Power steering and methods for adjusting power loss generated in a final stage and / or electric motor of an electric power steering system

Abstract

Method for adjusting power loss generated in a final stage (17) and / or an electric motor (1) of an electric power steering system (2) of a means of transport (10) comprising the steps: - Determining (100) a current thermal situation of the power steering (2), in particular of the means of transport (10), - Reading (400) thermodynamic information of the power steering (2) from a data storage device (3), - Determining (500) a future power demanded by the power steering (2) based on an upcoming driving situation of the means of transport (10), - Determining (600) a future temperature arising within the power steering system (2) based on the thermodynamic information and the requested power, and responding to it - Adjusting (700) the operating behavior of the power steering (2).

Description

State of the art

[0001] The present invention relates to a power steering system and a method for adjusting the power loss generated in an electric power steering system of a means of transportation. In particular, the present invention relates to a method for reducing the power loss in a timely manner.

[0002] In electric power steering (EPS) systems, which are equipped with, for example, permanent magnet synchronous motors (PMSMs) as electric motors, rare earth elements are used, among other things, to prevent temperature-induced demagnetization of the permanent magnets. Due to cost pressures, however, the proportion of these materials must be kept low. This reduction must not, however, affect the availability of the power steering. This means, for example, that the proportion of dysprosium may only be reduced to the point where demagnetization cannot occur within the steering system's operating range. To minimize the use of dysprosium, the steering system's operating temperature range must be monitored during operation, and the power steering output must be reduced in a timely manner.Component protection measures, such as so-called "temperature derating," generally reduce power steering assistance to approximately 50 to 60 percent. Such a reduction in assistance is clearly noticeable to the driver at the steering wheel, for example, in an electric power steering system. Therefore, this should be prevented for as long as possible to minimize any negative impact on the user experience, if any at all.

[0003] The closest related document to the application, DE 199 08 572 A1, discloses a method for adjusting the power loss generated in a final stage and / or an electric motor of an electric power steering system of a means of transport, wherein the steps of determining the current thermal state of the power steering system and reading thermodynamic information about the power steering system from a data storage device are performed. Furthermore, a power steering system comprising a sensor, a data storage device, a data input, and an evaluation unit is known, wherein the sensor is configured to determine the current thermal state of the power steering system. The evaluation unit is configured to read thermodynamic information about the power steering system from the data storage device.

[0004] DE 10 2008 028 055 A1 discloses a method for providing steering power to an electromechanical steering system, which determines the current driving state of the power-assisted vehicle based on a requested steering assistance and the corresponding motor current. If a driving state exists that requires additional steering power, more steering assistance can be generated by increasing the permissible motor current via software. Depending on the temperature of the electric motor and the associated electronic control unit, the additional steering assistance can be reduced again if necessary to prevent damage to the steering system.

[0005] DE 10 2009 046 966 A1 relates to a method for operating an electronic power steering system during a parking maneuver, in which a path to be driven by the vehicle is first determined and the steering settings required for driving along the path are calculated. If the automatic control of the parking position leads to overheating of the actuator used, the automatic control of the vehicle is aborted and control is handed over to the driver.

[0006] The aforementioned prior art does not fully exploit the fundamental possibilities for the timely reduction of steering assistance. It is therefore an object of the present invention to satisfy the need identified above. Disclosure of the invention

