GB2554478A

GB2554478A - A brake system controller, a brake system, a vehicle, a method, and a computer readable medium

Info

Publication number: GB2554478A
Application number: GB1702788.9A
Authority: GB
Inventors: Mathur Puneet
Original assignee: Horiba Mira Ltd
Current assignee: Horiba Mira Ltd
Priority date: 2016-09-22
Filing date: 2017-02-21
Publication date: 2018-04-04
Anticipated expiration: 2037-02-21
Also published as: GB201702788D0; WO2018055374A1; GB201616170D0; GB2554478B

Abstract

A brake system controller for a ground vehicle has a braking map based upon brake input position (e.g. pedal position) and rolling resistance coefficient (fr) where braking force = mass*g*fr*Cosθ. A required brake torque module outputs a required braking torque based upon this map. A first brake torque control module receives a signal representing at least part of the required braking torque and outputs a first brake output signal. The controller may include a second torque control module, and the first and second modules may correspond to friction braking and regenerative braking respectively. Said friction braking control module may receive a signal for actual regenerative braking torque and base the first brake output signal at least in part on the actual regenerative braking torque. The required braking torque may be further based on a dynamic rolling radius of a wheel and/or gross vehicle weight. Also disclosed is a brake system utilizing the abovementioned controller, a vehicle utilizing said controller, a method of generating a brake output signal for a braking system, computer readable medium which stores the abovementioned braking map, and a method of generating a rolling resistance map by performing one or more coast down tests.

Description

(71) Applicant(s):

Horiba Mira Limited

Watling Street, NUNEATON, Warwickshire, CV10 0TU, United Kingdom (72) Inventor(s):

Puneet Mathur (74) Agent and/or Address for Service:

Forresters IP LLP

Rutland House, 148 Edmund Street, BIRMINGHAM, B3 2JA, United Kingdom (56) Documents Cited:

EP 2570315 A WO 2015/114438

WO 2014/000035 A DE 010315889 A

DE 003805341 A US 4158961 A

US 4003241 A US 20160129791

US 20150094889 A US 20140066251

US 20130297164 A US 20130173127

US 20130134767 A

JP H06253406 JPH10267797 (58) Field of Search:

INT CL B60L, B60T, B60W, G01M Other: WPI, EPODOC (54) Title of the Invention: A brake system controller, a brake system, a vehicle, a method, and a computer readable medium

Abstract Title: A brake system controller, a brake system, a vehicle, a method, and a computer readable medium (57) A brake system controller for a ground vehicle has a braking map based upon brake input position (e.g. pedal position) and rolling resistance coefficient (fr) where braking force = mass*g*fr*Cos3. A required brake torque module outputs a required braking torque based upon this map. A first brake torque control module receives a signal representing at least part of the required braking torque and outputs a first brake output signal. The controller may include a second torque control module, and the first and second modules may correspond to friction braking and regenerative braking respectively. Said friction braking control module may receive a signal for actual regenerative braking torque and base the first brake output signal at least in part on the actual regenerative braking torque. The required braking torque may be further based on a dynamic rolling radius of a wheel and/or gross vehicle weight. Also disclosed is a brake system utilizing the abovementioned controller, a vehicle utilizing said controller, a method of generating a brake output signal for a braking system, computer readable medium which stores the abovementioned braking map, and a method of generating a rolling resistance map by performing one or more coast down tests.

fr coefficient vs. Brake pedal position

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

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Title: A brake system controller, a brake system, a vehicle, a method, and a computer readable medium

Description of Invention

Embodiments of the present invention relate to the provision of a brake system controller, a brake system, a vehicle, a method, and a computer readable medium. More particularly, embodiments concern the provision of a brake system controller for use with brake-by-wire systems which may obviate the need for vehicle speed feedback in the control of one or more brakes of the brake system.

In conventional brake systems for vehicles, an operator of the vehicle operates an input mechanism (e.g. a foot operated pedal or hand operated lever) which may, for example, be used to actuate a hydraulic brake system of the vehicle to cause the brakes of the vehicle to be activated. The brakes are typically friction brakes and may well comprise a disc and brake pads, for example. When the brakes are operated, the brake pads are pressed against the disc to slow rotation of the disc with respect to the pads and so to slow rotation of a ground engaging wheel of the vehicle which rotates with the disc. Other friction brake systems operate in a similar manner.

There is normally a correlation between the operation of the input mechanism and the braking force applied by the brake pads to the disc. In traditional brake systems for vehicles, the brakes are hydraulically operated and the input mechanism is coupled to drive movement of a piston of a master cylinder of the hydraulic system. Therefore, the braking force is generally proportional to a movement of the input mechanism. More recently, the control of this force with respect to the operation of the input mechanism by the operator has become more complicated - e.g. with the introduction of anti-lock braking systems and emergency brake assist systems.

Even more recently, brake-by-wire systems have been developed in which the operation of the input mechanism is no longer driving movement of the piston in the master cylinder. Instead, the input mechanism includes one or more sensors to sense the position of the input mechanism. This sensed position is then transmitted (e.g. via a communication bus) to a controller of the brake-bywire system which translates the sensed position of the input mechanism to a desired braking force and then actuates one or more brakes according to that desired braking force.

The operation of such brake-by-wire systems can often feel very different to the operator of the vehicle compared to conventional brake system operation. This can lead to uncertainty from the operator as to how the brakes will operate which makes controlling the vehicle more difficult and less familiar.

Some vehicles, such as electric and hybrid vehicles, have regenerative brake systems in which movement of the vehicle is used to drive a generator or motor-generator in order to generate electrical power. The electrical power may then be stored in a battery or other power storage device for later use to drive movement of the vehicle. As will be understood, using the movement of the vehicle in this manner will slow the vehicle and, therefore, have a braking effect.

Again, operation of regenerative brake systems can feel unfamiliar to operators of vehicles with such systems.

In vehicles which use a brake-by-wire system and a regenerative brake system, the controller of the brake-by-wire system has to use the sensed position of the input mechanism to blend the operation of the vehicle’s brakes and the regenerative brake system in order to slow the vehicle in the desired manner.

