Vehicle control device

Abstract

To provide a vehicle control device that can improve prediction accuracy of a failure of a differential device.SOLUTION: An input burden and oscillation surface temperature are calculated in each of oscillation units oscillating in each of a differential case and a built-in gear. Then, each calculation result of the input burden and oscillation surface temperature is applied to a relation having an area, which is determined that a failure of a differential device may occur ahead on the basis of the input burden and oscillation surface temperature, predetermined, and thereby, the failure of the differential device is predicted. By this prediction, heating and stress in each of the oscillation units can be directly predicted, which in turn, prediction accuracy of the failure of the differential device can be improved.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a control device for a vehicle equipped with a differential device. [Background technology]

[0002] There is a well-known control device for a vehicle including a power source and a power transmission device that transmits power from the power source to left and right drive wheels via a differential device and left and right drive shafts. For example, there is a vehicle control device described in Patent Document 1. Patent Document 1 discloses a method of acquiring information on the cumulative load of a bearing holder of a gear of the power transmission device based on information on the torque of the power source, information on the rotation speed of the gear of the power transmission device, and information on the operation time of the power transmission device, estimating the amount of wear of the bearing holder based on the acquired information on the cumulative load of the bearing holder and information on the dimensions of the bearing holder, and determining whether the level of noise and vibration caused by wear of the bearing holder is equal to or higher than a predetermined standard based on the estimated amount of wear, thereby identifying whether the cause of vibration and noise in the power transmission device is wear of the bearing holder. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-15063 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, in a differential device, when in a differential state, there are sliding points in the differential case, which houses the internal gear and to which the drive shaft is fitted so as to be capable of relative rotation, and in the internal gear. At this time, the durability of the differential device may be reduced due to seizure caused by the sliding. For this reason, it is desirable to predict failure (seizure) of the differential device. Referring to Patent Document 1, for example, it is conceivable to predict failure of the differential device using the torque of the power source, the rotation speed of the gears of the differential device, the time during which the differential device is in a differential state, and the like. However, if the accuracy of failure prediction is low, it may lead to vehicle malfunctions or increased costs due to incorrect replacement of parts.

[0005] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a vehicle control device that can improve the accuracy of predicting failures in a differential device. [Means for solving the problem]

[0006] The gist of the first invention is (a) a control device for a vehicle equipped with a power source and a power transmission device that transmits power from the power source to left and right drive wheels via a differential device and left and right drive shafts, (b) calculating an input load and a sliding surface temperature of a differential case of the differential device that houses an internal gear of the differential device and to which the drive shaft is fitted so as to be able to rotate relative to the drive shaft, and each of the sliding parts that slide on each of the internal gears, and (c) predicting a failure of the differential device by applying each of the calculation results of the input load and the sliding surface temperature to a predetermined relationship in which an area in which a future failure of the differential device is determined to be likely to occur based on the input load and the sliding surface temperature is predetermined. Effect of the Invention

[0007] According to the first aspect of the present invention, the input load and sliding surface temperature of each of the sliding parts that slide in each of the differential case and the built-in gear are calculated. Then, the calculation results of the input load and the sliding surface temperature are applied to a relationship in which a region in which a differential device failure is likely to occur in the future is determined based on the input load and the sliding surface temperature, thereby predicting a differential device failure. This makes it possible to directly predict heat generation and stress in each of the sliding parts. This makes it possible to improve the accuracy of predicting a differential device failure. [Brief description of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating a schematic configuration of a vehicle to which the present invention is applied; [Diagram 2] FIG. 2 is a diagram for explaining an example of a differential configuration, and also a diagram showing an example of a state before the differential and a drive shaft are assembled together. [Diagram 3] 2 is a diagram for explaining a control function and a main part of a control system for predictive control of a differential failure in a vehicle. FIG. [Figure 4] FIG. 4 is a diagram showing an example of a differential failure determination map. [Diagram 5] 4 is a flowchart illustrating a main part of the control operation of the electronic control device, and is a flowchart illustrating the control operation for improving the accuracy of predicting a differential failure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. EXAMPLES

[0010] Fig. 1 is a diagram illustrating a schematic configuration of a vehicle 10 to which the present invention is applied. In Fig. 1, the vehicle 10 includes an engine 12 as a power source, drive wheels 14, and a power transmission device 16 provided in a power transmission path between the engine 12 and the drive wheels 14.

