Electrically Locked Differential

Abstract

A vehicle includes an anti-lock braking system (ABS), a stability control system (SCS), and an electronically lockable differential. A controller of the vehicle is programmed to unlock the differential in response to activation of the ABS or the SCS. The controller is further programmed to prohibit locking of the differential for a pre-defined period of time in response to deactivation of one of the ABS and the SCS that is activated.

Description

Technical Field

[0001] The present disclosure relates to an electronically lockable differential, and more particularly to a controller for controlling the locking and unlocking of a differential during certain operating conditions to prevent hardware damage to the differential. Background Art

[0002] A motor vehicle may include a differential on a drive axle to transfer torque generated by an engine to the vehicle's driven wheels. The differential allows the driven wheels to rotate at different speeds relative to each other. This allows the outer wheel to rotate faster than the inner wheel when the vehicle turns.

[0003] A typical open differential includes a ring gear that meshes with a pinion gear fixed to a drive shaft. The differential housing is fixed to the ring gear and is supported for rotation within the outer housing of the differential. The housing supports a pair of side gears and a pair of star gears that engage the side gears. The side gears are drivingly connected to the driven wheels. The star gears transfer torque from the housing to the side gears to propel the vehicle. When one of the driven wheels is on a low traction surface, it is difficult for an open differential to propel the vehicle because the torque from the engine is directed to the low traction wheel causing the wheel to spin.

[0004] Limited-slip differentials have been developed to overcome the disadvantages of open differentials. A typical limited-slip differential includes a clutch assembly and springs that cooperate to engage a side gear associated with the higher traction wheel with the housing in order to provide engine torque to both driven wheels.

[0005] A lockable differential includes a locking mechanism configured to rotationally lock the side gears relative to each other such that the left and right driven wheels rotate in unison. Unlike limited-slip differentials that rely on wheel spin to compress a clutch assembly, a lockable differential includes a locker that mechanically locks the half shafts for unison rotation. The locker can be engaged manually or electronically. Such differentials are commonly used in light trucks and sport vehicles to improve off-road performance. Summary of the Invention

[0006] According to one embodiment, a vehicle includes an anti-lock braking system (ABS), a stability control system (SCS), and an electronically lockable differential. The vehicle's controller is programmed to unlock the differential in response to activation of the ABS or SCS. The controller is further programmed to prohibit locking the differential for a predefined period of time in response to deactivation of one of the ABS and SCS that has been activated.

[0007] According to another embodiment, a vehicle includes an anti-lock braking system (ABS), a stability control system (SCS), and a locking differential having an electronic control lock configured to lock the differential. A vehicle controller is programmed to energize the lock to lock the differential in response to (i) the vehicle speed being less than a threshold, (ii) the accelerator pedal position being less than a threshold, and (iii) the steering angle being less than a threshold, and to de-energize the lock to unlock the differential in response to the activation of at least one of the ABS and the SCS. The controller is further programmed to prohibit energizing the lock for a predefined period of time in response to the deactivation of an activated one of the ABS and the SCS.

[0008] According to yet another embodiment, a method of controlling an electronic locking differential includes locking the differential in response to the presence of an engagement condition. The method further includes unlocking the differential in response to the activation of at least one of an anti-lock braking system (ABS) and a stability control system (SCS), and prohibiting locking the differential for a predefined period of time that begins in response to the deactivation of an activated one of the ABS and the SCS. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a schematic view of a vehicle including a controller and a differential in accordance with one or more embodiments of the present disclosure.

[0010] Figure 2 is Figure 1 an exploded view of the differential.

[0011] Figure 3 is a cross-sectional view of the differential taken along cutting line 3-3.

[0012] Figure 4 is a flowchart showing an algorithm for controlling the differential. DETAILED DESCRIPTION

[0013] Embodiments of the present disclosure are described herein. However, it is to be understood that the disclosed embodiments are merely examples and other embodiments may take various and alternative forms. The drawings are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, the specific structural and functional details disclosed herein are not to be construed as limiting, but merely as a representative basis for teaching one skilled in the art to variously implement these embodiments. As will be understood by one of ordinary skill in the art, the various features shown and described with reference to any one of the drawings may be combined with features shown in one or more other drawings to produce embodiments not explicitly shown or described. Combinations of the features shown provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for a particular application or implementation.

