Method and related system for avoiding extra forces when operating the parking brake

Abstract

The invention relates to a control method for combined parking brake calipers ( referred to as ECS by the Applicant ) or standalone parking brake calipers ( referred to as EP by the Applicant ). The control method allows avoiding extra forces in the system when the vehicle is on level ground (or with a low slope ) but it is not possible to correctly estimate the road slope when the application request is received. By virtue of the method of the invention, it is possible to reduce the mechanical sizing of the calipers (avoiding overdesign or increasing the duration of the component, the design being equal ). In the case of combined calipers, the method of the invention can be applied to both control systems utilizing only the electromechanical application and control systems also utilizing the hydraulic support. In the latter case, the invention allows reducing the working cycles of the system generating the hydraulic support. The invention also relates to a braking system including a control unit configured to perform the steps of the method of the invention.

Description

[0001] Method and related system for avoiding extra forces when operating the parking brake

[0002] To : Brembo S . p . A .

[0003] Inventors : Andrea Butti

[0004] The present invention relates to a method and a related system for avoiding extra forces when operating the parking brake (preferably on level ground) when the request to operate the parking brake occurs with the vehicle not completely stationary .

[0005] Background art

[0006] A strategy is known of controlling the parking brake based on the approach depending on the slope, where the parking force required varies with the road slope in order to avoid applying, in every situation, the force required for the maximum slope condition, thus reducing the overall load applied to the system . In such a strategy, the road slope of the vehicle is calculated at the instant in which the parking brake engagement request is received . Such a slope value is determined according to the longitudinal acceleration value of the vehicle .

[0007] I f the engagement request occurs at the limit of the static-dynamic threshold of the vehicle, considering that in this scenario the vehicle is not completely stationary, the subsequent slope estimation is affected by the speed of the vehicle and by the pitch movements of the vehicle . In fact :

[0008] - The vehicle speed affects the estimation since the contribution of the deceleration of the vehicle is measured by the longitudinal acceleration sensor

[0009] (measurement used by the slope estimation algorithm) . Therefore, it is essential to identify the contribution of such a deceleration level to separate this contribution from the overall longitudinal acceleration value in order to identify the portion caused by the road slope, thus allowing the value of the slope itself to be identified . The deceleration value of the vehicle can be estimated from the measurement of the speed of the individual wheels . Once this contribution has been determined, the portion of the longitudinal acceleration value caused by the road slope can be determined as :

[0010] Long_Slope = TOT_Long_Acc -Vehicle_Decel .

[0011] However, it is difficult to completely eliminate the contribution given by the deceleration of the vehicle, and therefore an error coefficient is to be considered in the road slope estimation . This error must then be added to the estimated road slope value . As a result , the parking force applied to the system is overestimated with respect to the actual need .

[0012] — The pitch movements of the vehicle during the braking action cause a variation in the measurement of the longitudinal acceleration with the problem that it is difficult to separate the contribution caused by these movements from that caused by the road slope . This contribution could be attenuated by a filtering action performed on the longitudinal acceleration value . However, it can cause a delay in the estimation of the road slope ( it is necessary to wait for the filter to reach the operating speed) , causing an increase in the application time because the beginning of the parking brake application maneuver is affected by the estimation of the road slope and therefore in the associated parking force target . Moreover, this contribution cannot be zeroed because the filtering keeps a final estimation error thereof (which error could be minimized resulting in an impact on the application times because the filter convergence times would increase ) . Therefore, also in this case, an error is introduced in the slope estimation with the consequences described above .

[0013] Given that these aspects affect the slope estimation, in order to avoid an increased error value and avoid increases in the application times , in these cases the slope value is invalidated and set to the maximum value ; therefore, the maximum target force that the brake must apply for parking is selected .

[0014] This strategy causes the following problems (this scenario is widely present for couriers ' vehicles ) :

[0015] 1 - all the application actions also on a flat surface are performed at the maximum force : this causes a stress on the caliper, resulting in an increase in the application time ;

[0016] 2 - in the case of combined brake calipers (used for both service parking and parking where both the hydraulic pressure and the gear motor act , by means of a transmission system, on the same maneuvering piston) , there can be an application strategy in which the hydraulic support is utilized; i . e . , before moving the caliper with the electromechanical actuator, pressure is applied so that the final force is given by the two contributions ( strategy commonly known as HPO - Hydraulic Pressure Overlay or HPS - Hydraulic Pressure Support ) . This strategy can be adopted for all individual parking brake operations or only in the case of high slopes , when the maximum parking force is required, conditions for which the force applied by the electromechanical actuator alone is not sufficient . In the latter case, the number of application cycles required by the hydraulic support is greater than the limits defined during the design . Considering that the hydraulic support is generated by the pump of the ESC systems, a strategy of this type impacts the duration limit s of the pump itself .