The operation of the controller in such systems is not a simple task because the operation of the regenerative brake system is dependent on a number of factors and there is a need to make the blending of the operation of the brakes and regenerative brake system substantially invisible to the operator. The slowing of the vehicle also has to be in the manner the operator is expecting i.e. consistent and familiar based on conventional brake systems.

Typically, such controllers for road vehicles have used closed loop control methods with a plurality of sensors providing feedback regarding the current operation of the vehicle - such as the vehicle speed, the acceleration/deceleration of the vehicle, the forces acting on the vehicle, wheel speed, and the like. The controllers then operate to provide a predetermined reduction in vehicle speed on actuation of the brake system - with the current speed of the vehicle being checked frequently to confirm that the desired reduction is occurring and to modify the operation of the brakes according to this feedback. As such, the controllers and their associated sensor systems are complex, expensive, and prone to problems.

There is a need, therefore, to alleviate one or more problems associated with the prior art.

Accordingly, an aspect of the invention provides a brake system controller for a ground vehicle, the brake system controller including: a required brake torque module configured to receive a rolling resistance coefficient map and a brake input signal, the brake input signal being representative of the position of an input mechanism, and the required brake torque module being further configured to output a required braking torque indicating the braking torque to be demanded from a brake system; and a first brake torque control module configured to receive a signal representing at least part of the required braking torque and to output a first brake output signal for the braking system of the vehicle, wherein: the rolling resistance coefficient map maps each of one or more input mechanism positions to respective rolling resistance coefficients,the required brake torque module is further configured determine a rolling resistance coefficient based on the rolling resistance coefficient map and brake input signal, and the required braking torque is output by the required brake torque module based on the determined rolling resistance coefficient.

The brake system controller may further include: a second brake torque control module configured to receive a signal representing at least part of the required braking torque and output a second brake output signal for the braking system of the vehicle; and a braking distribution module configured to distribute the required braking torque between the first and second brake torque control modules such that the signal representing at least part of the required braking torque received by each of the first and second brake torque control modules is a distributed part of the required braking torque.

The first brake torque control module may be a friction brake torque control module and the second brake control module may be a regenerative brake torque control module.

The friction brake torque control module may be further configured to receive an actual regenerative braking torque signal representative of the actual regenerative braking torque and to base the first brake output signal at least in part on the actual regenerative braking torque.

The required brake torque module may be configured to determine the required braking torque further based on one or more of a dynamic rolling radius of a ground-engaging wheel and a gross vehicle weight.

Another aspect provides a brake system, including: a brake system controller as above; and a first brake sub-system configured to slow a vehicle when activated, wherein the brake system controller is configured to control the brake sub-system using the first brake output signal.

The first brake sub-system may be a friction brake sub-system.

The brake system may further include: a second brake sub-system configured to slow a vehicle when activated, wherein the brake system controller is configured to control the second brake sub-system using the second brake output signal.

The second brake sub-system may be a regenerative brake sub-system.

Another aspect provides a vehicle including a brake system controller as above or a brake system as above.

Another aspect provides a method of generating a brake output signal for a braking system of a vehicle, the method including: receiving a rolling resistance coefficient map and a brake input signal, the brake input signal being representative of the position of an input mechanism and the rolling resistance coefficient map mapping each of one or more input mechanism positions to respective rolling resistance coefficients; determining a rolling resistance coefficient based on the rolling resistance coefficient map and brake input signal; outputting a required braking torque based on the determined rolling resistance coefficient, the required braking torque indicating a braking torque to be demanded from the brake system of the vehicle; receiving a signal representing at least part of the required braking torque; and outputting a first brake output signal for the braking system.

The method may further include: receiving a signal representing at least part of the required braking torque; outputting a second brake output signal for the braking system of the vehicle; and distributing the required braking torque between the first and second brake torque control modules such that the signal representing at least part of the required braking torque received by each of the first and second brake torque control modules is a distributed part of the required braking torque.

The method may further include: receiving an actual regenerative braking torque signal representative of the actual regenerative braking torque, wherein the first brake output signal is based at least in part on the actual regenerative braking torque.

Determining the required braking torque may be further based on one or more of a dynamic rolling radius of a ground-engaging wheel and a gross vehicle weight.

Another aspect provides a method of generating a rolling resistance coefficient map for use in a brake system of a vehicle, the method comprising: performing one or more coast down tests in which the vehicle is allowed to coast down from one or more respective predetermined speeds with one or more predetermined brake input mechanism positions; recording the deceleration of the vehicle over time during the one or more coast down tests; determining at least one rolling resistance coefficient in relation to the or each cost down test; using the at least one rolling resistance coefficient to form a rolling resistance coefficient map; and storing the rolling resistance coefficient map in a computer readable medium.

Another aspect provides a computer readable medium having stored thereon a rolling resistance coefficient map for use in a brake system of a vehicle, the rolling resistance coefficient map mapping at least one brake input mechanism position to one or more rolling resistance coefficients.

Embodiments of the present invention are described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a vehicle according to some embodiments;

Figure 2 shows a brake system according to some embodiments;

Figure 3 shows an activation sub-system according to some embodiments;

Figure 4 shows a controller according to some embodiments;

Figure 5 shows rolling resistance coefficient map according to some embodiments and as used in some embodiments;

Figure 6 shows a graphical representation of tests performed in accordance with some embodiments; and

Figure 7 shows a graphical representation of a comparison between the operation of a vehicle with a conventional brake system and a brake system according to some embodiments.

Embodiments include a brake system 1 for use with a vehicle 100 - i.e. a vehicle brake system 1.

The vehicle 100 may be a road vehicle such as a car, a van, a lorry, a truck, or the like, which is intended to travel primarily on a paved road surface or the vehicle 100 may be an off-road vehicle which is primarily intended to travel on unpaved roads or another unpaved ground surface. The vehicle 100 may include one or more towed parts such as a trailer and, indeed, the brake system 1 may be a trailer brake system 1 in some embodiments.

Figure 1 shows an example of the vehicle 100 in accordance with some embodiments. The depicted vehicle 100 is a road vehicle and, in particular, a car but this is as an example only and the embodiments described with reference to figure 1 could equally be applied to other types of vehicle 100.

