ST 001-10 Lohr, 2010-01-19

"Tier 4 final" emissions regulations: It’s time for lower emissions

The Rexroth high-performance travel drive with an A4VG pump

The Rexroth high-performance travel drive with an A4VG pump and the A6VM motor clears the way for a downsizing of the diesel engine. It can also be used to reduce fuel consumption by lowering engine s

The beginning of 2014 sees much stricter limits for mobile equipment emissions coming into effect. These new limits are placing enormous demands on manufacturers. This is because in order to meet the requirements of "Tier 4 final", many systems will need to be redeveloped from the ground up. The year 2010 will be decisive in determining who will find the new standards to be a stumbling block and who will find them to be an opportunity.

There is a well-known phenomenon for hikers that a distant mountain summit can seem deceptively easy to reach. Only as the hiker gets closer to the top can the details of the journey -- and the difficulty -- be clearly seen. The situation is similar with regard to meeting the new European Union (EU) and United States emissions regulations.

Since 1999, the EU has had a roadmap in place for improving the environmental performance of diesel-powered mobile equipment. This involves steady reductions in allowable limits for emissions of nitrogen oxide (NOx), carbon monoxide (CO), hydrocarbon (HC) and soot particles, with reductions scheduled for four stages over 15 years. The US has mandated a comparable emissions reductions schedule, which differs only slightly in specific limits and deadlines.

Today’s mobile equipment is designed to meet existing Tier 3 and Tier 4 interim regulations, which means emissions have been cut in half compared with Tier 1 regulations. However, we are now reaching the final stage in the emissions reduction schedule, Tier 4 final, which becomes binding for machine production starting in 2014. This means NOx emissions have to be cut in half once more, compared with Tier 3 NOx levels.

Technical challenges

Seen from a distance, reducing emissions by one-half once again may seem to be a realistic goal. But a closer looks shows that the cards are being entirely reshuffled for Tier 4 final. For one thing, the new limits are so strict that it will not be enough to simply optimize individual areas. In the past, more efficient diesel engine, improved energy management or an improved exhaust gas treatment have often been sufficient to clear reduced-emissions hurdles. But the bar has been set much higher for Tier 4 final.

The challenges associated with Tier 4 final should not be underestimated. For example, the combination of exhaust gas treatment and particle filters will have to be optimized. This will increase development outlay and costs, both for components regarding the exhaust gas treatment system and for additional post-treatment catalytic converters. The same is true for the diesel particle filter. All this will mean drastically increasing space requirements for dealing with emissions, which will force vehicle manufacturers to perform significant redesigns and develop new concepts especially for small to medium-sized construction machinery. In other words, to reach the upcoming emissions goals, a holistic system design approach will be necessary.

One of the best ways to support this approach is the energy-saving, emissions-reducing hydrostatic travel drive. In a variety of applications including construction machinery, this drive’s capabilities represent a way for engineers to deal with the economic and technical fallout of the new emissions limits.

The hydrostatic travel drive represents an approach to conserve dynamic energy and cut engine emissions. Overcompensation is even possible depending on the starting conditions. The first key to success is increased pressure level in the system. Proper dimensioning of the hydrostatic drives with high-pressure pumps and motors can significantly increase the efficiency of the travel drive. This clears the way for reducing diesel engine size or lowering fuel consumption through reduced engine speed while design performance is maintained.

Progressive components for new system solutions

However, high-pressure components are subject to a critical system challenge: Higher loads normally result in the potential for greater wear and reduced service life. To meet this challenge, Rexroth has already developed a new generation of pumps and motors which are designed to meet the requirements of Tier 4 final.

To optimize hydrostatic travel drives, our A4VG axial piston pump for the new Series 40 and the A6VM axial piston pump for the Series 71 have been completely revised and fitted with newly-developed high-performance rotary groups. These allow rated pressure to be increased from 400 to 450 bar (peak pressure: 500 bar), while at the same time improving rated speed and component efficiency.

To take into account the greatest possible range of market and application requirements, the new axial piston pump series includes a modular controller concept. This means system designers and users can employ any control method from simple mechanical control to hydraulic control to On-Board-Electronics (OBE) to achieve the optimum control strategy.

The pumps and motors for this new generation were first introduced in 2007 and have already proven throughout three years of service that their rugged design meets the highest expectations for durability and quality.

More performance even with reduced engine power

The performance leap in the components makes possible a reduced diesel engine size, as the same nominal size axial piston can now transfer significantly more power. That allows the increased pressure level to compensate for lower diesel engine output not only at the take-off point, but also over the entire control range of the travel drive. This feature has allowed Rexroth engineers, using their application know-how, to improve the entire system’s overall efficiency by up to 15 percent in various applications.

