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Decoding the shift from hydraulic systems to electric actuators Author: Danaher Motion, Al Wroblaski Source: DesignNews Many off-road machinery manufacturers have replaced hydraulic cylinders with electric actuators in order to eliminate components such as water pumps, hoses, and valves, thereby making the vehicles smaller, lighter, and quieter. They took advantage of the flexibility in connecting electric actuators to control systems, thereby achieving numerous new capabilities. For example, electric actuators can be easily connected to vehicle controllers to enable more complex movements, such as performing a specified number of cycles at different positions, thereby improving the performance and operational efficiency of off-road machinery. Today, the benefits of electric actuators are already evident in practical applications – they enable an increase in the maximum static load to 5,000 pounds and the maximum dynamic load to 3,000 pounds, with the rated load continuing to increase each year. Currently, higher load requirements are placed on hydraulic cylinders, with the load ratio for moving loads required to reach 100%. However, there are now some misunderstandings regarding electric actuators, which have led OEMs and end-users to overlook the various advantages they offer in many applications, thereby delaying their adoption. Below, we will shed light on these misconceptions and explore the possibility of integrating electric linear actuators into non-road vehicles and machinery such as recreational vehicles, sprayers, snow blowers, lawn equipment, garden machinery, construction equipment, and agricultural equipment. Misconception 1: Electric actuators cannot be used in harsh environments. Hydraulic technology has been in use in off-road vehicles for decades, and engineers are well aware of the durability of this technology in environments with high-frequency shocks and vibrations, high dust concentrations, high water levels, corrosive chemicals, and other potential hazards. Compared to their electric counterparts, hydraulic actuators have traditionally held an advantage in high-power applications, enabling improved performance in most demanding conditions. However, many non-highway engineers are not aware that over the past decade, the performance of electric actuators has made significant progress in terms of high power and use in field environments, whereas hydraulic actuators have seen little or no progress in these areas. Figure 1: The design of electric actuators no longer relies on modular assembly; instead, the key components are concentrated within a closed unit to protect them from shocks and vibrations, thereby optimizing environmental protection. The power density of hydraulic actuators depends largely on the system pressure, and for reasons related to safety and cost, these pressures have remained stable over the past decade. On the other hand, thanks to advances in magnetic materials, the efficiency of screws and ball screws, construction, manufacturing processes, and electronics, the power density of motors has increased significantly during this period. The most important benefit it brings is the ability to generate greater power while maintaining high efficiency. The advantages of motors are also evident in power transmission, which is mainly achieved through gearboxes, allowing for optimal performance to meet the requirements of electric linear actuators. Therefore, electric actuators can provide high power density in various applications, simplify the installation process, and reduce vehicle weight. Today, electric linear actuators for off-highway applications are designed specifically to handle harsh environments. Finite element analysis was used for the castings to improve their load-handling capacity. The design of electric actuators no longer relies on modular assembly; instead, the key components are housed within a sealed unit to protect them from impacts and vibrations. Multi-axis vibration testing and analysis have demonstrated that electric linear actuators can withstand mechanical loads in practical applications. Another advantage of electric actuators is that they do not require wiring connected to a motor controller; instead, the connector is fixed inside the housing, and the control system cable is inserted into it. This method provides better encapsulation, protecting the motor connections from damage. In short, the durability of electric linear actuators used in off-highway machinery is, by all accounts, no less than that of hydraulic actuators. Misconception 2: Electric linear actuators are less reliable than hydraulic actuators. Many engineers assume that hydraulic actuators are more reliable, perhaps because they often encounter reliability issues when using traditional electric linear actuators. However, the reliability of electronic products and electrical materials has improved significantly nowadays, and electric linear actuators have also benefited from this. The structure of an electric linear actuator consists only of a motor, a gearbox, a lead screw (or ball screw), and a clutch, making it simpler than similar hydraulic products. The hydraulic system has many components, including an oil tank, a water pump, a DC motor, a motor relay, solenoid valves, check valves, hydraulic cylinders, and a button-based control panel. Thanks to highly reliable electronic technology and minimal risk of failure, the reliability of electric linear actuators has improved in recent years, making them more durable in most applications than machines equipped with hydraulic actuators. Electric linear actuators are maintenance-free, which means they rarely experience failure issues resulting from inadequate maintenance. The hydraulic system requires careful maintenance, including regular replacement of the fluid and filters, to ensure that there is sufficient fluid within the system. In harsh off-road applications, the hydraulic fluid is prone to contamination, and when contaminated fluid flows through the system, it can trigger a chain