Function of oil pump (compound oil pump) - RA18001202000X(18-2000)

WARNING: This page does not describe the selected car, but rather 42 other vehicles, including the 1999 Mercedes-Benz S600, 1999 Mercedes-Benz S500, 1999 Mercedes-Benz S420, 1999 Mercedes-Benz S320, and 1999 Mercedes-Benz CL600. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Identifying Oil Pump Components

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

General

Using the compound oil pump in place of the conventional gear oil pump reduces the hydraulic power losses caused by the bypass operation and also improves noise characteristics while offering the same delivery capacity. The compound oil pump channels some of the oil under zero pressure via parallel pump chambers. Only the oil quantity required for the particular oil pressure is pumped (see oil pressure operating curves).

Fig 2: Identifying Oil Pressure Operating Curves

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Design and function

The compound oil pump consists of a primary and secondary stage each having a pair of externally toothed gears (2a and 3a) and also (6 and 7). The gears (2a) and (6) are fixed on the drive shaft (2). The gear (3a) is fixed and the gear (7) sits loose on the oil pump shaft (3). The primary oil flow passes directly into the main oil gallery (arrow), while the secondary oil flow passes through the timing case (9) before entering the main oil gallery.

Fig 3: Identifying Externally Toothed Gears, Oil Pump Shaft, Timing Case And Oil Gallery

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Primary and secondary stages have a common suction chamber (E) and separate pressure chambers (primary stage P), (secondary stage S).

Fig 4: Identifying Suction Chamber And Pressure Chambers

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Primary and secondary oil flow are led to the control piston (10) separately.

Fig 5: Identifying Control Piston

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

The pressure relief bore (G) enables the control piston (10) to operate in the piston guide without oil back-pressure.

Fig 6: Identifying Pressure Relief Bore And Control Piston

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Control piston in rest position

The primary oil flow (P) is passed directly into the main oil gallery (F) while the secondary oil flow (S) passes through the timing case (9) before entering the main oil gallery.

Benefit:

Greater delivery during starting and hot idling.

Fig 7: Identifying Primary Oil Flow In Oil Gallery And Secondary Oil Flow In Timing Case

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Control piston in blow-off position

The pressurized oil is passed through the damper bore (15) in the control piston (10) into the working chamber (16) and moves the control piston (10). The secondary flow (S) is led back into the suction chamber (E) (only flow losses). All of the primary oil flow (P) passes into the main oil gallery.

Benefit:

Low hydraulic losses at high engine speeds.

Fig 8: Identifying Damper Bore, Control Piston And Working Chamber

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

NOTE: The plate valve (5) ensures a pressure balance between primary and secondary flows when the control piston (10) is moving from the rest into the blow-off position.

Control piston in bypass position

The secondary oil flow (S) is passed completely into the suction chamber (E).

Part of the primary oil flow (P) is passed via the front piston edge of the control piston into the suction chamber (E) (bypass control).

Fig 9: Identifying Suction Chamber And Secondary Oil Flow

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.