U.S. patent application number 15/933926 was filed with the patent office on 2019-09-26 for method of determining gap spacing for vehicles in platoons.
The applicant listed for this patent is Southwest Research Institute. Invention is credited to Thomas E. Reinhart.
Application Number | 20190294180 15/933926 |
Document ID | / |
Family ID | 67984434 |
Filed Date | 2019-09-26 |
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United States Patent
Application |
20190294180 |
Kind Code |
A1 |
Reinhart; Thomas E. |
September 26, 2019 |
Method of Determining Gap Spacing for Vehicles in Platoons
Abstract
A method of determining the optimum vehicle gap distance for a
vehicle in a platoon, the vehicle having a cooling fan and a
coolant-based cooling system. The vehicle's vehicle control system
determines a base gap distance, based on safety considerations
related to platoon operation. A gap control process stores a fan
turn-on threshold temperature, which is less than the coolant
temperature that will result in the vehicle's cooling fan becoming
activated. During vehicle operation, the gap control process
receives a current coolant temperature value, and compares that
value to the fan turn-on threshold temperature. If the coolant
temperature is at or above the fan turn-on threshold temperature,
the vehicle is operated to increase the base gap distance.
Inventors: |
Reinhart; Thomas E.;
(Boerne, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Southwest Research Institute |
San Antonio |
TX |
US |
|
|
Family ID: |
67984434 |
Appl. No.: |
15/933926 |
Filed: |
March 23, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B60K 11/06 20130101;
G05D 2201/0213 20130101; B60W 2556/65 20200201; B60W 30/16
20130101; B60K 11/04 20130101; B60W 2556/45 20200201; G08G 1/22
20130101; G05D 1/0295 20130101; B60W 30/165 20130101 |
International
Class: |
G05D 1/02 20060101
G05D001/02; B60K 11/06 20060101 B60K011/06; G08G 1/00 20060101
G08G001/00; B60W 30/16 20060101 B60W030/16; B60K 11/04 20060101
B60K011/04 |
Claims
1. A method of determining the optimum gap distance for a following
vehicle in a platoon, the vehicle having a cooling fan and a
coolant-based cooling system, comprising: storing a fan turn-on
threshold temperature, representing a coolant temperature at or
above which the cooling fan will become activated; determining a
base gap distance, representing a gap distance from another vehicle
in front of the vehicle, the base gap distance based on the
following vehicle's braking capability; receiving a current coolant
temperature value; comparing the coolant temperature value to the
fan turn-on threshold temperature; if the coolant temperature is
below the fan turn-on threshold temperature, operating the vehicle
to maintain the base gap distance; and if the coolant temperature
is at or above the fan turn-on threshold temperature, operating the
vehicle to increase the base gap distance such that the fan is not
activated; and using a feedback loop of repeated coolant
temperature measurements to determine the amount of increase of the
base gap distance; and wherein coolant temperature is the only
parameter used for predicting fan activation.
2. The method of claim 1, wherein the safety considerations
comprise at least the minimum gap distance required to avoid a
collision with a preceding vehicle during a braking event.
3. The method of claim 1, wherein the step of operating the vehicle
to increase the base gap distance is performed by reducing engine
power.
4. The method of claim 1, wherein the step of operating the vehicle
to increase the base gap distance is performed by applying
braking.
5. The method of claim 1, wherein the coolant-based cooling system
has a radiator, and the coolant temperature is measured with a
thermometer at the radiator.
6. (canceled)
Description
TECHNICAL FIELD OF THE INVENTION
[0001] This invention relates to operating motor vehicles in
platoons, and more particularly to determining the optimal gap
spacing between the vehicles.
BACKGROUND OF THE INVENTION
[0002] Operating vehicles as a group, such as platoons (sometimes
also called convoys) is not new, but has become an area of research
for applications such as autonomous vehicles and automated
highways. Platoons and convoys are familiar in military
applications for a variety of vehicle types and terrain, but for
roadway travel, research is more recent.