[0014] Reference Figure 1 Vehicle 20 includes front wheels 22 and rear wheels 24. In the illustrated embodiment, the vehicle is rear-wheel drive, and the rear wheels 24 are powered by a powertrain including an engine, an electric motor, or a combination thereof. A drive shaft (not shown) can transmit the power generated by the powertrain to the rear wheels 24 via a differential 26 and a left half shaft 28 and a right half shaft 30. An accelerator pedal 40 allows a driver of the vehicle 20 to control the power output of the powertrain. The vehicle 20 can also be front-wheel drive, all-wheel drive, or four-wheel drive, in which case the front wheels can include an associated differential.

[0015] The vehicle 20 also includes a steering system for turning the front wheels 22. The illustrated rack and pinion steering system 33 can include a steering wheel 32 that rotates a steering shaft 34. Rotation of the steering shaft 34 is transmitted to the front wheels 22 via a steering rack 36 and tie rods 38 to turn the wheels 22 in response to rotation of the steering wheel 32. Other types of steering systems are known and can be used in the vehicle 20.

[0016] The vehicle 20 includes a controller 42. Although shown as one controller, the controller 42 can be part of a larger control system and can be controlled by various other controllers throughout the vehicle 20, such as a vehicle system controller (VSC). It should be understood that the controller 42 and one or more other controllers can be collectively referred to as a "controller" that controls various actuators in response to signals from various sensors to control functions, such as operating the powertrain, the front wheels 22, the rear wheels 24, the steering system 33, and the differential 26 (for example). Any reference to a "controller" in the claims refers to one or more controllers. The controller 42 can include a microprocessor or a central processing unit (CPU) in communication with various types of computer-readable storage devices or media. The computer-readable storage devices or media can include, for example, volatile and non-volatile storage devices such as read-only memory (ROM), random access memory (RAM), and keep-alive memory (KAM). KAM is persistent or non-volatile memory that can be used to store various operating variables when the CPU is powered down. The computer-readable storage devices or media can be implemented using any of a number of known memory devices, such as PROM (programmable read-only memory), EPROM (electronically erasable PROM), EEPROM (electrically erasable PROM), flash memory, or any other electronic, magnetic, optical, or combination memory device capable of storing data, some of which represent executable instructions used by the controller to control the engine or the vehicle.

[0017] The controller 42 communicates with various sensors and actuators via an input / output (I / O) interface, which can be implemented as a single integrated interface that provides various raw data or signal conditioning, processing, and / or conversion, short-circuit protection, and so on. Alternatively, one or more dedicated hardware or firmware chips can be used to condition and process specific signals before they are provided to the CPU. In the illustrated embodiment, each of the wheels includes a wheel speed sensor that communicates with the controller 42. Each wheel speed sensor outputs a signal indicative of the rotational speed of that wheel. The wheel speed sensors can be used to control an anti-lock braking system (ABS), a traction control system, and / or a stability control system. The steering system 33 also communicates electronically with the controller 42 to provide the controller 42 with a parameter indicative of the steering angle. For example, the steering shaft 34 can include an associated sensor 44 that measures the rotation of the steering shaft 34 and outputs a signal indicative of the steering angle. Alternatively, the steering angle can be inferred from other components such as the steering rack 36. The signal from the steering system can be used by the controller as a parameter indicative of the steering angle. The accelerator pedal 40 can include a sensor that measures the actuation of the pedal 40 and outputs a signal indicative of the accelerator pedal position to the controller 42. The controller 42 can use the pedal position signal to operate the differential 26, which will be described in more detail below. The vehicle 20 can include a display 46, such as a touchscreen radio head. The display 46 is configured to display information to the passengers of the vehicle 20 and can include capacitive touch elements that allow the driver to provide information to the controller 42. The vehicle 20 includes a speed sensor 92 that is configured to output a signal indicative of the vehicle speed to the controller.

