Limited-slip differential with variable characteristics

Abstract

A differential used to distribute input torque is provided with: a housing to receive the input torque; a differential gear set mounted in the housing to distribute the input torque to a first and a second side gear; a clutch located between the housing and the first side gear to limit the compensating movement between the first and second side gears; an actuator to exert a pressure force on the clutch to control the compensating movement; and an electronic control unit configured to calculate a locking rate from a selected differential torque ratio, calculate a desired torque from a product resulting from multiplying the input torque by the locking rate, and control an electrical power supplied to the actuator based on the desired torque.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a limited-slip differential for a vehicle, and more particularly to a limited-slip differential that can change its characteristics depending on the situation. STATE OF THE ART

[0002] A differential is a commonly used device for transmitting torque to a pair of shafts, allowing for compensating movement between the shafts. If one of the shafts slips, the differential cannot even transmit the torque to the other shaft if it is unable to limit the compensating movement. Therefore, the differential is often equipped with a mechanism for limiting or temporarily stopping the compensating movement. A mechanism for limiting the compensating movement using friction is often called a limited-slip differential (LSD), and in particular, a mechanism that can dynamically change the limiting force depending on the input torque is called a torque-sensing limited-slip differential (LSD).When a mechanical device controls the limiting force, it can be called a mechanical limited-slip differential (LSD), and when an electronic control unit is used instead, it can be called an electronic limited-slip differential (LSD).

[0003] Patent Literatures 1 and 2 disclose related prior art. Citation listPatent literature PTL 1: International PCT Publication WO 2010 / 078937 A1 PTL 2: International PCT Publication WO 2020 / 129400 A1 SUMMARY OF THE INVENTION

[0004] With a well-designed electronic limited-slip differential (LSD), which can optimize the limitation of compensatory movement depending on the situation, a less-skilled driver could successfully control their vehicle even on difficult roads. For a skilled driver, however, inadvertent intervention of the electronic control would create an unnatural feeling, as if the vehicle were initiating unpredictable actions, and could thus hinder the desired driving behavior. Therefore, while skilled drivers may prefer the mechanical limited-slip differential because they can easily understand the vehicle's actions, the mechanical limited-slip differential is inflexible in its characteristics. If a different characteristic is desired, the limited-slip differential must be replaced.

[0005] The device disclosed herein was developed with these problems in mind. According to one aspect, a differential used for distributing input torque is provided with: a housing configured to receive input torque; a differential gear set supported in the housing and including first and second side gears, the differential gear set configured to differentially distribute the input torque to the first and second side gears; a clutch disposed between the housing and the first side gear for frictionally braking the first side gear relative to the housing to achieve the differential torque.to limit compensating movement between the first side gear and the second side gear; an actuator configured to exert a compressive force on the clutch to control the compensating movement; and an electronic control unit electrically connected to the actuator, wherein the electronic control unit is configured to calculate a lock-up rate from a selected differential torque ratio, calculate a desired or required torque from a product obtained by multiplying the input torque by the lock-up rate, and control an electric power to be supplied to the actuator based on the required torque. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of a vehicle having a differential according to the present embodiment. Fig. 2 is a perspective view of the differential. Fig. 3 is a sectional view of the differential in elevation. Fig. Figure 4 is a diagram schematically illustrating the arithmetic operations of an electronic control unit. Fig. Figure 5 is a diagram schematically illustrating an alternative method for arithmetic operations. Fig. 6 is a flowchart for arithmetic operations and control by the electronic control unit. DESCRIPTION OF THE EMBODIMENTS

[0006] Exemplary embodiments are described below with reference to the accompanying drawings.

[0007] Referring to Fig. 1, a conventional vehicle 1 comprises in particular a power source 3, for example an engine, and a transmission system with a gearbox 5 which transmits torque from the engine to the respective axles, and further a plurality of programmable electronic control units (ECUs) for electronically controlling these respective elements.

