Development of Plastic DL Pulley for Variable Displacement Compressor

Transcription

1 Development of Plastic DL Pulley for Variable Displacement Compressor Junichi OHGUCHI Yuichi AOKI Hideki OKA Kouji YAMADA Yoshihiro TANIMURA The needs of a variable displacement compressor are high with a view to an improvement regarding fuel cost saving, power saving, acceleration, and also reducing the ON/OFF shock. Commencing with the European market, the demand has tended to expand worldwide. In this report, we describe the development and design of material and shape for a simple structured material breaking type torque-limiter that is a built-in plastic DL (Damper & Limiter) pulley, and the development of excellent heat resistance plastic material for the plastic pulley that has achieved a 5% or more reduction in weight compared with the magnet clutch. Key words : Variable displacement compressor, Torque-limiter, Plastic pulley Variable displacement compressor Plastic pulley Limiter Fig. 1 Variable displacement compressor w/ DL pulley Damper Plastic pulley Hub (limiter) Fig. 2 Structure of DL pulley

2 Mass (kg) For compact vehicles Current product (Fe DL pulley) Company A Company DENSO Magnet clutch 55% DL pulley Plastic DL pulley Year Fig. 3 Weight reduction trend of pulley for compressor Function : elt protection at compressor lock Normal load Limiter part Compressor shaft Table 1 DL pulley specification comparison Over load Developing product Fe DL pulley LS3 magnet clutch Limiter breakage Only pulley rotates Structure Fig. 4 Limiter structure Diameter Length Mass Limiter torque variation 1 (1%) 27 (3%) 4g (55%) 15% (5%) 11 87g 3% g

3 Fatigue limit line (NG) Amplitude torque Ta Tm Compressor load Fatigue limit line (OK) OK area Average torque elt slip torque Water pump elt Power steering Fig. 7 Function demanded from limiter Alternator Compressor w/ DL pulley Engine crank pulley DL pulley Fig. 5 Engine layout Normal Compressor lock Torque Ta elt slip torque Tm Time Limiter part (breaking part) Fig. 6 Force acts on limiter Fig. 8 Shape of initial development Haul Cracking Compression Fig. 9 Stress distribution and cracking around limiter part

4 UG CAD shape FEM Patran Feedback isight Global & local searching Mesh Elastic-plastic analysis result Stress distribution haul acts Heterogeneous stress distribution compression acts Only the haul stress acts equally Marc Elastic-plastic analysis Patran Result process Value obtain Thickness twidth w AngleR Fig. 11 Optimal design flow chart R Evaluation Fig. 1 Optimal shape of limiter (homogenization of stress distribution) Estimated breaking torque (Nm) Probability density R1 Width Thickness Theta1 R Range Fig. 12 Contribution from tolerance design After modification Initial reaking torque (analytic value) Upper limit standard (belt slip torque) Fig. 13 Comparison of breaking torque variation

5 Amplitude stress W (MPa) 4 2 Cast iron Sinter metal S1C S45C Average stress (MPa) Powder mixing Compacting Sintering Fig. 14 Fatigue limit line figure of various materials Material strength (MPa) Tensile strength (1-5mm/min) Rotating bending fatigue strength (9SN) Fatigue limit ratio All C amount (wt%) Fig. 15 C amount and material strength Fatigue limit ratio Fig. 16 Production process of sintered metal limiter Steam treatment Rust-proofing Amplitude torque Ta (N m) Assembly confirmation result S Average torque Tm (N m) Shape reaking torque Target elt slipping torque Variation Fig. 17 Comparison of breaking torque variation

6 Table 2 Comparison of material required characteristic for typical plastic Low density Dimensional accuracy Strength Thermal shock Heat resistance Chemical resistance Productivity Judgement PF PA PAA PT PPS Steel GoodSome concernspoor Table 3 Product required items of plastic pulley. Section A Crack according to the belt tension Fatigue strength Problem Deterioration because of heat when belt slips Crack by the heat stress between the plastic and the metal Crack due to retentivity shortage of a metallic ring. Required item Heat resistant Fatigue strength Linear expansion coefficient (a) (b)-1 (b) mm 1.5 mm 2m Fig. 18 SEM micrographs of cross section surface

7 TG (%) Fig. 19 TG decomposition profile of material both before (initial) and after endurance test Temperature (ºC) Deterioration Initial After endurance test Deterioration (ºC) After endurance test Heat history (ºC) Fig. 2 Calibration curve of heat history and deterioration : Former shape Fig. 21 Investigation of the interface between plastic and metallic ring

8 The pulley inside diameter is expanded by heat of the bearing. The clearance is generated between metallic rings. Offset load elt load The stress concentrates on the pulley edge side. The crack occurs in the interface. Fig. 22 Presumption of crack generation mechanism No clearance Plastic Room Measurement Metallic ring Stress by tightening Inclination=Linear expansion coefficient difference of plastic and metal Development target :3ppm/ºC Conventional material :35ppm/ºC Interface High Run generation Plastic pulley Metallic ring rg generation Fig. 25 Simulation of interfacial amount of clearance generation (a) Rotated by the same phase (b) The phase of plastic pulley and metallic ring shifts Fig. 23 Phase difference between plastic pulley and metallic ring by clearance generation Stress A A rg Plastic pulley generation Metallic ring Fig. 24 Scheme of crack due to retentivity shortage of a metallic ring Stress A A Problem Table 4 Material development indicator 1. Control of foam 2. Thermal deformation Material development target value Pyrolysis 3ºC Linear expansion coefficient 3ppm/ºC Means Review of low boiling point agent Optimization of amount of inorganic filler

9 Deterioration TG (%) -5 Curing agent Flexibilizer A Target 3 Temperature (ºC) Resin Conventional material Flexibilizer Fig. 26 Thermal decomposition behavior of the ingredients contained in the conventional material No clearance Room Measurement Developed material Conventional material :35ppm/ºC After endurance test High Run Interface TG (%) -5 lister area -1 Conventional material Heat treatment (ºC) Excellent Fig. 28 Simulation of interfacial amount of clearance Developed material lister Fig. 27 TG decomposition profile showing blister formation if developed material

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