[0007] The aforementioned problem is solved according to the invention by a method for adjusting the power loss generated in a final stage and / or in an electric machine ("E-machine") of an electric power steering system of a means of transport, according to claim 1 and the components according to claims 9 and 11. An electric power steering system is understood to be an electrically assisted steering unit (as opposed to a hydraulically assisted steering unit). The means of transport can, in particular, be a vehicle, preferably a road vehicle. In a first step, the current thermal situation of the power steering system is determined. The thermal situation can, for example, include temperatures within the means of transport. Furthermore, the thermal situation can include temperature changes within the means of transport. It is fundamentally irrelevant whether the thermal situation is determined by sensors and / or computation.Components of the power steering system itself (e.g., the final stage and / or the electric motor) can also be included in the analysis of the thermal situation. Furthermore, thermodynamic information from the power steering system is read from a data storage device, which may have been populated with reference values, reference lines, reference maps, and / or similar data during development. Additionally, it is possible to take measurements during the operation of a delivered vehicle and to store the measurement results in relation to past operating conditions of the vehicle. In this way, a temperature model of the respective vehicle is created in the form of a mapping between thermal situations and operating states, based on which future operating states can be evaluated with regard to their thermal influence on the thermal situation of the electric power steering system.

[0008] Refining the factory-defined data set during operation has the advantage of taking into account the exact vehicle configuration (all optional equipment and engine variants are considered) as well as subsequent modifications (tuning, retrofitted air deflectors, performance enhancements, etc.). Additionally, the vehicle's upcoming driving situation is determined, which can be done, for example, using a tracking system (e.g., GPS, A-GPS, GLONASS, etc.) and / or wireless communication infrastructure (e.g., GSM, EDGE, LTE, UMTS, LTE-A, WLAN, etc.). Alternatively or additionally, traffic signs can be recognized, providing information about the vehicle's upcoming driving situation. Traffic reports (e.g., a traffic jam) can also be considered.Alternatively or additionally, optical signals from a camera can be analyzed, providing information about the (short-term) upcoming driving situation. Based on the vehicle's upcoming driving situation, the power required by the power steering and / or the expected electrical (loss) power are determined. If the upcoming driving situation suggests that the power steering will be used little (e.g., before driving on the highway), it can be assumed that the electric power steering will require little power. However, if a winding road or a parking maneuver is identified as the upcoming driving situation, a higher power requirement can be assumed. Subsequently, based on the thermodynamic information and the required power, the temperature that will develop within the power steering system is determined.In other words, the known environmental data, the predicted route data, and the thermodynamic model of the power steering system are used together to predict a future temperature profile of the power steering system. In particular, the temperature of the electric motor and / or a final stage of the power steering system can be determined. Based on this, the operating behavior of the power steering system (e.g., steering assistance power) can be adjusted, and in particular, reduced.

[0009] In this way, predictive control of the power steering output can be implemented, which, compared to a current threshold-based approach, offers the advantage that future thermal reserves can be better utilized and the electric power steering output needs to be reduced or suspended significantly less often. This improves user comfort and driving safety through increased availability of the power steering, or enables consistent comfort with reduced hardware requirements. In other words, components can be made less thermally resistant, thereby reducing the cost and weight of the vehicle.

[0010] The dependent claims describe preferred embodiments of the invention.

[0011] Preferably, the operating temperature of the power steering system can also be measured by sensors. Alternatively or additionally, the temperature of a component of the power steering system can be measured. According to the language of the present invention, the power steering system comprises at least the final stage, the motor, and an electronic control unit. The steering hardware (steering column, rack and pinion, steering gear, etc.) can also be considered part of the power steering system. The ambient temperature can be, for example, the ambient temperature of the vehicle (absolute ambient temperature) and / or a temperature in the immediate vicinity of the power steering system (within the vehicle, in particular the engine compartment). Since numerous thermal sensors are provided in the engine compartment for other purposes, the ambient temperature and the temperature of the power steering component can be determined in a largely hardware-neutral manner.

[0012] The current thermal situation of the power steering system can include measuring the temperature of the power steering system as well as determining the temperature change of the power steering system over time.

[0013] It is also possible to determine the current heat input into the power steering system in order to create a heat balance for the power steering system, for example, based on the current heat dissipation from the power steering system or the engine compartment. This involves not only temperature measurements but also considering thermally relevant operating conditions (e.g., the traction motor, the cruising speed, the position of variable air guides, the air density, etc.). The aforementioned information can sometimes be obtained via the vehicle's onboard network's information bus systems, thus minimizing the sensor requirements.