The vehicle 100 includes a plurality of ground-engaging wheels 101 which engage the ground and support a chassis and a body of the vehicle 100 with respect to the ground. Each ground-engaging wheel 101 is configured to rotate with respect to the vehicle 100 as the vehicle 100 moves across the ground.

The vehicle 100 may include an engine 102 which may be carried by the chassis of the vehicle 100 and which may be configured to drive rotation of at least one of the ground-engaging wheels 101 (and, hence, to drive movement of the vehicle 100 across the ground). In some embodiments, the vehicle 100 includes at least four ground-engaging wheels 101 and the engine 102, in such embodiments, may be configured to drive rotation of at least two or at least four of those ground-engaging wheels 101. The engine 102 may be an internal combustion engine (which uses petrol (i.e. gasoline), diesel, or liquefied petroleum gas, for example, as a fuel).

The vehicle 100 may include one or more electric motors 103 which may be carried by the chassis of the vehicle 100 and which may be configured to drive rotation of at least one of the ground-engaging wheels 101 - e.g. two or four ground engaging wheels 101 - and so to drive the vehicle 100 across the ground (or to contribute to driving the vehicle 100). In some embodiments, there are at least two electric motors 103 and each is associated with one or more ground-engaging wheels 101 and is configured to drive rotation of the associated one or more ground-engaging wheels 101. In some embodiments, there may be four or more ground-engaging wheels 101 and each may be associated with its own electric motor 103.

In some embodiments, the electrical power for the one or more electric motors 103 is provided by one or more batteries 104 of the vehicle 100. The one or more batteries 104 may be carried by the chassis of the vehicle 100.

In some embodiments, the vehicle 100 may be an electric vehicle 100 and the vehicle 100 may include a connector which is configured to be connected to an electrical power supply - such as a mains electrical power supply - to recharge the one or more batteries 104. In such embodiments, the vehicle 100 may not include the engine 102 (although see below for hybrid vehicle embodiments).

In some embodiments, the vehicle 100 may be a hybrid vehicle 100 and the vehicle 100 may include both one or more electric motors 103 and the engine 102. In such embodiments, the engine 102 may be configured to drive rotation of one or more of the ground-engaging wheels 101 (e.g. via a mechanical transmission) and/or through use of the one or more electric motors 103. In the latter case, the engine 102 may be coupled to an electrical generator 105 of the vehicle 100 of some embodiments and configured to drive the electrical generator 105. Accordingly, the electrical generator 105 may be configured to generate electrical power through the operation of the engine 102 to charge the one or more batteries 104 (the electrical power stored in the one or more batteries 104 then being used to power the one or more electric motors 103 to drive rotation of at least one of the ground-engaging wheels 101). In some embodiments, however, the vehicle 100 is configured such that one or more of the ground-engaging wheels 101 may be selectively driven by the engine 102 through the mechanical transmission or by the one or more electric motors 103 (one or more clutches may be provided to engage or disengage the mechanical transmission and/or one or more electric motors 103 for this purpose).

In some embodiments, the one or more electric motors 103 may provide a regenerative braking function. In particular, the one or more electric motors 103 may be configured to be driven by rotation of at least one of the groundengaging wheels 101 (e.g. in some embodiments, the or each electric motor

103 is configured to be driven by its associated ground-engaging wheel 101) such that the electric motor 103 acts as an electric generator. The electrical power generated through such operation may be delivered to one or more other parts of the vehicle 100 including, for example, the one or more batteries

104 (e.g. for storage and later use in driving movement of the vehicle 100). The or each electric motor 103 may, therefore, be considered to be an electric motor-generator 103 in some embodiments.

In some embodiments, the vehicle 100 may include one or more electric generators 106 which are each similarly associated with one or more of the ground-engaging wheels 101 in the same manner as the one or more electric motors 103 but the one or more generators 106 may not, in such embodiments, be configured for use as motors (and so are not used to drive movement of one or more of the ground-engaging wheels 101).

In the depicted vehicle 100 in figure 1, the rear ground-engaging wheels 101 of the vehicle 100 are depicted as associated with the one or more electric motors 103 and/or one or more electric generators 106. However, it will be appreciated that one or more of the front ground-engaging wheels 101 of the vehicle 100 may be associated with one or more electric motors 103 and/or electric generators 106.

As will be understood, different forms of hybrid vehicle 100 are known in the art and could be used in embodiments of the invention. Indeed, embodiments may be used with any vehicle 100 with a brake-by-wire brake system 1 whether it is a hybrid vehicle, a conventional vehicle using an internal combustion engine, or a fully electric vehicle.

The vehicle 100 may include the brake system 1 and/or the brake system 1 may be configured for use with the vehicle 100 and so may be configured to be fitted to the vehicle 100.

With reference to figure 2, the brake system 1 includes at least one input mechanism 12 which is configured to receive an input from an operator. The at least one input mechanism 12 may, therefore, include at least one of a foot operated pedal and a hand operated lever.

The at least one input mechanism 12 may each be associated with an input mechanism sensor 13 which is configured to sense the position of the input mechanism 12 within a range of motion of the input mechanism 12 (e.g. a range of movement with respect to a part of the vehicle 100). Accordingly, the input mechanism 12 may be moveable through a range of motion between a first position and a second position. The input mechanism 12 may be moveable by the operator from its normal position (the first position) to its actuated position (the second position) in order to activate one or more brakes 14 of the braking system 1.

The input mechanism sensor 13 may be configured to output a brake input signal which is indicative of the sensed position of the input mechanism 12 and which may be the position of the input mechanism 12 (e.g. according to a linear scale) within the range of motion of the input mechanism 12. In other words, the brake input signal may be a signal which represents a position of the input mechanism relative to the first or second position at the ends of the range of motion.

The or each brake 14 may be a friction brake and may include a first part which is configured to rotate with rotational movement one of the groundengaging wheels 101 and a second part which is substantially fixed with respect to another part of the vehicle 100 (e.g. a part of the chassis and/or part of a steering linkage). The first part may, for example, be a brake disc and the second part may be a brake calliper carrying a pair of brake pads configured to be located on opposing sides of the brake disc. In such embodiments, the brake 14 may be activated to cause the pair of brake pads to apply a braking force to the brake disc to slow rotation of the brake disc (and hence also the ground-engaging wheel 101) with respect to the chassis of the vehicle 100. As will be appreciated, each ground-engaging wheel 101 may be associated with a brake 14 and the brakes 14 for one vehicle 100 need not all be of the same configuration.

