Method for operating motor vehicle, computer program product, storage medium and computer device
By using redundant actuators of motor and wheel brake equipment in electric vehicles, combined with dynamic control of slip target value and torque target value, the problems of insufficient motor torque and wear of friction brakes are solved, and higher precision slip control and energy recovery are achieved.
Patent Information
- Application Number
- CN202510224027.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2024-02-29
- Filing Date
- 2025-02-27
- Publication Date
- 2025-08-29
AI Technical Summary
Prior Art In the wheel slip control of electric vehicles, the motor torque is not sufficient to set the required slip by itself, and the use of friction brakes leads to wear and dust, making it difficult to maximize energy recovery and vehicle acceleration without using friction brakes.
The motor is used as the main actuator, combined with the redundant actuator of the wheel brake equipment and the driving equipment, and dynamically control each actuator by presetting the slip target value and torque target value to achieve precise slip control and avoiding the use of friction brakes.
Higher precision slip control is achieved, reducing the energy demand and wear of the actuator, improving vehicle functionality and avoiding wear and dust problems of friction brakes.
Smart Images
Figure CN120552809A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a method for operating a motor vehicle, wherein the motor vehicle has at least one axle, the axle having at least one wheel, wherein the wheel is equipped with a wheel brake system, the wheel brake system having a controllable first actuator, in particular an electric motor, and wherein the wheel is equipped with a drive system, the drive system having a controllable second actuator, in particular an electric motor.
[0002] The present invention also relates to a computer program product which, when executed on a computer device, performs the above-described method. Furthermore, the present invention relates to a machine-readable storage medium having such a computer program product, and a computer device specially designed to execute the computer program product or to implement the above-described method. Background Art
[0003] It is known to implement slip control in motor vehicles. The purpose of slip control is to regulate a given target slip at the wheels, in particular by presetting a corresponding slip target value or speed target value. In motor vehicles, friction brakes are typically used. By controlling the clamping force, the braking torque acting on the wheels can be influenced to regulate the desired wheel slip, for example as part of an anti-lock braking system (ABS) or a drive slip control system (ASR, traction control system TCS). Slip control can therefore be used both during acceleration and during braking. Summary of the Invention
[0004] The method according to the present invention is characterized in that, depending on an acceleration or braking request, at least one torque target value and at least one other target value selected from a slip target value and a speed target value are predefined, a distribution coefficient for distributing the torque target value to the actuators is predefined for the torque target value, and at least one of the actuators, in particular exactly one actuator, is controlled according to the predefined target value and the distribution coefficient to satisfy the acceleration or braking request. This ensures particularly advantageous slip control, in which each actuator involved can utilize its maximum possible dynamic potential. As mentioned at the outset, slip control is typically performed at least via the wheel brake system. In electric vehicles, it is recommended to incorporate an electric drive motor for wheel slip control because it can provide torque very quickly and precisely. One challenge in this regard is to consider the operating limits of the drive motor in wheel slip control. This motor often cannot provide sufficient torque to set the required slip independently, i.e., without the support of other actuators such as friction brakes. At the same time, however, it is desirable to exploit the potential of the electric motor as much as possible. This maximizes energy recovery during braking and vehicle acceleration during driving. In both cases, it is best to avoid the use of friction brakes to minimize wear and brake dust. A control method that prioritizes actuators for slip control is conceivable. A distinction is made here between primary and secondary actuators. The primary actuator provides a very dynamic torque contribution to maintain wheel slip at a predetermined operating point. Each secondary actuator provides only a slow torque contribution, thus serving only as a long-term corrective measure, such as preventing the primary actuator from exceeding its operating limits. Therefore, in electric vehicle control methods, the electric motor can assume the role of primary actuator. As long as the required torque is within the drive's possible operating range, it can vary the torque very dynamically and precisely. This is ensured by the friction brake, which ensures the motor operates at its optimal operating point with the smallest and slowest possible contribution. With this allocation, if a sudden change occurs, such as due to a sudden increase in friction, the friction brake must briefly adjust the wheel when the motor approaches its operating limit to achieve the target slip. To achieve this, it is necessary to monitor the motor's torque relative to its operating limit in order to trigger the switchover in a timely manner. In this method, a waiting period must be maintained to give the control system an opportunity to independently correct minor disturbances through the motor. Therefore, switching actuator strategies is difficult, and there's a risk of losing the slip operating point for a period of time in order to readjust the distribution of actuator torque