[0017] Fig . 1 shows an example of a slope estimation algorithm 100 (each parameter can be calibrated) according to the prior art .

[0018] Start with the following initial conditions :

[0019] - SlopeErr=0 ( slope estimation error) ;

[0020] - IDx_a=0 ( filling index of the vector SLP_Array with subsequent acceleration values ) ;

[0021] - Whspd_DeadBand ( speed threshold detected under which the vehicle is considered stationary, usually equal to 0 . 7km / h) ;

[0022] - Max_Acc_Ths = 4 m / s2 ( longitudinal acceleration threshold) ;

[0023] - SlopeSize = 5 ( size of the vector with subsequent acceleration values ) ;

[0024] - ReliabTHS = 10 (algorithm iteration counter) considering the longitudinal acceleration measured in m / s2 ;

[0025] - k=10 (multiplicative factor of the average of the estimated slopes ) ;

[0026] - ErrTHS = 2% ( configurable value indicating the final error value allowed on the slope estimation) .

[0027] In block 101 it is verified if the vehicle speed is less than a predetermined threshold (Whspd_DeadBand) . This control allows verifying if the vehicle is stationary or still in motion (a typical value for the parameter Whspd_DeadBand is 0 . 7 km / h) . I f this is the case, one moves on to block 102 where it is verified if a valid road slope value was previously estimated . I f so, the algorithm ends (block 118 ) because the vehicle never moved and the previous estimated slope value can be confirmed . I f this is not the case, in block 103 it is verified if the longitudinal acceleration (LongAcc) of the vehicle is less than or equal to the threshold Max_Acc_Ths (usually equal to 4 m / s2) to avoid acceleration values not consistent with a slope measurement . From here, if it is actually less , one moves on to block 104 , where it is verified (by verifying the index Idx_a) if the vector SLP_Array of size "SlopeSize" containing the latter longitudinal acceleration values was completely filled during the preceding iterations of the algorithm ( condition of Idx_a > SLP_Array-l ) . If instead it is above the threshold in 103 , one moves directly on to block 110 which is described below .

[0028] From block 104 , if the condition on index Idx_a is verified, one moves on to block 105 where each element of the vector SLP_Array is translated by one position, thus freeing up the first position . I f instead the condition of block 104 is not verified, one moves on to block 107 where the current position of the vector is filled with the current longitudinal acceleration value ( SLP_Array [ Idx_a] =LongAcc) , the operating index Idx_a is increased by 1 , and then one moves on to block 108 which is shown below .

[0029] From block 105 , one moves on to block 106 where the position of the vector freed in block 105 is populated with the current Longitudinal Acceleration Value ( SLP_Array [ SlopeSize-1 ] =LongAcc) , and then to block 108 where a counter is set equal to 1 (Counter = 1 ) .

[0030] At this point , one moves on to blocks 112 , 113 and 114 where , in block 112 it is veri fied that Counter < SlopeSize-1 and if it is so, one moves on to block 113 where an error SlopeErr is calculated as the sum of the differences of the values of the adjacent elements of the vector SLP_Array ( SlopeErr = SlopeErr + | SLP_Array [ Counter] - SLP_Array [ Counter - 1 ] | ) ; then one moves on to block 114 where Counter is increased, and one starts again from block 112 .

[0031] I f the condition on the counter is not verified in 112 , one moves on to block 111 where it is verified if the previously calculated error value is less than a preset threshold ErrTHS ( SlopeErr < ErrTHS ) . I f it is verified, one moves on to block 116 described below, otherwise to block 110 where the parameter SlopeReliab is set equal to zero . Then one moves on to block 109 with the conclusion that the slope estimation is not valid, and therefore the slope value is set at the maximum value in a conservative perspective .

[0032] The parameter SlopeReliab is used as a robustness index and serves to monitor the stability of the longitudinal acceleration value by verifying that the error value SlopeErr is less than the threshold ErrTHS for a defined number (ReliabTHS ) of iterations of the algorithm . Such a control is performed in the aforesaid block 116 by controlling the condition SlopeReliab < ReliabTHS . I f such a condition is true, one moves on to block 115 where the parameter SlopeReliab is increased, and then to the final block 109 already described above . I f instead it is false, it means that the longitudinal acceleration value is stable, then one moves on to block 117 where the road slope is calculated, and then to the final block 118 which indicates that the slope estimation was estimated in a correct manner, therefore with the opposite conclusion to block 109 . In block 117 , the road slope is determined ( SlopeEst ) as the average of the elements of the vector SLP_Array multiplied by a factor k ( SlopeEst = k* (average between the elements of SLP_Array) ) . Such a factor k is defined based on the features of the longitudinal acceleration signal ( scaling, unit of measurement , etc . ) and approximating the trigonometric equations which allow the conversion from the longitudinal acceleration value to the road slope value .

