Automatic Transmission Fluid Pump
| ITEM | DESCRIPTION |
|---|---|
| 1 | Vane pump |
| 2 | Chain drive from torque converter cover |
The Automatic Transmission Fluid (ATF) pump is an integral part of the transmission.
The ZF 8HP45 ATF pump is a double stroke, vane type pump and is located below the transmission input shaft. The pump is driven by a chain drive from a sprocket located on the torque converter. The pump has a delivery rate of 50 cm3 per revolution. The drive sprocket is driven at engine speed through a splined connection in the torque converter shell.
The ATF pump is used to:
- Supply hydraulic pressure for the operation of the control valves and clutches
- Pass the fluid through the ATF cooler
- Lubricate the gears and shafts.
Automatic Transmission Fluid Pump Schematic Diagram
| ITEM | DESCRIPTION |
|---|---|
| 1 | System pressure valve |
| 2 | Automatic Transmission Fluid (ATF) pump |
| 3 | Intake pipe |
| 4 | Oil pan |
| 5 | Pressure pipe |
| 6 | Recycling of redundant fluid |
The Automatic Transmission Fluid (ATF) pump comprises the following components:
- Sprocket
- Rear cover with bearing
- Front cover with bearing
- Cylinder
- Rotor shaft
- Rotor with vanes.
A pressure relief valve is fitted in the pressure outlet gallery from the pump but is not an integral part of the pump itself.
A sprocket is located around the transmission input shaft. Splines on the torque converter nose and the sprocket ensure a positive drive. A simplex chain transmits the rotation of the torque converter cover into rotation of the pump rotor shaft via a second sprocket fitted to the rotor shaft. The gearing of the two sprockets rotates the pump rotor shaft at a speed slightly higher than the torque converter cover rotational speed, which is connected directly to the engine crankshaft.
The ATF pump contains seven vanes which are attached to the rotor and rotate within the cam shaped cylinder. As the vanes rotate, the eccentricity of the central hole in the cylinder causes the space between the vanes to increase. This causes a depression between the vanes and fluid is drawn into the space between the vanes via a suction port connected to the fluid pan. The fluid passes through the fluid pan filter before it is drawn into the ATF pump.
As the rotor shaft rotates further, the inlet port is closed by the vanes which have drawn in fluid, trapping the fluid in the space between the vanes. The eccentric hole in the cylinder causes the space between the vanes to decrease and consequentially compresses and pressurizes the fluid trapped between them.
Further rotation of the rotor shaft moves the vanes towards the outlet port. As the vanes pass the outlet port the pressurized fluid passes from the space between the vanes into the pressure gallery to the pressure relief valve.
As the ATF pump is a double stroke vane pump, this sequence is repeated twice per revolution of the rotor shaft.
The pressure relief valve controls the pressure and flow of fluid delivered to the transmission valve block, torque converter and other components. Pressure is controlled by a relief valve which limits the maximum system pressure to 32 bar (464 lbf/in2 ). The pressure control maintains a constant pressure of fluid irrespective of torque converter input shaft rotational speed. A metering orifice is subject to the pump output pressure. If the pressure in the orifice reaches a predetermined level, a spring loaded ball in the flow control valve is lifted from its seat and pressurized fluid is allowed to recirculate through the pump.