Engine Stop/Start System (ESS) is a prominent subsystem in the Micro Hybrid Systems, and helps to reduce greenhouse gas emissions and fuel consumption. Fundamentally, ESS detects the idle running of the engine, and shuts it down autonomously, and allows the driver to restart the engine, with a routine action like pressing or releasing the clutch or brake pedal.
When an engineer designs a system like ESS, typical approach to trigger the system functions is by establishing a sequence of events, detecting it, and enabling the triggers. Influence of the functions on other vehicle systems or vice versa is also considered, and system design is revised to achieve the functional safety. This results in a set of hard rules to be followed for the system functions to work. In the case of ESS in a Manual Transmission (MT) vehicle, basic events which trigger the system functions are vehicle at rest, transmission status, and clutch pedal status, and other vehicle systems like HVAC, brake, closures, etc. However, the conditions which disable an auto stop/start event are more than those which enable it. Some of these conditions are so latent and routine, that the auto stop/start function is defunct most of the times, in real time driving conditions. As a result there is a wide gap in fuel consumption between laboratory and real time driving conditions.
This paper reviews such conditions, and discusses the implementation of “Design Thinking” process, to improvise the ESS Control Algorithms. A goal was set to bridge the gap between benefits obtained in laboratory conditions and real time driving conditions. Design Thinking was implemented to identify the modes in which the ESS system would be defunct in actual city driving conditions in India through a field work. Data collected from the fieldwork was analyzed to identify the various causes and their dominance on the ESS functions. Design inputs were generated for redesigning the ESS system through the process of Ideation, to eliminate such causes and yet ensuring the same levels of functional safety. The new algorithm was validated in a simulation environment. An improvement in fuel efficiency of 20% over the conventional vehicle and 16% over conventional ESS system was demonstrated during the simulation.