Improvements relating to brake control
The present invention relates to a brake control system for a motor vehicle. In particular,
though not exclusively, it relates to a brake control system for facilitating the control of a
motor vehicle on a slope. Aspects of the invention relate to a system, to a method and to a
vehicle.
There are a number of existing brake control systems for facilitating the control of motor
vehicles on slopes.
EP 0 784 551 B 1 discloses a brake control system comprising a hill descent mode in
particular for vehicles used in off-road conditions. The brake control system comprises an
electronic control unit and a brake control system to control brakes associated with each
wheel of the vehicle. A driver interface in the form of a switch is used to cause the control
unit to enter a hill descent mode when the vehicle is also detected to be in gear. In this mode
the control unit controls the speed of the vehicle by braking to slow the vehicle when a
detected vehicle speed is above a preset target speed.
When driving a motor vehicle off road it might be necessary to come to a standstill on a
slope. In this context, EP 1 777 133 A 1 discloses a brake control system in which a brake
control means is arranged to detect when the vehicle is stationary and is held on a slope by
a braking effort supplied by brakes in accordance with the operation of a brake command
means (such as a brake pedal). The release of the braking effort is controlled as a function
of the steepness of the slope following operation of the brake command means to release
the brakes.
Whilst the brake control system of EP 1 777 133 A 1 helps to smooth transition from a
stationary position to hill descent to a degree, it does not exercise control over the vehicle
once it is in hill descent. The system of EP 1 777 133 A 1 may of course be used in
conjunction with the system of EP 0 784 551 B 1, but this can still lead to jerky (and
therefore, to a degree, uncontrolled) hill descent in some circumstances, for example if the
vehicle gathers speed following the release of the brakes by the system of EP 1 777 133 A 1
and then has to be braked heavily when the target speed of the system of EP 0 784 551 B 1
is exceeded.
It is an aim of this invention to provide an improved brake control system that overcomes or
minimises the above problem. Other aims and advantages of the invention will become
apparent from the following description, claims and drawings.
Summary of the invention
Aspects of the invention therefore provide a system, a method and a vehicle as claimed in
the appended claims.
According to another aspect of the invention for which protection is sought, there is provided
a brake control system for a motor vehicle having a plurality of wheels, brakes for applying a
braking effort to one or more of the wheels, and movement sensing means for detecting
movement of the vehicle, the system comprising: brake actuation means for actuating the
brakes to supply a braking effort; and brake control means for controlling the brake actuation
means, wherein the brake control means is arranged to determine an acceleration of the
vehicle based on movement detected by the movement sensing means and to ensure that
the brake actuation means supplies a braking effort if the determined acceleration exceeds a
set acceleration limit.
By ensuring that the brake actuation means supplies a braking effort when the acceleration
of the vehicle exceeds a set acceleration limit, the system of the invention enables smooth
hill descent throughout, thus enhancing control over the vehicle.
Advantageously, the brake control means may be arranged to determine the acceleration of
the vehicle based on movement of the vehicle detected during a time cycle, preferably of
100 milliseconds or less. Of course the acceleration of the vehicle may conveniently be
determined continuously whilst the system is activated, for example based on a plurality of
time cycles each preferably of 100 milliseconds or less, more preferably 50 milliseconds or
less, most preferably 20 milliseconds or less. Shorter time cycles lead to more accurate and
immediate determination of acceleration and hence a more accurate and immediate braking
response, which in turn ensures even smoother hill descent and even better control over the
vehicle.
It will be appreciated that the determination of the acceleration of the vehicle may occur
within the movement sensing means itself. Thus the brake control system, and in particular
the brake control means, may function integrally with and/or include the movement sensing
means. More generally the brake control means may comprise a single electronic control
unit or one or more control units.
The brake control means may be configured (or arranged) to set the acceleration limit as a
fixed value, e.g. a value below 1 ms 2. The fixed acceleration limit may be based on a user
input, e.g. via an interface. Alternatively, and more preferably, the brake control means may
be arranged to set the acceleration limit dynamically based on one or more vehicle
conditions or driver inputs.
In an embodiment, the brake control means may be arranged to measure a desired drive
torque and to set the acceleration limit dynamically based on the desired drive torque. The
brake control means may measure the desired drive torque form the signal of an accelerator
pedal position sensor of the vehicle, optionally further taking into account a signal from a
gear selection sensor. An accelerator pedal position sensor and/or a gear selection sensor
may thus function integrally with and/or form part of the brake control system.
