GB2442492A

GB2442492A - Vehicle speed control

Info

Publication number: GB2442492A
Application number: GB0619525A
Authority: GB
Inventors: Christophe Gillett
Original assignee: Autoliv Development AB
Current assignee: Autoliv Development AB
Priority date: 2006-10-03
Filing date: 2006-10-03
Publication date: 2008-04-09
Also published as: GB0619525D0; WO2008041899A1

Abstract

A safety system for a vehicle has a prediction arrangement, such as a GPS device, which provides information about the path of the road on which the vehicle is driving, a curve identification device for identifying critical curves on the road ahead of the vehicle, means to determine the safe maximum speed of the vehicle around the curves and a processor to determine a maximum safe braking amount for the vehicle so that a signal can be produced to assist in reducing the speed of the vehicle.

Description

Ref: P21123GB A Vehicle Safety System

Description of Invention

THIS INVENTION relates to a vehicle safety system, and in particular concerns a system for assisting a driver of a vehicle in negotiating sharp curves at a safe speed.

It has previously been proposed to provide a system for determining whether a vehicle travelling along a road is approaching one or more sharp curves, and this can be achieved, for example, by using stored map of the surroundings of the vehicle in conjunction with a positioning system such as GPS. It has further been proposed to determine a maximum speed at which a sharp curve can be safely negotiated, and to apply automatic braking if it appears that, without such measures, the vehicle will enter the curve at a speed that is too high to be deemed safe. Systems of this type are disclosed, for example, in published US Patent Applications Nos. US2005/0187694 and US2005/0251 335.

It is an object of the present invention to seek to provide an improved vehicle safety system of this type.

Accordingly, one aspect of the present invention provides a safety system for a vehicle, comprising: a prediction arrangement operable to provide information regarding the curvature of a road on which the vehicle is travelling; a curve identification arrangement for identifying critical curves on a portion of the road ahead of the vehicle, and a safe maximum speed at which the vehicle may safely negotiate a critical curve; a processor for determining, for each part of the road between the position of the vehicle and a critical curve, a maximum safe retardation based at least partly on the curvature of the road; and a signal generation arrangement for generating an output signal to assist in reducing the speed of the vehicle in response to the current vehicle speed, the maximum speed for the critical curve and the determined safe retardation for the road between the position of the vehicle and the critical curve.

Advantageously, the maximum safe retardation is based at least partly on the coefficient of friction between the vehicle and the road surface.

Preferably, the safety system further comprises a friction determining arrangement operable to estimate the coefficient of friction.

Conveniently, the friction determining arrangement takes into account the ambient temperature, past or current weather conditions and/or the structure of the road surface in estimating the coefficient of friction between the vehicle and the road surface.

Advantageously, the safety system further comprises a memory arrangement operable to store values for the coefficient of friction between the vehicle and the road surface.

Preferably, a current speed is calculated by integrating the maximum safe retardation from the current vehicle position to the critical curve and adding the integrated retardation to the maximum speed for the critical curve, the output signal being generated in response to the current speed and the current maximum speed.

Advantageously, the output signal is generated if the current speed exceeds the current maximum speed.

Conveniently, a curve is classified as critical if the maximum safe speed at which the curve may be negotiated safely is lower than the current speed of the vehicle.

Advantageously, if the vehicle is travelling above a warning speed, which is less than the current maximum speed, the signal generation arrangement generates an output signal to provide a warning to the driver.

Preferably, if the current vehicle speed exceeds the current maximum speed, the signal generation arrangement generates an output signal to apply automatic braking to the vehicle.

Conveniently, the automatic braking applied to the vehicle is calculated to reduce the speed of the vehicle at the maximum safe retardation rate for the part of the road on which the vehicle is travelling.

Advantageously, if the vehicle speed exceeds the current maximum speed, the signal generation arrangement generates an output signal to reduce the speed of the vehicle at the maximum safe retardation rate.

Preferably, a maximum comfortable retardation rate is calculated for each part of the road between the position of the vehicle and a critical curve, and a maximum current safe speed is calculated by integrating the maximum comfortable retardation rate between the current vehicle position and the critical curve, the signal generation arrangement generating an output signal to apply automatic braking to the vehicle at the maximum comfortable retardation rate if the current speed exceeds the current safe speed.

