VEHICLE-WHEEL SEPARATION AND ASSOCIATED TAX PROCEDURE

Abstract

Vehicle that includes the following: a differential (24) which has an input shaft (44), a first axle shaft (60) and a second axle shaft (62), a first wheel (26) which is rigidly coupled to the first axle shaft (60), a second wheel (28) which is selectively coupled to the second axle shaft (62) by a clutch (30), a power output unit (PTU, 18) configured to selectively couple a rear axle gearbox (12) with a drive shaft (20), a rear drive unit (RDU, 22) configured to selectively couple the drive shaft (20) with the differential input shaft (44), characterized by a control device (32) that is programmed to respond to a request to enter an all-wheel drive (AWD) mode by The clutch (30) and the power output unit (18) engage only if the ratio of the rotational speed of the differential input shaft (44) to the rotational speed of the first axle shaft (60) is less than a first threshold value, and Inhibiting the engagement of the clutch (30) and the power output unit (18) if the ratio exceeds the first threshold.

Description

TECHNICAL AREA

[0001] The present disclosure relates to the field of vehicle powertrain control devices. STATE OF THE ART

[0002] Two vehicle powertrain configurations dominate the modern passenger car market: rear-wheel drive (RWD) and front-wheel drive (FWD). With additional components, these two configurations can be adapted to direct power to all four wheels. Since traction at any one wheel may be limited at certain times, the ability to direct power to all four wheels improves mobility. However, the additional components introduce extra friction losses, increasing fuel consumption even under conditions that do not require this capability.

[0003] In a typical rear-wheel-drive configuration, the engine is longitudinally oriented within the vehicle, so that the crankshaft axis aligns with the direction of vehicle movement. A transmission mounted on the engine drives a rear driveshaft at a speed that may be lower or higher than the engine's crankshaft speed, depending on the vehicle's current requirements. The rear driveshaft connects to a rear axle, which reverses the axis of rotation, reduces the speed, and drives a left and right rear axle, while allowing for slight speed differences between the axles when the vehicle turns. A rear-wheel-drive configuration can be adapted to also drive the front wheels by adding a transfer case between the transmission and the rear driveshaft.In addition to driving the rear driveshaft, the transmission housing drives a front driveshaft, which in turn drives a front axle. Some transmission housings incorporate a planetary gear set that shares torque between the front and rear driveshafts while allowing slight speed differences. Other transmission housings have a torque-on-demand (TOD) clutch that drives the front driveshaft only under specific conditions, such as when a control device detects a loss of traction at the rear wheels.

[0004] In a typical front-wheel-drive configuration, the engine is mounted transversely in the vehicle so that the crankshaft axis aligns with the wheels' axis of rotation. A transmission mounted to the engine drives a front differential at a speed appropriate for the current vehicle requirements. The front differential is typically integrated into a common housing with the transmission. The front differential drives a left and right front axle, while allowing slight differences in rotational speed between the axles as the vehicle corners. A front-wheel-drive configuration can be adapted to also drive the rear wheels by adding a power take-off unit (PTU) that drives a rear driveshaft at a speed proportional to the rotational speed of the front differential.A rear drive unit (RDU) typically has a TOD clutch which, when engaged, drives a rear differential which in turn drives a left and right rear axle.

[0005] German patent application DE 10 2009 005 378 A1 discloses a drivetrain for a motor vehicle with a permanently driven primary axle, wherein the drivetrain has a torque transmission section for driving a secondary axle. The torque transmission section is generally to be kept in a disengaged state, even in an automatic four-wheel drive mode, and is only coupled to the secondary axle in a rotationally fixed manner by closing the second clutch when wheel slip is detected on the primary axle.

[0006] German patent application DE 10 2013 106 644 A1 discloses a control system for a vehicle drivetrain in which a clutch connecting a differential output to a wheel is disengaged and a differential component is rotated through a lubrication sump. This minimizes parasitic losses in the AWD system.

[0007] Document US 2014 / 0190758 A1 discloses a motor vehicle and a method for controlling the motor vehicle with a drivetrain for connecting the drive unit to a first and second group of wheels, such that the first group can be driven by the drive unit when the drivetrain is in a first operating mode, and the second group can additionally be driven by the drive unit when the drivetrain is in a second operating mode. For this purpose, the drivetrain includes an auxiliary section in which a first detachable torque transmission means is operable to allow slippage between input and output sections, thereby modulating the amount of transmitted torque. SUMMARY OF THE REVELATION

[0008] The object of the present invention is to create a vehicle powertrain configuration in which power can be directed to all four wheels, while avoiding interference losses.

[0009] The problem is solved with a vehicle having the features of independent claim 1.

