Make or buy turbos? Daimler decides

Daimler AG is manufacturing diesel engine turbochargers in-house. It is another ground-breaking development by the vehicle builder on its relentless climb to the sunlit uplands of dominance.

Tucked away in the press release for the latest version of the OM471 truck engine from Daimler, with its 3 per cent fuel economy gain, is the revelation that the company is manufacturing turbochargers in-house.

Inevitably, while this is a gain for Mercedes-Benz it represents a loss of sales business to a vendor; even a loss of face in the wake of lost euro revenue from such a prestige German customer as Daimlerwhich, for the first time, becomes the only truck-making OEM to make irs own turbochargers.

In 2014, Daimler made 496,000 trucks, 295,00 vans and 33,000 buses equipped with diesel engines. (the company does not disclose how many diesels it produces in a year). If the company decided to equip all its diesel engines with in-house turbochargers, this could amount to a market of 824,000 units, a sizable volume to justify in-house manufacture.

The development by Mercedes-Benz engineers of their own turbocharger raises several important questions: what was wrong with the previous bought-in design? How can an engine manufacturer justify not only the design and development costs of an in house turbocharger but manufacture also? It must be cheaper to buy a turbocharger than make it in-house. How many other engine makers produce their own turbocharger?

After all, there is a handful of world-class turbocharger makers, including BorgWarner, Bosch Mahle Turbo Systems, Cummins Turbo Technologies (i.e. Holset), Honeywell and IHI, to mention but five. Cummins Turbo Technologies is constantly launching a stream of new turbo designs; its designs should be at the cutting edge of technology. Certainly, Mercedes uses Cummins Turbo Technology turbochargers for its turbo-compound 15-litre OM571 engine. And it used BorgWarner turbos on the previous generation OM471.

And there is another question. How can an engine manufacturer accrue the hydrodynamic knowledge and manufacturing expertise to produce a turbocharger that only matches the thermodynamic efficiency of vendor-made turbos, but has comparable, or even better reliability?

What was it that caused Mercedes-Benz engineers (and their senior management) to say, in effect: "Hey you guys, why don't we make our own turbochargers?" Why would they even give a moment’s consideration to such an outlandish prospect? What prompted such action?

Only those inside Daimler know the true answers as the investment in euros is significant, but still lost within the €60 million spent on the OM 471.

On the face of it, one might think that any world-class turbocharger maker knows much more about the ins and outs of designing, developing and making turbochargers than Mercedes-Benz. How can Mercedes-Benz engineers cull together so much experience in such little time to produce a turbocharger that is better than one purchased from a world-class vendor? Daimler's only known, and current, yet previous history of turbocharger development and manufacture is at Mercedes High Performance Engines, Brixworth, UK whihc designs, develops and manufacturers turbochargers for F1 engines.

In addition, surely the volumes produced by the likes of BorgWarner, Cummins Turbo Technology, Honeywell and IHI might suggest their cost of manufacture is much less than that which Mercedes-Benz could even come close to matching.

So, why would the Stuttgart-based diesel engine maker even begin to consider making these components one-house? Everything seems to be stacked against it.

But then the same could be said about transmissions. At one time, Mercedes-Benz sourced most, if not all, its commercial vehicle gearboxes from ZF. Until, that is, it decided to make its own. Now the truck builder makes credit-worthy gearboxes in-house. Experience shows it has made a success of this.

By the same token, it can be said that some years ago, Mercedes-Benz's Mannheim foundry began to cast cylinder heads for the OM 471 engine in vermicular graphite iron (or compacted graphite iron - CGI) using its own in-house process control technology. Only the cylinder heads of the OM 471 use CGI material.

Even this week, Dr. Andreas Gorbach of Daimler’s platform management HDEP/MDEG, told Auto Industry Newsletter: "We have been using CGI only for cylinder heads for all OM47x worldwide. These have been cast in Mannheim since the SOP (start of production) of the DD15 in 2008. The cylinder block has been designed in such a way that (CGI) it is not required."

So why not turbochargers? If the Mercedes-Benz commercial vehicle and diesel engine departments can employ the new turbocharger in other in-house engines, thereby achieving sensible volumes and economies of scale, then it should make it easier to reduce unit costs and secure “holistic” economic viability, possibly even to the extent of making one million turbos a year long-term.

This will require Daimler to spread in-house turbos as far and wide as possible. So no doubt other engines will follow. Which engine is next? As Dr. Gorbach observes: "Wait and see."

     

                                          Why turbochargers

So, why not turbochargers? Well, the Daimler press release gives a clue. It states:

“A new asymmetric turbocharger is partly responsible for the swift and substantial increase in power delivery at low rev speeds. It was developed by Mercedes-Benz and is manufactured in the Mannheim engine plant. An in-house turbocharger ensures customised adaptation to the requirements of the OM 471. The turbocharger excels for its outstanding efficiency. Very tight production tolerances are a guarantee of supreme quality and durability.”

“As before, the asymmetric turbocharger features a fixed-geometry turbine. From a technical standpoint, this variant is far less complex and thereby less prone to faults than a VNT turbocharger, for instance. It also does without a wastegate valve, further simplifying the design. This measure reduces the turbocharger's complexity and avoids a potential source of faults, such as leaks – another plus point as far as the robustness and durability of the OM 471 are concerned.”

Mercedes-Benz declares that it is not using a wastegate, yet gives no hint as to how it is compensating for the loss of the wastegate without complicating the design in any way, Company press releases have a habit of being economical with the truth. 