[0003] The general concept of a platoon of vehicles on a roadway is
that the vehicles travel at a synchronized speed. The goal is to
reduce traffic accidents, increase road capacity, and provide more
efficient travel. The efficiency benefit results in part from
reduced aerodynamic drag. When a vehicle operates in the wake of
another vehicle, both vehicles experience a reduction in
aerodynamic drag. This effect applies, at least to some extent, to
all vehicle types from cars to large trucks.
[0004] The composition of a platoon need not be fixed. The platoon
may include a wide variety of vehicle types and sizes. Vehicles can
join and leave a platoon.
[0005] As compared to random traffic, platoons control the
distances between vehicles by using automated control processes.
This allows for a closer headway between vehicles by eliminating
reaction distance needed for human response. This capability allows
many cars or trucks to accelerate or brake simultaneously.
[0006] To optimize aerodynamic drag and thus fuel efficiency, a
platoon should drive with very little gap between vehicles, such as
one meter or less. However, other factors limit how close the
spacing in a platoon can be. For example, the response time of
vehicle controls and variations in braking capability must be taken
into account, so that vehicles do not hit each other during
acceleration, braking, or turning events. Safety considerations
regarding human operated vehicles that that might attempt to insert
themselves into a platoon may also limit how closely vehicles
within a platoon can operate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] A more complete understanding of the present embodiments and
advantages thereof may be acquired by referring to the following
description taken in conjunction with the accompanying drawings, in
which like reference numbers indicate like features, and
wherein:
[0008] FIG. 1 illustrates an example of vehicles traveling in
platoons on a roadway.
[0009] FIG. 1A illustrates an example similar to that of FIG. 1,
but with only semi-trucks in the platoon lane.
[0010] FIG. 2 illustrates a vehicle suitable for use in a platoon,
with automated driving controls and including a gap distance
control process in accordance with the invention.
[0011] FIG. 3 illustrates the gap distance control process of FIG.
2.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The following description is directed to a method of
determining gap spacing for vehicles traveling in a platoon. For
purposes of this description, a "platoon" is defined as a group of
vehicles traveling in single file. Typically, the vehicles will be
traveling on a roadway, but other applications are possible.
[0013] FIG. 1 illustrates a roadway 100 having three traffic lanes
for motor vehicles, with one lane being a platoon lane 101. In
platoon lane 101, one or more platoons of vehicles travel as a
group in a single line. In the example of FIG. 1, there are two
platoons of five vehicles and one platoon of three vehicles. The
number of vehicles in an actual platoon may vary from any number of
two or more.
[0014] For purposes of this description, it is assumed that the
"motor vehicles" in the platoon lane 101 are of a type designed to
travel on a roadway, such as an automobile, truck, bus, or similar
motor-driven conveyance. The vehicles may have any type of
powertrain, including internal combustion engines, electric motors,
or hybrids. The motor vehicles in a platoon may or may not be of
uniform size and type, that is, the platoon may be a "mixed
vehicle" platoon.
[0015] FIG. 1A illustrates an example of platoons, similar to that
of FIG. 1, but with only semi-trucks in the platoon lane 101. This
is a likely application of the gap spacing method of the present
invention.
[0016] Referring to both FIGS. 1 and 1A, each vehicle may or may
not have a driver, and thus, all or some of the vehicles may be
autonomous. The lead vehicle may or may not make executive
decisions. For purposes of this description, the significant
feature of each vehicle is a "vehicle gap distance control process"
on board each vehicle, which controls the gap spacing between
vehicles within a platoon.
[0017] The spacing between vehicles is referred to herein as the
"vehicle gap distance". In general, as the gap distance decreases,
the fuel economy benefit from platoon travel increases. However,
vehicle spacing is constrained by safety considerations, and in
particular, a vehicle's control system response time and
accuracy.
