For decades, spool-type flow dividers have proven themselves well in the differential locks of hydraulic traction drives. In recent years, however, the demands of mobile machine operators have risen to a new level. For example, market requirements now include:
• More intuitive operation.
• Better vehicle control, particularly when driving under difficult conditions.
• Optimization and automation of work functions.
• Increased traction and higher wheel power.
• A reduction in energy consumption.
In line with these trends, Bucher Hydraulics, Klettgau, Germany, has developed a new series of differential lock valves that reportedly offer several innovative features.
The new DL14 types complement the company’s proven differential lock valves MT..DV (for 2 motors), MT..DVD (3 motors) and MT..DVV (4 motors). Like the previous versions, the DL14s are intended for use in hydrostatic drives with parallel-connected hydraulic motors in either open- or closed-loop mode, and are available for two, three or four motors.
The unit features orifices connected in parallel, so the DL14 units can also be used for more than four motors. The flow dividers are bi-directional, which means the differential-lock function works in forward or reverse travel. When the differential lock is deactivated, hydraulic flow distributes itself among the hydraulic motors freely, and with minimal pressure losses. When it is activated, the hydraulic motors are compelled to operate with parallel connections, according to the company.
The flow-optimized behavior of the new valve block and a re-engineered orifice design make it suitable for operation at high pressures. DL14 valve blocks with a 2-way differential lock function handle flow rates up to 250 l/min, the 4-way differential lock is approved for flows of up to 500 l/min.
In addition, the new design has a wider operating range. Previously, two sizes were necessary for a particular operating range: size 08 up to 100 l/min and size 16 up to 250 l/min. The new DL14 covers this range with just one size.
Low pressure losses
The new valves have also been designed with low pressure losses both when the differential lock is deactivated and activated. More wheel power is thus available. Compared with conventional spool-type flow dividers with a fixed orifice, the energy saving when the lock is activated is noteworthy, said company officials.
Pressure loss with a 2-way differential lock is then only 5 bar at a nominal flow of 150 l/min and just 11 bar at 250 l/min — and only 3 bar and 5 bar respectively when the unit is deactivated. In the case of a 4-way differential lock in the activated condition and with an inlet flow of 100 l/min, the pressure loss is around 56 bar less than with current state-of-the-art devices. This corresponds to a hydraulic power saving of 9.3 kW. Switching from drive mode to differential mode is performed via a 3/2-way switching valve in the low-pressure circuit (maximum 50 bar).
Efficient division
Another goal at the top of the developers’ specifications was to implement a locking effect almost from the point when the mobile machine begins to move, said Bucher officials. The solution involved a metering orifice controlled by the incoming flow, with division of the incoming flow beginning at flow rates of less than 10 liters/min. In particular, this noticeably improves starting on slippery surfaces. Personnel can concentrate fully on work functions during difficult driving maneuvers and forward/backward operations.
Pressure compensators for each motor or actuator are integrated in the valve block. Mobile machines, especially in agricultural, forestry and construction sectors, benefit from the large working range and the fact that the supply to the wheel motors is independent of the load pressure. In line with the trend towards higher operating pressures, Bucher has designed and tested the new differential lock valves for a continuous pressure of 450 bar and a peak pressure of 520 bar.
As with the previous MT..DV, MT..DVD and MT..DVV lock valves, integrated make-up valves and anti-shock valves are also available for the DL14. Where fuel savings and better traction are concerned, the features of the new DL14 lock valves will provide particular benefits to a wide range of mobile machines: self-propelled field sprayers, timber harvesters, aerial work platforms from 15 meters, asphalt cold-milling machines, road pavers and many more.
In the case of partially electrified machines (hybrid machines) with hydraulic travel drives, greater emphasis will be placed on the energy savings possible with the DL14 shut-off valves. Whether conventional or partially electrified, said company officials, this innovation offers an update with more wheel power, more traction and greater energy efficiency.
Bucher Hydraulics
www.bucherhydraulics.com
Filed Under: Mobile Hydraulic Tips