Methods for reliably determining a system standstill

Abstract

Method (10) for determining a standstill of a system (100, 110), wherein: - an initial velocity (v0) is determined based on received measurement data from at least one digital counting sensor (111, 113), - a braking torque (F) is determined and / or set based on received measurement data from at least one sensor (112) and / or based on at least one property of a braking system, - a braking time (t, t2) is calculated based on the initial velocity (v0) and the braking torque (F), and - after the calculated braking time (t, t2) has elapsed, a standstill is determined.

Description

The invention relates to a method for detecting a standstill in a technical system, which includes digital sensors that count pulses. The invention further relates to a vehicle and a control unit configured to execute the method. A vehicle's speed is typically measured using digital speed sensors. These sensors count the pulses of a sensor wheel as it moves past the actual speed sensor. A problem with this type of measurement is accurately detecting when the vehicle is stationary. If, for example, the sensor wheel is positioned relative to the speed sensor in such a way that it is precisely at the sensor's trigger point, even the slightest movements or vibrations can result in a false speed reading. Such movements can be caused by wind, passing vehicles, roadworks, and similar factors. Because of these false-positive speed readings, speed sensors cannot reliably detect movements below a threshold of approximately 0.7 km / h. Several applications require precise detection of a standstill. For example, reliable detection of vehicle standstill is essential for implementing a parking lock using two engaged gears on a single shaft, as the gear synchronizers would have to brake any potential vehicle movement, for which they are not designed. This would lead to the destruction of the synchronizers. German patent DE 10 2013 000 032 A1 describes a method for engaging a parking lock in the powertrain of a hybrid vehicle. To engage the parking lock, the vehicle's speed is determined and, if necessary, reduced using the electric drive. This prevents the vehicle from braking abruptly at low speeds. German patent application DE 10 2019 218 151 A1 discloses a method for operating a parking brake. The parking brake is only electrically applied when the speed falls below a certain threshold. The relevant speed is detected, for example, by a wheel speed sensor or a GPS sensor. A standstill is registered using an additional acceleration sensor. The invention is based on the objective of providing a method for the technically simple and reliable detection of a standstill in a moving system. This objective is achieved by the features specified in claim 1. Further advantageous embodiments of the invention are described in the dependent claims. According to one aspect of the invention, a method for determining when a system has come to a standstill is provided. The system can be a translational or a rotational system. For example, the system can be a vehicle, a transmission, a machine tool, a linear guide, and the like. In one step of the process, an initial velocity is determined based on received measurement data from at least one digital counting sensor. For the purposes of the present invention, the at least one digital counting sensor is to be understood as a digital sensor that counts pulses from a sensor wheel or a corresponding "scale" of a linear guide. The counting sensor can, for example, be a speed sensor. Additionally, a braking torque is determined and / or adjusted based on received measurement data from at least one sensor and / or based on at least one characteristic of a braking system. Such measurement data is already available without the use of additional sensors and can typically be obtained from at least one vehicle control unit. In a further step, a braking time is calculated based on the initial velocity and the braking torque. This takes into account the scenario where the initial velocity is actually present and braking to a standstill would be necessary. This can be reliably implemented regardless of a false-positive measurement of the initial velocity. After the calculated braking time has elapsed, a standstill is determined or confirmed. This measure provides a technically simple guarantee for the vehicle or a drive shaft to remain stationary. In particular, it can also support functions that depend on the reliable stationary state of a drive shaft. One such function could be a parking lock or parking brake activated by two engaged gears on a single shaft. According to another aspect of the invention, a vehicle is provided which is equipped to carry out a method according to the invention. The method can be used to determine the standstill of the vehicle or the standstill of at least one shaft of the vehicle. In particular, the determination of standstill can be related to a rotational movement or a linear movement. The method can be implemented particularly advantageously from a technical point of view if a standstill of the vehicle or at least one shaft of the vehicle, determined by the method, is used to actuate a parking brake or to enable the actuation of the parking brake. To solve the problem of current speed sensors, a second physical quantity, the braking torque or braking force, is used. Along with the actual or maximum mass of the vehicle, a translational braking force F = m * a is required to decelerate the vehicle. From the braking torque at all wheels, the translational braking force F on the vehicle can be determined using the wheel diameters. From this, using a = F / m, the maximum braking time required to safely decelerate the vehicle from a speed of, for example, 0.7 km / h to a standstill can be calculated. According to a further aspect of the invention, a control unit is provided which is designed to implement the method according to the invention. The control unit can, for example, be a vehicle-side brake control unit which can receive and evaluate the measurement data from at least one sensor of a brake system. All necessary measurement data is available in the control unit so that the method according to the invention can generate an additional signal "vehicle is stationary / wheels are definitely not rotating". The method can, in principle, be used for the reliable detection of the standstill of a rotating shaft or linear system, where digital counting sensors, such as speed sensors, are used for measurement and a braking torque acting on the shaft or system is also known. Therefore, the method is not limited to vehicles or vehicle-related systems. In particular, the method overcomes the problem of reliably determining the standstill of the shaft, which arises from the operating principle of digital speed sensors. According to a further embodiment, the initial velocity is determined as the smallest velocity measurable by the counting sensor. This allows the smallest velocity that can still be reliably measured by the counting sensor to be used to determine the braking time. Preferably, potential measurement errors in determining the initial velocity can be taken into account. The velocity can be defined as an angular velocity or rotational velocity, or as a linear or translational velocity. Inadmissible or faulty measurement data from counting sensors during an actual standstill can be ignored if measurement data received from at least one counting sensor after the calculated braking time has elapsed are discarded. According to a further embodiment, the initial speed is determined based on received measurement data from at least one speed sensor of a vehicle-side ESP function and / or from at least one speed sensor of a shaft and / or from at least one speed sensor of a transmission. This measure allows any speed sensor to be used in determining the initial speed. Preferably, a speed sensor in a drivetrain of the vehicle can be