Method for operating motor vehicle, computer program product, storage medium, computer device

Abstract

To implement a requested braking force and / or a requested braking torque.SOLUTION: In the method, a motor vehicle includes at least one axle having a wheel, where the wheel is assigned a wheel braking device having an activatable actuator, in particular, electric machine. The actuator is activated, depending on a braking request, selectively with continuous or cyclic control of an operating point of the actuator for implementing a requested braking force and / or a requested braking torque.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for operating a motor vehicle, the motor vehicle having at least one axle with wheels, to which wheel brake devices with actuatable actuators are attached, in particular electric machines.

[0002] Furthermore, the invention relates to a computer program product, i.e., said computer program product implementing the above method when said computer program product is run on a computer arrangement, and further to a machine-readable storage medium comprising such a computer program product, and to a computer arrangement specially equipped for running said computer program product or for implementing said method. [Background technology]

[0003] All modern automobiles use braking force optimization methods at the wheels. These methods are required for the anti-lock systems (ABS) specified in most markets. In this case, the aim of the ABS is to adjust the axial force at the wheels as optimally as possible without locking the wheels, while at the same time ensuring steering. In this case, it is known to continuously or periodically control the operating point of the actuators associated with the corresponding wheel brake devices in order to meet the corresponding braking demands. Summary of the Invention

[0004] The method according to the present invention, which has the features of claim 1, is characterized in that, depending on the braking demand, the actuator is selectively activated by continuous or periodic control of the actuator's operating point to achieve the required braking force and / or brake torque. Thus, according to the present invention, whether the operating point is controlled continuously or periodically is determined depending on the situation. Depending on the situation, either continuous or periodic control is particularly advantageous, so that the method according to the present invention optimizes the overall braking action within the context of an anti-lock system. In periodic control, for example, an increase in braking force or brake torque at each wheel exceeds the maximum tire friction value, which is obtained, in particular, from a correspondingly known friction-wheel slip characteristic curve, so that the wheel is now in the unstable range. By reducing the braking force or brake torque, the wheel is accelerated again into the stable range. As soon as the wheel acceleration is sufficiently high, a new cycle of increasing the braking force or brake torque and periodic control is performed. Continuous control, for example, attempts to stay near the maximum friction value for as long as possible without exceeding it, but still below it. Both cyclical and continuous control have different advantages and disadvantages. A disadvantage of cyclical control is that after exceeding the maximum friction value and after the next required brake force or brake torque reduction, the wheel brake force or wheel brake torque remains in the suboptimally braked range below the maximum friction value for a certain time until the wheel stabilizes. During this time, the wheel is not optimally braked. An advantage of cyclical control is that the maximum friction value is always exceeded, for example, in the event of changes in ambient conditions that affect the corresponding characteristic curve and / or in the event of changes in the brake coefficient (Cp value) or load, thereby enabling powerful optimization of the braking action. A further advantage is that cyclical control can be implemented with fewer sensor devices (e.g., four wheel speed sensors (WSS)), which advantageously results in high availability (e.g., fallback systems). The advantage offered by continuous control is that the braking force or braking torque is always kept close to the optimum level for a long time, resulting in a very high average braking force or braking torque.In addition, for example, in the case of hydraulic brake systems, the modulation of the brake force or brake torque is less, which is advantageous in terms of driving comfort. A disadvantage of continuous control is, on the one hand, the relatively high demands on vehicle speed assessment in order to identify brake slip, which requires relatively high sensor costs and, to that extent, reduces availability in the event of a sensor failure. On the other hand, knowledge of the aforementioned characteristic curve is required to determine the optimal target slip. Therefore, the present invention basically involves the concept of optimally adapting or combining these control methods to the respective driving situation, and in particular alternating or switching between them depending on the situation. In this way, the advantages of both control methods are combined in such a way that their weaknesses are fully compensated for.

[0005] According to a further advantageous embodiment of the present invention, continuous control is performed only within the linear portion of the friction value-wheel slip characteristic curve, and cyclic control is performed within either the linear portion or the non-linear portion of the friction value-wheel slip characteristic curve. The advantages of the method according to the present invention are particularly pronounced when corresponding characteristic curves are used in this manner. The non-linear range is defined, in particular, to begin near the maximum friction value and extend up to the maximum wheel slip. As already mentioned above, continuous control always falls below the maximum friction value, while cyclic control exceeds the maximum friction value at least briefly, after which the operating point is shifted back into the linear range. In this case, each operating point is either on or below the characteristic curve within the respective range.