[0018] The following description is directed to the recognition
that heat generated by vehicle engines can be a significant factor
in determining an optimum gap distance between vehicles. This is
particularly true for heavier duty vehicles. As the gap distance
decreases, the amount of cooling air coming to the following
vehicle is reduced. If a point is reached where the following
vehicle's cooling fan is required, the fan's power demand can
eliminate fuel economy benefits or can even cause an increase in
fuel consumption. The gap distance at which a cooling fan will
activate depends on various factors, such as the design of the
cooling system, the ambient temperature and altitude, the roadway
grade, and amount of payload.
[0019] As explained below, and in accordance with the invention, a
vehicle gap control process on-board each vehicle in a platoon
determines that vehicle's gap spacing from the vehicle in front of
it. This gap distance need not be uniform for the various vehicles
in a platoon, especially if the vehicles are of different sizes and
types.
[0020] FIG. 2 illustrates an example of a vehicle 10 suitable for
use in a platoon that uses gap distance control in accordance with
the invention. It is assumed that each vehicle 10 in the platoon
has appropriate propulsion, braking, and steering mechanisms. It is
further assumed that vehicle 10 has a coolant-based cooling system
with a radiator 11 or other coolant system, as well as a cooling
fan 12. For purposes of this description, "coolant" can be any heat
transfer fluid, and the "coolant-based cooling system" can be any
cooling system that circulates such fluid.
[0021] FIG. 2 further illustrates a vehicle control system 200 for
the case in which vehicle 10 is autonomous. In more sophisticated
autonomous driving systems, decisions can be made based on data
communicated from one or more other vehicles, thus, control system
200 includes a data communications unit 201. However, as explained
below, the gap control process may also be implemented in vehicles
with less sophisticated vehicle control systems.
[0022] It is further assumed that each of the processes described
in FIG. 2 is implemented with appropriate processing and memory
hardware. The processes are further implemented with programming,
hardware or software, to perform the tasks described.
[0023] In the example vehicle of FIG. 2, the vehicle control system
200 is for a fully autonomous vehicle and includes a vehicle
control unit 202 and a path control process 203. However, as an
alternative to being fully autonomous, vehicle 10 could easily be
adapted to make driving and/or path movements based on data from a
lead vehicle. It is also possible the vehicle 10 could have a human
operator, with driving decisions made by or aided by vehicle
control system 200. For a vehicle whose acceleration and braking
are fully in control of a human, platooning may be impractical if
safety issues prevent a small enough gap for fuel benefit. However,
a human operated vehicle with a vehicle control system that
implements adaptive cruise control may be suitable for
platooning.
[0024] Vehicle control unit 202 controls the vehicle's steering,
velocity, and braking, in accordance with the path designated by
path control process 203 and gap control process 204. With regard
to path control process 203, various techniques for navigating a
path are known in the art of autonomous vehicles. The present
invention is directed to control of the distance between vehicles
in the platoon, using gap distance control process 204.
[0025] FIG. 3 illustrates gap distance control process 204 in
further detail. As explained below, process 204 determines a gap
distance for each vehicle pair, based on the cooling system
requirements of the following vehicle and any additional
limitations such as safety. Process 204 applies to vehicles having
a fan-assisted cooling system.
[0026] As indicated above, when the gap distance within a platoon
decreases, larger and more heavy-duty vehicles are more likely to
run into cooling issues than smaller vehicles. In typical highway
driving, large vehicles have a higher average power demand. For
example, to run a fully loaded semi-truck at 60 mph on level ground
requires 150 to 200 horsepower, whereas a small car might require
only 20 HP to run the same speed. Therefore, the large truck has
much higher heat rejection requirements. Also, the wind shadow, or
wake, behind a large truck (the area where limited cooling air is
available to a following vehicle) is much larger for a large
vehicle than for a small vehicle. Both of these factors (heat
rejection and wind shadow) require a larger distance gap for one
truck following another truck.
