Electronically-controlled limited slip differential

Abstract

To achieve optimal LSD control.SOLUTION: A differential comprises: a casing; a differential gear set that is housed and supported in the casing, has first and second side gears connected to an output shaft and differentially distributes torque to them; a clutch that is interposed between the casing and the first side gear and frictionally brakes the first side gear relative to the casing to limit a differential motion between the first side gear and the second side gear; an actuator that applies pressing force to the clutch to control the differential motion; and an electronic control unit electrically connected to the actuator, the electronic control unit being configured to calculate a demand torque value from the input torque, compare a wheel load with a threshold value to determine a correction value, correct the demand torque value with the correction value to calculate a demand value, and control an electric power to be supplied to the actuator according to the demand value.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The following disclosure relates to an electronically controlled limited slip differential for a vehicle, and more particularly to an electronically controlled limited slip differential capable of changing characteristics depending on the magnitude of the wheel load. [Background technology]

[0002] In vehicles, a device called a limited slip differential (LSD) is often used to absorb the differential between the left and right drive wheels, while still allowing torque to be output to the other drive wheel even if one of the drive wheels spins. A device that controls the limit of the differential using a mechanical mechanism is called a mechanical LSD, while a device that uses an electronic control device is called an electronically controlled LSD.

[0003] In electronically controlled LSDs, the differential limiting force may be optimized by using several additional parameters. For example, Patent Document 1 discloses a technique for controlling the differential limiting force by using the torque bias ratio and the lateral acceleration that the vehicle receives. Patent Document 2 discloses a technique for calculating the differential limiting force (initial torque) to be applied in advance and using this. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2006-183784 A [Patent Document 2] JP 2003-329105 A Summary of the Invention [Problem to be solved by the invention]

[0005] In order to put the above-mentioned technology into practical use, it is necessary to assume certain vehicle conditions. In other words, it is natural to reflect predetermined parameters such as the vehicle weight and wheelbase in the control, but in order to optimize the control, it is necessary to assume certain parameters that vary during actual use, such as the average weight and number of passengers and the weight of luggage loaded on the loading platform. If the actual vehicle is close to the assumed conditions, the behavior of the LSD will be close to desirable, but there are cases where luggage heavier than expected is loaded on the loading platform, or when going uphill or downhill, the distribution of the load to the front and rear wheels varies significantly. There are also cases where securing traction force is important, such as when towing another vehicle. The more the vehicle deviates from the conditions assumed at the time of design, the more undesirable behavior is inevitable. [Means for solving the problem]

[0006] The following disclosure has been devised in consideration of the above problems. According to one aspect, a differential used to distribute an input torque to a pair of output shafts in accordance with at least the input torque and a wheel load includes a casing that receives the input torque, a differential gear set that is housed and supported in the casing and has first and second side gears that are respectively connected to the output shafts, 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 and frictionally brakes the first side gear against the casing, thereby limiting the differential between the first side gear and the second side gear, an actuator that applies a pressing force to the clutch to control the differential, and an electronic control device electrically connected to the actuator and including a memory device that stores one or more threshold values, the electronic control device being configured to calculate a required torque value from the input torque, compare the wheel load with the threshold value to determine a correction value, correct the required torque value using the correction value to calculate a required value, and control power to be input to the actuator in accordance with the required value.

[0007] Preferably, the storage device is configured to calculate the required value by adding the correction value to the required torque value when the wheel load is greater than the threshold value. Also preferably, the correction value includes a vehicle speed correction value, and the electronic control device is configured to calculate the required value by multiplying the vehicle speed correction value by a coefficient of 1 or more when the wheel load is greater than the threshold value. More preferably, the storage device stores a vehicle speed data table, and the electronic control device is configured to calculate the vehicle speed correction value by checking the vehicle speed against the vehicle speed data table. Alternatively, preferably, the storage device stores two or more vehicle speed data tables, and the electronic control device is configured to select one vehicle speed data table from the storage device in response to a comparison between the wheel load and the threshold value, calculate a vehicle speed correction value from the vehicle speed and the selected vehicle speed data table, and calculate the required value by adding the vehicle speed correction value to the required torque value. Even more preferably, the electronic control device is connected to other electronic control devices via a network, and is configured to calculate the vehicle speed, the input torque, and the wheel load from data acquired via the network. Effect of the Invention

