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Under the microscope: 4MATIC - Added traction
OverviewActive safety: Helpful assistantsAerodynamics: As sleek as they comeFit for off-road excursions - Multi-talented: The new Mercedes-Benz GLAMultimedia features: Always well informed and entertainedPassive safety: A protection programme for every eventualitySuspension: The right set-up for every useThe body: Stable foundationThe design: Quality and self-assuranceThe engines: Four and 4x4The Mercedes-Benz management team on the GLA: "Element of our strategy for the future"The model range: Many ideas for individualisationThe transmissions: Shifting comfort combined with efficiencyUnder the microscope: endurance testing - A vehicle lifespan at time lapse speedUnder the microscope: GLA Edition 1 - Special incentive at the startUnder the microscope: Renewable raw materials - High-tech parcel shelfUnder the microscope: 4MATIC - Added traction
As the first SUV, the GLA is optionally available with the new generation of 4MATIC all-wheel drive with fully variable torque distribution.
The most innovative components of the new 4MATIC include the power take-off to the rear axle, which is integrated into the 7G-DCT automated dual clutch transmission, and the rear-axle gear unit with integrated, hydraulically actuated multi-disc clutch. This set-up allows fully variable distribution of the drive torque between the front and rear axles. Additional benefits of this design are a lower system weight compared with the competition and also high efficiency. As with their front-wheel-drive counterparts, all 4MATIC models also boast good energy efficiency.
Integrated power take-off unit (PTU) channels power to the rear axle
The new 4MATIC is combined with the 7G-DCT seven-speed automated dual clutch transmission. The power flow to the rear drive train is provided by a compact power take-off unit (PTU) which is fully integrated into the main transmission and supplied with lubricant from the latter's oil circuit. This configuration gives rise to substantial weight advantages over competitor systems that branch off power by means of an add-on component with its own oil circuit. In conjunction with the friction-minimised tapered roller bearings, the PTU thus achieves an excellent level of efficiency.
The low system weight of the 4MATIC system is not attributable solely to the PTU. Other weight-stripping measures include a compact rear-axle gear unit, inductively hardened, weight-optimised rear-axle side shafts and weight-optimised drive shafts. The system weight of this 4MATIC is up to 25 percent lower than in the all-wheel-drive versions offered by the competition.
The two-piece drive shaft is vibrationally decoupled. An axially moving joint at the front compensates for longitudinal movements of the engine transmission unit, while an elastic flexible coupling reduces the intrusion of high-frequency gearing vibrations at the rear-axle gear unit. To minimise crash loads, the drive shaft is fitted with an extendable element.
Completely new development with torque-on-demand rear axle
The electrohydraulically actuated multi-disc clutch integrated into the rear-axle gear unit is responsible for fully variable torque distribution. Fundamental operating principle: when the multi-disc clutch is open, the car is driven exclusively by the front axle. When the clutch is closed, the rear axle comes into play. However, the drive torque can be shifted in fully variable mode between front and rear axle according to the given situation (torque on demand).
The system pressure to activate the rear axle is supplied in milliseconds by the gerotor pump that is integrated into the rear-axle gear unit. The pump is activated automatically as soon as only minimal speed differences arise between front and rear axles, and pressure control and therefore torque control to the rear axle is performed by means of a proportioning valve integrated into the rear axle.
Motoring enjoyment thanks to intelligent control systems
The 4MATIC is activated according to the basic principle of "as often as necessary, as rarely as possible". This means that when the underlying conditions allow, the all-wheel drive compact models run in particularly economical front-wheel drive mode. As soon as the driving situation requires, drive torque is channelled to the rear axle as appropriate. The reverse process takes place just as quickly: as soon as additional drive torque is no longer necessary at the rear axle – e.g. in case of heavy braking manoeuvres with ABS intervention – the rear drive train is deactivated and torque is reduced to zero.
In case of impending understeer or oversteer under load, the drive torque is first of all distributed in such a way as to stabilise the vehicle. Only if these measures fail to have a stabilising effect do the control systems adapted to the conditions of 4MATIC, such as ESP® or 4ETS, intervene and keep the vehicle on course.
With this strategy, the developers have managed to combine two key requirements defined in the performance specifications: optimum energy efficiency coupled with maximum dynamic handling and driving safety.