Method and device for regulating the speed of a motor vehicle based on the vehicle's road grip

Abstract

The invention relates to a method for regulating the speed of a motor vehicle by means of a computer device installed on board. The invention also relates to a computer device (100) implementing such a method, as well as a motor vehicle (1) comprising such a device (100). Figure for the abstract: 1

Description

Title of the invention: Method and device for regulating the speed of a motor vehicle according to the vehicle's road grip Technical field of the invention

[0001] The present invention relates to the field of cruise control for motor vehicles. The invention relates in particular to a method of regulating the speed of a motor vehicle by means of a computer device installed on board the vehicle when it is traveling on a road. The invention also relates to a computer device implementing such a method, as well as a motor vehicle that includes such a device. Prior art

[0002] Most modern motor vehicles are equipped with cruise control. Generally, adaptive cruise control regulates the vehicle's speed to maintain a comfortable and safe distance from a vehicle ahead or, if there is no vehicle ahead, to maintain a set speed. Based on the current speed and the set speed, acceleration / deceleration rates are calculated and then converted into torque commands that are transmitted to the vehicle's actuators (i.e., powertrain, brakes).

[0003] Generally, cruise control is configured to apply acceleration values ​​between -3.5 m / s² and ±3.5 m / s² to produce a smooth and comfortable ride. However, the vehicle's road surface conditions are not taken into account when calculating these values. While it is reasonable to assume that a vehicle can achieve these acceleration values ​​under normal conditions, this may prove impossible when road surface conditions are poor (e.g., wet or snowy roads). This implies that known cruise control systems are not capable of correctly regulating speed regardless of road surface conditions. Summary of the invention

[0004] The invention aims to solve this problem. In particular, it aims to provide a solution for correctly regulating the speed of a motor vehicle regardless of the vehicle's road grip conditions. Through this, the invention aims to contribute to improved driving safety.

[0005] To achieve these goals, the invention relates, according to a first aspect, to a method of regulation by means of a computer device embedded on board a motor vehicle, of the vehicle's speed when traveling on a road, the process including the steps of: i. obtain data characterizing a value of the vehicle's adhesion to the road; ii. determine data characterizing a maximum achievable acceleration value based on the data obtained during step i); and iii. manage the operation of at least one vehicle actuator according to a torque command established based on the data determined during step ii).

[0006] According to one variant, step ii) may include the steps of: • determine data characterizing a maximum achievable torque value based on the data obtained during step i); and • determine the data characterizing a maximum achievable acceleration value as a function of the data characterizing a maximum achievable torque value, the radius of a wheel of the vehicle and the mass of the vehicle.

[0007] According to another variant, step iii) may include the steps of: • obtain data characterizing a value of the vehicle's current speed; • obtain data characterizing a desired acceleration value determined based on data characterizing a target speed and data characterizing the vehicle's current speed; and • determine data characterizing a usable acceleration value to establish torque control based on data characterizing a desirable acceleration value, data characterizing a maximum achievable acceleration value and at least one vehicle model.

[0008] According to yet another variant, the data characterizing an acceleration value usable for establishing the torque control can be determined as a function of data characterizing at least one disturbance influencing the available torque.

[0009] According to yet another variant, the torque control can be determined based on data characterizing at least one disturbance influencing the available torque.

[0010] According to yet another variant, the disturbance may concern the slope of the road, an aerodynamic force or the inertia of the vehicle's engine.

[0011] According to yet another variant, the data characterizing a value of the vehicle's road adhesion can be obtained by interacting with a remote vehicle server and / or an electronic vehicle trajectory corrector.

[0012] According to a second aspect, the invention relates to a device for regulating the speed of a motor vehicle when it is travelling on a road, the device comprising at least one information processing unit, including at least one processor, and a data storage medium configured to implement a method as described above.

[0013] According to a third aspect, the invention relates to a computer program comprising program code instructions for the execution of the steps of a process as described above when said program is executed by at least one processor.

[0014] According to a fourth aspect, the invention relates to a medium usable in a computer on which a program as described above is recorded.