[0018] The ABS can include hydraulic brakes (not shown) and a valve body (not shown) located at each wheel, and the valve body is used to independently control the fluid pressure to each brake. The valve body communicates electrically with the controller 42. The valve body can supply fluid pressure to the hydraulic brakes in response to the driver depressing the brake pedal, or the controller 42 can automatically apply the brakes without driver input. Each of the wheels can include a speed sensor (not shown) that communicates the respective wheel speed to the controller 42. The wheel speed sensors are used to determine whether the ABS needs to be activated.

[0019] The vehicle 20 can include a stability control system. The stability control system can include a plurality of sensors that are configured to measure vehicle acceleration, yaw, and other parameters. The controller 42 can be programmed to receive signals from the sensors and determine whether stability control is needed. During stability control, the controller 42 can reduce the powertrain torque delivered to each wheel and selectively apply the respective friction brakes.

[0020] Differential 26 is an electronically lockable differential that communicates with controller 42. Differential 26 includes an electronically actuated locker configured to lock left half shaft 28 and right half shaft 30 relative to each other when engaged and to permit relative rotation between half shafts 28 and 30 when disengaged. The locker communicates with controller 42 and locks differential 26 in response to a command from controller 42.

[0021] Many types of electronically lockable differentials are known and Figure 2 and Figure 3 only one exemplary differential 26 that can be used in vehicle 20 is shown. Differential 26 includes a housing (not shown) and a case 50 disposed within the housing. Case 50 is supported for rotation within the housing and is configured to receive power from a powertrain. Case 50 may support a pair of opposed first side gears 52 and second side gears 54 and a pair of opposed first spider gears 56 and second spider gears 58 that mesh with the side gears. A shaft 60 may interconnect spider gears 56, 58. First side gear 52 is configured to transfer torque to left half shaft 30 and second side gear 54 is configured to transfer torque to right half shaft 28. The half shafts may be splined to the side gears.

[0022] The electronically lockable differential 26 has: an unlocked state (disengaged) in which half shafts 28, 30 are permitted to rotate independently of each other; and a locked state (engaged) in which the half shafts are fixed against rotation relative to each other. The differential 26 can be placed in the locked state by fixing one of side gears 52, 54 to case 50 via an electronically actuated mechanism. Such a mechanism is commonly referred to as a locker.

[0023] Differential 26 includes an electronically controlled lock 62 configured to fix the axle gears 52 to the housing 50 when energized. In the illustrated embodiment, the lock 62 is a dog clutch. The lock 62 may include a locking ring 64 supported by an end cap 66. The end cap 66 is mounted to the housing 50. The end cap 66 defines a receiving area 68 for receiving the locking ring 64. The locking ring 64 defines an arm 70 configured to engage a post 72 of the end cap 66 to prevent rotation of the locking ring 64 relative to the housing 50 while allowing axial movement of the locking ring 64 relative to the axle gear 52. The locking ring 64 defines teeth 74 configured to engage teeth 76 formed on the back face of the axle gear 52. The differential 26 is locked by axially sliding the locking ring 64 into engagement with the axle gear 52 to fix the axle gear 52 to the housing 50. An electric coil 80 slides the locking ring 64 into the axle gear 52. The electric coil 80 is disposed adjacent the locking ring 64 on a rear hub 82 of the end cap 66. When energized, the electric coil 80 is magnetically attracted to the housing 50 and slides into engagement with a lever 84 supported within the end cap 66. The coil 80 rotates the lever 84, which in turn slides the locking ring 64 toward the axle gear 52 until the teeth 74 and 76 are engaged. The differential 26 is unlocked by de-energizing the electric coil 80. When the coil 80 is de-energized, a wave spring 86 may be used to push the locking ring 64 away from the axle gear 52.

[0024] For the lock 62 to lock, the teeth 76 of the axle gear 52 and the teeth 74 of the locking ring 64 must engage each other. The lock 62 relies on contact between the teeth 74, 76 to synchronize the speeds of the axle gear 52 and the locking ring 64 so that these teeth can fully engage. This is more likely to occur when the rotational speed difference (discrepancy) between the locking ring 64 and the axle gear 52 is below a threshold and low torque or no torque is being transmitted between the locking ring 64 and the axle gear 52. Excessive torque or speed differences can cause a ratcheting effect during the engagement process. The ratcheting effect causes wear on the teeth 74, 76, which reduces the life of the differential 26.

