A Thermal Study on Small Synchronous Reluctance Machine in Automotive Cycle M. A. H. Rasid*, A.Ospina**, K. El Kadri Benkara**, V. Lanfranchi** *Faculty of Mechanical Engineering, Universiti Malaysia Pahang, Malaysia ** EA1006 Laboratoire Electromecanique, Université de Technologie de Compiègne, Sorbonne Universités, France Abstract— Embedded automotive application has one of the harshest environment for electrical machine, especially in terms of thermal requirement. In this study, thermal evaluation of a small synchronous reluctance (Syncrel) machine intended to be used as clutch actuator is presented. A lumped parameter (LP) thermal model was built and validated experimentally. The results of the model subjected to a standardized WLTP cycle shows that the machine is thermally robust and apt for automotive application. Keywords— Synchronous reluctance machine, automotive application, thermal modeling, lumped parameter model, WLTP cycle. I. INTRODUCTION Functions in automotive that are being electrified involve more crucial and complex applications such as clutches, power steering, assisted brakes and others. Main requirements that are common to these applications can be divided into three categories: machine performance, volume and weight, and cost (Fig. 1). For thermal aspect, it becomes particularly challenging as these applications are often placed in a particularly high temperature environment (up to 140°C in the engine compartment). For a machine without permanent magnet, the conductor insulator is the component to be monitored carefully. Depending on the thermal class of the insulator, the critical temperature Tmax over which it will be deteriorated can be situated from 150°C to 240°C [1]. Having a precise and reliable thermal model predicting the temperature evolution in the stator slot of the machine is therefore essential in order to design an optimized machine. II. STUDY BACKGROUND A. Clutch actuator application A project named e-Clutch [5] project started in 2006 had an objective of replacing actual clutch actuator system that used a DC motor along with a spring compensation system as shown in Fig. 2. We wanted to have a less encumbering system (exterior diameter less than 43.5mm), with a more reliable motor that can be directly integrated into the housing of the clutch system. The condition in the clutch housing includes Fig. 1. Requirements related to automotive equipment actuator. high ambient temperature (140°C), tight space and intrusion of dust, oil and eventual used clutch lining. Fig. 2. The clutch actuator by compensation system, which can be found for example in the Toyota Aygo MMT. The whole system is then mounted onto the transmission system housing. B. Syncrel with segmented rotor Recent studies have shown that the Syncrel motor can be suitable for this type of application [2, 3, 4]. Taking into account requirements mentioned above along with manufacturing cost and feasibility, a totally enclosed non- ventilated Syncrel motor with segmented rotor was designed and prototypes were built. It is a 2 pole pair motor with passive segmented rotor and distributed winding. The