[0015] According to a fifth aspect, the invention relates to a motor vehicle which includes a device as described above. Brief description of the figures

[0016] Other features and advantages of the invention will become apparent from an examination of the detailed description below, and the accompanying figures, in which:

[0017] [Fig-1] is a diagram of a motor vehicle according to the invention;

[0018] [Fig.2] is a functional diagram of a device according to the invention;

[0019] [Fig.3] is a flowchart of the steps of a process according to the invention;

[0020] [Fig.4] is a functional diagram illustrating the implementation of at least one step of the process according to the invention;

[0021] [Fig.5] are graphs that illustrate the operation of a motor vehicle equipped with a conventional cruise control when the vehicle's road grip conditions are optimal;

[0022] [Fig. 6] are graphs that illustrate the operation of a motor vehicle equipped with conventional cruise control when road conditions are poor; and

[0023] [Fig.7] are graphics that illustrate the operation of the motor vehicle according to the invention when the adhesion conditions are degraded. Detailed description of the invention

[0024] Figure 1 schematically illustrates a motor vehicle 1 according to the invention. This vehicle is equipped with a cruise control system 2, preferably adaptive, which allows the vehicle's speed to be regulated according to a set speed and a distance (or time) separating vehicle 1 from another vehicle. is located ahead. Furthermore, the cruise control 2 of the vehicle 1 according to the invention is preferably configured to be able to adapt the vehicle's speed based on contextual information concerning, for example, the presence of certain road signs (speed limits, road type, etc.), the presence of certain infrastructure (roundabouts, traffic circles, right-of-way rules, merging lanes, etc.), or ongoing disruptions (accidents, traffic jams, etc.). The vehicle according to the invention also includes radio frequency signal communication equipment 3 in order to communicate (i.e., send and receive data) with a remote communicating entity using conventional wireless communication protocols and networks. It also includes an electronic trajectory correction system 4, which is capable of determining the vehicle 1's road grip.

[0025] Advantageously, the vehicle 1 according to the invention further incorporates a device 100 for regulating the speed of a motor vehicle when it is travelling on a road within the meaning of the present invention, as described below, which implements a method for regulating the speed of a motor vehicle when it is travelling on a road within the meaning of the present invention, as briefly summarized below and described in detail below.

[0026] During implementation of the method, the device 100 according to the invention first obtains a value for the vehicle 1's road grip. To do this, it interacts, for example, with the electronic stability control system 4 or, by means of the radio frequency communication equipment 3, with a remote server of the vehicle 1 configured to monitor and establish the current road grip of the vehicle 1. Next, the device 100 according to the invention advantageously establishes a maximum achievable acceleration value based on the vehicle's road grip value that has been obtained. Finally, it manages the operation of at least one actuator of the vehicle 1 according to a torque command that it establishes based on the previously determined maximum achievable acceleration value.As will be seen below, this is how the device 100 according to the invention makes it possible to regulate the speed of the vehicle 1 by taking into account the vehicle's grip on the road, and thus contributes to an improvement in driving safety.

[0027] Figure 2 schematically illustrates the device 100 according to the invention of speed regulation of a motor vehicle when it is traveling on a road. It is essentially a computer device, which includes at least one information processing unit 101, comprising one or more processors, a data storage medium 102, on which is recorded, in particular, a program which includes program code instructions for the execution of the steps of the process according to the invention described below, and an input and output interface 103 enabling the reception and transmission of data.

[0028] Preferably, the device 100 according to the invention is hosted on an independent computer and interacts via its input and output interface 103 and by means of a wired vehicle communication network (e.g., CAN, Ethernet, MOST) – represented in [Fig. 1] by the double-direction arrows – with the cruise control 2, with the radio frequency signal communication equipment 3, and with the electronic stability control 4. Alternatively, the device 100 according to the invention is an integral part of the cruise control 2. As a result, the device 100 according to the invention can, in particular, obtain data characterizing a value of the vehicle's road grip and it can manage the operation of at least one vehicle actuator.

[0029] According to the invention, all the elements described above contribute to enabling the implementation of a method for regulating the speed of a motor vehicle when it is travelling on a road, as described below in relation to figures 3-7.

[0030] Figure [Fig. 3] illustrates by means of a flowchart the steps of the process according to the invention.