[0025] Vehicles equipped with an electronically lockable differential typically include a controller for monitoring vehicle speed and engine torque such that the differential is not commanded to lock when the vehicle speed or the torque of the powertrain exceeds a threshold. However, these typical checks may not be sufficient to prevent the ratcheting effect under all operating conditions of the vehicle.

[0026] Return to reference Figure 1, vehicle 20 includes an activation mechanism 90 used by a driver to request locking of the differential 26. The activation mechanism is located in the passenger compartment, such as on the instrument panel. The activation mechanism 90 can be a button, switch, knob, toggle switch, or capacitive touch element of the display 46. The activation mechanism 90 is in electronic communication with the controller 42 and is configured to output a differential lock signal. The controller 42 is programmed to receive the differential lock signal and set a flag. The controller 42 is further programmed to attempt to lock the differential whenever the flag is present, but to issue an engagement command to the lock 64 only when necessary vehicle operating conditions are verified. For example, the controller 42 will command the differential 26 to lock in response to the presence of the flag, the vehicle speed being less than a threshold, the pedal 40 being depressed less than a threshold, and the angle of the steering shaft 34 being less than a threshold. The controller 42 is also programmed to automatically unlock the differential 26 in the case where the vehicle speed exceeds a threshold such as 25 miles per hour (mph), regardless of the presence of the flag. (The speed threshold may be higher or lower than 25 mph.) If the differential 26 is unlocked due to excessive vehicle speed, the controller is programmed to re-engage the lock 62 once the speed drops below the threshold, in the presence of the flag and when other locking conditions are met.

[0027] Due to the vehicle speed cycling above and below the threshold, the differential 26 is particularly prone to ratcheting during the automatic re-engagement of the lock 62. Speed cycling typically occurs at turns where the driver decelerates to negotiate the turn and then accelerates upon leaving. When the vehicle is decelerating due to a turn, the vehicle speed and accelerator pedal conditions are typically below their respective thresholds. Thus, vehicle 20 relies on steering angle monitoring to prevent activation of the lock 62 during a turn, which can cause ratcheting of the dog clutch.

[0028] The controller 42 can be programmed to de-energize the lock 62 to allow independent rotation of the driven wheel 24 in response to the activation of the ABS and / or SCS. The controller 42 can be programmed to re-energize the lock 62 at the end of the ABS and / or SCS event. The ABS and SCS events can be activated and deactivated within a very short time window. This time window can be shorter than the disengagement time required for the lock. This causes the differential 26 to attempt to re-engage the partially engaged lock 62. Re-engaging the partially engaged lock 62 can cause damage to the teeth of the lock 62 and / or the side gear 52. To avoid this, the controller 42 can be programmed to have a time delay to reduce the likelihood of issuing an engagement command before the differential is fully disengaged. The time delay can be a predetermined calibratable value pre-programmed into the controller 42. In one or more embodiments, the time delay can have a value between 0.5 seconds and 2 seconds, including the end values.

[0029] The control logic or functions executed by controller 42 may be represented by flowcharts or similar diagrams in one or more of the figures. These diagrams provide representative control strategies and / or logic, which may be implemented using one or more processing strategies, such as event-driven, interrupt-driven, multitasking, multithreading, etc. Thus, the various steps or functions shown may be executed in the order shown, executed in parallel, or in some cases may be omitted. Although not always explicitly stated, one of ordinary skill in the art will recognize that one or more of the steps or functions shown may be repeated depending on the particular processing strategy used. Similarly, the order of processing is not necessarily required to implement the features and advantages described herein, but is provided for ease of illustration and description. The control logic may be implemented primarily in software executed by a microprocessor-based vehicle, engine, and / or powertrain controller, such as controller 42. Of course, depending on the particular application, the control logic may be implemented in software, hardware, or a combination of software and hardware in one or more controllers. When implemented in software, the control logic may be provided on one or more computer-readable storage devices or media having stored data representing code or instructions executed by a computer to control the vehicle or its subsystems. The computer-readable storage device or media may include one or more of a variety of known physical devices that utilize electrical, magnetic, and / or optical storage to hold executable instructions and associated calibration information, operating variables, etc.

