2/11/10

Overview: BMW X3

BMW has been building four-wheel drive cars since 1985. The permanent all-wheel drive system of the 325iX, unveiled 25 years ago, channelled drive torque to the front and rear wheels with a constant 37:63 percent split. Viscous couplings in the transfer case and final drive took responded to differences in rotation speed between the front and rear wheels to provide virtually complete locking if required.

Three years later came the arrival of all-wheel drive in the 5-series, accompanied by the début of electric systems controlling the distribution of torque. This new drive system deployed multi-plate clutches which could be controlled automatically and continuously to vary the usual distribution of drive, normally 36:64. Initially, a hydraulically controlled multi-plate clutch was used at the rear axle, but this was later replaced by electronically controlled brake inputs. The control unit of the all-wheel drive system took into account wheel speed signals from the anti-lock braking system, the rotational speed and position of the engine’s throttle valves and the status of the brakes.

Not exactly recommended: a BMW 325ix goes off-road in the eighties.

In 2004, BMW introduced the X3. At the time it was unique, and had its own niche for several years.

BMW’s newly-developed xDrive all-wheel-drive system, introduced for the BMW X5 alongside the launch of the BMW X3, boasted a fast-working, electronically-controlled multi-plate clutch in the transfer case and linked up with the DSC driving control system. Driving conditions could be analysed not only on the basis of wheel speed, but also using data supplied by the DSC system on steering angle, accelerator position and lateral acceleration. The new BMW X3 succeeds this model after six years.

Initially, two very different power-units are offered: BMW’s all-alloy two-litre turbodiesel, offering 184PS, and the Company’s three-litre Twin Power petrol unit, whose two turbochargers help it deliver a startling 306PS. The yawning gap between these two models will be filled later.

The four-cylinder diesel’s maximum torque of 380Nm is developed between 1750rpm and 2750rpm. BMW claims that the X3 diesel will reach 100km/h from rest in 8.5s and go on to a maximum speed of 129mph. Overall fuel consumption in the E.U. rolling road test régime is 5.6l/100km, or 50.4mpg; its CO2 yield is 147g/km with ZF’s 8HP eight-speed automatic gearbox, or two grammes more for the manual version. The common-rail injection system runs at a maximum of 1800 bar (180MPa) and uses piezo injectors. The single turbocharger has variable intake geometry.

An issue which has confronted manufacturers over recent years is that of low-speed engine vibration. Good modern diesels are capable of running efficiently and cleanly at quite low engine speeds — 1200rpm - 1500rpm, say — so long as loads aren’t too high. This means that very good fuel economy can be achieved in gentle driving if the driver changes up early. Unfortunately, four-cylinder diesels do not run smoothly at these crankshaft speeds, so a lot of effort has been put into improving engine-mounting techniques. BMW’s answer is a mounting design it calls the ‘centrifugal force pendulum’, which absorbs engine vibration and improves the damping capacity of the engine’s dual-mass flywheel.

The three-litre straight-six petrol engine is directly fuelled and features BMW’s Valvetronic system to control valve-timing and lift. Its maximum torque of 400Nm is available over a remarkable range, between 1200rpm and 5000rpm. BMW quotes a figure of 5.7s for the 0-100km/h sprint, with a maximum speed of 151mph. Fuel consumption over the E.U. test cycle is 8.8l/100km or 32.1mpg, with a CO2 yield of 204g/km.

The new BMW X3 xDrive35i is equipped as standard with ZF’s eight-speed automatic transmission; it’s an optional extra on the diesel model. A sports automatic transmission, with shift paddles on the steering wheel, is available on the 35i. Interestingly, the eight-speed automatic is only ten kilos heavier than BMW’s six-speed manual.

The automatic transmission is combined for the first time with Bosch’s stop-start system. Stop-start is also a standard feature in the manual diesel. All models have brake energy regeneration — charging the battery on overrun and during braking — along with EPS Electric Power Steering, demand-controlled ancillary components and low rolling-resistance tyres.

The X3 comes with BMW’s xDrive four-wheel drive system as standard. Its electronic control unit, which is interlinked with the DSC Dynamic Stability Control, is designed to counteract any tendency to oversteer or understeer.

The new X3’s running-gear has been reworked. A double-joint spring-strut axle at the front is combined with five-link location at the rear. The new car runs with a wider track than its predecessor.

Electric Power Steering, including the Servotronic function for speed-dependent assistance, is fitted to all versions of the new X3. The optional variable sports steering is higher geared.

A further option is dynamic damper control. The electronically-controlled dampers adapt to road surface conditions and the driver’s style of driving. The driver can select different control maps for the dampers, with a choice of ‘Normal’, ‘Sport’ and ‘Sport+’. As well as controlling damper behaviour, accelerator pedal progression, engine response, the characteristic map of the power steering, DSC response thresholds and the gearshift dynamics of the automatic transmission are also affected.

A good variety of optional extras are available, as you would expect: a head-up display, adaptive cornering headlights, high-beam assistant and a reversing camera number among them. BMW’s ConnectedDrive system allows unrestricted use of the internet inside the car, a comprehensive integration of the Apple iPhone and other smartphones, and the use of web-based services for navigation and entertainment functions. The reversing camera can be combined with a system called Top View, which uses two additional cameras in the side mirrors; the image generated from the recorded vehicle data and its environment is displayed on the car’s monitor, showing the vehicle and its environment in a bird’s eye view.

The new BMW X3 is produced at the Company’s plant in Spartanburg, South Carolina. This facility is also responsible for building the X5 and X6, and BMW describes it as the ‘competence centre’ for BMW X models within the BMW Group’s worldwide production network. Annual production capacity is 240,000 vehicles, and the plant has ISO 14001 certification. Fifty per cent. of the Spartanburg factory’s energy needs are met using methane gas obtained from the biological decomposition of waste materials at a waste dump 16km away.

BMW X3 20d 35i
Cylinders 4I 6I
Valves 4 4
Bore/stroke 90.0/84.0 89.6/84.0
Swept volume 1995cc 2979cc
Compression
ratio
16.5:1 10.2:1
PS/rpm 184/4000 306/5800
Nm/rpm 380/1750 400/1200
Maximum speed 129 151
0-100km/h 8.5 5.7
Urban MPG
(l/100km)
42.1
(6.7)
25.2
(11.2)
Combined MPG
(l/100km)
50.4
(5.6)
32.1
(8.8)
CO2 g/km 149 204
Emissions EU5 EU5
Transmission M6 (A8) A8
Driven wheels All All
Fuel tank 67l 67l
Kerb mass * 1715 1805
Trailer
(braked) (12%)
2000 † 2400
PS/t 107 169
Nm/t 221 221
Brakes: front
— rear
328v
330v
328v
330v
Wheels 7.5Jx17LM 8Jx18LM
Tyres 225/60R17V 245/50R18W
Approach
Departure
25.7°
22.6°
25.7°
22.6°
CdxA 0.33x2.65m² 0.35x2.65m²
* DIN. EU kerb mass = DIN + 75kg.
† Towing limit with manual transmission. Limit with automatic gearbox 2400kg.
Click here for dimensions.
BMW X3
gear ratios
20d
M6
20d
A8
35i
A8
1
2
3
4
5
6
7
8
Final drive
4.110
2.248
1.403
1.000
0.802
0.659


3.727
4.714
3.143
2.106
1.667
1.285
1.000
0.839
0.667
3.077
4.714
3.143
2.106
1.667
1.285
1.000
0.839
0.667
3.385
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