(1) LOW STARTING TORQUE TORSION SPRING COUPLING. BACKGROUND OF INVENTION. (01) The need for this invention arose after attempting to operate a positive displacement piston pump directly from a solar power panel array, utilising a commercially available multi input voltage electric induction motor designed for solar power operation. This solar powered compatible electric motor was originally designed to operate low starting torque devices like centrifugal pumps and fans where the starting load is minimal and only increases as the motor speed rises. (02) The starting torque for positive displacement pumping is higher as the pump can effectively pump water at very low speed. In researching this problem, in the United States of America to utilise the benefits of piston pumps using solar power, they operate their systems with brushed direct current motors (D.C.) to obtain the required starting torque. The system is connected from the solar array power supply via Linear Current Booster known as a (L.C.B.) controller. This is used to modify the solar power supply and prevent the motor stalling during periods of low solar power supply. (03) While the D.C. type motor drive and L.C.B. combination works well, it is a far more expensive method of solar powering a piston pump then the proposed multi voltage induction motor drive system. This only requires using the commercially available solar power compatible electric motors that can operate on a range of 30-300 VDC or 90-240 VAC, these solar compatible electric motors have in built Maximum Power Point Tracking known as (M.P.P.T.) technology as an alternative to LCB technology, resulting in a significantly lower unit cost than an equivalent D.C. motor and separate L.C.B. system. The major problem to overcome was the low starting torque characteristic of this design of motor, while utilising its unique solar power drive compatibility.
(2) (04) To overcome the high inertia of starting a piston pump using the selected solar powered electric motor with its inherent low starting torque characteristics was a challenge. Research was conducted of all low starting torque drive couplings available on the market. Of these the fluid drive and centrifugal clutch type couplings offered the benefit of low starting torque. Although both required the motor to reach significant speed before the transmission of motor power to the pump load would occur. This is unacceptable for solar operation where the motor speed fluctuates and is often substantiality reduced during periods of low solar radiation. (05) During testing the solar powered electric motor selected to drive the piston pump would start successfully if the piston pump had stopped during the inlet stroke however it would stall and fail to start in the higher load position of the delivery stroke. Therefore the major problem to overcome was to ensure the motor always started with a low torque load. As there were no suitable commercially available couplings to perform this duty. A new coupling drive was invented. A prototype was built and tested to ensure the electric motor was always starting in a low torque position. This enabled the motor via the reduction drive pulley ratio to commence rotation before the pump load was engaged.
(3) SUMMARY of INVENTION (06) To enable the required disengagement from a high starting torque load position the torsion spring drive coupling was developed. The electric motor rotational power is transmitted via a lugged timing belt with a reduction drive of motor speed. This is achieved by a size difference of the pulleys, a small lugged pulley is fitted to the motor drive shaft, a much larger lugged pulley is fitted to the free to rotate shaft of the low starting torque torsion spring coupling assembly. The power from the small motor pulley is transmitted by the lugged drive belt to the larger pump coupling pulley. With a significant turn down ratio to suit the pumps optimum operating speed in revolutions per minute. (07) In operation on start up when the motor is energised, it begins turning and the pump pulley rotates forward compressing the torsion spring onto and tightening the spring around the pump shaft mounting block. This then transmits the motor power into the pump, commencing the reciprocal pumping stroke and the pump commences pumping water. The torsion spring wind up phase enables the motor to have free rotation and develop sufficient torque to overcome the starting inertia of the piston pump, whatever stroke position the pump is in on start-up of the drive motor. (08) On a motor shut down the compressed torsion spring reserve power unwinds the drive pulley, it rotates backwards and as a result of the turndown ratio produces a corresponding several rotations of the motor shaft drive pulley, creating the inbuilt free turning motion for the wind up that will be required to enable the motor to start rotating on the next start up in a low torque manner without stalling. The low torque spring coupling begins to rotate on re-starting of the electric motor this enables the coils of the torsion spring to compress onto and around the pump shaft mounting block. Once the spring is fully compressed the full motor rotational power is transmitted into the pump shaft by the locking friction of the compressed spring coils around the pump shaft mounting block. The pump then continues to operate in this manner as long as the motor is rotating regardless of the actual rotational speed that may vary with solar radiation.
(4) (09) To ensure the spring reserve power is sufficient to achieve the required free play wind back, it was necessary to use a lugged timing belt power transmission system. Friction vee belt drives would not freely unwind under spring reserve power. Therefore the invented torsion spring drive system incorporates a lugged timing belt and lugged pulley drive system. The use of aluminium alloy lugged timing pulleys consistently produced perfect start up and operating results (5) INVENTATION ADVANTAGE (10) The advantage of this drive system enables practical efficient operation of positive displacement piston pumps using solar power to operate from a low starting torque motor. At even slow speed a piston pump supplies some water at an almost constant head pressure a feature not found with centrifugal pumps. Another benefit of piston pumps compared to centrifugal pumps for solar power applications are their efficient use of power that is ideally suited to small off grid solar power production. The piston pump can achieve high suction lift capabilities of up to eight meters that assists in pump mounting site location away from any potential flood problems. From small motor power capacity high discharge head pressures of sixty meters or more can be obtained making pumping from low level water sources to places of high level requirement possible. The piston pump solar compatible motor combination produces a substantial reduction in capital outlay cost compared to any alternative above ground solar powered system to achieve the same pumping performance. (11) At present many of these high lift pumping requirements in remote off electrical grid situations, utilise internal combustion motors driving centrifugal pumps. With the proposed solar powered piston pump system operators would have an alternative, a viable option to achieve significant energy and maintenance cost savings while also reducing carbon gas emissions by eliminating the need for an internal combustion drive motor (6) DESCRIPTION of DRAWINGS (12) Drawing Sheet number, 1/6 shows the complete low torque torsion spring drive assembly with sectional view A. A. of torsion spring (Fig 4) retained between pump shaft mounting block (Fig 5) and rotating shaft spring compressor (Fig 3). Also shown is other major parts the barrel spring cover (Fig 1) and the pulley shaft cover plate (Fig 2). Minor parts. Barrel holding set screws four off (Fig 6) Fabrication assembly fillet weld (Fig 7). (13) Drawing sheet number, 2/6 Fig 1 shows the barrel spring cover, with four retaining set screw holes. (14) Drawing sheet number, 3/6 Fig 2 shows the pulley shaft cover plate with two taped holes for the barrel cover set screws. (15) Drawing sheet number, 4/6 Fig 3 shows rotating pulley shaft spring compressor, made in two parts then fabricated with a fillet weld. (16) Drawing sheet number 5/6 Fig 4 shows the torsion spring that compresses under load around the pump shaft mounting block to transmit motor power and provide the spring reserve power to counter rotate the drive assembly on de-energisation. (17) Drawing sheet number 6/6 Fig 5 shows the pump shaft mounting block with two taped holes for barrel spring cover set screws. A taped shaft locking screw hole to enable secure spring coupling connection to the actual piston pump drive shaft.