In today’s transportation industry, perceived vehicle quality can be related to reducing or eliminating NVH. Less noise and more smoothness are important design attributes for potential buyers and operators of most every type of vehicle. This includes passenger cars and light-duty trucks, as well as two-wheelers, heavy commercial vehicles, and even off-road equipment.
As a result, effective NVH control gets priority attention from vehicle development engineers, and the task is challenging. It involves shaping both tactile (smoothness) and audible (quietness) vehicle characteristics. Different manufacturing processes, component variations, dissimilar design materials, mild to harsh operating conditions, and unpredictable driving and service habits just add to the complexity. Yet, some of the best NVH solutions are simple.
Synthetic noise-damping lubricants such as the Molykote brand Smart Lubrication solutions from Dow Corning Corp. can be economical, long-lasting answers to achieve quiet comfort and added smoothness in many transportation applications. Molykote lubricants, in particular, were initially based on molybdenum disulfide (MoS2), processed from molybdenite ore, which was first used in the late 1800s for strengthening steel. Blazing the trail for transportation NVH solutions, settlers in America also used the “slippery metal” to lubricate and quiet their squeaky wagon wheels.
Various lubricating solids, such as MoS2, graphite, and PTFE (polytetrafluoroethylene), are blended with different base oils, thickeners, binders, solvents, rust and corrosion inhibitors, and anti-wear and extreme-pressure additives. The synthetic lubricants to help solve NVH problems now also include silicones and other noise-damping lubricant formulations in the form of pastes, anti-friction coatings, greases, powder additives, oils, and dispersions.
Lubrication solutions for quieting noise and adding smoothness are found in most vehicle systems. For instance, anti-friction coatings (AFCs) are applied to piston skirts and rings with a special process to help reduce engine noise, scuffing, and wear. Increased fuel efficiency and reduced emissions are added benefits. In one application of Molykote AFC, a major manufacturer of pickup trucks found no loss of engine power ratings and little to no piston or cylinder wall wear after 165,000 mi (265,500 km) of rigorous testing and service. The process extends to gasoline and diesel engines in many regions, and even for boosting fuel efficiency while quieting noise on two-wheelers in India, for example.
Other noise-damping lubricant solutions for powertrain applications include using grease for clutch dual-mass flywheels and an AFC for HVAC compressor pistons. These high-performance lubricants also can be used to reduce noise from camshafts and tappets, while coated exhaust manifold gaskets can eliminate the “ping” in exhaust systems. And, solid-lubricant coatings and sprays help reduce noise, wear, and maintenance on tractor clutch tubes and control cables.
Examples of brake-system NVH control include using Molykote Lubolid powder additives in pad and lining matrices to reduce frictional noise, vibration, and wear. Caliper pin grease helps to quiet noise on brakes, and AFC for brake-pad retainer clips reduces friction, noise, and potential roughness. Good lubrication also can help control NVH that might arise from back plates, shims, boosters, and pedal bearings and pivots. The same wear and corrosion resistance extends the life of loading-arm connecting pins for construction equipment such as backhoes.
Controlling noise from body systems is important, too. Noise-damping greases are applied to slider guides for sunroofs and panoramic roofs. Colorless, non-staining AFCs are used on seals for windows and doors. Other lubrication solutions enhance the tactile quality and help deliver smooth-operating outside mirrors and antennas, as well as door, trunk, and liftgate latching mechanisms.
As the volume of engine, road, and wind noise has been lowered, the need to control buzzes, squeaks, and rattles (BSR) inside the vehicle has soared. With more comfort-and-convenience content inside vehicles, unwanted noises can become real owner/operator irritants as well as costly warranty-repair problems. Also, the just-right tactile feel on interior components contributes plenty to perceived quality.
Noise-damping lubricants can be used throughout a vehicle’s interior. They eliminate noise and add a velvety touch to media controls and a full range of rocker-, toggle-, and slider-switch technologies. They are especially effective for quieting noise and smoothing operation of miniaturized motors with plastic gear sets.
Some greases help enhance operation of airbag modules, seating components, and window-lift regulators and cable systems. AFCs help to eliminate stick-slip squeaks from materials used for door and seat trims, instrument panels, consoles, cupholders, glove boxes, and clips and fasteners. Colorless, non-staining lubricating films stifle noise and add smoothness to sun visors, mirrors, head-rest sliders, and seat guides. Grease-like silicone compounds are used on HVAC vents, parking brake cables, and wiring harness routing.
What’s next in the lubricants area? The vast majority of today’s transportation vehicles are powered by internal-combustion engines, and these gas- or diesel-fueled power plants will be with us for some time to come. The need for high-performance, noise-damping lubrication will not soon abate. The challenge for vehicle development engineers to solve NVH issues—both tactile and audible—will only increase with quieter-running electric, hybrid, and other alternate-powered vehicles.
Matt Hagemeyer, Application Engineer and Technical Service, Molykote Lubricants, Dow Corning Corp., wrote this article for SAE Magazines.