Method and controller for shunting a vehicle with a defect of an individual wheel steering adjuster of a driven wheel

Abstract

The invention relates to a method for shunting a vehicle (100) with a defect (106) of an individual wheel steering adjuster (102) of a driven wheel (104) of the vehicle (100), wherein a torque is set on the wheel (104) on the basis of the steering angle of an opposite wheel (104) of the vehicle (100) for shunting purposes.

Description

[0001] Description

[0002] Method and control device for maneuvering a vehicle with a defect in an individual wheel steering actuator of a driven wheel

[0003] Field of the invention

[0004] The invention relates to a method for maneuvering a vehicle with a defect in an independent wheel steering actuator of a driven wheel, a corresponding control unit, and a corresponding computer program product.

[0005] State of the art

[0006] A vehicle may have an electromechanical steering system. A driver's steering input is transmitted from the vehicle's steering wheel via a mechanical connection to the vehicle's steered wheels. The steering input is detected and assisted by an electric actuator. If the actuator fails, the driver can continue to steer the steered wheels, even if increased resistance must be overcome.

[0007] In a vehicle with independent wheel steering actuators, there is no mechanical connection between the steering wheel and the steered wheels. The steering impulse is converted into an electrical signal at the steering wheel, and the independent wheel steering actuators are controlled using this signal.

[0008] If an independent wheel steering actuator is defective, the affected wheel can no longer be steered as intended. The defect can be a complete failure or simply a functional limitation. If the independent wheel steering actuator fails completely, it can be configured so that it exerts no actuating forces and, if any, only minimal holding forces on the wheel. This allows the wheel to self-center via its caster while driving, thus maintaining emergency running capability. However, self-centering via the caster only works when the vehicle is moving.

[0009] Disclosure of the invention

[0010] Against this background, the approach presented here provides a method for maneuvering a vehicle with a defect in an independent steering actuator of a driven wheel, a corresponding control unit, and a corresponding computer program product according to the independent claims. Advantageous further developments and improvements of the approach presented here emerge from the description and are described in the dependent claims.

[0011] Advantages of the invention

[0012] When a vehicle with a defective independent wheel steering actuator starts moving from a standstill, the self-centering of the wheel controlled by the defective independent wheel steering actuator only functions above a certain speed. Below this speed, the wheel's angular position is strongly influenced by the torque applied to the wheel, for example, by the drive or brake.

[0013] In the approach presented here, the torque applied to the wheel is influenced in order to prevent an undesired change in the angular position and / or to bring about or promote a desired change in the angle.

[0014] The approach presented here allows the vehicle to start from a standstill despite a defect in an independent wheel steering actuator, without the wheel with the defective independent wheel steering actuator turning transversely to a desired direction of travel and thus preventing it from starting.

[0015] A method for maneuvering a vehicle with a defect in an individual wheel steering actuator of a driven wheel of the vehicle is presented, wherein for maneuvering a torque at the wheel is adjusted as a function of a steering angle of an opposite wheel of the vehicle or as a function of the steering wheel angle.

[0016] Ideas for embodiments of the present invention can be considered, among other things, to be based on the thoughts and findings described below.

[0017] A vehicle with independent wheel steering actuators can have a right independent wheel steering actuator and a left independent wheel steering actuator on a steered axle. The vehicle can also have independent wheel steering actuators on multiple axles. Each independent wheel steering actuator acts on a separate steerable wheel of the vehicle. The independent wheel steering actuators or the wheels of the steered axle are not mechanically coupled to each other or to the vehicle's steering wheel. The independent wheel steering actuators are controlled via data signals from a central sensor on the steering wheel or a steering lever of the vehicle.

[0018] If one of the independent wheel steering actuators is defective, the other is unaffected. If the independent wheel steering actuator is defective, it may be completely non-functional or only have limited functionality. If the independent wheel steering actuator is completely non-functional, it can exert no or only minimal steering torque on the wheel. The defective independent wheel steering actuator may also exert a slight braking torque on the wheel. If the independent wheel steering actuator is defective, it may, for example, exert a reduced steering torque on the wheel and / or apply a reduced steering speed.