[0011] The engine 12 is a known internal combustion engine, and the engine torque Te of the engine 12 is controlled by an engine control device 50 including a fuel injection device and the like provided on the vehicle 10, which is controlled by an electronic control device 60 described later.

[0012] The power transmission device 16 includes a transmission section 20, a driven gear 22, a driven shaft 24, a final gear 26, a differential 28, and the like, housed in a non-rotatable case 18 attached to the vehicle body. The differential 28 is a known differential device (also synonymous with differential gears) having a differential ring gear 28a, a differential case 28b, a differential side gear 28c, a differential pinion 28d, and a pinion shaft 28e. The power transmission device 16 also includes a pair of (left and right) drive shafts 30 connected to the differential 28, and the like. Note that the above "left and right" refers to the left and right with respect to the forward direction of the vehicle 10.

[0013] The transmission unit 20 is connected to the engine 12. The driven gear 22 meshes with a drive gear 20a, which is an output rotating member of the transmission unit 20. The driven shaft 24 fixes the driven gear 22 and the final gear 26 so that they cannot rotate relative to each other. The final gear 26 has a smaller diameter than the driven gear 22 and meshes with a differential ring gear 28a. The differential ring gear 28a is an input rotating member of the differential 28. The differential 28 distributes power from the engine 12 to the left and right driving wheels 14. A vertically lower portion of the differential 28 is immersed in lubricating oil FLD stored vertically below the case 18. This lubricating oil FLD is scooped up by the differential ring gear 28a.

[0014] The power transmission device 16 configured in this manner is suitable for use in FF (front engine, front drive) or RR (rear engine, rear drive) vehicles. The power transmission device 16 transmits the power output from the engine 12 to a driven gear 22 via a transmission unit 20. The power transmission device 16 transmits the power transmitted to the driven gear 22 to the left and right drive wheels 14 via a driven shaft 24, a final gear 26, a differential 28, left and right drive shafts 30, etc. in this order.

[0015] Fig. 2 is a diagram for explaining an example of the configuration of the differential 28, and also a diagram showing an example of a state before the differential 28 and the drive shaft 30 are assembled. In Fig. 2, the differential 28 has a pair of differential side gears 28c, a pair of differential pinions 28d, and a pinion shaft 28e housed inside a differential case 28b. The differential 28 has a differential ring gear 28a integrally connected to the outside of the differential case 28b. The drive shaft 30 includes a spline fitting portion 30a, a bore fitting portion 30b, and the like.

[0016] The differential case 28b is fixed to the case 18 via bearings so as to be relatively rotatable. The differential case 28b is formed with a bore portion 28b1 which is a through hole into which the drive shaft 30 is fitted so as to be relatively rotatable. The differential case 28b is formed with a shaft hole 28b2 which is a through hole into which the pinion shaft 28e is fitted so as not to be relatively rotatable. The differential case 28b is a carrier of the differential 28 which houses the differential side gears 28c, the differential pinions 28d, etc., and into which the drive shaft 30 is fitted so as to be relatively rotatable.

[0017] The differential side gear 28c and the differential pinion 28d are built-in gears 28bing of the differential 28. The differential side gear 28c has a through hole in which the drive shaft 30 is fitted so as not to rotate relative to the differential side gear 28c, and has spline teeth formed on an inner peripheral surface 28c1. The differential pinion 28d has teeth that mesh with the differential side gear 28c. The differential pinion 28d is supported by the pinion shaft 28e so as to be rotatable relative to the differential case 28b. The pinion shaft 28e is fitted into a shaft hole 28b2 and fixed to the differential case 28b.

[0018] The spline fitting portion 30a is formed at the end portion on the differential 28 side. The spline fitting portion 30a has spline teeth formed on its outer circumferential surface, and is fitted to an inner circumferential surface 28c1 of the differential side gear 28c so as not to rotate relative to the spline fitting portion 30a. The bore fitting portion 30b is formed adjacent to the spline fitting portion 30a on the drive wheel 14 side. The bore fitting portion 30b is fitted to a bore portion 28b1 of the differential case 28b so as to be rotatable relative to the spline fitting portion 30a.

