Variable characteristic limited slip differential

Abstract

A differential used to distribute input torque comprises: a casing that receives input torque; a differential gear set that is housed in and supported by the casing, that comprises first and second side gears, and that differentially distributes the input torque to the first and second side gears; a clutch that is interposed between the casing and the first side gear, that frictionally brakes the first side gear against the casing, and that thereby limits a differential between the first side gear and the second side gear; an actuator that exerts a pressing force on the clutch to control the differential; and an electronic control device electrically connected to the actuator, the electronic control device being configured to calculate a lock rate from a selected differential torque ratio, calculate a required torque from a product obtained by multiplying the input torque by the lock rate, and control electric power supplied to the actuator in accordance with the required torque.

Description

[Technical Field]

[0001] The following disclosure relates to a limited slip differential for a vehicle, and more particularly to a limited slip differential that can change characteristics depending on the situation. [Background technology]

[0002] A differential is used to output torque while allowing differential motion between a pair of shafts. Without a differential limit, when one shaft spins freely, the other shaft cannot output torque. Therefore, differentials often have a mechanism to limit or temporarily stop differential motion. A mechanism that limits differential motion, for example, by friction, is often called a limited slip differential (LSD), and a mechanism in which the differential limiting force changes dynamically depending on the input torque is called a torque-sensitive LSD. A mechanism in which the limiting force is controlled by a mechanical mechanism is called a mechanical LSD, and a mechanism that uses an electronic control device is called an electronically controlled LSD.

[0003] Patent Documents 1 and 2 disclose related techniques. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Patent Application Publication WO2010 / 078937A1 [Patent Document 2] International Patent Application Publication WO2020 / 129400A1 Summary of the Invention

[0005] A well-designed electronically controlled LSD optimally limits differential movement depending on the conditions, allowing the driver to drive the vehicle on difficult road surfaces without great skill. However, for experienced drivers, the intervention of electronic control that is not intended by the driver can cause the vehicle to behave in an unexpected way, making it difficult to achieve the desired driving experience. Therefore, experienced drivers prefer mechanical LSDs, which allow for an intuitive understanding of the vehicle's behavior. However, mechanical LSDs have fixed characteristics. If different characteristics are required for different road surfaces, the entire LSD must be replaced.

[0006] The device disclosed below has been created in view of the above problem. According to one aspect thereof, a differential used to distribute input torque comprises: a casing that receives the input torque; a differential gear set housed and supported in the casing, including first and second side gears, and differentially distributing the input torque to the first and second side gears; a clutch interposed between the casing and the first side gear and frictionally braking the first side gear against the casing, thereby limiting the differential between the first side gear and the second side gear; an actuator that exerts a pressing force on the clutch to control the differential; and an electronic control device electrically connected to the actuator, the electronic control device configured to calculate a locking ratio from a selected differential torque ratio, calculate a required torque from a product obtained by multiplying the input torque by the locking ratio, and control power input to the actuator in accordance with the required torque. The electronic control device includes a storage device that stores two or more differential torque ratios, and the electronic control device is configured to select one of the stored differential torque ratios according to the sign of the input torque. . [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a block diagram of a vehicle including a differential according to this embodiment. [Figure 2] FIG. 2 is a perspective view of the differential. [Figure 3] FIG. 3 is a cross-sectional elevation view of the differential. [Figure 4]FIG. 4 is a diagram that schematically shows the calculations performed by the electronic control unit. [Figure 5] FIG. 5 is a diagram that schematically illustrates an alternative method for calculating the initial torque. [Figure 6] FIG. 6 is a flowchart of the calculations and controls executed in the electronic control unit. DETAILED DESCRIPTION OF THE INVENTION

[0008] Some exemplary embodiments are described below with reference to the accompanying drawings.

[0009] Referring to FIG. 1, a typical vehicle 1 comprises a power source 3, such as an engine, and a gear system including a transmission 5 that transmits torque from the engine to each axle, as well as a plurality of programmable electronic control units (ECUs) to electronically control each of these components.

