Limited slip differential transmission

Abstract

The invention relates to a limited slip differential transmission (1), comprising three connection points (2, 3, 4) in the form of a transmission input (5) and two transmission outputs (6, 7), as well as a differential gear set (8), via which a drive torque introduced at the transmission input (5) can be distributed to the transmission outputs (6, 7) and via which a speed equalisation between the transmission outputs (6, 7) can be represented. In addition, a locking device (16) is provided, which is positioned in the power flow parallel to the differential gear set (8) between two of the connection points (2, 3, 4) and via which a locking torque can be automatically generated between the transmission outputs (6, 7). The locking device (16) is designed to generate the locking torque automatically as a function of a difference angle acceleration effective between the transmission outputs (6, 7).

Description

[0001] Limited-slip differential

[0002] The invention relates to a limited-slip differential gear, comprising three connection points in the form of a transmission input and two transmission outputs as well as a differential gear set, via which a drive torque introduced at the transmission input can be distributed between the transmission outputs and via which a speed compensation between the transmission outputs can be achieved, wherein a locking device is provided which is placed in the power flow parallel to the differential gear set between two of the connection points and via which a locking torque can be automatically generated between the transmission outputs.

[0003] Differential gears are used in motor vehicle drivetrains to distribute the drive torque introduced on the input side to the output sides via the respective differential gear, thus enabling different speeds between the output sides by speed compensation, for example when cornering. Depending on the specific integration of the respective differential gear, the distribution takes place either in the sense of transverse distribution to the drive wheels of a drive axle or in the sense of longitudinal distribution to several drive axles. In the case of varying traction or even in the event of an extreme inclination, the speed compensation made possible can result in spinning on one output side while the other output side remains stationary. In this case, the associated vehicle may then be unable to move.In addition to differentials with differential locks that can be actively engaged by the driver, limited-slip differentials are also known, in which the respective speed compensation is automatically limited. A distinction must be made between active limited-slip differentials, in which a locking effect is controlled, and passive limited-slip differentials, in which a locking effect is either permanently generated or occurs automatically depending on a parameter.

[0004] EP 3 453 921 A1 discloses a limited-slip differential designed as a bevel gear differential and having a transmission input in the form of a differential housing and two transmission outputs in the form of output bevel gears of a differential gear set. The transmission input and the transmission outputs form connection points to which the limited-slip differential can be integrated into a motor vehicle drivetrain. Via the differential gear set, a drive torque introduced via the differential housing can be distributed between the two output bevel gears, whereby speed differences between the output bevel gears can be enabled by implementing speed compensation via the differential gear set.The limited-slip differential is also equipped with locking devices that can create a locking effect between the transmission input and each of the transmission outputs, effectively resulting in a locking torque between the transmission outputs. The locking effect is configured depending on the drive torque applied to the differential housing.

[0005] Based on the prior art described above, it is now the object of the present invention to provide a limited-slip differential gear in which a locking effect and thus a restriction of a speed compensation is automatically brought about, wherein this should be designed as optimally as possible with regard to the driving dynamics of a motor vehicle having the limited-slip differential gear.

[0006] This object is achieved based on the preamble of claim 1 in conjunction with its characterizing features. The dependent claims that follow each of these claim set forth advantageous developments of the invention.

[0007] According to the invention, a limited-slip differential comprises three connection points in the form of a transmission input and two transmission outputs, as well as a differential gear set, via which a drive torque introduced at the transmission input is distributed among the transmission outputs and via which a speed compensation can be achieved between the transmission outputs. Furthermore, a locking device is provided, which is positioned in the power flow parallel to the differential gear set between two of the connection points and via which a locking torque can be automatically generated between the transmission outputs. The limited-slip differential according to the invention thus has three connection points, one of which is a transmission input and the remaining connection points are two transmission outputs.At the transmission input, drive torque can be fed into the limited-slip differential and distributed between the two transmission outputs via the limited-slip differential's differential gear set. The differential gear set allows for speed differences between the transmission outputs to compensate for speed differences. The differential gear set thus functions as a differential gear set, connecting the three connection points of the limited-slip differential to each other.

