Eddy current braking apparatus

Details Eddy current braking apparatus Eddy current braking apparatus

2001-02-08

2004-04-27

Lavinder, Jack (Department: 3683)

Brakes

Operators

Electric

C188S156000

Reexamination Certificate

active

06725982

ABSTRACT:

FIELD OF THE INVENTION
The present invention is directed to an eddy current braking apparatus and, in particular, to a single-row rotating-type braking apparatus.
BACKGROUND ART
Large vehicles such as buses and trucks are equipped with a foot brake as a main braking apparatus. In addition, these large vehicles are equipped with an exhaust brake as an auxiliary braking apparatus (retarder). Furthermore, on a portion of an output shaft or a power transmission shaft such as the rear of the transmission or the midportion of a propeller shaft, these large vehicles are equipped with an eddy current braking apparatus as an auxiliary braking apparatus. An eddy current braking apparatus performs stable deceleration even on a long downhill slope, and it decreases the frequency of use of a foot brake. For this reason, abnormal wear of brake linings and the occurrence of fading can be prevented, and the braking distance can be shortened. Typically, electromagnets and permanent magnets are used as the magnets for generating the magnetic force in these types of eddy current braking apparatuses, with permanent magnets being used more since no electric current is required during braking.
One type of an prior art eddy current braking apparatus used in the prior art is a single-row rotating-type eddy current braking apparatus
1
using permanent magnets as shown in FIG.
30
and disclosed in Japanese Published Unexamined Patent Application Hei 1-298948. The eddy current braking apparatus
1
has a support body
4
made of a non-magnetic material such as an aluminum alloy casting. The body
4
is supported with respect to an output shaft or a power transmission shaft
2
such as the rear of a transmission or a propeller shaft of a large vehicle (collectively referred to below in this specification as a “power transmission shaft”) by bearings
3
. The support body
4
has a support ring
5
, which serves as a yoke and is made of steel, for example, and is rotatably supported through bearings
6
.
A plurality of permanent magnets
7
are disposed on the outer peripheral surface of the support ring
5
. The magnets
7
are disposed at constant intervals in the circumferential direction of the support ring
5
, with the polarity of adjoining magnets being opposite from each other. A plurality of switching plates
8
made from a ferromagnetic material are magnetically insulated from each other, and are disposed on the support body
4
with a prescribed separation from the outer peripheral surface of the plurality of permanent magnets
7
.
A rotor
9
is mounted on the power transmission shaft
2
with the inner peripheral portion of a cylindrical surface
9
a
thereof opposing the switch plates
8
with a prescribed separation therefrom. The support ring
5
is designed to rotate by only a prescribed angle with respect to the support body
4
.
Still referring to
FIG. 30
, reference number
4
a
indicates an installation portion for installing the support body
4
on its mounting member, and reference number
9
b
indicates a cooling fin for radiating heat of the rotor
9
.
FIG. 31
shows another type of an eddy current braking apparatus
10
that is a two-row rotating type and which is disclosed in Japanese Published Examined Patent Application Hei 7-118901. The apparatus
10
has a rotor
12
mounted on a power transmission shaft
11
. A permanent magnet group
13
is supported by a fixed support ring
14
from the fixed side opposing the rotor
12
, and the magnets of group
13
are arranged with a predetermined spacing in the circumferential direction of the fixed support ring
14
with the north poles and the south poles alternating with each other. The apparatus
10
has a moveable support ring
16
which can rotate with respect to the fixed support ring
14
. Another permanent magnet group
15
is mounted on the moveable support ring
16
. Bearings
18
permit sliding movement between the support ring
16
and the support body
4
. A plurality of ferromagnetic switching plates
17
are disposed between the rotor
12
and the permanent magnet groups
13
and
15
. The switching plates
17
extend from above the permanent magnets
13
of the fixed support ring
14
to above the moveable support ring
16
.
The apparatus of
FIGS. 30 and 31
are not without their drawbacks though. Single-row rotating-type braking apparatus such as that shown in
FIG. 30
exhibit a drag torque during a non-braking state that is higher than for the two-row rotating-type eddy current braking apparatus
10
shown in FIG.
31
. Consequently, single row eddy current braking apparatus
1
have not gained acceptance at the present time.
However, these single row eddy current braking apparatus can be beneficial in that their use can greatly decrease the number of braking components such as permanent magnets
7
, support rings
5
, and the retaining members that support the permanent magnets
7
and the support rings
5
. Thus, the use of these types of eddy current braking apparatus increases durability and reliability, and lowers the cost of manufacturing. Furthermore, the single row eddy current braking apparatus can restrict the magnet rotational angle to about half that of the permanent magnets
15
of the double row eddy current braking apparatus, thereby permitting a decrease in the size of pneumatic cylinders employed for driving the permanent magnets
15
and a decrease in air consumption.
A further advantage of single row eddy current braking apparatus relates to the size of the pneumatic cylinder used to alternate between braking and non-braking states. Switching from a braking state to a non-braking state is typically accomplished simply by rotating the support ring
5
such that two adjoining switching plates
8
are each straddled by a permanent magnet
7
. The magnetic force of permanent magnets
7
and the attractive force between the permanent magnets
7
and the opposing switching plates
8
is larger than for two-row eddy current braking apparatus
10
of FIG.
31
. Consequently, the stroke of a pneumatic cylinder for driving the support ring
5
of the single row braking apparatus can be reduced by about half. As a result, the length of the pneumatic cylinder can be decreased, thereby reducing costs, installation fits problems, and air consumption. However, although the stroke or magnet rotational angle is reduced with a single-row eddy current braking apparatus, the required force to rotate the magnet is not reduced.
Although the single-row eddy current braking apparatus have advantages over two-row current braking apparatus, another problem of drag torque in the non-braking state exists. Referring to
FIGS. 30
,
32
a
, and
32
b
, the non-braking state in the single-row eddy current braking apparatus is achieved by rotating the support ring
5
from the braking position shown in
FIG. 32
a
so that the permanent magnets
7
straddle adjoining switching plates
8
and overlap half of each one. As shown by the arrows in
FIG. 32
b
, a short circuited magnetic circuit is formed by the support ring
5
, adjoining permanent magnets
7
, and one of the switching plates
8
. Therefore, magnetic flux from the permanent magnets
7
no longer acts on the cylindrical portion
9
a
, eddy currents do not flow in the cylindrical portion
9
a
, a so-called non-braking state is assumed, and the braking torque disappears.
To achieve the braking state as shown in
FIG. 32
a
, the support ring
5
is rotated so that the permanent magnets
7
are aligned with the switching plates
8
. In this state, a magnetic circuit shown by the arrows is formed by the support ring
5
, the adjoining permanent magnets
7
, the adjoining switching plates
8
, and the cylindrical portion
9
a
of the rotor
9
. As a result, the flux from the permanent magnets
7
acts on the cylindrical portion
9
a
and generates eddy currents, and a so-called braking state occurs whereby a braking torque is generated.
In the non-braking state shown in
FIG. 32
b
, ideally no braking torque (drag torque), which acts as running resistance, is generated

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