An electromagnetic clutch assembly may include a first clutch plate, a second clutch plate, and a synchronizer. The second clutch plate may define an aperture. A portion of the synchronizer may be configured to extend through the aperture. In the absence of a magnetic field, the first clutch plate and the first surface of the second clutch plate may define an air gap and the portion of the synchronizer may extend into the air gap. In response to a first magnetic field, the portion of the synchronizer may contact the first clutch plate. In response to a second magnetic field, the portion of the synchronizer may translate in the aperture toward the second clutch plate and the first clutch plate and the second clutch plate may close the air gap.

A method of operating a vehicle drivetrain for rocking the vehicle free. The drivetrain has a transmission with an input and an output that can be coupled by a clutch. The input and output are connected to a drive aggregate and a drive output, respectively. The clutch is actuated based on driver actuation of an accelerator and a rotational speed of the drive output such that following accelerator actuation, when its actuation decreases, the clutch disengages with a first opening gradient. Then, based on a calculated point in time at which drive aggregate torque upon the clutch corresponds to torque on the clutch from the drive output, the clutch disengages with a second, smaller opening gradient. And depending on a rotational speed of the drive output relative to a limit value, the clutch either initiates or terminates engagement with a first closing gradient.

Methods and systems are provided for operating a vehicle that may be propelled via a primary axle and a secondary axle. In one example, a propulsion source of a secondary axle may be decoupled from at least one wheel via a dog clutch that includes teeth. The dog clutch may be disengaged in a way that reduces driveline noise and may reduce a possibility of driveline degradation.

Embodiments of the present invention provide an electric machine control system for a vehicle, the electric machine control system comprising one or more controllers, wherein the vehicle comprises an electric machine arranged to be selectively coupleable to provide torque to at least one wheel of an axle of the vehicle, the control system comprising input means arranged to receive a speed signal (410) indicative of a speed of the vehicle and a status signal (470) indicative of a status of a coupling of the electric machine to the at least one wheel of an axle of the vehicle, output means (340) arranged to output a coupling signal to control coupling of the electric machine to the at least one wheel of the axle, and processing means arranged to determine (1210) a coupling state of the electric machine to the at least one wheel of the axle and to control the output means to output (1220) a coupling signal indicative of the determined coupling state, wherein the processing means is arranged, in dependence on the status signal being indicative of a failure (1230) to change the coupling state of the electric machine to the at least one wheel of the axle in dependence on a change in the determined coupling state, to control the output means to output the coupling signal (345) indicative of a retry (1250) of the change in the coupling state in dependence on the speed signal.

An electromagnetic clutch assembly may include a first clutch plate, a second clutch plate, and a synchronizer. The second clutch plate may define an aperture. A portion of the synchronizer may be configured to extend through the aperture. In the absence of a magnetic field, the first clutch plate and the first surface of the second clutch plate may define an air gap and the portion of the synchronizer may extend into the air gap. In response to a first magnetic field, the portion of the synchronizer may contact the first clutch plate. In response to a second magnetic field, the portion of the synchronizer may translate in the aperture toward the second clutch plate and the first clutch plate and the second clutch plate may close the air gap.

Controlling a clutch by means of an actuator, wherein at least one first shaft can be torque-transmittingly connected to a second shaft by means of the clutch, the clutch in one of at least three states, where in an disengaged first state, a torque cannot be transmitted, in a second state, a torque can be transmitted such that the speeds of the first shaft and the second shaft are synchronized in the second state, and in an engaged third state, a required torque can be transmitted; wherein, in various states and in an operating mode associated with the particular state, the actuator is adjusted at a different speed in order to adjust the clutch.

A method of operating a vehicle drivetrain for rocking the vehicle free. The drivetrain has a transmission with an input and an output that can be coupled by a clutch. The input and output are connected to a drive aggregate and a drive output, respectively. The clutch is actuated based on driver actuation of an accelerator and a rotational speed of the drive output such that following accelerator actuation, when its actuation decreases, the clutch disengages with a first opening gradient. Then, based on a calculated point in time at which drive aggregate torque upon the clutch corresponds to torque on the clutch from the drive output, the clutch disengages with a second, smaller opening gradient. And depending on a rotational speed of the drive output relative to a limit value, the clutch either initiates or terminates engagement with a first closing gradient.

A control device is mountable on a four-wheel drive vehicle including a main drive wheel and an auxiliary drive wheel, and is configured to control a drive force transmission device configured to transmit a drive force to the auxiliary drive wheel. The control device includes a processor and a memory storing a program, when executed by the processor, to cause the control device to change a control characteristic of the drive force transmission device that indicates a relationship between a vehicle state of the four-wheel drive vehicle and a drive force transmitted to the auxiliary drive wheel in response to an input from the input device.

An electromagnetic clutch assembly may include a first clutch plate, a second clutch plate, and a synchronizer. The second clutch plate may define an aperture. A portion of the synchronizer may be configured to extend through the aperture. In the absence of a magnetic field, the first clutch plate and the first surface of the second clutch plate may define an air gap and the portion of the synchronizer may extend into the air gap. In response to a first magnetic field, the portion of the synchronizer may contact the first clutch plate. In response to a second magnetic field, the portion of the synchronizer may translate in the aperture toward the second clutch plate and the first clutch plate and the second clutch plate may close the air gap.

A friction engagement element control system is provided, which includes a friction engagement element including friction plates, which are an input-side friction plate and an output-side friction plate, and an actuation system configured to engage the input-side friction plate with the output-side friction plate with a pushing force, the friction plates having a characteristic in which a friction coefficient thereof decreases as a rotational difference between the friction plates increases. The device includes a controller configured to control the pushing force so that the negative slope characteristic becomes a positive slope characteristic in which a frictional force of the friction engagement element decreases as the rotational difference decreases, when engaging the friction engagement element.