It perhaps should be pointed out here that as a turboocharger can rotate at speeds far beyond what is require, or what it is safely capable of, its speed has to be controlled. A wastegate is the most common mechanical speed control system and is often augmented with an electronic boost controller. The main function of the wastegate is to allow some of the exhaust to bypass the turbine when the required boost pressure is achieved. The wastegate's absence, and the multiplicity of associated sensors required for its efficient operation, suggests Mercedes engineers have found a clever way to duplicate its effect by controlling turbne speed and optimising transient behaviour. Clearly, in the past Mercedes has suffered reliability issues of some kind in this area.

So why adopt in-house turbochargers? What is the real technical justification for the move? The answer appears to centre on one word Mercedes-Benz engineers mutter under their breath as they discuss their new turbochargers - reliability. Any hint of unreliability is not required for the 12.8-litre engine which has emission control based on SCR technology, EGR (using three of the six cylinders) and particulate filter to meet Euro V1.

The implication is that there have been some reliability issues with vendor turbochargers. Whether these issues are directly linked to vendor turbochargers or associated components, such as sensors or other items is not clear.

But the reliability issues must have been so significant as to prompt engineers even to contemplate in-house manufacture. It also implies frustration - even reaching supervisory board level. It cannot have been an easy decision. But whoever made the decision to manufacture turbochargers was taking the long view - and a holistic view

The OM 471 is just the start. No doubt the company will use Mannheim as the location to make turbochargers for other truck diesel engines, just as the facility makes CGI cylinder heads for worldwide use.

There is another reason for using in-house turbos. Turbochargers sourced from vendors are inevitably a compromise as one design has to meet the requirements of various customers. However, by designing in house to meet the very specific – and demanding – requirements of Mercedes-Benz engines, engineers can get very close to the optimum. And if necessary in future it is easier to make minor changes to turbocharger design to meet specific market (and emissions) needs.

Turbochargers, together with the delicate handling of inlet and exhaust gases, are at the root of meeting emissions requirements and improving brake specific fuel consumption – and indirectly vehicle fuel economy.

The conclusion has to be drawn that by designing, developing and manufacturing its own turbochargers, Mercedes-Benz engineers can have a much tighter control over not only the performance of their engines – and this includes emissions performance as well as durability – but, per se, the  entire manufacturing cost. It is just conceivable that the new Mercedes-Benz turbochargers are not cheaper than their counterparts purchased from BorgWarner. But the engine maker could be recouping the cost by producing an engine which, overall, is more reliable and which in turn brings cost-benefits.

Closely linked to the word reliability is the word simplicity. The new Mercedes-Benz turbochargers are simple in design – and that means less complex, easier to machine and assemble, and cheaper. There are no variable guide vanes and no waste gate and this turbocharger uses an aluminium impeller – not expensive titanium. All of this implies that engineers have managed to reduce the number of sensors too.

But their nature, sensors can be the root cause of error codes and faulty displays. It is known too that in respect of emissions – NOx and particulates – that legislation is streets ahead of sensor technology. So until sensor technology catches up engineers have to reduce the sensor’s field of influence.

Research in the US has shown that EPA 2010 diesel engines are less reliable than their forebears, which may explain why gliders are popular among some operators.

So Daimler has taken note. Engine reliability and truck down-time are vital parameters for operators. They can decide which truck an operator buys.

Interestingly, although Daimler claims improved fuel economy arising from the new engines, not all of it is down to the engine alone as other factors play their part. It should also be noted that while fuel economy is said to be improved Adblue consumption has risen from 3.5 per cent to 5 per cent of fuel consumption.

                                                 Key Component

A key component of the new generation of engines and thier improved fuel economy is the latest-generation X-Pulse version of Bosch’s APCRS amplified-piston common rail fuel injection system – the unique common-rail system with pressure booster in the injector and “unrestricted flexibility” for modelling the injection system. It is understood that Mercedes-Benz is the only OEM to use this system, suggesting a tightly-written control between the two German companies, or some exclusive arrangement for a number of years to give the truck-maker unrivalled leadership. It is the only OEM running at such high injection pressures.

Maximum rail pressure has been increased from 900 to 1,160 bar, resulting in a maximum injection pressure of 2,700 bar. It is understood the rail pressure can be raised further if necessary increase the injection pressure to 3,000 bar – a pressure that has been mentioned in some quarters. Sturman Industries Inc. for example has run its injectors at 3,300 bar.

The injection nozzle, which is the only region to experience these magnification pressures, is an eight-hole nozzle (previously seven holes), increasing the maximum flow rate by around ten percent.

Additional modifications include the piston bowl geometry, the sizeable increase in compression ratio from 17.3:1 to 18.3:1, along with a reduced exhaust gas recirculation rate (EGR rate). All these measures add up to a further improvement in efficiency across the entire engine performance map. This in turn lowers fuel consumption significantly. The optimum values in the consumption characteristic map have followed the new torque curve towards lower rev speeds.

Systematically configuring the engine for low fuel consumption means that untreated NOx emissions rise but is countered by the SCR

Meanwhile, the loss of an important customer such as Mercedes-Benz cannot be an easy pill for any vendor to swallow.

The name Mercedes-Benz is synonymous with quality and reliability. To be associated with the name is to share the prestige of the vehicle builder. To be sidelined is enough for questions to be asked at vendor board level: why, how and what can we do to mitigate it, are but three.

The decision by Daimler at board level to make turbochargers is surely a message to the management of all vendors.  Lurking in the background is the veiled implication that if vendor technology, quality, reliability, cost, etc., etc., fall short of Daimler's requirements, then the company will take action to bypass it and, if necessary manufacture it in-house. Turbochargers could represent the latest in a series of important lessons.

Meanwhile, BorgWarner's manufacturing facility in Seneca, South Carolina, this week received an Excellence in Quality Award from Honda North America. Since 2002, the plant has received 12 supplier awards from Honda, including seven for quality, four for delivery and one for engineering innovation.The plant supplies Interactive Torque Management all-wheel-drive technology for the Honda Pilot..