[0010] A vehicle comprises a differential, first and second wheels, and a control device. The first wheel is stationary and coupled to a first axle shaft. The second wheel is selectively coupled to a second axle shaft via a clutch. To reduce noise losses, the control device disengages the clutch to decouple the second wheel from the second axle shaft while the vehicle is in front-wheel-drive mode. In response to a request to engage all-wheel-drive mode, the control device engages the clutch if the ratio of a differential input speed to a first axle shaft speed is less than a first threshold. If the ratio exceeds the first threshold, the control device prevents the clutch from engaging. The differential may also include a temperature sensor.The control unit can prevent the clutch from engaging if the temperature sensor indicates a temperature exceeding a second threshold. If the temperature then drops below the second threshold, the control unit can engage the clutch. If the temperature remains above the second threshold for more than a predetermined duration, the control unit may not engage the clutch, even if the temperature does not drop below the second threshold. The control unit can display a message to the driver when it prevents the clutch from engaging, either because the temperature exceeds the first threshold or because the temperature exceeds the second threshold. The control unit can also prevent the engagement of a power output unit.

[0011] A method for operating a vehicle involves disengaging a clutch in a front-wheel-drive mode and engaging the clutch in response to a request to switch to an all-wheel-drive mode only under specified conditions. Clutch disengagement disconnects a rear wheel from a first rear axle. Clutch engagement is prevented if the ratio of a rear differential input speed to a second rear axle speed exceeds a first threshold. Clutch engagement is also prevented if a differential fluid temperature exceeds a threshold. The control device may also display a message to the driver. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic representation of a vehicle powertrain. Fig. Figure 2 is a schematic cross-sectional representation of a rear differential designed for use in the drivetrain of the Fig. 1 is suitable. Fig. Figure 3 is a flowchart showing state transitions for the operation of the vehicle's powertrain. Fig. 1 indicates. Fig. 4 is a flowchart that shows a process for performing the security check in the flowchart of the Fig. 3 illustrated. DETAILED DESCRIPTION

[0012] Embodiments of the present disclosure are described here. It is understood, however, that the disclosed embodiments are merely examples and that other embodiments may take diverse and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed here should not be interpreted as limiting, but merely as a representative basis for teaching a person skilled in the art how the present invention can be used in various ways.It is obvious to a person skilled in the art that various features illustrated and described with reference to any of the figures can be combined with features illustrated in one or more other figures to create embodiments not explicitly shown or described. The combinations of illustrated features provide representative embodiments for typical applications. However, various combinations and modifications of the features, corresponding to the teachings of this disclosure, may be desirable for specific applications or implementations.

[0013] Fig. Figure 1 schematically illustrates an all-wheel-drive vehicle powertrain. The thick lines indicate the flow of mechanical power, while the dashed lines indicate the flow of information. An internal combustion engine 10 generates mechanical power by converting stored chemical energy into a fuel source. The rear axle transmission 12 adjusts the speed and torque of the mechanical power generated by the engine to meet the current requirements of the vehicle. The rear axle transmission 12 has a multi-speed gearbox and also a front differential that provides approximately equal torque to the left and right front wheels 14 and 16, while accommodating slight differences in speed, such as when the vehicle is cornering. A power output unit (PTU) 18 selectively drives the output of the rear axle transmission's multi-speed gearbox to the drive shaft 20.The rear drive unit (RDU) 22 selectively transmits power from the drive shaft 20 to the rear differential 24. The rear differential 24 transmits approximately equal torque to the left and right rear wheels 26 and 28, while accommodating slight differences in rotational speed. The wheel end separator 30 has a controlled clutch that selectively engages or disengages the right rear wheel 28 from the corresponding side of the rear differential 24.

[0014] The wheel end disconnect 30 and the PTU disconnect can be synchronizing devices incorporating friction clutches with sufficient torque capacity to bring the components to the same rotational speed before a positive-locking dog clutch is engaged. Alternatively, one of them can be a dog clutch only, and the RDU clutch can be used to synchronize the rotational speeds before engagement. Alternatively, engagement can be limited to times when the vehicle is stationary.

[0015] The control device 32 adjusts the state if multiple components, including the PTU 18, RDU 22, and the wheel end disconnect 30, are involved. Specifically, when the vehicle is in front-wheel drive (FWD) mode, the control device 32 signals the PTU 18 to disconnect the drive shaft 20 from the rear axle differential 12 and signals the wheel end disconnect 30 to disconnect the right rear wheel from the rear differential 24. This allows the drive shaft to remain stationary while the vehicle moves, reducing rolling resistance associated with drive shaft rotation and improving fuel economy. When the vehicle is in all-wheel drive (AWD) mode, the control device signals the PTU 18 and the wheel end disconnect 30 to connect the corresponding components in a driveable manner.The control device 32 then monitors vehicle traction and signals the RDU 22 to transfer power from the drive shaft 20 to the rear differential 24 when it detects a dip in traction at the front wheels. The control device 32 can also signal the RDU 22 to execute this power flow path before maneuvers that are likely to cause a loss of front-wheel traction. The control device 32 can receive input signals from other components, such as the PTU 18, RDU 22, and the rear differential 24. The control device 32 can be an autonomous drive shaft control device and can be integrated into another control device, such as a rear axle differential control device or a powertrain control device.

