C7 Industrial Engines Systems Operation – Fuel System

Actuation Oil Pressure Control

(26) Control valve solenoid

(27) Poppet valve

(28) Armature

(29) Actuator spring

(30) Sliding sleeve

(31) Actuator piston

(32) Eccentric drive plate

(33) Idler

(34) Spill port

(35) Pump outlet ports

(36) Drive gear

(37) Check valve

(38) Piston

The unit injector hydraulic pump is a variable delivery piston pump. The variable piston pump uses an angled drive plate which rotates. The pistons do not rotate. The pistons move in relation to the angled drive plate. The pistons move in the sliding sleeves.

The unit injector hydraulic pump is driven by the gear train on the front of the engine. The drive gear on the front of the pump turns the common shaft. The angled drive plate is mounted on the common shaft. The rotation of the angled drive plate causes the pump piston to move in and out within the sliding sleeves.

As the pistons move out of the sliding sleeves, oil is drawn into the inside of the pistons through the passage in the drive plate. Oil is forced out of the piston when the piston is pushed back into the sliding sleeve and the ports are exposed.

Changing the relative position of the sliding sleeve to the spill port changes the volume of oil in the piston. The location of the sliding sleeve is continuously changing. The location of the sliding sleeve is determined by the ECM. Changing the location of the sliding sleeves changes the flow of the pump. The result is the amount of oil that can be pressurized.

The pressure of the injection actuation system is controlled by matching pump outlet flow and resulting pressure to the pressure demand for the injection actuation system. The position of the sliding sleeves is changed in order to control the pump outlet flow. Moving the sleeves to the left covers the spill port for a longer distance. This increases effective pumping stroke and pump outlet flow. Moving the sleeves to the right covers the spill ports for a shorter distance which reduces the effective pumping stroke. This also reduces the pump outlet flow.

The sliding sleeves are connected by an idler. One sleeve is connected to an actuator piston. Moving the actuator piston right or left causes the idler and sleeves to move the same distance to the right or to the left.

Control pressure is determined by the amount of current from the ECM to the solenoid. A small amount of pump outlet flow goes through a small passage in the actuator piston. This small amount goes out of an orifice and into the control pressure cavity. The pressure in this cavity is limited by a small poppet valve. The opening of the poppet valve allows a portion of the oil in the cavity to flow to drain. A force holds the poppet valve closed. This force on the poppet valve is created by a magnetic field that acts on an armature. The strength of the magnetic field determines the required pressure in order to overcome the force of the actuator spring.

An increase of current to the solenoid causes an increase to the following items:

 

• The strength of the magnetic field
• The force on the armature and poppet valve
• The control pressure which causes the actuator piston to move to a position that results in more flow

A reduction of current to the solenoid causes a reduction to the following items:

 

• The strength of the magnetic field
• The force on the armature and poppet valve
• The control pressure which causes the actuator piston to move to a position that results in less flow

The ECM monitors actuation pressure. The ECM constantly changes current to the pump control valve in order to control actuation pressure. Three components work together in a closed loop circuit in order to control actuation pressure:

 

• ECM
• Sensor for the Injection Actuation Pressure (IAP)
• Pump control valve

The closed loop circuit works in the following manner:

 

• The ECM determines a desired actuation pressure by gathering information from sensor inputs and software maps.
• The ECM monitors actual actuation pressure through a constant signal voltage from the IAP sensor.
• The ECM constantly changes control current to the pump control valve. This changes the pump outlet flow.

There are two types of actuation pressure:

 

• Desired actuation pressure
• Actual actuation pressure

Desired actuation pressure is the injection actuation pressure that is required by the system for optimum engine performance. The desired actuation pressure is established by the performance maps in the ECM. The ECM selects the desired actuation pressure. The selection is based on the signal inputs from many sensors. The ECM is getting signal inputs from some of the following sensors: throttle position sensor, boost pressure sensor, speed-timing sensors and coolant temperature sensor. The desired actuation pressure is constantly changing. The change is based on various signal inputs. The changing engine speed and engine load also cause the desired actuation pressure to change. The desired actuation pressure is only constant under steady state conditions (steady engine speed and load).

