1. Heavy-Duty On-Board Diagnostics and Cooling Systems

1.1. Hybridized Cooling Systems

LO 11-09: Explain the application of heavy-duty on-board diagnostics and the use of electrical actuators and electronic controls in hybridized diesel engine cooling systems.

 

Hybridized Cooling Systems

Heat rejected from an internal combustion engine, such as by the cooling system or exhaust, represents a significant loss of energy and engine thermal efficiency. GHG regulations are the driving force behind the increasing hybridization of the cooling system, wherein mechanical components are integrated with electric actuators and motors as well as electronic controls. Electrification of cooling system components enables more efficient engine operation compared to that achieved with the use of only mechanical components. In fact, experimental demonstration of cooling systems with electric components and controls have shown performance improvements of 5% to as much as 20% reduction in fuel consumption during steady-state operation Figure 74. 

Reasons explaining the performance improvements in engine thermal efficiency using hybridized cooling systems include:

  • Parasitic power consumption by the cooling fan, water pump, and belt can be reduced when electric motors replace mechanically driven parts.
  • Engine temperature can be reached more quickly and raised to increase combustion efficiency. Thinner oils can reduce friction and heat rejection because the oils absorb less heat.
  • Oil temperature can be raised to reduce viscosity-related friction and parasitic power loss.
  • Heat exchanger size can be reduced if they operate on an on-demand basis—only when needed.
  • Less restriction to coolant flow is achievable in electrically controlled and operated heat exchangers and valves.
  • EGR, oil, and transmission cooling can be handled independently through separate heat exchangers with electric cooling fans.
   Fig11_74

FIGURE 11-74: A hybridized cooling system is electronically controlled and integrates electric motors and actuators into traditional mechanical devices.

 

Brushless, direct current (BLDC) electric motors, which have permanent magnets supplying repulsive magnetic force energy, are better than 95% efficient. These motors can drive water pumps and engine fans only when needed. Using multiple BLDC that is turning faster rather than a single large motor for an electric fan drive is even more efficient because motor speeds can be set to operate independently of engine speed and not draw power away from the engine all the time. Motor speed can be adjusted to match optimal coolant flow for any given engine speed and load condition.

Electric thermostats are another example of a hybridized cooling system component. Using a thermostat that is opened or closed with a solenoid eliminates the problems associated with inaccurate wax-based devices. Engine operating temperature can be held to less than ±2% accuracy, and engine warm-up time is reduced using an on/off-, open/closed-type thermostat. Because high restriction to coolant flow is present in a partially opened or closed wax-based thermostat, this translates into increased pumping losses. Energy loss in electrically controlled thermostats, which are either open or closed and not in between, means an electronically controlled thermostat minimizes pumping losses.

 

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