[0008] An electronically controlled limited slip differential is provided that achieves optimal differential limiting regardless of the vehicle condition. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram of a vehicle including a differential according to this embodiment. [Diagram 2] FIG. 2 is a block diagram of a vehicle in which both the front and rear wheels are equipped with power sources. [Figure 3A] FIG. 3A is a schematic diagram showing a vehicle and a wheel load. [Figure 3B] FIG. 3B is a schematic diagram including a towed vehicle. [Figure 4] FIG. 4 is a cross-sectional elevation view of the differential. [Diagram 5] FIG. 5 is a diagram showing a schematic diagram of the calculations performed by the electronic control device. [Figure 6] FIG. 6 is a diagram showing a schematic example of a calculation performed by changing settings according to a load. [Figure 7] FIG. 7 is a diagram showing a schematic example of multiplying a coefficient by a load. [Figure 8] FIG. 8 is a diagram showing a schematic diagram of another example in which the settings are changed depending on the load to perform calculations. [Figure 9A] FIG. 9A is a graph that diagrammatically illustrates an example in which different correction values ​​are adopted depending on the load. [Figure 9B] FIG. 9B is a graph that illustrates another example in which different correction values ​​are adopted depending on the load. [Figure 10] FIG. 10 is a flowchart of the calculations and controls executed in the electronic control unit. [Figure 11] FIG. 11 is a flowchart for improving NVH. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Several exemplary embodiments are described below with reference to the accompanying drawings.

[0011] Referring to FIG. 3A, the engine or motor, which accounts for a large part of the vehicle weight, is often mounted at the front of the vehicle 1. Therefore, the front wheel load Wf is usually somewhat larger than the rear wheel load Wr (solid arrow). In the prior art, the behavior of the differential is optimized on the premise of such a load balance. However, the vehicle 1 is not always empty, and there are cases where a heavy object is loaded in the luggage compartment, and the weight Wb is added, and the rear wheel load Wr becomes large to a degree that cannot be ignored (broken arrow). This difference is particularly noticeable in vehicle types such as pickup trucks. Alternatively, the vehicle 1 may tow another vehicle 9, such as a camper, as in the example of FIG. 3B. In that case, the rear wheel load Wr may further increase. The following disclosure relates to an apparatus or system that realizes an optimal differential limiting force in any of various vehicle conditions.

[0012] Referring to FIG. 1, a typical vehicle 1 comprises a power source 3 consisting of an engine and / or motor, a gear system including a transmission 5 that transmits torque from the power source 3 to each axle, and multiple programmable electronic control units (ECUs) to electronically control each of these parts.

[0013] Torque is taken from the power source 3 through the transmission 5, input to the differential 7, and distributed to both drive wheels. In the example of FIG. 1, the power source 3 is placed at the front of the vehicle 1, and the rear wheels are the drive wheels, but of course the power source 3 may be placed at the rear of the vehicle 1, and in either case the front wheels may be the drive wheels. When the front wheels are the drive wheels, it goes without saying that a differential 7' is interposed between the front wheels. This embodiment can also be applied to a so-called four-wheel (or all-wheel) drive vehicle in which both the front and rear wheels are drive wheels. Alternatively, to realize a four-wheel (or all-wheel) drive vehicle, as shown in FIG. 2, a power source 3', a transmission 5', and a differential 7' may be placed not only on the front wheels but also on the rear wheels, and each may drive the front wheels and the rear wheels independently. This embodiment can be applied to any of these forms.

[0014] Each ECU has a storage device that stores commands and data, and a microcontroller that can read these from the storage device and execute the commands. A typical vehicle has several dozen ECUs, but only six of them are shown in Figures 1 and 2. These ECUs 11 to 17 are connected to each other by a bus 19, and can communicate and share information, for example, by communication via a so-called controlled area network (CAN).

[0015] Each ECU controls each part of the vehicle while sharing information with the other ECUs. For example, ECU 11 is connected to various acceleration sensors and can read longitudinal acceleration, lateral acceleration, yaw acceleration, etc., applied to the vehicle. ECU 13 reads and controls the torque generated by the power source 3. ECU 15 is connected to sensors that read, for example, load and angular velocity, and can read the load on each axle and the angular velocity of each axle. ECU 17 controls the differentials 7, 7'. The read information is received by CAN communication via a bus 19 and can be used for control by other ECUs, and one ECU can also send a request to another ECU.