[0006] It is particularly advantageous to determine the type of braking request depending on at least one, particularly multiple, decelerations and / or on several parameters characterizing the sensor status, and to activate the actuator depending on the type of braking request. Thus, the selection of the corresponding control method, i.e., the selection of periodic or continuous control, is preferably derived from the type of braking request, particularly the required deceleration. Based on the required deceleration, it is possible to determine, for example, whether comfort braking or emergency braking is required, or, based on the availability of corresponding sensors, it is possible to determine whether the corresponding control is particularly suitable for assisting in determining values ​​related to the driving state (e.g., the vehicle's actual driving speed, friction values, and / or target values ​​for wheel slip). This advantageously ensures that the optimal control strategy is selected for each particular situation.

[0007] According to an advantageous further embodiment of the present invention, continuous control is implemented if a braking request is recognized within a predetermined deceleration range. The predetermined deceleration range is selected in particular so that it is within the comfort braking range, i.e., when the deceleration is relatively low, but at least provides a gap for emergency braking. In this case, in the case of pure comfort braking, it is preferable to completely omit cyclic control in order to achieve a more comfortable ride. Therefore, in such cases, selecting continuous control advantageously results in an improved comfortable ride, since continuous control is less noticeable to the driver than cyclic control, for example, due to a smaller travel when wheel pressure changes, a smaller pedal reaction, an improved NVH ratio, and a smaller volume consumption. In this case, the deceleration range particularly corresponds to one of the aforementioned parameters characterizing deceleration.

[0008] It is particularly advantageous to implement cyclic control if a braking request for maximum deceleration and / or a braking request for exceeding a predetermined threshold value for friction values ​​is recognized during a braking request. Such braking requests should be initiated, in particular emergency braking, where achieving the shortest possible braking distance is particularly important. In contrast, the aforementioned improvement in driving comfort, as in the case of comfort braking, is less important. For example, if the friction value / wheel slip characteristic curve is not known, continuous control during such ABS braking would require the characteristic curve to be determined for the first time, which would require a correspondingly long time and, in the case of emergency braking, for example, would initially increase the braking distance until the appropriate target slip is found. In this case, it is advantageous to implement cyclic control on at least one wheel at least at the start of the corresponding braking to achieve maximum braking effect. This has several advantages: on the one hand, if the characteristic curve is not known, the friction value maximum can be reliably exceeded for a short time and periodically exceeded for the purpose of indicating the characteristic curve; on the other hand, it is particularly easy to determine the appropriate brake pressure valve actuation point based on knowledge of the maximum value, since the corresponding state variables are known and can be calculated separately in a special way. In this case, the maximum deceleration and / or the threshold value correspond in particular to one of the aforementioned parameters characterizing the deceleration.

[0009] According to an advantageous further embodiment of the present invention, if a request for determining the actual vehicle speed, friction value, and / or target value for wheel slip is recognized during a braking request, cyclic control is implemented. As already mentioned above, cyclic control is particularly suitable for determining the actual vehicle speed, and as a result, improved vehicle speed support is achieved by implementing at least a short-term cyclic control on at least one wheel. That is, as mentioned above, by reducing the braking force or braking torque at a wheel after exceeding a maximum value, the wheel is re-accelerated to the current vehicle speed. This process within one cycle is advantageous because, on the one hand, it is carried out more quickly than the conventional adjustment phase of continuous control, in which the wheel must be purposefully underbraked, and, on the other hand, the wheel is overbraked, resulting in less loss of braking force. The corresponding request for determining the actual vehicle speed, friction value, and / or target value for wheel slip is also one of the parameters for supporting the determination of the sensor value, which, as mentioned above, characterizes the sensor status here. This is because the control can achieve the support of the corresponding values ​​or can change and / or adjust values ​​determined in other ways, in particular measured or assessed values.

[0010] It is particularly advantageous to implement cyclic control if a failure of a sensor device, especially an inertial sensor device, associated with the vehicle is detected during a braking request. This particularly advantageously increases the availability of the corresponding control. Depending on the available sensor devices, the control preferably has a more or less cyclic component. If the sensor device is only partially faulty, for example, a switchover to cyclic control is performed for at least a predetermined time, or an alternation between continuous control and cyclic control is performed at predetermined intervals. If, for example, the entire inertial sensor device is faulty, exclusively cyclic control is implemented, especially a switchover from continuous control to cyclic control. The failure of the sensor device is detected, in particular, as the respective sensor status of the corresponding sensor, which in this case corresponds to one of the aforementioned parameters.