[0019] If one of the independent wheel steering actuators is defective, essentially only the wheel on the steered axle that is coupled to the other intact independent wheel steering actuator can be fully steered. If the vehicle is rolling and the wheel with the defective independent wheel steering actuator rolls freely or only small moments act on the wheel, the wheel with the defective independent wheel steering actuator can center itself via its caster, i.e. essentially adapt its angle to the direction of movement of the vehicle. If external torques, such as a drive torque or braking torque on the wheel with the defective independent wheel steering actuator exceed the self-centering torque and / or the inhibiting torque of the defective independent wheel steering actuator, the wheel can collapse and its angle can therefore deviate from the direction of movement of the vehicle, i.e. be oriented at an angle or perpendicular to the direction of movement.

[0020] When maneuvering, the vehicle is stationary, starts moving from a standstill, and travels at very low speeds. The wheel's self-centering via the caster may therefore function only to a limited extent or not at all. When maneuvering, for example, the vehicle travels in a speed range between zero and seven km / h.

[0021] If the torque would turn the wheel in a direction opposite to a steering angle at the other wheel and would therefore inhibit the directional movement of the vehicle, the torque can be prevented, delayed and / or at least reduced.

[0022] The torque can also be adjusted depending on the current angular position of the wheel. If the current angular position of the wheel essentially corresponds to the steering angle of the other wheel, for example, only a portion of the normally used torque can be applied so as not to change the angular position of the wheel significantly. If, however, the angular position deviates significantly from the steering angle, a forward or reverse torque can be applied to actively bring the angular position of the wheel at least closer to the steering angle. The torque for aligning the wheel can be applied before the drive torque is applied to the opposite wheel, so that the wheel is already at least approximately aligned before the vehicle starts rolling. When the vehicle starts rolling, the wheel can easily center itself using its caster.

[0023] The torque can also be adjusted depending on the drive torque on the opposite wheel. The applied torque can be set to be lower than the drive torque. Only a portion of the drive torque can be adjusted at the wheel. This can prevent folding. The torque can also be adjusted in the opposite direction to the drive torque, allowing a slightly folded wheel to be unfolded again. When the wheel is unfolded, only a portion of the drive torque can be adjusted in the direction of the drive torque. The torque can be adjusted to be lower by a proportionality factor than the originally intended drive torque. For example, the torque can be set to be 1 / 3 or 1 A of the drive torque can be set.

[0024] The torque can be adjusted with a time delay relative to the drive torque at the opposite wheel. The drive torque can be applied first to get the vehicle rolling. This allows the wheel with the defective independent wheel steering actuator to align itself with the steering direction of the functioning wheel. The torque can then be adjusted. A reduced torque can also be set.

[0025] A torque gradient can be reduced. A drive torque gradient can also be reduced. By reducing the gradient, wheel jerking can be avoided and the wheel can be prevented from folding. Alternatively, the torque gradient can be set smaller than the drive torque gradient. This allows the torque to increase more slowly than the drive torque. This gives the wheel time to self-center.

[0026] The torque can be adjusted depending on the vehicle's speed. The torque can be set lower the slower the vehicle is traveling. The wheel's self-centering ability increases with increasing speed. This allows for increasing torque to be transmitted without the wheel collapsing.

[0027] The method is preferably computer-implemented and can be implemented, for example, in software or hardware or in a mixed form of software and hardware, for example in a driver assistance system.

[0028] The approach presented here further creates a control unit, wherein the control unit is designed to carry out, control or implement the steps of a variant of the method presented here in corresponding devices.