[0030] Figure 4 is a flowchart 100 of an algorithm for controlling the operation of the lock 62. The algorithm begins at operation 102 when the driver requests a differential lock, i.e., the vehicle is in the differential lock mode. The driver may request the differential lock mode by actuating an activation mechanism. At operation 104, the controller sets a flag in response to receiving the request to lock the differential. At operation 106, the controller determines whether the flag exists. If not, control transfers to operation 108 and the differential lock mode is exited. (The flag may remain valid until the driver actuates the activation mechanism again.) If so, control transfers to operation 110, and the controller determines whether the differential is currently locked. If the differential is not currently locked at operation 110, control transfers to operation 112 and the controller determines whether a lock condition exists. For example, the controller may determine that the vehicle speed is less than a threshold, the accelerator pedal position is less than a threshold, and the steering angle is less than a threshold. If all of these conditions are met, control transfers to operation 114, and the controller issues a lock command to the differential. The lock command may include sending power to a coil to engage the lock.

[0031] Once locked, the disengagement conditions of the differential are monitored. Algorithm 100 includes operation 116 for monitoring whether there is a disengagement condition. The disengagement condition may include the vehicle speed exceeding a threshold. If there is a disengagement condition at operation 116, control transfers to operation 118 and the differential is commanded to unlock. The differential can be commanded to unlock by de-energizing the coil to allow the return spring to disengage the lock. If there is no disengagement condition at operation 116, control transfers to operation 120.

[0032] At operation 120, the controller determines whether the ABS or SCS is activated. If so, control transfers to operation 122 and the controller commands the differential to unlock. At operation 124, the controller starts a timer to prevent automatic relocking of the differential for a desired period of time. Once the timer is started at operation 124, the controller periodically determines at operation 126 whether the timer has expired. Once the timer expires, control transfers to operation 106, and the controller determines whether the flag is still valid. The controller continuously executes algorithm 100 at a frequency such as every 500 milliseconds, and will continuously attempt to lock the differential as long as the flag is set as shown in operation 106, and will command the differential to lock if the locking condition is met at operation 112.

[0033] If the locking condition is not met at operation 112, the controller will not issue a locking command. And the controller will wait to lock the differential until the locking condition of operation 112 is satisfied.

[0034] While the above describes exemplary embodiments, it does not mean that these embodiments describe all possible forms covered by the claims. The words used in the specification are descriptive rather than restrictive, and it should be understood that various changes can be made without departing from the spirit and scope of the present disclosure. As previously mentioned, the features of various embodiments can be combined to form other embodiments of the invention that may not be explicitly described or illustrated.

[0035] According to the present invention, there is provided a vehicle having: an anti-lock braking system (ABS); a stability control system (SCS); an electronically lockable differential; and a controller programmed to: unlock the differential in response to activation of the ABS or SCS, and prohibit locking of the differential for a predefined period of time in response to deactivation of one of the ABS and the SCS that is activated.

[0036] According to one embodiment, the controller is further programmed to command locking of the differential in response to expiration of the predefined period of time.

[0037] According to one embodiment, the controller is further programmed to command locking of the differential in response to a request to lock the differential and satisfaction of an engagement condition.

[0038] According to one embodiment, the controller is further programmed to command locking of the differential in response to a request to lock the differential, satisfaction of an engagement condition, and expiration of the predefined time period.

[0039] According to one embodiment, the engagement condition includes a steering angle less than a threshold.

[0040] According to one embodiment, the time period begins when one of ABS and SCS that is activated is deactivated.

[0041] According to one embodiment, the time period is from 0.5 seconds to 2 seconds, inclusive of the end values.

[0042] According to the present invention, there is provided a vehicle having: an anti-lock braking system (ABS); a stability control system (SCS); a locking differential including an electronic control lock configured to lock the differential; and a controller programmed to energize the lock to lock the differential in response to (i) a vehicle speed less than a threshold, (ii) an accelerator pedal position less than a threshold, and (iii) a steering angle less than a threshold, de-energize the lock to unlock the differential in response to activation of at least one of ABS and SCS, and prohibit energization of the lock for a predefined time period in response to deactivation of one of ABS and SCS that is activated.

