Inside the Future of Automotive A/C systems: Porite’s New Sintered Guide Bush Wins
Japan Powder Metallurgy Association (JPMA) 2025 Effort Award

Porite Co., Ltd. has received the 2025 Effort Award from the Japan Powder Metallurgy
Association for its newly developed sintered guide bush used in automotive A/C electric
control valves (ECVs). These are adjusted electrically rather than mechanically or
hydraulically.

Technical Overview

Porite has developed a high-performance sintered guide bush for use in automotive
air-conditioning compressor capacity control valves (ECVs) in variable-displacement
systems. Variable-displacement compressors rely on an ECV to stabilize discharge
temperature and reduce compressor load. Traditionally, these valves used a machined
brass bush to guide the movable valves in the sliding direction. However, the need to
improve sliding performance and reduce manufacturing costs prompted the transition to a
sintered bush. In this application, “sliding” refers to the linear movement of the valve spool
as it moves back and forth inside the guide bush to control refrigerant flow.

The outer geometry of the new sintered bush was optimized to secure adequate refrigerant
flow while accommodating manufacturing constraints (for example if the wall of a
cylindrical part is too thin or too thick, the powder cannot be compacted uniformly).

For material selection, Porite adopted a Cu–Sn–P–C-based alloy containing 2.0–3.0 %
graphite as a solid lubricant. Since oil-impregnated lubricants are displaced by refrigerant,
this oil-free formulation ensures stable low-friction performance without impregnation. As
a result, sliding characteristics were improved, and manufacturing costs were reduced by
more than 50% compared with conventional machined parts.

Key Points of Evaluation

The award evaluation highlighted two major achievements:

• Cost Reduction: By replacing machined brass components with a sintered Cu–Sn–P–C material and incorporating a dispersed solid lubricant (graphite) this enabled a 50% reduction in manufacturing cost.
• Market Impact: A production volume of 3.68 million units per year suggests that the use of the sintered bush (verses the machined brass bush) is expected to expand in the future as the use of electric control valves (ECV’s) expands.

Key Technologies

Optimized Flow Path Geometry:

The former brass bush used two deep grooves. Porite’s new design uses eight smaller
grooves, while keeping the part from deforming during press-fitting. This results in more
stable dimensions and smoother sliding performance.

Advanced Oil-Free Material

Since refrigerant displaces oil in conventional oil-impregnated bearings, Porite created a
Cu-Sn-P-C (copper-based sintered alloy with added tin, phosphorus and carbon), and 2–
3% graphite for built-in lubrication.

This provides:

• Low friction without oil
• Stable sliding in refrigerant
• Strong, wear-resistant performance

Burr-Less Inner Diameter (Bore) Design

A rounded edge was added to the bore, the inner hole of the bush where the valve moves,
to prevent burrs and maintain consistent sliding. A special BL-treatment sizing step further
smooths the bore for accurate, high-quality finishing.

Tumbling Process for Anti-Galling Performance

A post-sintering tumbling step smooths the bush’s edges to prevent galling (a type of
surface damage where metals rub and seize under pressure) during press-fitting into the
yoke (the outer housing that holds the guide bush within the valve structure), helping the
part insert straight and ensuring stable valve operation.

Performance Benefits

This new sintered guide bush delivers:

• Reliable sliding performance in refrigerant
• Oil-free, low-maintenance operation
• Higher assembly accuracy and stability
• Lower friction and improved durability
• Substantial cost reduction over machined brass

Conclusion

Porite’s new sintered guide bush proves how thoughtful design and advanced materials can
deliver measurable gains in performance, durability, and cost. This JPMA-recognized
innovation not only enhances today’s compressor technology but also strengthens the
foundation for the next generation of efficient, reliable automotive A/C systems! Please
view the link for more information.