Patent Application
20250128690
The present invention relates to a method for estimating a braking torque of a braking system using friction maps.
The present invention is also directed to a similar method for estimating a pressure to be applied to a braking system using friction maps.
The general technical field of the present invention is thus that of estimating, by means of electronic processing, quantities related to the operation of a braking system, based on measured or detected operating parameters.
Until relatively recent times, the characterization of the frictions that are created on the brake disc of a vehicle during a braking event was carried out exclusively by means of experimental test cycles, each of which referred to a specific operating condition and/or situation, or as a function of the disc temperature.
Such a methodology was affected by the obvious and severe drawback of not providing an estimate of the friction for all the possible operating conditions different from those experimentally tested. This implied the further disadvantage of needing to perform a specific characterization test for each use condition of interest.
To partially solve this problem, a more general model was introduced, from which to take significant estimates of friction for a wide range of possible operating conditions, each associated with specific significant variables of values at stake (e.g., temperature of the brake disc and pressure applied to the brake disc).
The results of these models are typically reported in the form of tables (i.e., “friction maps”), which can be consulted to make estimates of friction on the brake disc under different operating conditions.
The friction estimate, in turn, can be useful for estimating other important operating quantities of the braking system (e.g. braking torque, or pressure to be applied to the brake disc to obtain a certain braking torque).
Regarding this, the prior art does not provide any automatic solutions, which is adaptable to a plurality of operating conditions (ideally, usable on any operating condition) and such as to be usable in real time, during the operation of the braking system, and to provide highly reliable results.
Therefore, many needs remain unmet in such a domain, needs for which the solutions known to date do not provide fully effective solutions.
It is the object of the present invention to provide a method for estimating a braking torque of a braking system, which allows at least partially obviating the drawbacks complained of above with reference to the prior art, and responding to the aforementioned needs particularly felt in the technical field considered. Such an object is achieved by a method according to claim 1.
Further embodiments of such a method are defined in claims 2-15.
It is also an object of the present invention to provide a method for estimating quantities related to the operation of a braking system for vehicles. Said object is achieved by a method according to claim 16.
Further embodiments of such a method are defined in claims 17-18.
It is also an object of the present invention to provide a method for estimating a pressure to be applied to a braking system of a vehicle. Such an object is achieved by a method according to claim 19 and by a method according to claim 26.
Further embodiments of such a method are defined in claims 20-25 and 27.
Finally, it is also an object of the present invention to provide a method for actuating a braking system mounted on a vehicle provided with brake-by-wire, using the methods mentioned above. Said object is achieved by a method according to claim 28.
Further features and advantages of the method according to the invention will become apparent from the following description of preferred embodiments, given by way of non-limiting indication, with reference to the accompanying drawings, in which:
With reference to
This method comprises a step a) of detecting or calculating a first input quantity and a second input quantity which are representative of operating conditions of the braking system.
The first detected or calculated input quantity comprises a temperature T of a brake disc of the braking system.
The second detected or calculated input quantity comprises a quantity depending on a pressure P of the braking system or on a contact pressure PC between friction surfaces of the braking system.
The method then includes a step b) of determining, based on said detected or calculated first input quantity and second input quantity, a braking friction coefficient μ representative of the braking friction or efficiency expected under the conditions defined by the detected or calculated values of said first input quantity and second input quantity.
Such a determining step b) is carried out by consulting, by means of electronic processing, a predefined friction map, or a corresponding predefined friction map table, which are digitally stored.
The method finally comprises a step c) of estimating the braking torque C based on the aforesaid determined braking friction coefficient μ and on geometric and/or structural and/or operating parameters of the braking system.
In accordance with different possible embodiments of the method, the aforesaid second input quantity is any one of the following quantities:
According to an implementation option, the method is performed with reference to a braking system comprising at least one brake caliper and at least one brake disc, and where the aforesaid friction surfaces of the braking system are the surfaces of the braking system disc and the surfaces of the brake caliper pads, that are configured to come into mutual contact during a braking event.
In that case, the aforesaid rotation speed vr is the rotation speed of the wheel on which the brake disc and the brake caliper of the braking system act.