contributions. However, to ensure that higher-level functions (such as the anti-lock braking system and / or drive slip control) always operate optimally, it's best not to lose this slip operating point. The method according to the present invention completely avoids these undesirable behaviors. To this end, the present invention predefines another target value: a slip target value or a speed target value. This provides the target slip for each wheel to ultimately be controlled.The present invention describes a control method for wheel slip control that controls multiple redundant actuators mechanically coupled to the wheels to perform slip control tasks. A special feature is that each actuator can utilize its maximum dynamic potential without prioritization. This allows for greater precision in wheel slip control than with previous approaches, in particular avoiding deviations from target slip, even when the actuators are operating at their limits, i.e., generating maximum torque. The corresponding wheel slip control advantageously further improves vehicle functions such as anti-lock braking systems and drive slip control, while reducing the energy demand of the actuators on energy storage devices (in particular, high-voltage batteries) and avoiding brake wear. The control method according to the present invention consists of two parts: firstly, target value presetting, by which a target torque operating point and a target slip (or target speed) are predefined for at least one, in particular, each, actuator, and this target value presetting is performed, for example, in a higher-level system, in particular, a central control unit. This is preferably based on an input interface to a higher-level vehicle function that requests wheel slip control and provides a wheel-specific target slip (or target speed). On the other hand, the method includes a mixed control of target slip and target torque operating points, with each actuator being controlled separately by controlling the actuator accordingly based on the target value. Preferably, the slip control of each actuator includes determining an actual slip value and taking this actual slip value into account in addition to the predetermined individual target slip in the wheel control. In summary, the advantages of the method according to the present invention include: avoiding slip operating point losses by switching actuators (e.g., when the operating limit of an individual actuator is reached); more precise slip control by fully utilizing the full dynamic characteristics of each actuator; better utilization of the torque potential of the electric machine; constant redundancy, as no explicit switching is required in the event of an actuator failure, but the surviving actuator immediately reacts to slip deviations caused by the failure; the ability to distribute functional components between controllers, as a clear distinction can be made between slow and fast functional components; scalability of the control method with respect to actuator types and actuator topologies in the vehicle; and finally, the ability to operate one actuator closer to its maximum operating value, thereby achieving a behavior in which the actuator has only minimal dynamic characteristics in its torque contribution, for example to enhance NVH (noise, vibration, and harshness) performance.
[0005] According to a preferred embodiment of the present invention, the axle has second wheels, and each of the wheels is equipped with a wheel brake system. In this regard, at least one actuator, i.e., a wheel brake system, is also equipped for the second wheel, which is controlled or controllable according to a preset target value and a distribution coefficient. The method according to the present invention thus ensures an overall favorable control of multiple wheels, thereby improving the slip control of the entire motor vehicle on at least one axle, as described above.
[0006] Particularly preferably, the wheels are jointly assigned a drive or individually assigned a drive, wherein the corresponding first and second actuators are each preset with at least one of the other target values. This results in the advantage that the overall system consisting of at least three actuators (i.e., two first actuators and at least one second actuator, each first actuator being assigned a different wheel brake system and the second actuator being assigned a drive) is advantageously optimized with respect to slip control. The drive preferably acts on both wheels via an open differential.
[0007] According to a preferred embodiment of the present invention, when a braking request is detected, a second actuator or the respective second actuator is controlled as a function of the torque target value and the respective other target value, and / or the respective first actuator is controlled solely as a function of the respective other target value. This creates a particularly advantageous control strategy for a braking request, in which all affected actuators are controlled using slip control, and only the actuators of the drive unit are additionally controlled using torque control.
[0008] Particularly preferably, when an acceleration request is detected, the respective first actuator is controlled as a function of the respective torque target value and the respective other target value, and / or one second actuator or the respective second actuator is controlled only as a function of the respective other target value. This creates a particularly advantageous control strategy for acceleration requests, in which all affected actuators are controlled using slip control and only the actuators of the wheel brake systems are additionally controlled using torque control.
[0009] According to a preferred development of the invention, an actual torque value of the actuator is determined and a corresponding torque target value is predefined as a function of the actual torque value. This advantageously ensures that the corresponding torque target value is predefined in a particularly robust manner.