[0019] Here, in the differential 28, when a differential state is established in which there is a difference in rotational speed between the left and right drive wheels 14, the differential case 28b and the built-in gear 28bing each have sliding parts 40 which slide against other parts.

[0020] The sliding portion 40 includes a first sliding portion 42, a second sliding portion 44, a third sliding portion 46, and a fourth sliding portion 48. The first sliding portion 42 is a sliding portion between the members of the differential case 28b and the differential pinion 28d. The second sliding portion 44 is a sliding portion between the members of the differential pinion 28d and the pinion shaft 28e. The third sliding portion 46 is a sliding portion between the members of the differential case 28b and the differential side gear 28c. The fourth sliding portion 48 is a sliding portion between the members of the differential case 28b and the drive shaft 30. In other words, the fourth sliding portion 48 is a sliding portion between the members of the bore portion 28b1 and the bore fitting portion 30b. In this way, the sliding portion 40 is a sliding portion of the parts in each of the built-in gear 28bing and the bore portion 28b1.

[0021] However, the durability of the differential 28 may decrease due to seizure caused by sliding in the sliding parts 40. For this reason, it is desirable to predict failure (seizure) of the differential 28. In this case, if the accuracy of predicting failure of the differential 28 is low, it may lead to vehicle malfunctions or increased costs due to incorrect replacement of parts.

[0022] Fig. 3 is a diagram for explaining the main parts of the control function and control system for predictive control of a failure of the differential 28 in the vehicle 10. In Fig. 3, the vehicle 10 is provided with an electronic control device 60 as a controller including a control device of the vehicle 10 that performs predictive control of a failure of the differential 28. The electronic control device 60 is configured to include a so-called microcomputer equipped with, for example, a CPU, RAM, ROM, an input / output interface, etc. The CPU performs signal processing according to a program previously stored in the ROM while utilizing the temporary storage function of the RAM.

[0023] The electronic control unit 60 is supplied with internal information 70 of the power transmission device 16 (=power transmission device internal information) and vehicle information 72, etc., as input factors based on detection values ​​by various sensors and the like provided in the vehicle 10. In addition, the electronic control unit 60 is supplied with manufacturing information (=differential manufacturing information) 74 of the differential 28 as manufacturing traceability data, that is, parts information (=differential parts information) of the differential 28, as input factors stored in advance in the vehicle 10, for example. Various display command signals Sinf are output from the electronic control unit 60 to, for example, a monitor 80 provided in the vehicle 10.

[0024] The power transmission device internal information 70 includes, for example, the power source torque, i.e., the engine torque Te, the differential ring gear rotation speed Nd, which is the gear shaft rotation speed, i.e., the input rotation speed of the differential 28, the differential time TMd, which is the time during which the differential 28 is in a differential state, i.e., the time during which a differential rotation occurs between the left and right drive wheels 14, the lubricant temperature THfld, which is the temperature of the lubricant FLD of the differential 28, and other internal information α. ​​The other internal information α includes, for example, the flow rate of the lubricant FLD to the differential 28, the oil level of the lubricant FLD in the case 18 in which the differential 28 is immersed, and the like. The flow rate of the lubricant FLD and the oil level of the lubricant FLD are determined, for example, by the differential ring gear rotation speed Nd, i.e., the speed (amount) at which the lubricant FLD is scooped up, the shape of the differential case 28b, and the like.

[0025] The vehicle information 72 includes left and right wheel rotation speeds Nw, which are the rotation speeds of the left and right drive shafts 30, i.e., the rotation speeds of the left and right drive wheels 14, a steering angle θsw, which is the turning angle of the wheels, i.e., the steering angle of the steering wheel, and other vehicle information β. The other vehicle information β includes, for example, the longitudinal acceleration Gx of the vehicle 10, the lateral acceleration Gy of the vehicle 10, and the vehicle weight WTv, which is the weight of the vehicle 10. The longitudinal acceleration Gx and the lateral acceleration Gy are factors that affect, for example, the inclination of the drive shaft 30 and the inclination of the oil level of the lubricating oil FLD. The vehicle weight WTv is a factor that affects, for example, the inclination of the drive shaft 30.