Conveniently, a lowest possible speed at the critical curve, based on the current vehicle speed, is determined by integrating the maximum possible retardation between the current vehicle position and the critical curve and subtracting the integrated retardation from the current speed, the output signal being generated in response to the lowest possible speed exceeding the maximum speed for the critical curve.

Advantageously, estimated or stored values for lateral slope of the road are used in calculating the maximum safe speed for the critical curve.

Preferably, estimated or stored values for longitudinal slope of the road are used to calculate the maximum safe speed for the critical curve.

Conveniently, a maximum speed at which the critical curve may be negotiated without lateral slipping occurring, and a maximum speed at which the critical curve may be negotiated without the vehicle rolling, are calculated, and the overall maximum speed for the critical curve is selected as being the lowest of thesetwo speeds.

Advantageously, if the curve identification arrangement identifies more than one critical curve, the critical curve having the lowest maximum speed is used in determining the lowest maximum speed of the vehicle.

Preferably, the prediction arrangement comprises a positioning system and a stored map of the vehicle surroundings Another aspect of the present invention provides a vehicle incorporating a safety system according to any preceding claim.

A further aspect of the present invention provides a computer program comprising computer program means adapted to perform all of the steps of any of the above when run on a computer.

Another aspect of the present invention provides a computer program according to the above, embodied on a computer-readable medium.

In order that the present invention may be more readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying figures, in which: Figure 1 is a schematic representation of a road which includes a critical curve; Figure 2 is a graph of vehicle speed along the road depicted in figure 1; and Figure 3 shows forces acting on a vehicle during braking.

With reference to figure 1, this figure shows a schematic view of a road, seen from above, along which a vehicle is travelling. The vehicle (not shown) is initially at position x0, and is travelling along the road (to the right as shown in figure 1) at an initial speed v0.

The vehicle is provided with a prediction arrangement, which is operable to provide information regarding the curvature of the road on which the vehicle is travelling, and in particular the curvature of the road that is ahead of the vehicle. In preferred embodiments of the invention, the prediction arrangement relies upon a combination of a stored map of the vehicle surroundings and a positioning system, such as GPS, to identify the position and direction of travel of the vehicle, and hence to identify which sections of road will be encountered as the vehicle progresses.

A curve identification arrangement analyses the road ahead of the vehicle, and identifies curved section of road that will be encountered by the vehicle.

In the example of the road shown in figure 1, it is determined by the curve identification arrangement that the road comprises three substantially straight sections (from points x0 to x,, x2 to x3 and x4 to x5) and three curved sections (between points x1 and x2, x3 and x4 and x5 and x6). The curve between points x5 and x6 is classified as a critical curve, since there appears to be a risk of entering the curve at too high a speed. In preferred embodiments of the present invention, a curve is classified as critical if the maximum speed at which the curve be safely negotiated by the vehicle (discussed in more detail below) is less than the current vehicle speed.

It is envisaged that, for a curve in a road on which the vehicle is travelling, two maximum speeds will be determined, namely vmax, which is the maximum speed at which the vehicle may negotiate the curve without sliding laterally, and which is the maximum speed at which the vehicle may negotiate the curve without rolling over. These safe maximum speeds may be defined by the following formulae: VM =11.28./('r0 +tan/3).r (inkph) /road tanfl Where rk is the road curvature at a given point of the road, 3 is the angle of bank of the curve and Mroad is the coefficient of friction between the vehicle tyres and the road surface, and (b 2.h +tan/3J.rk v=lI.28. (inkph) 1-*tan/J 2. h Where b is the vehicle track width (i.e. the distance between the left and right-side tyres) and h5 is the height of the centre of gravity of the vehicle.