[0010] Particularly preferably, the distribution factor is predefined as a function of the maximum torque that can be generated by the respective actuator. This has the advantage that the torque potential of the respective actuator can always be optimally utilized.
[0011] According to a preferred refinement of the present invention, the target values are preset by a central control device, and / or each actuator is equipped with its own control device, in particular a control device that is separately connected to the central control device for communication, wherein each actuator is controlled by its associated control device. The advantage of presetting the target values by the central control device is that, as described above, the target values are pre-set and valid for all actuators. If each actuator uses an independent control device, the advantage is that the actuators can always be controlled safely and independently of each other. A combination of a central control device and independent control devices is particularly advantageous, whereby the central control device presets the target values and transmits them to the control devices via a communication connection, so that the control task falls to multiple control devices.
[0012] The computer program product according to the invention for execution on a computer device is characterized in that, when used as intended, it performs the method according to the invention. This leads to the advantages mentioned above.
[0013] The machine-readable storage medium according to the present invention is characterized in that a computer program product according to the present invention is stored thereon.
[0014] The computer device according to the present invention is characterized in that it is specifically designed to execute the computer program product according to the present invention or to carry out the method according to the present invention. This also brings about the advantages already mentioned above. Preferably, the computer device is a control unit and / or a control device assigned to a motor vehicle (in particular, arranged in a motor vehicle).
[0015] For example, a corresponding motor vehicle has at least one axle with at least one wheel, wherein the wheel is equipped with a wheel brake system having a controllable first actuator, in particular an electric motor, and wherein the wheel is equipped with a drive system having a controllable second actuator, in particular an electric motor. Characteristically, at least one computer device according to the present invention is designed as a central control device and / or the computer device according to the present invention is designed as a control device assigned to at least one actuator. This results in the advantages mentioned above. Particularly preferably, the motor vehicle has at least a first wheel and a second wheel on the axle, wherein the first wheel, in particular assigned to the left side of the motor vehicle, is equipped with a first wheel brake system having a controllable first actuator, in particular an electric motor, and the second wheel, in particular assigned to the right side of the motor vehicle, is equipped with a second wheel brake system having another controllable first actuator, in particular an electric motor, and wherein these wheels are equipped with a common drive system or each wheel is equipped with a separate drive system having one or more controllable second actuators, in particular electric motors. This also results in the advantages mentioned above. BRIEF DESCRIPTION OF THE DRAWINGS
[0016] From the above description, further preferred features and feature combinations can be derived. The present invention will be described in more detail below with reference to the accompanying drawings. In particular:
[0017] Figure 1 shows an advantageous method of slip control at the wheel level,
[0018] Figure 2 Shown by Figure 1 The first application of the method derived at the axle level,
[0019] Figure 3 Shown by Figure 1A second application of the derived method is at the axle level. DETAILED DESCRIPTION
[0020] Figure 1 The steps of an advantageous method for slip control at the wheel level of a motor vehicle 1 are shown, wherein the motor vehicle 1 has at least one axle 2 with at least one wheel 3. The method is therefore shown for a single first wheel 3, wherein the motor vehicle 1 preferably has at least one further second wheel 4 on the axle 2, for which the same control structure is provided.
[0021] This is Figure 2 and Figure 3 The following are explained in Figure 1 The resulting extension of this method to the axle level involves two wheels 3, 4, each of which is assigned to a different side of the motor vehicle, in particular, the first wheel 3 on the left and the second wheel 4 on the right. For example, axle 2 is the front axle or the rear axle. It is also conceivable to provide the illustrated arrangement for both the front and rear axles, for example in all-wheel drive vehicles.
[0022] Figure 1 The wheels 3 in each case are equipped with a wheel brake system 5 having a controllable first actuator 6, which is designed as an electric motor in this case. Figure 2 and Figure 3 As shown, wheel 4 is also equipped with its own wheel brake system 5, which has its own first actuator 6. The two wheels 3, 4 are also equipped with a common drive device 7 by means of a differential 9 arranged on the axle 2, which has a controllable second actuator 8, which is designed as an electric motor in this case.
