Case Study: EHCU repair solution cuts the customer´s warranty costs by 75%

By Ángel López, PhD, and Iker Ibisate, Product Engineering Managers at RPK Technological Center

When a supplier quality issue affected several Electronic Hydraulic Control Units installed in a fleet of vehicles, the customer faced a major challenge: the unit was originally designed as "non-serviceable" (motor-only replacement was deemed impossible), and the original production line had been dismantled.

The challenge

When a defective motor is removed from the HCU, two spring-loaded pump pistons extend into the bore, blocking the replacement motor.

• Constraint 1: Retract and hold the pistons without damaging internal components or contaminating the hydraulic circuit.
• Constraint 2: Drastically reduce warranty repair costs compared to replacing complete HCU assemblies.
• Constraint 3: Guarantee strict dimensional tolerances for the retainer sleeve, as it remains permanently embedded inside the unit.

RPK Group´s proactive engineering solution

While the customer’s initial request focused on the concept of the retainer sleeve, RPK Group delivered an ad-hoc, end-to-end industrialization solution:

• RPK Group provides the customer with the design service procedure and the custom multi-stage tool. The tool retracts the pistons in two phases (5 mm via a rotating cam mechanism and an additional 4 mm via a scissor linkage). It places the retainer sleeve (Assembly Aid Retainer) between the pistons with high precision. Installing the new motor pushes the sleeve deeper into the bore, releasing the pistons and locking the motor in place.
• RPK Group designed and manufactured all production machinery to produce the sleeve, service tools, and subcomponents at scale (including springs, actuation levers, and linkages).
• Because the sleeve remains inside the hydraulic unit, dimensional accuracy is critical. RPK Group integrated an automated 3D vision inspection system into the serial production machine to measure key critical dimensions on 100% of the manufactured sleeves in real time. If the part meets the drawing's critical requirements, the system engraves a Laser QR code. Every good single retainer sleeve is laser-marked with a unique QR code, providing full lifetime traceability (batch data, date, and 3D inspection results).

Results & Business Impact

• ~75% Warranty Cost Reduction: Replacing only the motor avoided replacing complete HCU assemblies, saving millions in warranty costs.
• Ad-hoc Engineering Solution Delivery: The customer received a complete solution spanning from initial service concept to ready-to-operate serial production machinery.
• Quality Assurance: 100% inline 3D vision inspection ensured no out-of-spec parts reached the field.
• Traceability: Individual QR marking for complete lifecycle tracking.

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