselves.

This new sensor system is capable of taking dynamic brake system measurements both on-vehicle at test track facilities as well as in Testing Laboratories using dynamometers.

By measuring the displacement data on a brake rotor in motion, measurements can be collected and analyzed to show the following characteristics:

Drum Brake Ovality Analysis Sensors

Figure 3
Two non-contact capacitive sensors work in tandem to measure the ovality of the inside diameter of truck brake drums during brake operation to detect deformations caused by extreme braking conditions.

On large drum braking systems such as those found on heavy trucks, manufacturers are very concerned about the deformation of the brake drum during high temperature and pressure situations. An example of where these conditions exist is when brakes are applied for long periods of time in high temperature environments. When the combination of temperature and pressure is excessive the drums of these braking systems become deformed. This could occur in emergency braking situations or in prolonged downhill braking. In these cases the drum changes from the normal round shape to an oval shape causing potential malfunction of the braking system.

At Robert Bosch, the measurement of this drum deformation required the development of a custom on-board measurement system. The system consisted of Capacitec model HPC-150 non-contact high temperature brake probes installed to measure the changes in shape of the brake drum. The sensor lead wires were routed through the wheel drums and connected to special Capacitec Model 4200GP electronics bolted to the outside circumference of the wheel. The electronics were made to survive the high G forces incurred when the wheel rotated at high speed.

The system was successfully used to measure drum brake deformation during development testing at a southwestern US desert proving ground. The ambient temperature during the tests exceeded 120°F (49°C)

2. Powertrain Systems

Vehicle manufacturers are constantly researching improved designs and manufacturing methods for engines and transmissions. This research requires advanced displacement and gap sensors that have the following characteristics:

Non contact measurement
Ability to withstand high temperature/pressure
No re-calibration due to variations in types of metal
Operation in oil or transmission fluid
Very small size to penetrate inside tight spots
Resistant to magnetic fields
High frequency response to track rapid rotation or axial movements

Capacitec sensors thrive in these harsh and demanding environments. Here are some specific examples:

Diesel fuel injection systems

Cummins Engine relies on Capacitec to solve a very difficult application for the measurement of precise injection nozzle closure in their diesel heavy truck engines. The final closure position of the injection nozzle is very important for the efficient functioning as well as noise maintenance of large engines. If the nozzle is not closed enough there is a waste of fuel. If the nozzle is too far closed it causes a "ringing" vibration that leads to premature nozzle failure.

A particular challenge in this application is the fact that the measurement had to be taken in an environment of high magnetic field caused by the very high magnetic generator coils. Adding to the challenge was the very high-speed articulated motion of the nozzle stem, which required a response of 30kHz.

Capacitec met this challenge offering a model CMC60 sensor probe, which is immune to magnetic fields and has a special matched magnetic case. This sensor not only functioned perfectly under the high magnetic field present but also did not jeopardize the strength of the field that is powering the injector itself. The special electronic package used to meet the high-speed requirement was the Capacitec model 6100SC amplifier with 200kHz output.

The successful solution from Capacitec allowed Cummins to produce diesel engines that meet efficiency and the new Federal regulations on fuel economy and emissions while at the same time reducing noise and increasing mean time between failure (MTBF) for the engine.

Ring position in an engine piston head

Figure 4
While fully immersed in engine oil, two high temperature Capacitec displacement sensors measure 0.002" (50 micron) movements in the piston rings for Caterpillar Tractor.

Caterpillar Tractor came to Capacitec with another very difficult problem that they were facing. In long term testing of their engines they found that carbon buildup could actually seize the piston rings allowing oil to pass into the combustion chamber and causing emissions problems. To solve this problem they needed to measure the motion of a piston, which was cooled by oil. They therefor needed a precise non-contact displacement sensor that could operate while fully immersed in engine oil. The application also required embedding a small sensor into the moving piston with the sensor monitoring the up and down "flapping" motion of the rings operating at the engine temperature of 482°F (250°C).

Capacitec met the challenge again by installing very small diameter cylindrical style sensors (4mm diameter) with special very thin diameter coaxial cable (1mm diameter) that had to pass through a "grass hopper link" assembly to be taken out through the oil pan and then over to the on-board electronics. The solution also required that the sensors operated with 100% immersion in engine oil.

The Capacitec solution allowed Caterpillar to produce engines that met the new diesel emissions and fuel consumption guidelines, which began in the year 2000 in the US.