The operation of the or each brake 14 may be driven (i.e. activated) by any suitable activation sub-system 15 - for example a hydraulic or pneumatic or electromechanical sub-system 15 of the brake system 1.

The operation of the activation sub-system 15 may controlled by a controller 16 of the brake system 1. Accordingly, the controller 16 may be configured to receive the brake input signal from the or each input mechanism sensor 13 and to output a first brake output signal to control the operation of the one or more brakes 14 based, at least in part, on the received brake input signal.

The activation sub-system 15 (see figure 3) may, for example, include an activation control unit 15a and one or more other components 15b which are controlled by the activation control unit 15a. The one or more other components 15b may include, for example, one or more motors (such as one or more servo-motors), one or more fluid conduits, one or more valves, and/or one or more piston-cylinder devices. The one or more other components 15b are configured to operate together, under control of the activation control unit

15a, to cause selective activation of the or each brake 14 (e.g. by selectively delivering pressurised air or a hydraulic fluid to the or each brake 14). Accordingly, it may be the activation control unit 15a which is configured to receive the first brake output signal.

For the avoidance of doubt, in embodiments in which there may be more than one brake input signal received - e.g. because there is more than one input mechanism 12 - the controller 16 may be further configured to determine which of the brake input signals to use in determining the first brake output signal. This may include, for example, the controller 16 basing the brake output signal on one of the brake input signals which indicates that the operator is attempting to activate the one or more brakes 14 or the brake input signal which indicates the greater desired braking force to be applied by the one or more brakes 14.

In some embodiments, the brake system 1 includes a regenerative brake function. Accordingly, in such embodiments, the brake system 1 includes or is configured to be associated with the one or more electric motors 103 of the vehicle 100 (see above) and/or the one or more electric generators 106 of the vehicle 100 (also see above). The brake system 1 may be configured to output a second brake output signal (in addition to or instead of the first brake output signal) to control the operation of the one or more electric motors 103 and/or electric generators 106 based at least in part on the received brake input signal.

In some embodiments, the activation sub-system 15 is further configured to control the operation of the one or more electric motors 103 and/or electric generators 106 based on the second brake output signal. In this regard, the one or more other components 15b may include one or more actuators to operate the one or more clutches, for example, which selectively couple the or each electric motor 103 and/or electric generator 106 to be driven by rotation of one or more of the ground-engaging wheels 101. In some examples, the one or more further components 15a may include one or more actuators to demand a regenerative torque from the or each electric motor 103 and/or electric generator 106 (e.g. via a communication bus). This may include altering the control of the or each electric motor 103 and/or electric generator 106. In such embodiments, the one or more clutches may not be provided.

Accordingly, in some embodiments, the activation control unit 15a is further configured to receive the second brake output signal and to control the regenerative brake function of the brake system 1 (e.g. by selective coupling of the one or more electric motors 103 and/or electric generators 106 when the vehicle 100 is slowing). In some embodiments, a second activation control unit is provided for this purpose - separate from the activation control unit 15a described above (which may still control activation of the one or more brakes 14).

The controller 16 may be further configured to receive one or more signals in relation to the operation of the vehicle 100. These one or more signals may include one or more of an actual regenerative braking torque signal, and a maximum regenerative braking torque signal.

The actual regenerative braking torque signal may include, in some embodiments, a signal representative of the actual regenerative braking torque for each of a plurality of the one or more electric motors 103 and/or one or more electric generators 106. In some embodiments, the actual regenerative braking torque signal includes a signal indicative of the actual regenerative braking torque for each electric motor 103 and/or generator 106 or for groups of electric motors 103 and/or electric generators 106. Indeed, as each electric motor 103 and/or electric generator 106 is associated with one or more of the ground-engaging wheels 101, the signal is also indicative of the actual regenerative braking torque for those one or more ground-engaging wheels.

For example, the actual regenerative braking torque signal may include a signal indicative of the actual regenerative braking torque associated with one or more ground-engaging wheels 101 at the front of the vehicle 100 and a signal indicative of the actual regenerative braking toque associated with one or more ground-engaging wheels 101 at the rear of the vehicle 100 (those ground-engaging wheels 101 each (or in groups) being associated with a respective electric motor 103 or electric generator 106, as described above).

The maximum regenerative braking torque signal may be a signal indicative of the maximum permitted braking torque collectively for all of the electric motors 103 and/or electric generators 106 of the vehicle 100 which are available for use in regenerative braking. This maximum regenerative braking torque may vary over time or may be substantially constant over time, and may be dependent on one or more factors such as the current state of charge of the one or more batteries 104 and/or one or more other physical restrictions on the maximum permitted braking torque. These physical restrictions may be based on, for example, the dynamic rolling radius of the relevant ground-engaging wheels 101, a selected gear ratio for the driving of the relevant groundengaging wheels 101, and conversion efficiencies between the operation of the or each electric motor 103 and/or electric generators 106 and the rotation of the associated ground-engaging wheel 101.

The controller 16 may be further configured to receive one or more rolling resistance coefficient (fr) maps (see figure 5 which depicts the input mechanism 12 position (“brake pedal position” and rolling resistance coefficient in graphical form) associated with the operation of the vehicle 100. The or each rolling resistance coefficient map provides a mapping between the position of the input mechanism 12 (as determined by the input mechanism sensor 13) and the required braking torque to be used in determining the control of one or more brake sub-systems of the brake system 1. It will be appreciated that the one or more rolling resistance coefficient maps may each comprise a respective lookup table, for example.

The or each rolling resistance coefficient map may be stored in a computer readable medium 17 which is part of the controller 16 or which can be accessed by the controller 16.