For each curved section of the road that is identified by the curve identification arrangement, the maximum speeds can be compared to the current vehicle speed, and this allows the classification of curves as critical if the current vehicle speed exceeds either of these maximum speeds. In preferred embodiments, the lowest of these two safe speeds is selected and determined to be the overall maximum speed for as particular curved section of road.

h is a property of an individual vehicle, and should not vary greatly depending on the number of occupants of the vehicle. Clearly, h will be significantly different for a vehicle such as a sports car compared to a sports utility vehicle (SUV) and the type of vehicle that is being driven will dictate the value of the v. The parameters 13 and J.iroad may be determined either by dedicated sensors, as is known in the art, or may be estimated from dynamic parameters of the vehicle. Alternatively, or in addition, stored information may be used to calculate these parameters. The estimated coefficient of friction may also be set manually, for instance by allowing the driver to include the type of road surface and for current road conditions. Detected weather conditions, including the presence of water or ice on the road surface, may also be taken into account.

Returning to the example of figure 1, the curved portions of road between points x1 and x2 and between points x3 and x.4 are not considered to be critical, since the current vehicle speed, v0, is less than the determined maximum speeds for these curves. However, the curved portion of road between points x5 and x6 is classified as a critical curve, since the current vehicle speed is higher than the maximum speed for this curve.

If the critical curve is to be negotiated safely, therefore, the speed of the vehicle will need to be reduced before the vehicle reaches the beginning of the curve. To this end, the vehicle further comprises a processor for determining, for each part of the road between the current vehicle position and the critical curve, a maximum safe retardation. This safe rate of retardation is based at least partly upon the curvature of the road.

For straight or substantially straight portions of road, the maximum safe retardation rate may be expressed as -p g. However, for curved portions of road, the maximum safe retardation rate is less, and may expressed as IaxLax I(p.g)2 -a where a rk For a curved section of road, it is not possible to use all of the frictional force between the road surface and the car tyres for braking, because some of this force must be used for lateral acceleration as the car negotiates the curve.

Referring to figure 3, it can be seen that, if a car is turning right and simultaneously braking, the frictional force between the road surface and the tyres of the car must have a lateral component, and hence the "braking' component of the force (which points directly downwards in figure 3) is less than if the vehicle was travelling in a straight line.

Referring to figure 2, a graph is shown of possible vehicle speeds as a vehicle progresses along the road shown in figure 1. The topmost line of the graph, designated as Vmax, indicates the absolute maximum speed that the vehicle may have on all parts of the road if the vehicle is to enter the critical curve at the determined maximum speed. A vehicle travelling in this manner will be applying the maximum retardation rate along all parts of the road as the critical curve is approached, arriving at the entrance to the critical curve at the maximum speed for negotiating the curve, It will therefore be understood that speed vomax, which is the speed of the vehicle at point x0, is the fastest speed at which the vehicle may enter the section of road depicted in figure 1 if the critical curve is to be negotiated safely. If a vehicle was to enter this section of road at a speed higher than vomax, even if the maximum retardation was applied thereafter at all times between points x0 and x5, the vehicle would still enter the critical curve at a speed higher than the maximum speed for this curve.

At any moment, the current maximum speed may be calculated by integrating the maximum safe retardation from the current vehicle position to the critical curve, and adding the integrated retardation to the maximum speed at which the critical curve can be negotiated. An alternative, but broadly equivalent method is to determine, at any moment, a lowest possible speed at which the vehicle can reach the critical curve, by integrating the maximum possible retardation between the current vehicle position in the critical curve and subtracting the integrated retardation from the current vehicle speed.

It is generally desired to avoid applying the maximum retardation to the vehicle, for reasons of driver and passenger comfort and safety. It is therefore envisaged that a safety margin will be built into the determined maximum retardation, for instance by assuming a coefficient in friction tsafe which is 80% of the real coefficient of friction, or by assuming that the maximum safe speed vsafe is 90% of the real maximum speed vmax. A maximum comfortable retardation rate is therefore established, and the maximum safe speed (i.e. the maximum speed at which the vehicle can be decelerated by an appropriate amount before the start of the critical curve using the maximum comfortable retardation rate) is also indicated on figure 2. It will be understood that the slope of Vsafe in figure 2 is less than that of Vmax, indicating a lesser rate of retardation.

A warning speed Vrfl, which is less than Vsafe, is also indicated on figure 2. At this speed, which is close to the maximum safe speed, it is preferred that a warning should be given to the driver of the vehicle.