[0014] In most cases, the inventive method will be carried out repeatedly (e.g., time- and / or event-controlled) to provide a reliable information base for adapting the operating behavior of the power steering system. The use of sensors or mathematical algorithms can be adapted depending on a change in the thermal situation and / or a change in a future driving situation (modified driving situation forecast). For example, the thermal situation and / or the future driving situation can be compared over time with a reference (e.g., a previous value). If the current value deviates from the reference value by more than a predefined threshold, the entire inventive method for adapting the power loss generated in the final stage and / or electric motor can be carried out at an earlier time point based on the respective value.In this way, the prediction can be refined as soon as input variables have changed (e.g., to an unexpected extent). If the changes in the thermal situation and / or the future driving situation with respect to a given reference are small or negligible, the method according to the invention can be repeated at a later time to reduce computing capacity and power loss.

[0015] The thermodynamic information of the power steering system can include, for example, heat capacity and / or radiation behavior and / or material-related maximum temperature values.

[0016] In this way, a mathematical analysis of the power steering system can better represent dynamic relationships (heat flow balances).

[0017] The future driving situation of the vehicle can be determined, for example, based on information from a navigation system and / or the current vehicle speed and / or the operating status of a turn signal and / or the operating status of a parking assist sensor and / or a signal from a traffic sign recognition camera. While the operating status of a turn signal and / or a parking assist sensor indicates upcoming curves in the short term, explicit or implicit speed limits as well as road profile information can be provided based on the camera signals. While speed limits reduce heat dissipation from the engine compartment, road profile information can indicate future electrical power losses in the power steering system.Alternatively or additionally, the accelerator pedal position and / or a prediction of a driving profile and / or a detected class of a currently executed or future steering maneuver can be taken into account when determining the future power demand from the power steering system over time. The aforementioned information provides a broad basis for predicting the future power demand as a measure of the heat input into the power steering system and enables a precise determination of the need to adjust the operating behavior of the power steering system.

[0018] If adjusting the power steering system's operating characteristics is unavoidable, the system can be supplied with reduced electrical energy depending on the driver's steering torque. This can be implemented in a frequency-dependent manner, such that high-frequency changes in steering torque receive less assistance than low-frequency components (of the basic steering angle). In this way, driving safety is less affected than the directness of the steering response when transmitting the steering input from the road to the steering wheel.

[0019] According to a second aspect of the present invention, a power steering system is proposed comprising a first sensor, a data storage device, a data input, and an evaluation unit. The sensor is configured to determine the current thermal state of the power steering system. The evaluation unit is configured to determine the power demanded by the power steering system in the future by means of the data input. The evaluation unit can read thermodynamic information about the power steering system from the data storage device. Based on this thermodynamic information and the demanded power, the evaluation unit can determine the future temperature within the power steering system and, by adjusting it accordingly, issue a control command to adapt the operating behavior of the power steering system.In this way, the power steering system according to the invention is able to realize the aspects and combinations thereof, and the resulting advantages, of the method according to the first-mentioned aspect of the invention. To avoid repetition, reference is therefore made to the above statements.

[0020] According to a third aspect of the present invention, a means of propulsion is proposed, which may, for example, be a vehicle (e.g., a car, van, truck, or other land vehicle). According to the invention, the means of propulsion includes a power steering system as described in connection with the second aspect of the invention. Brief description of the drawings

[0021] Exemplary embodiments of the invention are described in detail below with reference to the accompanying drawings. The drawings show: Fig. 1 a schematic view of components of an embodiment of a power steering system according to the invention; Fig. 2. A schematic view of the criteria for an upcoming driving situation of a means of transport; and Fig. 3 A flowchart illustrating the steps of an embodiment of a method according to the invention. Embodiments of the invention

