Method for emulating a passive torque-sensing multi-plate limited-slip differential

Abstract

Method for the electronic emulation of a torque-sensing multi-disk limited-slip differential in a vehicle, wherein - in a first step (S1), an applied torque on one or more driven axles is determined and transmitted to a control unit, - in a second step (S2), a degree of locking associated with the torque is determined based on a predetermined locking characteristic curve, and - in a third step (S3) a locking torque is calculated from the torque and the locking degree, characterized in that - in a fourth step (S4), an electrical control signal is specified in such a way that, depending on a sum wheel torque applied to the axle concerned, a locking torque which acts analogously to a passively operating lock is specified and transmitted to an electric motor arranged on the limited-slip differential for moving the plates (2), so that a passive lock is emulated.

Description

[0001] The invention relates to a method for emulating a passive torque-sensing multi-disk limited-slip differential for a vehicle according to the preamble of patent claim 1.

[0002] An open differential allows the driven wheels of an axle to have different speeds when necessary, e.g. when cornering. The torque is distributed equally between the driven wheels (apart from the self-locking component). However, with sporty driving styles the problem arises that if the load is relieved on one of the wheels, the torque can no longer be transmitted effectively and thus the torque of the other wheel is also limited. This effect also occurs on road surfaces with different surfaces, e.g. when one wheel is on a patch of ice and the other wheel is not, i.e. one wheel has normal traction and the other wheel has significantly reduced traction.

[0003] Controlled limited-slip differentials are typically installed on the primary drive axle of a vehicle and, using an electronic actuator, apply a locking torque, thereby negating the effect of an open differential. This allows, for example, torque to be transferred to the wheel with grip even when one wheel is spinning on one side, allowing the vehicle to move forward on slippery surfaces.

[0004] In general, a broad distinction is made between passive, i.e., mechanical, and active, i.e., electronically controlled, differential locks. A (partially) locked limited-slip differential usually causes understeer when cornering under traction. This is undesirable in everyday driving. In clubsport, for example, high-quality torque-sensing multi-disk self-locking differentials are used. These adjust the degree of locking depending on the applied ring gear torque and demonstrate a high degree of reproducibility of handling. Torque-sensing refers to the ability to generate locking torques dependent on the applied ring gear torque.

[0005] Active differential locks or limited-slip differentials are used to provide greater freedom of control, including 100% locking when pulling away with different friction coefficients on each tire, i.e., with µ-split. The disadvantage of the common control strategies for active limited-slip differentials is that they are complex and reactive. Exceptions can be traction pre-control or load change compensation, where pre-controlled components are active. A reproducible driving style is therefore difficult - if not impossible - to achieve. Due to the complex manufacturing processes, high-quality and reproducible passive multi-plate limited-slip differentials are expensive depending on their quality and area of application. In addition, they are each only tuned for a specific application (race track, friction coefficient, tires, vehicle type) and cannot be completely switched off.

[0006] Active limited-slip differentials are known, for example, from DE 102 48 090 B4, DE 10 2010 039 265 A1, DE 10 2014 118 407 A1 or DE 10 2006 026 188 A1.

[0007] In view of the above-mentioned disadvantages, it is an object of this invention to provide an improved control of an electronic limited-slip differential that overcomes the aforementioned disadvantages. This object is achieved according to the invention by the features of the independent patent claims. Advantageous embodiments are the subject of the dependent claims.

[0008] The invention proposes a method for the electronic emulation of a torque-sensing multi-plate limited-slip differential in a vehicle, wherein the torque applied to one or more driven axles is determined and transmitted to a control unit. From a predetermined locking characteristic curve, which is known, for example, from the setup of the passive multi-plate limited-slip differential, the degree of locking associated with the torque or drive torque can be determined. Finally, the required locking torque can be calculated from the torque or drive torque and the degree of locking, which is then specified as an electrical control signal such that a passive lock is emulated. The degree of locking is preferably determined by looking up information in a predetermined table.

[0009] A classic mechanically operated multi-disk limited-slip differential, i.e. a passive limited-slip differential, is Fig. 1 is shown schematically and comprises, for example, two thrust rings 10 and 20 which can move axially in the housing due to the application of force and which pass the forces acting on them on to the slats 2 via a more or less V-shaped notch 11 and 21. Lamellae 2 are located at the outer ends 12 and 22 and are pressed depending on the force applied, i.e. by displacement of the bolt 30 within the notch 11, 21. The locking value or degree of locking and thus also the locking characteristic are determined by the shape of the notch 11, 21 and possibly also of the bolt 30 which moves within the notch 11, 21 when a force is applied and thereby exerts force on the slats 2 because it moves the thrust rings 10, 20. Such a multi-disk limited-slip differential can be preloaded by inserting disc springs (not shown), which can lead to understeer even in a neutral position between thrust and traction.This type of limited-slip differential reacts immediately (without delay) to changes in the distribution of torque to the wheels because it reacts to mechanical changes.

