Energy recovery systems role

Although the internal combustion engine is likely to dominate the automotive landscape for the next decade, the increasing mismatch between energy consumption (available resources) and tighter legal restrictions on engine emissions, is creating a demand for improvements to existing automotive technologies and the development of reduced friction, energy efficient, ‘greener’ alternatives.

Barden is at the forefront of the latest developments in innovative, energy efficient, low friction, super precision ball bearings for these emerging technologies.

Turbochargers

In order to support growing demand for more energy efficient, low carbon emission vehicles, manufacturers of automotive turbochargers are being asked to provide more compact, higher efficiency turbocharging systems that are both durable and affordable.

Barden first manufactured ball bearings for turbocharger systems in 2004 and has since led the way in the development of new low friction double row angular contact ball bearings for turbochargers. These super precision ball bearings are helping to set new performance benchmarks for the future, particularly in the high-end passenger car and commercial truck markets, where the individual cost of the bearing is less of an issue and where the fuel savings and reduced emissions are more immediate and noticeable.

Advantages of ball bearing turbochargers over traditional hydrostatic oil-filled turbocharger bearing sub-systems stem from the fundamental change in the friction mechanism present. Multiple rolling elements replace a thin oil film in high shear, significantly reducing system friction. This results in a significant improvement in system friction at operating temperature (typically up to 50%) and even greater improvements during the first minute of an engine cold start. Turbocharger studies have shown that the ‘ball bearing effect’ is most pronounced at low engine speeds, just where a down-speeding or downsizing concept needs the most help from the turbocharger system.

With the more conventional hydrostatic, oil filled turbocharger systems, the oil is very viscous in cold conditions, particularly during engine start up. The time taken to heat up the oil means that engine emissions suffer during this period. However, with ball bearing turbochargers, the air is available to the system immediately on cold start up, resulting in a more energy efficient system with reduced emissions.

Most Barden ball bearings for turbochargers are angular contact. Typically, these bearings utilise ceramic balls, cages, anti-rotation devices, an outer ring, a compressor inner ring, a turbine inner ring and a series of oil flow control jets. These types of bearings rotate up to six times faster than any other vehicle bearing. In hot shutdown conditions, these bearings reach temperatures of up to 400˚C. The bearing is cooled by the lubricating oil flow.


Kinetic energy recovery systems

Barden super precision ball bearings are also playing a vital role in the development of innovative kinetic energy recovery systems (KERS).

In automotive applications, KERS normally involve some kind of motor generator unit and an electrical flywheel. These bearing systems accumulate energy from the kinematic motion of the vehicle. This recovered ‘free’ energy is then stored and re-used to accelerate the vehicle back up to speed.

Barden is working closely with a number of companies using these same principles, including applications in HGVs, elevators, lifting gear, cranes, buses, trains and trams.

Most bearings for automotive KERS applications are angular contact ball bearings configured as double row cartridges, with built in axial play or preload. These bearings often have standard phenolic cages but typically use ceramic balls, which weigh 60% less than steel balls. Another key requirement for the bearings is that they provide long grease life with no relubrication required. Typical bearing speeds can reach 1.4 million Ndm.

In industrial KERS, single row angular contact ball bearings are normally provided. In a recent elevator application, for example, Barden supplied the customer with single row angular contact ball bearings, which were designed to support the weight of the flywheel and motor. The bearings were custom designed with special, larger grease reservoirs that maximise the bearing grease life.