Measurement of 10 to 50 micron Piston ring movement

The companies AVL List GmbH in Graz (Austria) and Federal Mogul in
Burscheid (Germany) have carried out a joint experiment to study the
piston ring dynamics of a utility wagon diesel engine. They tracked first and second piston ring axial motions by means of Capacitec Model HPB-80 four-millimeter diameter capacitive probes placed on either sides of each piston ring inside a reference piston. In conjunction with complementary local pressure tracking they were successful in gathering all necessary physical data that were relevant to the understanding of the complex dynamics of piston assembly. The aim of this study was to investigate the possibilities of reducing the burn-off of engine oil. Reduction of engine oil burn-off has important implications to user's costs, the length of car service intervals and exhaust gas emissions concerns.

Additional Powertrain applications

Additional applications where advanced Capacitec technology met customers' special demands included the following:

Control of outer diameter of individual blades of a Honda Turbocharger using 800°C probes and Model 6100 200kHz electronics package.
Measurement of a rotating Turbocharger for Allied Signal to measure radial runnout (Lissajous technique).
Measurement of shaft motion at the crankshaft bearing while entirely submersed in oil for Roush Technologies racing division.

3. Vehicle Assembly

Figure 5
Example of a contact type gap sensor for use in measuring exterior gaps.

Exterior Surface Gap Measurement

Consistent and precise measurement of the various gaps around a vehicle's exterior surface has proven to be quite a challenge for vehicle manufacturers around the globe. This is a very difficult measurement problem due to the fact that there are a wide variety of gap locations each with differing requirements. Following is a partial list of the variables to consider that exist in different gap locations:

· Different materials to be measured (metal, rubber, composite etc.)
· Various contact/non-contact requirements (prevention of scratches)
· wide range of gap sizes (0.2 to 10mm)
· wide range of target geometry (flat to radius, radius to sharp edge etc.)
· signal processing differences
· instrument portability

Capacitec has developed a number of products for this application based on their experience in the Aircraft Industry. Smooth surfaces on the exterior of an aircraft are crucial to assuring proper aerodynamics. This in turn has an important effect on an aircraft's safety, noise and fuel economy. The same issues found in aircraft assembly are more and more prevalent in today's aerodynamic ground based vehicle designs.

Based on their experience with Airbus and Boeing, Capacitec developed a variety of specialized contact and non-contact gap and flushness sensing systems. Non contact gap sensors are used when both sides of the target materials are conductive or where there is sensitivity to finished surfaces such as the painted exterior of vehicles at the end of the production line.
The contact sensor system is often the preferred solution when the target material is non-conductive or has an unusual shape.

One example of an exterior surface gap measurement application is the control of flushness between a mounting bracket and the glass on a sunroof for General Motors. Because the sunroof is curved, there is a variation in the amount of glue required in different locations between the sunroof glass and the sunroof bracket. The way the process works is that the glass is first positioned into a fixture. The fixture has Capacitec sensors mounted in eight locations around the sunroof. The sensors control the amount of epoxy distributed between the glass and bracket assuring a consistent geometry to each sunroof.

By using the Capacitec gap and flushness measurement system, General Motors was able to achieve a ± 0.004" (100 micron) tolerance on a gap of 0.060" (1.5mm). This in turn led to a sunroof that was flush against the top of the vehicle dramatically reducing noise while contributing to aerodynamics and fuel economy.

4. Automotive Glass Production

The European market leader in the supply of Automotive windshield and commercial plate glass has been successfully using Capacitec non contact displacement technology over the past 20 years to maximize the throughput and quality of their high volume glass products.

In the automotive application car windshields are manufactured in high volume 24 hours a day with very demanding environmental conditions. The capacitive sensors control the tooling geometry as part of the feedback loop to control parts quality of the windshields. The sensors are exposed to 700°C in the high temperature glass molding operation. They are also required to survive daily thermal shock cycles from 25°C to 700°C. Laser technology sensors were tried in the past but could not survive this high temperature environment due to degradation of the cable fibers over time.

Advances in non-contact displacement sensors are bringing new levels of quality and efficiency to the research labs and assembly lines of vehicle manufacturers worldwide.

From Brake Testing Systems that survive the Mojave Desert test track to miniature sensors that are exposed to the most severe temperature, pressure and vibration environments, Capacitec sensors will enable automotive engineers to continue designing safer, clearer and more efficient vehicles into the next millennium. … and beyond.

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January 2009

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