Development of Multi Stage Hybrid System for New Lexus Coupe 2017-01-1173
Lexus launched the new hybrid luxury coupe LC500h in 2017 to help enhance its brand image and competitiveness for the new generation of Lexus. During the development of the LC500h, major improvements were made to the hybrid system by adopting the newly-developed Multi Stage Hybrid System, which combines a multi stage shift device with the transmission from the previous hybrid system to maximize the potential of the electrically-controlled continuously variable transmission. Optimum engine and electrical component specifications were designed for the new vehicle and transmission. As a result, the LC500h achieves a 0-to-60 mph acceleration time of 4.7 seconds, with a combined fuel economy of 30.0 mpg while satisfying SULEV emissions requirements. Two controls were constructed to help resolve the issues that arose due to adding the shift device. A model-based shift control that calculates the torque for the electrical components during shifts was established using an optimal control method. The power management control, which ensures the input and output power of the lithium-ion battery in the LC500h, was modified by applying compensators to reduce delays in detecting speeds of electrical components and providing torque request to the electrical components. Additionally, a control simulating a ten-speed transmission was established to enhance dynamic drivability in line with the intentions of the driver when accelerating, to eliminate the rubber band effect using the characteristics of the shift device.