9 SERVICE TECH Vol.475 04-12

The previous session outlined the different types of common rail system.This section details the main common rail system components, and will explain the HPO type supply pump.

The HPO type supply pump supports the number of engine cylinders by changing the number of peaks on thecam. The supply pump rotates at half the speed of the engine, and the relationship between the number of enginecylinders and the supply pump pumping is shown in the table below.By increasing the number of cam peaks to handle the number of engine cylinders, a compact, two-cylinder pump

unit is achieved. Furthermore, because this pump has the same number of pumping strokes as injections, itmaintains a smooth and stable rail pressure.

The HP0 supply pump is mainly made up of a pumping systemas in conventional in-line pumps (two cylinders), a PCV (pumpcontrol valve) for controlling the fuel discharge quantity, acylinder recognition sensor (TDC (G) sensor), and a feed pump.(Refer to the cutaway sample.)

Number of Engine Cylinders Speed Ratio (Pump : Engine)

Supply PumpNumber of Pumping Rotations

for One Engine CycleNumber of Cylinders Cam Peaks

4 Cylinders

1：22

2 46 Cylinders 3 6

8 Cylinders4

84 2

11 HPO Type Supply Pump Construction and Features

External View

Feed Pump

Cam × 2

PCV (Pump Control Valve)

Tappet

Element (Plunger & Cylinder)

Cylinder Recognition Sensor

{TDC (G) Sensor}

Pulsar for TDC (G) Sensor

Overflow Valve

Delivery Valve

Cutaway Sample

10SERVICE TECH Vol.475 04-12

The feed pump, which is integrated in the supply pump, draws fuel from the fuel tank and feeds it to the pumpchamber via the fuel filter. There are two types of feed pump, the trochoid type and the vane type.

Component FunctionFeed Pump Draws fuel from the fuel tank and feeds it to the pumping mechanism.Overflow Valve Regulates the pressure of the fuel in the supply pump.PCV (Pump Control Valve) Controls the quantity of fuel delivered to the rail.

Pumping Mechanism

Cam Actuates the tappet.Tappet Transmits reciprocating motion to the plunger.Plunger Moves reciprocally to draw in and compress fuel.

Delivery Valve Stops the reverse flow of fuel pumped to the rail.Cylinder Recognition Sensor Detects the engine cylinders and sends a signal to the engine ECU.

The camshaft actuates the outer/inner rotors of thefeed pump, causing them to start rotating. Inaccordance with the space produced by themovement of the outer/inner rotors, the feed pumpdraws fuel in from the suction side, and pumps it outthe discharge side.

The camshaft actuates the feed pump rotor and thevanes slide along the inner circumference of theeccentric ring. As the rotor turns, the pump draws fuelfrom the fuel tank and discharges it to the PCV andpumping mechanism.

22 HPO Type Supply Pump Components and Functions

2-1 Feed Pump

Trochoid Type

To Pump Chamber

From Fuel Tank

Outer Rotor

Inner Rotor

Suction PortDischarge

Port

Camshaft

Vane Type

Suction Port

Discharge Port

Rotor

Eccentric Ring

Vane

Camshaft

11 SERVICE TECH Vol.475 04-12

The PCV (Pump Control Valve) regulates the quantity of fuel discharged from the supply pump in order toregulate the rail pressure. The fuel quantity discharged from the supply pump to the rail is determined by the ON/OFF timing of the signal output from the ECU to energize the PCV. In the actual circuit, the signal is output fromthe engine ECU to PCV1 and PCV2 as shown in the diagram below.The engine actuates the camshaft, and the cam actuates the plunger via the tappet to pump the fuel sent by the

feed pump. The PCV controls the discharge quantity. Fuel is pumped from the feed pump to the element, and thento the delivery valve. (Refer to the cutaway sample on page 9 to view the element and delivery valve.)

The cylinder recognition sensor uses the alternating current voltage generated by the changes in the lines ofmagnetic force passing through the coil to send the output voltage to the ECU. The cylinder recognition sensorgenerates a recognition signal for the engine cylinders. Construction and operation of the engine speed sensorinstalled on the engine side is the same as that of the cylinder recognition sensor. This type of sensor is known asan MPU type.In addition to the MPU type cylinder recognition sensor, there is also an MRE type that outputs a rectangular

voltage wave to the ECU.

2-2 PCV: Pump Control Valve

Camshaft

Feed Pump

PCV (Pump Control Valve)

Pulsar for TDC (G) Sensor

IG Switch

+B

PCV Relay

PCV1

PCV2

Engine ECUPlunger

Tappet

Cam

Rail

2-3 Cylinder Recognition Sensor (TDC (G) Sensor)

MPU Type MRE Type

12SERVICE TECH Vol.475 04-12

Fuel is drawn by the feed pump from the fuel tank and sent to the pumping mechanism via the PCV. The PCVadjusts the quantity of fuel pumped by the pumping mechanism to the necessary discharge quantity, and this fuelis pumped to the rail via the delivery valve.

The plunger pumps the fuel sent from the feed pump, and the PCV controls the discharge quantity in order toadjust the rail pressure. Actual operation is as follows.

• Suction Stroke (A)On the plunger's descent stroke, the PCV is open and low-pressure fuel is suctioned into the plunger chamber

via the PCV.• Pre-Stroke (B)

Even when the plunger enters its ascent stroke, the PCV remains open while it is not energized. During thistime, fuel drawn in through the PCV is returned through the PCV without being pressurized. (Pre-Stroke)

• Pumping Stroke (C)At a timing suited to the required discharge quantity, current is supplied to close the PCV. This closes the

return passage, and pressure in the pumping mechanism rises. The fuel then passes through the delivery valveand is pumped to the rail. Specifically, by varying the timing of the PCV closing (the end point of the plunger pre-stroke), the dischargequantity is altered to control the rail pressure.

• Suction Stroke (A')When the cam exceeds the maximum lift, the plunger enters its descent stroke and pressure in the pumping

mechanism decreases. At this time, the delivery valve closes and fuel pumping stops. In addition, the PCVopens because it is de-energized, and low-pressure fuel is suctioned into the pumping mechanism. In otherwords, the system goes into state A.

33 Supply Pump Operation

3-1 Supply Pump Overall Fuel Flow

3-2 Fuel Discharge Quantity Control

PCV and Plunger Operation During Each Stroke

Cam Lift

PCV

OperationClosed

Valve

Suction Stroke Pumping Stroke

Pre-StrokeOpen

Valve

PCV

Pump Operation

Plunger

Return

To Rail

Closed

Valve

Pumping the Required

Discharge Quantity

(A) (B) (C) (A')

Delivery Valve

From Fuel Tank

Pumping

Mechanism

When Discharge Quantity Increases When Discharge Quantity Decreases