Setting the acceleration limit dynamically based on a desired drive torque enables
particularly smooth hill descent of the vehicle since it ensures that the acceleration of the
vehicle conforms with the intention of the driver. In this regard it is advantageous that the
brake control means be configured to increase the set acceleration limit with increasing
desired torque.
Determining the desired drive torque based on the signal of the gear selection sensor may
involve multiplying the signal of the accelerator pedal position sensor by a factor associated
with a selected gear. Advantageously, the brake control means may be arranged to set the
acceleration limit independently of the signal of the accelerator pedal position sensor if no
gear is selected (i.e. the vehicle is in neutral).
For maximum conformity with driver intentions, the brake control means may be arranged to
determine a desired acceleration associated with the desired drive torque and to set the
acceleration limit at a threshold equal to or above the desired acceleration. The desired
acceleration may conveniently correspond to an estimate of the acceleration that would
result from the desired drive torque in a zero gradient state of the vehicle (i.e. on level
ground). Advantageously, the brake control means may be arranged to set the acceleration
limit at a value in the range of from 0 to 1 ms 2 above the desired acceleration.
The brake control means may also be arranged to set the acceleration limit in dependence
on the gradient of the vehicle. The gradient of the vehicle may be detected by a gradient
sensing means of the vehicle, such as an inclinometer, which may function integrally with
and/or form part of the brake control system. The brake control means may be arranged to
lower the acceleration limit in response to an increased gradient of the vehicle.
Advantageously, the direction of travel of the vehicle may be monitored by the brake control
means (by communication with the movement sensing means). The brake control means
may advantageously be arranged to determine whether the vehicle is travelling in an
intended direction or an unintended direction with reference to a selected gear.
Advantageously, the brake control means may be arranged to set the acceleration limit in
dependence on the direction of travel, with the acceleration limit optionally being set lower
when the vehicle is moving in an unintended direction than when the vehicle is moving in an
intended direction
The brake control system may optionally have activated and deactivated states, which may
be selectable via a user interface. The brake control means may deactivate the system
either conventionally, by placing the system in standby, or, conveniently, by setting the
acceleration limit to a high level that cannot be achieved by the vehicle.
The system may comprise a driver brake pedal and a brake pedal position sensor in
communication with the brake control means. In some cases driver input will obviate the
need for additional braking effort in which case the brake control means simply monitors the
braking effort. Thus the brake control means may preferably only add to the supply of
braking effort when the relevant braking effort is not already being provided by input from a
driver, e.g. though a brake pedal. In the present invention braking effort may advantageously
be supplied as needed to supplement driver input. Braking effort may be supplied to all
wheels of the vehicle to maximise traction.
The brake control system may be integral or function in conjunction with other brake control
systems, for example such as those described in EP 0 784 551 B 1 and/or EP 1 777 133 A 1.
According to a further aspect of the invention for which protection is sought, there is provided
a method for controlling the brakes of a motor vehicle, the method comprising: measuring a
desired drive torque, setting an acceleration limit of the vehicle based on the desired drive
torque, determining an acceleration of the vehicle and, if the determined acceleration
exceeds the set acceleration limit, ensuring that the brakes supply a braking effort.
According to a still further aspect of the invention for which protection is sought, there is
provided a motor vehicle comprising a brake control system according to one aspect of the
invention or adapted to use a method according to another aspect of the invention.
Within the scope of this application it is envisaged that the various aspects, embodiments,
examples, features and alternatives set out in the preceding paragraphs, in the claims and/or
in the following description and drawings may be taken independently or in any combination.
Features and advantages recited in respect of the one aspect of the invention apply mutatis
mutandis to any other aspect of the invention, except where there is incompatibility of
features.
Detailed description of the invention
The invention will now be described by way of example with reference to the accompanying
drawings of which:
Figure 1 is a schematic drawing of a brake control system for a motor vehicle embodying
one form of the present invention, and
Figure 2 is a flowchart summarising the working of the brake control system of Figure 1 in an
operational mode.
Referring to Figure 1, there is shown a motor vehicle 10 in a dashed outline with a brake
control system having a hill descent mode, according to a first embodiment of the invention.
When the hill descent mode is activated, the brake control system is in an activated state for
the purpose of the invention. By contrast, when the hill descent mode is deactivated, the
brake control system is deactivated for the purpose of the invention.
The brake control system, and in particular the hill descent mode, may additionally perform
other brake functions not related to the invention, such those described in EP 0 784 551 B 1
or EP 1 777 133 A 1.
