Today, there is also a trend towards larger timber transport vehicles that consume less energy.
One way engineers can keep up with these demands is by taking advantage of a new sort of hydraulic linear actuator technology, embodied in the Hydraulic Infinite Linear Actuator (HILA). It can help improve vehicle aerodynamics, accommodate varying load sizes and weights to raise productivity, and automate dangerous manual tasks to enhance safety. It is also suited for agricultural operations to ensure high-yield and sustainable farming. Here’s a closer look at HILA fundamentals and applications.
The HILA generates long actuator strokes from a short cylinder body. It is based on well-known hydraulic clamping technology, where the piston and rod can be coupled and uncoupled by means of a clamping element. The HILA actually combines two short-stroke cylinders with two coordinated, engaging and disengaging clamping mechanisms into one actuator with a long stroke length.
The motion of each single short-stroke piston, linked together by the internal clamping mechanisms, drives the piston rod. One piston at a time connects to the rod, shifting the load from one cylinder to the other and alternatingly moves the rod in a kind of “hand-over-hand” rope climbing motion. Simple logic valves control the flow.
The clamping mechanism, essentially a hydraulically activated membrane, maintains friction and load-holding capacity. It is pressurized and engaged by a separate port through the piston using a dedicated 3/2 valve. Here, minimal flow is needed to pressurize the small membrane volume, so a small and fast-operating valve can be used. Piston movement and clamping actions are independently controlled by a timing procedure.
Because piston areas in the cylinders are symmetrical, there is marginal variation of oil volume during operation, compared to conventional hydraulic actuators. Another advantage is that the system needs only a fraction of the hydraulic oil versus an ordinary long-stroke hydraulic cylinder and, thus, requires a much smaller oil reservoir.
One challenge is to generate linear motion with a low pulsation level. In many applications, however, smaller pulsations are acceptable. The technology is best suited for applications with relatively slow dynamics and where movements are largely kinematic and well-understood.
In contrast, traditional long-stroke cylinders face several hurdles. Buckling is probably the main problem. It can be overcome in some applications using a pulling cylinder. Hydraulic stiffness and hydraulic capacitance can also have an unfavorable effect on dynamic behavior and controllability. Longer hydraulic cylinders usually face difficulties at high pressure, as it reduces the system natural frequency. Thus, advantages normally associated with hydraulics — compactness and high power density — diminish with increasing stroke length.
The Hydraulic Infinite Linear Actuator solves these problems. HILA provides long strokes at high system pressure, with a higher stiffness compared to conventional hydraulic cylinders. Each HILA cylinder has a much shorter body, so a sufficiently high natural frequency can be achieved at high system pressures. And bulk modulus increases slightly with increasing pressure. These are favorable factors in terms of actuator control design.
The compact and lightweight system, built with robust and cost-effective standard components, is well suited for tough and demanding environments, especially in mobile applications, where there presently are no alternative solutions.
Strokes as long as 7 to 8 m (23 to 26 ft) are possible, depending on the piston rod diameter, for pulling loads in horizontal applications. Even longer strokes can be implemented in vertical applications, such as in elevators. As the HILA technology needs small cylinders and low oil volumes, it is possible to design compact and long stroke electro-hydraulic actuators (EHA). Symmetrical piston areas simplify the design.
HILA technology also lets several active actuators to be positioned and locked on the same piston rod, which can be advantageous in certain applications. This means that several processes can be performed in parallel instead of serially, without the need for a dedicated actuator for each element. Here’s a look at two such applications. One involves timber vehicle aerodynamics and logistics; the other shows how HILAs can flexibly and optimally position row units on agricultural planters, to secure productive and sustainable farming.
More-efficient timber trucks
There is a great need in forestry transport to reduce fuel consumption and limit variable costs and carbon dioxide emissions. One solution is to develop larger vehicles that carry greater loads and reduce transport cost per mile.
There are likewise opportunities to improve vehicle aerodynamics, as air and rolling resistance are two of the most important factors that hurt fuel economy. Truck manufacturers put a lot of effort into reducing air resistance through better aerodynamic design of the cab and chassis. For the trailers, no similar development has taken place.
