Method for controlling an automatic transmission of a motor vehicle

Abstract

Method for controlling an automatic transmission of a motor vehicle (1) during a braking procedure before a curve (22), wherein: based on route data, a projected The cornering speed (vk) is determined A target curve-driving gear (G-target) is determined, at which an engine speed (D) is in a defined target speed range (D-target) at the expected curve-driving speed (vk), and downshift points (t-rs), at which a downshift to a next lower gear (G) is performed, are set in such a way that a relatively high engine braking effect is achieved and the target curve-driving gear (G-target) is set when entering the curve (22).

Description

[0001] The present invention relates to a method for controlling an automatic transmission of a motor vehicle, in particular a method for controlling an automatic transmission of a motor vehicle during a braking process.

[0002] From DE 10 2011 006 741 A1 a method for controlling an automatic transmission of a motor vehicle when driving through a curve is known, wherein a gear to be engaged is determined based on a difference speed between a speed of the motor vehicle and a reference speed for the curve being driven through.

[0003] From DE 10 2010 001 873 A1 a method for determining and switching an optimal gear before entering a curve in a motor vehicle is known, wherein the optimal gear is determined based on a curve limit speed and a sportiness counter.

[0004] US Patent 2009 / 0319138 A1 discloses a method for driver assistance in a motor vehicle, wherein different transmission ratios are determined and set for successive curve sections.

[0005] From DE 10 2014 215 259 A1 a method for automatically selecting a driving mode on a motor vehicle is known, wherein a maximum lateral acceleration is determined for an upcoming curve and the driving mode is selected based on the determined maximum lateral acceleration.

[0006] It is known from the prior art to set downshift points during braking, at which a downshift to the next lower gear is performed, in such a way that the engine speed remains relatively high in order to achieve a relatively high engine braking effect. However, this can lead to an undesirably high engine speed at the point when the braking process ends, which is detrimental to subsequent acceleration of the vehicle. This problem occurs particularly during braking before a curve, since acceleration of the vehicle is usually necessary after braking.

[0007] Against this background, the challenge is to enable relatively strong braking before a curve and relatively strong acceleration after the curve without entering unwanted rev ranges.

[0008] This problem is solved according to the invention by a method for controlling an automatic transmission of a motor vehicle during a braking process before a curve, with the features of claim 1.

[0009] In the method according to the invention, a predictable curve negotiation speed is determined based on route data. The route data can, for example, include map data from a navigation system stored in the vehicle. It is also conceivable that the route data includes processed information about curvature profiles, information about the condition of the road surface, information about current traction conditions, information about lane width, and / or information about historical data from other sensors of a vehicle traveling on the route. Advantageously, when determining the predictable curve negotiation speed, information about the characteristics of the vehicle, for example, weight information, size information, and / or information about the vehicle's tires, as well as information about the driving behavior of the current driver of the vehicle, are also used.

[0010] In the method according to the invention, a target curve-giving gear is further determined, at which the engine speed of a motor vehicle's engine is within a defined target speed range at the expected curve-giving speed, i.e., when the motor vehicle is traveling at the expected curve-giving speed. The target speed range is advantageously defined such that the motor vehicle exhibits a torque maximum and / or a power maximum within the target speed range, enabling the motor vehicle to accelerate relatively quickly when the engine speed falls outside the target speed range.Preferably, the target engine speed range is defined based on current traction conditions, particularly the current road friction coefficient. A lower target engine speed range is defined for relatively low road friction coefficients (e.g., in wet conditions) than for relatively high road friction coefficients. The target engine speed range can also be determined using artificial intelligence. However, it is also conceivable that the target engine speed range could be set manually by the driver.

[0011] In the method according to the invention, downshift points, at which a downshift to the next lower gear is performed, are set such that, on the one hand, a relatively high engine braking effect is achieved and, on the other hand, the desired cornering gear is selected when entering the curve, i.e., at the end of the braking process. To achieve the relatively high engine braking effect, the downshifts are performed at relatively high engine speeds, which are preferably above the target speed range. Particularly preferably, the downshift points are set such that the engine speed immediately after the downshift is as close as possible to the maximum engine speed of the vehicle, i.e., at least 75%, preferably at least 85%, and particularly preferably at least 95% of the maximum engine speed.The total number of downshifts performed during the braking process is determined in such a way that the target gear for cornering is set at the end of the braking process.