reaction that damages multiple components, each of which may then require repair or replacement. Hydraulic systems generally control multi-axis movement, which affects many aspects of machine operation. For example, if a shaft has a high load, it will reduce the circuit pressure, affecting other shafts. Another impact is that when there are problems with the hydraulic system, such as a pipe rupture, it becomes impossible to manually drive the affected shafts. In comparison, modern electric linear actuators require no maintenance at all, and even no lubrication. In electric linear actuators, the various axes do not interfere with each other, and each axis has its own drive motor; therefore, if one motor fails, it will only affect the actuator it controls, making maintenance easier. To ensure load control, the hydraulic system requires additional power; if the hoses or valves fail, the system’s ability to control loads is significantly reduced. On the other hand, electric actuators provide variable loads and can be controlled in the absence of power, with almost no flow or back-driving. Finally, if there are problems with the power supply or the motor of the actuator, the electric linear actuator can still achieve overload protection easily through manual reset. Misconception 3: Electric linear actuators are more expensive. Some people think that electric linear actuators are more costly, perhaps because each electric shaft requires a motor, a lead screw, and a gearbox, whereas adding a hydraulic shaft only needs a hydraulic cylinder. But in fact, the hydraulic cylinder is just a component in a hydraulic system used to support an axis. Valves, hoses, and accessories are also necessary; in many cases, it is not possible to install a new shaft on the hydraulic pump. The economic efficiency of a hydraulic transmission system depends to a large extent on the number of shafts driven by that hydraulic system. If a hydraulic pump needs to be added to handle another shaft, the hydraulic system is usually much more expensive than an electric linear actuator. Generally speaking, when hydraulic systems handle single-axis, dual-axis, and three-axis motion, they can usually be replaced by electric linear actuators at a lower cost. The number of hydraulic system ports in many agricultural machinery applications can also be used to compare the costs of electric actuators and hydraulic systems. Every component of a hydraulic system requires a port, and increasing the number of ports is very costly, as it entails adding valves, hoses, and connectors, not to mention a filling pump. In contrast, electric linear actuators can have additional components added without the need for ports. If the shaft in the hydraulic system is located far away from the pump, it is necessary to use hoses to connect the pump and the cylinder, which incurs significant labor and material costs; whereas electric linear actuators do not require such expenses, highlighting their cost advantage. The operating cost of electric linear actuators is usually much lower than that of hydraulic systems, as electric linear actuators consume energy only when they are in operation, whereas even the most efficient hydraulic systems remain active at all times, resulting in high energy consumption. The simple design of the electric linear actuator also significantly reduces its installation costs. Electric linear actuators require no maintenance, whereas the fluid and filters in hydraulic systems need to be replaced regularly. Misconception 4: Electric linear actuators increase design complexity. Some people believe that electric linear actuators add complexity to the design process, perhaps because they are not yet installed in many off-road vehicles. Therefore, adding an electric linear actuator requires it to work in conjunction with two types of actuators, rather than just one. Furthermore, many off-highway equipment engineers are not very familiar with electric linear actuators; they are only acquainted with older types of actuators that require the selection and assembly of various components such as motors, gearboxes, controllers, etc. Today’s electric linear actuators have been simplified; their configuration and design are much easier than those of hydraulic systems. They can be installed successfully by simply connecting two wires and a double-pole double-throw switch. Determining the size of an electric actuator requires only three steps: measuring the load, determining the load ratio, and specifying the stroke length and retraction length. The exact load on the actuator may not be known due to the effect of intermediate connections. The exact load can be determined using software packages for simulating mechanical systems or by installing pressure-sensing elements on the actuators. Manufacturers can easily configure electric linear actuators to meet various application requirements by adjusting the gear ratio, lead screw, motor, and electronic control parameters. The one-to-one principle of electric actuators prevents interference between them, allowing engineers to focus entirely on the design of the shaft. Conversely, engineers of hydraulic transmission systems need to consider the impact that the energy consumed by a new shaft will have on other shafts. After analyzing these misconceptions, it is clear that electric linear actuators have advantages over hydraulic systems in many off-highway applications. The robustness of electric linear actuators has improved significantly in recent years, with durability and reliability comparable to those of hydraulic systems. Problems such as susceptibility to contamination and temperature fluctuations are major concerns when using hydraulic systems, whereas electric linear actuators are not affected by these issues. The cost of electric systems depends on the specific application; they are generally cheaper than hydraulic systems in single-axis, dual-axis, and multi-axis applications. Finally, today’s integrated electric linear actuators are very easy to design and can be readily installed in various off-road equipment.