Method and control device for combined control of a plough brake and a drive unit / service brake

Abstract

The present invention relates to a method for combined control of a plough brake and a drive unit / service brake, wherein in order to decelerate the vehicle (100) at low speed (106), a steered right wheel (108) and a steered left wheel (108) of the vehicle (100) are steered with opposite toe-in angles (110), in order for a pitching movement (122) of the vehicle caused by the deceleration to be at least partially compensated by a vertical movement (120) due to the oppositely steered wheels (108).

Description

[0001] Description

[0002] Method and control unit for combined control of plough brake and drive / service brake

[0003] Field of the invention

[0004] The invention relates to a method for the combined control of plough brake and drive and / or service brake, a corresponding control device, and a corresponding computer program product

[0005] State of the art

[0006] To steer a vehicle, a right and left wheel on one axle are traditionally steered by a steering wheel via a common steering gear. With a "steer-by-wire" steering system, a mechanical connection between the steering wheel and the steering gear, and thus to the steered wheels, is omitted. Steering movements are converted into electrical signals at the steering wheel and transmitted to the control unit of the actual steering actuator. In a central steer-by-wire system, the right and left wheels continue to be steered by a common steering gear and are thus kinematically coupled.

[0007] In order to avoid the need for a mechanical connection between the right and left wheels, each wheel in "steer-by-wire" steering systems can be controlled by an individual wheel steering actuator.

[0008] Disclosure of the invention

[0009] Against this background, the approach presented here presents a method for the combined control of the plough brake and the drive / service brake, 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.

[0010] Advantages of the invention

[0011] When a vehicle wheel is turned, the vehicle's chassis kinematics raise or lower the wheel in the area of ​​that wheel. This reaction is based on various chassis parameters. These include, in particular, the spread of the steering axis relative to the vehicle's vertical axis and the lever arm of the caster path, defined as the distance between the point where the steering axis passes through and the wheel contact point at road level in the x-direction.

[0012] With independent wheel steering actuators, different toe angles can be set independently on each steered wheel of a vehicle. The different toe angles allow the chassis kinematics to be utilized and a vertical movement of the vehicle's axle kinematics to be controlled individually over each wheel.

[0013] In addition, the wheels on an axle roll in different directions due to different toe angles when the vehicle is moving. Since the vehicle, including its wheels, can only move in one resulting direction, the different toe angles create slip angles at the steered wheels relative to the vehicle's orientation, and thus lateral forces or transverse forces. Depending on the severity of these lateral forces, the chassis is tensioned. This tension can also raise or lower the vehicle at the steered wheels. The components of the lateral forces directed in the direction of vehicle movement when the toe angles of the individual wheels are symmetrically adjusted create a braking effect.

[0014] When the vehicle decelerates, a pitching moment occurs due to its mass inertia. This pitching moment causes the suspension to compress on the front axle in the direction of travel. The vehicle lowers at this axle due to the pitching moment. When the vehicle accelerates, an opposite pitching moment results. This pitching moment causes the suspension to rebound on the front axle in the direction of travel.

[0015] In the approach presented here, the lifting or lowering of the vehicle due to the kinematics and / or bracing of the chassis is used by wheel-specific toe angle actuation to at least partially compensate for the lifting or lowering due to a pitching moment. Furthermore, the pitching motion of the vehicle can be influenced by targeted acceleration or deceleration of the vehicle.

[0016] The approach presented here can at least partially prevent pitching movements of the vehicle body. By balancing the pitching moment caused by propulsion or braking and the toe angles in plow position, the pitching movements can even be essentially completely compensated.

[0017] The approach presented here can be applied both when driving forward and when driving backward, with the toe angles being adjusted accordingly.

[0018] A method for combined control of the plough brake and drive / service brake is presented, wherein when a braking torque is applied to braked wheels of the vehicle at low speed, a steered right wheel and a steered left wheel of the vehicle are steered with opposite toe angles in order to at least partially compensate for a pitching movement of the vehicle caused by the braking torque by a vertical movement due to the oppositely steered wheels, wherein when a drive torque is applied to driven wheels of the vehicle, the steered wheels are steered back in order to at least partially compensate for a pitching movement caused by the drive torque by an opposite vertical movement due to the back steering.

[0019] Ideas for embodiments of the present invention can be regarded, among other things, as being based on the thoughts and findings described below. Different toe angles on the wheels of an axle of a vehicle can cause the wheels to diverge or converge when the vehicle is moving. A plow angle or a V-angle can be set between the wheels. The plow angle or the V-angle braces the chassis of the axle. At the plow angle, the wheels converge towards a center of the axle. The plow angle can cause a lateral compressive force on a chassis of the axle in the y-direction of the center of the axle. At the V-angle, the wheels diverge outwards. The V-angle can cause a tensile force on the chassis in the y-direction of the vehicle away from the center.