[0010] Torque is extracted from the transmission 5 and input to the differential 7, where it is distributed to both drive wheels. The example shown in FIG. 1 relates to a so-called FR vehicle, in which the power source is located in the front and the rear wheels are driven, and the differential 7 of this embodiment is interposed between the propeller shaft and the rear axle and is used to distribute torque. The LSD of this embodiment is of course not limited to FR vehicles, but can also be used in FF vehicles, MR vehicles, all-wheel drive vehicles, etc. Furthermore, if a vehicle has multiple differentials, the LSD of this embodiment can be used in multiple differentials, not just one of them, and can be used for output to any shaft, not just an axle.

[0011] Each ECU has a storage device that stores commands and data, and a microcontroller that can read these commands from the storage device and execute them. A typical vehicle has dozens of ECUs, but Figure 1 shows only six of them. These ECUs 11 to 17 read the status of each part of the vehicle using various sensors and are connected to each other via a bus 19. The ECUs 11 to 17 communicate and share information, for example, via a so-called controlled area network (CAN). This information includes not only the read status but also requests to other ECUs, and each ECU uses this information to control each part of the vehicle.

[0012] For example, ECU 13 reads and controls the torque generated by power source 3, and ECU 15 reads and controls the state of the transmission. Similarly, ECU 17 controls differential 7, and can receive information about the torque generated by power source 3 via CAN communication via bus 19 and use it for control. Of course, the information sent and received is not limited to torque.

[0013] 2, a general electronically controlled limited slip differential (LSD) can be used as the differential 7. That is, the differential 7, by way of example only, includes a casing 21 that is rotatable about an axis X, a differential gear set 23 housed in the casing 21, a friction clutch 25 that limits the differential movement of the differential gear set 23, and an actuator 27 that exerts a controlled pressing force on the clutch 25. The actuator 27 is solely controlled by the ECU 17.

[0014] In the following, an example in which a bevel gear type differential gear set is applied to the differential 7 will be described, but of course face gear types, planetary gear types, or other types may be used instead. Also, an example in which a multi-plate clutch type is used as the friction clutch will be described, but cone clutches or other types may be used instead. Furthermore, an example in which a gear and cam type with an external motor is used as the actuator will be described, but the motor may be built-in and directly drive the rotary plate without using gears, or a type that generates thrust force using hydraulics or the like without using a cam, or other appropriate types may be used.

[0015] 3 in combination with FIG. 2, bosses 21R and 21L protrude in the axial direction from both ends of casing 21, and are supported by carriers via bearings such as ball bearings, allowing casing 21 to rotate around axis X. A flange 21F protrudes radially from the outer periphery of casing 21, to which, for example, a ring gear is fixed. The end of the propeller shaft is provided with a gear that corresponds to the ring gear, and by meshing with each other, casing 21 receives torque from power source 3.

[0016] The differential gear set 23 includes, for example, a pinion shaft 31 fixed to the casing 21, a pinion 33 rotatable around the pinion shaft 31, and side gears 35R and 35L meshing with the pinion 33. The side gears 35R and 35L each have, for example, splines on their inner peripheries, and are connected to output shafts. The output shafts are typically the right and left axles. As will be easily understood, the side gears 35R and 35L are capable of differential rotation relative to each other, and therefore the differential gear set 23 distributes torque received by the casing 21 to the side gears 35R and 35L while allowing differential rotation, and outputs the torque to both axles, respectively.

[0017] The clutch 25 is, for example, a multi-plate clutch and includes a group 29 of alternating inner and outer plates interposed between the casing 21 and, for example, the right side gear 35R. For example, the right side gear 35R has lugs for engaging with the inner plates, and the inner plates have corresponding grooves for engaging with each other. Similarly, the inner surface of the casing 21 also has lugs, and the outer plates engage with the casing 21. When the actuator 27 applies a pressing force to the group 29 of plates, the clutch 25 frictionally brakes the right side gear 35R against the casing 21, thereby limiting differential rotation between the side gears 35R and 35L. Needless to say, the clutch 25 may brake the left side gear 35L instead of the right side gear 35R.