In accordance with an embodiment of the method, the aforesaid detecting or calculating step a) comprises detecting the first input quantity and the second input quantity based on a real-time acquisition of said quantities during the operating conditions of the braking system.
According to another embodiment, the aforesaid detecting or calculating step a) comprises calculating the first input quantity and the second input quantity off-line based on telemetrically acquired data related to the operating conditions of the braking system.
In accordance with an embodiment of the method, the aforesaid friction map table comprises a predefined lookup-type table indicating the braking friction coefficient μ as a function of the aforesaid first and second input quantities.
In that case, the determining step b) comprises determining the braking friction coefficient μ based on a reading and/or interpolation carried out on the aforesaid lookup table by means of electronic processing.
According to an implementation option, the aforesaid friction map comprises a predefined color friction map, showing, by means of color graphics, the braking friction coefficient μ as a function of the first and second input quantities.
In that case, the determining step b) comprises determining the braking friction coefficient μ based on a reading of such a color map.
According to an embodiment, the aforesaid geometric and/or structural and/or operating parameters of the braking system used in the method in the estimating step c) comprise geometric parameters related to pistons of the brake caliper and operating parameters of the brake caliper.
According to an implementation option, the braking torque C is calculated as the product of the friction coefficient μ multiplied by the sum of the area Apist of the pistons of the brake caliper (both sides) multiplied by the effective radius Reff of the brake caliper multiplied by the system pressure Pimp of the brake caliper:
According to an embodiment of the method, one or more friction maps, or one or more corresponding friction map tables, constructed based on experimental assessments, are stored in a control unit of the vehicle or of the vehicle braking system.
Each of such one or more friction maps, or one or more corresponding friction map tables, is characterized by respective specific first and second input quantity, each expressed in a respective unit of measurement.
In accordance with an implementation option, the method comprises the further step of preparing the first input quantity and the second input quantity based on detected and/or measured quantities provided to the control unit as a function of the specific first and second input quantities, and respective measurement units, provided by the specific friction map or corresponding friction map table, among those stored, which is used in the determining step b).
According to an implementation option, the aforesaid step of preparing input quantities comprises adapting the units of measurement of the detected quantities to the units of measurement provided in the friction map, or corresponding friction map table, that is used.
In accordance with a particular implementation option, the step of preparing input quantities further comprises calculating the first and/or second input quantity based on the acquired quantities so as to make them consistent with the provision of the friction map, or corresponding friction map table, that is used.
In other words, if there is no immediate consistency between the quantities acquired and the quantities provided for a particular friction map to be used, or there is no immediate consistency between the units of measurement of the quantities acquired and the units of measurement with which the map was constructed, the method comprises a step of pre-processing the input quantities such as to determine such a consistency.
Those skilled in the art easily understand that such a step can be applied in many different examples:
According to another embodiment, still in order to guarantee, but in a different way, the consistency between the quantities acquired and the quantities used for consulting a friction map, the method comprises providing, by the control unit, a friction map or corresponding modified friction map table, based on of the quantities that are actually acquired and the respective units of measurement.
For example, according to a possible implementation example, if different units of measurement are used, various friction maps are constructed by changing unit of measurement (e.g. both on the x-axis and the y-axis).
According to an embodiment, the method is performed on a braking system comprising a plurality of brake calipers and respective brake discs, and where said steps a), b), c) of the method are carried out for each of the plurality of brake calipers and respective brake discs.
According to an implementation option, the braking friction coefficient μ is determined for each axle of the braking system, i.e., a single braking friction coefficient value μ is determined for both brake calipers and respective brake discs of an axle.
According to an implementation option, the braking friction coefficient μ is determined for each brake caliper and respective brake disc of an axle.
In other words, in different possible implementation options, the friction coefficient can be calculated, based on the available inputs, both at axle level (a single value for both front or rear brakes) and at corner level (thus the value of the friction coefficient on the right brake can be different from the value of the friction coefficient on the left brake, also on the same axle).
According to an implementation option, all the steps of the aforesaid embodiments of the method for estimating a braking torque are performed by electronic processing means.
A method is described below for estimating quantities related to the operation of a braking system for vehicles.
