 Pump-injector 1
The pump-injector principle has a much longer tradition than common rail. It was actually invented during Rudolf Diesel's lifetime. Not all diesel engines have combined their pumping elements
into a single injection pump. Once the engine exceeds a certain size, the elements separate and become so-called plug-in pumps (pictured below), which are driven by the engine's camshaft.
There are also pumps with their own drive.
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Because the principle had existed for so long, naturally without electronics, pump-injector systems were initially superior to common rail systems. With their higher injection pressure, they
generated more power. Aside from the fact that the entire cylinder head had to be adapted to the new principle, the idea had potential to build pressure precisely where it was needed.
The fuel consumption of VW's PD diesels is legendary, but so is their harsh sound. Slight uncertainty arose from the higher shock load on the timing belt, which led to a partial transition back
to a chain drive for the camshaft. And then came the Euro 5 standard with particulate filters, which finally put an end to the pump-injector unit. Regeneration of the filter required injections that
had to be carried out so late that their combustion was guaranteed only in the exhaust system.
And that's precisely what the pump-injector could no longer do. Its stroke doesn't last forever, and injection is only possible during that time. Later, common rail replacement solutions emerged
that prevented unburned injected diesel fuel from diluting the engine oil, for example. Toyota, for example, relocated the additional injection to the exhaust tract, more specifically to the
exhaust manifold on the fourth cylinder.
And that's precisely what the pump-injector could no longer do. Its stroke doesn't last forever, and injection is only possible during that time. Later, common rail replacement solutions emerged
that prevented unburned injected diesel fuel from diluting the engine oil, for example. Toyota, for example, relocated the additional injection to the exhaust tract, more specifically to the
exhaust manifold on the fourth cylinder.
| Pump-injector element for a truck |
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Since the system is called pump-injector, the injection itself is still mechanical-hydraulic, but the control is electronic. The blocking vane pump (pictured below) is somewhat typical, although the
fuel could, of course, have been pumped to the PD elements by other pump designs at 3 to 8 bar. A rounded triangle is driven by the camshaft and, with the spring-loaded blocking vanes on
the left and right, forms two independent pump chambers, each with a suction and pressure side.
Considering the unusual upper limit of 8 bar for fuel delivery, the requirements in the pump-injector system are probably somewhat higher than, for example, in common rail systems. This is
obviously due to the fact that after the end of injection, the feed pump must deliver the fuel to the pumping element's branches without cavitation (a gaseous state due to excessive vacuum).
Overall, the system appears to operate with higher resistance than common rail, as only the first systems with high-pressure control required a fuel cooler (pictured below) in the return line.
This is even more common in later pump-injector systems.
This brings us to the actual engine design, as the rest of the fuel delivery is similar for all systems. There are basically two methods for supplying fuel to the individual pump elements: through
bores in the cylinder head or a separate cable guide, as shown below, for supply and return. The latter should significantly reduce heat transfer from the cylinder head to the fuel.
The image below clearly shows the changes the cylinder head had to undergo. The camshaft received an additional cam, which is even slightly more strong than the one for a single valve.
Two overhead camshafts, as is common in diesel engines today, would have been difficult to integrate, as would a possible switch to a zero-cam, etc.
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While the valves are controlled directly, the pump element is controlled via roller rocker arms. The piston springs are similar to those of the valves. The fuel forerun is integrated into this cylinder head. The electrical wiring
and its plug contacts are also located in the oily part of the cylinder head.
The individual sensors and actuators are listed here. Among the latter, the most important are, of course, the solenoid valves on the individual cylinders. Apart from heating the intake fuel, which is also necessary with other
injection systems and at low temperatures, not much else is controlled here.
The individual sensors and actuators are listed here. Among the latter, the most important are, of course, the solenoid valves on the individual cylinders. Apart from heating the intake fuel, which is also necessary with other
injection systems and at low temperatures, not much else is controlled here.
The most important sensors include the foot pedal and the coolant temperature. It would also be possible to include the fuel temperature in this system. The crankshaft sensor and the camshaft sensor (not shown here)
are, of course, essential for calculating the start of injection. Below is a picture of a pump-injector element for cars.
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