[0008] The differential gear set of the limited-slip differential according to the invention can be designed within the scope of the invention such that the differential gear set distributes the drive torque introduced at the transmission input evenly between the two transmission outputs, i.e., it divides it equally between the transmission outputs. The limited-slip differential can then be designed as a transverse differential, although it could also be configured as a longitudinal differential with an even distribution. Alternatively, an uneven distribution of the drive torque between the two transmission outputs via the differential gear set is also possible within the scope of the invention, in which case the limited-slip differential is designed as a longitudinal differential.

[0009] The limited-slip differential also features a locking device, which is arranged parallel to the differential gear set in the power flow between two of the connection points. Accordingly, these two connection points can be coupled via the locking device parallel to the differential gear set. The locking device in the limited-slip differential is designed to automatically generate a locking torque between the transmission outputs. The generation of a "locking torque" between the transmission outputs means that the locking device can automatically change the torque ratio between the transmission outputs and thus specifically allocate a higher torque component to one of the transmission outputs, thereby also limiting the speed compensation achievable via the differential gear set.A key feature of the invention is that the locking device can automatically generate a locking torque between the transmission outputs. "Automatically," as used herein, means that the locking torque is generated automatically by the locking device, i.e., it is neither actively triggered by a vehicle driver nor by a control or regulation system or corresponding actuator. The locking device thus generates the respective locking torque itself, without any drive technology and based on physical effects.

[0010] The invention now includes the technical teaching that the locking device is configured to automatically generate the locking torque as a function of a differential angular acceleration acting between the transmission outputs. In other words, the locking device automatically generates the locking torque as a function of a current difference between the angular accelerations of the transmission outputs and thus as a function of a change in the current difference between the angular velocities of the transmission outputs.

[0011] Such a design of a limited-slip differential has the advantage that it allows a locking effect generated via the locking device to be optimally designed with regard to the driving dynamics of a motor vehicle equipped with the limited-slip differential according to the invention. This is because the automatic generation of the locking torque depends on the differential angular acceleration acting between the transmission outputs, on the one hand, a locking torque is generated as soon as rapid acceleration occurs at one of the transmission outputs compared to the other transmission output, for example due to lower traction. On the other hand, however, when cornering, no locking torque is exerted when driving through a load-free apex of a curve, which would otherwise have an effect counteracting the yaw motion of the vehicle.In this respect, compared to a load-dependent generation of a locking torque, a locking torque can also be generated when no torque can be transmitted due to a lack of or low traction, or when the transmittable torque is low. This is also possible without a general increase in the locking effect, which would otherwise have a negative impact on the driving dynamics in other areas. In comparison to a generation of the locking torque depending on a differential angular velocity effective between the transmission outputs or a constant superposition of a locking torque, no locking torque is generated when cornering when passing through a load-free apex. Overall, the generation of a locking torque in the locking device according to the invention therefore represents an optimal compromise solution with regard to the driving dynamics of a motor vehicle.

[0012] In the case of EP 3453 921 A1, a load-dependent generation of a locking torque is realized via the locking device, whereby when using the limited-slip differential gear of EP 3 453 921 A1, a locking torque can no longer be built up in the event of a complete loss of traction at one of the transmission outputs, for example due to a complete loss of road grip.

[0013] According to one embodiment of the invention, the locking device comprises a high-inertia device. This has the advantage that the inventive, automatic generation of the locking torque can be realized in a reliable and simple manner using a device with a high moment of inertia. Preferably, a moment of inertia of the high-inertia device corresponds at least 50% to a moment of inertia of a respective output to be connected to the individual transmission output. Depending on the design of the output to be connected to the individual transmission output, the moment of inertia of the output can be essentially defined by a moment of inertia of a vehicle wheel.

[0014] According to an alternative or supplementary embodiment of the invention, the locking device comprises a hydraulic device and / or a pneumatic device and / or an inductive device and / or an electromechanical device. The desired effect, namely the automatic generation of a locking torque as a function of a differential angular acceleration acting between the transmission outputs, can also be achieved using one or more of the devices described above. Further alternatively or additionally, the locking device comprises a device via which energy absorbed by the locking device during the generation of the locking torque can be released, stored, converted, and / or internally dissipated.This enables appropriate use of the absorbed energy, depending on the specific design of the limited-slip differential and its integration into a vehicle drive train.