[0020] When the plow angle or the V-angle is adjusted symmetrically, lateral slip on the wheels generates a decelerating force in the x-direction of the vehicle when the vehicle is moving, counter to the vehicle's movement. The vehicle is braked by the plow angle or V-angle. The more the wheels are turned, the more the vehicle is braked. This is a non-linear relationship that only applies up to a certain slip angle limit. Slip can cause wear on the wheels. Therefore, the approach presented here is preferably recommended for driving at low speeds up to 20 km / h so that wear can be limited. Additional braking torque can be provided by wheel brakes.

[0021] Particularly on the front axle, a pitching motion caused by starting off can be compensated for by lowering the chassis when steering back. The drive torque can be applied to the unsteered wheels and / or the steered wheels. In particular, no braking torque can be applied to the steered wheels. As a result, the steered wheels are either driven or roll freely. This means that low steering forces can be required. By steering back when applying the drive torque, harmonious acceleration of the vehicle can be achieved, since the braking effect steadily decreases due to the wheels steering back in opposite directions.

[0022] The steered wheels can be steered with different opposing toe angles if the vehicle pulls to one side during deceleration. The resulting plow angle or V-angle can remain constant. Variable toe angles allow the vehicle to be kept under control. The different toe angles allow the vehicle to be steered straight ahead.

[0023] The steered wheels can be steered with different opposing toe angles when the vehicle is steered in one direction during deceleration. The resulting plow angle or V-angle can remain constant in magnitude. The different toe angles allow the vehicle to be steered along a predetermined trajectory even while using the approach presented here.

[0024] Braking torque can be applied asymmetrically to at least one right wheel and at least one left wheel of the vehicle if the vehicle pulls to one side during deceleration. Asymmetric braking can generate a stabilizing yaw moment. Different steering of the wheels can still occur.

[0025] After the vehicle has come to a standstill, the steered wheels can be turned with opposite toe angles to hold the vehicle in place. The oppositely turned wheels can prevent the vehicle from rolling away due to the resulting lateral forces in the vehicle's longitudinal direction. Wheel brakes can assist in holding the vehicle in place.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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 or a device.

[0030] 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.

[0031] Short description of the drawing

[0032] Embodiments of the invention are described below with reference to the accompanying drawings, wherein neither the drawings nor the description are to be interpreted as limiting the invention.

[0033] Fig. 1 shows a representation of a plow position in a vehicle with independent wheel steering actuators using a method according to an embodiment; and Fig. 2 shows a sequence of a plow brake actuation according to an embodiment.

[0034] The figure is merely schematic and not to scale. Like reference numerals denote like or equivalent features.

[0035] Embodiments of the invention

[0036] Fig. 1 shows a representation of a plow position in a vehicle 100 with independent wheel steering actuators 102 using a method according to an exemplary embodiment. The vehicle 100 has the independent wheel steering actuators 102 on at least one axle 104. The independent wheel steering actuators 102 are controlled electronically in a steer-by-wire system. The illustrated axle 104 is a front axle of the vehicle 100. However, the axle 104 can alternatively or additionally also be a rear axle of the vehicle 100.

[0037] When the vehicle 100 is traveling at a low speed 106, for example, below 20 km / h, wheels 108 of the vehicle 100 are steered with opposite toe angles 110 when the vehicle is decelerated. Here, the wheels 108 are steered with symmetrical toe angles to form a plow brake 112. The wheels 108 have a plow angle relative to each other. Steering generates lateral forces 114 at the wheels 108. The lateral forces 114 act proportionally in the vehicle's longitudinal and transverse directions. The transverse forces 116 are opposite at the two wheels 108 and, in particular, brace the chassis of the axle 104 via the chassis parameters of wheel splay and caster. The longitudinal forces 118 are directed in the same direction and brake the vehicle 100.

[0038] An inclination of the wheels 108 by the toe angle 110 causes a vertical movement 120 of the body of the vehicle 100 above the axle 104 due to the steering axes of the chassis being aligned obliquely to the ground due to the spread and caster. In addition, the bracing of the chassis can amplify the vertical movement 120.

[0039] The vertical movement 120 counteracts a pitching movement 122 of the

[0040] Vehicle 100 due to a braking torque for decelerating the vehicle 100. The vertical movement 120 can at least partially compensate for the pitching movement 122.

[0041] In one embodiment, the plow brake 112 is released when the vehicle 100 starts moving. Upon release, the wheels 108 are again aligned substantially parallel to each other, and the vehicle 100 can start moving without braking. The braking effect of the plow brake 112 is reduced smoothly, rather than abruptly. This allows for a smooth start.

