Users are demanding a hydraulic power unit (HPU) design that eliminates the need for a separate unit in the plant and all its piping, and instead integrates it into the machine structure, resulting in a more compact, more energy-efficient system with a lower overall cost. The new unit has been developed by MFP Automation Engineering.
Provides clamping force during the test phase of the user’s machine cycle. During this phase, high flow is provided to quickly move the part into the clamping position, but little to no flow is required to maintain clamping pressure until the test phase is complete. At the end of the test phase, high flow is applied again to release the clamp and remove the part. Since high flow is only required for 6 seconds of the 81-second test cycle, this application is ideal for reducing energy consumption.
The reduction in size and power consumption is primarily due to the transition from a typical induction motor to a PMAC motor with a VFD controller. Moving the equipment off the factory floor and placing it inside the machines frees up more space for other uses. Because the PMAC motor eliminates the magnetizing current created by the induction motor, it can save about 10% of the total energy consumption at full load. The most significant reduction in energy consumption occurs during the clamping phase of the machine cycle, as the motor speed is reduced. The new design also reduces the overall cost of the system. Although the cost of the major components for the VFD and PMAC motor design is about 10% higher, simplifying the valves needed to control the equipment reduces the overall cost.
The hydraulic power unit (HPU) is driven by a Parker Hannifin NX series brushless servo motor, producing 132 ft-lbs (15 Nm) of continuous torque and up to 13.6 hp (10.1 kW) of short-term power. During most of the machine’s duty cycle (when the machine is running sequentially), the motor produces a rated power of 4.6 hp (3.4 kW) at 2200 rpm, but during this period, motor power can vary from 1.3 hp (0.97 kW) to 6.7 hp (4.9 kW). Motor speed is adjusted by the machine cycle depending on the flow requirements of the various functions. This eliminates the need for separate flow controllers and minimizes energy loss.
The upgraded hydraulic power unit uses a variable frequency drive, which reduces energy consumption by 74% compared to traditional fixed-speed hydraulic power units.
The pump is a Parker PD018 variable displacement axial piston pump with a capacity of 18 cc/rev and a maximum continuous pressure of 4000 psi. This application uses a standard direct acting pressure compensator set at 1500 psi. Many servo applications use a constant displacement pump to maintain pressure and reduce the drive speed to maintain the pressure in a clamped or static condition. The compensator used here allows the pump to be returned to its minimum displacement in the duty cycle. This reduces the torque and current draw of the servo motor and addresses user concerns about high motor temperatures and potential machine contact/overheating hazards. While most constant displacement pump systems have motor torque and current that remain constant from idle to pressure, this system’s displacement drops from 0.55 cc/rev (9 cc/rev) to 0.11 cc/rev (1.5 cc/rev). in/rev (1.8 cc/rev). The motor current drops almost proportionally, as does the heat generated and the energy consumed.
Both conventional and upgraded power units are equipped with a Parker PD01 variable displacement axial piston pump, which is rated at 280 bar continuous pressure and designed for high-speed, low-noise operation.
The system also includes a maximum flow limiter set at 0.55 cu in/rev (9 cc/rev), which provides a flow rate of 7 gpm (25.5 lpm) at the design speed for this application. The pump speed range is 50 to 3700 rpm. Another benefit of this pump design is the pulsation chamber technology, which reduces pressure pulsation at the pump outlet by 40-60%. This significantly reduces the noise level in the system without the need to purchase additional noise suppression components.
Other system components include an integrated manifold that allows filtration through automotive pressure and return filters. Also included is a small air-to-oil cooler that provides airflow to the PMAC engine and helps cool the oil as needed in the unit’s smaller oil tank. Machine controls include a 10-way manifold assembly containing seven Parker D03 directional control valves, four Parker pilot-operated check valve modules, four direct-acting pressure reducing valves, and two counterweight modules for vertical load support.
Not only does this conventional hydraulic unit consume more power than the VFD hydraulic unit, it is also much larger at 594 in.
The new system replaces the traditional hydraulic power unit (HPU), which consisted of a 5 hp asynchronous motor that also drove a Parker PD018 piston pump, and included a pilot compensator with heat exchanger and an automotive-style pressure and return oil filter. The traditional system also includes an eight-way manifold assembly consisting of seven Parker D03 directional control valves, four Parker pilot-operated check valve modules, seven pressure reducing valves, five flow regulators and a steel manifold with BSPP ports.
The new variable frequency drive power supply provides better control of pump speed and significantly reduces the footprint above the tank lid. Variable frequency drives reduce operating costs by reducing pump speed when the pump is in a steady state. Variable flow, pressure compensated pumps deliver the required flow only when pressure is present. Lower power consumption also reduces heat generation, allowing smaller tanks to be used without sacrificing machine performance. In addition, better speed and flow control allows fewer manifolds, reducing potential leak points and failure modes.
Some systems combine conventional drives and similar pumps with load cells and accumulators, allowing the use of smaller pumps and motors while still delivering maximum flow intermittently. However, the variable frequency power supply used in this system can provide feedback on the health of the hydraulic power unit (HPU) and the machine itself. Not only does the power supply more closely match requirements and simplify the system by reducing the number of components, it also simplifies initial machine mapping and monitors torque, current, and speed to detect performance degradation throughout the machine’s life cycle.
Roger Betten is president of MFP Automation Engineering in Hudsonville, Mich. For more information, call (616) 538-5700 or visit the company’s website.
Post time: Apr-28-2025