How to Boost Mobile Machine Performance with Electrohydraulics

Electrohydraulics is the combination of electrical and hydraulic technologies to control fluid power systems. Electrohydraulic systems are widely used in mobile machines, such as construction, agricultural, and mining equipment, because they offer high power density, precise control, and fast response. However, electrohydraulic systems also face challenges, such as energy consumption, noise, and emissions, especially in the context of electrification and environmental regulations. Therefore, there is a need to improve the efficiency and performance of electrohydraulic systems using advanced techniques and solutions.

Components Level

One way to increase the efficiency of electrohydraulic systems is to optimize the design and performance of the components, such as pumps, valves, cylinders, and motors. For example, Bosch Rexroth has developed a new A10VO Series 60 pump that is tailored for electric drives and electronic control. The pump has a compact and lightweight housing, a pre-compression volume to reduce pulsation and noise, a higher nominal pressure and rotary speed to increase power density, and pressure and angle sensors to enable power management. The pump also offers two options for control: mechanical or electronic, allowing flexibility for the user. Compared to the previous product, the new pump has a relative efficiency improvement of 7%, which in turn increases the operation time by almost 7%.

Another example of component optimization is the use of proportional valves, which can modulate the flow and pressure of the hydraulic fluid according to the input signal. Proportional valves can improve the accuracy, stability, and responsiveness of the electrohydraulic system, as well as reduce energy losses and heat generation. Proportional valves can be either direct or pilot operated, depending on the required flow and pressure range. Direct operated proportional valves have a simple and robust structure, but they have limited flow capacity and are sensitive to pressure variations. Pilot operated proportional valves have a higher flow capacity and are less affected by pressure changes, but they have a more complex and expensive structure and require a pilot pressure supply.

Systems Level

Another way to increase the efficiency of electrohydraulic systems is to integrate and coordinate the components into a complete system that can perform the desired functions and tasks. For example, Parker Hannifin has developed a hybrid hydraulic drive system that can recover and store the braking energy of a vehicle and use it to assist the engine during acceleration. The system consists of a hydraulic pump/motor, a high-pressure accumulator, a low-pressure reservoir, and a controller. The system can operate in four modes: propulsion, where the engine drives the pump/motor to propel the vehicle; regeneration, where the pump/motor acts as a generator and charges the accumulator with the kinetic energy of the vehicle; boost, where the pump/motor acts as a motor and assists the engine with the stored energy from the accumulator; and idle, where the engine is shut off and the pump/motor maintains the system pressure. The system can reduce the fuel consumption and emissions of the vehicle by up to 40%, as well as improve the performance and drivability.

Another example of system integration is the use of load-sensing technology, which can adjust the pump output according to the load demand of the system. Load-sensing systems consist of a variable displacement pump, a load-sensing directional valve, and a pressure compensator. The load-sensing valve can sense the highest pressure in the system and send a feedback signal to the pump. The pressure compensator can regulate the pump displacement and output flow to match the load pressure plus a constant margin. Load-sensing systems can eliminate the throttling losses and excess flow in the system, as well as reduce the heat generation and noise. Load-sensing systems can also improve the controllability and stability of the system, as well as enable independent and simultaneous operation of multiple actuators.

Software Level

Another way to increase the efficiency of electrohydraulic systems is to implement software functions and algorithms that can optimize the control and operation of the system. For example, Danfoss has developed a software function called Adaptive Load Sensing, which can dynamically adjust the pressure margin of a load-sensing system based on the system conditions and requirements. The software function can measure the flow and pressure signals of the system and calculate the optimal pressure margin for each actuator. The software function can then control the pump and the valves to achieve the desired pressure margin, which can be either constant or variable. The software function can reduce the energy consumption and heat generation of the system, as well as improve the responsiveness and smoothness of the system.

Another example of software optimization is the use of model-based control, which can use a mathematical model of the system to predict and regulate the system behavior and performance. Model-based control can be either feedforward or feedback, depending on the use of measurement and error signals. Feedforward control can use the model to calculate the optimal control input for a given reference output, without relying on measurement and error signals. Feedback control can use the model to estimate the system state and output, and compare them with the measurement and error signals to correct the control input. Model-based control can improve the accuracy, robustness, and adaptability of the system, as well as compensate for the nonlinearities, uncertainties, and disturbances of the system.

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