[0012] By achieving a relatively high engine braking effect, the method according to the invention enables relatively strong deceleration of the vehicle before the curve. Because the desired curve-driving gear is selected at the end of the braking process, i.e., when entering the curve, the curve is negotiated at an engine speed at which the vehicle exhibits relatively high torque and / or relatively high power, thus enabling relatively strong acceleration after the curve.

[0013] Preferably, the expected cornering speed is determined based on historical driving data to enable a particularly accurate prediction of the expected cornering speed. Preferably, the historical driving data includes information about acceleration behavior, braking behavior, and / or other parameters reflecting the driving style of the vehicle's driver. Preferably, the historical driving data also includes information about the route traveled, so that information about the driver's driving behavior in curves comparable to the upcoming curve can be derived from the historical driving data. It is also conceivable that the historical driving data includes information about a previous driving of the upcoming curve, for example, information about a previous lap on a circuit.

[0014] Preferably, a curve limit speed, i.e. a theoretical maximum curve speed, is determined based on the track data, and the expected curve speed is determined based on the curve limit speed.

[0015] In this case, it is particularly preferred to determine an ideal line for driving through the curve based on the track data, i.e. a way to drive through the curve as quickly as possible, and to determine the curve limit speed based on a radius of curvature of the ideal line.

[0016] Preferably, a maximum lateral force value is also determined, which indicates the maximum lateral force that can be transmitted between the vehicle's tires and the road surface, and the cornering limit speed is determined based on this maximum lateral force value. The maximum lateral force value can be estimated, for example, based on information contained in the road data regarding the condition of the road surface, the status of the vehicle's windshield wipers, information from a rain sensor, ambient temperature, tire pressure, tire temperature, aerodynamic settings of the vehicle (e.g., the angle of attack of a spoiler), and / or other parameters influencing traction conditions.

[0017] Preferably, an initial racetrack detection is performed, and if the racetrack detection yields a negative result, i.e., if the vehicle is not on a racetrack, the process is terminated, so that the technical effect of the method according to the invention is only available when driving on a racetrack. Racetrack detection can be achieved, for example, by comparing the current location of the vehicle, determined, for example, by GPS, with the coordinates of known racetracks. It is also conceivable that driving on a racetrack is manually activated by the driver of the vehicle. In principle, it is also conceivable to link the execution of the method according to the invention to any other manual activation or input by the driver of the vehicle.

[0018] Preferably, if the racetrack detection is successful, i.e., if the vehicle is on a racetrack, the track data is at least partially retrieved from a racetrack database, making detailed, high-resolution track data available. In principle, the racetrack data can be retrieved from any source that provides racetrack data online or offline.

[0019] An embodiment of the present invention is described below with reference to the accompanying figures. These show: Fig. 1. A motor vehicle with an automatic transmission during a braking maneuver before a curve, and Fig. 2. By way of example, a highly simplified course of an engine speed and a course of a set gear of the motor vehicle during the braking process when carrying out a method according to the invention.

[0020] Fig. Figure 1 shows a motor vehicle 1 with an automatic transmission driving on a race track 2, wherein the motor vehicle 1 is equipped to perform a method according to the invention for controlling the automatic transmission during a braking process before a curve.

[0021] In the embodiment of the method according to the invention described here, racetrack recognition is initially performed by comparing the current location of the motor vehicle 1, determined by GPS, with the coordinates of known racetracks. Alternatively, racetrack recognition could also be performed using a route-based approach, whereby, for example, driving data (e.g., selected gears and / or speeds) are stored as a reference while driving a lap on the racetrack.

[0022] If the racetrack recognition yields a negative result, i.e., if the current location could not be assigned to any known racetrack, the inventive method is terminated and a standard method for controlling the automatic transmission, which is not specified in detail here, is executed.

[0023] If the racetrack detection is successful, meaning the current location can be matched to a known racetrack, track data for the detected track is retrieved from a racetrack database. If a racetrack with multiple possible track variations is detected, the driver of vehicle 1 is preferably shown a selection menu to choose the desired track variation.

[0024] When a braking process is initiated, i.e., when the brake pedal of vehicle 1 is pressed, the system checks, based on the current location of vehicle 1 and the route data, whether vehicle 1 is moving as described in Fig. 1 is shown, located within a braking zone 21 before a curve 22 of the race track 2.

