Section 8. Theory of Operation
Model 4700 Maintenance Manual
Auxiliary Functions
Standard Lever Controls
Auxiliary Functions
Sideshift
NOTE: A priority valve is used to ensure adequate hydraulic pressure to the steering system at all times. If adequate flow is not available for steering, the priority valve diverts fluid from any other requested function.
When sideshift is requested, the sideshift switch (SW13) closes, which is sensed by the VM. The Pump Power Amplifier (PPA) receives the RPM request via the CAN-Bus. The pump motor operates at a fixed RPM that is configurable using the FlashWare program.
Auxiliary functions are activated by the operator moving one of the auxiliary function levers or optional fingertip controls. Tilt and Sideshift are discussed below for both configurations. Operational theory for the 4th function is similar to tilt and sideshift.
Oil is pumped through the activated side of the sideshift valve to the sideshift cylinders. Return oil flows from the cylinders, through the sideshift valve, and back to the reservoir.
Standard Lever Controls
When sideshift is not requested, all fluid bypasses the sideshift valve and is either available for use by other functions or returned to the reservoir.
Tilt
Optional Fingertip Controls
When tilt is requested, the tilt switch (SW12) closes, which is sensed by the VM. The Pump Power Amplifier (PPA) receives the RPM request via the CAN-Bus. The pump motor operates at a fixed RPM that is configurable using the FlashWare program.
Tilt
Oil is pumped through the activated side of the tilt valve to the tilt cylinders. Return oil flows from the other side of the cylinders through the tilt valve, and back to the reservoir. When tilt is not requested, all fluid bypasses the tilt valve and is either available for use by other functions or returned to the reservoir. There are two flow controls in the tilt system. One flow control, located in the spool valve, provides the correct flow rate. The second flow control (V2) is located in the adapter fitting on the control valve assembly. V2 controls fluid flow in the return circuit when tilting forward. If fluid flow in the return circuit is excessive (for example: the tilt system is supplied with fluid at the lift system delivery rate), the control restricts the return flow to reduce forward tilt speed.
8-10
When tilt is requested, the tilt switch (SW19 or S20) closes, which is sensed by the Armrest Board. Output voltage from the tilt pot (P5) is also sensed by the Armrest Board. The Armrest Board encodes the tilt request into a digital message and communicates it to the Hydraulic Control Board via the CAN-Bus. The Hydraulic Control Board relays the RPM to the PPA. The PPA generates the correct voltage to the pump motor to run the pump. The Hydraulic Control Board interprets the message and provides controlling voltage to the tilt solenoids (EV3 or EV4) from a coil driver located on the board. A flow control valve (V2) between the tilt solenoid valves and tilt cylinders prevents excessive forward tilt speed when lift and tilt are requested simultaneously. This valve also keeps the forks from drifting when the tilt command is removed from the tilt solenoid. When tilt is not requested, all fluid bypasses the tilt valve and is either available for use by other functions or returned to the reservoir.
Publication 1160093, Issued: 20 May 2013