[0029] The control unit can be an electrical device with at least one computing unit for processing signals or data, at least one memory unit for storing signals or data, and at least one interface and / or a communication interface for reading in or outputting data embedded in a communication protocol. The computing unit can be, for example, a signal processor, a so-called system ASIC, or a microcontroller for processing sensor signals and outputting data signals depending on the sensor signals. The memory unit can be, for example, a flash memory, an EPROM, or a magnetic storage unit. The interface can be designed as a sensor interface for reading in the sensor signals from a sensor and / or as an actuator interface for outputting the data signals and / or control signals to an actuator.The communication interface can be configured to read or output data wirelessly and / or via a wired connection. The interfaces can also be software modules, which are present, for example, on a microcontroller alongside other software modules.

[0030] Also advantageous is a computer program product or computer program with program code that can be stored on a machine-readable carrier or storage medium such as a semiconductor memory, a hard disk memory or an optical memory and is used to carry out, implement and / or control the steps of the method according to one of the embodiments described above, in particular when the program product or program is executed on a computer, in a control unit or a device.

[0031] It should be noted that some of the possible features and advantages of the invention are described herein with reference to different embodiments. A person skilled in the art will recognize that the features of the control device and the method can be combined, adapted, or exchanged as appropriate to achieve further embodiments of the invention.

[0032] Short description of the drawings

[0033] Embodiments of the invention are described below with reference to the accompanying drawings, whereby neither the drawings nor the description are to be interpreted as limiting the invention. Fig. 1 shows a representation of a vehicle with a defective

[0034] Single-wheel steering actuator during maneuvering using a method according to an embodiment; and

[0035] Fig. 2 shows a representation of steering angle curves and torque curves according to a method according to an embodiment.

[0036] The figures are merely schematic and not to scale. Like reference numerals denote like or equivalent features.

[0037] Embodiments of the invention

[0038] Fig. 1 shows a representation of a vehicle 100 with a defective independent wheel steering actuator 102 during maneuvering using a method according to an exemplary embodiment. The vehicle 100 has front-wheel drive. Front wheels 104 of the vehicle 100 are thus steerable and coupled to a drive system of the vehicle 100. The drive system is designed to provide individually adjustable torques to both front wheels 104. The torque at the front wheel 104 with the defective independent wheel steering actuator 102 is referred to here as the torque. The torque at the front wheel 104 with the functioning independent wheel steering actuator 102 is referred to as the drive torque.

[0039] Here, for example, the left independent wheel steering actuator 102 has a defect 106. The right independent wheel steering actuator 102 is fully functional. The defective independent wheel steering actuator 102 cannot exert any steering torque on the left front wheel 104. Due to the defect 106, the independent wheel steering actuator 102 could alternatively only provide a reduced steering torque. Here, the defective independent wheel steering actuator 102 exerts only a slight holding torque on the left front wheel 104. When the vehicle 100 rolls, the left front wheel 104 can therefore adapt its steering angle to a direction of movement of the vehicle 100 via its caster if a torque generated by the caster is greater than the holding torque and an external torque generated by braking or driving the front wheel 104.

[0040] Here, for example, the vehicle 100 is parked in a parking space between two obstacles 108, such as other parked vehicles, parallel to the right curb 110. To exit the parking space, the vehicle 100 must roll forward and be steered with large steering angles. Since the distance to the front obstacle 108 is greater than the distance to the rear obstacle 108, it is necessary to roll forward and steer to the left.

[0041] By applying a torque to the steered wheel, an external moment is generated via a steering roll radius and / or a disturbance force lever arm, which would cause the wheel to fold around a steering axis of the wheel.

[0042] At the right front wheel 104 of the vehicle 100, the intact right independent steering actuator 102 supports this external torque, thus preventing uncontrolled folding to the left. The right independent steering actuator 102 applies the steering torque to steer the right front wheel 102 to the left. At the right front wheel 104, the external torque and the steering torque thus complement each other. This only applies here because an inward steering movement is taking place.

[0043] On the left front wheel 104, the defective left independent steering actuator 102 can only support the external torque via the remaining holding torque. If the external torque exceeds the holding torque, the left front wheel 104 will fold to the right and thus be positioned perpendicular to the desired direction of travel.

[0044] In the approach presented here, the torque at the front wheel 104 is controlled by the defective independent wheel steering actuator 102 depending on a desired starting direction of the vehicle 100 in order to prevent folding.