[0025] If the test is successful, an ideal line 3 for negotiating curve 22 is determined based on the track data. Furthermore, based on factors including the status of the vehicle's windshield wipers, the ambient temperature, tire pressure, tire temperature, current aerodynamic settings, the road friction coefficient, and other parameters influencing traction, a maximum lateral force value Fy-max is estimated. This value represents the maximum lateral force that can be transmitted between the tires of vehicle 1 and the road surface. Based on the maximum lateral force value Fy-max, the radius of curvature R of the ideal line 3, and the mass m of vehicle 1, a cornering limit speed vk-max is determined as follows: v−k−max=F−y−max⋅Rm

[0026] Based on the maximum cornering speed vk-max, a sportiness factor determined from historical driving data, and / or historical driving data from comparable corners, a predicted cornering speed vk is calculated, at which the vehicle 1 is expected to negotiate curve 22. Alternatively, the predicted cornering speed vk can also be determined using a self-learning algorithm based on artificial intelligence methods.

[0027] Based on the expected curve speed vk, a target curve passage gear G-target is determined, at which an engine speed D is located in a defined target speed range D-target at the expected curve passage speed vk, in which the vehicle 1 has a particularly high drive power or a particularly high torque.

[0028] Based on a current speed, a current gear G and the expected curve speed vk, downshift times t-rs, at which a downshift to the next lower gear G is performed, are determined according to the invention in such a way that, on the one hand, a relatively high engine braking effect is achieved, i.e., the engine speed D is kept relatively high, and on the other hand, without an intermediate upshift, the target curve-driving gear G-target is set when entering curve 22, so that the engine speed D is in the target speed range D-target when entering curve 22.

[0029] Fig. Figure 2 shows, by way of example and in a very simplified manner, the resulting curves of the engine speed D and a selected gear G of the motor vehicle 1 when carrying out the method according to the invention during the braking process.

[0030] At the braking time tb, the braking process is initiated, which reduces the speed v of the motor vehicle 1 and consequently lowers the engine speed D.

[0031] At a downshift time t-rs-1, a first downshift to the next lower gear G occurs, causing the engine speed D to jump to a maximum engine speed D-max and then drop again due to the reduction in speed v caused by braking.

[0032] At downshift times t-rs-2 to t-rs-4, further downshifts to the next lower gear G take place, whereby the engine speed D jumps each time to the maximum engine speed D-max or at least close to the maximum engine speed D-max, thereby achieving a relatively high engine braking effect.

[0033] At the downshift point t-rs-4, the target curve driving gear G-target is set, so that no further downshifting takes place afterwards.

[0034] The downshift points t-rs, and in particular the number of downshift points t-rs, are set in such a way that when entering curve 22, i.e. at the end of the braking process, the target curve passage gear G-target is set, the engine speed D is therefore in the target speed range D-target, and the engine speed D remains at a relatively high level in the meantime in order to achieve a relatively large engine braking effect. Reference symbol list 1 motor vehicle 2 race track 21 Braking zone 22 Curve 3 Ideal line D Engine speed D-max maximum engine speed D-target target speed range G Gang G-target target curve passage gear R radius of curvature tb braking point t-rs downshift points v speed vk expected cornering speed

Claims

Method for controlling an automatic transmission of a motor vehicle (1) during a braking process before a curve (22), wherein: based on route data, an expected curve speed (vk) is determined, a target curve speed (G-target) is determined at which an engine speed (D) at the expected curve speed (vk) is in a defined target speed range (D-target), and downshift times (t-rs), at which a downshift to a next lower gear (G) is performed, are set such that a relatively high engine braking effect is achieved and the target curve speed (G-target) is set when entering the curve (22). Method according to claim 1, wherein the expected curve speed (vk) is further determined based on historical driving data. Method according to one of the preceding claims, wherein a curve limit speed is determined based on the track data and the expected curve passage speed (vk) is determined based on the curve limit speed. Method according to claim 3, wherein an ideal line (3) for driving the curve (22) is determined based on the track data and the curve limit speed is determined based on a radius of curvature (R) of the ideal line (3). Method according to claim 3 or 4, wherein a maximum lateral force value is determined which indicates a maximum lateral force that can be transmitted between the tires of the motor vehicle (1) and a surface, and the cornering limit speed is determined based on the maximum lateral force value. Method according to one of the preceding claims, wherein an initial racetrack detection is performed and the method is terminated if the racetrack detection yields a negative result. Method according to claim 6, wherein the track data is retrieved at least partially from a racetrack database.

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