The initial speed of the vehicle in the example shown in figure 1 vo, is also marked on figure 2. It can be seen that, as the vehicle passes along the sections of road between points x0 and x1 and x, and x2, the speed is less than Vsafe, and hence, taking into account the critical curve which is ahead of the vehicle, the vehicle is not travelling at an excessive speed.

However, between points x2 and x3, the speed of the vehicle becomes equal to, and rises above, the speed Vwarn at which a warning should be provided to the vehicle driver. At this point, a signal generation arrangement of the safety system provides an output signal to a warning system, which provides the driver with a visual, audible and/or other warning, which may take any suitable form.

In the example shown in figure 2, the driver does not reduce the vehicle speed in response to the warning (which will be discussed in more detail below) and maintains the initial speed v0 of the vehicle. At a later time, the speed of the vehicle becomes equal to Vsafe, and at this point the signal generation arrangement generates an output signal to assist in reducing the speed of the vehicle. In preferred embodiments of the invention, the output signal causes automatic braking of the vehicle at the maximum safe retardation rate. As discussed above, this maximum safe or comfortable retardation rate is greater along straight portions of road, and is reduced along curved portions of road.

The automatic braking continues between points x3 and x4 and x4 and x5, so that, when the vehicle enters the critical curve at point x5, the vehicle speed is below the determined maximum speed at which the vehicle may safely negotiate the critical curve.

It wilt therefore be appreciated that, in use of the safety system, automatic braking is applied to reduce the speed of the vehicle, at a rate which will be both safe and comfortable along all portions of the road approaching the critical curve, to ensure that the speed of the vehicle on entering the critical curve is not too high to negotiate the curve safely.

If the curve identification arrangement determines that several curves which may be classified as critical are ahead of the vehicle, the safe speed for the vehicle is determined to be the speed at which the most severe curve (i.e. that requiring a lowest maximum speed) may be negotiated safely.

While a maximum comfortable rate of retardation is defined, being less than the maximum rate of retardation, if at any point the safety system determines that the vehicle is travelling towards a critical curve at a speed which requires a more rapid rate of retardation, the automatic braking will be applied in such a manner as to reduce the speed of the vehicle at the maximum retardation rate.

In such circumstances, avoiding a crash or skid is deemed to be of greater importance than the comfort of the vehicle occupants during automatic braking.

In identifying curved sections of road ahead of the vehicle, the curve identification arrangement will generally attempt to identify sections of road that are substantially straight, and these may be defined as having a curvature below a predetermined threshold. Other sections of road having a curvature above this threshold will be designated as curved sections of road.

It is appreciated that, in reality, a road may consist of a series of sequential curves, with the radius of curvature altering continuously along the road. In such cases, the curve identification arrangement will attempt to identify sections of road which have a substantially constant radius of curvature, so that a maximum safe or comfortable retardation rate can be determined for these curved sections. However, this will not always be possible, and if the radius of curvature of the road is continually variable then it may be necessary simply to divide the road ahead of the vehicle into sections of a predetermined length (for instance, 50m, lOOm or 200m), and to take an average radius of curvature for each section.

In this specification, an output signal to assist in reducing the speed of the vehicle may consist only of a signal for the generation of a warning to be provided to the driver, and in such embodiments it is hoped that the driver will be prompted to take action to reduce the vehicle speed. This may occur without any active control of the vehicle's driving systems. It should also be appreciated that active control of the vehicle's driving systems (e.g. braking and steering) may also occur, alternatively or in combination with a warning, in response to the output signal.

It will be appreciated that embodiments of the present invention provide a safety system that will reduce the risk of accidents caused by skidding and rolling over as vehicles attempt to negotiate sharp curves.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1. A safety system for a vehicle, comprising: a prediction arrangement operable to provide information regarding the curvature of a road on which the vehicle is travelling; a curve identification arrangement for identifying critical curves on a portion of the road ahead of the vehicle, and a safe maximum speed at which the vehicle may safely negotiate a critical curve; a processor for determining, for each part of the road between the position of the vehicle and a critical curve, a maximum safe retardation based at least partly on the curvature of the road; and a signal generation arrangement for generating an output signal to assist in reducing the speed of the vehicle in response to the current vehicle speed, the maximum speed for the critical curve and the determined safe retardation for the road between the position of the vehicle and the critical curve.