[0045] In one embodiment, the torque is adjusted depending on the drive torque set at the right front wheel 104. The torque is set smaller than the drive torque. For example, the torque is set smaller than the drive torque by a proportionality factor. The reduced torque also reduces the tendency of the left front wheel 104 to collapse.

[0046] In one embodiment, the torque at the left front wheel 104 is applied more slowly than the drive torque at the right front wheel 104. Due to the slow application, the torque increases less per unit of time than the drive torque. In other words, the gradient, or increase, of the torque relative to the drive torque is reduced. The slower increase reduces the tendency of the left front wheel 104 to collapse.

[0047] In one embodiment, the torque is applied to the left front wheel 104 with a time delay. The drive torque is first applied to the right front wheel 104, and the torque is applied to the left front wheel 104 with a time delay. Due to the time delay, the left front wheel 104 rolls without torque and can freely align or stabilize itself. After the left front wheel 104 has been aligned or stabilized, the torque is applied.

[0048] In one embodiment, the torque is applied depending on the vehicle's speed. At low speeds, only a small amount of torque is applied, while at higher speeds, a higher torque is applied. Due to the speed, the wheel stabilizes itself through its caster and can support the external torque through the torque generated by the caster.

[0049] Fig. 2 shows a representation of a steering angle curve 200, an angular position curve 202, a drive torque curve 204, a torque curve 206, and a speed curve 208 when maneuvering a vehicle using a method according to an exemplary embodiment. The vehicle essentially corresponds to the vehicle in Fig. 1. The steering angle curve 200 shows a time curve of a steering angle of the right front wheel. The right front wheel is steered by the functional independent wheel steering actuator. The angular position curve 202 shows a time curve of an angular position of the left front wheel. The left front wheel is coupled to the defective independent wheel steering actuator. The steering angle curve 200 and the angular position curve 202 can be referred to as toe angle curves. The drive torque curve 204 shows a time curve of a drive torque on the right front wheel.The torque curve 206 shows a time curve of the torque at the left front wheel. The speed curve 208 shows a time curve of the vehicle's speed.

[0050] The curves are shown in a diagram with time on the abscissa and the angular position, steering angle, drive torque, torque, and speed on the ordinate. Initially, the steering angle and angular position are zero degrees (0°). The two front wheels are thus aligned in the same longitudinal direction. To maneuver out of the parking space, the vehicle is steered to the left. Due to the defect in the left independent steering actuator, only the steering angle of the right front wheel changes. The angular position of the left front wheel remains constant at zero degrees.

[0051] The drive torque is then applied to both front wheels. The torque is applied depending on the steering angle.

[0052] In one embodiment, a lower torque is applied to the left front wheel with the defective independent steering actuator than the drive torque applied to the right front wheel.

[0053] In one embodiment, one third of a total torque is applied to the left front wheel, while two thirds of the total torque is applied to the right front wheel.

[0054] In one embodiment, the torque is applied with a lower gradient than the drive torque.

[0055] In an embodiment not shown, the torque is applied with a time delay after the drive torque.

[0056] Due to the different application of torque and drive torque, the vehicle begins to roll and the speed increases. During the roll, the angular position of the left front wheel changes to the left, even briefly exceeding the target steering angle based on the steering angle of the reference wheel.

[0057] After the angular position of the left front wheel has adjusted to the steering angle of the right front wheel, the vehicle rolls out of the parking space and the right front wheel is turned to the right. As the rolling speed increases, the left front wheel begins to self-center, and the angular position of the left front wheel follows the steering angle of the right front wheel to the right with a slight delay.

[0058] The right front wheel is then centered again. The left front wheel follows the centering movement again with a slight delay. Once both front wheels are essentially aligned in the vehicle's longitudinal direction again, the torque and drive torque are reduced, and the vehicle comes to a stop. The maneuver was thus completed despite the defective left independent wheel steering actuator and is now complete.

