DE102022201596A1 - Method and control device for setting a target torque of a slip controller for at least one wheel of a vehicle - Google Patents

Abstract

The present invention relates to a method for setting a target torque (104) of a slip controller (106) for at least one wheel (108) of a vehicle (100), the target torque (104) by a step (110) with a step value (112 ) is increased if, as a first condition, a wheel slip (114) on the wheel (108) falls below a predetermined slip value (116), as a second condition the wheel slip (114) is less than a target slip value (118) of the slip controller (106), and as a third condition, a wheel acceleration (120) of the wheel (108) is less than a predetermined acceleration value (122) and/or a jerk (124) on the vehicle (100) is greater than a predetermined jerk value (126).

Description

field of invention

The invention relates to a method for setting a target torque of a slip controller for at least one wheel of a vehicle, a corresponding control unit and a corresponding computer program product.

State of the art

A vehicle may include a traction controller. The slip controller can be referred to as a traction controller for acceleration processes. For deceleration processes, the slip controller can be referred to as a brake slip controller.

So that power can be transferred from the wheels to the ground when accelerating or decelerating, the slip controller regulates a driving or braking torque of the wheels in such a way that slip occurs at the wheels, at which a coefficient of adhesion required to transfer the force occurs between the wheels and the ground. The maximum possible coefficient of adhesion depends on the friction value of the substrate.

If the vehicle accelerates or brakes on a surface with a low coefficient of friction, for example ice and/or snow, the maximum coefficient of adhesion is low and the force that can be transmitted is limited. So often less power can be transmitted than requested. The torque at the wheels is limited.

If the vehicle then drives onto a surface with a high coefficient of friction, such as asphalt, the maximum coefficient of adhesion increases and the wheels can suddenly transfer considerably more power to the surface. Since the previously set torque is less than an actually required torque and less than a torque that is now possible, a control target for the torque is increased in initially small and ever-increasing steps until the required slip with the increased coefficient of friction between the wheels and the Base adjusts to transmit the requested torque.

Until the torque is high enough, the full acceleration potential or deceleration potential of the high-friction surface cannot be exploited.

Disclosure of Invention

Against this background, with the approach presented here, a method for setting a target torque of a slip controller for at least one wheel of a vehicle, a corresponding control unit and a corresponding computer program product are presented according to the independent claims. Advantageous developments and improvements of the approach presented here result from the description and are described in the dependent claims.

Advantages of the Invention

In the approach presented here, a control target for a torque on at least one wheel or at least one axle of a vehicle is suddenly increased immediately if an increase in the coefficient of friction of a substrate under the wheel or the wheels of the axle is detected. This change is detected by evaluating various parameters of the wheel or the axle and the vehicle. The jump in the control target is significantly larger than a control step of a conventional slip controller.

A method for setting a target torque of a slip controller for at least one wheel of a vehicle is proposed, the target torque being increased by a step with a step value if wheel slip falls below a predetermined slip value as the first condition and wheel slip falls as the second condition than a target slip value of the slip controller, and as a third condition a wheel acceleration of the wheel is less than a predetermined acceleration value and/or a jerk on the vehicle is greater than a predetermined jerk value.

Ideas for embodiments of the present invention can be regarded as being based, among other things, on the ideas and findings described below.

A slip controller can be a traction controller and/or brake slip controller. As a traction controller, the slip controller can regulate a drive torque individually for each wheel in a single-wheel drive. With an axle drive, the slip controller can regulate the drive torque for the wheels of an axle. As a brake slip controller, the slip controller can regulate a braking torque individually for each wheel, even if the wheels of the axle are driven together.

The slip controller regulates torque at the wheel or axle. The slip controller sets a target torque for the torque so that a wheel slip required to transmit a desired force is achieved at the wheel or axle. A force that can be transmitted from the wheel to the ground increases with the wheel slip up to a maximum coefficient of adhesion of the respective ground and falls again after the maximum coefficient of adhesion as the wheel slip continues to increase. The coefficient of adhesion depends on the friction value of the substrate.

The target torque can be a control target for the torque on the wheel or axle controlled by the slip controller. If the ground changes, the maximum coefficient of adhesion also changes. When changing from a surface with a low coefficient of friction to a surface with a high coefficient of friction, the wheel slip that occurs with the low coefficient of friction will almost immediately disappear, since suddenly much more force can be transferred between the surface and the wheel and the surface virtually pulls the wheel along. The wheel then rotates approximately at an instantaneous vehicle speed of the vehicle and the wheel slip is approximately zero since the torque that has been regulated is now clearly too low.