[0023] exist Figure 1 In the example of FIG, the actual slip control method (it is also possible to directly preset or control the speed without controlling the slip) works as follows for a single wheel 3: First, according to the acceleration request or the braking request, the first torque target value M is preset by the working point target value generator 10. 1S The operating point target value generator 10 is in particular part of a central control device.
[0024] In order to determine the torque target value M 1S , determine the torque actual values of the actuators 6 and 8 acting on the wheel 3 as input variables of the operating point target value generator 10, namely the first torque actual value M1 of the first actuator 6 of the wheel brake device 5 equipped with the wheel 3 and the second torque actual value M2 of the second actuator 8 of the drive device 7. In addition, for the torque target value M 1S The torque target value M is preset 1S Distribution coefficients assigned to actuators 6 and 8.
[0025] The distribution coefficient allows a certain ratio of the torque contributions of the individual actuators to each other to be set, in particular, only one of the actuators provides torque, or both actuators provide torque in a given ratio, such as 1:1, 2:1, 3:1, etc.
[0026] In particular, one actuator may provide maximum torque contribution, while the torque contribution of another actuator may only reach a certain limit. Furthermore, by determining a central operating point target value, it is also possible to adjust only the affected controller to a certain extent until the total torque of all actuators is reached, at which point further adjustments are no longer effective because the affected actuator can no longer transmit any more torque.
[0027] Now, at the first torque target value M 1S A difference is formed between the first torque actual value M1 and the first actual torque value M2, which is transmitted to the operating point controller 11, and another target value selected from the slip target value and the speed target value is preset. In this example, the first slip target value S is preset for the first wheel 3. 1R , and the slip target value S for actuator 6 1S Determined as the adjustment slip value S preset by the operating point controller 11 1T and the target slip value S 1R The sum of the following, where the adjustment slip value S 1T The slip change at the wheel 3 is determined in order to reach the corresponding operating point.
[0028] The purpose of this operating point control is to regulate the torque contribution of the respective actuator 6 , 8 to a target value by determining a corresponding adjustment slip, by which the actuator 6 , 8 increases or decreases slip to achieve the desired operating point. The described method can also be applied if the wheel speed is defined as the controlled variable instead of slip, and a higher-level vehicle function provides a corresponding target speed for each wheel.
[0029] Then, the slip target value S of the wheel 3 is 1S The difference between the determined first slip actual value S1 and the actual slip value S1 is then transmitted to the slip torque controller 12. The slip torque controller 12 then controls the first actuator 6 according to a predefined target value and a distribution factor to satisfy the acceleration request or braking request. The slip torque controller 12 and / or the operating point controller 11 are, for example, part of a control device associated with the actuator 6.
[0030] All other actuators 6, 8 have the same structure and ultimately contribute to the wheel slip control (addition) through mechanical coupling with the corresponding wheels 3, 4. The torque actually acting on the wheel 3 is obtained by the sum of the first torque actual value M1 and the second torque actual value M2.
[0031] The operating point control is connected upstream of the slip control and is preferably arranged slower than the slip control. This ensures that achieving a target slip ratio for a high-level vehicle function is prioritized by the actuator, while adjusting the operating point is prioritized less, which is advantageous for achieving high-level vehicle functions.
[0032] like Figure 2 and Figure 3 As shown, the described actuators (e.g., two first actuators 6 and one second actuator 8) can now be integrated into the control unit using the described control structure. Here, the operating point control is only applied to n-1 actuators, since the physical degrees of freedom of the system cannot be further utilized and would otherwise be overdetermined.
[0033] Advantageously, in order to control the slip of the electric vehicle, an operating point control is performed by the drive unit during braking. Figure 2 The control procedure in a corresponding first application of the method is shown when a braking request is detected.
[0034] Then, only the second actuator 8 is driven according to the corresponding third torque target value M 3S and a corresponding target value (similar to Figure 1 , is the third slip target value S for axle 2 3A ). The target value is determined in the calculation unit 13 as Figure 1 The first slip target value S for the first wheel 3 has been considered in 1R and the corresponding second slip target value S for the second wheel 4 2R The average value of .
[0035] and Figure 1 Similarly, the third torque target value M 3S The input variables are: Figure 1 The torque actual value M2 of the second actuator 8 already considered in , on the other hand, is the minimum value determined by a further calculation unit 14 from the first torque actual value M1 of the actuator 6 associated with the first wheel 3 and the third torque actual value M3 of the actuator 6 associated with the second wheel 4 .
