The S-RAM is more efficient than crankshaft, swash plate, and bent axis motors and pumps

The extremely low frictional losses of the S-RAM result Imagein increased torque and overall efficiency in hydraulic devices as well as low heat generation, higher starting torque and virtually zero slip stick. S-RAM motors and pumps can be built in variable stroke, double-ended, and fixed and rotating barrel configurations. The S-RAM has outstanding performance at reduced displacements. This is particularly desirable in energy recovery applications such as transportation, wind, geothermal, etc.

Key S-RAM benefits

Improved Torque and Overall Efficiency

The extremely low frictional losses of the S-RAM result in increased torque and overall efficiency in hydraulic pumps and motors. The S-RAM has high torque efficiency over a wide range of speed and partial displacements.  The S-RAM also has excellent low rpm torque efficiency similar to a radial piston motor and matches or exceeds this efficiency at high speed when compared to a bent axis motor.  These characteristics also provide an expanded bandwidth.  Another remarkable feature is the performance at reduced displacement.  Full, 3/4, and 1/2 displacements are all within a few percentage points of 90%.  This is particularly important for energy recovery applications.

Variable stroke

Stroke of the S-RAM can be varied while maintaining a constant head clearance, which is not possible with other drive mechanisms. Unswept volume remains close to zero as the capacity of a pump or motor is varied in a continuous fashion.  This allows the efficiency to remain high at partial capacity (reduced displacements).  Piston friction is also proportional to the stroke length so reduced stroke further reduces piston and bearing friction losses, improving mechanical efficiency.

Near Perfect balance

Motion of the S-RAM pistons is near sinusoidal and the harmonic components are unusually small. There are no even harmonics since the piston motion is symmetrical about the midpoint of travel. Any number of pistons three or greater that are evenly spaced can be near perfectly balanced.  A variable stroke S-RAM can also be balanced.

Double-Ended operation

The S-RAM can be easily configured with a double-ended piston that will operate 180 degrees out of phase with the first. This can dramatically increase the performance and the power density of the machine, with little change in physical size and weight of unit.

Low heat generation

Low piston friction in the S-RAM leads results in minimal heat being generated within the body of the operating mechanism. Measurements taken from a working 20 HP hydraulic motor showed a temperature rise of only 40F (20C) at full load.  All of our pump and compressor machines run this cool or cooler.  Reduced heat generation can in some cases eliminate the need for an oil cooler, but in any case, reduce the size of the required cooler.

Open-Cylinder architecture

The S-RAM is a new mechanism to drive pistons.  Architecture arrangement allows a designer to use the same valves, cylinders, manifolds, etc that complete the system and conversion from any current design can be fairly straightforward.

Fixed or Rotating-Barrel designs

The S-RAM drive can be used in rotating or fixed-barrel configurations. We have built both.

Wear and Life expectancy

Tests on our prototype S-RAMs have shown very low wear, which one would expect as a result of low friction. Bearing surfaces on the S-RAM 500 HP pump showed no measurable wear after several hundred hours of operation under full load.

ReduceD parts count and weight

The S-RAM uses significantly fewer parts and less weight than crankshaft mechanisms and similar parts count as compared to swash plate and bent axis mechanisms.

Scaling to higher horsepower

Cool running of the S-RAM allows higher horsepower to be achieved.  The 500 HP pump prototype ran with a low temperature rise such that a 3,000 HP pump was deemed feasible. At reduced power levels a fractional horsepower compressor with low friction allowed oil-less plastic bearings to run with little wear.  Scalability is similar to that of a crankshaft mechanism in that no scaling problems arise as the square or higher power of linear dimensions.

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Current Developments

We are currently designing a 7-cylinder hydraulic motor/pump for mobile applications. This prototype is for a direct-drive application that will demonstrate improved low-speed torque efficiency and increased overall efficiency at high speeds and operating pressures.

Next Prototype

Testing of the original S-RAM hydraulic motor/pump revealed improved mechanical and volumetric performance over a wide speed and displacement range. This type of performance is not typical for standard hydraulic pump/motors currently produced.

The design of the next generation prototype is targeted for direct drive skid steer and hybrid vehicle applications where partial displacement performance will coincide with high-speed operation. The prototype meets the following specifications:

  • 500 cm3 with variable displacement with over-center capability
  • High overall efficiency (>90%) over the entire
    operating range of pressure, temperature and speed
  • High overall efficiency over a displacement of 40% to 100% maximum displacement
  • Operating pressure up to 5,500 psi

The S-RAM hydraulic motor/pump will demonstrate the following advantages:

  • Elimination of gearbox elements in power train drives
  • Reduced fuel consumption for a specific operation
  • Improved productivity by widening the range of machine operation
  • Lower operating cost through improved efficiency
  • Lower total capital costs by eliminating components in a specific application through the use of direct pump control strategies.

Past Prototypes

We have built and tested several hydraulic motors and pumps. The results of the prototypes have been very positive and we have continued to improve the efficiency, balancing and variable stroke features of the S-RAM technology. A brief description of past prototypes is included below.

Hydraulic motor/pump

  • 7 Cylinders
  • Stroke, variable 0-54.29mm (2.138 in)
  • Bore, 26.5mm (1.04 in.)
  • Displacement, 0-210 cc (12.79 cu in)
  • Pressure to 3,500 psi

Large Variable slurry pump for Oil Industry

  • 3 Cylinders
  • Variable stroke
  • 500 hp
  • Confidential

Variable Water Displacement Pump

  • Stroke, .970 in.
  • Bore, .574 in.
  • Bore, 26.5mm (1.04 in.)
  • Pressure, 3,500. psi

Fixed-Displacement Water Pump

  • 3 and 6 cylinder
  • Stroke, .970 in.
  • Bore, .574 in.
  • Displacement 1.506 cid
  • Pressure, 3,500. Psi
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