Oil pressure regulating valve
For the volume-flow-controlled oil pump, the oil pressure control valve has been integrated.
The following graphic shows the oil pressure control valve and the volume-flow-controlled oil pump on the N55 engine.
| Index | Explanation |
|---|---|
| 1 | Oil pressure regulating valve |
| 2 | Volume-flow-controlled oil pump |
The characteristic map control influences the oil pressure in the control oil chamber. Two valves are involved in the characteristic map control:
- Oil pressure regulating valve
- Pressure limiting valve as fallback level.
The oil pressure control valve can influence the oil pressure in the control oil chamber steplessly. The further the oil pressure is reduced, the more volume the volume-flow-controlled oil pump delivers. The main spring in the volumetric-flow-controlled oil pump that affects the slider is softer than in conventional systems. The slider is easier to move to a centered position, which means that the volume-flow-controlled oil pump adjusts to minimum delivery even with slight oil pressure in the control oil chamber. This reduces the pressure ratio in the oil circuit, which in turn means less energy to drive the volumetric-flow-controlled oil pump.
The use of characteristic map control for the volumetric-flow-controlled oil pump enables oil supply in line with requirements and a reduction in the average pressure level in the oil circuit. The oil pressure control valve enables the Digital Engine Electronics (DME) to control the fuel delivery rate individually.
As a second stage of the characteristic map control, there is a pressure limiting valve located in the housing of the volumetric-flow-controlled oil pump between the oil pressure control valve and the control oil chamber. The pressure limiting valve is a 3/2-way valve that can switch the main oil pressure into the control oil chamber of the volumetric-flow-controlled oil pump. Oil from the main oil duct presses a piston back against a spring until the duct to the volumetric-flow-controlled oil pump is released. The oil pressure from the oil pressure control valve affects the other side of the piston.
| Index | Explanation |
|---|---|
| 1 | Connection from main oil duct |
| 2 | Connection from oil pressure control valve |
| 3 | Pressure limiting valve |
| 4 | Duct to the control oil chamber |
| 5 | Connection to counterbalance shaft |
| 6 | Control oil chamber |
The oil pressure control valve is closed when de-energised. This means the oil circuit is automatically in the fallback level in the event of failure of the oil pressure control valve and the pressure limiting valve ensures an oil pressure of approx. 5.5 bar. During characteristic map operation, the oil pressure lies between 1.5 and 4.5 bar.