[0015] In a further embodiment of the invention, in addition to the locking device, at least one further locking device is provided, which is also positioned in the power flow parallel to the differential gear set between two of the connection points and is designed to permanently generate a constant locking torque between the transmission outputs or to automatically generate a locking torque between the transmission outputs as a function of a drive torque introduced at the transmission input or as a function of a differential speed acting between the transmission outputs. By combining the locking device with at least one further locking device, an overall representable characteristic of a locking effect in the limited-slip differential gear according to the invention can be suitably designed.In this case, several additional locking devices can also be provided, in which either a constant locking torque is permanently generated, a load-dependent locking torque is automatically generated or a speed-dependent locking torque is automatically generated.

[0016] When combining the aforementioned embodiment with the previous variant, further locking functions of one or more further locking devices can be connected downstream of the forces / torques resulting from the locking device.

[0017] According to one possible embodiment of the invention, the locking device comprises an element designed to limit the forces and / or torques generated by the locking device when the locking torque is generated. In a further development of the invention, the locking device is arranged in the power flow between the transmission input and one of the transmission outputs. Alternatively, the locking device can also be arranged between the two transmission outputs within the scope of the invention.

[0018] According to one embodiment of the invention, the differential gear set is in the form of a planetary gear set, a spur gear set, or a bevel gear set. This allows a suitable design for a limited-slip differential to be realized in each case.

[0019] An advantageous embodiment of the invention, which is explained below, is shown in the drawing.

[0020] The sole figure shows a schematic representation of a limited-slip differential 1, which is designed according to a preferred embodiment of the invention. The limited-slip differential 1 has three connection points 2, 3, and 4, of which connection point 2 is a transmission input 5 of the limited-slip differential 1, while connection points 3 and 4 each represent a transmission output 6 and 7, respectively.

[0021] The limited-slip differential 1 further comprises a differential gear set 8, which is designed as a planetary gear set 9. Accordingly, the limited-slip differential 1 is designed in the manner of a planetary gear differential. The planetary gear set 9 is specifically designed as a positive planetary gear set and comprises a ring gear 10, a sun gear 11, and a planet carrier 12, in which at least one planetary gear pair 13 is rotatably mounted. In the at least one planetary gear pair 13, a planetary gear 14 meshes with the sun gear 11, and a planetary gear 15 meshes with the ring gear 10, wherein the two planetary gears 14 and 15 also mesh with each other within the planetary gear pair 13.

[0022] The ring gear 10 of the differential gear set 8 is connected in a rotationally fixed manner to the transmission input 5, whereas the sun gear 11 is connected in a rotationally fixed manner to the transmission output 6 and the planet carrier 12 is connected in a rotationally fixed manner to the transmission output 7. The transmission input 5 is thus coupled to the two transmission outputs 6 and 7 via the differential gear set 8, whereby a drive torque introduced at the transmission input 5 is distributed to the two transmission outputs 6 and 7 via the differential gear set 8, and speed differences between the transmission outputs 6 and 7 can be permitted by implementing speed compensation via the planet gears 14 and 15 by executing rotary movements in the planet carrier 12.

[0023] In the limited-slip differential gear 1, a locking device 16 is also provided in the power flow parallel to the differential gear set 8, wherein this locking device 16 is specifically arranged between the sun gear 11 and the planet carrier 12 and thus between the two transmission outputs 6 and 7. The locking device 16 can be used to couple the transmission output 6 to the transmission output 7 parallel to the differential gear set 8, thereby generating a locking torque between the transmission outputs 6 and 7 in order to change the torque distribution between the transmission outputs 6 and 7 and to limit the speed compensation via the differential gear set 8.

[0024] The blocking torque is generated automatically via the blocking device 16, whereby this automatic generation is carried out as a function of a change in the differential angular velocity acting between the transmission outputs 6 and 7 and thus as a function of the differential angular acceleration acting between the transmission outputs. Specifically, this generation takes place according to the relationship

[0025] , where AM is the locking torque, t is the time and Ao67 is the differential angular velocity effective between the gearbox outputs 6 and 7.

[0026] In order to be able to realize the aforementioned generation of the locking torque AM, the locking device 16 comprises a highly inertial device which has a moment of inertia which corresponds to at least 50% of a moment of inertia of a respective output to be connected to the individual transmission output 6 or 7, preferably at least 50% of a moment of inertia of a respective vehicle wheel coupled to the individual transmission output 6 or 7.