[0016] 4, a general electronically controlled limited slip differential (LSD) can be used for the differential 7. That is, the differential 7, which is merely an example, includes a casing 21 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 pressing force on the clutch 25 in a controlled manner. The actuator 27 is exclusively controlled by the ECU 17.

[0017] 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 type, planetary gear type, or other types may be used instead. Also, an example in which a multi-plate clutch type is used for the friction clutch will be described, but cone clutches or other types may be used instead. Furthermore, as for the actuator, a gear and cam type using an external motor will be described, but the motor may be built-in and directly drive the rotary plate without using gears, or a thrust force may be generated by hydraulic pressure or the like without using a cam, or other appropriate types may be used.

[0018] Bosses 21R, 21L protrude in the axial direction from both ends of the casing 21, and are supported by a carrier via bearings such as ball bearings, allowing the casing 21 to rotate around the axis X. A flange 21F protrudes radially from the outer periphery of the casing 21, to which, for example, a ring gear is fixed. The end of the propeller shaft is provided with a gear corresponding to the ring gear, and the casing 21 receives torque from the power source 3 by meshing with the ring gear.

[0019] 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, a spline on their inner periphery, and are connected to output shafts. The output shafts are usually the right and left axles. As will be easily understood, the side gears 35R and 35L are capable of differential rotation with respect to each other, and therefore the differential gear set 23 distributes the torque received by the casing 21 to the side gears 35R and 35L while allowing differential rotation, and outputs the torque to both axles.

[0020] The clutch 25 is, for example, a multi-plate clutch, and is interposed between the casing 21 and, for example, the right side gear 35R, and includes a group of alternately stacked inner and outer plates. For example, the right side gear 35R includes lugs for engaging with the inner plates, and the inner plates include corresponding grooves for engaging with each other. Similarly, the inner surface of the casing 21 also includes lugs, and the outer plates engage with the casing 21. When the actuator 27 applies a pressing force to the group of plates, the clutch 25 frictionally brakes the right side gear 35R against the casing 21, thereby limiting the differential 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.

[0021] The actuator 27 includes, for example, a rotary plate 41, a support plate 43, and a cam mechanism 45 that is disposed between the rotary plate 41 and generates a thrust force. The rotary plate 41 can rotate around an axis X, for example, and has gear teeth 41G on its outer periphery. Although not shown in FIG. 4, the actuator 27 further includes a motor for driving the rotary plate 41, and the shaft of the motor meshes 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 structure for preventing rotation, which is prevented from rotating by engaging with a carrier. The cam mechanism 45 includes, for example, a cam slope formed on one or both of the plates 41 and 43 and inclined in the circumferential direction, and a cam ball that rolls on the slope. When the rotary plate 41 rotates relative to the support plate 43, the cam ball rolls and rises or falls on the slope, and the cam mechanism 45 converts the rotational force into a thrust force.

[0022] The actuator 27 is disposed adjacent to the clutch 25 and adjacent to the end wall of the casing 21 in order to apply the thrust force to the clutch 25. The actuator 27 may also include a plunger 49 for outputting the thrust force, and the plunger 49 is connected to the clutch 25 through the end wall of the casing 21. Thus, the actuator 27 applies a thrust force to the clutch 25 according to the rotation angle given to the motor.

[0023] 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. In the illustrated example, the support plate 43 exerts the thrust force, but instead the rotary plate 41 may exert the thrust force.

[0024] 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, and the proportion that passes through the gear set 23 decreases. Conversely, if the rotation angle of the rotary plate 41 decreases, the proportion that passes through the clutch 25 decreases, and the proportion that passes through the gear set 23 increases.

[0025] The ECU 17 calculates the required torque value T req is calculated, and the actuator 27 is controlled based on the calculated torque, thereby dynamically controlling the clutch torque.

