Radial-piston high-pressure pumps produce higher injection pressures than axial-piston high-pressure pumps. Consequently,they also require more power to drive them (as much as 3.5...4.5 kW compared with 3 kW for axial-piston pumps).

Design

The radial-piston high-pressure pump (Fig. 2 overleaf) is driven directly by the distributor-
pump drive shaft. The main pump components are:
 the cam ring (1)
 the roller supports (4) and rollers (2)
 the delivery plungers (5)
 the drive plate, and
 the front section (head) of the distributor shaft (6)
The drive shaft drives the drive plate by means of radially positioned guide slots.The guide slots simultaneously act as the locating slots for the roller supports. The roller supports and the rollers held by them run around the inner cam profile of the cam ring that surrounds the drive shaft. The
number of cams corresponds to the number of cylinders in the engine.
The drive plate drives the distributor shaft.The head of the distributor shaft holds the delivery plungers which are aligned radially to the drive-shaft axis (hence the name "radial-piston high-pressure pump").The delivery plungers rest against the roller supports. As the roller supports are forced outwards by centrifugal force, the delivery plungers follow the profile of the cam ring
and describe a cyclical-reciprocating motion (plunger lift 3.5...4.15 mm).
    Solenoid-valve controlled distributor injection pumps High-pressure stage of the radial-piston distributor injection pump

1 Pump drive shaft
2 Vane-type supply pump
3 Angle-of-rotation sensor
4 Pump ECU
5 Radial-piston highpressure pump
6 Distributor shaft
7 High-pressure solenoid valve
8 Delivery valve

1 Solenoid-valve-controlled radial-piston distributor pump (cutaway view)

When the delivery plungers are pushed inwards by the cams, the volume in the central plunger chamber between the delivery plungers is reduced. This compresses and pumps the fuel. Pressures of up to 1,200 bar are achievable at the pump.Through passages in the distributor shaft,the fuel is directed at defined times to the appropriate outlet delivery valves (There may be 2, 3 or 4 delivery plungers depending on the number of cylinders in the engine and the type of application.Sharing the delivery work between at least two plungers reduces the forces acting on the mechanical components and permits the use of steep cam profiles with good delivery
rates. As a result, the radial-piston pump achieves a high level of hydraulic efficiency.
The direct transmission of force within the cam-ring drive gear minimizes the amount of "give", which also improves the hydraulic performance of the pump.Solenoid-valve controlled distributor injection pumps High-pressure stage of the radial-piston distributor injection pump

For the sake of clarity,various components are shown end-on rather than side-on.
1 Pump ECU
2 Radial-piston high pressure pump
3 Distributor shaft
4 High-pressure solenoid valve
5 Delivery valve
a For 4- or 6-cylinder engines
b For 6-cylinder engines
c For 4-cylinder engines
1 Cam ring
2 Roller
3 Guide slot in drive shaft
4 Roller support
5 Delivery plunger
6 Distributor shaft
7 Plunger chamber