[0026] The differential manufacturing information 74 is traceability data relating to the dimensions and surface roughness of the differential 28, for example, and includes information on the shape of the differential case 28b, information on the clearance (= gap) of the bore portion 28b1, information on the surface roughness of the sliding portion 40, and other part information γ. The information on the shape of the differential case 28b is the design value of the dimensions of the differential case 28b, for example, the design value of the inner diameter of the bore portion 28b1, the design value of the axial length of the bore portion 28b1, the design value of the radius of the first sliding portion 42 on the differential case 28b side, and the design value of the radius of the third sliding portion 46 on the differential case 28b side. The information on the clearance of the bore portion 28b1 is the design value of the clearance at the fitting portion between the differential case 28b and the drive shaft 30, for example, the design value of the difference between the inner diameter of the bore portion 28b1 and the outer diameter of the spline fitting portion 30a. The information on the surface roughness of the sliding portion 40 is a design value of the surface roughness of the sliding portion 40 of the differential case 28b, and includes, for example, a design value of the surface roughness of the inner peripheral surface of the bore portion 28b1, a design value of the surface roughness of the sliding surface of the differential case 28b side of the first sliding portion 42, and a design value of the surface roughness of the sliding surface of the differential case 28b side of the third sliding portion 46. The other part information γ includes a design value of the rigidity of the differential case 28b, and a design value of the relative position of the built-in gear 28bing with respect to the differential case 28b. The design value of the rigidity of the differential case 28b includes, for example, a design value of the material properties (Young's modulus, Poisson's ratio, etc.) of the differential case 28b.

[0027] The electronic control unit 60 includes an input stress calculation unit 62, a sliding surface temperature calculation unit 64, and a differential failure prediction unit 66 in order to realize predictive control of a failure of the differential 28 in the vehicle 10.

[0028] The input stress calculation unit 62 calculates the input load in each of the sliding parts 40. The input load is a load (load) input to the sliding part 40, and is, for example, an input stress STin (=P×V×t) represented by a multiplication value of the surface pressure P, the sliding speed V, and the sliding time t in the sliding part 40. The input stress calculation unit 62 calculates the surface pressure P, the sliding speed V, and the sliding time t, respectively, using the power transmission device internal information 70, the vehicle information 72, and the differential manufacturing information 74, and calculates the input stress STin. The surface pressure P is particularly influenced by factors such as the engine torque Te, the steering angle θsw, and the information on the shape of the differential case 28b. The sliding speed V is particularly influenced by factors such as the differential ring gear rotation speed Nd and the left and right wheel rotation speeds Nw. The sliding time t is particularly influenced by factors such as the differential time TMd. When there is no effect of the sliding speed V, the input stress STin (=P×t) is calculated from the surface pressure P and the sliding time t. When there is no effect of the surface pressure P, the input stress STin (=V×t) is calculated from the sliding speed V and the sliding time t.

[0029] The sliding surface temperature calculation unit 64 calculates a sliding surface temperature THs of each sliding part 40. The sliding surface temperature THs is the temperature of the sliding surface due to sliding in the sliding part 40, and corresponds to the amount of heat generated during sliding. The sliding surface temperature THs is calculated using the power transmission device internal information 70, the vehicle information 72, and the differential manufacturing information 74.

[0030] The differential failure prediction unit 66 predicts a failure of the differential 28, that is, judges whether or not there is a possibility of a failure of the differential 28 occurring in the future (in the near future), using the input stress STin calculated by the input stress calculation unit 62 and the sliding surface temperature THs calculated by the sliding surface temperature calculation unit 64. For example, the differential failure prediction unit 66 predicts a failure of the differential 28 by applying the calculation results of the input stress STin and the sliding surface temperature THs to a differential failure judgment map as shown in FIG.

[0031] FIG. 4 is a diagram showing an example of a differential failure judgment map. In FIG. 4, the differential failure judgment map is a relationship determined in advance through experiments, on a two-dimensional coordinate system with the horizontal axis representing the input stress STin and the vertical axis representing the sliding surface temperature THs, and has a boundary line BL between an OK region (see "OK" in the figure) and a NG region (see "NG" in the figure). The OK region is a region for determining that there is no (or low) possibility that the differential 28 will fail in the near future. The NG region is a region for determining that there is a (or high) possibility that the differential 28 will fail in the near future. In this way, the differential failure judgment map is a relationship in which a region for determining that there is a possibility that the differential 28 will fail in the future is determined in advance based on the input stress STin and the sliding surface temperature THs.