Such a method includes carrying out a method for estimating a braking torque of a braking system according to any one of the embodiments previously illustrated, and then estimating at least one further quantity related to the operation of the braking system, based on the estimated braking torque and further detected or measured operating parameters.
According to different embodiments of such a method, the aforesaid at least one further quantity related to the operation of the braking system comprises:
According to an embodiment, a power dissipated during the braking action is estimated by multiplying the estimated braking torque by a speed of the wheel.
According to an implementation option, the aforesaid estimated power dissipated during the braking action is used in association with a thermal model for estimating the temperature of the brake or other components of the braking system of a wheel.
According to another embodiment, an aerodynamic resistance or other parameter associated with the vehicle dynamics is estimated based on the estimated braking torque and a detected or calculated traction torque of the vehicle.
According to another embodiment, based on of the estimated braking torque on an axle directly controlled by the driver in a brake-by-wire, BBW, actuation system, at least one braking torque target is estimated for at least one respective other axle of the brake-by-wire actuation system.
According to an implementation option, all the steps of the aforesaid embodiments of the method for estimating quantities related to the operation of a braking system are performed by electronic processing means.
A method, also encompassed by the present invention, for estimating an actuation pressure P to be applied to a braking system of a vehicle to obtain a target braking torque value Ct is described below.
Such a method comprises the steps i) of detecting or calculating a temperature T of a disc brake of the braking system and ii) determining, based on the aforesaid temperature T of the brake disc and the aforesaid target braking torque value Ct, the pressure P to be applied to the braking system.
The determining step ii) is carried out by consulting, by means of electronic processing, a predefined inverse friction map, or a corresponding predefined inverse friction map table, that are digitally stored.
According to an implementation option, the aforesaid inverse friction map or corresponding inverse friction map table is calculated from a friction map or corresponding friction map table, and stored before carrying out the steps of the method.
According to an embodiment of this method, the aforesaid inverse friction map table comprises a predefined lookup inverse table which indicates the pressure P to be applied to the braking system as a function of the temperature T of brake disc and the braking torque C.
In that case, the determining step ii) comprises determining the pressure P to be applied to the braking system based on a reading and/or interpolation carried out on said lookup inverse table by means of electronic processing.
According to an implementation option, the aforesaid inverse friction map table comprises a predefined lookup inverse table which provides, as a function of the temperature T of brake disc and the braking torque C, an output value PV equal to the product of the pressure P to be applied to the braking system multiplied by a speed of the wheel on which the braking system acts.
In that case, the determining step ii) comprises:
In accordance with an implementation option, the detected or calculated speed of the wheel is the angular speed ωr of the wheel.
In that case, the step of calculating the pressure P to be applied to the braking system comprises dividing the output value PV by the angular speed ωr of the wheel, according to the formula:
According to an implementation option, the aforesaid steps of detecting or calculating the temperature T of a brake disc of the braking system and the speed of the wheel comprise detecting or calculating such quantities based on a real time acquisition of such quantities, during the operating conditions of the braking system.
According to another implementation option, the aforesaid steps of detecting or calculating the temperature T of a brake disc of the braking system and the speed of the wheel comprise detecting or calculating such quantities based on off-line calculations based on telemetrically acquired data related to the operating conditions of the braking system.
In accordance with an embodiment of this method, one or more inverse friction maps, or one or more corresponding inverse friction map tables, are constructed based on experimental assessments or based on a re-elaboration of direct friction maps, and are stored in a control unit of the vehicle or the braking system of the vehicle.
Each of such one or more inverse friction maps, or one or more corresponding inverse friction map tables, is associated with specific measurement units of the temperature T of brake disc and of the target braking torque Ct.
According to an embodiment, the method comprises the further step of preparing the quantities for consulting the inverse friction map, or corresponding inverse friction map table, by adapting the units of measurement of the detected quantities to the units of measurement provided by the inverse friction map, or corresponding inverse friction map table.
A further method, also encompassed by the invention, for estimating an actuation pressure P to be applied to a braking system of a vehicle to obtain a target braking torque value Ct is described below.