[0018] The actuator 27 includes, for example, a rotary plate 41, a support plate 43, and a cam mechanism 45 disposed between them to generate a thrust force. The rotary plate 41 is rotatable, for example, around axis X and has gear teeth 41G on its outer periphery. Although not shown in FIGS. 2 and 3 , the actuator 27 also includes a driving motor, whose shaft engages with the gear teeth 41G to rotate the rotary plate 41. The support plate 43 is adjacent to the rotary plate 41 and includes a rotation-preventing structure 43A, which is prevented from rotating by engaging with a carrier. The cam mechanism 45 includes, for example, circumferentially inclined cam ramps formed on one or both of the plates 41 and 43, and a cam ball that rolls on the ramps. When the rotary plate 41 rotates relative to the support plate 43, the cam ball rolls and moves up or down the ramp, thereby converting the rotational force into a thrust force.

[0019] The actuator 27 is disposed close to the clutch 25 and close to the end wall of the casing 21 so as to apply this thrust force to the clutch 25. The actuator 27 may also be provided with a plunger 49 for outputting the thrust force, and although it is difficult to see from the drawing, the plunger 49 communicates with the clutch 25 through the end wall of the casing 21. Thus, the actuator 27 applies a thrust force to the clutch 25 that corresponds to the rotation angle given to the motor.

[0020] Needless to say, the cam mechanism does not have to use a cam ball, and any structure that converts rotational force into thrust force can be used. Also, in the illustrated example, the support plate 43 generates thrust force, but instead, the rotary plate 41 may generate thrust force.

[0021] In the actuator 27 configured as described above, a thrust force acts on the clutch 25 in accordance with the rotation angle of the rotary plate 41. Normally, the thrust force increases as the rotation angle increases from the initial position, and therefore the proportion of torque (clutch torque) transmitted to the side gears 35R, 35L via the clutch 25 increases, while the proportion via the gear set 23 decreases. Conversely, if the rotation angle of the rotary plate 41 decreases, the proportion via the clutch 25 decreases, and the proportion via the gear set 23 increases.

[0022] The ECU 17 calculates the required clutch torque as follows, and controls the actuator 27 based on this to dynamically control the clutch torque.

[0023] Referring mainly to Figure 4, the degree of differential restriction in a torque-sensitive LSD is usually evaluated by the differential torque ratio (or torque bias ratio; TBR). The differential torque ratio is defined as the ratio of the torque transmitted to the slower axle (usually the larger torque) to the torque transmitted to the faster axle. The clutch lock ratio f required to achieve the target TBR is LSD is calculated by the formula (TBR-1) / (TBR+1). diffWhen input is given, the lock rate f LSD The clutch torque T that should be generated under LSD For example, the formula T diff ×f LSD Of course, instead of this formula, T can be calculated from other formulas. LSD It is possible to apply an appropriate formula to suit the actual structure of the mechanical LSD to be simulated.

[0024] In mechanical LSDs, the clutch is sometimes preloaded, which causes the initial torque T i To simulate preload, the clutch torque T LSD Initial torque T i (input represented by symbol a in Fig. 4) is added to the required torque value T req Alternatively, the clutch torque T LSD and initial torque T i The required torque value T is the larger of either req It can also be adopted as.

[0025] An upper limit of the required torque value can be set so that an excessive input is not applied to the motor, the actuator 27, or the clutch 25. For example, the maximum value T etm_Lim is determined in advance, and the calculated required torque value and the maximum value T etm_Lim The smaller of the two is the required torque value T req If this is adopted, excessive input can be prevented.