[0031] According to a first step 301 of the method according to the invention, the device 100 according to the invention obtains data characterizing a value of the vehicle's road adhesion. To do this, it interacts with the electronic trajectory corrector 4 or, by means of the radio frequency signal communication equipment 3, with a remote server of the vehicle 1 which is configured to monitor and establish the vehicle 1's road adhesion on which the vehicle is traveling. Thus, at the end of this first step of the method, the device 100 according to the invention advantageously holds data that define a value of the vehicle 1's road adhesion at the current moment.

[0032] Next, according to a second step 302 of the method according to the invention, the device 100 according to the invention determines data characterizing a maximum achievable acceleration value based on the data obtained during the previous step, in other words, the vehicle's road grip. To do this, it uses a tire model, for example, the Dugoff model, to estimate the forces applied to each of the vehicle's wheels as a function of the vehicle 1's road grip. For each of the wheels (i,j), the device 100 according to the invention thus determines an estimate of the lateral force Fvjj and the vertical force F^j applied at the tire's contact point as a function of the vehicle 1's current road grip obtained during the previous step.

[0033] Next, using the concept of the friction ellipse, the device 100 according to the invention determines the maximum force that can be applied to the wheel at time t. Thus, for each of the wheels, we have: [NECK]

[0035] where is the vehicle's road grip that was obtained during the previous step of the process and Fxij is the maximum force that can be transmitted to the wheel at at time t. It follows that:

[0037] The device 100 according to the invention then determines the maximum achievable torque, in other words a value of the maximum torque that can be passed to the front wheels, Vfrota- For this, it solves the following equation:

[0038] — R x {Fx jij1MX +Fxfr^ax}

[0039] where R is the radius of the wheel, Fx fijnax is the force applied to the front left wheel and Fx frmax is the force applied to the front right wheel.

[0040] Note that the above formula applies to a two-wheel drive vehicle. Similarly, for an n-wheel drive vehicle, we obtain:

[0041] p = i?x Y” F • * drive_wheels “ximax

[0042] where max is the force applied to wheel i.

[0043] Next, the device 100 according to the invention uses the maximum achievable torque value thus established to determine the maximum achievable acceleration value. To do this, it uses the mass of the vehicle by solving the following equation:

[0044] Tfmnt = Rx mass _yéhicule x maximum_attainable_acceleration

[0045] Thus, at the end of this second step of the process, the device 100 according to the invention has determined a maximum achievable acceleration value which advantageously depends on the current adhesion of the vehicle 1 to the road.

[0046] According to a third step 303 of the method according to the invention, the device 100 according to the invention manages the operation of at least one actuator of the vehicle based on a torque command established according to the data determined during the previous step of the method, in other words, the maximum achievable acceleration value which was established according to the vehicle's road grip. To this end, the device 100 according to the invention operates as follows.

[0047] Initially, the device 100 according to the invention interacts with the speed regulator 2 in order to obtain data characterizing an acceleration value It is desirable that the cruise control 2 establishes a set speed based on a target speed, which is determined, for example, based on the distance between vehicle 1 and a vehicle in front of it, and the current speed of vehicle 1. To do this, the cruise control Speed ​​control 2 comprises, for example, a first feedforward controller that receives the setpoint speed as input and is coupled to a second proportional feedback controller. The latter receives as input a comparison between the vehicle's current speed and an anticipated speed value established by the feedforward controller. The outputs of the feedforward controller and the proportional feedback controller are combined to establish the desired acceleration value obtained by the device 100 according to the invention. This is the acceleration to be applied, taking into account the setpoint speed and the vehicle's current speed, but without yet considering the vehicle's road grip.

[0048] Next, the device 100 according to the invention determines data characterizing a usable acceleration value for establishing torque control based on data characterizing a desired acceleration value, data characterizing a maximum achievable acceleration value, and at least one vehicle model. To this end, the device 100 according to the invention proceeds in the manner schematically illustrated by the functional diagram shown in [Fig. 4].

