Off-highway vehicle producers are facing difficult challenges in the next few years, with four major aspects at play: environment, energy, costs, and functionality. Manufacturers are working to reduce emissions, while at the same time increasing the efficiency and performance of their vehicles and keeping costs manageable. At Bosch Rexroth, our philosophy in meeting these challenges is to consider a holistic design approach.
As manufacturers seek to satisfy Tier 4 Final regulations by 2014, legislatures in many countries are once again tightening the standards for exhaust and noise. For the diesel engine, the standard powerplant for vehicles and machinery, the squeeze is getting even tighter. Satisfying the new exhaust requirements and subsequent regulations will require optimizing not only the diesel engine but the entire system as well—including auxiliary equipment and travel drives.
One of the best ways to support emissions goals is the energy-saving, emissions-reducing hydrostatic travel drive. Proper sizing and optimization of the hydrostatic drives with high-pressure pumps and motors can significantly increase the efficiency of the travel drive.
The performance leap in the components makes it possible to reduce the diesel engine size, where increased hydraulic pressure levels compensate for lower diesel engine output not only at the beginning movement of the machine but also over the entire control range of the travel drive—improving the entire system’s overall efficiency by up to 15% in various applications.
Another approach to maintaining the high dynamics of the travel drive and implement hydraulics, even at the reduced engine speeds of Tier 4 Final engines, is the intelligent networking of hydraulic and diesel engine control. Rexroth’s Diesel Hydraulic Control system, for example, allows the hydraulics and diesel engine to communicate directly with each other and work together to reduce fuel consumption and emissions while maintaining the lively performance that operators expect from the travel and implement hydraulics.
Reducing engine size is just one approach to the Tier 4 Final challenge. The concept of energy recovery seems well suited to reconciling demands on the engine by simply storing excess energy and making it available again when needed.
It is also possible to recover energy not just from the drivetrain but also in the working hydraulics, where peak power requirements could be met with superfluous energy that had been stored beforehand—allowing the diesel engine to run in the speed range for ideal energy efficiency.
Intelligent energy management will contribute to significantly increased efficiency in the future. For instance, vehicles in which the powertrain and working hydraulics are subjected to extreme start-and-stop loading can reduce energy consumption by incorporating hybrid hydraulic solutions. For example, our Hydrostatic Regenerative Braking system reduces fuel consumption by as much as 25%, also lowering maintenance costs and pollutant levels.
In the future, energy-on-demand solutions will play a large part in mobile equipment. While not new, as a way to increase efficiency developers have “rediscovered” hydraulic fluid for functions such as driving engine and transmission cooling fans, as well as hydraulic oil coolers installed at a distance from the diesel engine. This is an alternative to direct belt drive.
Variable pump drives and sophisticated solutions drawn from the fields of gearbox technology, hydraulics, and electronics help machines work more efficiently and in so doing keep emissions levels below the limits. Combining hydraulics, gearbox technology, and digital control electronics with intelligent software offers the opportunity for improving both existing and new machine concepts.
Tier 4 Final is just an intermediate stop along the way. Demands for environmental protection and efficiency enhancement will continue. Energy recovery, more efficiency, and reduced noise emissions are just preliminaries. The main goal will be zero-emissions drives with lower overall costs and more functionality, even with smaller components.
Ken Hank, Vice President Sales USA, Mobile Applications, Bosch Rexroth Corp., wrote this article for SAE Off-Highway Engineering.