Bosch 02112706 – The Feed Pump That Smooths Low-Pressure Pulsations for Stable SCV Response

In a common-rail diesel engine, the suction control valve (SCV) meters the fuel entering the high-pressure pump plungers. The SCV's response is determined by the pressure at its inlet - the pressure delivered by the feed pump. If the feed pump pressure pulsates - if it fluctuates with each rotation of the pump gears - the SCV sees a varying inlet pressure, and its response is not stable. The 02112706 is a Bosch feed pump that is designed with a pressure-smoothing chamber that attenuates the pulsations, delivering a steady pressure to the SCV. It is the pump that keeps the SCV's inlet pressure stable, so the SCV's response is consistent.

The feed pump is a gear pump - it has two gears that rotate and create a pulsating flow. The pulsations are small, but they are at the same frequency as the pump speed - 50-100 Hz at idle, and 200-400 Hz at rated speed. The SCV is a fast-acting valve - it responds to the pressure at its inlet, and if the pressure pulsates, the SCV's response is not stable. The SCV opens and closes in response to the ECU's command, but the varying inlet pressure creates a varying flow, and the rail pressure is not stable. The 02112706 addresses this with a pressure-smoothing chamber that attenuates the pulsations, reducing the pressure ripple at the SCV inlet by over 80 %. The chamber is a cavity that is integrated into the pump body, and it is sized to match the pulsation frequency - the chamber volume and the connecting passages are calibrated to the pump's speed and displacement.

The pressure-smoothing chamber is a cavity that is integrated into the pump body. The chamber is connected to the pump outlet through a calibrated passage - the passage limits the flow into the chamber, and the chamber acts as a hydraulic capacitor. The chamber volume is sized to match the pulsation frequency - the volume is calculated using the pump's displacement and the speed range. The chamber is filled with fuel, and the fuel is compressed by the pulsations - the compression absorbs the energy of the pulsations. The result is a pressure at the pump outlet that is smooth, with a ripple of less than 0.2 bar peak-to-peak.

Installing the 02112706 is a mechanical procedure - remove the old pump, clean the mounting surface, replace the O-ring, and torque the pump to 25 Nm. The pump must be primed before starting the engine.

Aftermarket pumps often do not include the pressure-smoothing chamber - the pulsations are not attenuated, and the SCV's response is not stable. The genuine 02112706 is manufactured with the pressure-smoothing chamber, ensuring that the SCV receives a stable inlet pressure.

Q1: How can I tell if my feed pump pressure is pulsating? → The engine hunts at idle, and the rail pressure fluctuates.

Q2: Can I use a universal feed pump as a replacement? → A universal pump may not have the pressure-smoothing chamber.

Q3: Why does my engine hunt at idle? → The SCV is receiving a pulsating inlet pressure - the feed pump may not have a smoothing chamber.

Q4: What is the most common cause of pump failure? → Worn gears - the gears wear, and the pump loses its pressure.

Q5: Does the pump work with biodiesel? → Yes, but biodiesel can accelerate the wear rate.

Q6: What is the warranty on the pump? → The pump has a 12-month warranty.

 

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