When the first production automobiles hit the road, it rapidly became apparent that both a lack of skill and surplus of distraction could easily lead to an accident. Manufacturers subsequently sought ways in which to augment the inputs of the driver, or systems to reduce their workload, in order to boost safety.
In the early 1920s, for example, the concept of anti-lock braking was explored. If a driver panicked and slammed on the brakes, the anti-lock system would momentarily release any locked brakes in order to avoid an uncontrolled skid. This process would help cut the stopping distance in emergency situations and also allow the driver to continue to steer the vehicle.
Due to the complexity and cost of the hardware involved, it would take until the 1960s for a production automotive anti-lock braking system to reach the market - in the form of the Dunlop Maxaret ABS-equipped Jensen FF in 1966.
Chrysler then unveiled its Bendix-soured 'Sure-Brake' multi-channel ABS system in late 1970. Around the same time, Buick released the 'Max-Trac' traction control system. As developments continued and the technology spread, many manufacturers were soon able to regulate both a car's acceleration and deceleration. This made their vehicles easier to drive and safer, particularly in inclement conditions.
Problems could still arise, however, if drivers pushed too hard in corners or took sudden, sharp, evasive action. The forces that resulted from such a manoeuvre would often cause a momentary loss of control and an alarming deviation from the desired path; if the driver reacted poorly, or took no action, the situation could quickly worsen.
If the car understeered, and ploughed into something, the saving grace was that at least the most would be made of front crumple zone - and the various safety systems, if fitted, would perform to the best of their capabilities.
If oversteer was experienced, though, then the incident that followed would often end in the car striking an object with its side - which was not a strong point of the structure. Similarly, the function of the safety systems would either be moot or impaired by a side impact.
However, getting a driver to understand the dynamics of the vehicle in these situations - without any training - was not easy. General Motors, among others, was all too aware of this issue. 'In motor vehicle operation, proper steering control requires driver response to lateral acceleration of the vehicle whether caused by external disturbances or by deliberate driver effort,' wrote GM engineer Virgil Helgeson in 1957.
'In certain conditions of vehicle operation, the driver is without sufficient information to make the proper corrective action necessitated by lateral acceleration,' he observed. 'For example, in the case of an incipient skid, the road forces which normally give the driver front wheel position information tend to disappear and the proper corrective action is unknown.'
Helgeson, at the time, proposed a 'lateral acceleration computer' which would warn the driver if the forces reached 'excessive values which might result in a vehicle skid or loss of control.' A servo-based control system, which interacted with the power steering assembly, would further work to help counter the instability and indicate to the driver the 'proper corrective action'.
Similar stabilisation systems were also proposed during the late 1950s but, presumably due to a lack of suitable and affordable hardware, they seemingly went no further. The concept unquestionably had merit, though, and when ABS and traction control arrived manufacturers were suddenly granted a way in which to help stabilise the vehicle without driver input.
Porsche development engineer, Helmuth Bott, saw the potential of such a set-up. Bott, a former tank crewman, had studied engineering and joined Porsche as a factory assistant in 1952. He soon made his mark and quickly became well regarded for his understanding of chassis dynamics; he played a significant part in the design of the front suspension of the new Porsche '901' and, later, held the position of chief test engineer and head of the experimental department.
In part no doubt due to handling difficulties related to Porsche's rear-engined layouts, Bott proposed combining several systems into one overarching device that would employ 'suitable means for maintaining a vehicle in a stable driving condition.'
Bott, in a patent submitted in December 1969, stated: 'It is the purpose of the present invention to increase the driving safety of vehicles by the avoidance of unstable driving conditions resulting in skidding of the vehicle, as is produced, in particular, due to the effects of a shock incurred by untrained drivers.'
His proposed system would 'automatically actuate one or more mechanisms for maintaining the track of the vehicle in the proximity of the stability limit independently of the reaction of the driver and solely dependent on the actual driving condition.'
Wheel speeds, steering angle, throttle position, roll, pitch and yaw information - including input from a three-axis gyroscope - would be fed into an analogue computer that would function as the 'automatic control mechanism'.