[0016] Fig. Figure 2 illustrates the structure of the rear differential 24. The differential is enclosed in a housing 40. In vehicles with independent rear suspension, the housing 40 is attached to the vehicle structure. In vehicles with a rigid rear axle, the housing 40 is sprung and moves with the axles. The housing does not rotate in either vehicle type. The housing 40 is partially filled with fluid that provides lubrication for moving components and convects heat generated by friction between the components to the housing, from where the heat is dissipated. The temperature sensor 42 sends an electronic signal to the control device indicating the temperature of the fluid.

[0017] Power enters the rear differential from the RDU via the stub shaft 44, which is attached to the drive pinion 46. The drive pinion 46 is constantly engaged with the ring gear 48. The axes of rotation of the pinion 46 and the ring gear 48 are offset by 90 degrees. They can also be vertically offset, in which case the geometry of the hypoid gear is conventional. The ring gear 48 is fixed to the differential carrier 50. A number of planetary shafts 52 are attached to the inside of a differential carrier 50. A number of bevel gear sets are mounted for rotation relative to each of the planetary shafts. Alternatively, the planetary gears could be mounted on the planetary shafts, and the planetary shafts could rotate relative to the carrier. Each of the bevel gear sets 54 engages with a left-hand side gear 56 and a right-hand side gear 58.The left side wheel is attached to a left axle shaft 60, while the right side wheel is attached to a right axle shaft 62.

[0018] When the vehicle travels in a straight line with the wheel end separator 30 engaged, the differential carrier 50, the left axle shaft 60, and the right axle shaft 62 rotate at the same speed in the same direction. In this condition, there is no movement between the planet gears 54, the side gears 56 and 58, and the planet shafts 52. The stub shaft 44 rotates at a speed proportional to the speed of the differential carrier 50, the ratio depending on the number of teeth of the gear set 46 and the ring gear 48. When the vehicle turns left, the axle shaft 60 rotates slightly slower than the differential carrier 50, and the right axle shaft 62 rotates slightly faster than the differential carrier 50. The planet gears 54 rotate about planet shafts 52 at a speed proportional to the speed difference between the left axle 60 and the right axle 62.The speed sensors 64 and 66 send electronic signals to the control unit indicating the rotational speeds of the left axle shaft 60 and the right axle shaft 62, respectively. Due to the rotational speed relationships between the components, two sensors are sufficient to calculate the rotational speeds of all rotating components within the differential. Alternatively, one or both speed sensors could detect the rotational speed of a different component, and the control unit could calculate the rotational speed of each axle shaft based on these rotational speed relationships.

[0019] When the wheel end separation 30 is engaged, the rotational speed of the left axle shaft 60 is proportional to the vehicle speed, but the rotational speeds of the other components are determined by disturbance rolling resistance. Since the rolling resistance is generally greater on components associated with the differential carrier 50 than the rolling resistance on components associated with the right axle 62, the carrier 50 is stationary. With the differential carrier 50 stationary, the right axle shaft rotates at the same speed as the left axle shaft, but in the opposite direction. The planet gears 54 rotate relative to the planet shafts 52 at speeds that are much higher than during connected speed differential. This condition can also be maintained for much longer periods than the duration of turning maneuvers.

[0020] During this operation at high relative planetary gear speed, some heat is generated by friction between the planet gears and the planet shafts. If fluid flows past this surface, the amount of heat generated is significantly reduced due to the lubricating effect, and this heat is effectively removed from the area by the fluid's movement. However, if fluid does not flow past this interface for any reason, a large amount of heat is generated, making the components near the interface extremely hot. If the relative movement ceases, for example, because the vehicle temporarily stops, the planetary gears can effectively weld to the planetary shafts. The fluid flow can be interrupted for several reasons. If there is a leak in housing 40, the fluid volume will decrease.The differential carrier 50 can stop in a position where one of the planetary shafts and the corresponding planetary pinion are above the fluid level.

