Design considerations must encompass not only manufacturing processes but also the ease of assembly for OEMs. During the trial production phase of a new automotive model, frequent assembly difficulties arose with the air conditioning refrigeration piping, leading to substantial redesign costs later on. By implementing synchronous engineering for final assembly, virtual assembly analysis and design constraints were applied during the development of the refrigeration piping. This approach effectively reduced production costs during final assembly and enhanced manufacturing efficiency. This paper outlines the assembly and design challenges encountered in synchronous engineering analysis for air conditioning refrigerant piping, along with corresponding solutions. It offers valuable guidance for the development of refrigerant piping systems in new vehicle models.

Introduction to Synchronous Engineering for Final Assembly

Synchronous Engineering (SE) for final assembly refers to the process whereby final assembly processes participate concurrently in the design and development stages of automotive development. It primarily involves conducting process analyses of assembly digital models, production lines, equipment, and assembly procedures, thereby providing feasible process design modifications for the design team. Its primary purpose is to identify and address potential issues in product design during the drawing design and digital model generation stages. This enables proactive measures to be taken against potential problems during process implementation, ensuring new vehicle models possess production feasibility and equipment/tool compatibility.

Air Conditioning Pipe Assembly and Design

1. Composition of the Automotive Front Compartment Air Conditioning Refrigerant Piping System

The air conditioning refrigerant piping primarily comprises the air conditioning high/low-pressure pipe assembly, air conditioning exhaust pipe assembly II, air conditioning exhaust pipe assembly I (which may be integrated with assembly II depending on assembly feasibility), air conditioning low-pressure pipe assembly I, and air conditioning high-pressure pipe assembly I (which may be integrated with the high/low-pressure pipe assembly depending on assembly feasibility). 

2. Design and Assembly Issues in Air Conditioning Refrigerant Piping

(1) At the connection point between the high/low-pressure pipe assemblies and the HVAC expansion valve, the foam gaskets integrated into the high/low-pressure pipes are excessively thick and rigid. This causes significant interference with the front panel, making pipe assembly difficult.

(2) The air conditioning high/low-pressure pipe assembly incorporates its own mounting brackets (secured to the fuselage side panels and longitudinal beams). The mounting holes are circular, with insufficient clearance allowance for X-axis hole offset. Due to precision fit requirements and cumulative tolerances, bolt holes may fail to align correctly.

(3) The air conditioning refrigeration lines are connected via bolts and nuts. During prototyping, insufficient operating space for tightening tools (such as impact wrenches) may occur. Interference persists even when short sockets are used as replacement tightening tools.

(4) During assembly of the pipe joint clamping plate, refrigeration oil cannot be applied, resulting in refrigerant leakage upon completion. The connection between the air conditioning high- and low-pressure pipe assemblies lacks a flexible hose section, making rigid pipe connection difficult and prone to deformation.

(5) The pipework design is suboptimal, frequently resulting in issues such as abnormal noises and inadequate assembly rationality. For instance, the pipework routing does not sufficiently hug the engine compartment, and the air conditioning filling port is positioned too low to permit refilling.

3. Design Constraints for Air Conditioning Refrigeration Piping

Design constraints are binding specifications derived from the compilation of recurring issues encountered during the introduction and prototyping of new vehicle models. They serve to identify areas requiring improvement in subsequent product designs. In response to the aforementioned assembly issues, the following design constraints are established:

(1) The foam material within the pressure plate at the connection point between the high/low-pressure air conditioning pipe assembly and the HVAC expansion valve shall be specified as PUR material, with a thickness preferably less than 15mm.

(2) On the air conditioning high/low pressure pipe assembly bracket, all mounting holes except the primary locating hole shall be elliptical in the X-direction (e.g. 8×10, subject to bolt specifications) to accommodate cumulative tolerances. The bracket connection points to the vehicle body must incorporate anti-rotation restraints (e.g., locking clips) to prevent bracket rotation during bolt torque tightening, which could cause duct deformation. Air conditioning duct brackets must be positioned on rigid pipe sections to avoid scratching flexible hoses.

(3) During initial data design, allowance must be made for operational clearance when tightening pipe connections. When using an elbow gun, the riveting head must be positioned more than 85mm from the stud tail; when using a straight gun, the riveting head must be positioned 40mm from the stud tail.

(4) For pipe joints, the male end must face upwards in the Z-direction (no requirement in the X-direction) to facilitate application of refrigeration oil. Rigid pipes must not connect directly to other rigid pipes; one connection must incorporate a flexible hose transition. Sealing at the joint must be correctly managed, such as by adding a sealing gasket.

(5) Above the high- and low-pressure filling ports of the air conditioning pipe assembly, a clearance of 50mm diameter and 250mm height must be maintained free of obstructions. Additionally, the spacing between the high- and low-pressure filling ports must be appropriately arranged (determined by the size of the filling gun nozzle).

Conclusion

This paper summarises common issues encountered during the final assembly of refrigeration piping systems for automotive air conditioning units. By implementing concurrent engineering during the early stages of new model introduction, SA constraints were incorporated into the design phase. This approach mitigated deficiencies in product design, optimised the manufacturability of final assembly processes, and reduced production costs for the enterprise. Furthermore, it provides valuable guidance for the development of refrigeration piping systems in future vehicle models.