VW pump audit: variable speed pumps save energy

Volkswagen needed a higher purity of lubricating and cooling fluids (LCF) in its engine production in Salzgitter, Germany. In modernizing the LCF filter technology for a honing system, the company upgraded its LCF supply pumps to Grundfos variable-speed NK models. The result: better quality lubricant and less energy.

These numbers are enough to impress anyone: At its Salzgitter plant, Volkswagen manufactures up to 7,000 engines a day in a production area comprising 320,000 m2 (80 acres). Here, the company produces more than 370 varieties of diesel and gasoline engines, plus industrial engines, marine engines and cogeneration plants. The production range includes engines from three to 16 cylinders, with engine power ranging from 55 kW to 736 kW.

In order to be able to manufacture such a wide variety of engines, the Salzgitter plant has around 6,200 machine tools ready to mill, bore, turn and grind delivered cast parts and ingots into engine blocks, cylinder heads, camshafts and crankshafts. The plant also produces various engine components like intake manifolds, oil pans, flywheels and oil and water pumps. The components pass through twelve assembly lines to complete each engine.

Cooling lubricant: Vital for honing

Nils-Stefan Bang has been working in an engine production planning capacity at the Salzgitter plant for the past eleven years. Along with his colleagues, he is responsible for ensuring that the processing machines are seamlessly supplied with various operating media like cooling water, chilled water, compressed air and lubricating and cooling fluids (LCF)and to ensure smooth disposal of emulsions and oils laden with metal filings.

"As supply technicians, we look at the honing system almost like a ‘black box’ – it must provide the given cooling lubricant at the required characteristics while consuming as little energy as possible."

Niels-Stefan Bang, Volkswagen Salzgitter

The Salzgitter plant has over 120 cooling lubricant systems constantly circulating approximately 6000 m3 of cooling lubricants in the machining process. In addition, nearly 100 tonnes of metal filings must be recovered every day.

Nils-Stefan Bang undertakes planning for more than just LCF systems. His daily work has more to do with adjusting existing systems to new regulations and to new engine designs, along with modernising outdated technology.

The honing system used to machine four-cylinder crankcases recently underwent this type of upgrade. The cylinder crankcase is the central engine component in which the engine's cylinders and crankshaft operate after assembly – an especially high level of surface quality is required here. According to Niels-Stefan Bang, using honing as a finishing polish reduces friction losses in the engine; a micro-fine cross-groove structure guarantees that motor oil will adhere better during subsequent operation and that the oil film will not break off.

The specific task was to further increase the purity of the cooling lubricant required for honing. The quality of cooling lubricant indirectly affects the quality (i.e. the subsequent performance and cost effectiveness) of the engine. The better the finishing polish (reducing friction losses), the lower the tolerances that can be achieved.

"Experience shows that it is always an advantage if a system like this is able to 'breathe.' A variable-speed pump is flexible in terms of both flow rate and discharge pressure."

Niels-Stefan Bang, Volkswagen Salzgitter

Speed control offers flexibility

In May 2011, Volkswagen installed two Grundfos, variable-speed, standard NK pumps (click the tab "Grundfos supplied" at the top of this story) at the plant, using them in alternation. With them, the company also installed a Grundfos CUE frequency converter (37 kW) and CIU 150 communication interface with Profibus connection to the PLC control.

Why were these pumps provided with speed control?

"Experience shows that it is always an advantage if a system like this is able to 'breathe.' A variable-speed pump is flexible in terms of both flow rate and discharge pressure," explains Niels-Stefan Bang. A variable-speed pump always pumps at the rate required by the process at any given time. It can also be adapted to various plants, meaning that it can be reused. "Using a frequency converter-controlled pump, it is very easy for me to run or simulate a variety of operating states," he adds. This saves a great deal of electrical energy that would otherwise be discharged in the form of heat into the cooling lubricant.

In this case, additional cleaning is provided by Knoth boxes, in which the machine work piece is blasted with air or – using a LCF duct – at high pressure and with large volumes of cooling lubricant. This is a clocked process using 10 to 15 minute intervals, to which the cooling lubricant pump must respond.

Other benefits

A variable-speed pump also provides benefits in weekend operation. When the cooling lubricant is not used, it must not be left to stand for too long without moving – stagnation increases the risk of microbial contamination. A variable-speed pump can be used to configure the process so that the system does not waste a lot of energy or become contaminated.

An estimated 10% of all filter systems at Volkswagen are currently equipped with variable-speed pumps. Nils-Stefan Bang believes that it makes economic sense to retrofit gradually around 30% of the systems with variable-speed pumps. Frequency-controlled pumps offer a variety of benefits compared to fixed-speed pumps, in addition to energy savings:

• The frequency converter permits simple wiring procedures (this is especially the case when using a Grundfos MGE motor up to 22 kW, which has an integrated frequency converter)
• There is no need for energy-consuming transfer ports, line throttling and valve controls to set the duty point
• Time-consuming adjustment work is no longer required in the event of changes to the production line
• The Grundfos R100 infra-red remote control and parameter adjustment device can be used to monitor, change and save current operating states for the individual pumps
• No pressure surges occur during system warm-up, thanks to soft start technology, resulting in a positive impact on tool lifetime
• Alternating, defined duty points are easily adjustable.

Standard vs. end-suction

In this case, a standard pump was chosen. Standard pumps offer the user benefits in terms of service, spare parts and maintenance. The process design enables simple removal of the coupling, bearing bracket and impeller without needing to disassemble the pump housing or the pipelines. The mechanical shaft seals meet the EN 12756 standard.

Grundfos offers NK standard pumps as well as NB end-suction pumps in accordance with EN 733 (European water standard) as well as NKG and NBG pumps in accordance with EN 22858 (EU chemical standard) employing various housing materials (grey cast iron, stainless steel, duplex) and gasket variants.

Standard NK and NKG pumps are equipped with a spacer coupling by default. The benefits are that whenever maintenance or repair is required on the pump or on the gasket, the engine remains mounted on the base plate. The coupling can be removed without disassembling the engine. After that there is enough space left to remove the entire shaft/impeller unit from the pump housing (back pullout) and then reinstall it after maintenance. This work can be carried out by a single person with the assistance of a crane. It is not necessary to realign the pump shaft and drive unit using spacer couplings – this reduces the costs associated with downtimes.

A frequency converter-controlled pump makes it very easy for me to run or simulate a variety of operating states.

Niels-Stefan Bang, Volkswagen Salzgitter

Story by Heinz Maier, Industry Division, Key Account Manager Automotive, Grundfos GmbH, Germany