[0008] Torque is taken from the gearbox 5, introduced into the differential 7 and distributed to the two drive wheels. The illustration in Fig. 1 refers to a so-called FR (front engine, rear-wheel drive) vehicle, in which the power source is located at the front and driven by the rear wheels. The differential 7 is arranged between the propeller shaft and the rear axles and serves to distribute the torque to these axles. The limited-slip differential (LSD) according to the present embodiment is, of course, not limited to the FR vehicle, but can also be applied to any other vehicle, including FF (front engine, front-wheel drive), MR (mid-engine, rear-wheel drive), and all-wheel drive vehicles.Even in a case where the vehicle is equipped with a plurality of differentials, the limited-slip differential (LSD) according to the present embodiment is applicable not only to one but to two or more of these differentials, and is also used for transmission not only to the axle shafts but also to arbitrary shafts.

[0009] Each electronic control unit (ECU) is equipped with a memory unit that stores commands and data, as well as a microcontroller that can read them and execute the commands. The number of ECUs in a typical vehicle can be several dozen or more, but Fig. Figure 1 shows only 6 of these ECUs. These ECUs 11-17 read the states of the respective vehicle elements and are connected to each other via a bus 19 or bus line. The ECUs 11-17 communicate with each other or exchange information, for example, via a so-called controller area network (CAN). The information contains not only the read states but also requests or queries to other ECUs, and the respective ECUs use this information to control the corresponding elements of the vehicle.

[0010] For example, ECU 13 reads and controls the torque generated by power source 3, while ECU 15 reads and controls the states of the transmission. ECU 17 similarly controls differential 7 and also receives information about the torque generated by power source 3, for example, through CAN communication via bus 19, to use the information to perform its control. Of course, receiving and transmitting information is not limited to torque.

[0011] Referring to Fig. 2, any general electronically controlled limited-slip differential (LSD) can be used as the differential 7. Specifically, the differential 7, by way of example only, is provided with a housing 21 rotatable about an axis X, a differential gear set 23 housed in the housing 21, a friction clutch 25 for limiting the compensating movement of the differential gear set 23, and an actuator 27 for exerting a pressing force on the clutch 25. The ECU 17 primarily controls the actuator 27.

[0012] Although the following description refers to an example in which a bevel gear set is used for the differential 7, a spur gear set, a planetary gear set, or any other type is naturally applicable. Furthermore, while the description refers to an example in which a multi-disk clutch is used as the friction clutch, a cone clutch or any other clutch may be used instead. Furthermore, in the described example, the actuator uses a gear cam mechanism driven by an external motor, although a motor may also be provided internally to directly drive a rotary disk without gears. Or, a hydraulic system or the like may be used to generate thrust without a cam mechanism, or any other suitable type is usable.

[0013] Referring to Fig. 3 in conjunction with Fig. 2 shows that hub portions 21R, 21L project axially from both ends of the housing 21 and, supported by a carrier with intermediate bearings, such as ball bearings, are rotatable about the axis X. A flange 21F extends radially from an outer periphery of the housing 21 and serves for attachment, for example, to a ring gear. Since a longitudinal drive shaft has a gear at its end corresponding to the ring gear, the housing 21 absorbs the torque from the power source 3 through their mutual engagement.

[0014] The differential gear set 23 includes, for example, a differential pin 31 attached to the housing 21, pinion gears 33 rotatable thereabout, and side gears 35R, 35L, each meshing with the pinion gears 33. The side gears 35R, 35L are each provided with splines on their inner peripheries, which are each connected to output shafts. The output shafts are generally right and left axle shafts. As can be easily seen, the side gears 35R, 35L are capable of compensating movement relative to one another, and therefore the differential gear set 23 distributes the torque introduced by the housing 21 to the side gears 35R, 35L, enabling compensating movement between them and thereby transmitting the torque to both axle shafts.

[0015] The clutch 25 is, for example, a multi-disk clutch with a disk group 29 of alternately arranged inner and outer disks, which is arranged between the housing 21 and, for example, the right side gear 35R. The side gear 35R is, for example, provided with projections for engagement, and the inner disks are provided with corresponding grooves, whereby these elements engage with each other. An inner periphery of the housing 21 is also provided with projections with which the outer disks engage. When the actuator 27 exerts pressure on the disk group 29, the clutch 25 frictionally brakes the right side gear 35R relative to the housing 21 in order to limit the differential or compensating movement between the side gears 35R, 35L. It is understood that the clutch 25 can also be configured to brake the left side gear 35L instead of the right side gear 35R.

