LO 11-9 Explain the application of heavy-duty on-board diagnostics and the use of electrical actuators and electronic controls in hybridized diesel engine cooling systems

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

Heavy-Duty On-Board Diagnostics and Cooling Systems

An OBD system for diesels is required to monitor the cooling system for correct operation so that proper cooling system temperature is reached within a reasonable time. This is an important requirement to enable other OBD monitors and any emissions control strategy dependent upon the cooling system quickly reaching its correct temperature. Data derived from the engine coolant temperature (ECT) sensor will indicate whether the engine has reached near the thermostat’s regulating temperature within a predetermined amount of time. Slow or inadequate engine warm-up will set fault codes.

1.1. Hybridized 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.

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.

1.2. Rankine Cycle Waste Heat Recovery Systems

Rankine Cycle Waste Heat Recovery Systems

Repurposing normally wasted exhaust and coolant heat to drive electrically or hydraulically operated devices is another example of a hybridized cooling system. Alternators and accessory drive components can literally be driven by steam power Figure 75. These devices operate on the principle of the Rankine cycle, where an intermediate heat exchanger is added to a loop in the hot cooling system. The heat exchanger contains a fluid with low boiling temperatures. The vapor pressure of this liquid, when heated and boiled in an expander, can be used like steam to drive mechanical devices. Wasted heat from the exhaust or cooling system is sent to a Rankine cycle expander where the liquid is evaporated. Following its use, a condenser converts the Rankine cycle vapor back into a liquid to start the cycle over again Figure 76.

FIGURE 11-75: A Rankine cycle device mounted to the frame rail can extract heat from the exhaust or cooling system to power mechanical accessories, such as alternators, power steering pumps, A/C compressors, or other accessory drive devices.

FIGURE 11-76: A schematic of a Cummins-Rankine waste heat recovery system. Coolant heat is repurposed to drive a device by converting heat energy to power a mechanical drive gear connected to the geartrain.