In some embodiments, the rolling resistance coefficient map selected for that vehicle 100. Accordingly, in some embodiments there may be more than one rolling resistance coefficient map available (e.g. stored on the computer readable medium 17) and the correct rolling resistance coefficient map may be determined by the controller 17 through the use of a vehicle identifier (which may be received from an electronic system of the vehicle 100 or which may be selected by a manufacturer on installation).

In some embodiments, the controller 16 may be further configured to receive an ideal braking distribution for the braking torque applied to a plurality of the ground-engaging wheels 101 (i.e. the braking torque applied through the brakes 14 and electric motor 103 and/or electric generator 106 associated with each ground-engaging wheel 101 or group of wheels 101).

In some embodiments, the ideal braking distribution includes an ideal relative braking torque for each electric motor 103 and/or generator 106 or for groups of electric motors 103 and/or electric generators 106 (the braking torques being relative to each other (e.g. a ratio)). For example, the ideal braking distribution may include an ideal braking torque distribution of one or more ground-engaging wheels 101 at the front of the vehicle 100 compared to one or more ground-engaging wheels 101 at the rear of the vehicle 100 (those ground-engaging wheels 101 each being associated with an electric motor 103 or electric generator 106, as described above).

The ideal braking distribution may be stored in the computer readable medium 17, for example.

In some embodiments, the ideal braking distribution selected for that vehicle 100 and/or determined by safety requirements. Accordingly, in some embodiments there may be more than one ideal braking distribution available (e.g. stored on the computer readable medium 17) and the correct ideal braking distribution may be determined by the controller 17 through the use of the vehicle identifier.

The force required to slow the vehicle 100 in any given scenario may be determined by use of the following equation:

Force = Aerodynamic resistance + acceleration force + rolling resistance and slip + gradient resistance [equation 1]

More specifically, this equation may be written as:

F = (1/2 p Cw A V²) + (λ m a) + (m g fr CosO) + (m g SinO) [equation 2] where:

F = the force required to slow the vehicle p = the mass density of air

Cw = the drag coefficient

A = the frontal area of the vehicle

V = the velocity of the air relative to the vehicle λ = rolling inertia coefficient m = mass of the vehicle a = acceleration g = gravitational acceleration fr = rolling resistance coefficient θ = road angle

It should be noted that:

the mass of the vehicle can be assumed to be constant and substantially equal to the gross vehicle mass (GVM), the front area of the vehicle can be assumed to be constant, the drag coefficient can be assumed to be constant, and the rolling inertia coefficient can be assumed to be constant.

Assuming that the road angle is zero (see below), equation 2 can be split into two components:

F = (1 /2 p Cw A V²) + (λ m a) + (m g fr Cos0) [equation 3]

The first part of the first above component of equation 3, (1/2 p Cw A V²) represents the fixed forces acting on the vehicle 100 as a function of parameters of the vehicle 100 whereas the second part of the first above component is an acceleration/deceleration in the term (λ m a) and is the result of a braking force applied. As determined by the inventor, many of these parameters can be considered to be constant - including the mass of the vehicle 100. Others of the variables in this component cannot be controlled by the brake system 1 - such as V - in order to impact the force required to slow the vehicle 100 in a given situation (i.e. travelling at a given speed and/or with a given acceleration).

Therefore, the second above component of equation 3, (m g fr CosO), provides a variable which can be varied, fr, to impact F.

Accordingly, in some embodiments, the force and torque required to slow the vehicle may be transformed for the purposes of control of the brake system 1 to:

Force, F = m g fr CosO [equation 4] and,

Torque = Rdyn* m g fr CosO [equation 5] where:

Rdyn = the dynamic rolling radius of the ground-engaging wheel(s)

Accordingly, the braking torque to be applied to the ground-engaging wheels 101 can be determined to achieve the braking force.

For non-zero road angles then operators of vehicles 100 are conventionally used to varying the relative position of the input mechanism 12 to provide greater or less braking torque for the conditions.

Therefore, in some embodiments, the position of the input mechanism may be used to determine a rolling resistance coefficient which can then be used by the controller 16 to determine a braking torque to slow the vehicle 100.

From the braking torque required to slow the vehicle 100, one or more brake sub-systems - such as a regenerative brake sub-system 18 and/or a friction brake sub-system 19 - may be used to determine the degree of activation of these brake sub-systems which is required in order to achieve the desired slowing of the vehicle 100 in accordance with the expectation of the operator moving the input mechanism 12. In some embodiments, this is achieved without requiring, for example, active determination of the current vehicle speed by the controller 16 during the braking operation (i.e. without requiring closed loop control based on the actual vehicle speed).

The or each rolling resistance coefficient map - see above - may, therefore, map the input mechanism position to an associated rolling resistance coefficient in order to determine the required braking force, F, and have the required braking torque.

Accordingly, the controller 16 may take the form depicted in figure 4.

The controller 16 may include one or more modules which are each configured to perform a portion of the functionality of the controller 16.

The one or more modules may include, for example, a required brake torque module 16a which is configured to determine a brake torque which the brake system 1 is required to provide. The required brake torque module 16a may, therefore, use one or more of the rolling resistance coefficient maps to determine this brake torque.

The one or more modules may include, for example, a braking distribution module 16b which is configured to receive the brake torque which the brake system 1 is required to provide (e.g. from the required brake torque module 16a) and to determine a distribution of the brake torque requirement. This distribution may be a distribution between a plurality of ground-engaging wheels 101 or between a plurality of groups of ground-engaging wheels 101. For example, the distribution may be between rear ground-engaging wheels 101 of the vehicle 100 and front ground-engaging wheels 101 of the vehicle 100. In this respect, the braking distribution module 16b may use the ideal braking torque distribution.

The one or more modules may include, for example, a friction brake torque control module 16c. The friction brake torque control module 16c is configured to receive at least part of a distributed brake torque requirement (e.g. from the braking distribution module 16b) and to determine one or more friction brake control signals based on the received requirement. The one or more friction brake control signals may, therefore, be the first brake output signal as described herein. The friction brake torque control module 16c may also take into account the amount of regenerative braking which is taking place and so may use the actual regenerative brake torque signal.