[0026] Input torque T diff Since TBR and T can be calculated or estimated from the torque generated by the power source 3, the ECU 17 can acquire them at any time via CAN communication. i can be stored in advance in the storage device of the ECU 17, so the ECU 17 can req The ECU 17 is electrically connected to the motor of the actuator 27 and can calculate the calculated required torque value T reqThe rotation angle of the rotary plate 41 is controlled as needed by applying power based on the torque, thereby dynamically controlling the clutch torque. The relationship between the power applied to the motor, the rotation angle of the rotary plate 41, and the clutch torque can be stored in advance in the form of a formula or a data table in a storage device, and the ECU 17 uses this to control the differential 7. The clutch torque achieved adequately simulates that achieved by a mechanical LSD with a given differential torque ratio TBR.

[0027] The TBR can also be changed when the vehicle accelerates or decelerates. Whether the vehicle is accelerating or decelerating is indicated by the signed T diff That is, referring to the bottom left of Figure 4, the signed T diff When is a positive value, the forward TBR Drive is used as the TBR, and when it is negative, it is used as the reverse TBR. Coast can be adopted as the TBR. Forward TBR Drive and reverse TBR Coast For example, the forward TBR can be set to a different optimal value. Drive = 2.7 and reverse TBR Coast =2.3, but of course it is not limited to these.

[0028] It is important to note here that TBR and T i can be stored in advance as a fixed value in a storage device, or multiple sets of values ​​can be stored and selected from multiple sets as needed. Furthermore, these do not have to be a combination of discrete (discrete) values, but can be changed continuously. As already mentioned, the characteristics of a mechanical LSD are fixed when it is installed in a vehicle, but according to this embodiment, TBR and / or T can be changed appropriately each time the vehicle is driven or even while the vehicle is being driven. iThe differential characteristics can be changed by changing the differential setting. The change can be made manually by the driver via the console, or automatically controlled by another ECU. The driver can select the differential characteristics as desired and enjoy driving the vehicle.

[0029] It should also be noted that, according to this embodiment, T diff The differential 7 can be controlled simply by utilizing the value of . Controlling the differential 7 does not require various additional sensors, nor does it require various types of information such as vehicle speed and the rotational speed of each axle. In other words, the differential 7 according to this embodiment can be used interchangeably with a conventional differential without any special additional configuration.

[0030] Needless to say, this embodiment can utilize additional configurations. For example, the ECU 17 may acquire the input torque by, for example, providing an independent sensor without using CAN communication, or may calculate the input torque from other information and utilize this.

[0031] Furthermore, the required torque value can be calculated or corrected using additional information other than the input torque. Correction can also be performed using so-called deviation feedback control, such as control based on the deviation calculated from the target yaw rate value and the actual yaw rate value. Furthermore, to avoid impairing the driver's predictability of vehicle behavior, the system may be configured using only feedforward control, with an output predetermined by the input torque and a correction output predetermined based on the current vehicle state, such as vehicle speed and / or acceleration. In this case, response delays due to calculations and sudden intervention of correction control can be suppressed.

[0032] Referring to FIG. 5, the required torque value T req For example, the initial torque T iAlternatively, T may be increased until the vehicle speed reaches the reference value. i is set as a constant value, and when it exceeds the reference value, the initial torque T i Alternatively, the torque T may be increased, or may be set to another constant value after reaching another reference value. Alternatively, the torque T may be controlled according to an appropriate control curve, rather than changing based on the reference value. The data table required for the control may be stored in advance in the storage device of the ECU 17. Similarly, the additional torque T may be controlled according to the acceleration (deceleration) rate. GX The initial torque T i May be added to T GX The T may also be varied according to an appropriate reference value or an appropriate control curve. i and T GX Tonowa T-shirt sup can be added to the equation in Figure 4 instead of the initial torque (symbol a in Figures 4 and 5).

[0033] Furthermore, tire slippage is detected and the required torque value T req For example, the rotational difference between the left and right axles can be detected, and correction can be made to increase the locking ratio according to the rotational difference. Such a correction value can be added to the calculation as the value added to the symbol a in Figure 4, for example.