Complicating matters, a timber trailer is like two completely different vehicles, loaded and unloaded. When unloaded, several points experience strong turbulence, specifically around the vertical stakes that support the logs; and around the horizontal banks — the structural cross-members that hold the stakes in place and on which the logs sit.
Simulation studies show that the biggest aerodynamic problems for unloaded timber trucks are turbulence under the trailers, and air resistance due to stakes and banks that stand upright in the air stream. Bundling stakes and banks together at one point would significantly reduce air resistance, depending on vehicle speed. The trend is toward timber vehicles that drive longer distances at higher average speeds, due to fewer and larger sawmills and pulp mills. As air resistance increases with the square of the speed, the need for consolidated banks and stakes is even more important for fuel economy.
The same holds for aerodynamic resistance and turbulence that banks and stakes create on unloaded timber train carriages. While unloaded timber trucks drive at maximum speeds of around 100 km/hr (60 mph) in the U.S. and Canada, freight trains travel at even higher speeds. Studies show that covering unloaded coal wagons can reduce air resistance by more than 40%.
HILA systems can address these issues. With HILA technology, banks and stakes on timber vehicles can be individually positioned, automatically, with high locking force. The system can also significantly increase vehicle flexibility and open up more combinations that facilitate cost-effective and environmentally friendly logistics for both timber and complementary goods flow. Key functions on towing vehicles and timber trailers include:
Timber trailers can have up to eight banks. With HILA actuator technology, adjustment between 2, 3 and 4-stack combinations can be done smoothly via an in-cab display. This eliminates the difficult and hazardous manual work needed to push the heavy banks and stakes between various positions, significantly improving driver safety and saving considerable time.
Precision seed drills
A key to productive and sustainable farming is planting seeds at an optimal distance from each other. However most present seeders have a fixed row distance and, thus, low adaptability for different crops or soil conditions. Even when possible, changing row spacing is time consuming and expensive, as it can take two working days to manually adjust row spacing on a precision seed drill. Further, the machine is out of production, especially critical in the spring planting season.
One possible solution for variable row spacing is to densely pack seeding units on the machine arms and only activate certain ones to obtain the proper row spacing. But driving around with excessive dead weight is impractical.Most farm seeders are built with fixed row spacing, which limits adaptability for different crops or soil conditions. Mounting numerous seed drills on a HILA permits fast and variable row spacing on machines for precision sowing. | courtesy of Per Frankelius, Linköping University
HILA technology enables numerous seeding elements to be positioned along a row, with high locking force. Operators can implement fast, efficient, and variable row spacing on machines for precision sowing, inter-row cultivation and crop harvesting. This means that the same machine can be used for different crops and meet farmers’ demands for common multi-purpose equipment.
A HILA can quickly shift the position of drill units as needed. Operators can vary the distance between drill units from a display in the tractor cab, and fine-tune the inter-row spacing depending on the types of crops and soils. The HILA concept allows for countless configurations for different seeds, and spacing can be independently adjusted with high precision.A HILA can quickly shift the position of a seed-drill unit, and hold it in place with high locking force.
Operators can also reconfigure spacing on-the-fly if one unit fails, so planting can continue without having to wait for a service technician. This contributes to higher productivity. Similarly, for easier servicing, it is possible to open large spaces around a specific row unit with the push of a button.
While it is beyond the scope of this article, HILA technology can also let operators vary the arm width of seed drills and planters, and fold the arms for transport on roads. It offers the possibility of longer arms and a simpler and faster folding mechanism, with a more optimal center-of-gravity, more stable vehicle dynamics and higher travel speeds.
A demonstrator has been successfully tested and meets the initial functional requirements. The next step will be to build a full scale seed drill. As part of Sweden’s Agtech 2030 innovation program, the project involved collaboration among Saab Ventures, Sweden’s Rural Economy and Agricultural Societies, GN Tech, and Landberg Solutions. The hydraulic research division (FLUMES) at Linköping University has been instrumental in this work.
Contact: David Song
Add: Room 603,Xinsheng building 2#, Xinluo Road, Gaoxin district, Jinan, Shandong province, China