Engine peripherals work hard, but not cheap. Efforts to make them work smarter could help cut costs.
The driver of a 400-hp. rig cruising along on level highway might not be able to sense a loss of performance when the engine cooling fan kicks in, but that accessory uses power when it engages -- and power equals fuel.
Although no one knows precisely, it's probably fair to say that over an engine's lifetime 10% of the fuel burned goes to running accessories. Surely, the functions these devices perform -- cooling the engine, supplying the electricity to recharge the batteries, compressing air to keep brake reservoirs full, and pumping fuel, as well as providing power steering pressure and A/C service -- are vital.
But what if the parasitic penalty exerted by engine peripherals could be minimized? There would be more power available to the drive wheels, which would mean better vehicle performance. Furthermore, since parasitics are "deductions" from the bank account of power that is created by the combustion of fuel in the engine, a portion of the 10% in fuel now used by accessories would be saved.
While much attention has been focused on curbing the cooling fan's power appetite, diesel-engine makers are quietly working toward a grander strategy -- an accessory load-management system.
The OEMs are reluctant to go into detail, but this much is known: Uniting the fan and alternator controls electronically could be a way to help prevent untimely parasitic stackups that now occur when these peripherals kick in simultaneously.
Such episodes are most likely to be felt during long hill climbs at maximum power on warm days. They are annoying because not only can they hit suddenly, but they also require drivers to make more downshifts, which lengthens trip times and wastes fuel.
In a worst-case scenario, when all accessories are loading at the same time, so much power can be temporarily lost that a 400-hp. engine will be reduced to performing like a 320 or 325. Here's why: A 9-blade cooling fan spinning at maximum rpm can sap up to 60 hp. of engine output; the loading 12-cfm air compressor filches 3.5 hp.; the air-conditioning compressor pulls an additional 5 hp.; a 130-amp alternator in full-field mode siphons 8-10 hp.; and the power-steering takes a constant 3/4 hp.
Accessories can draw power even when they're not loading. Although it's possible that some accessories could be re-engineered to produce less inherent friction, changes would have to be such that product durability and reliability would be preserved. Otherwise, long-term savings would be jeopardized.
A more productive approach would be to join peripherals in an electronic network orchestrated by the engine ECU. Such a data-linked network would be similar to the one uniting electronic engines, transmissions, and ABS/traction control systems; it would work over the same J1939 serial communications bus.
The game plan would call for the engine ECU to direct accessory operations. For instance, the ECU could decide to defer alternator loading until such time as the engine was operating at a 75% load factor, a period during which recharging would be least costly.
In fact, the first element in the net, a new generation of cooling-fan controls that are actuated by pulse-width modulated signals sent by engine ECUs, is now undergoing field-testing.
In engine-temperature regulation today, fan response is either full-on or full-off. But since a fan's horsepower draw is the cube of its speed, it has long been recognized that significant fuel could be saved if fan speed were modulated, that is, pegged more directly to engine cooling needs.
In an effort to achieve this level of control, Horton Vehicle Components took the variable-pitch route. It has developed what it calls Adaptive Cooling System (ACS) technology, which works by adjusting the fan blades' angle of attack.
Remote coolant and charge-air-temperature sensors feed data to the ECU, which in turn transmits pulse-width signals to the fan control. The control responds by varying the blade pitch. The software that guides pitch angle actually allows the fan control to "learn," adapting to changing cooling needs as the vehicle ages.
Under the ACS system, coolant temperature could still be tightly maintained (within a 3 degree F band), and the fan should rarely have to come on full force. Modulation will also avoid potentially damaging full-on/full-off shock loads to the engine and fan control. Horton is currently gathering data on how much fuel can be saved with ACS.
Kysor Cooling Systems NA has developed Direct Sensing Technology, which uses a viscous approach to fan speed control. The system works off an ECU-generated pulse-width signal that's predicated on coolant and charge-air-cooler temperature. Fan modulation is achieved by varying the amount of viscous fluid in the clutch reservoir, thus changing the degree of clutch lockup and matching fan speed to engine-cooling need.
Alternators are also candidates for the network. Light-vehicle makers are already doing this by taking advantage of controls that block alternators from loading when vehicles are in the kick-down mode and drivers need every bit of passing power they can get. Load response -- gradual rather than all-out to current load demands -- prevents sudden alternator loads from reducing engine rpm.
Another approach is gain control, which uses a voltage-regulator override to accomplish the same goal. When the driver calls for maximum engine power, the engine controller senses the increase in load and drops voltage set-point from 13.5V to "just above" battery voltage. This lasts until a normal driving situation returns.
Efficient-alternator technologies such as these could eventually be used in heavy-duty models and marketed to engine makers. On new trucks with ABS, establishing priorities will be essential since providing enough electrical voltage to maintain vital safety systems takes precedence over reducing parasitic losses.