2. A safety system according to Claim 1, wherein the maximum safe retardation is based at least partly on the coefficient of friction between the vehicle and the road surface.

3. A safety system according to Claim 2, further comprising a friction determining arrangement operable to estimate the coefficient of friction.

4. A safety system according to Claim 3, wherein the friction determining arrangement takes into account the ambient temperature, past or current weather conditions and/or the structure of the road surface in estimating the coefficient of friction between the vehicle and the road surface.

5. A safety system according to any preceding claim, further comprising a memory arrangement operable to store values for the coefficient of friction between the vehicle and the road surface.

6. A safety system according to any preceding claim, wherein a current maximum speed is calculated by integrating the maximum safe retardation from the current vehicle position to the critical curve and adding the integrated retardation to the maximum speed for the critical curve, the output signal being generated in response to the current speed and the current maximum speed.

7. A safety system according to Claim 6, wherein the output signal is generated if the current speed exceeds the current maximum speed.

8. A safety system for a vehicle according to Claim 6 or 7, wherein a curve is classified as critical if the maximum safe speed at which the curve may be negotiated safely is lower than the current speed of the vehicle.

9. A safety system according to any one of Claims 6 to 8 wherein, if the vehicle is travelling above a warning speed, which is less than the current maximum speed, the signal generation arrangement generates an output signal to provide a warning to the driver.

10. A safety system according to any one of Claims 6 to 9 wherein, if the current vehicle speed exceeds the current maximum speed, the signal generation arrangement generates an output signal to apply automatic braking to the vehicle.

11. A vehicle safety system according to Claim 10, wherein the automatic braking applied to the vehicle is calculated to reduce the speed of the vehicle at the maximum safe retardation rate for the part of the road on which the vehicle is travelling.

12. A safety system according to Claim 11 wherein, if the vehicle speed exceeds the current maximum speed, the signal generation arrangement generates an output signal to reduce the speed of the vehicle at the maximum safe retardation rate.

13. A safety system according to any one of Claims 6 to 12, wherein a maximum comfortable retardation rate is calculated for each part of the road between the position of the vehicle and a critical curve, and a maximum current safe speed is calculated by integrating the maximum comfortable retardation rate between the current vehicle position and the critical curve, the signal generation arrangement generating an output signal to apply automatic braking to the vehicle at the maximum comfortable retardation rate if the current speed exceeds the current safe speed.

14. A safety system according to any preceding claim, wherein a lowest possible speed at the critical curve, based on the current vehicle speed, is determined by integrating the maximum possible retardation between the current vehicle position and the critical curve and subtracting the integrated retardation from the current speed, the output signal being generated in response to the lowest possible speed exceeding the maximum speed for the critical curve.

15. A safety system according to any preceding claim, wherein estimated or stored values for lateral slope of the road are used in calculating the maximum safe speed for the critical curve.

16. A safety system according to any preceding claim, wherein estimated or stored values for longitudinal slope of the road are used to calculate the maximum safe speed for the critical curve.

17. A safety system according to any preceding claim, wherein a maximum speed at which the critical curve may be negotiated without lateral slipping occurring, and a maximum speed at which the critical curve may be negotiated without the vehicle rolling, are calculated, and the overall maximum speed for the critical curve is selected as being the lowest of these two speeds.

18. A safety system according to any preceding claim wherein, if the curve identification arrangement identifies more than one critical curve, the critical curve having the lowest maximum speed is used in determining the lowest maximum speed of the vehicle.

19. A safety system according to any preceding claims, wherein the prediction arrangement comprises a positioning system and a stored map of the vehicle surroundings.

20. A vehicle incorporating a safety system according to any preceding claim.

21. A computer program comprising computer program means adapted to perform all of the steps of any of claims I to 19 when run on a computer.

22. A computer program according to Claim 21, embodied on a computer-readable medium.

23. A safety system substantially as hereinbefore described, with reference to the accompanying drawings.

24. A vehicle substantially as hereinbefore described, with reference to the accompanying drawings.

25. A computer program substantially as hereinbefore described, with reference to the accompanying drawings.

26. Any novel feature or combination of features disclosed herein.