[0043] According to one embodiment, the controller is further programmed to re-energize the lock to lock the differential in response to expiration of the time.

[0044] According to one embodiment, the controller is further programmed to re-energize the lock to lock the differential in response to (i) expiration of the time, (ii) a request to lock the differential, and (iii) satisfaction of an engagement condition.

[0045] According to one embodiment, the engagement condition includes a steering angle less than a threshold.

[0046] According to one embodiment, the lock includes an electric coil.

[0047] According to one embodiment, the time period begins when one of ABS and SCS that is activated is deactivated.

[0048] According to one embodiment, the time period is from 0.5 seconds to 2 seconds, inclusive of the end values.

[0049] According to one embodiment, a further feature of the above invention is: an activation mechanism configured to send a differential lock signal to the controller, and wherein the driver requests locking of the differential via the activation mechanism.

[0050] According to the present invention, a method of controlling an electronically lockable differential includes: locking the differential in response to the presence of an engagement condition; unlocking the differential in response to the activation of at least one of an anti-lock braking system (ABS) and a stability control system (SCS); and prohibiting locking of the differential for a predefined time period that begins in response to the deactivation of the one of the ABS and the SCS that is activated.

[0051] According to one embodiment, a further feature of the above invention is that the differential is relocked in response to the expiration of the time period.

[0052] According to one embodiment, a further feature of the above invention is that the differential is relocked in response to (i) the expiration of the time and (ii) satisfaction of the engagement condition.

[0053] According to one embodiment, the engagement condition includes a steering angle less than a threshold.

[0054] According to one embodiment, the time period is from 0.5 seconds to 2 seconds, inclusive.

Claims

1. A vehicle, which comprises: an anti-lock braking system (ABS); a stability control system (SCS); an electronically lockable differential; and a controller configured to: unlock the differential in response to activation of the ABS or the SCS, and prohibit locking of the differential within a predefined time period in response to deactivation of one of the ABS and the SCS that is activated.

2. The vehicle according to claim 1, wherein the controller is further configured to command locking of the differential in response to expiration of the predefined time period.

3. The vehicle according to claim 1, wherein the controller is further configured to command locking of the differential in response to a request to lock the differential and satisfaction of an engagement condition.

4. The vehicle according to claim 1, wherein the controller is further configured to command locking of the differential in response to a request to lock the differential, satisfaction of an engagement condition, and expiration of the predefined time period.

5. The vehicle according to claim 4, wherein the engagement condition includes that the steering shaft angle is less than a threshold.

6. The vehicle according to claim 1, wherein the predefined time period starts when one of the ABS and the SCS that is activated is deactivated.

7. The vehicle according to claim 1, wherein the predefined time period is from 0.5 second to 2 seconds, including the end values.

8. A vehicle, which comprises: an anti-lock braking system (ABS); a stability control system (SCS); a lockable differential including an electronically controlled lock configured to lock the differential; and a controller configured to: energize the lock to lock the differential in response to (i) the vehicle speed being less than a threshold, (ii) the accelerator pedal position being less than a threshold, and (iii) the steering angle being less than a threshold, de-energize the lock to unlock the differential in response to activation of at least one of the ABS and the SCS, and prohibit energizing of the lock within a predefined time period in response to deactivation of one of the ABS and the SCS that is activated.

9. The vehicle according to claim 8, wherein the controller is further configured to re-energize the lock to lock the differential in response to expiration of the predefined time period.

10. The vehicle according to claim 8, wherein the controller is further configured to re-energize the lock to lock the differential in response to (i) expiration of the predefined time period, (ii) a request to lock the differential, and (iii) satisfaction of an engagement condition.

11. The vehicle according to claim 10, wherein the engagement condition includes that the steering shaft angle is less than a threshold.

12. The vehicle according to claim 8, wherein the lock includes an electric coil.

13. The vehicle according to claim 8, wherein the predefined time period starts when one of the ABS and the SCS that is activated is deactivated.

14. The vehicle according to claim 8, wherein the predefined time period is from 0.5 second to 2 seconds, including the end values.

15. The vehicle according to claim 8, further comprising an activation mechanism configured to send a differential lock signal to the controller, and wherein the driver requests locking of the differential via the activation mechanism.

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