[0033] The strategy can be improved by including a compensation for the deceleration of the vehicle and a filtering action to remove the pitch movements . However, it is not possible to be certain that the convergence of the algorithm be ensured in all instances of use . Due to the various approximations and the lack of convergence in certain cases , the parking force applied to the system is overestimated with respect to the actual need .

[0034] Object and subject-matter of the invention

[0035] It is the object of the present invention to provide a method and system for avoiding extra forces when operating the parking brake, preferably on level ground, when the request for application occurs with the vehicle not completely stationary, which solves the problems and overcomes the drawbacks of the prior art .

[0036] A method and system according to the appended claims is the subject-matter of the present invention .

[0037] Detailed description of embodiments of the invention

[0038] List of Figures

[0039] The invention will now be described by way of nonlimiting illustration, with particular reference to the figures in the accompanying drawings , in which :

[0040] - Figure 1 shows a method of estimating the road slope based on which the force to be applied to the parking brake is determined according to the prior art ;

[0041] - Figure 2 shows a method of estimating the force to be applied to the parking brake according to an embodiment of the invention .

[0042] It is here specified that elements of different embodiments can be combined to provide further embodiments , without restrictions, while respecting the technical concept of the invention, as those ordinarily skilled in the art will effortlessly understand from the description .

[0043] The present description also refers to the prior art for the implementation thereof in relation to the detail features not described, such as elements of minor importance usually used in the prior art in solutions of the same type, for example .

[0044] When an element is introduced, it is always understood that there can be "at least one" or "one or more" .

[0045] When a list of elements or features is given in this description, it is understood that the finding according to the invention " comprises" or alternatively " consists of" such elements .

[0046] When listing features within the same sentence or bulleted list , one or more of the individual features can be included in the invention without connection with the other features in the list .

[0047] Two or more of the parts (elements , devices , systems ) described above can be freely associated and considered as a part kit according to the invention . Embodiment s

[0048] Fig . 2 describes the method 200 of the invention, which also includes the hydraulic support (optional ) .

[0049] When the brake engagement request 213 is received, the slope estimation is optionally, but not necessarily, performed in the first block 210 . Otherwise, one moves directly on to block 230 disclosed below .

[0050] In particular, in block 211 , it is verified that the speed of the vehicle is greater than a first predetermined threshold THR (Vehicle_Speed > Speed_THR) , below such a threshold the vehicle is considered substantially stationary . I f yes , one moves on to the first application of a force in block 230 , disclosed below . I f the speed of the vehicle is instead less than the first predetermined threshold, one moves on to the verification, in block 212 , of the fact that the slope estimation algorithm reached convergence, thus having determined a slope estimation value . I f yes , one moves on to the standard strategy of the prior art in 220 , where the parking force is defined according to the road slope estimation value calculated by the algorithm . Then, once the parking force has been correctly applied, the final parking condition achieved in 260 is considered . I f not (or in the absence of block 210 ) , one moves instead on to block 230 .

[0051] In fact , the invention works when the estimation of the slope according to the prior art has not reached convergence . In particular, in the two cases yes and not of blocks 211 and 212 , respectively, again one moves on to block 232 , where a target force to be applied is set to a minimum predetermined force (Force_Target = F_Min) . Such a minimum force value is determined in order to ensure the parking of the vehicle up to a known percentage of road slope ( SLP_THS) , also considering the possible estimation value given also by the measurement uncertainty of the longitudinal acceleration sensor . At the same time, the slope is continuously estimated in block 231 before moving to macro-block 240 . During the first application 230 , the force applied thus allows stopping the vehicle ( in the case of application with speed other than zero) and attenuating the pitch movements , which therefore will affect the slope estimation much less .

