Brakes – Elements – Cooling and lubricating
Reexamination Certificate
1999-07-19
2004-02-17
Rodriguez, Pam (Department: 3683)
Brakes
Elements
Cooling and lubricating
C188S267100, C188S267200, C482S903000
Reexamination Certificate
active
06691839
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention generally relates to a reduced drag wet disc brake system and more particularly to a reduced drag wet disc brake system that uses a fluid with a viscosity that can be changed to achieve desired braking characteristics.
Braking systems in vehicles are used to reduce the speed of a moving vehicle or to bring the vehicle to a stop. To reduce the vehicle's speed or bring the vehicle to a stop, a force must be exerted to overcome the force of the engine and the inertia of the vehicle. Braking systems produce the needed force. Several types of known braking systems are used on vehicles, including, but not limited to, dry disc brakes and wet disc brakes.
A dry disc brake system for a single wheel on a vehicle essentially consists of a disc connected to and rotating with the axle hub that drives the vehicle's wheel, two brake pads and two pistons. One brake pad sits on each side of the rotating disc. Each piston sits adjacent to a brake pad on the side of the brake pad opposite the rotating disc. There is a similar system for each wheel on the vehicle.
A brake force is transmitted by hydraulic fluid forcing a piston to press against a brake pad. The brake pad then exerts a frictional force against the rotating disc causing the disc to decrease in rotational speed or stop rotating. One disadvantage of using dry disc brakes is frequent maintenance of the brake components.
Wet disc brake systems essentially have the same configuration as the dry disc brake system, except that there is a fluid contained within the brake housing that surrounds the rotating disc and the brake pads. Typically, hydraulic fluid is used to fill the brake housing.
Known wet disc brake systems are primarily used in low speed applications. The reason is due to the large drag force created by the fluid within the brake housing on the rotating disc. Therefore, the vehicle's engine must exert a large force to overcome the drag created by the fluid at higher traveling speeds. This results in an inefficient system at higher traveling speeds. However, wet disc brake systems have advantages over dry disc brake systems because the components in wet disc brakes encounter less wear than the components in dry disc brakes.
It would be advantageous to use a wet disc brake system on a vehicle in high-speed applications since that type of braking system experiences less wear.
SUMMARY OF THE INVENTION
In general terms, the disclosed wet disc brake assembly overcomes the above problem with standard wet disc brake assemblies. A reduced drag wet disc brake assembly is disclosed that can be efficiently used at low and high speeds.
The reduced drag wet disc brake assembly of the present invention includes a brake housing having a cavity that contains a fluid with a controlled viscosity. One appropriate fluid is an electrorheological fluid. Electrorheological fluids are fluids that change viscosity depending upon the electric current experienced by the fluid. The brake assembly further includes a hub rotatingly connected to the brake housing. A tire is connected to the hub. At least one rotating plate is disposed within the cavity and rotatingly connected to the hub. A plurality of non-rotating plates surround the rotating plate and are disposed within the cavity. The non-rotating plates are connected to the brake housing. A current source preferably applies a charge to the plurality of stationary plates and an opposed charge to the rotating plate.
When the electrorheological fluid within the cavity experiences no electric current, the fluid has a low viscosity. A fluid with a low viscosity flows easily. Therefore, the fluid produces a very low drag force on the rotating plate. On the other hand, when the fluid experiences an electric current, its viscosity increases. A fluid with a high viscosity has a high resistance to flow. Therefore, the fluid produces a higher drag force on the rotating plate.
Therefore, in the current invention, when the plates are not charged, the electrorheological fluid does not experience an electric current and therefore has a lower viscosity. A low drag force is thus exerted on the rotating plate by the electrorheological fluid. As a result, the wet disc brake assembly can be used in high-speed applications. When the plates become charged, the electrorheological fluid experiences an electric current and therefore, the viscosity of the fluid increases. The increased viscosity results in a larger drag force exerted on the rotating plate by the electrorheological fluid. The increased drag force causes the rotating plate to decrease in angular velocity. Since the rotating plate is connected to the hub, the hub mirrors the activity of the rotating plate and also decreases in rotational speed, resulting in a reduced vehicular speed or causing the vehicle to completely stop.
An alternative embodiment of the present invention has a slightly different configuration. A first difference is an additional coiled conductive wire that receives an electric current from the current source. A second difference is that the cavity is filled with a magnetic rheological fluid. Magnetic rheological fluids change viscosity depending upon the magnetic field experienced by the fluid. An electric current through the coiled wire creates a magnetic field.
When the magnetic theological fluid is not exposed to a magnetic field, the viscosity of the fluid is low. On the other hand, once the magnetic rheological fluid is exposed to a magnetic field, the viscosity increases. Similar to the preferred embodiment, a fluid with a high viscosity exerts a drag force on the rotating plate that causes the rotational speed of the rotating plate, and ultimately the hub, to decrease.
An additional feature of the brake assembly is a piston disposed within the cavity and adjacent the stationary and rotating plates. The piston provides a supplemental force. When an additional force is needed to reduce the speed of the vehicle, the piston is used to apply a normal load against the rotating plate to decrease the plate's angular velocity.
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AxleTech International IP Holdings, LLC
Howard & Howard
Rodriguez Pam
LandOfFree
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