Land Rover Discovery: Variable Coolant Pump

1. Electrical connector - ECM position sensor 5V supply
2. Electrical connector - shroud control solenoid 12V supply
3. Position sensor
4. Variable coolant pump body
5. Drive pulley hub
6. Seal
7. Shroud
8. Pump impeller

The variable coolant pump is located on the upper left side of the engine within a cavity in the cylinder block. The pump is attached to the cylinder block with six bolts and uses a silicon bead seal. The pulley connects to the variable coolant pump hub using three bolts and is driven by the primary drive belt. The variable coolant pump has two electrical connectors for operation of the solenoid and shroud position feedback to the Engine Control Module (ECM).

Coolant flow control enables the use of fast engine warm up strategies and optimum temperature control of critical engine components utilising a patented internal control mechanism to modulate the flow output from the pump.

The variable coolant pump has a shroud that slides over the impeller to reduce the flow of engine coolant being pumped into the cylinder block.

The solenoid controlled shroud is used to reduce the flow provided to the cylinder block. The solenoid operates in combination with an internal hydraulic pump to generate hydraulic pressure which is used to move the shroud to restrict flow through the cylinder block. Pressure is generated with every rotation of the pump impeller. The pressure is diverted either to the shroud assembly or leaked back to the coolant system, controlled by a solenoid valve. The shroud will not move if there is no rotation of the pump impeller. Requests from 0 - 100% flow can be fulfilled at most engine speeds to contribute to the whole engine thermal management strategy.

The solenoid operates in combination with an internal hydraulic pump to generate hydraulic pressure which is used to move the shroud to restrict flow through the cylinder block

1. To engine coolant outlet
2. From engine coolant inlet

1. 100% open - Full flow
2. 50% open - Restricted flow
3. 0% open - Zero flow

The Engine Control Module (ECM) receives input signals from other engine control components to determine the required level of cooling such as cylinder head metal temperature, EGR temperatures, ambient temperatures, drive mode, coolant temperature and minimum flow map.

The calibration is able to control the variable coolant pump flow in five steps and is controlled by an open-loop map.

Flow modes: 0 = zero flow, 4 = Full Flow

The control of the shroud solenoid is by a Pulse Width Modulation (PWM) signal from the ECM. The internal pressure within the pump acts against a return spring in the housing. Without a signal from the ECM the solenoid is de-energized, the shroud is at its default position held under return spring force, resulting in full flow from the pump.

During an engine cold start, the impeller is fully covered by the shroud (flow mode 0), therefore no coolant is circulated through the cylinder block. As the engine coolant temperature increases, the flow requirement will increase in 4 stages (flow mode 1-4). The variable coolant pump is controlled by the ECM to provide the minimum flow to support all cooling requests from the engine systems. When the engine coolant temperature reaches 85ºC (185ºF), the solenoid is de-energized and the shroud will move to its default fully open position (flow mode 4) allowing maximum circulation through the cylinder block. Temperature control and flow is then managed by the ECM and the electric thermostat.

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