Thanks to the higher performance of the new A4VG pump and the A6VM motor, it is possible to maintain machine performance even when the installed drive output is reduced. Such downsizing can ideally mean performance below the "magic" 56 kW limit for the diesel engine.

Energy recovery for power smoothing

Reducing engine size, however, is just one approach to the Tier 4 Final challenge. Intelligent hydraulics can contribute in many areas as well. For instance, diesel engines and their exhaust treatment systems operate best at constant diesel RPMs. Operating within the smallest possible fluctuation band (barely detectable load changes) reduces consumption, and with it, exhaust emissions.

The challenge is that typically, mobile machines vary greatly in their power demands. But energy recovery seems well suited to reconciling this wide range of demands, by simply storing excess energy and making it available again on demand.

To make this approach a reality, Rexroth employs a proven technique for open circuit pumps: Mooring control. A variable implement hydraulics pump can swivel past the zero point into the negative range to recover excess energy. Specially developed software modules permit precise control of power storage and output to the system. A custom optimized control program for the proven A10VO pump has also been developed. In addition, Rexroth has made the newly developed Series 40 of the A11VO pump mooring-capable. This new generation of the A11VO pumps provides a pressure increase of ten percent with a significant improvement in efficiency.

Networking the diesel engine and hydraulics control

There’s another approach to maintaining the high dynamics of the travel drive and the implement hydraulics on mobile equipment, even at the reduced diesel engine speeds used in Tier 4 final engines. This approach is intelligent networking of hydraulic and diesel engine control. With Diesel Hydraulic Control DHC, Rexroth together with Bosch has developed a process which changes the traditional chain of command. This process monitors travel and implement hydraulics to signal in advance the expected load demands on the diesel engine, allowing the system to anticipate changing loads and avoid serious fluctuations. Hydraulics and diesel engines thus communicate with each other and work together to reduce consumption and emissions while maintaining the lively performance users expect from travel and implement hydraulics.

Time is short

2014 seems a long way off. But the reality is that manufacturers will need to have finished their system redesigns by the end of this year. That’s because after the prototype stage, there is little time left to test the systems and bring them to series-production readiness. This means that 2010 will become the decisive year, and that anyone who has not completed a basic redesign concept this year has little chance of developing Tier 4 final-compliant finished machines by the start of 2014.

Because drive train concepts need to be revised and adapted for each different type of mobile equipment application, many basic and important decisions await system designers. With our application know-how, Rexroth supports OEMs in conceiving individual, application-specific solutions which precisely match the new Tier 4 requirements. Progressive hydraulic components, already proven in the field, have a key role to play, because only a solid base of reliable components can produce sustainable improvements in energy efficiency on a system level. That opens up a range of potential applications for Rexroth’s lineup of Diesel Hydraulic Control, energy recovery or high-performance travel drives.


Image 1:

The Rexroth high-performance travel drive with an A4VG pump and the A6VM motor clears the way for a downsizing of the diesel engine. It can also be used to reduce fuel consumption by lowering engine speed while maintaining design performance.

Image 2:

With greater nominal pressure and higher power density the new Rexroth Series 40 A4VG axial piston pump reduces emissions for high-performance travel drives used in mobile equipment.

Image 3:

The new Series 71 of Rexroth A6VM axial piston motors offers improved slow-running by combining higher nominal pressure, larger specific displacement and higher speed.

Image 4:

The use of high-pressure components means an overall system efficiency increase of up to 15%

Image 5:

"Tried and tested hydraulic high-performance components are a prerequisite to safely reach the goals of Tier 4 final." Peter Dschida, Director of Sales Pumps and Motors in the Hydraulics Business Unit of Bosch Rexroth AG

Rexroth at bauma 2010: hall A4, booth 317/510

Bosch Rexroth AG is one of the world’s leading specialists in the field of drive and control technologies. Under the brand name of Rexroth the company supplies more than 500,000 customers with tailored solutions for driving, controlling and moving. Bosch Rexroth is a partner for industrial applications and factory automation, mobile applications and using renewable energies. As The Drive & Control Company, Bosch Rexroth develops, produces and sells components and systems in more than 80 countries. In 2008 Bosch Rexroth AG, part of the Bosch Group, achieved sales of around 5.9 billion Euro with 35,300 employees.

For more information please visit:


Search press releases


Susanne Herzlieb
Maria-Theresien-Straße 23
97816 Lohr am Main
Phone: +49 9352 18-1573