[0011] According to a further advantageous embodiment of the invention, it is provided to switch from continuous control to periodic control at least for a certain time depending on the braking demand, which is particularly advantageous since it increases the robustness of the method. As mentioned above, such a switch is performed, for example, in the event of only a partial failure of the sensor device and / or for implementing a driving speed support, for determining a friction value and / or for adjusting a setpoint for wheel slip.

[0012] A computer program product according to the invention for execution on a computer arrangement with the features of claim 9 is characterized in that the computer program product, when used as specified, implements the method according to the invention, which results in the advantages already mentioned.

[0013] A machine-readable storage medium according to the invention with the features of claim 10 is characterized in that it has stored thereon a computer program product according to the invention.

[0014] A computer arrangement having the features of claim 11 is characterized in that it is specially equipped to run the computer program product according to the invention or to carry out the method according to the invention, which also results in the advantages already mentioned above. Preferably, the computer arrangement is a control arrangement associated with a motor vehicle, in particular arranged in the motor vehicle.

[0015] For example, a corresponding motor vehicle has at least one axle with at least one wheel, characterized in that the wheel is provided with a wheel brake device with an actuatable actuator, in particular an electric machine, and has at least one computer mechanism according to the invention formed as a control mechanism. This leads to the advantages already mentioned. Particularly advantageously, the motor vehicle has at least one first and second wheel on the axle, in which the first wheel, in particular on the left side of the motor vehicle, is provided with a first wheel brake device with an actuatable first actuator, in particular an electric machine, and the second wheel, in particular on the right side of the motor vehicle, is provided with a second wheel brake device with an actuatable second actuator, in particular an electric machine. This leads to the advantages already mentioned.

[0016] Further advantageous features and feature combinations are apparent from the foregoing description and the claims.The invention will now be explained in more detail with the aid of the drawings. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 illustrates an advantageous method of operating a vehicle. [Figure 2A] 10 is a graph of period control for the present method. [Figure 2B] 1 is a graph of the continuous control for the present method. [Figure 3] 1 is a graph of the combined control when implementing the method. [Figure 4] This is a graph of the slip value, which is important in this case. DETAILED DESCRIPTION OF THE INVENTION

[0018] An advantageous method for operating a motor vehicle will now be described with reference to Figure 1. For this purpose, Figure 1 illustrates the method on the basis of a flow chart. In particular, the method ensures that the braking action of the motor vehicle is optimized within the scope of anti-lock control.

[0019] The motor vehicle has at least one axle with wheels, each of which is provided with a wheel brake device, in particular an electric machine, with an actuatable actuator. The method according to the invention relates to wheel-level control of the actuator.

[0020] In step S1, the method begins by identifying a braking request, which requires that an actuator be correspondingly activated to satisfy the braking request. To this end, the actuator can essentially be activated using continuous or periodic control of the actuator's operating point to achieve the braking force and / or braking torque required in response to the braking request.

[0021] The periodic control that can be used within the scope of the method is illustrated in Figure 2A by three graphs positioned one above the other. Correspondingly, Figure 2B shows a similarly usable continuous control in three other graphs positioned one above the other. The top graph of the three graphs shows the friction value vs. wheel slip characteristic curve, in which the friction value μ is plotted against the wheel slip λ.

[0022] In this case, the characteristic curves each have a first linear section I and a second non-linear section II, the non-linear section II corresponding to the maximum friction value μ max and extends to the maximum value of wheel slip λ.

[0023] In the case of periodic control, the maximum value μ of the tire friction value obtained from the friction value-wheel slip-characteristic curve is obtained by increasing the braking force or braking torque at each wheel. max For this reason, for example, a first operating point B1 of the actuator on the characteristic curve is entered before the exceeding, and a second operating point B2 below the characteristic curve is entered after the exceeding, this second operating point B2 being below the characteristic curve within the non-linear portion II, at which operating point the wheel is in the region of instability.

[0024] The reduction in braking force or torque accelerates the wheel back into the stable range, in particular back to the operating point B1 on the characteristic curve inside the linear portion I. As soon as the wheel acceleration is high enough, a new cycle of braking force or torque increase and periodic control is carried out, as indicated by the corresponding arrow.

[0025] On the other hand, in the case of continuous control, the maximum value of the friction value μ max , but stays below it for a long time without exceeding it. For this reason, for example, if a first operating point B1 of the actuator, also on the characteristic curve, and a second operating point B2 on the characteristic curve are plotted, both first operating point B1 and second operating point B2 are inside the linear portion I and the wheel is in the stable region. As indicated by the corresponding double arrows, there is a constant alternation between the two operating points before the maximum value.