[0052] In macro-block 240 , at block 241 , one moves on to the same verification as in block 212 (block for the verification of the convergence of the slope estimation) . I f yes , in block 243 one verifies if the slope estimation is greater than the slope threshold ( Slope Estimation > SLP_THS ) used to determine the minimum parking force applied in block 232 . I f the estimated slope is less than threshold SLP_THS, this means that the minimum force applied in block 232 is such as to ensure the parking of the vehicle, and therefore the parking action is ended and the correct parking state is achieved in 260 . I f instead the slope estimation is greater than the threshold, one moves on to the macro-block 250 of second force application . I f the verification in block 241 is negative (there is no convergence in the slope estimation) , in the optional block 242 it is verified if the speed of the motor vehicle is greater than a predetermined speed threshold, 0 . 7 km / h, for example . I f the motor vehicle has a greater speed, the aforesaid macro-block 250 is also reached in this case . Instead, if the motor vehicle has a lesser speed, one moves on to the waiting macroblock 270 , which is optional . If there is no waiting macro-block, one moves on again to block 250 (also in the absence of 242 ) and moves on to the second application . The (waiting) time window serves to give the algorithm more time to converge, and thus avoid the second application if not required .

[0053] Describing now the macro-block 250 , in the first block 251 , set the target force equal to a predetermined maximum force (Force_Target = F_Max) , and then one moves on to the request 252 of applying the hydraulic support (optional, made by the EPB - Electronic Parking Brake - system to the ESC - Electronic Stability Control - system or any system in charge of generating pressure for the hydraulic support ) and then to block 253 , where it is verified if it is available or not ( i . e . , it is not in a fault state ) and if the hydraulic pressure target requested (portion of the braking force achievable by the hydraulic system) was achieved . I f yes , in block 254 , once the hydraulic support has been applied (or directly from block 251 and if the hydraulic support is not provided) , the electromechanical force is applied ( for the portion thereof to complete the hydraulic force or in any case to complete the target force ) and the parking action is ended in 260 . I f not (again only with the option of the hydraulic support ) , in block 255 it is signaled that the parking action ended with a fault state . Therefore, the system will not be in the correct parking state but in an unknown situation, and an error will be reported to the driver as a result .

[0054] As mentioned, if the hydraulic support is not required in the application, the steps 252 , 253 and 255 are not present . In this scenario, once the force target has been determined in block 251 , one moves directly on to the electromechanical actuation in block 254 .

[0055] Returning to the description of the optional block 242 , if the speed of the motor vehicle is less than the predetermined speed threshold, a waiting counter (Waiting Cnt ) is decreased in block 275 , and in the next block 274 it is verified if such a waiting counter is still greater than zero . I f not , one returns to the block 251 described above . I f yes , one moves on to the slope estimation in block 273 and then with the verification 272 as in block 212 ( convergence verification of the slope estimation) . In the case of negative convergence verification, one returns to decreasing the waiting counter in 275 ; in the case of positive convergence verification (the convergence exists ) , one moves on to block 271 , where it is verified if the slope estimation is greater than the slope threshold ( SLP_THS ) , as done and described in block 243 . I f the estimation is greater, one returns to block 251 ; if instead it is less , then the parking action in 260 is ended . The waiting time (number of cycles to be calibrated and defined if required based on the type of vehicle and the minimum force value in 232 ) is preferably provided to ensure the exhaustion of the oscillation transistors when the application after dynamic braking is requested (due to the action of the service brake or the dynamic operation of the parking brake ) . The convenience of the waiting time occurs if the vehicle is not stationary and the algorithm does not converge during the first force application, as can occur in special cases where a force application action is required after dynamic braking downhill . In these cases , once the first target has been achieved, a little more time is left for the algorithm to move on to convergence . If once this time has lapsed the convergence cannot be reached, a backup strategy is applied by setting a predetermined maximum force . However, such situations of application of the maximum force only occur in remote cases , i . e . , in a much smaller number of cases than that of the prior art .

[0056] In the flow diagram described, the second assessment 240 can optionally be performed in advance just before the end of the application at Fmin in 232 to carry out the calculation without interrupting the maneuver (useful in the case of application without hydraulic support ) .

[0057] The above-described steps of the method can be performed by an electronic control unit on board the wheeled motor vehicle . "Electronic control unit" means any means or electronic system capable of making the calculations and providing the above-described commands . Alternatively, the steps of the method can also be performed in a Cloud and the related commands sent to an ECU of the vehicle for the implementation .

[0058] Advantages of the invention

[0059] The invention relates to a control method for combined parking brake calipers ( referred to as ECS by the Applicant ) or standalone parking brake calipers ( referred to as EP by the Applicant ) .

[0060] The control method allows avoiding extra forces in the system when the vehicle is on level ground (or with a low slope ) but it is not possible to correctly estimate the road slope when the application request is received .

