Power steering pumps typically run all the time to handle worst-case needs of low-speed vehicle turning and maneuvering. Virtually all heavy-duty trucks have power steering systems to assist with the turning of the vehicle when necessary. The power steering system consists of a hydraulic engine-driven power steering pump, a steering gear, control valves to route the hydraulic fluid depending on the direction of the turn, a small fluid reservoir, and hydraulic hoses to route fluid to the appropriate components. In addition, a fluid cooler is sometimes required to keep the hydraulic fluid in the proper temperature range. The power steering pump turns and generates pressure/flow any time the engine is running.
New systems take into account the fact that line-haul tractors spend the vast majority of their operating hours going nearly straight down a highway when little steering effort is necessary. The dual displacement power steering pump works by using the full displacement available when the engine is at a low speed. Once the engine/pump speed is sufficient, the dual displacement power steering pump automatically switches to the pump with smaller displacement that takes less horsepower to turn.
It is important to note that power steering pumps typically consume 0.3–0.6% of the truck’s fuel to perform their function, so any fuel economy gains from new technology will be modest.
The study team developed a Confidence Matrix, an OEM Availability Matrix and an Engine-driven Accessories Power Use Chart to assist fleets. The Confidence Matrix is designed to inform fleets of the study team’s confidence in the technology being studied vs. the payback the fleet should expect to receive from the technology. Technologies in the top right of the matrix have a short payback, usually thanks to their low upfront cost, and moreover are found to have enough performance data that fleets can be highly confident in those short payback times, usually because the technology is more mature or otherwise has a more substantial track record of results. The OEM Availability Matrix shows the current availability (as of March 2017) of these engine-driven accessories at the various truck builders. The Engine-driven Accessories Power Use Chart shows the various places the energy from fuel is used in a Class 8 truck.