[0027] Optionally, in addition to this highly inertial device, the locking device 16 can also include a hydraulic device and / or a pneumatic device and / or an inductive device and / or an electromechanical device. Furthermore, the locking device 16 can comprise a device by which energy absorbed by the locking device during the generation of the locking torque can be released, stored, converted, and / or internally dissipated. Furthermore, the locking device 16 can include an element configured to limit the forces and / or torques generated by the locking device 16 when the locking torque is generated.

[0028] Furthermore, optionally, as indicated by dashed lines in the figure, the limited-slip differential gear also has at least one further locking device 17, which is also arranged parallel to the differential gear set 8 in the power flow and, as indicated here, can be placed in the power flow between the transmission input 2 and the transmission output 7. This at least one further storage device 17 can be designed to permanently produce a constant locking torque between the transmission outputs 6 and 7 or to automatically generate a locking torque between the transmission outputs 6 and 7 as a function of a drive torque introduced at the transmission input 5 or as a function of a differential speed effective between the transmission outputs 6 and 7.

[0029] By means of the design according to the invention, a locking effect and thus a restriction of speed compensation can be automatically induced in a limited-slip differential, whereby this can be optimally designed with regard to the driving dynamics of a motor vehicle having the limited-slip differential.

[0030] Limited-slip differential Connection point Connection point Connection point Gearbox input Gearbox output Gearbox output Differential gear set Planetary gear set

[0031] Ring gear Sun gear Planet carrier Planet gear pair Planet gear Planet gear

[0032] Locking device Locking device

Claims

Patent claims 1. Limited-slip differential gear (1), comprising three connection points (2, 3, 4) in the form of a transmission input (5) and two transmission outputs (6, 7) as well as a differential gear set (8), via which a drive torque introduced at the transmission input (5) can be divided between the transmission outputs (6, 7) and via which a speed compensation between the transmission outputs (6, 7) can be achieved, wherein a locking device (16) is provided which is placed in the power flow parallel to the differential gear set (8) between two of the connection points (2, 3, 4) and via which a locking torque can be automatically generated between the transmission outputs (6, 7), characterized in that the locking device (16) is designed to automatically generate the locking torque as a function of a differential angular acceleration effective between the transmission outputs (6, 7).

2. Limited-slip differential gear (1) according to claim 1, characterized in that the locking device (16) comprises a highly inertial device.

3. Limited-slip differential gear (1) according to claim 2, characterized in that a moment of inertia of the highly inertial device corresponds at least to 50% to a moment of inertia of a respective output to be connected to the individual transmission output (6, 7).

4. Limited-slip differential gear (1) according to one of claims 1 to 3, characterized in that the locking device (16) comprises a hydraulic device and / or a pneumatic device and / or an inductive device and / or an electromechanical device.

5. Limited-slip differential gear (1) according to one of the preceding claims, characterized in that the locking device (16) comprises a device via which energy absorbed by the locking device (16) during the generation of the locking torque can be re-released, stored, converted and / or internally dissipated.

6. Limited-slip differential gear (1) according to one of the preceding claims, characterized in that in addition to the locking device (16), at least one further locking device (17) is provided, which is also placed in the power flow parallel to the differential gear set (8) between two of the connection points (2, 3, 4) and is designed to permanently produce a constant locking torque between the transmission outputs (6, 7) or to automatically produce a locking torque between the transmission outputs (6, 7) as a function of a drive torque introduced at the transmission input (5) or as a function of a differential speed effective between the transmission outputs (6, 7).

7. Limited-slip differential gear (1) according to one of the preceding claims, characterized in that the locking device (16) comprises an element which is designed to limit forces and / or torques arising when the locking torque is generated via the locking device (16).

8. Limited-slip differential gear (1) according to one of the preceding claims, characterized in that the locking device (16) is arranged in the power flow between the transmission input and one of the transmission outputs or between the two transmission outputs (6, 7).

9. Limited-slip differential gear (1) according to one of the preceding claims, characterized in that the differential gear set (8) is in the form of a planetary gear set (9), a spur gear set or a bevel gear set.

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