[0027] As indicated in Step 30, each vehicle stores a "fan turn-on
temperature" threshold. This threshold is a temperature slightly
below the coolant temperature at which the vehicle's cooling fan
will turn on. Typically, the fan turn-on temperature is measured at
the vehicle's radiator, but other measurement locations may be
used. A measure commonly referred to as the "top tank temperature",
measured at a location where hot coolant from the engine enters the
radiator, may be used.
[0028] Step 31 is performing a safety-based gap distance process. A
"base gap distance" is determined by determining the minimum
distance the vehicle may follow behind a preceding vehicle in the
platoon, based on the following vehicle's braking capability and
other safety considerations. It is assumed that this process
includes receiving appropriate input data representing the
vehicle's current speed and distance from the vehicle ahead of it,
and that the vehicle has appropriate sensors for determining this
data. The result of Step 31 is a current base gap distance.
[0029] Step 33 is receiving data representing the vehicle's current
coolant temperature and determining whether this temperature is
approaching the vehicle's fan turn-on temperature. The comparison
of temperatures can leave any desired margin below the fan turn-on
temperature as a threshold.
[0030] Basically, the idea is to keep each vehicle's (except for a
lead vehicle) coolant temperature just below the coolant
temperature that would cause that vehicle's cooling fan to turn on.
The cooling fan consumes power, thus running the fan has a fuel
economy penalty. A closer following distance reduces the
aerodynamic load on a truck, improving fuel economy until the point
where the fan comes on. Each vehicle in the convoy uses its own
coolant temperature to determine the spacing to the vehicle in
front of it. Each vehicle in the convoy determines its own spacing,
driven by its own cooling requirements. The most efficient platoon
operation occurs when the vehicles follow as closely as possible,
based on safety considerations and keeping the vehicle coolant
temperature of each following vehicle just below the point where
the cooling fan is required.
[0031] Referring again to FIG. 2, each platoon vehicle 200 is
equipped with a thermometer or other means for measuring the
coolant temperature. The current coolant temperature is typically
measured at the vehicle's radiator, but any measure may be used if
it can be used for a reliable comparison to the stored fan turn-on
temperature described above.
[0032] Step 34 is performed if the coolant temperature is below the
fan turn-on temperature threshold. In this case, the vehicle is
operated so as to maintain the base gap distance.
[0033] Step 35 is performed if the coolant temperature is at or
above the fan turn-on temperature threshold. In this case, the
vehicle is operated to increase the base gap distance. In most
cases, reducing engine power will be adequate to increase the gap
distance, but in rare cases, braking may be required. The amount of
increase to the gap distance is controlled by a coolant temperature
feed-back loop built in to the process of Step 33, combined with
the safety-based process of Step 31.
[0034] Referring again to FIG. 2, for implementation in a platoon
vehicle already equipped with a primary vehicle control system 202,
Steps 30 and 33 are performed by gap control process 204. The
vehicle control process 202 determines the base gap distance,
receives data from gap control process 204 to determine whether or
not to maintain the base gap distance, and operates the vehicle
accordingly.
[0035] The gap distance control process 204 is repeated at desired
intervals. The interval period may be constant, or it may be
decreased or increased depending on road conditions. For example,
conditions such as uphill travel, travel in hot climates, or
frequent changing of vehicles in the platoon, may call for a more
frequent monitoring of gap distances.
[0036] The above-described gap distance monitoring process is
useful for most vehicles, in that most vehicles from pickup trucks
and large SUVs on up to semi-trucks typically have engine-driven
cooling fans or relatively powerful electric-driven fans. Lighter
vehicles generally have less powerful electric cooling fans, and
may run into safety limits on following distance before the fan
activates. However, there may be exceptions to this if a light
vehicle is following a much larger vehicle.
[0037] Referring again to FIG. 2, although the gap control process
204 is shown described herein in use with an autonomous vehicle,
semi-autonomous or human operated vehicles can also benefit from
the gap distance control process. For example, a human operator
driving in a platoon could receive data informing the operator of a
suggested gap distance.
* * * * *