[0026] Referring mainly to FIG. 5, the torque T input to the differential 7 is diff is notified to the ECU 17 via communication. The ECU 17 determines, for example, the clutch locking rate f required to realize a target TBR based on a differential torque ratio (or a torque bias ratio; TBR). LSD For example, the formula T diff ×f LSD The clutch torque T LSD The TBR can be stored in advance in a storage device of the ECU 17. Different TBRs can be used for the forward direction and the reverse direction. An example of such a TBR is forward direction TBR=2.7 and reverse direction TBR=2.3, but the present invention is not limited to these.

[0027] The ECU 17 further uses other parameters to determine the clutch torque T LSDThe corrected required torque value T req For example, the required value can be corrected in consideration of the differential limiting force (initial torque) to be applied in advance. i may be stored in advance in the storage device of the ECU 17, or may be stored in the storage device of the ECU 17 in advance in accordance with the vehicle speed V v For example, as shown by the broken line CV1 in FIG. 9A, v When is relatively small, the initial torque T i The differential between the left and right wheels can be made relatively small, which emphasizes turning ability. v When is relatively large, the initial torque T i In this way, it is possible to realize an optimum differential limiting function according to the expected gripping force of the tires.

[0028] Initial torque T i For example, the vehicle speed V v and initial torque T i A data table correlating the actual vehicle speed V v Therefore, the initial torque T i Alternatively, it may be calculated based on a formula prepared in advance. As shown in FIG. 5, the initial torque T i Clutch torque T LSD The required torque value T req or the larger value is used as the required torque value T req It may be adopted as.

[0029] Referring back to FIG. 5, an additional torque T GX T GX Alternatively, the acceleration G xIt goes without saying that the calculation may be based on a data table or a mathematical formula.

[0030] The obtained required torque value T req In order to remove excessive fluctuations, the corrected required value may be passed through an appropriate low-pass filter (LPF). Alternatively or in addition to this, an upper limit for the required torque value may be set so that an excessive input is not applied to the actuator 27. 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 required torque value T req It can be adopted as.

[0031] Since the above-mentioned calculations are standardized, 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-mentioned calculations.

[0032] Referring to FIG. 6, in this embodiment, the required torque value T req For example, the required torque value T req On the other hand, if a large heavy object is loaded in the luggage compartment, a larger value T req The load applied to the drive wheels is compared with a preset appropriate threshold value (load judgment value), and T req ,T req When the load applied to the drive wheels is above a certain level, the larger value T req ' is adopted, thereby making it possible to increase the differential limiting force of the differential 7.

[0033] As already described, the value to be compared with the load judgment value may be the output value of the load sensor acquired by the ECU 17 via the bus 19. Alternatively, the load applied to the drive wheels may be estimated from other parameters and used for the comparison. For example, the output value of a stroke sensor may be used for the estimation.

[0034] Required value T req ' is calculated, for example, by the value T req Alternatively, a data table set for heavy loads can be prepared separately from a data table set for unladen loads, and when the wheel load is below the threshold, the former can be used to calculate T req When the threshold is exceeded, the latter is used to calculate T req ' may be calculated.

[0035] Or, when it is above the threshold, the correction value T LSD ,T i ,T Gx For example, the initial torque T i Multiply by a factor of 1 or more to get the required value T req Of course, as shown in FIG. req The required value may be calculated by multiplying the entire value by a coefficient of 1 or more.

[0036] Alternatively, as shown in FIG. 8, a formula F1 for an unladen vehicle and a formula F2 for a heavy vehicle may be prepared, and the former may be used to calculate the required value when the wheel load is equal to or less than a threshold value, and the latter may be used to calculate the required value when the wheel load is equal to or more than the threshold value.

[0037] Furthermore, in the examples of FIGS. 6 to 8, a selection is made from two settings, but a selection may be made from three or more settings, and in that case, the threshold value is not limited to one, but may be two or more.

[0038] Referring mainly to FIG. 9A, according to this embodiment, when the load on the drive wheels is relatively small, the required torque T req When the load on the drive wheels is relatively large, the tire grip limit is also large, so the required torque T req Alternatively, as shown in FIG 9B, control can be performed so that the required torque value is not changed much in the low speed range, and the difference becomes larger in the high speed range.

