Beyond Omniseal® Blog

3 Factors To Consider With Thermoplastic & Thermoset Seal Rings in Automotive Variable Valve Timing Systems

Jul 31, 2019 / by Richard Williams

Reducing emissions, improving fuel economy and drawing greater performance out of engines: requirements that are driving automotive manufacturers to seek out technology that will help them achieve these goals. One such technology on the rise is the variable valve timing (VVT) system, which influences the flow of gasses in and out of the combustion chamber through the opening and closing of the VVT valves to improve engine efficiency and fuel consumption.  Many earlier systems worked only on valves and had no lift variation. Today, most modern systems can control timing and lift, and many automobiles rely on this core system, giving drivers a smoother, more even performance at higher RPM. 

With higher demand for larger SUVs and trucks in the U.S, growing emphasis on performance and fuel economy, and increasing regulations on emissions, the need for VVT systems has expanded. The VVT market is expected to reach up to USD 50.79 Billion during the years 2019 to 2025 with a growth of 6.35%, according to MarketWatchAs the leading region for automobile production worldwide, Asia Pacific is the leader in VVTs. Europe and North America are also gaining ground with this technology. Different VVT systems are being used today; the most common type uses a camshaft actuator or phaser mounted on the cam drive gear, and an oil flow control valve solenoid that routes oil pressure to the cam phaser.  Engines require large amounts of air to operate efficiently at faster speeds, however, without these critical VVT systems, valve timing would be consistent across speeds and conditions … so timing is everything!

Leading Factors For Seal Ring Selection In VVT systems 

Like many industries, the automotive industry is fueled by performance. Maintaining quality and low costs are essential - key factors for Tier 1s and automotive manufacturers in selecting critical parts such as Meldin® seal rings for VVT systems that are key to enabling high-speed efficiency or low-speed power. Leading factors to consider in selecting these parts include:

1. Manufacturing Efficiency: Tier 1s and manufacturers who can assemble parts faster can produce more parts per hour. However, this becomes a challenge with inferior seal rings that may be too pliable, not holding their shape well as they are fitted onto camshaft grooves. Assembling parts with these types of seals tend to be a more tedious, cautious process and a sleeve may need to be used to calibrate them back to their original shape after assembly, resulting in a loss in efficiency.

2. Leakage Performance: With the trend to squeeze even more performance from engines, a tight seal is needed to ensure uniform, reproducible leakage for over hundreds of thousands of camshafts assembled.

VVT performance influences:

  • fuel efficiency, and
  • power output from the engine

The more precise the valve timing, the better one or both of the above is achieved.

In older cars, the camshaft angle was set physically by the camshaft, sprocket, and the driver chain/belt. Today, however, the cam phase angle—or the differential angle between how the cam lines up with zero phasing—is more variable and can be controlled and moved forward and back.

Rings on the camshaft bring pressurized engine oil from a pump through the camshaft into the cam phaser, a hydraulically activated unit that controls the phase angles. The changing of the angle is influenced by oil pressure and responsiveness of the VVT system. The higher the pressure, the more increase in cam shift and the more the valve will open. The oil pump drives the pressure; solenoid vales open and close by a certain amount to influence engine performance, specifications of which are dictated by microprocessors.

When this motion of the cam phase angle can be more precisely controlled, the VVT can achieve a more accurate performance. The more precise the angle, the more power output generated, and the better the fuel efficiency. However, performance of every part is necessary in this process, and seal rings play an instrumental role. If some oil leaks through the seal ring gap or past it, then the system may no longer be able to accurately control pressure in the camshaft. Pressure may be too low or too high for the VVT to optimize tolerance.

With varying seal performance and tolerance, manufacturers cannot consistently program processor timing, and instead may need to use different tolerances on each cam phaser as a result. Considering that three seal rings are used on each camshaft, and perhaps a million camshafts may be manufactured, this can be a big undertaking.

Conversely, with more precise systems, and seals providing the same level of uniform, reproducible leakage, manufacturers can more easily program processor timing to optimize engine efficiency, most done in high-end vehicles. Meldin® seal rings are used often in engines that go much faster such as sports or racing cars, which need a system that increases the time the valves stay open.  High RPM engines need to have the exhaust valve open sooner so the pressure has a better chance to exit the cylinder.  Overall, specific timing is critical for successful operation of any vehicle.