[0032] The differential failure prediction unit 66 applies the calculation results of the input stress STin and the sliding surface temperature THs to the differential failure judgment map to judge whether or not they are in the NG region. If the differential failure prediction unit 66 judges that they are in the NG region, it judges that there is a possibility that a failure of the differential 28 will occur in the near future. The failure of the differential 28 is, for example, a failure of an internal part of the differential 28 (internal gear 28 ing).

[0033] The differential failure prediction unit 66 notifies the driver of the result of the prediction of a failure of the differential 28. For example, when the differential failure prediction unit 66 determines that the differential is in the NG region, it outputs a display command signal Sinf to display on the monitor 80 a message indicating that a failure of the differential 28 may occur in the near future. The content displayed on the monitor 80 may be, for example, a message encouraging maintenance or inspection of the differential 28, a message encouraging replacement of some parts of the differential 28, or a message encouraging replacement of the lubricating oil FLD. In addition to or instead of displaying on the monitor 80, the result of the prediction of a failure of the differential 28 may be informed to the driver by voice.

[0034] FIG. 5 is a flowchart for explaining the main control operations of the electronic control unit 60, and is a flowchart for explaining the control operations for improving the accuracy of predicting a failure in the differential 28, and is executed, for example, repeatedly.

[0035] In FIG. 5, first, in step S10 (hereinafter, steps are omitted) corresponding to the functions of the input stress calculation unit 62 and the sliding surface temperature calculation unit 64, the power transmission device internal information 70, the vehicle information 72, and the differential manufacturing information 74 are used to calculate the input stress STin (= contact pressure P × sliding speed V × sliding time t) and the sliding surface temperature THs due to component sliding in the differential 28. Next, in S20 corresponding to the function of the differential failure prediction unit 66, the calculation results of the input stress STin and the sliding surface temperature THs are applied to the differential failure judgment map (see FIG. 4) to judge whether they are in the NG region or not. If the judgment in S20 is negative, this routine is terminated. If the judgment in S20 is positive, in S30 corresponding to the function of the differential failure prediction unit 66, a failure of the differential 28, for example, an internal part is judged (predicted), that is, it is judged that a failure of the differential 28 may occur in the future. Next, in S40, which corresponds to the function of differential failure prediction unit 66, the result of the prediction of failure of differential 28 is notified to the user (for example, the driver).

[0036] As described above, according to this embodiment, the input load (e.g., input stress STin) and sliding surface temperature THs in each of the sliding parts 40 are calculated. Then, the calculation results of the input stress STin and the sliding surface temperature THs are applied to the differential failure determination map to predict a failure of the differential 28. This makes it possible to directly predict heat generation and stress in each of the sliding parts 40. This makes it possible to improve the accuracy of predicting a failure of the differential 28.

[0037] According to this embodiment, the input load is an input stress STin (=P×V×t) represented by a multiplication value of the surface pressure P, the sliding speed V, and the sliding time t in the sliding portion 40. This allows the input load (for example, the input stress STin) to be appropriately calculated.

[0038] According to this embodiment, the input stress STin and the sliding surface temperature THs are calculated using power transmission device internal information 70 including engine torque Te, differential ring gear rotation speed Nd, differential time TMd, and lubricating oil temperature THfld, vehicle information 72 including left and right wheel rotation speeds Nw and steering angle θsw, and differential manufacturing information 74 including design values ​​of the dimensions of the differential case 28b, design values ​​of the clearance at the fitting portion between the differential case 28b and the drive shaft 30, and design values ​​of the surface roughness at the sliding portion 40 of the differential case 28b. As a result, the input stress STin and the sliding surface temperature THs are calculated appropriately.