Dave Reynolds, applications engineer, Prestolite's Leece-Neville Div., thinks that safety considerations can be satisfied through logic questioning within the engine ECU. "The ECU must consider many variables and make sure all vital systems have sufficient power before the alternator set voltage could be reduced."
Although "smart" alternators will ultimately save some fuel, they might also add a new level of complication to technicians' lives. Unless techs are smart-alternator savvy, they might be perplexed to see the voltmeter needle drop to 12V when they rev engines, instead of rising to 14. Such a reading would not necessarily be a sign of a battery problem, but rather an indication that the alternator gain control was working properly.
Sandin International, a major producer of heavy-duty A/C compressors, says the most promising parasitic-load reducing technology for this peripheral is the variable displacement compressor currently used in light-duty vehicles. This type of compressor has a swash plate angle that changes to produce precisely the pressure needed to control refrigerant flow and provide cooling to the driving compartment, yet at the same time maintain constant suction. (Standard compressors have fixed-angle swash plates that move compressor pistons back and forth.)
The advantage to this variability is that it enables the compressor to run in a partially loaded mode. Depending on ambient temperature in the cab, the compression stroke can be decreased from a maximum of 150 cc to 50 cc, greatly reducing the compressor's power draw.
To make this technology practical for heavy-duty trucks, the industry would have to standardize on a single style compressor -- which means reducing the number of compressor mounting styles and configurations on the market, says Sandin.
Flange-mounted air compressors are the least likely candidates to join an accessory-management system because they run directly off engine gearing and are intended to work continuously.
By NHTSA mandate, the air compressor must provide air on demand to the wet tank whenever tank pressure drops to 100 psi. But in many truck applications, the low-pressure pump that delivers fuel to the unit injectors runs off the air compressor. This flow cannot be interrupted, and as a result the air compressor will continue to function much as it does today.
According to AlliedSignal, however, improved intake-valve design is expected to help its air compressors reduce their 0.8-hp. power draw in the unloaded mode to 0.4, thus saving some fuel.
Semi-integral power-assisted steering systems, which lessen the amount of driver effort needed to turn the steering wheel, also contribute to parasitic power loss. Powered by constant-displacement pumps, these systems maintain a constant pressure head while trucks are operating.
Jerry Oxley, director of engineering-power steering, TRW Commercial Steering Div., mentions two promising technologies for addressing this, both of which make the control valves that direct oil pressure to the pistons smarter. In the first, valves could be re-engineered to handle varying pressure demand by reacting to changes in vehicle speed, thus varying the fluid flow rates.
The second involves using the control valve to vary fluid flow based on driver input loads, thus increasing or reducing pump flow rate in response to need. Oxley questions, however, whether either method will be incorporated into heavy trucks, because at today's fuel prices it's too hard to prove a payback.
Thus far, major gains in fuel efficiency and engine performance have come through better combustion proficiency and improved drivelines. Parasitic-loss control is likely to result in a number of small but collectively significant improvements, while making operation of accessories transparent to drivers.
A reduction in external peripheral parasitic draw means more available horsepower and increased fuel savings. When it comes to internal parasitic load -- from bearing drag, piston ring/cylinder wall friction, and fuel injection forces -- engine makers can see an advantage to maintaining a reasonable amount of draw. It can help achieve optimum engine deceleration rates. And when engine reciprocating assemblies slow down at satisfactory rates, drivers find it easier to complete shifts.
But when internal parasitic draw becomes too high, it needs to be offset. For example, if injection pressures are bumped up to achieve lower brake-specific fuel consumption, parasitic forces tend to rise accordingly. When Mack Trucks' new E-Tech unit-injected engine showed an increase in internal friction at 27,000 psi, the OEM compensated by switching to lower-friction roller-type valve followers.
During the development of the Signature 600, Cummins Engine overcame a parasitic friction increase from higher injection and cylinder-firing pressures by carefully optimizing each engine system. For example, the new engine's cooling system requires only one-half to two-thirds of the coolant pressure needed by other heavy-duty engines. This means lower water-pump parasitics.
On the other hand, there are times when a driver depends on an increase in internal parasitics to control speed. For example, every time a driver engages the engine brake, intake- and exhaust-valve motion is altered deliberately to convert the engine from a power producer to a power absorber, and the internal parasitic force increases by several levels of magnitude.
When vehicles with Cummins Celect, Caterpillar, and Detroit Diesel Corp. engines are operated in the engine-braking mode, the internal retarding effect of the Jake Brake can be augmented by the external parasitic load of the cooling fan. This is because the two can be joined by means of a programmable switched input. On DDC Series 60 engines with the dynamic braking option, for example, the parasitic effect of the Jake Brake (in the max mode) increases by 35 to 40 retarding hp. when the fan kicks in.