PRODUCTS & SERVICES
POCLAIN HYDRAULICS
69
Recovering energy with
electrohydraulic solutions
iVTInternational.com June 2019
EACH TYPE OF TRANSMISSION BRINGS A DIFFERENT BENEFIT TO
ELECTROHYDRAULIC SOLUTIONS
Poclain Hydraulics continues to enhance its
motor technology with new developments. Its
MHP range, the fifth generation, is the most efficient and
power-dense. Radial piston technology delivers high
efficiency across the entire motor range. It offers
multiple displacements, smooth changes in the
direction of rotation and zero-drag freewheeling.
Electric and hydraulic motors operate in unison. Both
can perform just as well in forward and reverse, and they
are both capable of accelerating and decelerating the
vehicle. When working together, they enable batteries to
operate for more hours.
When accelerating and operating in forward drive,
both the electric and hydraulic motors function at optimal
efficiency. When decelerating and operating in forward
drive, the hydraulic and electric motors perform at
optimal efficiency. The driver has control over the
machine, whether on a flat terrain or driving downhill.
Electric motor deceleration enables the brakes to last
longer. As the driver decelerates, the hydraulic motor
that powers the wheel acts as a pump, the pump acts as
a motor, and the electric motor acts as a generator,
feeding the battery with the energy it has recovered.
In reverse drive, the electric and hydraulic motors
offer the same performance levels.
In an internal combustion (IC) and hydraulic motor
configuration, the performance levels vary. An IC engine
cannot operate in the opposite direction when the
vehicle drives in reverse. In addition, an IC engine has
limited deceleration capabilities; the driver has to use
the brakes to counteract the vehicle’s inertia.
Electrohydraulic versus pure electric
An all-electric vehicle comprised of an electric motor
coupled with a fixed ratio axle does not offer a variable
ABOVE: An electrohydraulic
system depicted in
a wheel loader
BELOW: The performance of
an IC motor, compared with
an electric motor
transmission ratio. This means that the driver cannot
choose the torque and speed levels required from the
electric components for a given power level. When
driving up a 25% grade, the driver does not have the
ability to shift into a lower gear.
An electrohydraulic transmission, comprised of an
electric motor for propulsion, a variable displacement
pump with electronic control and hydraulic motors in
the wheels, allows the user to modulate the transmission
ratio on-the-fly. The pump swashplate angle adjusts
itself to combine the most efficient levels of electric
motor and hydrostatics at the required flow and
pressure. As a result, the electric motor current
decreases, less heat is generated in the motor and
battery autonomy increases.
Slew drives and grape harvesters
If you take the example of an hybrid or electric
excavator, shifting from an open-loop to a closed-loop
hydraulic circuit slew drive allows for energy recovery
when the turret slows down. The energy can be
transferred to other functions in real-time, and/or stored
thanks to ultra-capacitors or hydraulic accumulators,
both of which can withstand large power peaks.
Performance and operating range are enhanced.
Likewise, an off-road vehicle that mostly operates
on a grade (such as a grape harvester) can integrate
a hybrid engine with the electric motor taking when
the vehicle is operating in downhill working mode.
The operator has more control over their machine
and the energy recovered in the battery can be utilized
to boost the engine when extra power is required.
The OEM can downsize the IC engine, given that the
power requirement with a hybrid solution capable of
energy recovery, is lower – and the operator will save
on fuel too. iVT
Author: Jean Heren, systems advanced engineering
manager, Poclain Hydraulics
FREE READER INQUIRY SERVICE
To learn more about this advertiser, visit
www.magupdate.co.uk/pivt
/iVTInternational.com
/pivt