A slip value can be stored in a configuration of the slip controller. The slip value can be a fixed threshold. The slip value can be 0.1 m/s, for example. A target slip value may be dependent on an acceleration request or braking request for the wheel or axle and the maximum coefficient of adhesion. A wheel acceleration of the wheel can be derived from a wheel speed of the wheel. The wheel speed can be measured by a sensor on the wheel. An acceleration value can be stored in the configuration of the slip controller. The acceleration value can be a fixed threshold. A jerk to the vehicle may be a change in vehicle acceleration of the vehicle. The vehicle acceleration can be measured by an inertial sensor, for example. The vehicle acceleration can also be derived from a vehicle speed of the vehicle. Vehicle speed can be determined using multiple wheel speeds. A jerk value can be stored in the configuration of the slip controller. The jerk value can be a fixed threshold.

A jump can be significantly larger than a control step of the slip controller under approximately constant conditions. A jump value can indicate a height of the jump.

The target torque can be increased by a further step if the wheel acceleration increases after the previous step and falls below the acceleration value again within a short period of time. The wheel or axle may have a very short response time. The changes in the slip controller are reflected directly in the wheel acceleration. A short period of time can include, in particular, a few computing cycles of the slip controller. For example, the short period of time can include two computing cycles. The short period of time can be significantly less than one second. The short period of time can be in the millisecond range. For example, the short period of time may be 30 to 200 milliseconds.

After the further jump, the target torque can be kept constant for a vehicle reaction time. A vehicle reaction time can be significantly longer than the reaction time of the wheel or axle because the vehicle has a much higher inertia than the wheel or axle. For example, the vehicle response time may be 150 to 800 milliseconds. Waiting can prevent the target torque from increasing too much. In this way, the slip controller cannot overshoot, or at least with a reduced probability.

The jump value may be determined using a vehicle reference acceleration and a change in vehicle reference acceleration. a vehicle reference acceleration can be averaged over a past period of time from acceleration values of the vehicle. Using the vehicle reference acceleration, a basis for the step value can be read from a stored acceleration characteristic. The change in vehicle reference acceleration may be referred to as the vehicle reference acceleration gradient. Using the change, a factor for the grade rule can be read from a stored change characteristic. The grade rule can be calculated by multiplying the base by the factor.

The step value for another step can be determined using the torque during the previous step, a current torque, and a change in torque. The torque during the previous jump can be subtracted from the current torque, and using a result, a basis for the jump value can be read from a stored torque characteristic. A factor for the step value can be read out from a change characteristic using the change in torque. The grade rule can be calculated by multiplying the base by the factor.

A first skip value may be determined using the vehicle reference acceleration and the change in vehicle reference acceleration. A second step value may be determined using the torque during the previous step, the current torque, and the change in torque. The larger jump value can be used for the jump.

The method can be implemented, for example, in software or hardware or in a mixed form of software and hardware, for example in a control unit.

The approach presented here also creates a control device which is designed to carry out, control or implement the steps of a variant of the method presented here in corresponding devices.

The control device 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 one communication interface for reading in or outputting data that are embedded in a communication protocol, be. The arithmetic unit can be, for example, a signal processor, a so-called system ASIC or a microcontroller for processing sensor signals and outputting data signals as a function of the sensor signals. The storage 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 designed to read in or output the data in a wireless and/or wired manner. The interfaces can also be software modules that are present, for example, on a microcontroller alongside other software modules.

A computer program product or computer program with program code, which 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 for carrying out, implementing and/or controlling the steps of the method according to one of the embodiments described above, is also advantageous used, especially when the program product or program is run on a computer or device.

It is 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 recognizes that the features of the control device and of the method can be combined, adapted or exchanged in a suitable manner in order to arrive at further embodiments of the invention.

character list

• 1 zeigt eine Darstellung eines Fahrzeugs mit einem Steuergerät gemäß einem Ausführungsbeispiel; und
• 2 zeigt eine Darstellung eines Einstellens eines Zielmoments mit einem Sprung bei einem Verfahren gemäß einem Ausführungsbeispiel.

Embodiments of the invention are described below with reference to the accompanying drawings, neither the drawings nor the description being to be construed as limiting the invention.

• 1 shows an illustration of a vehicle with a control device according to an embodiment; and
• 2 12 shows an illustration of setting a target torque with a jump in a method according to an embodiment.

The figures are merely schematic and not true to scale. The same reference symbols denote the same features or features that have the same effect.

Embodiments of the invention

1 FIG. 1 shows a representation of a vehicle 100 with a control device 102 according to an exemplary embodiment. Control unit 102 is designed to set a target torque 104 of a slip controller 106 for at least one wheel 108 of vehicle 100 . Target torque 104 is increased by a step 110 with a step value 112 if wheel slip 114 on wheel 108 falls below a slip value 116, wheel slip 114 is less than a target slip value 118 of slip controller 106 and wheel acceleration 120 of wheel 108 is less than one Acceleration value 122 or a jerk 124 on vehicle 100 is greater than a jerk value 126 .