[0026] Thus, continuous control is performed only inside the linear portion I, and periodic control is performed either inside the linear portion I or inside the non-linear portion II.

[0027] The second graph in the middle of the three graphs shows the vehicle speed v F and wheel speed v R In the case of periodic control, the wheel speed v during R is the vehicle speed v at both operating points B1 and B2. F On the other hand, the wheel speed v R is the vehicle speed v F It can be seen that the intervals are clearly narrower than those of the first and second values, and the fluctuations are not as large.

[0028] The third lower graph plots the corresponding time course of the brake pressure p at each wheel over time t, and it can be seen that in cyclic control the brake pressure p reaches a maximum value after a first increase, in particular the locking pressure, which then drops again with the aforementioned decrease and rises again in the next cycle, whereas in continuous control the brake pressure p only fluctuates in small increments.

[0029] As already explained in detail above, both control methods have their own advantages and disadvantages. Therefore, the method according to the present invention aims to maximize the corresponding advantages and avoid the disadvantages as much as possible. For this purpose, in step S2, the actuator is selectively activated in continuous control or periodic control depending on the braking request. Preferably, the type of braking request is determined depending on at least one, particularly multiple, decelerations and / or depending on multiple parameters characterizing the sensor status, and the actuator is activated depending on the type of braking request.

[0030] Continuous control is performed if a braking request is recognized as a parameter within a predetermined deceleration range. Periodic control is performed if a braking request for maximum deceleration and / or a predetermined threshold value for the friction value during the braking request is exceeded, a request to determine the actual vehicle speed, the friction value and / or a setpoint value for wheel slip, and / or a failure of a sensor device, in particular an inertial sensor device, associated with the vehicle is recognized as a parameter during the braking request. If the braking request is then met, the method is terminated in step S3.

[0031] Preferably, the control is switched from continuous to periodic control for at least a predetermined time depending on the braking demand. Examples of this type are further illustrated in Figures 3 and 4, where Figure 3 shows four top and bottom graphs of the combined control when implementing the method, and Figure 4 shows graphs of the relevant friction and slip values.

[0032] Continuous control must be tailored to a specific tire or is based on specific tire characteristics established by the friction values, wheel slip, and characteristic curves discussed above. Changes in the tire, tire condition, and / or tire temperature can cause deviations in the target slip. The target slip adjustment method is time-consuming and is only performed during ABS braking. To remedy this, the illustrated embodiment switches to at least one cycle of cyclic control during continuous control, thereby achieving faster and more advantageous target slip adjustment and condition assessment.

[0033] The wheels are initially in continuous control. In the top graph of the four graphs, the binary time course of the switching signal for switching to periodic control is plotted. This switching signal is initially at logic 0. In the second graph of the four graphs, the time course of the speed is again plotted, in this case the vehicle speed v F , wheel speed v R actual value of the wheel speed, the first target value v S1 , the second target value of the wheel speed v S2 The velocity over time is again plotted.

[0034] First target value of wheel slip λ S1 First, find the corresponding formula.

[0035]

number

[0036] The switchover to periodic control is now effected via a switchover signal that is currently at logic 1. As previously mentioned, the switchover signal is triggered via parameters corresponding to the braking request (e.g., friction value and / or slip), and in this embodiment for the purpose of target slip adjustment, in particular for determining the actual friction value and / or target slip according to the request. Additionally or alternatively, the corresponding switchover signal can also be triggered via other parameters explicitly mentioned above, i.e., in particular, if a predetermined target value for the braking request and / or friction value for maximum deceleration during a braking request is exceeded, a request for determining the actual driving speed of the vehicle, and / or an at least partial failure of a sensor device associated with the vehicle during a braking request is recognized as a parameter.

[0037] Now, the braking force or braking torque is increased by periodic control until it exceeds the maximum value of the friction value. The basic mechanism has already been described above, so it will not be repeated here.

[0038] However, in Figure 3 it can be seen how the periodic control is implemented in the third of the four graphs for the time course of the wheel acceleration a, and in the fourth of the four graphs below the time course of the corresponding brake pressure p at the wheel.

[0039] As can be easily seen by comparing Figures 2A and 2B, correspondingly, continuous control is performed up to a first time point t1, periodic control is performed between the first time point t1 and a second time point t2, and continuous control is performed again from the second time point t2 onwards.