The one or more modules may include, for example, a regenerative brake torque control module 16d. The regenerative brake torque control module 16d is configured to receive at least part of a distributed brake torque requirement (e.g. from the braking distribution module 16b) and to determine one or more regenerative brake control signals based on the received requirement. The one or more regenerative brake control signals may, therefore, be the second brake output signal as described herein. The regenerative brake torque control module 16d may use the maximum regenerative braking torque signal to determine the or each regenerative brake control signal based on the received requirement (as the regenerative braking cannot provide more than the maximum braking torque as indicated by this signal).

More particularly, the required brake torque module 16a is configured to receive the brake input signal from the input mechanism sensor 13 and to use at least one of the rolling resistance coefficient maps in determining a required braking torque.

In particular, the required brake torque module 16a may be configured to access at least one rolling resistance coefficient map as described herein and to use the rolling resistance coefficient map to determine a rolling resistance coefficient based on the input mechanism position (as indicated by the brake input signal).

The required brake torque module 16a may be further configured to determine a rolling resistance factor. The rolling resistance factor may be dependent on one or more of the mass of the vehicle (which may be assumed to be the gross vehicle weight), gravitational acceleration, the road angle, and the dynamic rolling radius of one or more of the ground-engaging wheels 101.

The required brake torque module 16a may be further configured to use the determined rolling resistance coefficient (potentially in combination with the rolling resistance factor in some embodiments) to determine the brake torque which the brake system 1 is required to provide, or the required braking torque - which may be output as a signal. As will be appreciated, the required brake torque module 16a may, therefore, use equation 5 to determine the required braking torque.

The regenerative brake torque control module 16d may be configured, in particular, to receive the required braking torque which the brake system 1 is required to provide along with the maximum regenerative braking torque signal. If the required braking torque is greater than the braking torque indicated by the maximum regenerative braking torque signal, then the regenerative brake torque control module 16d is configured to output the second brake signal including a signal representative of the total regenerative braking to be demanded in relation to all electric motors 103 and/or electric generators 106 of the vehicle 100 (which are available for regenerative braking) and this signal may indicate a total regenerative brake torque demand which is equal to the braking torque indicated by the maximum regenerative braking torque signal.

The regenerative brake torque control module 16d may be further configured to receive the at least part of a distributed brake torque requirement (e.g. from the braking distribution module 16b) and to determine one or more regenerative brake control signals based on the received requirement. This may be, for example, a regenerative brake control signal which forms part of the second brake signal and which is representative of the regenerative braking torque demanded in relation to a sub-set of the electric motors 103 and/or electric generators 106 - for example, demanded in relation to the electric motor(s) 103 and/or electric generator(s) 106 associated with one or more rear or front ground-engaging wheels 101 of the vehicle 100. Accordingly, the at least part of the distributed brake torque requirement may be used to determine a portion of the total regenerative brake torque demand which is to be demanded from the sub-set.

The friction brake torque control module 16c is configured to receive at least a part of a distributed brake torque requirement (e.g. from the braking distribution module 16b) which may be different from the at least a part which is received by the regenerative brake torque module 16d. As such, the at least a part of the distributed brake torque requirement received by the regenerative brake torque module 16d may be referred to as a first part, and the at least a part of the distributed brake torque requirement received by the friction torque control module 16c may be referred to as a second part. The two parts may be distinct from each other in the sense that they relate to the torque requirement associated with different ones of the ground-engaging wheels 101 (or different groups thereof). In some embodiments, however, the first and second parts of the distributed brake torque requirement include the brake torque requirement associated with at least one common ground-engaging wheel 101. Indeed, in some embodiments, both the first and second parts may include the brake torque requirement for the same groups of groundengaging wheels 101 - e.g. the front and the rear ground-engaging wheels 101 - such that both the friction brake torque control module 16c and the regenerative brake torque control module 16d receive information concerning the brake torque requirement associated with the same ground-engaging wheels 101.

The friction brake torque control module 16c may be further configured to receive the required braking torque (e.g. from the required brake torque module 16a).

In some embodiments, the friction brake torque control module 16c is configured to receive the actual regenerative brake torque signal.

Accordingly, the friction brake torque control module 16c may be configured to compare the received at least a part of the distributed brake torque requirement to the actual regenerative braking torque (as received in the actual regenerative braking torque signal), both the requirement and the actual regenerative braking being associated with the same ground-engaging wheel(s) 101. Using this comparison, the friction brake torque control module 16c may be configured to determine the additional braking torque which is required for those or that ground-engaging wheel or wheels 101. At least one of the friction brake control signal is then based on this additional braking torque, such that the brake or brakes 14 controlled using the at least one friction brake control signal are activated to provide the additional braking torque.

This same process may be performed using the information and signals associated with different ones of the ground-engaging wheels 101 and/or different groups thereof. So, for example, the friction brake torque control module 16c may be configured to determine a friction brake control signal for front ground-engaging wheels 101 of the vehicle 100 and another friction brake control signal for rear ground-engaging wheels 101 of the vehicle 100.

As such, the at least a part of the distributed brake torque requirement received by the friction brake control module 16c may include a brake torque requirement for each of the different ones of the ground-engaging wheels 101 and/or the different groups thereof. The actual regenerative braking torque signal may similarly include the actual regenerative braking torque signal for the same ones and/or groups of ground-engaging wheels 101.

In some embodiments, the distributed brake torque requirement received by the friction brake control module 16c for at least one ground-engaging wheel 101 is used with the required braking torque to determine the required brake torque requirement for at least one other of the ground-engaging wheels 101 (e.g. by subtraction).

As described herein, the activation sub-system 15 may be configured to receive the first and second brake output signals and to control the operation of the relevant parts of the vehicle 100 (e.g. the one or more brakes 14 and the one or more electric motors 103 and/or the one or more electric generators 106) accordingly.

As such, in some embodiments, the activation sub-system 15 is configured to receive the first brake output signal and to use the characteristics of the one or more brakes 14 to determine how to control the one or more brakes 14 to achieve the brake torque indicated by the first brake output signal. In some embodiments, however, this has already been done by the friction brake control module 16c and so the first control signal already takes into account the characteristics of the one or more brakes 14. These characteristics may be stored in a computer readable medium which may be the computer readable medium 17 described herein. The characteristics may take the form of a mapping between the required brake torque and the control signal for the one or more brakes 14 to achieve that torque (the control signal may be, for example, a required hydraulic line pressure).