[0016] The actuator 27 is equipped, for example, with a rotary ring 41, a support ring 43, and a cam or cam mechanism 45 arranged therebetween to generate a thrust force. The rotary ring 41 is rotatable, for example, about the axis X and is provided with a toothing 41G on its outer circumference. Although in the Fig. 2 and Fig. 3, the actuator 27 is further provided with a motor for driving the actuator 27, which rotates the rotary ring 41 when its shaft is engaged with the gearing 41G. The support ring 43 is arranged adjacent to the rotary ring 41 and is provided with a rotation preventing structure 43A that engages the carrier to prevent rotation of the support ring. The cam mechanism 45 is provided, for example, with ramp slopes extending obliquely to the circumferential direction, which are formed on one or both of the plates or rings 41, 43, and with control balls that roll on these slopes. When the rotary ring 41 rotates relative to the support ring 43, the control balls roll up or down on the slopes, so that the cam mechanism 45 converts the rotational force into a thrust force.

[0017] The actuator 27 is arranged near the clutch 25 to exert the thrust force on the clutch 25 and is also arranged near a side wall of the housing 21. The actuator 27 can be provided with a plunger 49 to exert the compressive force, and the plunger 49 passes through the side wall of the housing 21 to have a structural connection with the clutch 25, although this may be less clear from the drawing. The actuator 27 thereby exerts the thrust force on the clutch 25 depending on the rotation angle specified by the motor.

[0018] It should be understood that the cam mechanism does not necessarily need to use control balls, but can instead utilize any structure capable of converting the rotational force into a thrust force. While in the illustrated example, the support ring 43 exerts the thrust force, the rotating ring 41 can also exert the thrust force.

[0019] Through the actuator 27 constructed as described above, the thrust force acts on the clutch 25 depending on the rotation angle of the rotating ring 41. Normally, as the rotation angle increases from its initial position, the thrust force increases, thus increasing the rate of torque transmitted to the side gears 35R, 35L via the clutch 25 (clutch torque), and decreasing the rate of torque transmitted through the gear set 23. Conversely, as the rotation angle of the rotating ring 41 decreases, the rate of torque transmitted through the clutch 25 decreases, and increasing the rate of torque transmitted through the gear set 23.

[0020] The electronic control unit (ECU) 17 calculates a required or desired torque in the manner described below and, based thereon, controls the actuator 27 for dynamic control of the clutch torque.

[0021] With particular reference to Fig. 4, the degree of limitation in a torque-sensitive limited-slip differential (LSD) is generally estimated by a torque bias ratio (TBR). The torque bias ratio is defined as the ratio between a torque value transmitted to a slower axle or shaft (normally, greater torque is transmitted there) and a torque value transmitted to a faster axle or shaft. A locking rate f LSD required to achieve a TBR target value is calculated by a formula (TBR-1) / (TBR+1). If a torque T diff is introduced into the differential 7, a clutch torque T LSD , which is below the blocking rate f LSD to be generated, for example by a formula T diff × f LSD Of course, any other formula for determining T LSDand a formula selected according to the actual structure of a mechanical limited-slip differential (LSD) to be simulated can be used.

[0022] In a mechanical limited-slip differential (LSD), a certain pressure can be applied in advance to a clutch, creating an initial torque T i can be generated. To simulate this pre-pressure, the sum of the clutch torque T LSD and an initial torque T i (a number identified by a reference symbol in Fig. 4 shown input) as desired or required torque T req Alternatively, the clutch torque T LSD and the initial torque T i , whichever is greater than the required torque T req be taken over.

[0023] For the required torque T reqAn upper limit value can be set to avoid excessive input power acting on the motor, the drive 27 and the clutch 25. For example, a maximum value T etm_Lim be determined in advance, then the calculated required torque value or the maximum value T etm_Lim , whichever is smaller, as the required torque T req which prevents excessive input power.

[0024] Since the input torque T diff can be calculated or estimated from the torque generated by the power source 3, the ECU 17 can retrieve this value at any time via CAN communication. Since TBR and T i can be stored in advance in the memory unit of the ECU 17, the ECU 17 can at any time T reqThe ECU 17 is electrically connected to the motor and applies a controlled electrical power to it based on the calculated required torque value T req to control the rotation angle of the rotating ring 41 at any time, thereby dynamically controlling the clutch torque. The relationship between the electric power applied to the motor, the rotation angle of the rotating ring, and the clutch torque can be stored in advance in the form of a data table in the storage unit, and thereby the ECU 17 controls the differential 7. The resulting clutch torque sufficiently corresponds to that of a mechanical limited-slip differential (LSD) with the given torque balance ratio TBR.