[0042] The drive or service brake thus causes the vehicle to pitch, which counteracts the tension and the associated vertical movement (caused by the plow steering). The point is not the braking process itself, but rather the combination of the plow position with the drive and service brake to enable the most comfortable driving experience with minimal pitching when starting or braking.

[0043] In one embodiment, the orientation of the plow brake 112 is adjusted when the vehicle executes a yaw motion. To do this, the toe angle 110 of one wheel 108 is reduced, while the toe angle 110 of the other wheel 108 is increased. For example, the vehicle 100 can execute the yaw motion if one of the wheels 108 has a different coefficient of friction than the other wheel against a surface. The different coefficient of friction directly causes different lateral forces 114 and, accordingly, an imbalance of the forces acting on the vehicle 100. By changing the plow brake 112, balanced lateral forces 114 are created, and the vehicle 100 continues to move straight ahead.

[0044] In one embodiment, the orientation of the plow brake 112 is changed when the vehicle 100 is to steer to one side. To do this, the toe angle 110 of one wheel 108 is reduced, while the toe angle 110 of the other wheel 108 is increased. The different toe angles 110 result in different lateral forces 114. The different lateral forces 114 cause a yaw moment that causes the vehicle 100 to rotate about its vertical axis. In one embodiment, the wheels 108 are left in the plow brake 112 after the vehicle 100 has come to a standstill. The plow brake 112 prevents the vehicle 100 from rolling, for example, on a slope.

[0045] Fig. 2 shows a sequence of plow brake actuation according to one exemplary embodiment. Situation detection 200, which can be performed, for example, visually, acoustically, via inertial sensors, or based on traffic flow, detects situations 202, such as stop-and-go on a downhill slope, approaching a traffic light or stop sign, an emergency braking situation, a right-of-way situation, a hill-hold situation or a starting situation on an uphill slope, or starting off after parking. Depending on the situation, a combined control 204 of the individual wheel steering actuators, drive system, or braking system then takes place. For example, the plow brake is actuated during deceleration, then released again, and the drive is engaged when the chassis relaxes.

[0046] In the following, possible embodiments of the invention are summarized again or presented with slightly different wording.

[0047] A strategy for intelligent control of the plough brake by individual wheel actuators in special driving situations to increase comfort is presented.

[0048] Today's steering systems consist of a central actuator that turns the left and right wheels approximately equally. In the majority of vehicles available on the market, such a central actuator is only installed on the front axle, and there is a mechanical connection between the steering wheel and the steered wheels.

[0049] By-wire systems generally eliminate the traditional mechanical connection between the driver and the actuator system (steering, brakes, etc.). In the case of the steering, the corresponding actuation is carried out purely via one or more actuators. Centralized and decentralized by-wire steering actuators are already being used on the rear axle (e.g., ZF: AKC). Initial prototype vehicles with by-wire independent wheel steering actuators are already known for the front axle, such as the Speed ​​E research vehicle (RWTH Aachen).

[0050] By-wire systems with wheel-specific steering actuators can set different steering actuator positions and thus different wheel steering angles depending on the driving profile and the selected ratio between the steering wheel angle and the wheel steering angle. Due to the lack of kinematic coupling between the left and right wheels, the actuators of such a steering system can also be steered in opposite directions, thereby decelerating the vehicle, a process known as plow braking.

[0051] In addition to reducing the vehicle's speed, the system can also be used as a parking brake, preventing unintentional movement of the vehicle. Depending on the design, this parking brake function can be used in conjunction with other braking systems (friction brakes, transmission / drivetrain brakes) to meet the requirements for parking brake functionality. In this case, one system alone does not assume the entire holding function, but can, and may even be, supported by another system only in specific situations.

[0052] To date, there is no concept for the automated initiation or release of the plow brake as a deceleration system or as a parking brake in corresponding situations in combination with drive interventions. Previous concepts envision the plow brake's function as a holding brake as a manually activated system, which, like the parking brake, is actively engaged and also manually deactivated accordingly.

[0053] The plough position of the wheels achieves a chassis tension that can be cleverly supported simultaneously by the drive when closing and opening the plough position in order to achieve smooth driving behavior.

[0054] This paper presents a concept for intelligently using the plow brake as a parking brake / holding function in certain situations, and for smoothly transitioning from this braking / parking situation to normal driving mode. The focus is on increased comfort through simultaneous drive interventions to compensate for the vehicle's pitching motion during deceleration or initial acceleration.

[0055] Central to this is the automated, intelligent detection of situations in which the holding or deceleration function of the plow brake is considered advantageous, and the corresponding control of the function in combination with drive interventions. Furthermore, a control concept for the transition from the plow position to regular driving is presented.

