Turner Two-Speed (TTS) Cylinder 

(Patent Pending)

 Up to 50% Faster Cylinder Extension

Up to 60% Faster Cylinder Retraction        

Up to 50% Less Horsepower & Flow Input

More Consistent Load Motion

Gravity Down Instead of Power Down

  TTS is an answer to improving the efficiency of “declining force” applications, such as dump truck bodies and scissor lifts.  These are typical examples of applications where high force is required to get the load moving, and a proportionally lower force is required to keep it moving.  If an application requires only 50% of the initial force at 50% of the cylinder’s extension, then TTS can provide a 25% gain solution.  At least a  25% faster cycle time, or 25% less horsepower and flow. 

Our initial test simulated a dump truck-style operation, which required approximately 33% of the initial force at 33% of the cylinder stroke.  Although the extension time was 50% faster for the TTS, the retraction time was over 60% faster.  The test uses identical off-the-shelf cylinders; one being internally modified with TTS. 

            TTS recognizes that the optimum, efficient cylinder shape for a declining force application is a tapered bore.  The area of a tapered cylinder bore would match precisely the force curve needed as the cylinder extends.  With a constant flow source, the cylinder rod would extend at an increasing speed as the cylinder bore narrowed.  The surface area and rod speed are inversely proportional.

            Unfortunately, it is impossible for a piston to travel through a tapered bore cylinder.  TTS uses the optimum tapered bore calculations and transcribes them into the shift points for the cylinder.  The piston and cylinder bore area are utilized for the first stage of high force and the rod area, or a smaller piston on the rod, is used for the lower force but higher speed stage.  This shift is pre-engineered into the internal cylinder components, with the basic TTS cylinder having no more moving parts than the rod and piston.  More stages can be designed into the cylinder, simulating even closer to the tapered bore calculations, but may only be cost effective for certain applications, for long strokes or safety overload protection on scissor lifts or booms.     

The mechanics of the two-speed are rather simple. In a quest for getting the piston to carry the rod at high force, but then let go of the rod, so it can extend more rapidly, a cup-shaped piston was designed. The main-bore piston is much longer than a standard piston and is not attached to the end of the rod, and it may only travel half of the cyllinder's stroke. It tops out against the gland, and has ports letting fluid get into the inside of the cup portion of the piston. As fluid goes to the insode of the piston, it displaces the rod up through the piston. The piston can be made with a honed inner wall, and the rod can have a smaller piston on it, so there is essentially a cylinder within a cylinder. Two pistons are at work , one in the large, main bore; and the other inside the main-bore piston, attached to the rod.

            TTS can also be used to lower the horsepower and flow input required for an operation.  It is easy to see that if keeping the flow the same would provide a 50% increase in speed, then decreasing the flow by 50% would yield the same extension time as a conventional cylinder.  However, the cycle time would most likely improve up to 30%, as a TTS cylinder will retract up to 50% faster.  On extreme applications, whole cycle times may be maintained with 66% decrease in horsepower.  On hydraulic systems this allows for 66% smaller pumps, valves, hoses and reservoirs. 

Double acting cylinders are often used to power down a cylinder in an application where gravity cannot satisfactorily overcome the residual force of the cylinder in its extended position.  An empty aluminum dump body or scissor lift is a good example.  TTS cylinders eliminate the need for double acting cylinders on some applications, as they displace less oil as they retract, and virtually multiply the effects of gravity on the mechanism.  In one scissor lift application where power down was used, the safety props were not removed prior to retraction, which caused catastrophic failure.  TTS can eliminate the possibility of this type of accident and provide a safer system.

          Safety can also be increased in another way using TTS cylinders on certain applications such as scissor lifts or booms.  Almost all scissor lifts and booms can be overloaded when the cylinder is extended.  As an overloaded boom or scissor lift is lowered, the pressure in the cylinder can increase to dangerous levels.  If there is a relief valve in the cylinder circuit, once the pressure setting of the valve is reached, the cylinder will retract uncontrollably, completely lowering the load.  In the same example, a TTS cylinder would be several times more sensitive to overloading, allowing only a fraction of the overload that a conventional cylinder would allow.  Overloading can still occur, but the result is substantially different.  An overloaded TTS cylinder would retract uncontrollably as well, but it would do so at a higher point and unless severely overloaded, would only do so until it reached the first stage, where the area of the full bore would lower the system pressure and stop the retraction.  At that point the overload can be dealt with before it lowers completely by itself.  Using a three-speed cylinder in these applications would further enhance the overload sensitivity, and decrease the amount of possible overload and uncontrolled retraction.

            Several optional features can be incorporated into the design of the TTS cylinders.  Following are some examples of optional configurations.  The cylinder can be designed with ramps and cushions at either end of both stages.  Flow controls can be installed to limit the speed of the retraction, while allowing the extension to be at full speed.  Each application receives a custom solution delivering the desired results.  Cylinders can be used to retract over-center loads.  Double acting cylinder designs are available.  For some applications, the fast speed can initiate first, but only for a preset distance, where a partial load only needs to be moved a partial distance.  For overload protection, a relief valve can be installed on the piston as long as the rod port is connected to a reservoir.

            The end result of using the TTS design is an energy-efficient, matched system where the horsepower input is more effectively used throughout the entire motion, where the simple design with few moving parts and no external valves leads to a cost saving, productive fluid power solution.  TTS breaks the paradigm of conventional engineering, where jamming more fluid into a cylinder is the only way to make it go faster...  And TTS addresses the need for an efficient retraction time.

TTS is not just for hydraulics. Pneumatics may have just as many applications, and be able to utilize the two-speed cylinder to deal with break-away issues as well.  

            Email Dan Turner at dt@turnerhydraulics.com to get the specifics on how your product, or your production, can benefit from this latest technology.