Can we really get improved performance from a hydraulic system AND reduce the operating cost? When I started out in hydraulics, that idea would have been absurd. I learned that to get better control and better performance, we need higher pressure drop across the proportional, or servo-valve. More pressure drop across the valve means that control can be more dynamic without getting into natural frequency problems. However, more pressure drop requires more energy. 30 years ago, that was simply the cost of better performance. To make matters worse, that additional energy heats up the oil. We need more energy and hardware to remove that heat.

Provide Exactly the Flow & Pressure Required; Not More

One way to avoid these losses is to control the flow at the pump, aka primary control. That is, we only produce the flow required; no throttling. For directional control of the flow, we use a simple directional valve with very minimal pressure drop. We could have done this 30 years ago, but only for the slowest of systems (very poor dynamics).

Race Horse of Hydraulics – Rexroth Servo Variable Pump (SVP)

The Race Horse of Hydraulics

With the invention of high speed electronic control and synchronous (servo) motors, the “playing field” has changed drastically. Bosch Rexroth has incorporated this technology into their hydraulic portfolio for about 15 years. I call their “Servo Variable Pump” (SVP) “the race horse of hydraulics”, because it is just incredibly fast.

Rexroth Servo Variable Pump (SVP)

Precise Control of Flow, Pressure, Force, Power

Due to the design and smaller diameter of a permanent magnet servo-motor, it is very fast in acceleration and deceleration. In addition to precise, dynamic flow control, we can control pressure and therefore, also force and perform power limitation.

High dynamics means that we can go from zero to full flow in 100 millIseconds. Of course smaller fluctuations can be proportionally quicker.

Rexroth has customized the firmware in the controller for hydraulic systems. Through years of research & development, they’ve improved it to provide the best possible control. For example, it has the detailed characteristics of the pump, including the complete efficiency profile. Together with the built-in rotary encoder we get precise flow control, but also volume control. That is, we can control precisely how much oil is pumped into a cylinder or motor. Therefore, we get position control without an encoder on the cylinder, or motor.

With all this knowledge built in, the controller also tells us when the pump is starting to wear out. Therefore, we can prepare for a pump change and prevent an unexpected shut-down. Furthermore, the controller can be re-calibrated to compensate for additional leakage, so we can continue to operate with accurate control.

Regenerate Electricity

Using a servo-drive controller with an active front end, we can also regenerate electricity from deceleration or lowering activities. Relative to a conventional power unit, we can save up to 80% on energy costs, possibly more.

Condition Monitoring

Multi-Ethernet communications => easily monitor multiple operating characteristics of your machine remotely, which improves maintenance and machine uptime. Of course, this also reduces the overall cost of production.

I’m only touching on the possibilities here. There are many more valuable goodies inside the controller.

In summary, using the dynamic performance and highly variable speed of the synchronous (servo) motor, we can accurately control:

  1. flow => speed
  2. volume => position
  3. pressure => force
  4. flow & pressure => power

Additionally, we can:

  • Save on energy costs, because we’re only providing hydraulic power as required
  • regenerate electricity
    • Significant greenhouse gas reduction
  • Monitor key system characteristics
    • more system uptime
    • consistent quality
  • enjoy a much quieter working environment
  • reduce or eliminate the need for expensive noise enclosures

Conclusion

This technology opens up many exciting possibilities for excellent, reliable performance at reduced cost of ownership. As with many “building blocks”, imagination is the limit.

So let your imagination run wild. If you have an idea and want to see if this technology is right for your application, please let me know.

What’s next?

In my next articles, I’ll be presenting some novel inventions/systems that utilize the technologies discussed so far. To get a preview of these systems, you can download the PDF here. (it’s on page 2)