1. Field of the Invention
The present invention relates to drive systems for motor vehicles in general, and more specifically, a vehicular drive system including a fluidly actuated friction clutch assembly actuated with a fluid pump integrated with one of hydraulic systems of the motor vehicle.
2. Description of Related Art
Differential assemblies are arranged in the power transmission system of a motor vehicle to allow a pair of output shafts operatively coupled to an input shaft to rotate at different speeds, thereby allowing the wheel associated with each output shaft to maintain traction while the vehicle is turning. The differential distributes the torque provided by the input shaft between a first and second output shaft. The most basic and common type of differential is known as an open differential.
Although open differentials may be adequate for most driving conditions, they are generally unsuitable for slippery conditions where one wheel experiences a much lower coefficient of friction than the other wheel. If one wheel of a vehicle is located on a patch of ice or mud and the other wheel is on dry pavement, the wheel experiencing the lower coefficient of friction loses traction. If even a small amount of torque is directed to the wheel without traction, the torque will cause the wheel to “spin out”. Since the maximum amount of torque that can be developed on the wheel with traction is equal to torque on the spinning wheel without traction, the engine is unable to develop any torque and the wheel with traction is unable to rotate. The spin out results in an overspeed of the shaft associated with the spinning wheel (the first shaft) relative to the shaft associated with the wheel with traction (second shaft). To address this problem, a differential has been developed that limits the rotational speed of first shaft relative to the speed second shaft so that torque is directed to the shaft associated with the wheel that has traction (the second shaft). Such differential assemblies are typically called limited slip differentials.
Limited slip differentials can be used in front or rear axle drive systems. In addition to limiting slip by reducing the difference between the speed of two wheels (shafts) on a common axle, limited slip differentials can also be used in other clutch-type applications that require torque to be selectively transferred from an input shaft to a single output shaft. For example, a limited slip differential can be used in the driveline between the front and rear axles.
Limited slip differentials can be either actively or passively controlled. In a passively controlled limited slip differential, when the first output shaft begins to overspeed, force from the input shaft is automatically redirected from the first output shaft to the second output shaft, thereby retarding the speed of the first shaft and redirecting the torque to the second shaft. Actively controlled differential systems control the amount of torque directed to each of the output shafts based on the configuration and programming of the actively controlled system. When the relative rotational speed of a first shaft exceeds a pre-determined threshold, a variable amount of hydraulic pressure is directed to a multi-disc clutch pack within the actively controlled differential. The variable pressure applied to the clutch pack allows a selective amount of engagement between the input shaft and the output shafts associated with each wheel so that the rotational speed of the overspeeding first shaft is retarded and torque is directed to the second shaft.
Hydraulic power to engage the clutch pack can be generated in various ways including a specially dedicated remotely located hydraulic pump powered by the engine, or through a pumping system that is integral with the differential, such as a gerotor pump. However, both of these types of designs increase the complexity of the system and expenditures on materials.
The need exists for an apparatus that utilizes an existing hydraulic system to provide the hydraulic pressure to an active differential controller. The current invention integrates the differential control mechanism with one of hydraulic systems of the motor vehicle exterior to the limited slip differential. This design significantly reduces overall system complexity and cost, and increases system control capability.