[0039] The control procedure by the ECU 17 will be described with reference to Fig. 10. The ECU 17 first acquires or calculates parameters such as input torque and vehicle speed using CAN communication or the like (S1). Next, the ECU 17 calculates clutch torque by selecting from a pre-stored data table or according to set conditions (S2). If necessary, correction values ​​and coefficients for the initial torque, additional torque, etc. are calculated.

[0040] Next, the load applied to the drive wheels (load judgment value) is acquired or calculated (S3), and this is compared with a preset threshold value to determine a correction method for the clutch torque (S5-1, 2, or 3). The required torque value is corrected based on the determined correction method to calculate a required value (S6). If necessary, the calculated value is subjected to filtering or other processing to calculate a final required value (S7).

[0041] Referring to Fig. 11, additional control may be performed. For example, when the differential between the side gears 35R, 35L in the differential 7 becomes excessive, or when excessive fluctuations are added to the torque applied to the friction clutch 25, noise, vibration, and harshness (hereinafter referred to as NVH from the initials of these three terms) often occur. Therefore, control for preventing the occurrence of NVH can be added. For example, a condition for the occurrence of NVH can be set in advance, and it can be determined whether or not the condition is satisfied (S8). If the condition is not generated (false), the required value is maintained (S9-2), and if the condition is generated (true), the required value is decreased (S9-1) or increased (S9-3).

[0042] In response to the obtained demand value, the ECU 17 applies power to the actuator to control the rotation angle of the rotary plate 41, thereby controlling the differential limiting force. These procedures are constantly repeated, thereby dynamically controlling the differential limiting force.

[0043] As can be understood from the above description, according to this embodiment, the setting is switched according to the load applied to the drive wheels, so that the differential limiting force can be optimized regardless of the state of the vehicle. For example, when the load is relatively light, control can be performed that emphasizes turning performance, and when the load is relatively heavy, control can be performed that emphasizes traction force. This embodiment realizes optimal LSD control regardless of the state of the vehicle.

[0044] Although several embodiments have been described, the embodiments can be modified or altered based on the above disclosure. [Industrial Applicability]

[0045] An electronically controlled limited slip differential is provided that achieves optimal differential limiting regardless of the vehicle condition. [Explanation of symbols]

[0046] 1 vehicle 3,3' power source 5,5' Transmission 7,7' differential 9 Other vehicles 11,13,15,17 ECU 19 Bus 21 Casing 23 Differential gear set 25 Clutch 27 Actuator 35R, 35L side gear 41 Rotary Plate 45 Cam mechanism 49 Plunger X-axis

Claims

1. A differential used to distribute an input torque to a pair of output shafts in accordance with at least the input torque and a wheel load, a casing that receives the input torque; a differential gear set that is housed and supported in the casing, includes first and second side gears that are respectively connected to the output shaft, and differentially distributes the input torque to the first and second side gears; a clutch interposed between the casing and the first side gear for frictionally braking the first side gear against the casing, thereby limiting differential motion 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 and including a storage device that stores one or more thresholds, the electronic control device being configured to calculate a required torque value from the input torque, determine a correction value by comparing the wheel load with the thresholds, correct the required torque value using the correction value to calculate a required value, and control power input to the actuator in accordance with the required value; A differential equipped with.

2. 2. The differential of claim 1, wherein the storage device is configured to calculate the required torque value by adding the correction value to the required torque value when the wheel load is greater than the threshold value.

3. 2. The differential of claim 1, wherein the correction value includes a vehicle speed correction value, and the electronic control unit is configured to calculate the required value by multiplying the vehicle speed correction value by one or more coefficients when the wheel load is greater than the threshold value.

4. 4. The differential of claim 3, wherein said storage device stores a vehicle speed data table, and said electronic control device is configured to calculate said vehicle speed correction value by comparing the vehicle speed with said vehicle speed data table.

5. 2. The differential of claim 1, wherein the storage device stores two or more vehicle speed data tables, and the electronic control device is configured to select one vehicle speed data table from the storage device in response to a comparison between the wheel load and the threshold value, calculate a vehicle speed correction value from the vehicle speed and the selected vehicle speed data table, and calculate the required value by adding the vehicle speed correction value to the required torque value.

6. 6. The differential according to claim 2, wherein the electronic control unit is connected to other electronic control units via a network and is configured to calculate the vehicle speed, the input torque, and the wheel load from data acquired via the network.

Images