Marginal Column

Let´s get closer!

When developing a new pneumatic valve, the most unlikely solution turned out to be the best. Developers Christophe Champouillon and Wolf Gerecke report on why the AV03 valve unit can be close both to the actuator and to the customer.

 

The products now on the market have in the meantime become quite similar. That is why our goal was to set the new valve apart from the competition. We saw room for innovations and improvements in two prime areas: their size and their capacity for integration. It was clear that this wasn’t going to be a straightforward job.

Using available space in perfect fashion

Even while drafting the specifications, we attached great importance to making the new pneumatic valve even more compact. Some requirements were clear from the very outset. One customer had quite definitely specified 53 millimeters as the maximum height. That was because the valve unit had to be ready for integration directly into the moving drilling head of his woodworking machine. The overall geometry of the valve unit thus largely determined the maximum height.

At the same time, it was clear that we would require a flow rate of at least 200 liters per minute to properly integrate this new item into our product line. The fundamental challenge was thus to satisfy two targets which, by nature, are contradictory: high flow rate and compact dimensions.

Illustration | Bosch Rexroth AG

The diagonal design of the AV03 reduces the valve’s overall volume

 

Two development teams were assigned to the project, one in Bonneville, France, and the other in the town of Schwieberdingen, Germany. When tossing around engineering ideas for the valve, they presented more conventional solutions at the outset. But during initial meetings we found that the customary approach promised no significant improvements over existing products. Neither could the specified maximum height be met. Then the French colleagues posed the decisive question: “Couldn’t we make better use of the available space by simply placing the main valve along diagonal?”

Skepticism prevailed at first, because we assumed that this skewed position would cause difficulties in manufacturing or when interfacing with other components – or both. A detailed examination revealed that these doubts were unfounded. This gave us our fundamental approach to solving the problem. We shaved dimensions even further by using our own pilot valves, first developed in Schwieberdingen. They are so compact that they can be integrated right into the valve case.

High-strength plastic

It was possible to place the main valve diagonally only because we have been using plastics in our valves for more than thirty years. These materials make our design latitude far greater than when machining metal. Further refinements in plastics, lending them greater strength, made it possible to manufacture complex and lightweight components. Today’s parts carry out the same functions but are far smaller than would have been possible even just a few years ago.

Photo | Bosch Rexroth AG

Stress simulation at the valve case (red = severe strain, blue = low strain)

 

One good example of this is the base plate. Comparable models in the past were held together by two tie rods in order to distribute forces. To reduce the valve’s weight and dimensions, we thought about using just a single tie rod. We had to find a material that was both stable and airtight, even when only one tie is used.

The resin was not only to offer great strength; the complexity of the shape required that it be easy to work, as well. Following a number of studies and working models, we chose a high-strength, glass fiber reinforced polyamide that hardly changes shape when subjected to high pressure. Thus we reduced weight just by using that lightweight plastic. We also use far less material, since the AV03 has virtually no unused space. When compared with the models available on the market, this saves 45 percent in overall volume and 55 percent in weight.

Its light and compact design – and compliance with safety class IP65 – allowed the AV03 to be used closer to the actuator, without an enclosure. This eliminates line losses of up to 20 percent. And inside a switching cabinet, too, our valve unit consumes less space and makes for a smaller enclosure.

Maximum flow rate

Even during the development stage we used CAD models to analyze flow. This let us optimize internal diameters and the geometries of the edges. The crux was to find the perfect compromise between flow rate and manufacturability. Here we also profited from the main valve’s oblique position. We were able to flatten out the angle from the ports to the outside tubing; that minimized pressure loss. Using prototypes, we were able to verify a flow rate of 300 liters per minute. We measured the valve’s efficiency at 7 liters per minute, flowing through a cavity with a volume of one cubic centimeter. The efficiency value is 40 percent greater than for comparable products.

Great integration capacities

Nowadays the customer expects a valve system to integrate easily into his systems and, above all, into the topology of the field bus. The concept behind the AV03 makes it possible to link the AV03 not only using multi-pole connectors but also with field bus interfaces that may include integral I/O modules. The ability to connect sensors directly to the valve’s electronics means that installers will have to lay less cable back to the switchgear cabinet. Our colleagues in Laatzen have modified the size of the field bus module to match the valve. Entirely in the spirit of the modular concept for the pneumatic components, we have provided for retroactive adaptations and additions. Beginning with the second valve, the user can increase their number in steps of one, reaching as many as 40 monostable valves or 64 double-acting valves.

Photo | Bosch Rexroth AG

A valve system comprising the AV03, bus interface, and I/O module.

 

A further new development for the AV03 pertains to the indicator LEDs on the I/O modules, showing which inputs and outputs are active at any given moment. To keep the cables from concealing the LEDs, this being due to the modules’ extremely compact dimensions, we decided to put the LEDs in a different location. We laid optical waveguides in a ring around the connector port. Their broad luminous surface makes them highly visible.

The AV03 offers the customer a valve that is both compact and energy-efficient. At the same time it can be conveniently integrated into new or existing systems.

 
 

The Authors


 
Photo | Bosch Rexroth AG

Wolf Gerecke,

Product management and valve development, Schwieberdingen, Germany, Bosch Rexroth AG

Photo | Trumpf GmbH

Christophe Champouillon,

Valve development, Bonneville, France, Bosch Rexroth AG