[0036] The third torque target value M 3S and the third slip target value S 3A Used as Figure 1 The input variables of the operating point controller 11 and the slip torque controller 12 are designed similarly.
[0037] Therefore, the corresponding first actuator 6 is controlled only according to the corresponding other target value, that is, the actuator 6 associated with the first wheel 3 is controlled according to the first slip target value S for the first wheel 3.1R The simple slip controller 15 is used to control the actuator 6 of the second wheel 4 according to the second slip target value S for the second wheel 4. 2R It is controlled by means of a slip controller 15 .
[0038] For example, a freely definable portion of the maximum possible braking torque of the actuator 8 is used as the set torque target value M 3S , which is typically provided by the inverter or higher-level vehicle control. If the full torque potential is preset as the target value, the drive unit will, on average, make the maximum contribution to wheel slip control over time. However, if only a portion, such as 50% of the maximum possible torque, is preset, wheel slip control by the drive unit can still compensate for disturbances and dynamically increase or decrease its torque contribution without reaching its operating limits.
[0039] Particularly advantageously, when used for brake slip control in electric vehicles, the method fully utilizes the torque potential of the electric drive until the adjustable minimum contribution of the wheel brake systems is reached, so that they themselves do not violate their operating limits and continue to make a dynamic contribution to slip control.
[0040] For this application, one possible form of the function of the operating point target value generator (the delayed torque has a positive sign):
[0041] 1. Preset the maximum torque operating point of actuator 6 (friction brake),
[0042] 2. Preset the maximum value of the torque operating point of the actuator 8 (driver),
[0043] 3. Using the actual torque values M1, M2 or M2, M3 (corresponding to the tire potential), determine the sum of all actual torques acting on the respective wheels 3, 4, which originate from the actuators 6, 8,
[0044] 4. Determine the maximum of the zero value and the difference resulting from the sum determined in (3) and the maximum value predefined in (1) (the target value for the driving tire potential and the target value for the friction brake),
[0045] 5. Calculate the minimum value between the maximum value determined in (4) and the maximum value preset in (2), the maximum value preset in (2) corresponding to the torque target value M 3S , which is the final target operating point of actuator 8.
[0046] Advantageously, for electric vehicles whose drives are coupled via an open differential, wheels 3 and 4 with lower friction values are taken into account when determining the operating point of actuator 8. The slip controller can always apply a lower torque to these wheels via the friction brakes. It should be noted that the slip control of the drive can be achieved by detecting the rotational speed of the respective actuators or by providing an external signal representing the average rotational speed or average slip of wheels 3 and 4.
[0047] Advantageously, however, for control in the driving situation, the operating point is controlled via the wheel brakes (friction brakes), for example by presetting a torque target value of 0 Nm. This prevents unnecessary braking of the drive system while still enabling a response to disturbances that require intervention by the friction brakes (e.g., a negative jump in the friction value).
[0048] Therefore, for applications such as drive slip control, it is recommended to adopt a simulated operating sequence for the function of the operating point target value generator (acceleration torque has a positive sign and actuator 6 has a corresponding value between negative infinity and 0).
[0049] Advantageously, for drive slip control of an electric vehicle with axle drive and two friction brakes, the operating point of each friction brake is determined separately by taking into account the torque of the actuator 8 of each wheel 3, 4 when calculating the target value (the open differential distributes the engine torque evenly between the two wheels).
[0050] Figure 3 FIG. 4 shows the control operation mode in the second application of the method when an acceleration request is recognized. Figure 2 The difference is that only the two first actuators 6 are controlled as a function of their respective torque target values and the respective further target value, whereas the second actuator 8 is controlled only as a function of the respective further target value.
[0051] Therefore, the second actuator 8 is only controlled according to the corresponding third slip target value S for the axle 2. 3A It is controlled by means of the slip controller 15. Figure 2 As shown, this target value is determined in the calculation unit 13 as a first slip target value S for the first wheel 3. 1R and the second slip target value S for the second wheel 4 2R The average value of .
