Electrohydraulic drive controls on mobile working machines enable more flexible, more finely controlled driving behaviour than purely hydraulic solutions. The basic drive control by Völkel enables control of the diesel engine, the drive pump and a hydraulic motor and is pre-equipped with extensive functionalities. At the same time, the controller is designed in such a way that it is
also economical for smaller machines, such as wheel loaders.
Depending on the operating mode, different characteristics such as start-up behaviour, acceleration, deceleration as well as limit values such as the maximum velocity or the speed range of the diesel engine can be set. The range of functions is completed by the reversing mode for quick reversal of the direction of travel, a velocity control function, adjustable creep speed, an inching
function and load limit control to protect the diesel engine against overload.
The standard hardware platform for the DCB is the HCB controller. If the DCB is to be integrated into a machine controller, it can easily be ported to another Völkel hardware platform.
The functions in detail
Release and setpoint specifications
A specified procedure must be followed to set the machine in motion: First, the diesel engine must be started, then the driving release is given and only then may a driving velocity setpoint be generated. If this sequence is not observed, no control variable is generated. Depending on the machine type, the setpoint can be specified via a joystick or an accelerator pedal. If the machine is operated with a pedal, direction release via an FNR switch is required for forward and reverse travel.
Start-up and braking behaviour
The driving behaviour of the machine can be adjusted via characteristic curves and limit values for different operating modes. For example, the sensitivity of a setpoint generator (joystick, pedal) can be mapped linearly or reduced near the zero point and increased in the maximum range to enable a more finely controlled start-up. Static and dynamic acceleration and braking ramps can be set. Separate velocity limits can be set for each operating mode.
When the velocity control is activated, the control variables for the diesel engine, the pump and the hydraulic motor are frozen in order to maintain the active velocity at the time of activation in the open control loop. The velocity control is active until the button is pressed again or the brake is activated.
For loading operation of a wheel loader, it is necessary to drive at low speeds with increased diesel engine speeds in order to supply power to the lifting frame and shovel. The diesel engine speed is set by the accelerator pedal in relation to the driving velocity. With the inching pedal, the driving velocity is reduced again but the diesel engine speed is maintained.
In creep mode, the maximum velocity can be continuously limited independently of the currently selected operating mode. The driver then has the entire pedal travel available for the limited velocity range. This allows the machine to be even more finely controlled.
Load limit control
The load limit controller protects the diesel engine from stalling by limiting the hydraulic power in relation to the lowering of the diesel engine speed.