The target torque 104 and the target slip value 118 are dependent on an instantaneous torque request. Target torque 104 is a control target of slip controller 106. Slip controller 106 adjusts a torque 128 of a drive 130 or a brake system (not shown) of wheel 108 or an axle 132 of wheel 108 until target torque 104 is reached. Thus, the torque 128 can be positive or negative.

The wheel slip 114 results from a wheel speed 134 of the wheel 108 and a vehicle speed 136 of the vehicle 100. The wheel acceleration 120 is also from the Wheel speed 134 derived. The slip value 116, the acceleration value 122 and the jerk value 126 are stored and predetermined. The jerk 124 can be derived from a vehicle acceleration 138 of the vehicle 100 .

In one exemplary embodiment, target torque 104 is increased by a further jump 110 if wheel acceleration 120 increases after previous jump 110 and falls below acceleration value 122 again within a short period of time.

In an exemplary embodiment, the target torque 110 is kept constant for a vehicle reaction period after the further jump 110 .

In one embodiment, the jump value 112 is determined using a vehicle reference acceleration and a change in vehicle reference acceleration. Alternatively or additionally, the jump value 112 for a further jump 110 is determined using the torque 128 during the previous jump 110, a current torque 128 and a change in the torque 128. If two different jump values 112 result, the larger jump value 112 is used for the next jump 110.

2 10 shows an illustration of setting a target torque 104 with a jump 110 in a method according to an embodiment. The jump 110 is controlled by a control device as in 1 triggered. Jump 110 is shown as a positive step in a course of target torque 104 . The jump value 112 of the jump 110 is added to an instantaneous value of the target moment 104 . The course of the target torque 104 is shown in a time record with time courses of a large number of values.

Wheel speeds 134 of two wheels of the axle, a vehicle speed 136, the target torque 104, the torque 128, the wheel slip 114, a target slip range 200 and the vehicle acceleration 138 are plotted one above the other in the time plot.

The slip controller tracks the torque 128 with the target torque 104 . The greater the deviation between the target torque 104 and the torque 128, the greater the change steps in the torque 128. The change steps are for the most part significantly smaller than the step value 112 of the step 110. The step 110 causes the deviation to suddenly become larger. Consequently, after the jump 110, the increments of change in torque 128 also increase in order to quickly minimize the deviation.

In other words, a situation-dependent OnRef detection for jumps in engine torque is presented.

A slip control (Traction Control System, TCS) can be a functional module of an ESP system. The slip control can be used as traction slip control and brake slip control. For the sake of simplicity, only the traction control with a positive torque to be regulated is described below. In the case of brake slip control, the torque to be regulated is negative. The functional purpose of the traction control is that the wheels do not spin when a vehicle starts longitudinally and thus vehicle requirements in terms of stability, steerability and traction are met.

In a conventional controller strategy, a physically based actuator target value (engine/brake) should be able to optimally regulate corresponding driving situations. Detections, estimates and models are required for the target value determination. Controller parameters are used to ideally approach the setpoint and are determined manually by an application engineer. The PID controller principle is used here.

A vehicle state may be referred to as "OnRef". The OnRef situation describes a driving condition in which the driving wheels or the drive axle are no longer sufficiently in drive slip. Without slip, however, no/little driving force can be transmitted and this is accompanied by a loss of performance.

Conventional controllers have an OnRef logic, which builds up more engine torque in the event of an OnRef situation by increasing the integrative component of the traction slip controller. As a result, in some situations with a low coefficient of friction (low µ), the engine torque can be increased too late and then too quickly/highly, with the result that the slip on the drive axle increases far too much. The longer an On Ref situation lasts, the higher the integration component of the controller becomes.

At the beginning of the OnRef situation, the integration component is very small and therefore only has a minor effect on the control behavior. The slip therefore remains on the reference longer than necessary and does not lead to the desired acceleration of the vehicle. This leads to a loss of performance. If the OnRef situation lasts a long time, the proportion of integration is greatly increased. The previous increase is not sufficiently taken into account, so that at one point the engine increase can be so great that the wheels tear off very badly. Because of the strong demolition In this case, no traction can be transferred to the road surface, which is why there is a loss of performance.

In the approach presented here, the logic recognizes a situation in which the drive slip is too small so that propulsion can no longer occur and reacts to this with a sudden increase in engine torque. The level and frequency of the engine torque jumps depends on the vehicle situation (reference acceleration, engine torque, axle dynamics...).

The jumps in engine torque make it possible to react quickly to specific vehicle situations in order to ensure the highest possible acceleration. The use of many signals results in robust situation detection and no false triggers. Multiple jumps, during which the vehicle reaction and the axle reaction are awaited, can reduce slippage that is too high (wheel breakage when the engine torque is too high). This makes it possible to react to changes in the driving situation.