The brake control system includes in a conventional manner a braking arrangement with a
disc brake 11 on each of four wheels 12. Each disc brake 11 is hydraulically operated
through a hydraulic line 13 by a brake hydraulic control (HC) unit 14 which functions as a
brake actuation means. The HC unit 14 is controlled by an electronic control (EC) unit 15,
which functions as a brake control means. Figure 1 is only a diagram of the most important
functional components of the brake control system in accordance with the invention. Further
details of the brake control system are described in EP 0 784 551 B 1 and are included in the
description by reference and thus will not be further described.
The EC unit 15 receives a vehicle speed signal from movement sensing means in the form
of a vehicle speed sensor 16, an individual wheel speed signal from a wheel speed sensor
17 on each wheel 1 and a driver demand signal from an accelerator (or throttle) pedal 18,
which incorporates an accelerator pedal position sensor 19. The EC unit 15 also receives a
hill descent signal from a driver hill control switch 20, a gear signal from a drive gear sensor
2 1 and an inclination angle signal from a gradient sensing means, in this example an
inclinometer 22. The EC unit 15 receives a pedal braking signal from a brake light switch 9
on a brake pedal 24.
The brake pedal 24 is also associated with a master cylinder 8, which is connected to a
brake pressure sensor 23 forming part of the HC unit 14. The brake pressure sensor 23 is
arranged to send a driver braking signal from the brake pressure sensor 23 to the EC unit
15.
The EC unit 15 is active to control the HC unit 14 whenever the hill control switch 20 is
switched on by the driver to select hill descent mode. The EC unit can operate in conjunction
with (i.e. to supplement) operator inputs from the brake and accelerator pedals 24, 18.
When driving the motor vehicle 10 it may be desired to descend a slope. To assist drivers
with descending slopes in a controlled manner, the EC unit 15 is configured (arranged), in
the activated state of the system, to ensure that the brake actuation means supplies a
braking effort when the movement sensing means determines that the acceleration of the
vehicle exceeds a set acceleration limit.
In a first operational mode of the system, the acceleration limit is set at a fixed value of 0.5
ms 2. The EC unit 15 monitors the movement of the vehicle, as detected by the vehicle
speed sensor 16 and determines the acceleration of the vehicle in cycles of 10 milliseconds.
If the acceleration is found to exceed the acceleration limit of 0.5 ms 2 then the EC unit 15
checks the signal from the brake pressure sensor 23, which is also continuously monitored
by the EC unit 15, to determine if a suitable braking effort is already being applied by the
driver via the brake pedal 24. In the event that insufficient (if any) braking effort is being
applied via the brake pedal, the EC unit 15 issues a command to the HC unit 14 to apply and
maintain a braking effort to bring the acceleration of the vehicle within the limit of 0.5 ms 2.
A second operational mode of the system will now be described with reference to Figure 2.
In this mode the acceleration limit is set at a fixed value of 0.5 ms 2 only if the vehicle is not in
gear or is travelling in an unintended direction. If on the other hand the vehicle is travelling in
an intended direction associated with a selected gear, the acceleration limit is set
dynamically based on a desired drive torque.
In the second operational mode, once the hill descent mode is activated, the EC unit 15
checks, via the gear sensor 2 1 whether a gear is selected. If no gear is selected, or if the EC
unit determines through the vehicle speed sensor 16 that the vehicle is travelling in an
unintended direction (based on a selected gear), the EC unit 15 sets a fixed acceleration
limit of 0.5 ms 2.
However, if at any stage the EC unit 15 is notified by the gear sensor 2 1 that a gear is
selected and the vehicle is moving in the intended direction of travel associated with the
selected gear, the EC unit proceeds to set the acceleration limit dynamically based on a
desired drive torque indicated by the accelerator pedal position sensor 19.
Specifically, the EC unit dynamically determines (or looks up in a table or map) a desired
acceleration associated with the accelerator pedal position and the selected gear. The
desired acceleration corresponds to an estimation of the acceleration that would be
expected if the vehicle were in a zero gradient state, i.e. on level ground, and is thus based
on known information about the vehicle such as weight and drag.
The desired acceleration, which is determined in cycles of 10 milliseconds, serves as the
basis for setting the acceleration limit: the acceleration limit is set at 0.5 ms 2 above the
desired acceleration. In a variant of the second operational mode (not shown in Figure 2),
the EC unit 15 checks the signal from the inclinometer 22, adjusts the acceleration limit to be
equal to the desired acceleration if the vehicle is detected to be on a gradient greater than
20%.