Actual actuation pressure is the actual system pressure of the actuation oil that is powering the injectors. The ECM and the pump pressure regulator are constantly changing the amount of pump outlet flow. This constant changing makes the actual actuation pressure equal to the desired actuation pressure.

Pump Control Valve Operation

The pump control valve has the following three stages:

 

• Valve operation (engine off)
• Valve operation (cranking the engine)
• Valve operation (running engine)

Valve Operation (ENGINE OFF)

When the engine is off, there is no pump outlet pressure from the pump and there is no current to the control valve solenoid from the ECM. The actuator spring pushes the actuator piston completely to the left. The idler which is not shown and the sliding sleeves are moved to the left also. At this point, the pump is in the position of maximum output.

Valve Operation (ENGINE CRANKING)

During engine start-up, approximately 6 MPa (870 psi) of injection actuation pressure is required in order to activate the unit injector. This low injection actuation pressure generates a low fuel injection pressure of about 35 MPa (5000 psi). This low fuel injection pressure aids cold starting.

In order to start the engine quickly, the injection actuation pressure must rise quickly. Because the unit injector hydraulic pump is being turned at engine cranking speed, pump flow is very low. The ECM sends a strong current to the control valve solenoid in order to keep the poppet valve closed. With the poppet valve in the closed position, all of the flow to the drain is blocked. The hydraulic forces that act on each side of the actuator piston are equal. The actuator spring holds the actuator to the left. The pump produces maximum flow until the 6 MPa (870 psi) desired pressure is reached. Now, the ECM reduces the current to the pressure regulator solenoid in order to reduce control pressure. The reduced control pressure allows the actuator piston to move to the right. This reduces pump outlet flow in order to maintain the 6 MPa (870 psi) desired pressure.

Note: If the engine is already warm, the pressure that is required to start the engine may be higher than 6 MPa (870 psi). The values for the desired actuation pressures are stored in the performance maps of the ECM. The values for desired actuation pressures vary with engine temperature.

Once the unit injectors begin to operate, the ECM controls the current to the control valve. The ECM and the control valve solenoid will maintain the actuation pressure at 6 MPa (870 psi) until the engine starts. The ECM monitors the actual actuation pressure through the IAP Sensor that is located in the high pressure oil manifold. The ECM establishes desired actuation pressure by monitoring several electrical input signals and the ECM sends a predetermined current to the control valve solenoid. The ECM also compares the desired actuation pressure to the actual actuation pressure in the high pressure oil passage. The ECM adjusts the current levels to the control valve solenoid in order to make the actual actuation pressure equal to the desired actuation pressure.

Valve Operation (RUNNING ENGINE)

Once the engine starts, the ECM controls the current to the pump control valve in order to maintain the desired actuation pressure. The IAP Sensor monitors the actual actuation pressure in the high pressure oil passage in the cylinder head. The ECM compares the actual actuation pressure to the desired actuation pressure 67 times per second. The ECM adjusts the current levels to the pump control valve when the actual actuation pressure and the desired actuation pressure do not match. These adjustments make the actual injection actuation pressure equal to the desired injection actuation pressure.

Oil Flow (ENGINE RUNNING)

A small amount of pump outlet flow flows through the actuator piston and into the control pressure cavity. Control pressure increases and the increased pressure unseats the poppet valve. The open poppet valve allows flow to the drain. The ECM changes control pressure by increasing or reducing the current to the control valve solenoid and resultant force on the poppet.

The following items create a closed loop system:

 

• ECM
• IAP
• Pressure Regulator

This closed loop system provides infinitely variable control of pump outlet pressure. This pump outlet pressure has a range from 6 MPa (870 psi) to 28 MPa (4061 psi).