The logic presented here can be divided into the detection of an OnRef situation, the triggering of the engine torque jump and the calculation of the magnitude of the engine torque jump.

During detection, the OnRef situation should be determined clearly and as early as possible. When triggering, the frequency of the engine torque jumps should be controlled in order to quickly reach a higher level of slip without the wheels tearing off. In the calculation, the size of the engine torque jump should be estimated on the basis of vehicle sizes.

The OnRef situation is detected when a defined slip value (slip < 0.1 m/s) is undershot, as long as this value is below the target value of the controller, and when the deviation of the axis acceleration is smaller than a defined value, or when the integral of the Gradient of the reference acceleration of the vehicle (aRef_Gradlnt) is greater than a defined value and this value falls (aRef_Gradlnt_k1> aRef_Gradlnt). The integral of the gradient of the reference acceleration of the vehicle represents a measurable jerk on the vehicle, which is caused by inertial energy of an axle, which is transferred to the vehicle while the axle comes back from traction slip to vehicle speed due to a strong change in the coefficient of friction (µ).

The OnRef trigger for triggering the engine torque jump is set when an OnRef situation is detected, when a defined time has elapsed between the last trigger or the axle acceleration has already increased but falls again and the vehicle reaction time has expired.

For example, the first jump is triggered when OnRef is detected. The axis acceleration (Ya) then increases for two computing cycles but then falls again, whereupon another jump is triggered immediately. A defined time is then waited for the vehicle reaction.

The magnitude of the jump in engine torque can be calculated based on the vehicle acceleration. An "average" vehicle reference acceleration is calculated from the aRef_Min and aRef_Max values of the last defined period of time (currently 200 ms). This value is coupled with a parameter characteristic and results in the basis of the jump.

Furthermore, the integral of the vehicle reference acceleration is calculated based on the maximum gradient (aRef_Max). This value is linked to a parameter characteristic and results in a factor that is multiplied by the previous value.

This results in a first engine torque step height based on the vehicle reference acceleration and its change.

In addition, the magnitude of the engine torque jump can be calculated based on the current engine torque. An "average" current engine torque is calculated during the jumps. To do this, the current torque is subtracted from the engine torque at the last jump. (The first jump is never calculated by this logic - the axis acceleration has not changed much) So a low motor torque level leads to large jumps. This value is coupled with a parameter characteristic and results in the basis of the jump.

Furthermore, a rate of change of the engine torque during the OnRef situation is calculated. The larger the previous change of the current moment was, the smaller the next jump will be. This value is linked to a parameter characteristic and results in a factor that is multiplied by the previous value.

This results in a second engine torque jump height based on the height and change in the current engine torque if no effect of the last jump on the axis dynamics is visible.

The larger engine torque jump value is then used (maximum value formation) and the engine torque is increased accordingly.

Finally, it should be noted that terms such as "comprising," "comprising," etc. do not exclude other elements or steps, and terms such as "a" or "an" do not exclude a plurality. Any reference signs in the claims should not be construed as limiting.

Claims (9)

Method for setting a target torque (104) of a slip controller (106) for at least one wheel (108) of a vehicle (100), wherein the target torque (104) is increased by a step (110) with a step value (112) when the first Condition a wheel slip (114) on the wheel (108) falls below a predetermined slip value (116), as a second condition the wheel slip (114) is smaller than a target slip value (118) of the slip controller (106), and as a third condition a wheel acceleration (120 ) of the wheel (108) is less than a predetermined acceleration value (122) and/or a jerk (124) on the vehicle (100) is greater than a predetermined jerk value (126). procedure according to claim 1 , in which the target torque (104) is increased by a further step (110) if the wheel acceleration (120) increases after the previous step (110) and is again smaller than the acceleration value (120) within a short period of time. procedure according to claim 2 , in which the target torque (104) after the further jump (110) is kept constant for a vehicle reaction time. Method according to one of the preceding claims, in which the step value (112) is determined using a vehicle reference acceleration and a change in the vehicle reference acceleration. Method according to one of the preceding claims, in which the jump value (112) for a further jump (110) using a torque (128) during the previous jump (110), a current torque (128) and a change in torque (128) is determined. procedure according to claim 4 and 5 , in which a first grade rule (112) after claim 4 and a second skip value (112) after claim 5 is determined, with the larger jump value (112) being used for the jump (110). Control unit (102), wherein the control unit (102) is designed to execute, implement and/or control the method according to one of the preceding claims in corresponding devices. Computer program product that is set up to guide a processor when executing the computer program product to perform the method according to one of Claims 1 until 6 to execute, implement and/or control. Machine-readable storage medium on which the computer program product according to claim 8 is saved.

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