[0049] At the input of the upper branch, the vehicle's current speed is fed into a first module 401, which calculates a filtered derivative to obtain the acceleration measured at the current time. At the lower branch, the desired acceleration value is received as input, and a subtraction is performed between this value and a value corresponding to the difference between the measured acceleration and a modeled acceleration. This advantageously establishes an estimate of the divergence between the acceleration measured at the current time and the desired acceleration. Following the lower branch, this divergence is first saturated by means of a second module 402, which uses a first function, for example, a linear function, established as a function of the maximum achievable acceleration determined during the second step of the process.At the output of this second module 402, a third module 403 applies a second saturation by means of a second function, for example, a linear function over a first range of values ​​and a constant function over a second range of values, which is also determined based on the maximum achievable acceleration obtained during the second step of the process. Moving back up the branch, the output of the third module 403 enters a fourth module 404, which applies a third saturation by means of a third function, for example, a linear function over a first range of values ​​and a constant function over a second range of values, which is also determined based on the maximum achievable acceleration obtained during the second step of the process.Advantageously, these various saturations achieved by the second 402, the third 403, and the fourth 404 module allow for addressing different needs, for example, the need to enable energy-efficient driving. The output of the fourth module, 404, enters a fifth module, 405, which models the vehicle's powertrain. Finally, a sixth module, 406, models the vehicle, specifically its acceleration capabilities. The output of this sixth module, 406, provides an estimated acceleration that the vehicle can deliver, taking into account the maximum achievable acceleration. This estimate is then subtracted from the measured acceleration output of the first module, 401, as mentioned above.

[0050] As can be understood, this loop advantageously offers the behavior of an integral regulator. Indeed, a difference between the measured and estimated acceleration will be progressively compensated. The underlying idea is that if the vehicle can accelerate more than it actually does, then the acceleration can be increased, up to saturation by the maximum achievable acceleration, which is taken into account by the second module 402, the third module 403, and the fourth module 404. The output of this loop thus provides an acceleration value that can be used to control the operation of an actuator of vehicle 1.

[0051] According to an alternative embodiment, the saturations applied by the second 402, the third 403, and the fourth module 404 also take into account perturbations that influence the available torque. Such perturbations relate, for example, to the road gradient, an aerodynamic force, or the vehicle's inertia. Thus, according to this alternative, the device 100 of the invention determines a first torque value related to the road gradient by interacting with a sensor that measures the vehicle's inclination. Simultaneously, it determines a second torque value related to aerodynamic forces as a function of the vehicle's drag coefficient (Scx) and its speed. Furthermore, it determines a third torque value related to the engine's inertia as a function of the vehicle's speed (Sv).These torque values ​​are converted into acceleration values ​​using the calculation explained in connection with the first step of the process in which the wheel radius and the mass of the vehicle 1 are involved. These acceleration values ​​due to the disturbances are then used in the second 402, the third 403 and the fourth module 404. This gives a maximum saturation value, which corresponds to the maximum acceleration attainable depending on the vehicle's road adhesion determined during the second step of the process, minus the acceleration values ​​due to the disturbances, and a minimum saturation value, which corresponds to the maximum acceleration attainable depending on the vehicle's road adhesion multiplied by minus one, minus the acceleration values ​​due to the disturbances.For example, if the maximum achievable acceleration value that has been determined is 1 m / s² and the disturbances correspond to -0.2 m / s², the minimum saturation value will be -1.2 m / s² while the maximum saturation value will be 0.8 m / s².

[0052] According to another embodiment, the device 100 of the invention also weights the torque control, which is established as a function of the acceleration applied at the output of the loop, taking into account these same disturbances. All the torque values ​​due to the road gradient, aerodynamic forces, and engine inertia are thus added together, and the sum of these disturbances is added to the torque control established as a function of the acceleration applied at the output of the loop.

[0053] For clarity, Figure 5 illustrates the operation of a motor vehicle equipped with conventional cruise control when the vehicle's road grip is equal to 1, in other words, when grip conditions are optimal. The graph in the upper left shows the speed requested by the cruise control and the vehicle's actual speed. The graph in the upper right shows the torque requested. The graph in the lower left shows the requested acceleration and the vehicle's actual acceleration. The graph in the lower right shows the vehicle's road grip. As can be seen, the requested speed is correctly maintained, and the requested acceleration can be achieved at any time.