[0052] According to the first torque target value M for the first wheel 3 1S and the first sliding target value S 1R The first actuator 6 associated with the first wheel 3 is controlled accordingly. 1SThe first torque target value M1 of the actuator 6 associated with the first wheel 3 and the second torque target value M2 of the second actuator 8 are predefined by means of the corresponding operating point target value generator 10. 1S and the first slip target value S 1R Serves as an input variable for the operating point controller 11 and the slip torque controller 12.
[0053] According to the second torque target value M for the second wheel 4 2S and the second slip target value S 2R The first actuator 6 associated with the second wheel 4 is controlled accordingly. 2S The third torque actual value M3 of the actuator 6 associated with the second wheel 4 and the second torque actual value M2 of the second actuator 8 are predefined by means of the corresponding operating point target value generator 10. The second torque target value M 2S and the second sliding target value S 2R Used as input variable for the operating point controller 11 and the slip torque controller 12.
Claims
1. A method for operating a motor vehicle (1), The motor vehicle (1) has at least one axle (2), and the axle (2) has at least one wheel (3, 4); The wheels (3, 4) are equipped with a wheel brake system (5) having a controllable first actuator (6), in particular an electric motor; and The wheels (3, 4) are equipped with a drive device (7) having a controllable second actuator (8), in particular an electric motor; It is characterized in that According to the acceleration request or the braking request, at least one torque target value (M 1S 、M 2S 、M 3S ) and the slip target value (S 1R 、S 2R 、S 3A ) and at least one other target value selected from the rotational speed target value; is the torque target value (M 1S 、M 2S 、M 3S ) is preset to set the torque target value (M 1S 、M 2S 、M 3S ) distribution coefficients distributed to the actuators (6, 8); and According to the preset target value (M 1S 、M 2S 、M 3S 、S 1R 、S 2R 、S 3A ) and the distribution coefficient, controlling at least one actuator, in particular exactly one actuator, of the actuators (6, 8) to meet the acceleration request or the braking request.
2. The method according to claim 1, characterized in that The axle (2) has second wheels (3, 4), and the respective wheels (3, 4) are each equipped with a wheel brake device (5).
3. The method according to claim 2, characterized in that The wheels (3, 4) are equipped with the drive device (7) in common or are equipped with drive devices respectively, wherein the corresponding first actuator (6) and second actuator (8) are respectively preset with the other target value (S 1R 、S 2R 、S 3A ) in at least one of .
4. The method according to claim 3, characterized in that When a braking request is recognized, the second actuator (8) or the corresponding second actuator (8) is driven according to the torque target value (M 1S 、M 2S 、M 3S ) and the corresponding other target values (S 1R 、S 2R 、S 3A ) is controlled, and / or the corresponding first actuator (6) is controlled only according to the corresponding other target value (S 1R 、S 2R 、S 3A ) is controlled.
5. The method according to claim 3 or 4, characterized in that When an acceleration request is recognized, the corresponding first actuator (6) is driven according to the corresponding torque target value (M 1S 、M 2S 、M 3S ) and the corresponding other target values (S 1R 、S 2R 、S 3A ) is controlled, and / or the second actuator (8) or the corresponding second actuator (8) is only controlled according to the corresponding other target value (S 1R 、S 2R 、S 3A ) is controlled.
6. The method according to any one of the preceding claims, characterized in that Determine the actual torque value (M1, M2, M3) of the actuator (6, 8), and preset the corresponding torque target value (M1, M2, M3) according to the actual torque value (M1, M2, M3) 1S 、M 2S 、M 3S ).
7. The method according to any one of the preceding claims, characterized in that The distribution coefficient is predetermined according to the maximum torque that can be generated by the respective actuator (6, 8).
8. The method according to any one of the preceding claims, characterized in that The target value (M 1S 、M 2S 、M 3S 、S 1R 、S 2R 、S 3A ) is preset by a central control device, and / or each actuator (6, 8) is equipped with its own control device, in particular a control device that is technically connected to the central control device for communication, wherein each actuator (6, 8) is controlled by its equipped control device.
9. A computer program product for execution on a computer device, characterized in that The computer program product, when used as intended, performs a method according to any one of the preceding claims.
10. A machine-readable storage medium having the computer program product according to claim 9.
11. A computer device, in particular an electronic control unit and / or a control device, for a motor vehicle, characterized in that The computer device is specially designed to execute the computer program product according to claim 9.