In some embodiments, the activation sub-system 15 is configured to receive the second brake output signal and to use the characteristics of the one or more electric motors 103 and/or one or more electric generators 106 to determine how to control the one or more electric motors 103 and/or one or more electric generators 106 to achieve the brake torque indicated by the second brake output signal. In some embodiments, however, this has already been done by the regenerative brake control module 16d and so the second control signal already takes into account the characteristics of the one or more electric motors 103 and/or one or more electric generators 106. These characteristics may be stored in a computer readable medium which may be the computer readable medium 17 described herein. The characteristics may take the form of a mapping between the required brake torque and the control signal for the one or more electric motors 103 and/or one or more electric generators 106, and/or one or more clutches associated therewith, to achieve that torque.

The activation sub-system 15 may be further configured to provide the maximum regenerative braking torque signal and the actual regenerative braking toque signal to the controller 16.

As will be appreciated, the rolling resistance coefficient map or maps, along with other components described herein, allow the brake system 1 of some embodiments to provide the operator with vehicle braking in a manner which is familiar and predictable, without the need for complex feedback loops.

A rolling resistance coefficient map may be generated by running tests on a version of the vehicle 100 which uses a conventional brake system (i.e. a brake system which the brake system 1 of embodiments is mimicking). These test may include a coast down test in which the vehicle 100 is allowed to coast from one or more predetermined speeds (e.g. the vehicle maximum speed) to one or more other lower predetermined speeds (e.g. to a stop or when a vehicle antilock brake system is activated), with different input mechanism positions. This allows the speed of the vehicle over time to be determined under these test conditions from this determination, the rolling resistance coefficient can be determined for each test. The results of five example tests performed at different input mechanism 12 positions (“brake pedal positions”) can be seen in figure 6.

In some embodiments, a rolling resistance coefficient map may be generated using one or more tests of a three test process, including a first test, a second test, and a third test.

In accordance with the first test, the vehicle 100 may be driven at a first predetermined speed (e.g. at the maximum speed for the vehicle 100). The vehicle 100 may then be permitted to coast to a second predetermined speed (e.g. a stop or substantial stop). During the coasting process of the first test, the vehicle 100 may be operated without any simulated engine braking (which may otherwise be simulated by the vehicle 100 to provide similar behaviour as a vehicle with an internal combustion engine). In addition, no regenerative braking is applied. This test can provide useful information for determining the rolling resistance coefficient with the input mechanism position indicating no braking, to confirm one or more parameters of equation 2 above, for situations in which there is a high state of charge of battery of the vehicle 100 or a high voltage battery failure.

In accordance with the second test, the vehicle 100 may be operated in a similar manner to the first test but, instead, with simulated engine braking. This test provides useful information for electric vehicles and hybrid vehicles in which the internal combustion engine does not mechanically drive the wheels 101.

In accordance with the third test, the vehicle 100 may be operated in a similar manner to the second test except that the input mechanism position is altered.

In accordance with some embodiments, the third test includes a plurality of sub-tests in each of which the input mechanism is at a respective predetermined constant position. As such, the predetermined constant position of the input mechanism may be increased in 5% increments (relative to the range of possible positions of the input mechanism) for each sub-test. In each sub-test, the end of the sub-test may be determined when the vehicle 100 comes to a stop or when, for example, the vehicle antilock brake system is activated.

In one or more of the first, second, and third tests, the vehicle 100 may be operated in accordance with one or more of the following: using friction brakes of the vehicle 100 only, in a plurality of runs in opposing directions (to reduce the effects of wind and gradient changes and with the results averaged, for example), with vehicle 100 oils (including differential oil) at their normal operating temperature, with an initial friction brake temperature of less than 100°C (which may require cooling between tests/sub-tests or runs), with each test (or sub-test) performed in more than two runs (e.g. six runs, with three runs in each of two opposing directions), and with consistent simulated engine braking associated with each wheel 101.

Using the information gathered from the or each test, equation 2 (e.g. the simplified version in equation 4 or 5) may be used to determine values of the rolling resistance coefficient for different input mechanism positions in order to achieve a similar braking force as would be achieved using the conventional brake system.

As will be appreciated, the determined rolling resistance coefficient may be different in different tests for a given input mechanism position and, therefore, an average rolling resistance coefficient may be determined for one or more of the input mechanism positions and then used as the rolling resistance coefficient (which may, therefore, be referred to as an effective rolling resistance coefficient). In particular, the rolling resistance coefficient varies as a function of vehicle speed for a given input mechanism position, and, hence, the average rolling resistance coefficient can be determined for each given input mechanism position.

In some embodiments, this average is a mean, modal, or median of the determined rolling resistance coefficients. In some embodiments, the average is weighted. In particular, the majority of vehicle braking in normal operation of the vehicle 100 is likely to occur in order to achieve low deceleration (i.e. a slow reduction in vehicle speed). Occurrences of high vehicle deceleration are likely to be less common. Therefore, the weighted average may be weighted in favour of the rolling resistance coefficient determined for low deceleration.

Using equation 5, above, it is then possible to determine fr for each tested position of the input mechanism in order to achieve a comparable braking force, F, as was achieved in the tests. These discrete test points can then be extrapolated in order to determine a rolling resistance coefficient map. A graphical representation of an example rolling resistance coefficient map can be seen in figure 5.

Embodiments of the invention may, therefore, include a rolling resistance coefficient map which maps the input mechanism position to different rolling resistance coefficients for a particular vehicle, class of vehicle, make of vehicle, model of vehicle, type of vehicle, etc.

Embodiments of the present invention may be used to control the operation of a vehicle 100 equipped with a regenerative braking system but also a vehicle 100 which are equipped with brake-by-wire system but without a regenerative braking system. Embodiments of the invention may seek to blend the operation of more than one braking system type (e.g. friction brakes and regenerative brakes) in order to achieve familiar and consistent braking for the operator.

As will be understood, the one or more electric motors 103 and/or electric generators 106 are examples of the regenerative brake sub-system 18. Similarly, the one or more brakes 14 are examples of the friction brake subsystem 19.