[0022] Fig. Figure 1 shows an overview of components of an embodiment of a steering system according to the invention. A steering wheel 11 is connected via a steering column 12, on which a rotation angle sensor 13 is arranged, to a rack 16, by means of which the wheels 15 of a vehicle can be steered. The position of the rack 16 can also be determined via a sensor 14 and is supplied to an electronic control unit 9 as an evaluation unit. Within the electronic control unit 9, a data storage device 3 and a power stage 17 are provided, wherein the power stage 17 is configured to control an electric motor 1, the temperature of which is detected via a temperature sensor 7 and supplied to the electronic control unit 9.To determine an upcoming driving situation, a traffic sign recognition camera 6 is connected to an electronic control unit 20, which is also supplied with information about position and surroundings via an ultrasonic sensor 5 and a satellite-based positioning system 18 with a data storage device 19 and a receiver 21. A turn signal indicator 4 is also monitored by the electronic control unit 20, so that the operating status of the turn signal indicator 4 signals the user's intention to perform a predetermined maneuver.The electronic control unit 9 receives information via a data input 8 to determine the future temperature within the power steering system. This information is based on the thermodynamic data of the power steering system 2 stored in the data memory 3 and the power demanded by the power steering system 2, which can be determined from the data of the sensors connected to the electronic control unit 20. In this way, all data available to the control unit 20 can also be made available to the electronic control unit 9. In the setup described above, the temperature sensor 7 enables the determination of the current thermal status of the power steering system 2.

[0023] Fig. Figure 2 shows a car 10 as a means of transport and the route sections A, B, C of a calculated route 22 that it will travel in the future. The representation could also be understood as a display on a navigation system 18, as is the case in Fig. As already introduced, car 10 is currently on a straight section of track A, followed by a winding section B (e.g., a serpentine road). Both sections A and B are uphill, so the drive power of car 10's motor generates particularly high power losses and corresponding amounts of heat on section A. Additionally, losses occurring within the power steering system of car 10 on section B contribute to heat generation within the final stage or electric motor of the power steering system. Section B is followed by section C, which is essentially straight and without any significant gradient.For the current situation of car 10, or rather the thermal situation of the power steering, it can be deduced from this scenario that in the near future an increase in temperature is to be expected both within the engine compartment and within the electric power steering (sections A, B), while upon reaching the third section C a reduced heat development due to traction and steering is to be expected, which will ease the thermal situation of the power steering.

[0024] Fig.Figure 3 shows steps of an embodiment of a method according to the invention for adjusting the power loss generated in a final stage of an electric power steering system of a means of transportation. In step 100, the current thermal situation of the power steering system is determined, for which purpose an ambient temperature of the power steering system and a temperature of a component of the power steering system are recorded in steps 200 and 300. The component of the power steering system can be, for example, a final stage and / or an electric motor. Subsequently, in step 400, thermodynamic information of the power steering system is read from a data storage device.

[0025] The thermodynamic information can include, for example, heat capacities, operating-condition-related temperatures, and / or heat transfer coefficients. In other words, the thermodynamic information of the power steering system characterizes its thermal behavior under different operating conditions. In step 500, the power required by the power steering system in the future is determined based on an upcoming driving situation of the vehicle. In other words, the system uses available information to determine how the operating conditions of the vehicle will develop during the journey. This information can include details regarding the thrust / traction of a traction motor, its expected cruising speed, and a measure of the extent to which electric power steering will be used.In step 600, the temperatures that will develop within the power steering system are determined based on thermodynamic information and the power demanded by the system. In response, the operating behavior of the power steering system is adjusted in step 700. Frequency-dependent components of the power steering assist signal can be reduced to prevent overheating of the system in a timely manner and in consideration of the upcoming driving situation. Finally, in step 800, an average expected temperature value is calculated to determine the future temperature within the power steering system. Additionally, a pessimistic temperature estimate is performed to prevent an uncontrolled failure of the power steering assist due to a malfunction.The method described above can be (partially) executed again according to a schedule and / or event-driven in order to react to changed boundary conditions and forecast results. Therefore, the method according to the invention predominantly uses information and hardware that are already present in many production vehicles. In this way, the method according to the invention can be implemented cost-effectively.

