2 - TCA spa

FLOW DIVIDERSOne of the most common applications for flow dividers is forwheel motors in transmission circuits to give an element of‘Diff-lock’. The flow divider will ensure that there is always driveto both wheels even when one of them is over soft or slipperyground.Figure 5 shows a typical circuit where the flow divider isswitched in when needed. The flow divider works on pressuredrop so is intrinsically inefficient, even though the pressuredrop is low. In a transmission circuit this pressure drop wouldcreate excessive heat so it is necessary to have a system toselect the diff-lock when required.In a closed loop transmission circuit this can be achieved byusing logic elements around each side of the flow divider. Theyare vented when the diff-lock is not required. This will work inboth directions because the charge pump pressure is sufficientto keep the logic element open allowing the flow to passbackwards through the valve.The bypass can be achieved by using pilot operated spoolvalves or solenoid valves. By using one of these options thereis no loss of flow through the vent line however there is a limitto the flow rate that these kinds of valves can handle.Most of these machines are required to go round corners soone wheel has to go faster than the other. As previouslydescribed this would cause problems to the flow divider. It isalso true that it is not necessary to maintain a perfect divisionunder conditions requiring diff-lock. A limited slip differential isacceptable.It has become common place to fit an orifice across the two Ithas become common place to fit an orifice across the two legsof the flow divider to allow flow to pass from one side to theother when the vehicle is turning. As the differential pressuresgo up due to the extra load on the inner wheel a controlled flowcan pass from one side to the other. The size of this orificedepends on the turning circle of the machine. In this way onewheel will be able to move faster than the other but pressureand therefore torque will remain on both of the wheels.Figure 4. Diff-Lock valve including by-pass solenoid sector valves