May 2002
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May 2002 |
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Look at the A.C.S. Speed Sensitive Accelerator Pedal The accelerator pedal -- which has remained basically unchanged since the origin of the automobile -- is due for an upgrade. Soon it will evolve to be active and "intelligent" -- suitable to meet emerging needs of Intelligent Speed Adaptation and other systems requiring a cooperative interface. French inventor Alain Landerretche provided IVsource with information about one such interface -- the Speed Sensitive Accelerator. |
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Thanks to Alain Landerretche for the content of this article. The accelerator pedal has remained basically unchanged since the origin of the automobile. In the very near future it is expected to become an active and "intelligent" device, to enable more comfortable and safer motoring. Many automotive engineers in the world are today working on Intelligent Speed Adaptation and other Intelligent Vehicle systems which require a cooperative Human Machine Interface. This article examines the "Speed Sensitive Accelerator" with an inventive haptic actuator, which may be suitable for such emerging systems. Reliable
control of speed is a
constant concern when driving. To make matters more challenging, the comfort and silence of modern vehicles sometimes deprive drivers of usual and
necessary speed indicators. This is particularly true with automatic gearboxes
and soon even more so with hybrid cars. Cruise control is helpful when driving on the open road.
It is
of little use to the driver, however, when bad weather prevents safe use in
urban areas or in denser traffic. When cruise control is disengaged
the driver has to watch carefully --- both the surrounding traffic and the
speedometer. The Speed Sensitive Accelerator Pedal (patented in both the USA and the EU) is a new cooperative driver support system which allows an intuitive mastering of speed. It never has to be disengaged or reset, even in heavy urban traffic. It improves comfort and safety, relaxes drivers and leaves their attention entirely free to focus on the driving task. However, despite its effectiveness, it never deprives driver of their ability or responsibility for decision making. Operation The
Speed Sensitive Accelerator doesn't
control the engine management system but only the pedal force feedback. The gas
pedal can be a standard one (e.g., with a
Bowden cable) or a new 'drive-by-wire' gas pedal.
Speed Sensitive Accelerator System Overview The Speed Sensitive Accelerator is composed of an electronic control unit, a speed selector with a display, and an innovative 'feel forces actuator' linked to the gas pedal. The driver can preset three usual
speeds from 20 to 200 km/h (12 to 120 mph), then recall when necessary the
desired target speed to achieve. The driver can also select at any time the
desired instantaneous
speed.
When
the actual speed reaches the selected speed, the actuator transforms the error
of speed into a proportional Force
Feedback on the accelerator pedal. The natural balance between the
foot weight and the force feedback moves the pedal smoothly and stabilizes the speed
around the selected speed. The value of the force and the progressiveness of the
action are monitored by the actuator. The feeling is always 'soft' and the use of the system is completely intuitive. The driver can slow down by relaxing the accelerator pedal, or overpass the specified speed by exercising a moderate but voluntary pressure on the pedal. Furthermore, the Feel Forces Accelerator detects when the driver wants to dramatically accelerate (by the speed of the movement pedal) and inhibits quickly the return force for a preset time. The Speed Sensitive Accelerator is efficient and user-friendly in any traffic condition and at any speed -- even at very low speeds. It can work in combination with conventional cruise control or an ACC (Automatic Cruise Control) system to extend speed assistance from the highways to the urban areas. The features of the actuator are such that it cannot accelerate the car by itself or actually prevent the driver from accelerating or slowing. In case of a total system failure, the driver will experience only a limited and easily-overcome “hardening” of the accelerator pedal.
This synoptic shows a speed application, as implemented using a specific software approach. Note that the haptic gas pedal is also a generic Human-Machine Interface that can be used for other longitudinal control systems in the field of intelligent vehicle applications. The software can include other safety functions as well (for example, a rear obstacle sensing system). When a dangerous situation occurs, the force feedback increases quickly and improves driver vigilance and reflex time. The
haptic principles of this system make it akin to the well known "feel forces control" of
modern aircraft. The
actuator itself is a relatively cheap and simple mechatronic device, but its specific design
-- using a
passive force transducer -- presents unique
behavioral qualities :
Feel Forces Actuator The actuator is a servomechanism, which controls the return Force of the pedal by means of a controlled-position. Details of the operation are provided below -- refer to this chart for an explanation of the numbers.
