Hartridge Ltd Blog

High Pressure Testing is Nothing Without Control

Posted by Lee Jacobs on March 18, 2019

High Pressure testing is nothing without control

The significant advancements in injector technology to meet the Euro 6 emissions legislation include increased fuel injection pressure, optimised nozzle spray angles and patterns to enhance combustion, and how many injections are possible per combustion cycle. However, another technical advancement that is not so well documented is closed loop electrical drive logic to provide accurate control during the injection event and digital rate shaping to configure the profile of the injected fuel during the combustion stroke.

Understanding this essential engineering concept is vital to unlocking true control of high pressure testing. So how has Hartridge responded to provide a leading aftermarket test solution and what advanced controls have been implemented to achieve this?

Safety & control

Fuel injection pressures on the latest euro 5/6 CR injector applications are now exceeding 2000bar and therefore we need to provide, as a minimum, a test solution which can meet this requirement. But it’s not just a case of achieving high rail pressures, that’s the easier part of the puzzle.

The Sabre CRi Expert has a maximum pressure capability of 2700bar. When dealing with these kinds of pressures there are two essential considerations and they are safety and control. Safety is our number one priority and the Sabre CRi series machines have a number of safety interlocks and controls in place to protect the machine and operator.

We use the correct rated hardware components to allow the machine to operate safely at these conditions despite the unlikely event of pressure run-away or instability.

Controlling these extreme operating pressures is the most challenging aspect at 2000+bar.

It is very often overlooked, misunderstood or even worse manipulated so it appears better than it actually is!

It is very easy to achieve a maximum rail pressure and state this as a “peak” figure which looks very attractive on paper; while the reality is that it may struggle to reach those high pressures in a stable, controlled way. The control strategies for a truly high pressure test bench need to be as advanced as the injectors which are capable of generating them.

Advanced Pressure Control and Injection Synchronisation

So what are the advanced control strategies Hartridge is using to achieve its 2700bar rail pressure and what tangible benefits do they provide? To answer this question we go back to basics and ask, how does the Sabre CRi Expert generate its pressure?

Hartridge utilise an OE vehicle CR pump as the pressure source, this is an extremely reliable and organic method which provides engine-like running conditions. Depending on the machine specification the CR pump will either have 1 or 2 pumping elements, also known as hydraulic heads, and these are driven by a camshaft that has 2 cam lobes, therefore resulting in 2 pumping events per 360 degree revolution.

Each time the CR pump driveshaft is rotated through 360 degrees this will result in each pumping element compressing a particular amount of fuel twice. The compressed fuel is then transferred from the pumping elements into a rail and then from the rail to the injector being tested.

Common Rail pump rotationsEach time the pumping element compresses fuel there is an increase in volume which in turn creates a pressure “spike” within the rail; unfortunately this pressure spike cannot be eliminated as the electronic pressure control valve (PCV) is not able to react fast enough to dissipate the additional fuel volume.

Since the CR pump will be rotating at a fixed speed, typically 1500RPM, this results in a continuous pressure wave/ripple within the rail, which creates a sinewave profile. The same pressure wave/ripple is evident on a vehicle since the technology principles to generate the flow and pressure are the same.

Taking the Sabre CRi Expert pressure waveform as an example, the pressure amplitude between the pumping events is approximately 50 bar.

The Sabre CRi Expert pressuresNow imagine the characteristics of testing a CR injector at 2020bar and then again at 1970bar, we can be confident that the fuel delivery and response time of the injector will be different between the two operating conditions.

The 1970bar operating condition certainly has a lower fuel delivery and a slower response time. It is possible to compensate for this fluctuation in pressure without having any advanced injector control?

There is only 1 solution and that’s to fire the injector at an injection speed which provides results across the entire pressure wave and then performs a number of calculations to average out the result. There are some limitations and disadvantages to this strategy:

  • Firing the injector across the pressure waves considerably increases the test cycle time as a minimum number of “injection events” need to be measured and then post calculated before defining a pass/fail status.
  • Depending on the minimum number of “injection events” required can sometimes mean that a lower delivery “injection” is ignored due to the post calculation of averaging.
  • Pressure control during the pressure wave is uncontrollable as the electronic pressure control valve is constantly trying to adjust to achieve the target pressure, resulting in instability at certain running conditions.

