MAN’s new D15 engine is smaller, lighter and more efficient than the longstanding D20 it replaces. So does it have what it takes out on the road?
In the world of truck manufacturing, a brand new engine is a rare occurrence, and when new engines do appear, it’s often the biggest and most powerful ones that get the attention. MAN, though, is giving the full panoply of publicity to a new middleweight engine designed from a totally clean sheet. First seen at 2018 IAA Show in Hannover, the new D15 engine is now in full-scale production.
The 6-cylinder D15, the arrival of which coincides with the latest Euro-6d emissions standard, replaces the previous D20 unit after a decade and a half of service, and really is all-new from the sump plug upwards. Its 9.0-litre capacity comes from a bore and stroke of 115mm x 145mm, all figures smaller than the D20’s 10.5-litre capacity from 120mm x 155mm. In case you were wondering if the smaller number in the D15’s name possibly suggests a backward step, MAN’s engine nomenclature actually derives from the second and third digits in the bore size. Three ratings, nominally 330hp/1,600Nm, 360hp/1,700Nm, and 400hp/1,800Nm, are available in the TGS and TGX models, the 400 filling the gap between the 360hp D20 and the 430hp D26.
Another key number that is smaller is the weight, 860kg dry, which is 230kg lighter than the equivalent D20, giving the new engine a big advantage in payload critical operations, while retaining a one million kilometre design life. It’s worth pointing out that in the UK, MAN is still a key player in one of these weight-conscious sectors, ADR tankers, utilising the experience inherited from ERF. The weight reduction was designed in and comes from numerous sources, such as a composite sump and cam cover, and a singlestage turbocharger. In fact, two-stage turbochargers across the engine range have gone, replaced by single wastegate turbochargers up to 400hp and single variable geometry units above. Fuel supply is via a new two-stage filter, giving a longer and more reliable life and requiring less energy-sapping heating in cold conditions. The common-rail system now operates at 2,500 bar, while emissions control is totally SCR, the demise of EGR representing an ironic about-turn for those who recall MAN UK’s “Add nothing” campaign at the launch of Euro-4. AdBlue consumption is expected to be 5% to 8% of diesel consumption. MAN was reluctant to be specific about the fuel savings from the new engine, but we did extract an estimated saving of around 2% compared with a D20 under identical conditions.
Other efficiency savings come from ‘smart’ ancillaries, including an intelligent alternator that only charges the battery when the engine is under no-load conditions. Operators now have a choice of three air compressors, according to their operational needs. The basic single-cylinder unit simply turns on and off as required, while a smarter version works in the same way as the alternator, and a 2-cylinder on-off unit is available for high-demand applications.
There are also choices in secondary braking, with the basic EVBec engine brake giving up to 200kW of retardation, a new 350kW Turbo EVBec brake or a 3,500Nm ZF Intarder. The basic engine brake and the Intarder can be combined to give maximum retardation. Power take-off is from one or both of two locations, 11 o’clock and 1 o’clock when looking at the engine from behind. Many of these improvements are shared with the D26 engine range, with its three members getting an extra 10hp and 1,000Nm, resulting in new nominal ratings of 430hp, 470hp and 510hp.
Transmission-wise, little has changed, although MAN now seems less sensitive about mentioning the origins of the hardware on its two heavy-duty systems, the 12-speed ZF TraXon or the Scania-derived 12+2. However, it rightly points out that whichever box you get, the TipMatic operating software is all MAN’s own work. That’s academic when looking at the D15, as the 12+2 box is still only available on 6x2 tractors with the D26 engine. So the choice for D15 buyers is whether to have your TraXon in the overdrive or direct-drive version, with appropriate final drive ratio.
The TipMatic software, though, comes with a new addition, a DP (drive performance) mode, when you specify the Pro option. When fitted, this is selected by the driver and remains active until switched back to normal drive mode. This only acts on the transmission and provides a gearshift strategy that keeps the engine near its power peak rather than prioritising economy.
Alongside the new engine, MAN trucks also feature some new driving aids, which are covered below.
