Some of the major goals in car industry are to reduce the weight and size of the cars by reducing the mechanical parts and combining them into smaller electrical system to increase the fuel economy. One way to achieve part of this goal is to use an Interior Permanent Magnet (IPM) machine as an Integrated Starter Alternator (ISA) system. In this paper, we have accomplished two considerable improvements in IPM machine design for starter-alternator applications: first, a reduction in the amount of the magnet used in machine and as a result a reduction in the total cost and secondly, an increase in the amount of the produced power in generation mode by improved design of three-layer permanent magnet on the rotor.