[0025] The torque balance ratio (TBR) can change depending on whether the vehicle is accelerating or decelerating. Whether the vehicle is accelerating or decelerating can be determined by the signed value T diffIn particular, referring to the lower left part of the Fig. 4, the forward direction TBR Drive be assumed to be TBR if the signed value T diff has a positive value, and the reverse direction TBR Coast as TBR if the signed value T diff has a negative value. Independent optimal values ​​can be used as forward direction TBR Drive and as reverse direction TBR Coast According to an example of such a set, the forward direction TBR Drive = 2.7 and the reverse direction TBR Coast = 2.3, without being limited to it.

[0026] While TBR and T ican be stored in advance as constant values ​​in the storage unit, it should be noted here that multiple sets of values ​​can be stored, and each set can be selected depending on the situation. Furthermore, these values ​​do not have to be discrete values, but can also be continuously varied. While the properties or characteristics of a mechanical LSD, as already described, are fixed at the time of installation in a vehicle, the present embodiment allows TBR and / or T i can be adjusted as needed each time the vehicle is driven, or even while driving, thereby altering the properties or characteristics of the differential. The changes can be made manually by the driver via the console or automatically controlled by another ECU. The driver can select any characteristic as desired to enjoy the driving experience.

[0027] It should be further noted that the present embodiment performs the control of the differential 7 using only the value T diff which is constantly available via CAN communication. All additional sensors are unnecessary to control the differential 7, and various information such as the vehicle speed and the respective rotational speeds of the axles or shafts are also unnecessary. Specifically, any conventional differential is compatible and interchangeable with the differential 7 according to the present embodiment without any special additional configuration.

[0028] It should be understood that the present embodiment is open to any additional configuration. For example, the ECU 17 may receive the input torque data not via CAN communication, but, for example, from a sensor itself, or calculate and then use the input torque from other information.

[0029] In addition, information other than the input torque can also be used to calculate or correct the requested torque value. Correction by deviation feedback control is possible, in which the control is based on a deviation calculated from a yaw rate command value and an actual yaw rate value, or similar. Furthermore, the control can be configured from feedforward control based on the output predetermined by the input torque and a correction output predetermined by a current vehicle status such as vehicle speed and / or acceleration, so as not to impair the predictability of vehicle behavior by a driver, and in this case, delays in response caused by operations or sudden interventions of the correction control can be suppressed.

[0030] With reference to Fig. 5, for example, the vehicle speed and / or acceleration (deceleration) can be used to determine the required torque value T req For example, the initial torque T i be increased with increasing vehicle speed. Or an alternative control is possible in which the initial torque T i is kept constant until the vehicle speed reaches a reference value, and T iafter exceeding the reference value or is kept constant again when the speed reaches another reference value. Alternatively, instead of changing the value at a reference value, the value can also be controlled within the framework of a suitable control curve. A data table required for such control can be stored in advance in the memory unit of the ECU 17. Similarly, depending on the acceleration (deceleration), an additional torque T GX to the initial torque T i be added. T GX can also be changed in accordance with a suitable reference value or control curve. A value T sup as the sum of T i and T G x can be used instead of the initial torque in the formula of Fig. 4 (as reference symbol “a” in Fig. 4 and Fig. 5).

[0031] In addition, the required torque value T req be corrected when tire slippage or skidding is detected. For example, if a speed difference between the right and left axles or shafts is detected, the locking rate can be increased depending on the speed difference. A correction value thus obtained can be added as reference symbol "a" to the Fig. 4 shown calculation.

[0032] Furthermore, the required torque value T req be corrected depending on the accelerator pedal position. For example, a control is possible in which the lock rate is increased to increase traction when the accelerator pedal position is pressed downwards. Correction values, e.g., depending on the output of the accelerator pedal position sensor, can be stored as a data table in the memory unit of the ECU 17 and used to change the forward direction TBR. Driveaccording to the data table.