In order to evaluate the D15 in the real world, we spent around 90 minutes in each of three TGSs, an 18-tonne rigid and a couple of middleweight artics, in representative environments. All of the test trucks were equipped with MAN’s new Comfort Steering system. This is fundamentally a speed-sensitive variable assistance system, which ranges from so easy at low speed that an undernourished gerbil could easily turn the wheel to a much firmer feel better suited to highway speeds for your average homo sapiens. It also allows trucks to have Lane Return Assist, the third such system from different brands that we’ve tried recently. When travelling at over 60kph on a road with clear lane markings, if you veer across the lines without indicating, it will gently nudge you back into lane, as will the Volvo and Mercedes- Benz systems we’ve tried. The MAN seems to have an extra feature in that, if you move across to give space to a stationary vehicle on the hard shoulder, the system will know and won’t steer you back. In any case, if you steer firmly enough to overcome the system pressure, you will easily override it. In use, the system worked as it should, although multiple white and yellow lines in a roadworks contra‑ow caused it to give up in confusion, signalled by the green “system active” dash light going out.
Another refinement is ACC Stop&Go, which allows the adaptive cruise control to remain active in queuing traffic, even when stationary for up to two seconds, after which it will disengage until the accelerator is pressed to resume progress. The next addition is VAS (video turning assistant system), which has a video screen mounted on the passenger side screen pillar, activating when the nearside indicator is used. It can also incorporate ultrasonic sensing of blind spot intrusions. In truth, it’s very similar to the multitude of third-party devices available, but with the benefit of being supplied as part of the new vehicle spec. As normal with such devices, we found it contributing to a degree of information overload, almost to the point of being self-defeating. Finally, there’s EBA2, MAN’s emergency braking system, which takes detection of obstacles to a new level of sensitivity and certainly well beyond legal requirements.
The first TGS to be sampled was the 330hp four-wheeler, with an M day cab and a distribution box body, loaded to maximum GVW. In addition to the standard VAS screen on the nearside A-pillar, this one also featured a 360 degree bird’s-eye view camera mounted on the driver’s A-pillar, with a very smoothly rendered display active at up to 40kph, which should be a great benefit in tight urban delivery situations. Our drive actually took us into a number of small town centres and industrial estates. The Comfort Steering proved effective at low speeds, although we had the feeling that with the extra assistance, the steering ratio could be increased to reduce the amount of arm twirling on roundabouts. Talking of comfort, the steel parabolic front springs gave an impressively soft ride, slightly bouncy on the worst surfaces but a small price to pay to reduce driving stress. The drive progress was equally relaxing, the 2.71:1 axle ratio meaning that at 65kph in the direct 12th gear, the engine was happy to roll along at just 900rpm.
Next to be sampled was one of a pair of 400hp 4x2 artics, with very similar specifications to the 18-tonner. This was a 38-tonne distribution vehicle with a tandem axle curtainsider. We took this on a longer drive out into the country, although our route was hampered by our attempts to keep away from the autobahn where it seemed half of northern Europe was passing through Munich en route to the sun. We did find enough clear space to gain an impression of the DP mode. When engaged, it certainly helped performance by changing down sooner and changing up later, but it will take a very disciplined or effectively managed driver to resist the temptation to leave it on at the expense of fuel economy. With it turned off, the performance felt quite leisurely by comparison, but used in moderation, it was a definite aid to keeping up with stop-start traffic.
This example had the full-house secondary braking, including an Intarder, which worked very well. Like all versions, one push on the button on the end of the right-hand stalk gave maximum retardation, and we particularly liked the way it self-cancelled when we accelerated again.
One thing we didn’t particularly like, however, was the large blind spot behind the driver’s main mirror, not helped by the inner edge of its frame being much thicker than necessary. Hopefully, this will be addressed when the next generation appears.
Our final drive was in a 40-tonne tipper, with the longer L cab and the overdrive version of the TraXon transmission. Apart from its increased desire to drop into 11th gear, the driving experience was as similar as expected. We did get the chance for a bit of off-roading, albeit on disappointingly dry gravel tracks. With off-road mode engaged, the truck moved its 39 tonnes around with no other adjustments, and nothing more dramatic than a bit of wheelspin on a tight uphill bend. It obviously has plenty in reserve, but if that isn’t enough, the hydraulic front-axle option is available.