Operation: Control
of the return force is performed by a triangulation system (4,5,6) subjected to
the large initial tensile force of a spring (2). The return force (F) exerted by the lever on the pedal is controlled by the position of the spring anchor point (5), as a function of the speed difference. When point (5) is superposed on the axis (4) the return force is zero. It progressively increases when point (5) moves from (4) according the control of the ECU. The geometry of the mechanism and the large initial tensile force of the spring result in a return force that is only slightly dependent on the pedal movements: the force under the driver's foot is thus permanently controlled, soft, and perfectly resilient, without localized 'hardness.' The behavioral characteristics have been adapted for even greater comfort: the software controls the progressiveness with which the force increases or decreases and it can quickly release the force in particular situations. Advantages of the system include: •
The force is adjusted by a "passive" mechanism, with no
reaction time • The actuator acts in adjustments only; thus its performances are not critical and its workload is low (the motor is often stopped) •
Low cost of manufacture. •
The device is intrinsically a "positive safety device;" it doesn't need a safety clutch and no malfunction can endanger
the safety of the vehicle.
Actuator This
photo shows the prototype of an active pedal including the actuator, compatible
with a Bowden cable or a drive by wire sensor. The position sensor is back the
worm gear. It is a "hand made" prototype and an industrial product
will be more compact.
Combination of the Sensitive Accelerator and the Cruise Control A) The cruise control or ACC mode : on highways, drivers may normally use the cruise control (or ACC), with right foot free. Moreover, the active gas pedal allows drivers to put a foot down on the accelerator pedal, in the normal vicinity of the brake pedal, by controlling a sufficient return force under the pedal. Experience has confirmed that drivers feels no discomfort when they decide to accelerate, since the Feel Forces Accelerator instantaneously detects the driver's intention and releases the force quickly. B) The "Speed Sensitive Accelerator mode" : when the traffic circumstances or the driver's choice are ill-suited to the cruise control, the Speed Sensitive Accelerator delivers speed assistance by the controlled return force. This mode is also automatically activated from the previous mode if conditions of cruise control disconnection occur (braking, heavy traffic, etc.). Both modes have the same selected speed. The transition from one mode to the other will be totally natural and the driver never loses the speed assistance -- thus preventing driver distraction as well. In the case where an ACC is used, the ACC gap-keeping technology can keep the distance function for the "safe headway" while the force feedback pedal is activated. This combination is easy to manage from the same user interface. Ergonomics The first graph shows a law well known by experts in ergonomics : how a driver feels the gas pedal when the return force increases.
The return force of a standard accelerator pedals is about 20N when the pedal is up. It is between 40 and 60N when the pedal is down, more often around 40N. These values are in accordance with ergonomic recommendations for an accelerator pedal: the driver can move the pedal frequently without fatigue.
The Feel Forces Accelerator adds a variable return force, from zero to a maximum value, which is programmable (30N full scale for the prototype). This force increases progressively when the speed reaches the specified speed. Thus the driver's foot becomes unconsciously “lighter” and rises up with a soft and natural movement. This determines a new position of the pedal and a stable speed close to the specified speed with a perfect damping. The first graph shows that a modulated force of only 20N is enough for a measurable result. The Feel Forces Accelerator brings, in fact, a more efficient result because the modulated return force is not static, as is the return force of a normal pedal, but dynamic. Small changes in the usual values are enough to modify the balance between the foot force and the pedal force. Therefore the driver’s foot unconsciously follows the pedal. Thus the speed remains stable with a return force more often small and always pleasant. When the speed is around the selected speed, the small error of speed (+/- 3km/h) adjusts the right return force automatically. If the driver's foot is a bit "heavy," error of speed increases the force. If the foot is "light," error of speed decreases the force. After
a short time of use, the driver unconsciously adjusts behavior to achieve a good
balance, as with a normal pedal. The Feel Forces Accelerator is particularly
efficient and comfortable with modern cars, which often have a normal return force
near 40N. The force remains always moderate and the
active pedal is more comfortable than a normal pedal. Drivers actually find using
it to be enjoyable. The
adaptation of the pedal to what the driver expects suggests a 'friendly recommendation,'
and never produces a feeling of constraint. The Feel Forces Accelerator brings serenity and
increases safety, especially in bad visibility situations. It is important to note that the highest pedal force is mechanically limited; thus the force can’t overwhelm the driver -- the pedal can be pushed down easily at any time without diffculty. Recent Developments Many automotive engineers in the world are currently working on Intelligent Speed Adaptation and other Intelligent Vehicle systems which require a cooperative Human Machine Interface. Several experiments show that the Speed Sensitive Accelerator is particularly suitable to enhance such driver assistance systems. Some European car manufacturers already have ongoing projects using this HMI to develop an Intelligent Speed Limiter -- one that would be more pleasant and useful than the standard solution which tends to have a "dead pedal" effect. With a simple software adaptation, the same device would be able to cooperate with an ACC in assistance mode. The accelerator pedal has changed almost none since its automotive origins. In the near future it will be evolve to become active and "intelligent" to assist the broader goal of more comfortable and safer motoring. A final note on intellectual property: patents for
teh Speed Sensitive Accelerator are in force in USA and several European countries. [Top] ...
contact alain.landerretche@wanadoo.fr
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May 2002 |