used. The parking lock function, achieved by engaging two gears on a single shaft, can be implemented particularly efficiently by setting a braking torque that minimizes the braking time. Since engaging the parking lock is a time-critical process that must normally be completed within two seconds, a short braking period is especially useful for pre-testing the function. At speeds above 0.7 km / h, the signal or measurement data from the digital counter sensors can be used normally. According to another embodiment, the braking time is calculated using the formula, where v0 is the initial velocity, a is the braking deceleration, and t is the braking time. The formula for calculating the braking time can be rearranged to t = -v0 / a. This allows for a technically simple calculation of the braking time, especially since the braking deceleration a and the initial velocity can be known or at least estimated. Braking time can be calculated with particular precision when the moments of inertia of the wheels are taken into account. Alternatively, the moments of inertia of the wheels can be neglected to simplify and / or speed up the corresponding calculation of the braking time. Exemplary embodiments of the invention are explained in more detail below with reference to the drawings. Figure 1 shows a side view of a vehicle according to one embodiment of the invention, and Figure 2 shows a schematic flowchart illustrating a method according to the invention in one embodiment. In the figures, the same constructive elements each have the same reference numerals. Figure 1 shows a side view of a system 100, configured as an exemplary vehicle according to one embodiment of the invention. The vehicle 100 has a transmission 110 with a digital counting sensor in the form of a speed sensor 113. This can be used, for example, to measure the rotational speed of a shaft (not shown) and thus a speed. Depending on the configuration, the transmission 110 alone can also be considered a system within the meaning of the present invention. Vehicle 100 has a braking system which includes several sensors 112 for measuring brake pressure. For clarity, only one sensor 112 is shown, located in the area of ​​one wheel 130 of vehicle 100. Furthermore, the braking system has digital counter sensors 111 in the form of speed sensors on the wheels 130, of which only one sensor is shown. The sensors 111 and 112 are connected to a control unit 120 via data transmission. In the illustrated embodiment, the control unit 120 is designed as a brake control unit and can receive and evaluate the measurement data from the sensors 111, 112. The transmission 110 typically has a separate control unit (not shown) that can process internal signals from the transmission's internal speed sensors 113. However, the transmission 110 does not usually output the measured speeds to the brake control unit 120. Using the transmission's internal speed sensors 113 and the brake torque signals from the brake control unit 120, the transmission control unit or the control unit 120 can advantageously perform a plausibility check of the speeds and thus the vehicle speed. This is necessary, for example, for plausibility checks within the framework of safety requirements (ASIL / redundancy). The corresponding calculation or processing of measurement data from sensors 111, 112 in the brake control unit 120 is particularly advantageous, since physical models for recognizing the vehicle dynamic state of the vehicle 100 are usually implemented here, which are required for functions such as “ABS” or “ESP”. In an alternative configuration, the control unit 120 can also be designed as a central control unit, which can receive and evaluate the sensors of the brake system and the transmission 110 equally. Figure 2 shows a schematic flowchart illustrating a method 10 according to the invention in one embodiment. The method 10 serves to determine a standstill. In the illustrated embodiment, the method is described using the example of a vehicle standing still. In step 11 of the procedure 10, an initial velocity is determined based on received measurement data from at least one digital counting sensor 111, 113. Additionally, in step 12, a braking torque is determined and / or set based on received measurement data from at least one sensor 112 and / or based on at least one characteristic of a braking system of the vehicle 100. In the illustrated embodiment, a brake pressure is measured via a sensor 112 of the vehicle 100's braking system. A control unit 120 serves to receive and evaluate the measurement data from all sensors 111, 112. Furthermore, a coefficient of friction of the brake pads is used together with the measurement data from sensor 112 of the braking system to determine the braking torque or braking force. Other parameters, such as humidity, temperature, and the like, can also be taken into account when calculating the braking force. This can be done, for example, using a model. It is generally assumed that vehicle 100 will come to a standstill within a certain time when a braking torque is applied. This solves a problem for digital counting sensors 111, which determine rotational speed or translational movement by counting pulses. Such counting sensors can be, for example, speed sensors 111, 113, and below a certain threshold, they do not provide reliable measurement data. Therefore, it cannot be reliably determined whether vehicle 100 is stationary or moving slowly. For example, if the wind is "bumping" vehicle 100, pulses can be generated in the digital counting sensor 111, 113 even if the vehicle 100 is not moving. The digital counting sensor 111, 113 cannot distinguish how the pulses are explicitly generated. If the initial velocity v0 and the braking torque are known, the time it takes for vehicle 100 (or analogously, another technical system) to come to a standstill can be calculated. This time corresponds to the braking time t of vehicle 100. Initially, for translational systems: F = m * a, for rotational systems: M = J * α. In a further step 13, this braking time t is calculated based on the initial velocity v0 and the braking torque. This takes into account the case where the initial velocity v0 is actually present and braking to a standstill would be necessary. This can be reliably implemented regardless of a false-positive measurement of the initial velocity v0. After the calculated braking time t has elapsed, a standstill 14 is determined or confirmed. The braking time t or deceleration time is calculated below, taking into account the moments of inertia of the wheels Mraddes of vehicle 100. Moments MRadam wheel 130, the translational component is converted into a rotational component, where F corresponds to the wheel braking forces. The braking deceleration a of 7.748 m / s² is calculated based on the following assumptions: mvehicle = 3000 kg, corresponding to the mass of a vehicle without a trailer; Mwheel = 2000 Nm, assumed braking torque at one wheel of the vehicle; v0 = 0.7 km / h = 0.194 m / s; Uwheel = 2.123 m, circumference of one wheel corresponds to a radius of r = 0.338 mm; wheel = 24.69 kg; Jwheel = 1.5966 kg / m² Using these values ​​and the braking deceleration a, the braking time t can be calculated: If, however, the moment of inertia of the wheels 130 is not taken into account, the calculation simplifies to the following formula: The corresponding braking time t2 without taking into account the moment of inertia of the wheels 130 is 0.025 seconds and thus has a deviation of less than 1 ms. Reference symbol list 100 System / Vehicle 110 System / Transmission 111 Digital counter sensor on a wheel 112 Brake pressure sensor of the brake system 113 Digital counter sensor in the transmission 120 Control unit 130 Wheel 10 Procedure 11 Determining the initial speed 12 Determining a braking force 13 Calculating the braking time 14 Waiting for the braking time X Direction of travel / Longitudinal direction Y Lateral direction Z Vertical direction