3. Reliability: Additionally, the cost of failed seal rings can be expensive—from warranties, to recalls, reputation, and more. Worn or lower performing seal rings can result in declining fuel consumption, efficiency, acceleration, or failure to meet emissions requirements.

Costs can quickly mount for seal rings that need to be replaced, due to performance. Assuming that the parts take a half to a full day to fix at $50/hour, the cost could be $200 to $400 per vehicle, which could quickly grow to as much as $40 million for 100,000 automobiles. Hence, it is a replacement nightmare to be avoided at all costs.

Ensuring the Best Sealing Solution in VVT Systems 

Using the right seal ring in VVT systems, therefore, is important to ensure a tighter, more reliable seal that provides lifetime confidence. 

Frequently, PTFE rings are used in the VVT. However, these are often flexible and do not hold their shape, resulting in manufacturing issues described above. Conventional plastic seal rings may also be used. However, these typically produce a joint/gap that does not provide a tight seal.

Meldin® seal rings, conversely, minimize leakage and friction loss in VVT systems. These high-performance solutions include an array of thermoset polyimide materials and engineered thermoplastic products based on polyphenylene sulfide (PPS), polyetheretherketone (PEEK), and polyamideimide (PAI) to provide a number of options for manufacturers of automotive systems.

Comprised of polyphthalamide (PPA) and engineered for chemical inertness, Meldin® 51-868 material is often used in VVT and offers the highest thermoplastic economical material for chemical inertness. Specific benefits include:

  • Self-lubrication
  • Long durability under extreme temperature and load with service temperatures ranging from -50 to +150 °C, maximum loads of 25 MPa, and tolerance controls of +/- 30 μm
  • Capacity: >20 M/yr
  • Dimensional stability in chemicals    
  • Defects Program: 0 ppm

Other materials such as Meldin® 54-875 and Meldin® 73-995 are frequently used in VVT. Saint-Gobain Automotive Polymer Solutions’ products also offer immediate leakage benefits with special 2L and 2T joint/gap designs that can reduce leakage by a factor of ten and ensure uniformity across speeds and temperatures for better cam phasing control.

Designing From Conception Through Validation

With over 40 years of experience in developing sealing and polymer solutions for the automotive industry, and 26 in developing seal rings for VVT core systems for global automotive companies such as Tier 1s and a leading German luxury brand, Saint-Gobain Automotive Polymer Solutions is a leader in the design of these critical parts. We especially excel in unusual applications that have never been done before, pushing the boundaries of systems, and offering full support and design from initial conceptualization to successful application.

Quality is paramount, and we ensure it by controlling each factor going into our parts—materials, design tools and prototype parts--providing reliability in high-volume environments. We offer a complete solution with a one-stop shop for compounding tailored Meldin® thermoplastic and thermoset materials. 

We often co-develop solutions with customers’ engineers, based on shaft and bore materials, dimensions of the shaft and other elements in the design envelope, as well as their needs for oil viscosity, desired leakage rate based on components in engine, size of pump, level of friction, durability, and more.

The resulting design proposal addresses associated metal components (finish, hardware, groove needed, etc.), assembly design, unusual metals (and their ability to run against a particular hardness of steel, finish, etc.), testing (on test rigs, the customer’s hardware, etc.), and more.

When it comes to testing, service position testing can help to ensure a high degree of confidence across at all speeds, pressures, and real-world conditions over time. A full test report offers extensive insights for any future potential changes to the internal combustion engine. Application testing can offer full component data, not often provided in the full system test, and at a much quicker rate than assembling a full engine, putting it in a rig, running it, and tearing it down.

Finally, we leverage our extensive experience and know-how to ensure the performance of the product from prototype to production.

In addition to their use in VVT systems, our polymer solutions are used across transmission types and in clutches and dual mass flywheels, as well as in belt tensioners, throttle bodies, and fuel pumps to name just a few. Our components feature low friction, sealing, dampening properties, simplified assembly, and reduced weight to address some of the automotive industry’s biggest challenges.  Find out how our special-designed, rectangular seals make THE difference in transmissions and ball joint liners in steering systems.

Contact us today for your automotive applications and learn more about how we can help you with critical seals and other custom parts.

Topics: Automotive

Richard Williams

Written by Richard Williams