Michael Kelz, Chief Engineer for the new Mercedes-Benz E-Class, does not underestimate its present and future potential: “This car is a big step in the direction of autonomous driving. With our Drive Pilot, we have the possibility of processing really high rates of data, a very impressive system that can be used in many situations, including reaction to speed limits, the car decelerating or accelerating automatically.”
Kelz compares the knowledge requirements of autonomous driving systems with his kids’ need to gain and retain experience. Like them, the E-Class has great intelligence but it has to acquire knowledge. “The car has the necessary technology on board," he noted, but to drive fully autonomously it needs more precise street map data—and more knowledge of what is happening around it.
The MY2017 E-Class is already about 80% ready for autonomous driving on an autobahn, according to Kelz. He said the Drive Pilot can follow vehicles ahead at speeds up to 210 km/h (130 mph), and at up to 130 km/h (81 mph) will find its own way, "even in the absence of clearly visible lane markings."
Also, to make a lane change, the driver needs only to operate the indicator stalk for a couple of seconds and Active Lane-Change Assistant supports steering provided the adjoining lane is clear. And Active Brake Assist with cross-traffic function now has extended speed thresholds and when necessary also brakes on approach to the tail end of a traffic jam.
Evasive Steering Assist is another new system that adds torque to help a snap maneuver and its recovery, such as in pedestrian avoidance. Other advanced technology elements are being added, including heating for the front mounted radar for Distance Pilot Distronic.
A challenge for Mercedes, as with many OEMs, is to keep ahead of ultra-high profile software companies entering the auto sector that could change the dynamic of the industry’s comprehensive software and hardware business structure.
But the 10th generation E-Class’s driver assistance systems and their associated present and potential new technologies, represent just one (albeit very significant) aspect of the car’s capabilities. These span remote parking (via a smartphone app for very tight parking situations); new multi-chamber air suspension; aerodynamics honed to achieve 0.23 Cd; and a “world first” hand-motion swiping of steering wheel touch control buttons.
All-new OM654 diesel
Internally designated W213, the new model is nearly 2 in (51 mm) longer overall than its predecessor and rides on a 2.6-in (66-mm) longer wheelbase. Base powerplant for the European market is a new 4-cylinder 1950-cm3 diesel capable of 5300 rpm and rated at 400 N·m and 143 kW (192 hp) in its launch form. Other powertrains include the E350e plug-in hybrid with 2.0-L gasoline engine and total system output of 210 kW (282 hp); its 550 N·m proved very convincing to the author on a short test drive.
Despite some doubters, Mercedes maintains its continuing confidence in diesel technology. Dr. Thomas Weber, R&D head of Daimler Group research, said: “In our opinion, the diesel engine is indispensable in trucks and cars if we want to further reduce the CO2 emissions from traffic. The new diesels are designed to meet all future global emissions standards.”
The new 2.0-L diesel, designated OM654, was four years in development. It replaces the 2143-cm3 OM651 engine produced since 2008. Dr. Weber noted that the new diesel will play a significant role in Mercedes’ future powertrain programs. It is a modular design sharing a 500-cm3 cylinder, and capable of longitudinal and transverse applications in front-, rear- and all-wheel drivelines. Later, there will be what Mercedes engineers describe as “a series of innovations on the basic engine.”
The OM654 is Mercedes' first production diesel featuring all-aluminum construction, but it has steel pistons with stepped combustion bowls, riding in Nanoslide-coated cylinders (see http://articles.sae.org/10507/). The common rail injection is 4th generation. Particularly significant is the positioning of all exhaust treatment directly on the engine. The power unit is also 17% lighter than the its predecessor in the E-Class. Its use in other models requires all-new electronic architecture.
Mercedes has focused on reducing noise and vibration compared to the old OM651. Despite output raised from 125 kW to 143 kW (from 167 to 192 hp), fuel consumption and CO2 emissions are both reduced by some 13% for the E-Class, engineers told Automotive Engineering.
The 90-mm (3.54 in) cylinder spacing is 4 mm (.16 in) more compact than that of the OM651. It's also 46 kg (101 lb) lighter, in fully dressed form, than its predecessor. The mass reduction was achieved via the new engine’s reduced displacement, as well as the aluminum crankcase (designed to withstand peak pressure of 205 bar/2973 psi), Nanoslide cylinder coating, single instead of two-stage turbocharging, and plastic engine mounts.
With all relevant emissions reduction components installed directly on the engine, plus insulation and improved catalyst coatings, the new OM654 does not require temperature management during cold starts nor at low load, according to the engineers.
Multiway EGR (exhaust gas recirculation) combines both cooled high pressure and low pressure flows.
Piston bowls and safety systems
Further details of the engine design include twin Lanchester balancer shafts mounted on each side of the crankshaft rather than below it, to save height. Mercedes has been a leader in the adoption of steel pistons in passenger-vehicle diesels.
Engineers noted that thermodynamic efficiency is improved due to the lower heat conductivity of steel, allowing higher component temperatures for better combustion. The lower expansion rate of steel at normal engine operating temperatures also provides increased clearance between the “very compact, lightweight” pistons and the crankcase, thus reducing friction by up to 50%.
Last year Mercedes and piston supplier KS Kolbenschmidt won materials-industry awards for use of forged steel pistons in the all-aluminum V6 diesel of the E350 BlueTEC. Those "slugs" are forged using a patented technique which produces a sealed coolant passage. The resultant thinner wall between the coolant passage and the hot zone of the piston is the key to efficient cooling (http://articles.sae.org/7009/). Mercedes also uses steel pistons in other 4-cylinder engines.
Mercedes claims a “world first" for the stepped combustion bowl design incorporated in the OM654 pistons. Engineers said this geometry brings a "positive effect" to the combustion process (higher burning rate), the thermal loading of critical areas of the pistons, and the ingress of soot into the engine oil.
Driving the new E-Class at the car's European media launch in and around Lisbon, Portugal, the author found the 2.0-L diesel to be generally quiet and smooth and, considering it was propelling a 1680-kg (3700-lb) car, relatively vigorous. Complemented by its 9-speed transmission, 0 to 100 km/h acceleration takes 7.3 s. Vmax is 240 km/h (149 mph). But short of encapsulating the cabin, low-speed/high-load situations will inevitably transmit some diesel noise. The car is very quiet in the cruise.
Interesting new safety systems include an air chamber in the front seats to push an occupant away from the area of a side impact; and Pre-Safe Sound, which involves the stapedius reflex of the human inner ear.
If the risk of a collision is detected, the car’s sound system emits a short interference signal to action the reflex. This prepares the ears of the E-Class’s occupants for the sound of the accident (often rather loud!) and is said by Mercedes to help reduce stress. It should be noted that the author did not real-time test the car's safety aspects.