Once the acceleration limit has been set, either as a fixed value (when no gear is selected or
the vehicle is moving in an unintended direction) or as a dynamic value (when the vehicle is
moving in an intended direction, the EC unit 15 proceeds to monitor the movement of the
vehicle, as detected by the vehicle speed sensor 16, and determines the acceleration of the
vehicle continuously, in cycles of 10 milliseconds. If the acceleration is found to exceed the
acceleration limit then the EC unit 15 checks the signal from the brake pressure sensor 23,
which is also continuously monitored by the EC unit 15, to determine if a suitable braking
effort is already being applied by the driver via the brake pedal 24. In the event that
insufficient (if any) braking effort is being applied via the brake pedal, the EC unit 15 issues a
command to the HC unit 14 to apply and maintain a braking effort to bring the acceleration of
the vehicle within the limit.
The following operational examples are provided to illustrate the second mode of operation
of the brake control system according to the first embodiment of the invention:
• The vehicle 10 is driven down a steep slope in a downhill gear. Vehicle acceleration
exceeds desired acceleration plus 0.5 ms 2. The EC unit 15 sends a command to the
HC unit 14 to generate a braking effort and limits the vehicle acceleration to desired
acceleration plus 0.5 ms 2.
• The vehicle 10 is driven down a steep slope in a downhill gear. The driver changes
gear and the new gear results in a vehicle acceleration. The acceleration exceeds
desired acceleration plus 0.5 ms 2. The EC unit 15 sends a command to the HC unit
14 to generate a braking effort and limits the vehicle acceleration to desired
acceleration plus 0.5 ms 2.
It is possible to modify the second operational mode such that the acceleration limit
associated with movement an unintended direction is set based on desired torque, as
described in respect of movement in an intended direction.
More generally, it will be appreciated that a number of modifications can be made to the
brake control system of the first embodiment without departing from the scope of the
invention. For example, it is not necessary for the activation of the brake control system to
be dependent on the activation of a hill descent mode. Thus, the brake control system of the
first embodiment can, according to a second embodiment of the invention, be modified to
remain active whenever the vehicle is operated.
Claims
1. A brake control system for a motor vehicle having a plurality of wheels, brakes for
applying a braking effort to one or more of the wheels, and movement sensing
means for detecting movement of the vehicle, the system comprising: brake
actuation means for actuating the brakes to supply a braking effort; and brake control
means for controlling the brake actuation means, wherein the brake control means is
arranged to determine an acceleration of the vehicle based on movement detected
by the movement sensing means and to ensure that the brake actuation means
supplies a braking effort if the determined acceleration exceeds a set acceleration
limit.
2. The brake control system of claim 1 having activated and deactivated states and
wherein the brake control means is arranged to set the acceleration limit as a fixed
value.
3. The brake control system of claim 1 or claim 2 wherein the brake control means is
arranged to set the acceleration limit dynamically based on one or more vehicle
conditions and/or driver input.
4. The brake control system of any preceding claim wherein the control means is
arranged to measure a desired drive torque and to set the acceleration limit
dynamically based on the desired drive torque and to increase the set acceleration
limit with increasing desired drive torque.
5. The brake control system of any preceding claim wherein the control means is
arranged to set the acceleration limit independently of the signal of an accelerator
pedal position sensor of the vehicle if the vehicle is in neutral.
6. The brake control system of any preceding claim wherein the brake control means is
arranged to determine a desired acceleration associated with the desired drive
torque and to set the acceleration limit at a threshold equal to or above the desired
acceleration.
7. The brake control system of any preceding claim wherein the brake control means is
arranged to determine whether the vehicle is travelling in an intended direction or an
unintended direction with reference to a selected gear and to set the acceleration
limit in dependence on the direction of travel, with the acceleration limit being set
lower when the vehicle is moving in an unintended direction than when the vehicle is
moving in an intended direction.
. A method for controlling the brakes of a motor vehicle, the method comprising:
measuring a desired drive torque, setting an acceleration limit of the vehicle based
on the desired drive torque, determining an acceleration of the vehicle and, if the
determined acceleration exceeds the set acceleration limit, ensuring that the brakes
supply a braking effort.
. The method of claim 8 comprising detecting a gear selection of the vehicle and
setting the acceleration limit in dependence on the detected gear selection.
0. A motor vehicle comprising a plurality of wheels, brakes for applying a braking effort
to one or more of the wheels, movement sensing means for detecting movement of
the vehicle, and a brake control system according to any one of claims 1 to 7.

A. CLASSIFICATION OF SUBJECT MATTER
INV. B60T7/12
ADD.
According to International Patent Classification (IPC) or to both national classification and IPC
B. FIELDS SEARCHED
Minimum documentation searched (classification system followed by classification symbols)
B60T
Documentation searched other than minimum documentation to the extent that such documents are included in the fields searched
Electronic data