Method and apparatus for adaptive cruise control in a road vehicle
A method and an apparatus are described for adaptive cruise control in a road vehicle, as well as a road vehicle including such an apparatus. One of four control regions is determined and a set of control parameters chosen in dependence of the detected control region. An acceleration command is provided, based on the chosen set of control parameters, using a sliding surface and a control law that ensures convergence to the sliding surface.
1. A method for adaptive cruise control in a host vehicle, the method comprising:
monitoring a range and a range rate between the host vehicle and a target vehicle travelling in front;
monitoring a speed of the host vehicle;
determining a control region of the host vehicle by
comparing the range between the host vehicle and the target vehicle to a set-point range; and
if the range between the host vehicle and the target vehicle is greater than the set-point range, comparing the range rate between the host vehicle and the target vehicle with a first threshold range rate between the host vehicle and the target vehicle and determining a first control region if the range rate between the host vehicle and the target vehicle is greater than the first threshold range rate, and determining a second control region if the range rate between the host vehicle and the target vehicle is below the first threshold range rate;
if the range between the host vehicle and the target vehicle is less than the set-point range, comparing the range rate between the host vehicle and the target vehicle with a second threshold range rate between the host vehicle and the target vehicle, and determining a third control region if the range rate between the host vehicle and the target vehicle is greater than the second threshold range rate, and determining a fourth control region if the range rate between the host vehicle and the target vehicle is below the second threshold range rate;
choosing a set of control parameters specific for the determined control region of the host vehicle;
determining an acceleration command based upon the chosen set of control parameters applied to a sliding surface control law, wherein the chosen set of control parameters includes a first control parameter that controls the relative velocity the host vehicle should accelerate/decelerate to in order to achieve the set-point range, a second control parameter that controls how the host vehicle should accelerate/decelerate to adjust its position in order to achieve the set-point range, and a third control parameter that determines the speed of convergence to the sliding surface; and
utilizing the acceleration command to control operation of the host vehicle.
2. The method according to claim 1 wherein the sliding surface control law comprises a sliding surface, which once reached will never be left until the set-point inter-vehicle range is attained and a convergence sequence to that sliding surface.
3. The method according to claim 2 wherein the sliding surface is defined as
σ( x )=α 1 x 1 +a 2 x 2 =0
where (σ(x)) is the sliding surface, x 1 is the range and x 2 the range rate between the host vehicle and the target vehicle travelling in front of the host vehicle, and α 1 and α 2 are control parameters.
4. The method according to claim 2 wherein the sliding surface control law is piecewise constant depending on which side of the sliding surface the actual operating region is in.
5. The method according to claim 3 wherein the sliding surface control law that ensures convergence to the sliding surface is
u
=
-
1
α
2
(
-
α
1
x
2
+
μ
sign
(
σ
(
x
)
)
)
where x 1 is the range and x 2 the range rate between the host vehicle and the target vehicle travelling in front of the host vehicle, and α 1 , α 2 and μ are control parameters and σ(x) is the sliding surface.
6. The method according to claim 1 wherein the sliding surface control law, in order to compensate for target vehicle acceleration comprises an additional compensation term such that the control law is
u
=
-
1
α
2
(
-
a
1
x
2
-
α
2
x
¨
Target
+
μ
sign
(
σ
(
x
)
)
)
where x 1 is the range and x 2 the range rate between the host vehicle and the target vehicle travelling in front of the host vehicle, and α 1 , α 2 and μ are control parameters and σ(x) is the sliding surface and −α 2 {umlaut over (x)} Target is the target vehicle acceleration compensation term.
7. An apparatus for adaptive cruise control of a host vehicle, the apparatus comprising:
a measuring device or devices capable of sensing presence, range, and a range rate, between the host vehicle and a target vehicle in the same lane of travel;
a set-point calculating device arranged to receive a driver selected headway as well as a host vehicle velocity and range rate between the host vehicle and the target vehicle traveling in front of the host vehicle and calculate and output a set-point range;
a region detection unit that, from the set-point value, along with the range and range rate between the host vehicle and the target vehicle as well as a first threshold range rate and a second threshold range rate, is configured to detect one of four pre-determined control regions and output a signal representative thereof;
three switches, each one of which is configured to, based on the signal representative of the determined control region, select a control parameter appropriate for the determined control region from a plurality of control parameters; and
an acceleration control module arranged to provide an acceleration command based on the control parameters from the first, second and third control parameter switches as well as the range and range rate between the host vehicle and the target vehicle;
wherein the apparatus is configured to
monitor the range and the range rate between the host vehicle and the target vehicle;
monitor a speed of the host vehicle;
determine the control region of the host vehicle by
comparing the range between the host vehicle and the target vehicle to the set-point range; and
if the range between the host vehicle and the target vehicle is greater than the set-point range, comparing the range rate between the host vehicle and the target vehicle with a first threshold range rate between the host vehicle and the target vehicle and determine a first control region if the range rate between the host vehicle and the target vehicle is greater than the first threshold range rate, and determining a second control region if the range rate between the host vehicle and the target vehicle is below the first threshold range rate;
if the range between the host vehicle and the target vehicle is less than the set-point range, comparing the range rate between the host vehicle and the target vehicle with a second threshold range rate between the host vehicle and the target vehicle, and determining a third control region if the range rate between the host vehicle and the target vehicle is greater than the second threshold range rate, and determining a fourth control region if the range rate between the host vehicle and the target vehicle is below the second threshold range rate;
choose a set of control parameters specific for the determined control region of the host vehicle;
determine the acceleration command based upon the chosen set of control parameters applied to a sliding surface control law, wherein the chosen set of control parameters includes a first control parameter that controls the relative velocity the host vehicle should accelerate/decelerate to in order to achieve the set-point range, a second control parameter that controls how the host vehicle should accelerate/decelerate to adjust its position in order to achieve the set-point range, and a third control parameter that determines the speed of convergence to the sliding surface; and
utilize the acceleration command to control operation of the host vehicle.
8. A road vehicle comprising an apparatus for adaptive cruise control of a host vehicle according to claim 7 .