[0010] The degree of locking or locking value defines a maximum differential torque that can occur in the axle depending on the total gear torque transmitted to the axle. The quotient of this differential torque to the total is referred to as the degree of locking. The higher the degree of locking, the higher the proportion of the ring gear torque that can be set as the locking torque. This means that the driving behavior changes significantly compared to a vehicle without a lock or with a lock with a low degree of locking. The design of the degrees of locking under traction and overrun is a compromise between driving dynamics and boundary conditions such as axle tension during moderate driving or a tendency to understeer.

[0011] With the mechanical locking systems described above, the degree of locking can either be specified as a fixed value or a locking characteristic is determined by the shape of the notch and the pin. Complex shapes are possible, especially with high-quality limited-slip differentials, allowing for fine adjustment of the degree of locking.

[0012] It is therefore proposed to specify a locking torque, which acts analogously to a passively operating lock, depending on the total wheel torque applied to the affected axle. This is advantageously achieved by providing a calculation unit in a vehicle control unit. Due to the electrical control of the plates of the limited-slip differential, mimicry (pins and ramp shape) is no longer required. This means that the shape of the notch and also of the pin are transmitted directly or indirectly to an electric motor via a locking characteristic curve specified by the control unit and calculated by the calculation unit. The electric motor compresses the plates according to the (torque) requirement. This emulates a purely passive lock without the need to use additional vehicle data (such as wheel speeds).

[0013] By providing a purely electrical, i.e. active, control of the lock, any locking characteristic can be emulated. This means that, as described in one embodiment, the control unit can control the multi-plate limited-slip differential in such a way that it behaves like an open differential. On the other hand, any degree of locking, even a variable degree of locking, can be set—i.e., a locking characteristic—over a very wide range that is limited only by the mechanical limits of the plates or the actuators. Also, as with the mechanical counterpart, a difference in the locking effect during traction and overrun can be realized without having to provide a complex or difficult-to-manufacture mechanical geometry.

[0014] Also, as shown in one embodiment, a driver of the vehicle can specify the locking characteristic of the multi-disk limited-slip differential indirectly in the form of a preset, e.g. via control elements.

[0015] Since the control is purely electrical, the driver can be given the opportunity to individually adjust the locking characteristic or a locking degree - even while driving - depending on the desired vehicle behavior.

[0016] In addition to emulating the torque-sensing passive lock, additional functions can be provided in a separate calculation unit. These could include functions for understeer avoidance, traction control, yaw damping, etc.

[0017] Also provided is a control unit which is configured to provide electrical control of a multi-plate limited-slip differential and which is configured to receive an applied torque at one or more driven axles, and which is configured to determine a degree of locking associated with the torque based on a predetermined locking characteristic curve and to calculate a locking torque therefrom and to specify this as an electrical control signal such that the electronic multi-plate limited-slip differential is emulated as a passive lock.

[0018] In one embodiment, a software program product is provided that is configured to execute the described method. The calculation unit can calculate the control signal using appropriate software, i.e., a corresponding algorithm.

[0019] Further features and advantages of the invention will become apparent from the following description of exemplary embodiments of the invention, with reference to the figures of the drawing, which illustrate details of the invention, and from the claims. The individual features can be implemented individually or in combination in a variant of the invention.

[0020] Preferred embodiments of the invention are explained in more detail below with reference to the accompanying drawings. Fig. 1 shows a schematic representation of a structure of a passive barrier according to the prior art. Fig. 2 shows a schematic representation of a structure of an emulated passive barrier according to an embodiment of the present invention. Fig. 3 shows a method according to an embodiment of the present invention. Fig. 4 schematically shows essential components of the control device according to an embodiment of the present invention.

[0021] In the following descriptions of the figures, the same elements or functions are provided with the same reference symbols.