[0054] The operation of a vehicle is represented in the same way in [Fig. 6] In a car equipped with conventional cruise control, when the vehicle's road grip deteriorates (dropping from 1 to 0.1), the graph in the upper right shows that the vehicle is unable to apply the required torque due to the reduced road grip (the applicable torque is limited to between -250 Nm and 250 Nm due to the loss of grip). Thus, as shown in the graph in the upper left, the vehicle is unable to maintain the requested speed. Furthermore, as shown in the graph in the lower left, the cruise control loop continues to integrate at a value higher than the physically possible value. When a braking request is received while the requested acceleration is above the threshold, the integrator must return to a lower value, and during this time the vehicle does not brake and continues to accelerate.This graph shows, at the points marked by the arrows, that the acceleration is above the threshold for approximately 11 seconds, and it takes about 2 seconds for the setpoint with a negative derivative to return to the applicable range. We would observe similar behavior in the case of a positive acceleration request during braking with a torque below the lower threshold.

[0055] Figure 7 illustrates the same loss-of-traction situation managed by vehicle 1 according to the invention, which includes a cruise control system that incorporates or interacts with device 100 according to the invention. It can be seen that, since the vehicle cannot apply all the required torque from the moment the vehicle's traction on the road drops (top right graph), the acceleration is saturated. (Graph at bottom left). Thus, the acceleration does not exceed the maximum achievable acceleration, which means that the integrator is properly saturated. Subsequently, when braking is requested, the speed begins to decrease immediately without needing to wait for the integrator to return to this value. Vehicle 1 according to the invention can therefore advantageously produce the required speed despite the decrease in traction.

[0056] Thus, thanks to the method and device according to the invention described above, a solution is provided for correctly regulating the speed of a motor vehicle regardless of the vehicle's road grip conditions. In this way, the method and device according to the invention contribute to improved driving safety.

Claims

Demands

1. A method for regulating, by means of a computer device on board a motor vehicle, the speed of the vehicle when it is traveling on a road, characterized in that the method comprises the steps of: i. obtaining data characterizing a value of the vehicle's adhesion to the road; ii. determining data characterizing a maximum achievable acceleration value as a function of the data obtained during step i); and iii. managing the operation of at least one actuator of the vehicle as a function of a torque command established as a function of the data determined during step ii).

2. A method according to claim 1, characterized in that step ii) comprises the steps of: • determining data characterizing a maximum achievable torque value as a function of the data obtained during step i); and • determining data characterizing a maximum achievable acceleration value as a function of the data characterizing a maximum achievable torque value, the radius of a wheel of the vehicle and the mass of the vehicle.

3. A method according to any one of the preceding claims, characterized in that step iii) comprises the steps of: • obtaining data characterizing a value of the vehicle's current speed; • obtaining data characterizing a desired acceleration value determined based on data characterizing a value of a setpoint speed and data characterizing a value of the vehicle's current speed; and • determining data characterizing a usable acceleration value for establishing torque control based on data characterizing a desired acceleration value, data characterizing a maximum achievable acceleration value and at least one vehicle model.

4. Method according to claim 3, characterized in that the data characterizing an acceleration value usable for establishing torque control are determined as a function of data characterizing at least one disturbance influencing the available torque.

5. Method according to claim 4, characterized in that the torque control is determined as a function of data characterizing at least one disturbance influencing the available torque.

6. A method according to any one of claims 4-5, characterized in that the disturbance relates to the slope of the road, an aerodynamic force or the inertia of the vehicle's engine.

7. A method according to any one of the preceding claims, characterized in that the data characterizing a value of the vehicle's road adhesion are obtained by interacting with a remote vehicle server and / or an electronic vehicle trajectory corrector.

8. Device (100) for regulating the speed of a motor vehicle when it is travelling on a road, characterized in that the device comprises at least one information processing unit (101), comprising at least one processor, and a data storage medium (102) configured to implement a method according to any one of the preceding claims.

9. Computer program comprising program code instructions for carrying out the steps of a process according to any one of claims 1 to 7 when said program is executed by at least one processor.

10. A medium usable in a computer, characterized in that a program according to claim 9 is stored thereon.

11. Motor vehicle, characterized in that it comprises a device according to claim 8.

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