[0039] According to this embodiment, the power transmission device internal information 70 further includes the flow rate of the lubricating oil FLD to the differential 28, the vehicle information 72 further includes the longitudinal acceleration Gx, the lateral acceleration Gy, and the vehicle weight WTv of the vehicle 10, and the differential manufacturing information 74 further includes the design value of the rigidity of the differential case 28b and the design value of the relative position of the built-in gear 28bing with respect to the differential case 28b. This allows the input stress STin and the sliding surface temperature THs to be calculated more appropriately.

[0040] Furthermore, according to this embodiment, the driver is notified of the results of the prediction of a failure in the differential 28. This allows the driver to appropriately inspect the differential 28 and replace parts.

[0041] Although the embodiment of the present invention has been described in detail above with reference to the drawings, the present invention can be applied to other embodiments.

[0042] For example, in the above-described embodiments, the transmission unit 20 is an automatic transmission such as a known planetary gear type automatic transmission, a known belt type continuously variable transmission, a known synchronous meshing type parallel two-shaft automatic transmission, a known DCT (Dual Clutch Transmission), a known electric continuously variable transmission, or a known transmission in which an electric continuously variable transmission and a planetary gear type automatic transmission are arranged in series.

[0043] In the above embodiment, the vehicle 10 is equipped with the engine 12 as a power source, but the present invention is not limited to this. For example, the vehicle 10 may be an electric vehicle equipped with an electric motor as a power source, or a hybrid vehicle equipped with an engine or an electric motor as a power source. In an electric vehicle, the power source torque is the torque of the electric motor, that is, the motor torque. In a hybrid vehicle, the power source torque is the engine torque Te and the motor torque. The present invention can also be applied to vehicles such as FR (front engine, rear drive) type vehicles. In addition, in a series type hybrid vehicle, in which the engine torque Te is not mechanically transmitted to the drive wheels, the power source torque is the motor torque.

[0044] It should be noted that the above is merely one embodiment, and the present invention can be embodied in various modified and improved forms based on the knowledge of those skilled in the art. [Explanation of symbols]

[0045] 10: Vehicle 12: Engine (power source) 14: Drive wheels 16: Power transmission device 28: Diff (differential device) 28b: Differential case 28c: Differential side gear (internal gear) 28d: Differential pinion (internal gear) 28bing: Internal gear 30: Drive shaft 40: Sliding part 60: Electronic control device (control device) 70: Power transmission device internal information (internal information of the power transmission device) 72: Vehicle information 74: Differential manufacturing information (manufacturing information of the differential device) FLD: Lubricating oil

Claims

1. A control device for a vehicle including a power source and a power transmission device that transmits power from the power source to left and right drive wheels via a differential device and left and right drive shafts, Calculating the input load and the sliding surface temperature of each of the sliding parts that slide on a differential case of the differential device that houses the built-in gear of the differential device and to which the drive shaft is fitted so as to be capable of relative rotation, and each of the built-in gears; a region in which a future failure of the differential device is determined to be likely based on the input load and the sliding surface temperature, the region being determined to be likely to cause a future failure of the differential device based on the input load and the sliding surface temperature, and the calculation results of the input load and the sliding surface temperature are applied to a predetermined relationship, thereby predicting a failure of the differential device.

2. 2. The vehicle control device according to claim 1, wherein the input load is an input stress represented by a multiplication value of a surface pressure on the sliding portion, a sliding speed, and a sliding time.

3. The input stress and the sliding surface temperature are calculated using internal information of the power transmission device, including the torque of the power source, the input rotational speed of the differential device, the time the differential device is in a differential state, and the temperature of the lubricating oil of the differential device; vehicle information, including the rotational speeds of the left and right drive wheels and the steering angle; and manufacturing information of the differential device, including design values ​​of the dimensions of the differential case, design values ​​of the clearance at the fitting portion between the differential case and the drive shaft, and design values ​​of the surface roughness at the sliding portion of the differential case. The vehicle control device of claim 2.

4. The inside information further includes a flow rate of the lubricant; The vehicle information further includes a longitudinal acceleration of the vehicle, a lateral acceleration of the vehicle, and a weight of the vehicle, 4. The vehicle control device according to claim 3, wherein the manufacturing information further includes a design value of the rigidity of the differential case and a design value of the relative position of the built-in gear with respect to the differential case.

5. 5. The vehicle control device according to claim 1, further comprising: a driver notifying the driver of a predicted failure of the differential device.

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