[0033] These corrections are beneficial, for example, to prevent braking in tight corners (tight corner braking phenomenon).

[0034] Of course, other information such as rotational speeds of the respective axles or shafts, a steering angle, a yaw rate, a lateral acceleration rate, a side slip angle and a side slip speed can also be used supplementarily, in addition to or alternatively to calculate or correct the required torque value.

[0035] The calculated value of the required torque T req can be further passed through a suitable filter. For example, the use of a low-pass filter can effectively prevent a sudden change in vehicle behavior when the clutch torque increases and decreases.

[0036] Since the aforementioned calculations are formalistic or standardized, any independent calculation circuit or circuit can be used instead of the calculation by the ECU 17. In particular, an external calculation circuit controlled by the ECU 17 can perform the above-mentioned calculations.

[0037] A process of control by the ECU 17 will be described below with reference to Fig.6. First, the ECU 17 uses CAN communication to retrieve or calculate the input torque (S1). Next, the ECU 17 determines the TBR by selecting it from the pre-stored data table or in accordance with a preset condition (S2). From this, the ECU 17 calculates the lock-up rate (S3) and multiplies the result by the input torque to obtain the clutch torque (S4). If necessary, the initial torque is determined according to the predetermined condition (S5), and the sum of its result and the clutch torque is calculated to obtain the required clutch torque (S6). Here, as already described, instead of calculating the sum, the calculated clutch torque or the initial torque, whichever is the maximum, can be adopted as the required clutch torque. Furthermore, the ECU 17 corrects the TBR if necessary.the required clutch torque (S7). Furthermore, if necessary, the ECU 17 passes the calculated target clutch torque through a filter (S8). The ECU 17 delivers electrical power to the motor according to the determined required clutch torque, thus controlling the rotation angle of the rotating ring 41, thereby dynamically controlling the clutch torque. This process would be repeated continuously.

[0038] As can be seen from the above descriptions, the present embodiment can advantageously approximate the behavior of a differential to that of a conventional mechanical limited-slip differential (LSD), providing a smooth driving experience for a skilled driver. Furthermore, due to the electronic control nature that does not require differential replacement, the embodiment offers the advantage of being able to arbitrarily change various parameters without having to replace differentials and the ability to add various functions.

[0039] Although certain exemplary embodiments are described above, modifications and variations of the embodiments will be apparent to those skilled in the art in light of the above teachings. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] WO 2010 / 078937 A1

[0003] WO 2020 / 129400 A1

[0003]

Claims

[1] Differential for distributing an input torque, comprising: a housing configured to receive the input torque; a differential gear set supported in the housing and including first and second side gears, the differential gear set configured to differentially distribute the input torque to the first and second side gears; a clutch disposed between the housing and the first side gear for frictionally braking the first side gear relative to the housing to limit differential movement between the first side gear and the second side gear; an actuator configured to exert a compressive force on the clutch to control the differential movement; and an electronic control unit electrically connected to the actuator, the electronic control unit configured to calculate a lock-up rate from a selected differential torque ratio, calculate a required torque from a product obtained by multiplying the input torque by the lock-up rate, and control an electric power to be supplied to the actuator based on the required torque. [2] The differential according to claim 1, wherein the electronic control unit is configured to calculate a sum of the product and an initial torque, and adopt the sum as the required torque. [3] The differential according to claim 1, wherein the electronic control unit is configured only for feedforward control by an output determined in advance by the input torque and a corrected output determined in advance by a vehicle condition. [4] A differential according to claim 2, wherein the electronic control unit is configured to compare the sum and a limit torque value and to assume a smaller value of the sum or the limit torque value than the required torque. [5] The differential of claim 1, wherein the electronic control unit comprises a storage unit that stores two or more differential torque ratios and is configured to select one of the stored differential torque ratios in response to a sign of the input torque. [6] The differential of claim 1, wherein the electronic control unit is connected to other electronic control units via a network and is configured to retrieve the input torque via the network. [7] A differential according to claim 1, wherein the actuator comprises a rotary ring driven for rotation by a motor, a support ring secured against rotation, and a cam mechanism for causing one of the support ring and the rotary ring to generate a thrust force in response to rotation of the rotary ring relative to the support ring, and is arranged to apply the thrust force to the clutch.

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