Brakes – Operators – Electric
Patent
1998-05-14
2000-08-08
Dickson, Paul N.
Brakes
Operators
Electric
188 721, 188 728, 188162, B60L 700
Patent
active
060987634
DESCRIPTION:
BRIEF SUMMARY
This invention relates to improvements in electrically-operated disc brake assemblies for vehicles the kind in which a friction member is adapted to be applied to a rotatable brake disc by brake-applying means including an electric motor which forms part of the assembly, and transmission means adapted to apply an axially directed brake-applying force to the friction member in response to operation of the motor.
A brake of the kind set forth is known from EP-A-0 339 024. In the brake of EP-A-0 339 024 the electric motor is used to drive an input to a reduction gear box, and the gear box is adapted to translate high speed movement of the motor into a controlled high torque output to a transmission means in the form of a screw device in turn adapted to displace the friction member axially with respect to the disc.
In the brake of EP-A-0 339 024 the electric motor, the gear box, and the screw device are arranged in series. Since these components are arranged sequentially the brake assembly, in consequence, is of substantially large overall size. Moreover, the motor is displaced by the gearbox to a position which is some distance from mounting points for the brake. The large mass of the motor therefore applies a moment force to the brake assembly. Under normal running conditions of a vehicle, large accelerations or vibrations are applied to the wheel, and therefore to the brake, as the wheel passes over irregularities in the road. These already large forces tend to generate extremely large vibrations in the motor and the brake assembly, which may be made worse because the motor overhangs the brake mounting points. The brake of EP-A-0 339 024 needs to be sufficiently robust to withstand the all aforementioned vibrations and high forces which might otherwise lead to fatigue or similar stress failures within the motor and brake. Such robustness is normally achieved by strengthening the appropriate parts which adds to the overall mass of the brake assembly. This is obviously undesirable since increasing the unsprung mass of the vehicle can lead to vehicle handling problems associated both with steering and suspension design and control.
In the brake disclosed in EP-A-0 339 024, the screw device for applying a brake-applying force to the friction member is of unitary construction. The single screw applies a clamp load substantially at the geometric centre of the friction member. As the centre of pressure of the friction member is offset from the, geometric centre of the friction member, a single point loading offset from the centre of pressure can generate a reaction torque on the friction member which is in addition to the normal brake torque. Since the reaction torque and the normal brake torque have to be supported by the brake housing, it may be necessary for the support or abutment locations for the friction member to be strengthened. Again, any such additional strengthening will result in an increase in the overall mass of the brake assembly with the consequence advantages discussed above.
According to our invention, we provide an electrically operated disc brake assembly for vehicles comprising a friction member which is adapted to be applied to a rotatable brake disc by braking applying means, the brake applying means including an electric motor, and further comprising a transmission means which is adapted to apply an axially directed brake applying force to the friction member in response to operation of the motor, in which the transmission means acts on the friction member at circumferentially spaced locations and comprises a pair of circumferentially spaced screw devices, which are simultaneously rotatable by the electric motors to apply the axially directed forces to the friction member, characterised in that the electric motor is adapted to act on the screw devices, through a common gear train arranged to be located adjacent the rear face of the friction member.
This produces a substantially even loading across the friction member/disc interface, thereby reducing the magnitude of the reaction torque.
Pr
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patent: 5348123 (1994-09-01), Takahashi et al.
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patent: 5520267 (1996-05-01), Giering et al.
patent: 5722516 (1998-03-01), Forni et al.
patent: 5819884 (1998-10-01), Giering
Dickson Paul N.
Lipka Pamela J.
Lucas Industries Public Limited Company
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