[0026] In general, the cooling profiles of the steering system and its components at different ambient temperatures can be measured and / or calculated during the development of new vehicle projects or new steering systems. The corresponding findings can be stored in a data repository, which is accessed during the implementation of the method according to the invention. The ambient conditions (thermal environment) of the steering system can be determined using vehicle sensors and knowledge of the steering system's installation location and surroundings. Furthermore, the current state of the steering system (e.g., measuring the temperature of a predefined component such as the steering motor or electronic control unit) and, based on this, the component temperature reserve can be determined. The vehicle-based sensors enable a prediction of the future power steering system's performance requirements.In particular, knowledge of future driving conditions, road surfaces, and road profiles enables relatively accurate predictions. General environmental maps, as well as trip histories available within a specific vehicle, can be used for this purpose. These histories are created over repeated trips, consolidated, and stored in a data repository. Depending on the predicted operating conditions of the vehicle or the power steering system, the degree of power reduction can be determined automatically. This can initially occur without any noticeable loss of function for the driver. Specifically, based on the reduced driving profile, it can be determined which components of the assistance signal are most likely to be imperceptible to the driver. The following criteria simplify the estimation of future environmental conditions.Navigation information (e.g., route, altitude, position, etc.), current vehicle speed, operating status of the turn signals and parking assist sensors, traffic sign recognition information (particularly relevant here are speed limits, gradients, indications of winding roads, etc.), the outside temperature, the steering temperature (e.g., measuring points within the electronic control unit and / or the electric motor), the exhaust gas temperature, the coolant temperature, the oil temperature, the load condition of the drive system (e.g., an internal combustion engine), a signal from a mass airflow sensor (MAF sensor), information about the accelerator pedal position, the lateral / longitudinal acceleration, the steering torque (HLM), and the steering speed (change in steering angle over time). Furthermore, driver profiles can be created by evaluating vehicle sensors.In particular, information on the characteristics of the accelerator pedal position, lateral / longitudinal acceleration, steering torque (HLM), and steering speed is useful for predicting the upcoming driving situation. The following are exemplary application scenarios discussed to illustrate the respective influences of the predicted driving situations.

[0027] In the first scenario, the steering ambient temperature is 119 °C. The component temperature reserve of the currently critical component is 10 °K. It is then determined that a parking maneuver is imminent. This can be ascertained, for example, from the status of the parking assist system. Additionally, the duration of the maneuver, during which maximum steering power is required (e.g., three minutes), is estimated. Based on stored driving profile histories, it is then estimated that the electric motor used for steering assistance will operate at its rated power three times for five seconds each within this period. From the aforementioned information, a temperature increase of a maximum of 5 °K is then predicted. Accordingly, in a final step, it is decided that the assistance power does not necessarily need to be reduced.

[0028] In a second example scenario, a maximum temperature increase of 10 °K is determined compared to the first example scenario. Accordingly, the assistance power is reduced to a required maximum (e.g., 98 percent of the nominal assistance power of the power steering).

[0029] In a third example scenario, a sporty driving style is first identified based on the evaluation of steering torque, angular velocity, accelerator pedal input, and signals from acceleration sensors, etc. The current ambient temperature of the power steering system is 119 °C. The component temperature reserve is 10 °K. Additionally, the ambient temperature is classified as "high" due to a hot summer day. Based on information from a navigation system and automatically detected speed limits for the next three kilometers, the system identifies a winding country road. The estimated expected temperature increase of 8 °K suggests that no reduction in power assistance is necessary. Reference symbol list 1 electric motor 2 Power steering 3 Data storage 4 direction indicators 5 ultrasonic sensor 6 cameras 7 Temperature sensor 8 Data input 9 electronic control unit of the power steering 10 cars 11 Steering wheel 12 Steering column 13, 14 Steering angle sensors 15 wheels 16 Rack and pinion 17 Power stage 18 Navigation device 19 Data storage 20 central electronic control unit 21 receivers for satellite-based positioning 22 future route 100 to 800 process steps Sections A, B, C

