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High Flow Efficiency

The continual evolution in performance of SAI motors over recent years has led to the need to revise even the most basic design parameters of its motors to cope with the increased power throughput. A typical example of such a parameter lies in sizing of the oil passages inside the motor which are no longer suitable for the new performance capabilities.

The advent of the S-series high speed motors, made possible by improvements in the lubrication, surface treatment and guidance characteristics of the piston/cylinder assembly, has enabled the maximum speeds and power of the motors to be considerably increased.

The S-series motors, however, being based on the M-series, currently have the same casings and oil distribution systems, therefore with identical external dimensions and internal flow sections. While this means that the S-series motors have almost double the specific power (power:weight ratio) of the M-series, the S-series efficiency is penalised at high speed by the pressure drop caused by relatively small flow sections sized for the slower M-series motors. A good indication of the mechanical and fluid friction in a motor is given by the idling pressure (the pressure drop required to run the motor at a given speed without load); the M- and S-series motors have similar boost pressure characteristics

For example - M5 1800 cc at 300 rpm: idling press. approx. 18 bar; S5 1800 cc at 550 rpm: idling press. approx. 68 bar, that is, four times the value at 300 rpm. Therefore, with the M5 motor operating at maximum speed (300 rpm) with 100 bar, the mechanical and fluid friction absorb approx. 18% of the energy input, giving a mechanical efficiency of 82%, an acceptable value in most situations.

With the S5 motor, however, operating at maximum speed (550 rpm) with 100 bar, the fluid friction absorbs 68% of the energy input, giving an unacceptably low mechanical efficiency of 32%. It is evident therefore that the oil channel sizing for the old “low speed, high torque” motors is no longer suitable for the new “high speed, high torque” motors.

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Crankshaft Design Radial Piston

Hydraulic Motors

An extensive range of displacements from 40 cc/rev through to 1200 cc/rev in nine basic frame sizes is available. Options include variations on shafts, flanges, bearings, distributors, high pressure shaft seals, and competitor interchangeability.
High Speed Motors

High Torque

These motors offer the high speeds previously only associated with axial piston designs, and therefore the corresponding high powers. High running speeds of up to 2500 RPM and 2800 RPM freewheeling are possible with the smaller displacement motors. High-pressure versions are also available with peak pressure capability of 800 bar.
Wheel Drive Units

Wheel Motors

SAI offer both direct wheel drive units with or without automotive style drum brakes and combined motor/gearboxes with or without spring applied hydraulic pressure released brakes. These are ideally suited for a wide range of mobile applications, and displacements range from 60 cc/rev through to 4111 cc/rev.
Gearboxes and Brakes

High Torque, High Speed

A range of single stage epicyclic gearboxes is available enabling high torque to be achieved with compact dimensions. Spring applied, hydraulic pressure released brakes can also be incorporated into these units. SAI motors can also be easily fitted on to many proprietary gearboxes and SAI(GB) Ltd. can supply these as a package if required.