[0059] In the following, possible embodiments of the invention are summarized again or presented with slightly different wording.

[0060] An operating strategy for the drive torque distribution in the case of a defective individual wheel steering actuator for parking maneuvers is presented.

[0061] Today's vehicles are equipped with electromechanical steering connected to both wheels. Steering systems are increasingly moving toward by-wire systems, which are mechanically decoupled from the driver. This eliminates the traditional mechanical connection between the driver and the wheels via the steering wheel. In the case of the steering, the corresponding actuation is then achieved solely via one or more actuators. Centralized, as well as decentralized, by-wire steering actuators are already being installed on the rear axle (ZF: AKC). On the front axle, by-wire independent wheel steering actuators are being used in initial prototype vehicles, such as the Speed ​​E research vehicle.

[0062] Active torque shifts on an unsteered axle can support or influence the vehicle's cornering behavior. For independent wheel steering actuators, it has been shown that free steepening behavior without self-locking is advantageous in the event of a fault. Here, the torque shifts are adapted for the fault case of independent wheel steering actuators on driven wheels.

[0063] The approach presented here provides an optimized control strategy for parking with an independent wheel steering actuator in the event of a steering actuator failure. Front-wheel drive vehicles are particularly problematic due to the kinematic relationships between the drive torque and the resulting steering torque. Special handling of the drive and brakes is required in the event of an independent wheel steering actuator failure, as the axle centering effect is speed-dependent due to, among other things, caster. At low speeds, such as when parking, this is not yet sufficient to stabilize the wheel. This and other effects can cause a passively failed independent wheel steering actuator to collapse.

[0064] If the steering actuator were intact, the movement induced by the drive torque would be prevented by the actuator, or the target position would be set. A central element of the approach presented here is therefore to prevent the wheel from rotating unfavorably around the vertical axis due to the steering roll radius and a drive torque. Without adapted control of the drive and / or brake, the steering roll radius in combination with a drive torque can lead to unwanted wheel movements and even folding of the wheel when the actuator fails, which would prevent further maneuvering of the vehicle. Therefore, drive control strategies are proposed that prevent such negative behavior with front-axle drive.

[0065] To enable the vehicle to move forward out of a parking space with a failed independent steering actuator, various operating strategies are proposed. In the following analysis, the left inside-curve actuator has failed as an example.

[0066] Without further measures, when driving off with a steering wheel angle of 360° to 480° and adjusting the wheel steering angle accordingly, only on the intact actuator side, the front end will initially lift and then the defective steering actuator will fold in. The drive torque promotes the folding process, as it further increases the wheel's rotation around its vertical axis.

[0067] To counteract this, an uneven distribution of drive torque can be set between the intact and the defective wheel (in the example, right to left). By reducing the drive torque on the defective actuator side, the tendency for folding can be reduced or completely avoided. The unrestricted drive torque can continue to be applied on the intact side, or an increase can be applied to compensate for the reduction in drive torque on the defective actuator side.

[0068] Alternatively or additionally, the drive torque application can be extended until the target drive torque is reached, thus reducing the drive torque gradient accordingly. By slowing down, in this variant initially on both sides, the impulse of the unwanted wheel rotation is weakened.

[0069] The drive torque gradient can also be reduced only on the defective side. On the intact actuator side, the gradient can be set as in normal operation.

[0070] The operating strategies can be combined with each other. This means that a simultaneous left-right redistribution and a change in the temporal increase of the drive torque can be achieved.

[0071] Likewise, the drive torque can initially be applied only to the intact actuator side to initially cause the vehicle to roll. Only when the vehicle is rolling is drive torque also applied to the defective side. Alternatively or additionally, the steering angle on the intact actuator side can be applied directly or only when the vehicle is rolling slightly in order to utilize the caster effect on the defective side.

[0072] In addition, the target steering angle cannot be directly applied to the intact actuator in the normal ratio, but a modified characteristic curve can be used, which works with lower wheel steering angles when stationary and at low speeds, e.g. < 5 km / h.

