Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1998-10-01
2001-04-03
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S093000, C310S103000, C188S158000
Reexamination Certificate
active
06211590
ABSTRACT:
TECHNICAL FIELD
This invention relates in general to braking systems for electric powered vehicles, and in particular to a electric braking assembly which applies a graduated dynamic braking force.
BACKGROUND OF THE INVENTION
In materials handling vehicles such as fork lift trucks, it is desirable to vary the amount of braking force applied so that the vehicle may be gradually slowed and yet have a high static torque for parking the vehicle on inclines. Hydraulic brakes provide for great flexibility in the amount of braking force applied, but hydraulic brake systems are expensive because of the required space for hardware and plumbing. Electric brakes are frequently used in materials handling vehicles, particularly electrically powered vehicles, because of their size and simplicity. However, electric brakes normally do not lend themselves to being variable in the braking force applied, and they require separate parking and dynamic braking assemblies.
In another application, workers are routinely elevated above the body of the vehicle in a carriage. When a worker is in this position and the vehicle is in motion, it is also desirable to apply braking force gradually to minimize the amount of vibration experienced by the worker who is elevated in the carriage. Here again electric brakes are frequently used, but they can be marginally effective in these gradual braking force applications. An electric braking system which varies its braking force to gradually stop a vehicle without sliding the wheels and yet provide high static torque for parking the vehicle on inclines and the like is needed.
SUMMARY OF THE INVENTION
A graduated, two-step electric braking system has a rotor shaft which extends from and rotates with a wheel on the vehicle. A rotor rotates with the shaft within a housing. The housing also contains an electromagnetic coil and two armatures. The rearward armature is in contact with the coil while the forward armature is adjacent to the rotor. The rearward armature does not touch the rotor and is more strongly attracted to the coil than the forward armature. Each armature has springs which independently urge it toward the rotor. An electrical circuit causes the current supplied to the coil to gradually decay rather than abruptly stop so that the magnetic force it generates is slowly dissipated.
When the vehicle is subjected to static braking in a parked position, the coil is de-energized so that the armatures are forced toward the rotor by their springs. In this state, the rearward armature applies force to the forward armature to increase the pressure against the rotor. When the system is disengaged, the coil is energized to attract the armatures and allow the rotor to freely rotate. Finally, the moving vehicle may be slowed or stopped with dynamic braking which de-energizes the coil. In this state, the forward armature quickly overcomes the attraction of the coil so that it engages the rotor before the rearward armature applies additional force. An increased level of braking force is applied to the rotor when the rearward armature is released. Thus, a graduated dynamic braking force is applied to the rotor when the coil is de-energized.
REFERENCES:
patent: 3608679 (1971-09-01), Harrison
patent: 3624767 (1971-11-01), Kroeger
patent: 3750781 (1973-08-01), Lengsfeld
patent: 4430592 (1984-02-01), Manktelow
patent: 4498066 (1985-02-01), Fujiwara et al.
patent: 4703841 (1987-11-01), Lengsfeld et al.
patent: 5057728 (1991-10-01), Dammeyer et al.
patent: 5509509 (1996-04-01), Dammeyer et al.
patent: 5631510 (1997-05-01), Flaig et al.
patent: 5699883 (1997-12-01), Albrecht
Albrecht James W.
Fe Ming Liang
Bradley James E.
Felsman, Bradley, Vaden, Gunter & Dillon L.L.P.
Ramirez Nestor
Stromag, Inc.
Waks Joseph
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