[0061] According to the prior art , during the sizing of the components , the worst-case usage condition must also be assessed, therefore the case in which the system always applies the maximum force due to a non-possible estimation of the road slope . This scenario is strongly critical for delivery or door-to-door collection applications characterized by a high number of cycles , almost all on level ground, but almost all at the limit of the static-dynamic threshold of the vehicle . By virtue of this method, it is possible to reduce the mechanical sizing of the calipers (avoiding overdesign or increasing the duration of the component , the design being equal ) .

[0062] In the case of combined calipers , the method described can be applied to both control systems utilizing the electromechanical application only and control systems utilizing the hydraulic support . In the latter case, the invention allows reducing the working cycles of the system generating the hydraulic support . As a consequence of applying only the force required and not the maximum one, the invention also allows reducing the parking times when the actual road slope does not require the application of the maximum force .

[0063] Preferred embodiments have been described above and variations of the present invention have been suggested, but it should be understood that those skilled in the art may make modifications and changes without departing from the related scope of protection, as defined by the appended claims .

Claims

CLAIMS1. The method of operating (200) the parking brake of a wheeled motor vehicle in motion on a road, the motor vehicle comprising an electronic control unit configured to control said braking system of the vehicle, the method comprising performing the following steps by the electronic control unit:A. Receiving a signal (213) requesting engagement of the parking brake;C. Performing the following sub-steps:Cl. Applying (232) via said braking system a first predetermined minimum braking force to stop the vehicle up to a predetermined maximum slope limit (SLP_THS) ;C2. Executing (231) a road slope estimation algorithm on the basis of acceleration data as obtained from a vehicle longitudinal acceleration sensor;D. After step C, carrying out an assessment (240) of the vehicle situation according to the following substeps :DI. Verifying (241) the convergence of said slope estimation algorithm in C2;D2. In case the verification of step DI is positive, checking (243) if the slope estimation is greater than the predetermined maximum slope limit (SLP_THS) of step Cl;D3. If the verification of step DI is negative, moving on to step El (250) ;D4. In the event that the verification (243) of stepD2 is negative, considering a correct parking state as reached and terminating (260) the method (200) ;D5. If the verification (243) of step D2 is positive, moving on to step E (250) ;E. Carrying out the following sub-steps:El. Applying (251) via said braking system a target force equal to a predetermined maximum force;E2. Considering the correct parking as reached and terminating (260) the method (200) .

2. Method according to claim 1, wherein between step El and step E2 the following sub-steps are performed in the case in which the vehicle's braking system is equipped with both an electromechanical subsystem and a hydraulic subsystem:E3. Checking (253) if the hydraulic subsystem is functional and if a predetermined portion of the target force has been reached by the hydraulic subsystem;E . If the verification of step E3 is positive, activating (254) the electromechanical subsystem for the remaining part of the target force and moving on to step E2.

3. Method according to claim 1, wherein in step D the evaluation (240) is brought forward to a time instant close to the end of step Cl .

4. Method according to one of claims 1 to 3, whereinif the verification ( 241 ) of step DI gives a negative result , one or more waiting cycles are carried out in which said road slope estimation algorithm is carried out on the basis of the longitudinal acceleration data and :- if in a waiting cycle the road slope is greater ( 271 ) than the predetermined slope limit ( SLP_THS ) , or if one or more waiting cycles have been finished ( 274 ) , going back to step El ;- if in a waiting cycle the road slope is smaller ( 271 ) than the predetermined slope limit ( SLP_THS ) , moving on to step E2 .5 . Method according to claim 4 , wherein before the one or more waiting cycles it is verified that the speed of the vehicle is smaller than a predetermined speed threshold, wherein if not , one passes to step D2 without carrying out the one or more waiting cycles .

6. Method according to one of claims 1 to 5 , wherein between step A and step C the following step B is carried out :B . carrying out a preliminary assessment ( 210 ) of the vehicle situation according to the following substeps :Bl . Performing a road slope estimation algorithm based on acceleration data obtained from a vehicle longitudinal acceleration sensor;B2 . Verifying ( 211 ) that the longitudinal speed of the vehicle obtained from said acceleration datais greater than a first predetermined threshold (THR) ;B3 . In the event that the longitudinal speed of the vehicle is smaller than the first predetermined threshold (THR) , verifying ( 212 ) that the slope estimation algorithm has reached convergence ; wherein step C is performed if the verification of step B2 is positive, or if the verification of step B3 is negative .7 . A motorized wheeled vehicle braking system, the braking system comprising an electronic system configured to perform steps A-E of the method according to any of claims 1 to 6 .8 . Braking system according to claim 7 , wherein said electronic system includes a cloud server that carries out the operations of steps A-E and communicates with an ECU control unit of the wheeled motorized vehicle to acquire data and provide actuation commands .

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