This computer would run a 'program serving for maintaining the vehicle on course' and generate electric pulses that would regulate the control systems; these included an anti-lock braking set-up and a servomotor on the throttle. Bott also suggested that the system could have distinct modes to better account for dry, winter and wet roads.
'If a maximally possible transverse acceleration of 0.8 g. is detected, then the program for the control mechanism is set to about 0.75 g,' said Bott. 'This means that the brakes are actuated and the power control member of the engine is reduced to a lower driving power, independently of the driver's reaction, already below the critical threshold value. Consequently, the vehicle cannot enter a supercritical driving condition even when the driver incurs a shock reaction.'
While unquestionably of considerable benefit to the driver, such a system was limited to effectively just slowing the vehicle in order to help avoid a dangerous situation. Bosch, which had developed a production anti-lock braking system used by Mercedes-Benz in 1978, had also been investigating ways in which to further advance ABS and overcome this issue - and engineer Anton van Zanten had been tasked with improving its capabilities while cornering.
In 1982, while investigating ways to control the lateral dynamics of cars, Zanten had surmised that independently braking wheels could be used in order to 'steer' the car in the desired direction when the inputs and forces were otherwise too severe. This concept was backed up by the fact that, while testing cars on ice, simply slowing them was often not enough to rein in the lateral movements.
Having discussed the idea with Bosch, which began a fresh collaboration with Mercedes-Benz, real-world trials began in 1985. The system tested used sensors to compare the yaw rate of the vehicle with the driver's intended direction when the brakes were applied. If the vehicle was detected to be deviating from the desired path, the system would reduce the engine's power output and brake individual wheels to pull the car in the desired direction - stabilising it and reducing the chance of loss of control.
Mercedes-Benz engineer Frank-Werner Mohn, who unintentionally flung a car off the road during winter testing, had a similar idea. Mohn, however, wanted the hardware to operate all the time. This would greatly improve stability in general driving and also be of considerable use if a driver took evasive action.
Bosch and Mercedes were not the only company investigating such solutions, though, and in 1990 Mitsubishi took the first step towards an overarching production 'Electronic Stability Control' system. The Diamante, the company's luxury saloon, was the first to feature a traction control set-up that featured a 'Trace Control' mode.
This system monitored the car's steering angle, wheel speeds and throttle position in an effort to tackle understeer; if the steering angle was judged to be excessive for the current speed, then Trace Control would reduce the engine's output in order to avoid understeer - just as Bott had proposed. The system wasn't a true electronic stability control set-up, though, as it could not control the brakes.
Ford was also investigating ESC in the 1990s but, by March 1994, Mercedes-Benz and Bosch had completed development of the first production 'Electronic Stability Programme' - which would be utilised by the Mercedes-Benz S600 Coupe that arrived in May 1995. 'If all cars were equipped with the stability programme, over 20,000 of the serious accidents that result in over 27,000 victims on German roads could be avoided,' said Dr Thomas Weber, member of the Board of Management of Daimler AG.
Other manufacturers were not far behind; Toyota unveiled its 'Vehicle Stability Control' system in the Crown Majesta in August 1995 and Audi and GM followed in 1997. BMW also introduced the second generation of its 'Dynamic Stability Control' in 1995, in the E38 generation of 7 Series, which could 'mildly correct' lateral instability by using the rear brakes; by 1998, DSC III had arrived and this system could brake any wheel to combat oversteer and understeer.
In any case, the advantages to the active capabilities of these ESC systems quickly became obvious. Mercedes, partly in response to the catastrophic failure of the A-class in the 'Elk test', began making ESC a standard safety system in 1997. Just six years later, its data showed that the number of its cars involved in accidents had fallen by 42 per cent.
As costs fell, and the public clamoured for improved safety, more manufacturers began utilising electronic stability control systems - and, before long, it was a mandatory safety system in many countries.
The technology continues to advance, too, with features such as active rollover protection - which works to counter an impending rollover by sharply applying brakes on the relevant wheels - further improving the capabilities of ESC systems.
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