[0040] In this case, the characteristic curve and the target slip are adapted accordingly. The wheel pressure at the time of the pressure reduction corresponds to the force or torque at which the wheel becomes unstable and tends to lock, i.e., according to FIG. 2A, corresponds to the first maximum value in the cycle control. If the normal force is known, the maximum wheel slip value λ can be determined via this corresponding wheel pressure. maxcan be estimated approximately, and the maximum value of wheel slip λ max is plotted on the corresponding friction value-wheel slip characteristic curve in Figure 4, and the corresponding maximum value of friction value μ max is associated with.

[0041] The wheel speed at a given time is the first target value v S1 If it is smaller than (which is the case in this example), the target value of the wheel speed v S1 is too large, and the corresponding first target value of wheel slip λ, also plotted in Fig. 4, S1 It can be assumed that v is too small. In this case, a correspondingly lower second target value v of the wheel speed is set. S2 and therefore a second, higher target value λ of wheel slip. S2 Set the following.

[0042] However, since at the speeds considered the wheels tend to lock, it is advisable to set up a safety offset to keep the wheels in the stable range of the characteristic curve during continuous control, so that the second target value v of the wheel speed S2 Correspondingly, the second target value of wheel slip λ S2 Locked wheels slip on the curve λ B and the associated locking friction value μ B The corresponding lock-wheel slip λ is B In this case, the maximum value of wheel slip λ max can be approximately estimated, and the lock-wheel slip λ B and locking friction value μ B can be used to adjust the characteristic curve accordingly.

[0043] After the pressure is reduced, the wheels are accelerated again, and the friction value of the road is determined based on the maximum value of the acceleration a at this time. If the re-acceleration is small, the friction value is small, and if the re-acceleration is large, the friction value is large.

[0044] After re-acceleration, the wheel speed v RThis is preferable because it reaches a maximum value that represents the actual vehicle speed, thereby additionally determining the actual vehicle speed. As mentioned above, this type of reference support occurs through periodicity more quickly than other single wheel underbraking that is used in continuous control.

[0045] The transition from periodic control to continuous control occurs when the current wheel speed falls below the adjusted target wheel speed, i.e., when the actual value of the wheel speed v R is the second target value of the wheel speed v S2 As soon as it falls below t2, it is performed at time t2. [Explanation of symbols]

[0046] B1 actuator first operating point B2 actuator second operating point I. Friction value - wheel slip - linear portion of characteristic curve II. Friction Values, Wheel Slip, and Nonlinear Portions of Characteristic Curves

Claims

1. A method for operating a motor vehicle, the motor vehicle having at least one axle with wheels, the wheels being equipped with wheel brake devices with actuatable actuators, in particular electric machines, the method comprising the step of selectively controlling the actuator operating point (B) of the actuator depending on the braking demand. １ , B ２ ) by continuous or periodic control to implement the required braking force and / or required braking torque.

2. 2. The method according to claim 1, characterized in that the continuous control is performed only inside the linear portion (I) of the friction value-wheel slip characteristic curve, and the periodic control is performed either inside the linear portion (I) or inside the non-linear portion (II) of the friction value-wheel slip characteristic curve.

3. 3. The method according to claim 1, further comprising determining the type of braking request depending on at least one, in particular a number of, parameters characterizing deceleration and / or a sensor status, and activating the actuator depending on the type of braking request.

4. 4. The method according to claim 1, wherein the continuous control is performed if a braking request is recognized within a predetermined deceleration range.

5. 5. The method according to claim 1, wherein the periodic control is performed if a braking request for maximum deceleration and / or a friction value exceeding a predetermined threshold value is detected during a braking request.

6. 6. The method according to claim 1, wherein the periodic control is performed if, during a braking request, a request for determining a setpoint for the actual driving speed, a friction value and / or a wheel slip of the vehicle is recognized.

7. 7. The method according to claim 1, wherein the periodic control is performed if a fault in a sensor device, in particular an inertial sensor device, associated with the vehicle is detected during a braking request.

8. 8. The method according to claim 1, further comprising switching from the continuous control to the periodic control for at least a predetermined time depending on the braking demand.

9. 9. A computer program product for execution on a computer mechanism, characterized in that said computer program product, when used as specified, performs the method of any one of claims 1 to 8.

10. A machine-readable storage medium comprising the computer program product of claim 9.

11. A computer system, in particular an electronic control system for a motor vehicle, characterized in that the computer system is specially equipped to implement a computer program product according to claim 9.

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