The regenerative brake sub-system 18 and the friction brake sub-system 19 are examples of a brake sub-system and each brake sub-system may have an associated brake torque control module in the controller 16 (of which the friction brake torque control module 16c and regenerative brake torque control module 16d are examples).

Embodiments, therefore, seek to mimic a conventional brake system from the perspective of the operator controlling the input mechanism. Figure 7 shows a graphical depiction of a the mean fully developed deceleration for a vehicle using a conventional brake system (“OEM”) and for the same vehicle using an embodiment (“(BBW (fr - Testl)”) based on the position of the input mechanism 12 (“Brake pedal travel”).

Although some embodiments have been described with reference to road vehicles, some embodiments may include off-road vehicles. Some embodiments may be used in relation to autonomous or semi-autonomous vehicles. In some embodiments, the vehicle 100 may be provided with a gradient sensor which is configured to determine an angle of the vehicle 100 with respect to a plane or direction (e.g. with respect to gravity or a generally horizontal plane). In such embodiments, therefore, the angle, Θ, in equations 2-5 may be determined and a rolling resistance coefficient map may be determined for different gradients (i.e. angles of the vehicle as determined by the gradient sensor). Therefore, a plurality of such maps may be determined with each map being for a respective different gradient. The tests to generate the maps may, therefore, include runs at those different gradients.

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 brake system controller for a ground vehicle, the brake system controller including:

a required brake torque module configured to receive a rolling resistance coefficient map and a brake input signal, the brake input signal being representative of the position of an input mechanism, and the required brake torque module being further configured to output a required braking torque indicating the braking torque to be demanded from a brake system; and a first brake torque control module configured to receive a signal representing at least part of the required braking torque and to output a first brake output signal for the braking system of the vehicle, wherein:

the rolling resistance coefficient map maps each of one or more input mechanism positions to respective rolling resistance coefficients, the required brake torque module is further configured determine a rolling resistance coefficient based on the rolling resistance coefficient map and brake input signal, and the required braking torque is output by the required brake torque module based on the determined rolling resistance coefficient.

2. A brake system controller according to claim 1, further including:

a second brake torque control module configured to receive a signal representing at least part of the required braking torque and output a second brake output signal for the braking system of the vehicle; and a braking distribution module configured to distribute the required braking torque between the first and second brake torque control modules such that the signal representing at least part of the required braking torque received by each of the first and second brake torque control modules is a distributed part of the required braking torque.

3. A brake system controller according to claim 2, wherein the first brake torque control module is a friction brake torque control module and the second brake control module is a regenerative brake torque control module.

4. A brake system controller according to claim 3, wherein the friction brake torque control module is further configured to receive an actual regenerative braking torque signal representative of the actual regenerative braking torque and to base the first brake output signal at least in part on the actual regenerative braking torque.

5. A brake system controller according to any preceding claim, wherein the required brake torque module is configured to determine the required braking torque further based on one or more of a dynamic rolling radius of a ground-engaging wheel and a gross vehicle weight.

6. A brake system, including:

a brake system controller according to any preceding claim; and a first brake sub-system configured to slow a vehicle when activated, wherein the brake system controller is configured to control the brake subsystem using the first brake output signal.

7. A brake system according to claim 6, wherein the first brake sub-system is a friction brake sub-system.

8. A brake system according to claim 6 or 7 when dependent on claim 2, further including:

a second brake sub-system configured to slow a vehicle when activated, wherein the brake system controller is configured to control the second brake sub-system using the second brake output signal.

9. A brake system according to claim 8, wherein the second brake subsystem is a regenerative brake sub-system.

10. A vehicle including a brake system controller according to any of claims 1 to 5, or a brake system according to any of claims 6 to 9.

11. A method of generating a brake output signal for a braking system of a vehicle, the method including:

receiving a rolling resistance coefficient map and a brake input signal, the brake input signal being representative of the position of an input mechanism and the rolling resistance coefficient map mapping each of one or more input mechanism positions to respective rolling resistance coefficients;

determining a rolling resistance coefficient based on the rolling resistance coefficient map and brake input signal;

outputting a required braking torque based on the determined rolling resistance coefficient, the required braking torque indicating a braking torque to be demanded from the brake system of the vehicle;

receiving a signal representing at least part of the required braking torque; and outputting a first brake output signal for the braking system.

12. A method according to claim 11, further including:

receiving a signal representing at least part of the required braking torque;

outputting a second brake output signal for the braking system of the vehicle; and distributing the required braking torque between the first and second brake torque control modules such that the signal representing at least part of the required braking torque received by each of the first and second brake torque control modules is a distributed part of the required braking torque.

13. A method according to claim 12, further including:

receiving an actual regenerative braking torque signal representative of the actual regenerative braking torque, wherein the first brake output signal is based at least in part on the actual regenerative braking torque.

14. A method according to any of claims 11 to 13, wherein determining the required braking torque is further based on one or more of a dynamic rolling radius of a ground-engaging wheel and a gross vehicle weight.

15. A method of generating a rolling resistance coefficient map for use in a brake system of a vehicle, the method comprising:

performing one or more coast down tests in which the vehicle is allowed to coast down from one or more respective predetermined speeds with one or more predetermined brake input mechanism positions;

recording the deceleration of the vehicle over time during the one or more coast down tests;

determining at least one rolling resistance coefficient in relation to the or each cost down test;

using the at least one rolling resistance coefficient to form a rolling resistance coefficient map; and storing the rolling resistance coefficient map in a computer readable medium.

16. A computer readable medium having stored thereon a rolling resistance coefficient map for use in a brake system of a vehicle, the rolling resistance coefficient map mapping at least one brake input mechanism position to one or more rolling resistance coefficients.

17. A brake system controller substantially as herein described with reference to the accompanying drawings.

18. A brake system substantially as herein described with reference to the accompanying drawings.

19. A vehicle substantially as herein described with reference to the 5 accompanying drawings.

20. A method substantially as herein described with reference to the accompanying drawings.

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21. A computer readable medium substantially as herein described with reference to the accompanying drawings.

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

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