[0022] Fig. Figure 2 shows a schematic representation of the structure of an emulated passive multi-disk differential lock 1. Depending on an acting torque, e.g., the torque M1 of the ring gear of a transmission acting on an axle, and / or a torque M2 and M3 acting on both wheels, a force K1 acting on the plates 2 is set. This force K1 can be configured as a pushing or pulling force, depending on how strongly the plates are to be compressed, i.e., depending on whether a higher or lower locking torque is to be set. Fig. 2 it is a thrust force K1. The force K1 is transmitted to the plates 2 via an electric motor arranged on the limited-slip differential. The control signal, i.e. the command how much force K1 and in which direction the force K1 is to be transmitted to the plates 2, is transmitted via a control unit which carries out the corresponding calculation based on the applied torque (M1 or M2+M3). The electrical control, which compresses the plates according to a determined or calculated characteristic curve, allows the design of the limited-slip differential to be simplified, i.e. no complex and expensive mimicry, i.e. the shape of the notch and / or the bolt, is required to achieve the desired driving dynamics goals.

[0023] Fig. 3 shows a flowchart of the method according to one embodiment of the invention. In a first step S1, the torque applied to driven wheels of the same axle is determined and transmitted to a control unit or an actuation unit. One or more locking characteristics associated with predetermined torques are stored in the actuation unit. Based on the determined torque and the corresponding locking characteristic, the actuation unit determines a degree of locking associated with the torque in a second step S2 and calculates a locking torque therefrom in a third step S3. This locking torque is transmitted in a fourth step S4 as a corresponding control signal by the actuation unit, which is designed, for example, as a control unit, to the limited-slip differential or to an electric motor arranged on the limited-slip differential for moving the plates 2 in order to emulate a passive torque-sensing multi-plate limited-slip differential.Preferably, the locking degree is determined by a lookup in the corresponding table. In such a (lookup) table, information is defined statically to avoid complex calculations.

[0024] By means of the method of the present invention, which can also be implemented as a computer program product, which in turn can be executed on a computing unit such as a calculation unit in a control unit, an optimal compromise is achieved between the agility of a torque-sensing passive lock and the prevention of the understeering tendency of this lock by actively deciding when the limited-slip differential produces a turning or unscrewing effect in the vehicle.

[0025] Fig. 4 schematically shows a vehicle with two axles 200, each with two wheels arranged on each side of the vehicle. The vehicle is equipped with the control unit 100 according to the invention. The control unit 100 has an electronic control unit containing a function module (not shown in detail) programmed to carry out the method according to the invention. The control unit 100 receives information about the torque applied to one or more driven axles 200. The control unit 100 preferably also contains a lookup table 101 with defined locking characteristics. Based on this table and the transmitted torque, the control unit 100 or a function module contained therein can calculate a degree of locking. This is preferably done by means of a lookup in the table 101.After calculating the locking torque, an electrical control signal is then specified in such a way that the electronic multi-plate limited-slip differential is emulated as a passive lock. The specification is made by transmitting the signal to a corresponding device for executing the signal, for example, to an electric motor for controlling the electronic limited-slip differential. Fig. 4 also shows a setting unit 102, which allows the driver to select which locking characteristic curve should be used. The setting unit can be implemented as a control element in the vehicle, e.g., a button or touch element within a touch display, etc.

Claims

[1] Method for the electronic emulation of a torque-sensing multi-disk limited-slip differential in a vehicle, wherein - in a first step (S1) an applied torque on one or more driven axles is determined and transmitted to a control unit, - in a second step (S2), a degree of locking associated with the torque is determined based on a predetermined locking characteristic curve, and - in a third step (S3) a locking torque is calculated from the torque and the locking degree, characterized in that - in a fourth step (S4), an electrical control signal is specified in such a way that, depending on a sum wheel torque applied to the axle in question, a locking torque which acts analogously to a passively operating lock is specified and transmitted to an electric motor arranged on the limited-slip differential for moving the plates (2), so that a passive lock is emulated. [2] Method according to claim 1, wherein in the second step (S2) the degree of locking is determined via a lookup of information in a corresponding table. [3] Method according to one of the preceding claims, wherein any blocking characteristic can be emulated by specifying the control signal. [4] Method according to one of the preceding claims, wherein the control unit can control the multi-disk limited-slip differential in such a way that it behaves like an open differential. [5] Method according to one of the preceding claims, wherein a driver of the vehicle can specify the locking characteristic of the multi-disk limited-slip differential. [6] Method according to claim 5, wherein a driver can specify the locking characteristic curve indirectly in the form of a preset. [7] Control unit which is designed to provide an electrical control of a multi-disk limited-slip differential and is designed to receive an applied torque on one or more driven axles, and is designed to determine a degree of locking associated with the torque on the basis of a predetermined locking characteristic curve and to calculate a locking torque therefrom and to specify this as an electrical control signal in such a way that a passive lock is emulated. [8] A software program product adapted to carry out the method according to any one of claims 1 to 6.

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