[0056] Fig. 1 shows an example of the plow position of a steer-by-wire system with individual wheel actuators for a symmetrically positive toe angle. Other, smaller toe difference angles and even negative toe angles for applying the plow brake are possible or necessary depending on the driving situation (e.g., multi-split or stationary cornering).

[0057] The approach presented here can involve a cycle of situation recognition and combined control of the plow brake with the drive and braking system. The recognition of a specific driving situation, e.g. approaching a traffic light, starting on a hill, or stop-and-go situations, can be carried out visually with the support of sensor data from the inertial sensor system (change in gradient) as well as algorithms estimating road-tire contact. This can enable optimal control of the plow functionality. At high speeds, the plow brake should only be activated in an emergency due to the associated tire wear. The functions presented here are advantageous for low speeds up to approximately 20 km / h. If it is detected that deceleration to a standstill is necessary, the plow brake can initiate a slight lane change, which can then be supported by the friction brake if necessary.When a future resumption of travel is detected (on a hill / downhill / traffic light / parking), the plow position is released to the stationary toe-in and the drive is simultaneously switched on in order to enable a smooth transition from the stopping situation to the driving situation.

[0058] The pitching motion that occurs when braking or driving with a conventional steering system can be reduced by combined control of the plough brake and drive, thus increasing driving comfort.

[0059] In order to ensure the lowest possible steering forces when activating the plow function, a holding force can be applied by the drive, for example, when starting off on a hill, so that the tension in the chassis can be released more easily (steering forces are higher when a wheel is braked by the service brake). In one embodiment, when approaching a traffic light with a green phase but the car is still stationary, braking is carried out if there is a low residual speed by pulling the plow without using the friction brake. In order to bring the vehicle to a standstill, the chassis is tensioned evenly by simultaneous drive / brake system control until it comes to a standstill. To continue driving, the plow is slowly released depending on the distance to the vehicle in front, with simultaneous support from the drive for even further travel and pitch compensation.

[0060] In another embodiment, during stop-and-go traffic on a downhill gradient (e.g., with a trailer), a sinusoidal steering angle curve is applied during the corresponding phases of stop-and-go traffic. Depending on an estimated road surface condition, a slightly asymmetrical actuation can be used to maintain directional stability. On curved roads, a slightly asymmetrical release of the plow (non-symmetrical toe angle) with appropriate toe-in for cornering can be used. At the same time, intelligent drive control can be used to reduce vehicle pitching due to chassis tension and thus increase comfort.

[0061] One advantage of the plow brake compared to conventional brakes is particularly evident when starting off. The effect of the plow brake is based on the use of tire lateral forces. Thus, with the plow brake engaged, a drive torque (longitudinal tire forces) can be applied to start off. As soon as the vehicle is moving, the plow brake should be released again to reduce tire wear. However, a seamless transition between braking and starting is possible with reduced pitching of the vehicle.

[0062] 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. A method for the combined control of the plough brake and the drive / service brake, wherein when a braking torque is applied to braked wheels (108) of the vehicle (100) at low speed (106), a steered right wheel (108) and a steered left wheel (108) of the vehicle (100) are steered with opposite toe angles (110) in order to at least partially compensate for a pitching movement (122) of the vehicle caused by the braking torque by a vertical movement (120) due to the oppositely steered wheels (108), wherein when a drive torque is applied to driven wheels (108) of the vehicle (100), the steered wheels (108) are steered back in order to at least partially compensate for a pitching movement (122) caused by the drive torque by an opposite vertical movement (120) due to the back steering.

2. Method according to claim 1, wherein the steered wheels (108) are steered with different opposing toe angles (110) when the vehicle (100) pulls to one side during deceleration.

3. Method according to one of the preceding claims, in which the steered wheels (108) are steered with different opposing toe angles (110) when the vehicle (100) is steered in one direction during deceleration.

4. Method according to one of the preceding claims, in which the braking torque is applied asymmetrically to at least one right wheel (108) of the vehicle (100) and to at least one left wheel (108) of the vehicle (100) when the vehicle (100) pulls to one side during deceleration.

5. Method according to one of the preceding claims, in which, after a standstill of the vehicle (100), the steered wheels (108) are used to hold of the vehicle (100) with the opposing toe angles (110) are kept steered.

6. Control device, wherein the control device is designed to carry out the method according to one of the preceding claims in corresponding To execute, implement and / or control facilities.

7. Vehicle, in particular motor vehicle, comprising a control unit according to claim 6.

8. A computer program product configured to instruct a processor, upon execution of the computer program product, to execute, implement and / or control the method according to one of claims 1 to 5.

9. A machine-readable storage medium on which the computer program product according to claim 8 is stored.

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