Down to the wire

The road to full drive-by-wire technology may be littered with obstacles, but two suppliers are offering systems which are seen as important stepping stones to the real thing. David Fowler reports.

Drive-by-wire technology, which promises the biggest revolution in car design since the synchromesh gearbox, won’t be with us until the turn of the decade. The big car makers and suppliers agree that technical reliability and regulatory obstacles will need to be overcome, and consumer attitudes change, before steering columns and hydraulic brakes can be phased out altogether. But development won’t be standing still.

It’s 25 years since we first saw anti-lock brakes, and eight since electronic stability control appeared (as ESP on the Smart and Mercedes A-Class). With stability control now fitted to one in two cars made in Germany – in France it’s one in five, the UK one in 12 – component suppliers are seeking ways to use developments of the technology to offer big car makers new driver aids.

In recent weeks, two of the biggest suppliers have unveiled two very different pieces of kit which they see as important stepping stones to full drive-by-wire, yet could be offered on cars bought in a couple of years’ time. They also revealed contrasting ideas of what a brake-by-wire system could look like.

On a more practical note, for those who find the whole by-wire debate a bit esoteric but wish their clutch control was better, competing systems will soon be on offer to take the effort out of hill starts.

Last month Bosch, which pioneered both ABS and ESP, announced a series of new braking functions which it will add to ESP. ‘In the future Bosch will not be offering just a single ESP, but a modular system which allows an almost free combination of desired functions tailored to individual markets,’ said Bosch director Dr Bernd Bohr.

The new functions include:

Electronic Brake Prefill, activated if the driver lifts his foot off the accelerator suddenly. The system senses an emergency and moves the brake pads into contact with the discs in anticipation that the driver’s next action will be to brake.

Brake disc wiping is intended to counter the problem, in heavy rain, of moisture build-up on the discs by momentarily touching the brake pads against the discs at intervals.

Hill Hold Control prevents unintentional roll-back on hill starts. The brake system automatically maintains braking pressure until the driver presses the accelerator to move off.

Soft Stop reduces braking pressure just before the vehicle comes to rest, making stops smoother.

On the basis of complexity and cost, Bosch expects different features to be offered on different classes of vehicle. ABS and traction control are expected to be the minimum on small cars – within the EU. under a commitment given by the manufacturer’s organisation ACEA to the European Commission these will become standard on all cars from next year.

Compact and medium-sized vehicles – such as the Ford Focus – will be fitted with ESP and hill hold control, which can be incorporated into current ESP systems. By 2005 Bosch expects to be ready to go into series production with ESPlus, which will incorporate brake disc wiping and brake prefill, which are likely to be offered on sport utility vehicles.

Soft-Stop will be reserved for executive and luxury class cars.

More radical moves are afoot for steering, where Bosch and ZF have formed a joint venture, ZF Lenksysteme, to develop active steering. According to Colin Carter, the venture’s sales director, steer-by-wire is currently neither feasible nor permitted by EU regulations, which require a mechanical connection between the steering wheel and road wheels.

However, ZF Lenksysteme’s Active Steering, due to go into series production this year, is claimed to embody some essential steer-by-wire functions, while retaining the connection.

Active Steering uses a planetary gear system built into the steering column, which allows two inputs but just one output. One input comes from the steering wheel, the other from an electric motor under the control of a sensor system and control unit. The effect is to allow steering inputs to the front wheels to be made independently of the driver.

In practice, in normal circumstances active steering will simply allow the steering ratio to be varied depending on road speed. At low speeds, the electronic input will work with the driver to make parking and negotiating tight corners easier. At motorway speeds, the electric motor will be able to work against and reduce steering inputs by the driver to make the steering less direct and the car feel more stable. Sensors collect information 100 times a second so the system can rapidly react if it detects a changing situation.

However, Active Steering has been designed to link to ESP, so that it can use steering inputs to counter skidding. ESP currently resists skids by applying the brakes to selected wheels.

Carter accepts that driver psychology will be a decisive factor: ‘Drivers will only accept what brings an obvious benefit: any kind of paternalistic control will be rejected.’ But he added that the mechanical connection should make it easier for drivers to accept the new technology as active steering creates the best possible preconditions for a future launch of steer-by-wire.’

On the question of how brake-by-wire will eventually be achieved, there is considerable divergence of opinion among component suppliers. Bosch has gone into limited series production of its Sensotronic Brake Control, an electro-hydraulic brake system developed with Mercedes-Benz, but has scaled back the resources it is devoting to this. Bosch’s Bohr recently said: ‘We are fully aware of the fact that this, as a first step to realising brake-by-wire, will only remain a high-end solution for the time being,’ partly because of its complexity.

Bosch has also shelved development of an electro-mechanical brake for the time being, believing it will not be possible to offer it until cars go over to 42V electrical systems with duplicated wiring.

Rival tier one component supplier Delphi disagrees. Nick Jones of its Dynamics & Propulsion Innovation Centre, Paris, said of his company’s strategy: ‘We looked at electrohydraulics, decided it would be too complex and expensive, and decided to focus on pure electric braking.’

Delphi also rejected the idea that 42V electrics are essential: though it is assumed that the proliferation of electrical equipment in cars will mean a higher voltage system is needed medium term, it is not an imminent development.

The company also wanted to introduce an automatic, electronic parking brake or handbrake, but sought a more elegant solution than so far offered on a few mainly high-end models, which use an electric motor to pull the brake cable.

The result is its hybrid braking system, which combines conventional front hydraulic brakes with 12V electric callipers at the rear. ‘The objectives were to improve comfort and convenience, enhance performance and increase safety,’ said Jones.

The system retains almost standard front braking system hydraulics and stability system electronics. The rear braking system, hydraulics and cables are replaced with the electric callipers, each with a DC drive motor and actuator. They are connected by a dedicated Canbus to the main electronic control unit. In addition to the normal ABS and stability control sensors, a brake pedal travel sensor and brake pressure sensor are added for accurate interpretation of driver intent.

The benefits are that the electronic callipers function quicker than hydraulic ones, providing better pedal feel and response to ABS commands.

There is a built-in automatic intelligent electronic park brake to avoid depressing the footbrake for long periods in stop/start traffic or having to continually apply and release the handbrake. When parking, accelerometers measure the slope and work out how much brake pressure to apply. When the car stops on a hill the brake applies itself automatically, and unlatches when the driver presses the accelerator to drive off again. Reversing downhill speed is automatically limited to 2km/h.

For the manufacturer, there is greater freedom in cockpit design: the space normally taken up by the handbrake lever is freed for other uses, complexity is reduced on the assembly line and less space taken up by the master cylinder and servo.Delphi expects the system to appear in production in 2006, possibly on a European front-wheel drive car.

‘It’s a safe step to brake-by-wire,’ said Jones. ‘It doesn’t need the complicated architecture of a 42V system. It gives car makers good experience of brake-by-wire without technical risk.’

On the remaining obstacles to full brake-by-wire, Jones said: ‘The development of fault-tolerant communication and power distribution systems is still a fairly major task. Persuading brake engineers to abandon hydraulics will be difficult.’

Then there are the regulations: ‘We’ve just come to the end of two years of talks with the European Commission on fault-tolerant electric brake systems, just to get an initial understanding. We’d like to see new legislation within two years. Our ambition is to have full electro-mechanical braking in production before the end of the decade.’