[0073] With another control strategy, the desired drive torque can be applied to the intact side. On the defective side, a controller is used to apply torque via the drive motor, which rotates the wheel in the desired direction. This approach can be combined with also driving the failed wheel, provided the respective steering angle allows it.

[0074] In the approach presented here, a slight increase in maneuvering space in the event of a defective actuator is assumed to be tolerable, since this already represents a serious fault in the system and maximum maneuvering performance cannot be expected. Without the approach presented here, the vehicle would no longer be steerable.

[0075] The kinematic parameters of the steering roll radius and the disturbance force lever arm are largely responsible for the steering behavior of a wheel with a failed actuator. Especially for braking torques and resistances, the corresponding parameters can take on different values ​​and even change sign depending on the vehicle type and the condition of the wheel. This influence can be compensated for using the approach presented here.

[0076] The operating strategies presented here can therefore maintain the vehicle's good maneuverability even if the independent steering actuator fails. With electric drives and installed drives on the front and rear axles, it is also conceivable to disable the front-wheel drives in the event of an independent steering actuator failure, so that vehicle movement is realized solely via the rear-axle drive.

[0077] Figure 2 shows a torque curve for a drive torque distribution. The drive torque, which is normally distributed symmetrically, is adapted depending on the steering angle. The actual drive torque demanded at the wheel is calculated as follows:

[0078] If (reversing):

[0079] Else-If (Move Forward):

[0080] Otherwise:

[0081] Where k shT is a variable parameter that can depend, for example, on the vehicle speed and the axle kinematics. Furthermore, the factor k sh T positive for the front right wheel and negative for the front left wheel to achieve (together with the convention asteertngwheet > 0 for left steering) a reduction in the drive torque at the inside wheel. M or ig is the drive torque that would be required for a symmetrically distributed system. The ratio a S tar g wheei / a S tar g With wheeiMax, the effect is achieved that at low steering wheel and correspondingly wheel steering angles, no large differential torques are applied. At a high steering wheel angle, a correspondingly larger differential torque is requested, since in this case a comparatively large wheel steering angle is also required.

[0082] In principle, the operating strategy presented here is also applicable to a degraded single-wheel steering actuator, for example, with 50% of the steering torque remaining, should this no longer be sufficient to adequately counteract the drive forces or the actuator's target position be influenced too strongly. If the steering roll radius is precisely designed so that the drive torque favors a steering movement in the target direction, a correspondingly adjusted control of the drive torque distribution is also conceivable.

[0083] Finally, it should be noted that terms such as "comprising," "having," etc., do not exclude other elements or steps, and terms such as "a" or "an" do not exclude a plurality. Reference signs in the claims are not to be considered limiting.

Claims

Claims 1. Method for maneuvering a vehicle (100) with a defect (106) on an individual wheel steering actuator (102) of a driven wheel (104) of the vehicle (100), wherein for maneuvering a torque on the wheel (104) is set as a function of a steering angle of an opposite wheel (104) of the vehicle (100).

2. Method according to claim 1, wherein the torque is further adjusted as a function of a current angular position of the wheel (104).

3. Method according to one of the preceding claims, wherein the torque is further adjusted as a function of a drive torque at the opposite wheel (104).

4. Method according to claim 3, wherein the torque is set lower than the drive torque.

5. Method according to one of claims 3 to 4, wherein the torque is set with a time offset from the drive torque at the opposite wheel (104).

6. Method according to one of the preceding claims, in which a gradient of the torque is reduced.

7. The method according to claim 6, further comprising reducing a gradient of a drive torque at the opposite wheel (104).

8. Method according to one of the preceding claims, wherein the torque is further adjusted as a function of a speed of the vehicle (100).

9. Control device, wherein the control device is designed to execute, implement and / or control the method according to one of the preceding claims in corresponding devices.

10. Computer program product which is designed to control a processor at Execution of the computer program product to execute, implement and / or control the method according to one of claims 1 to 8.

11. Machine-readable storage medium on which the Computer program product according to claim 10.

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