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Solutions to Increase Performance in Automotive Transmissions

Transmissions play an integral part in maximizing a vehicle’s fuel economy and overall efficiency

Modern transmissions present new challenges to automakers. Corporate average fuel economy (CAFE) standards require vehicle manufacturers to meet certain average fuel efficiencies for the entire vehicle fleet they produce over a year. Design engineers are tasked with improving fuel economy by developing transmissions that react faster while minimizing the size and weight of corresponding subsystems. While advances in transmission design have improved system efficiency overall, demands for better fuel economy and lower emissions mean that older solutions may not be sufficient to meet the design challenges of an evolving – and increasingly electrified – automobile market.

The Lee Company offers innovative fluid control components that save vehicle designers space and weight in their transmissions. For over 75 years, we’ve supplied a vast range of miniature hydraulic components that have been field-proven in millions of vehicles around the world. Our sealing and flow technology solutions are engineered to deliver the highest levels of performance optimized within the smallest package size to meet any design challenge. Lee products range from expansion plugs and mechanical valves (such as check, flow metering, pressure relief, and shuttle valves), to flow restrictor orifices, safety screen filters, and air management products like air bleed orifices or vent valves – each designed to solve complex fluid control problems within automotive applications.

Design Challenge: High Pressure Requirements in Traditional Transmissions

Vehicle designers have historically looked to improve efficiencies in automatic, continuously variable (CVT), or dual-clutch transmissions (DCT) by adding gears and gear ratios in order to amplify available torque and boost fuel economy across all engine speeds. As design trends evolved, system pressures subsequently increased to accommodate the needs of higher speed transmissions and minimize additional weight. To meet these optimized vehicle performance standards, traditional transmissions require products proven for use in high pressure environments.

The Lee Company has developed a variety of precision fluid control components to specifically address the demands of such applications.

  • Our pressure relief valves are more than just reliable – they provide quiet, stable pressure control in a single assembly to protect systems from over pressurization or pressure spikes. Their design allows for higher flows and smaller package sizes than other traditional valves or in-house ball and spring designs, which may become unstable or emit noise as pressures increase during key-on events.
  • Lee check valves supply unmatched durability and performance in the smallest package size. Our check valves are rated for high pressures to prevent leakage and were created to assist in scenarios where in-house solutions fail under intense pressure or poor casting designs.
  • Lee expansion plugs are engineered to provide a leak-tight seal without the need for secondary retention, delivering repeatable performance even under the highest pressures. We offer a variety of external expansion plugs to accommodate pressures anywhere from under a vacuum to 483 bar.
Comparing Lee Expansion Plugs By Pressure Rating, Size, and Material
Rated Pressure Expansion Plug Series Expansion Plug Diameter Maximum Sealable Passageway Expansion Plug Length Expansion Plug Material Acceptable Housing Material*
35 bar Short Betaplug® 5 – 20 mm 4.5 – 19.32 mm 8.57 – 12.62 mm Aluminum Aluminum, Cast Iron, Stainless Steel, or Steel
69 bar DL Series Plug 4 – 8 mm 3.3 – 7.2 mm 3.0 mm Stainless Steel Aluminum
276 bar 6000 Series Betaplug® 7 – 8 mm 6.5 – 7.3 mm 11.69 – 13.08 mm Aluminum Aluminum, Cast Iron, Plastic, Stainless Steel, or Steel
483 bar 6000 Series Betaplug® 4 – 6 mm 3.6 – 5.5 mm 8.00 – 10.29 mm Aluminum Aluminum, Cast Iron, Plastic, Stainless Steel, or Steel

*Expansion plugs can be used in other housing materials. In order to find the appropriate solution for your specific application, review with your local Lee Sales Engineer.

The Lee Company offers an assortment of expansion plugs rated for different pressures, sizes, and materials, giving transmission designers the freedom to select the right component for their specific needs.

Design Challenge: Low Pressure Needs in Electric Vehicles

Electric vehicles (EV) use electric drive modules (EDM), electric drive units (EDU), or eAxles to distribute torque within the vehicle. These applications require significantly lower average pressures when compared to internal combustion engine (ICE) transmissions and have similar pressure profiles to cooling systems (in the range of 1 to 3 bar). While design engineers may be tempted to use conventional cooling component solutions previously reserved for water-based systems, these methods may not be appropriate to flow oil within an EDU due to their general lack of precision or performance.

The Lee Company offers an assortment of reliable fluid control components to replace traditional cup or freeze plugs in electric vehicle drive unit design. Cup plugs pose a significant leakage risk when they are used as an external plug. With no visual indicators to confirm proper installation, automakers typically need to use an adhesive to seal unseen gaps, adding unnecessary cure time and cost, as well as an additional processing step that can introduce new failure points that lead to rework or scrap. The Lee Betaplug® is a pre-assembled tapered expansion plug designed to seal cross-holes using the principles of controlled expansion, eliminating the limitations of older solutions. It is able to create a leak-tight seal without the use of any threads, O-rings, or sealant which simplifies the installation process and leads to a more reliable and cost effective manufacturing process. Similarly, in-house cooling jets made by drilling a large hole in a cup plug may fail to produce adequate or targeted flow to specific areas within the gearbox as pressures decrease. Our targeting orifices allow designers to more precisely cool hot spots while reducing the amount of coolant needed in their systems.

Design Challenge: Air Management in the Modern Transmission

Air can be a serious issue for any type of hydraulic system – whether within an automatic, dedicated hybrid transmission (DHT), or electric vehicle. The Lee Company has developed two product lines to specifically address issues related to air management. Our Air Bleed Orifice removes trapped air while minimizing hydraulic pressure losses. It contains a small precision flow orifice with an integral safety screen filter for contamination protection, making it ideal when used to remove a small amount of air trapped at a high point. Our vent valves provide a more efficient way to prime a system and minimize the effects of trapped air. They are utilized when pushing large amounts of trapped air out as systems are pressurized during startup events.

The vent valve is a normally closed valve that prohibits air from being drawn back into a hydraulic system while the system is shut down. The valve opens to allow trapped air out as system pressures increases during startup. As the system approaches its operating pressure, the valve closes and shuts off the flow to eliminate further hydraulic loss.

Field-Proven Products Provide a Zero Risk Solution for Transmission Designers

The Lee Company engineers precise, lightweight, and space-saving solutions for automotive transmission applications. Lee products are made in the USA and are 100% functionally tested to guarantee performance. Our Industrial Microhydraulics (IMH) division is IATF 16949-certified, PPAP ready, and ROHS/REACH compliant. By providing products field-proven for use in similar environments, we help transmission designers save valuable time so they can focus on system level challenges instead of component level problems. Our extensive experience and technical expertise mean that we are uniquely equipped to help automakers meet the performance and reliability standards required for next-generation transmission design.


For more than 75 years, The Lee Company has been a leading supplier of miniature, precision fluid control products to a wide range of industries including automotive, diagnostics, medical equipment, scientific instruments, aerospace, oil & gas, and off-highway equipment. Lee products are recognized worldwide for superior quality, reliability, and performance. If you are searching for a fluid control component for your transmission application or other new vehicle technology and would like to learn more about products offered by The Lee Company, click here or contact a Lee Sales Engineer today.