Claims

Method (10) for determining a standstill of a system (100, 110), wherein: - an initial velocity (v0) is determined based on received measurement data from at least one digital counting sensor (111, 113), - a braking torque (F) is determined and / or set based on received measurement data from at least one sensor (112) and / or based on at least one property of a braking system, - a braking time (t, t2) is calculated based on the initial velocity (v0) and the braking torque (F), and - after the calculated braking time (t, t2) has elapsed, a standstill is determined. Method according to claim 1, wherein the initial velocity (v0) is determined as a smallest velocity measurable by the digital counting sensor (111, 113). Method according to claim 1, wherein the initial speed (v0) is determined to be 0.7 km / h if the actual speed is 0.7 km / h or less. Method according to one of claims 1 to 3, wherein measurement data received from the at least one digital counting sensor (111, 113) after the calculated braking time (t, t2) has elapsed are discarded. Method according to one of claims 1 to 4, wherein the initial velocity (v0) is determined based on received measurement data from at least one digital counting sensor of a vehicle-side ESP function and / or from at least one digital counting sensor of a shaft (111) and / or from at least one digital counting sensor (113) of a transmission. Method according to any one of claims 1 to 5, wherein such a braking torque is set by which the braking time (t, t2) is minimized. Method according to any one of claims 1 to 6, wherein the braking time (t) is determined using the formula 0 = v 0 + a * t is calculated using v0 as the initial velocity, a as the braking acceleration, and t as the braking time. Method according to claim 7, wherein the braking acceleration (a) is determined from an estimated or measured braking force. Method according to any one of claims 1 to 8, wherein the braking time (t, t2) is determined taking into account moments of inertia of wheels (130) of a vehicle (100). Method according to any one of claims 1 to 8, wherein the braking time (t, t2) is determined without taking into account the moments of inertia of the wheels (130) of the vehicle (100). Vehicle (100) which is equipped to perform a method (10) according to one of the preceding claims. Vehicle according to claim 11, wherein a standstill of the vehicle (100) determined by the method (10) is used to actuate a parking brake. Vehicle according to claim 11 or 12, wherein a standstill of the vehicle (100) determined by the method (10) is used to enable the application of the parking brake. Control unit (120), wherein the control unit (120) is configured to perform a method (10) according to any one of claims 1 to 10. Control unit according to claim 14, wherein the control unit (120) is connected to at least one sensor (111, 112, 113) via data transmission.

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