[0021] If this welding phenomenon occurs, the differential carrier 50, the left axle shaft 60, and the right axle shaft 62 are forced to rotate at the same speed. If the wheel end disconnect 30 is disengaged, this results in a slight increase in the rolling resistance, which does not seriously impair the vehicle's operation. However, if the wheel end disconnect 30 is engaged, the left rear wheel 26 is forced to rotate at the same speed as the right rear wheel 28. In this condition, one or both wheels may lose traction when the vehicle turns, which could result in understeer or oversteer.

[0022] The Fig. 3 and Fig. Figure 4 illustrates a procedure for avoiding vehicle handling effects if the differential fails during differential engagement. When the driver selects front-wheel drive mode, the vehicle operates in FWD mode at 70. The driveshaft is disconnected at both the PTU and the wheel end to reduce disturbance driving resistance. The RDU clutch is disengaged. While operating in this mode, a timer is set to expire at regular intervals, such as every 90 seconds. When the timer expires, or when the driver requests engagement of all-wheel drive, the control unit performs a safety check at 72. The details of performing this safety check are discussed below. Three safety check outcomes are possible.If the differential appears to be differentially differentially engaged correctly, but the fluid temperature indicates a risk of failure, the safety check sends a "Warning" message, and the control unit remains in FWD mode. If the safety check indicates that the differential is unsafe, a message is displayed to the driver at 74, and the control unit enters fault mode at 76. In fault mode, the driveshaft disconnects, and the RDU continues to operate to provide front-wheel drive only. The control unit does not exit fault mode until service is performed and the control unit is manually reset. If the safety check indicates that the differential is operating normally, the control unit checks at 78 whether AWD is selected. If AWD is not selected, meaning the safety check was triggered by the timer, the control unit remains in FWD mode.The safety check may not correctly detect an unsafe condition when the vehicle is stationary. Regularly performing the safety check while the vehicle is in motion ensures that an unsafe condition is detected, even if the driver requests AWD while the vehicle is stationary. Performing the safety check at regular intervals also provides an opportunity to repeat the check if a previous one returned a warning. If AWD is selected, the control unit engages the disengagements at 80 and engages AWD mode at 82. In AWD mode, the rear differential lock (RDU) engages when front wheel slip is detected to transfer some engine power to the rear wheels.The RDU can also be activated preventively in conditions that are likely to cause front wheel slippage, such as a rapid increase in the power demanded by the rider.

[0023] Fig.Section 4 specifies how the safety check is performed. At 90, the control device calculates the rotational speed of the differential carrier and wheel 26. At 92, the control device calculates the ratio of the wheel rotational speed to the carrier rotational speed. Under normal operating conditions, the wheel rotational speed would be zero, so the ratio should be zero. If the differential fails during differential operation, the ratio is one. At 94, the control device compares the ratio to a calibratable threshold. If the ratio is lower than the calibratable threshold, the safety device sends "Unsafe". If the ratio is higher than the threshold, the control device proceeds to check the fluid temperature at 96. If the temperature is below a second calibratable threshold, the control device resets a counter at 98 to zero and sends "Safe".If the temperature is above the second threshold, the controller increments the counter to 100. Then, if the counter reaches 102 and is less than a third calibratable threshold, the controller sends a "Warning" message. If the counter is equal to the third threshold, indicating that the fluid temperature has remained above the second threshold for an extended period, the controller sends an "Unsafe" message.

[0024] Although exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms covered by the claims. The terms used in the description serve to describe rather than to limit the scope, and it is understood that various modifications can be made without departing from the intent and scope of the disclosure. As described above, the features of the various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. Although various embodiments may be described in such a way that they provide advantages over other embodiments or implementations according to the prior art with respect to one or more desirable characteristics,The average person skilled in the art understands that compromises can be made with regard to one or more features or parameters in order to achieve required properties of the overall system, which depend on the specific application and implementation. Therefore, embodiments that have been described as less desirable with regard to one or more features than other embodiments or implementations according to the prior art are not outside the scope of protection of the disclosure and may be desirable for specific applications.

Claims

[1] Vehicle comprising the following: a differential (24) which has an input shaft (44), a first axle shaft (60) and a second axle shaft (62), a first wheel (26) which is rigidly coupled to the first axle shaft (60), a second wheel (28) which is selectively coupled to the second axle shaft (62) by a clutch (30), a power output unit (PTU, 18) configured to selectively couple a rear axle gearbox (12) with a drive shaft (20), a rear drive unit (RDU, 22) configured to selectively couple the drive shaft (20) with the differential input shaft (44), characterized by a control device (32) that is programmed to respond to a request to enter an all-wheel drive (AWD) mode by The clutch (30) and the power output unit (18) engage only if the ratio of the rotational speed of the differential input shaft (44) to the rotational speed of the first axle shaft (60) is less than a first threshold value, and Inhibiting the engagement of the clutch (30) and the power output unit (18) if the ratio exceeds the first threshold.

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