Among the new products WABCO displayed at the recent IAA Hanover CV Show was an electrically driven compressor for heavy-duty air-braking systems.

“That’s a solution for vehicles where the diesel engine does not run all the time," Dr. Christian Wiehen, WABCO Chief Technology Officer, told Automotive Engineering. “That’s typically hybrid vehicles and of course full-electric vehicles, which need compressed air to operate the brakes, the trailer brakes, the suspension, clutch, gear shifting, and so on. Here you need air supply even if the engine is at a standstill. Typically vehicles with batteries and an electrical supply system on board and are just charging air reservoirs when needed. In comparison with engine-driven compressors, it’s not lubricated from the engine oil and so needs its own oil sump and has its own electric motor and supply and control system.”

WABCO calls this compressor its e-comp system.

“The main question is what operating principle do you use for the compressor? We use our reciprocating piston design; others are working with screw compressors. We have found that screw compressors have quite a few problems with water ingress and freezing. They also produce a high-frequency noise, which is not so nice, especially in buses, which is where many of the applications are," said Wiehen.

“The piston type compressors are also not totally quiet. Here the challenge is to provide the right shock absorbers to prevent the transmission of body noise, and I think we have solved that problem nicely. They are the more robust and cost-effective solution."

Wiehen said the company is in small series production for about 25 bus customers with up to 100 electric buses each in China, and the first European applications are coming now, "so we see an increasing interest in these compressors.”

For conventional diesel-powered vehicles using a mechanically driven air compressor, WABCO has progressively reduced energy losses from the device. Previously the compressor was designed to switch into a pumping mode where no pressure was produced although the pump was still operating, which still generated some mechanical losses—an energy drain of as much as 1 kW at higher rotational speeds. To overcome this deficiency, WABCO has designed a friction clutch for the compressor, known as its c-comp clutch air compressor range.

“It lets the compressor reach a standstill when there is no pumping required," said Wiehen. “And when the compressor needs to pump, you just engage the clutch."

The c-comp compressor is controlled by WABCO’s new FuelGuard Lean electronically controlled air-processing unit. WABCO claims that this is the first time that compressor control has been integrated on the antilock braking system (ABS) ECU, removing the need for a separate ECU for compressed air management. “This, together with the c-comp compressor, saves altogether two percent annually on fuel for a long-haul application," Wiehen said. Wherever possible, the ECU will ensure that the clutch is only engaged when the engine is on the overrun, so no fuel is being used while the compressor is pumping.

WABCO may be best known for its braking systems, and at the Hanover show it also demonstrated its new mBSP (modular braking system). It is designed to standardize brake components and software wherever possible on its ABS and EBS brake systems.

“We are now merging the ABS world, which is North America, Brazil and the emerging markets, with the EBS world, which is Europe Japan and Korea, since 1996," said Wiehen. ABS relies on air line pressure to open the brake valves on a vehicle and trailer, whereas EBS relies on an electrical signal to open the brake valve, speeding up the braking response times for a trailer.

“We are merging that on a common platform of components so that global truck manufacturers have to engineer and design the architecture for the system only once, and then later on in the application process decide whether they fit either ABS or EBS components into the same packaging space and into the same connection," Wiehen explained. “There is also modular controller software so that we can plug in pieces from a common library. Up to now we have been dealing with two worlds of braking systems.”