Claims

[1] Method for adjusting power loss generated in a final stage (17) and / or an electric motor (1) of an electric power steering system (2) of a means of transport (10) comprising the steps: - Determining (100) a current thermal situation of the power steering (2), in particular of the means of transport (10), - Reading (400) thermodynamic information of the power steering (2) from a data storage device (3), - Determining (500) a future power demanded by the power steering (2) based on an upcoming driving situation of the means of transport (10), - Determining (600) a future temperature arising within the power steering system (2) based on the thermodynamic information and the requested power, and responding to it - Adjusting (700) the operating behavior of the power steering (2). [2] Method according to claim 1 further comprising - Detecting (200) an ambient temperature of the power steering (2), and / or - Measuring (300) the temperature of a power steering component. [3] Method according to claim 1 or 2, wherein determining the current thermal situation - a measurement of the temperature of the power steering system (2), and / or - a determination of a temperature change of the power steering (2) over time, and / or - a determination of the current heat input into the power steering system (2), in particular as a function of the current heat dissipation from the power steering system, and / or - includes determining a current waste heat parameter of a thermally adjacent unit to the power steering system, in particular a traction motor, preferably based on information obtained via a bus system. [4] Method according to any of the foregoing claims, further comprising - Determining a change in a thermal situation and / or a change in a future driving situation, - Comparing the thermal situation and / or the future driving situation with a reference, in particular with a previously assumed thermal situation and / or a previously assumed future driving situation, and responding to the comparison result, and - repeated execution of the procedure to adjust the power loss generated in the final stage (17) at a first (earlier) or a second (later) time. [5] Method according to one of the preceding claims, wherein the thermodynamic information includes relationships for predicting a temperature of the power steering (2), in particular a mathematical model, and / or parameters of the power steering (2). [6] Method according to one of the preceding claims, wherein determining the future power required by the power steering (2) over time, in particular by means of - Information from a navigation system, and / or - a current vehicle speed, and / or - an operating state of a direction indicator (4), and / or - an operating state of a parking assist sensor (5), and / or - a signal from a camera (6) for traffic sign recognition, in particular explicit or implicit speed limits or road course information, and / or - a gas pedal position, and / or - a prediction of a driving profile, and / or - a recognized class of a steering maneuver currently being carried out or to be carried out in the future. [7] Method according to one of the preceding claims, wherein the adjustment (700) of the operating behavior of the power steering (2) comprises supplying the power steering (2) with an electrical power reduced depending on a hand torque of the driver, in particular frequency-dependent. [8] Method according to one of the preceding claims, wherein determining (600) the future temperature arising within the power steering system comprises calculating (800) a mean assumed temperature value or a pessimistic maximum value. [9] Power steering including - a sensor (7), - a data storage device (3), - a data input (8), and - an evaluation unit (9), wherein the sensor (7) is set up to determine a current thermal situation of the power steering (2), and the evaluation unit (9) is set up, - to determine a future power demanded by the power steering (2) by means of the data input (8), - to read thermodynamic information from the power steering system (2) from the data storage (3), - to determine a future temperature arising within the power steering system (2) based on the thermodynamic information and the required power, and in response to it - to issue a control command to adjust the operating behavior of the power steering (2). [10] Power steering system according to claim 9, which is configured to perform a method according to any one of the preceding claims 1 to 8. [11] Means of transport, in particular vehicle (10), comprising a power steering system (2) according to one of claims 9 or 10.

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