[0034] Furthermore, the required torque value T req For example, when the accelerator opening degree increases, the locking rate also increases, so that traction can be ensured. For example, correction values ​​according to the output of the accelerator position sensor may be stored in advance in the storage device of the ECU 17 as a data table, and the forward TBR may be adjusted according to the data table. Drive can be changed.

[0035] These corrections help to prevent tight corner braking phenomena, for example.

[0036] Of course, other information, such as the rotational speed of each axle, steering angle, yaw rate, lateral acceleration, sideslip angle and sideslip angular velocity, may be used as an auxiliary, additional or alternative means to calculate or correct the required torque value.

[0037] The calculated required torque value T req For example, by using a low-pass filter, it is possible to prevent a sudden change in vehicle behavior when the clutch torque rises and falls.

[0038] Since the above-described calculations are routine, they can be performed by an independent calculation circuit without relying on the ECU 17. That is, under the control of the ECU 17, an external calculation circuit may execute the above-described calculations.

[0039] The control procedure by the ECU 17 will be described with reference to FIG. 6. First, the ECU 17 acquires or calculates the input torque using CAN communication or the like (S1). Next, the ECU 17 determines the TBR by selecting it from a pre-stored data table or according to preset conditions (S2). The ECU 17 uses these to calculate the locking ratio (S3), and multiplies it by the input torque to calculate the clutch torque (S4). If necessary, the ECU 17 determines the initial torque according to preset conditions (S5), and calculates the required clutch torque by calculating the sum of the initial torque and the clutch torque (S6). At this time, as already mentioned, instead of calculating the sum, the maximum value of the calculated clutch torque and the initial torque may be used as the required clutch torque. Furthermore, if necessary, the ECU 17 corrects the required clutch torque (S7). Furthermore, if necessary, the ECU 17 filters the calculated required clutch torque (S8). In response to the obtained required clutch torque, the ECU 17 applies electric power to the motor to control the rotation angle of the rotary plate 41, thereby dynamically controlling the clutch torque. These procedures are constantly repeated.

[0040] As can be understood from the above explanation, this embodiment can approximate the behavior of the differential to that of a conventional mechanical LSD, providing a driving experience that is natural to experienced drivers. In addition, because it is electronically controlled, it offers the advantage of being able to freely change various parameters or add various functions without replacing the differential.

[0041] Although several embodiments have been described, modifications or variations of the embodiments can be made based on the above disclosure.

Claims

1. A differential utilized to distribute input torque, comprising: a casing that receives the input torque; a differential gear set housed and supported in the casing, including first and second side gears, for differentially distributing the input torque to the first and second side gears; a clutch interposed between the casing and the first side gear to frictionally brake the first side gear against the casing, thereby limiting differential movement between the first side gear and the second side gear; an actuator that exerts a pressing force on the clutch to control the differential; an electronic control device electrically connected to the actuator, the electronic control device being configured to calculate a locking ratio from a selected differential torque ratio, calculate a required torque from a product obtained by multiplying the input torque by the locking ratio, and control power input to the actuator in accordance with the required torque; A differential comprising: The electronic control unit includes a memory device that stores two or more differential torque ratios, and the electronic control unit is configured to select from the stored differential torque ratios depending on the sign of the input torque.

2. 2. The differential of claim 1, wherein the electronic control unit is configured to calculate the sum of the product and an initial torque and use the sum as the required torque.

3. 2. The differential of claim 1, wherein said electronic control device is configured solely for feedforward control using an output predetermined by an input torque and a correction output predetermined according to a vehicle state.

4. 3. The differential of claim 2, wherein the electronic control device is configured to compare the sum with a limit torque value and adopt the smaller value as the required torque.

5. 2. The differential of claim 1, wherein the electronic control unit is connected to other electronic control units via a network and configured to obtain the input torque through the network.

6. 2. The differential of claim 1, wherein the actuator comprises a rotary plate driven to rotate by a motor, a support plate that is prevented from rotating, and a cam mechanism that generates a thrust force on the support plate or the rotary plate in response to rotation of the rotary plate relative to the support plate, and is arranged to apply the thrust force to the clutch.

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