This methodology is acceptable for test plans that have a low number of measurement steps, or where cycle time is not a major concern, or for injector technology which requires less accuracy.

Synchronised injections events

So how have Hartridge advanced the test equipment to eliminate these limitations and disadvantages?

Hartridge have developed an advanced software & hardware combination solution to control injection and pressure.

Our One Pulse Per Revolution (1PPR) injection synchronisation sensor which enables the injection event to be synchronised to the CR pump pumping event so that the rail pressure is consistent throughout.

This means that the injection speed selection for the Sabre CRi is pre-defined to 3 selected speeds, 375IPM, 750IPM and 1500IPM due to the fixed CR pump speed.

The benefits of this are superior to other methods of attempting of regulating injector testing. The major advantage is cycle time, where typically test cycle times are reduced by up to 50% thanks to a reduced number of injection events being required to determine the injector performance.

For example, the cycle time for coding a Denso G2/G3 coil injector is reduced to 8 minutes even while this test plan includes the new closed loop test strategy which automatically trims the injector live during the test for each test point.

Without the synchronisation then the typical test cycle time for Denso is approximately 18-20 minutes per injector. Not only is the test cycle time reduced but the pressure accuracy and stability is far greater as the patented closed loop machine control learns to trim the pressure control valve live as the pressure drop is consistent for each injection event.

Synchronisation in the Sabre CRi ExpertThe same strategy applies for the latest Delphi F2x Euro 6 and Bosch CRIN4.2 applications, where the closed loop injection synchronisation provides the same advantages as above. The Delphi F2x Euro 6 injectors operate at 2500bar and 350mm3, depending on application type, so pressure stability and measurement accuracy is absolutely critical for these heavy duty applications.

The test plan criteria to comply with Euro 6 emissions standards means that some application specific test plans have 22 critical closed loop measurement points and result is a fully automatic test can be completed in just 13 minutes.

Sabre CRi Expert PCBThe Future of Diesel CR Technology – Digital Rate Shaping

The Bosch CRIN 4.2 injector is the 1st CR injector to utilise two solenoid valves to control pressure and nozzle lift. Pressure control is achieved by an intensifier piston, typically 2:1 ratio, which is housed inside the injector body and activated by a dedicated coil and valve assembly.

The benefits of utilising an intensifier piston is that the system rail pressure is significantly lower, typically in the region of 800-1200bar.

This puts less strain on the CR pump and external high pressure components as the pressure is amplified within the injector itself depending on the injection pressure requirements.

The injection event is activated by a separate dedicated coil and valve assembly which is extremely similar to any other CR injector design. The CRIN’s two control valves driven by two dedicated coils, one to control pressure and one to control injection, also need advanced control to derive accurate test results.

During extensive on-vehicle R&D testing it was identified that the rate of injection can be controlled by changing the firing relationship between the intensifier and nozzle valves and this relationship changes depending on the engine running condition.

For instance, firing the intensifier valve 500uS before the nozzle valve provided a very sharp and fast injection rate which would remain constant if the intensifier valve is left actuated while the nozzle is open. If the intensifier valve is actuated after the nozzle valve then the injection rate is at the system rail pressure during initial nozzle opening but increases significantly during the injection event period depending on the length of time the intensifier valve is energised for.

So how do I upgrade my Sabre CRi machine to benefit from the latest 1PPR synchronisation functionality?

The plus side is that if you already own a Sabre CRi Expert then you already have the required hardware built into the machine, and you simply need HM1026 calibration kit to activate the system.

If you own a Sabre CRi Master then the great news is that Hartridge have developed a cost effective kit, HJ089, which includes all the required machine hardware and HM1026 calibration kit so the machine can be easily upgraded and can be calibrated yearly.

The 1PPR synchronisation kit is a mandatory requirement for certain injector part numbers; this can easily be identified by referring to technical information bulletin - TB243/1.

The next version 4.0 of magmahTouch which will be released next month will have helpful icons indicating if 1PPR sensor needs to be fitted for the injector part number selected.


Topics: Sabre CRi Master, diesel injectors, injector testing, Common rail injectors, Sabre CRi Expert, 1PPR, injection event, pump synchronisation, injector synchronisation, 1PPR sensor

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