Such a method comprises the following steps:
According to an implementation option, the aforesaid second detected or calculated input quantity comprises the desired target braking torque Ct, or the product of the target braking torque Ct multiplied by the speed of the wheel on which the braking system acts.
According to an implementation option, all the steps of the aforesaid embodiments of the method for estimating a pressure to be applied to a braking system of a vehicle are performed by electronic processing means.
There is described below a method for actuating a brake-by-wire (BBW) braking system for a vehicle mounted on a vehicle, comprising a first braking axle directly controlled by the driver by applying a first axle actuation pressure Pa1, and a second axle controlled by a brake-by-wire control system configured to apply a second axle controlled pressure Pa2 to the second axle.
Such a method comprises the following steps:
According to an implementation option, all the steps of the aforesaid method for actuating a brake-by-wire type braking system are performed by electronic processing means.
It should be noted that, in possible implementation options of the methods illustrated above, all the calculations can be performed both in real time and off-line a posteriori.
Further details of the method will be given below, again referring to
Should the quantities originally detected not be consistent with the subsequent steps, a calculation or a conversion must be included so as to make them consistent with the friction map to be used in the next point 2.
The magnitudes can be acquired and used in real-time or off-line a posteriori.
Examples of direct friction maps are illustrated in
An example of a look-up table corresponding to a direct friction map is illustrated in
The friction coefficient can be calculated, based on the available inputs, both at axle level (a single value for both the front or rear brakes) and at corner level (right brake different from the left brake also on the same axle).
With respect to
In different implementation options, this includes:
All of the aforesaid calculations can be performed both in real-time and off-line a posteriori.
The second quantity can be one of the following:
Should the quantities originally detected not be consistent with the subsequent steps, a calculation or a conversion must be included so as to make them consistent with the friction map to be used at point 2 below.
The aforesaid quantities can be acquired and used in real-time or off-line a posteriori.
An example of an inverse friction map is illustrated in
A calculation example of an inverse friction map from a direct friction map is illustrated in
An example of a look-up table corresponding to an inverse friction map is illustrated in
The aforesaid target pressure can be calculated, based on the available inputs, both at axle level (a single value for both the front or rear brakes) and at corner level (right brake different from the left brake also on the same axle).
The output of the inverse friction map can directly be the target pressure or the product of the target pressure multiplied by the current wheel speed. In the latter case a further calculation step is necessary in order to extrapolate the target pressure only.
All of the calculations can be carried out both in real-time and off-line a posteriori.
In that case, the actuation pressure is estimated starting not from an inverse friction map, but through the following processing flow with iteration, from a direct friction map.
Should the quantities originally detected not be consistent with the subsequent steps, a calculation or a conversion must be included so as to make them consistent with the friction map to be used in point 3 below.
The quantities can be acquired and used in real-time or off-line a posteriori.
In particular, it is possible to use the braking torque estimate by (direct) friction map and the calculation of the target pressure in a combined manner on a vehicle provided with two braking axles, the first under the driver's direct control (who thus acts by means of braking pressure directly on the brake), the second under the control of a BBW system and which must thus apply a braking pressure based on the driver's action on the first axle and other logics inside a vehicle control unit (VCU).
The braking system to which reference is made is that illustrated in
The use of the friction maps in this context is illustrated in
As can be seen, the objects of the present invention, as previously indicated, are fully achieved by the methods described above by virtue of the features disclosed above in detail. The advantages and technical problems solved by the method according to the invention have already been mentioned above, with reference to the various features and aspects of the method.
In particular, the methods disclosed above allow estimating important operating quantities of the braking system, such as for example a braking torque or a pressure to be applied to the brake disc for obtaining a certain braking torque, automatically and reliably, also usable in real time, applicable to each operating condition of the braking system associable with a braking event.
In order to meet contingent needs, those skilled in the art may make changes and adaptations to the embodiments of the methods described above or can replace elements with others which are functionally equivalent, without departing from the scope of the following claims. Each of the features described above as belonging to a possible embodiment can be implemented irrespective of the other embodiments described.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102021000032420 | Dec 2021 | IT | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2022/062451 | 12/19/2022 | WO |
