[0001] The invention relates to a laundry dryer provided with a simple and reliable safety
device for preventing overheating of the laundry in case of stoppage of the drum due
to mechanical failure of the machine.
[0002] Conventional laundry dryers comprise a blower and heater elements for circulating
heated air through a conduit and the interior of a drum containing the laundry to
be dried and adapted to be rotated by means of an electric motor.
[0003] Machines of thsi type additionally comprise suitable safety devices electrically
connected to said heater elements for preventing the temperature during operation
of the machine from exceeding a predetermined level beyond which the laundry would
be overheated with the danger of being burnt.
[0004] Known safety devices of this type are associated with a filter included in the heated
air circulating conduit for retaining lint released by the laundry or any other foreign
matter.
[0005] These safety devices continually monitor the degree of obstruction of the filter
and thus serve to indirectly control the temperature of the circulating heated air
downstream of the filter.
[0006] As the filter is gradually obstructed, the circulating air reaches the predetermined
temperature level, whereupon the safety device operates to interrupt the electric
power supply to the heater elements, at the same time indicating this condition to
the user, so that the filter is then cleaned or replaced.
[0007] Other known safety devices are employed for continually monitoring the temperature
of the .heated air circulating within the laundry dryer and for interrupting the electric
power supply to the heater elements in case of electrical failure or interruption
of the power supply to the electric motors driving the drum or the blower.
[0008] Although these known safety devices are highly effective in protecting the laundry
dryer in case of any electric faults, they are not able to give similar protection
in case of mechanical faults resulting in stoppage of the drum or rotation thereof
at a reduced speed. Mechanical faults of this type may for instance be caused by rupture
or excessive elongation of the driving belt extending around the drum and a belt pulley
of the respective electric motor and kept under tension by a number of tensioning
rolls disposed in the lower rear portion of the machine.
[0009] In a case of this nature the blower and the heater elements of the laundry dryer
continue to be connected to the electric power supply, while the laundry remains stationary
or is moved at a reduced speed, so that the continuously circulating heated air causes
progressive overheating of the laundry with the danger of the laundry being singed
or burnt.
[0010] It is an object of the present invention to eliminate the above described shortcomings
of known laundry dryers by the employ of a safety device adapted to effectively protect
the dryer and the laundry contained therein in the case of mechanical failure of the
type indicated above.
[0011] According to the invention, a safety device of the type referred to above essentially
comprises an electric breaker switch connected to the electric circuit of the dryer
together with the heater elements'and mechanically connected to the transmission belt
in such a manner as to interrupt the electric power supply to the heater elements
in the case of rupture or excessive elongation of the belt.
[0012] These and other objects are attained according to the invention by a laundry dryer
comprising a blower driven by an electric motor and at least one heater element for
circulating heated air within a drum containing the laundry to be dried, said drum
being rotatively driven by a second electric motor via at leat one transmission belt
extending around said drum and a belt pulley of said second motor and kept under tension
by means of at least one tensioning roll carried by a spring-loaded lever pivotally
mounted in the lower rearward portion of the machine.
[0013] According to the invention, a laundry machine of this type is characterized by comprising
actuator means cooperating with said lever, said heater element and said motors so
as to control the connection and disconnection, respectively, of said heater element
and said motors to the electric power supply of the machine in response to the position
assumed by said lever.
[0014] For better understanding of the invention, preferred embodiments thereof shall now
be descriebd by way of example with reference to the accompanying drawings, wherein:
figs. 1 and 2 show diagrammatic elevational views of two embodiments of a safety device
according to the invention disposed in the rear portion of a laundry dryer, and
figs. 3 and 4 show portions of electric circuit diagrams associated with the embodiments
of figs. 1 and 2, respectively.
[0015] With reference to fig. 1, a laundry dryer according to the invention comprises a
frame 5 and a drum 6 mounted therein for rotation about a horizontal axis and adapted
to contain the laundry to be dried. The machine further comprises a blower and at
least one electric heater element (not shown) for generating a flow of heated air
through drum 6. Drum 6 is adapted to be rotated by an electric motor 8 provided with
a belt pulley 9 and mounted on a support 10 at the lower rear portion of the frame
of the machine.
[0016] In particular, drum 6 is rotated with the aid of a conventional transmission belt
11 extendign around pulley 9 of motor 8 and around drum 6 and kept under tension by
means of a tension roll 12. Tension roll 12 is carried by a lever 13 pivotally mounted
at one end thereof on the frame of the machine adjacent motor 8. Tension roll 12 is
continually biased into engagement with belt 11 by a return spring 14 having its respective
end anchored to lever 13 and support 10.
[0017] By properly selecting the characteristics of return spring 14, it is tbus possible
to keep belt 11 under sufficient tension for effectively transmitting the rotation
of motor 8 to drum 6 with a minimum of wear of the belt itself.
[0018] The described laundry dryer is further provided with a safety device for preventing
possible overheating and burning of the laundry in case of rupture or excessive elongation
of belt 11.
[0019] The safety device in the embodiment shown essentially comprises an electric breaker
switch 15 and an associated slider element 16, both mounted on a support 17 adjacent
motor 8 and lever 13.
[0020] Switch 15 is provided with a spring-loaded button 18 cooperating with a normally
open contact 19 connected to the electric circuitry of the machine in a manner to
be described.
[0021] Slider element 16 is adapted to slide back and forth alcna a horizontal guide 20
of support 17. Slider element 16 is connected to lever 13 by a compression spring
21 and provided with a plane surface portion 22 for actuating button 18.
[0022] Plane surface portion 22 is dimensioned such as to retain button 18 in its depressed
state, and thus"contact 19 in its closed position, also in case of small displacements
of slider element 16 due to the action of the resilient transmission belt 11 on tension
roll 12 and lever 13 during rotation of drum 6.
[0023] As evident from fig. 3, contact 19 is connected in series with the program unit 23
of the machine, said unit being adapted to control the connection and disconnection,
respectively, of the two motors 8 and 26 driving the blower and drum, respectively,
and of the heater element 27, itself connected in series with a conventional protective
thermostat 28.
[0024] During a normal drying cycle contact 19 is kept closed in the manner described, permitting
electric power to be simultaneously supplied to motors 8 and 26 and heater element
27 in series with thermostat 28.
[0025] In the case of rupture of belt 11, drum 6 stops and lever 13 is displaced in the
direction of arrow A by the action of return spring 14, resulting in a corresponding
displacement of slider element 16 by the action of spring 21 (fig. 1).
[0026] This results in plane surface portion 22 of slider element 16 releasing button 18,
causing it to snap back to its rest position, whereby contact 19 is permitted to open.
[0027] The open position of contact 19 is shown in dotted lines in fig. 3. In this position,
motors 8 and 26 as well as heater element 27 and thermostat 28 are disconnected from
the electric power supply.
[0028] As a result, the flow of heated air through the drum is discontinued, and overheating
or even burning of the laundry is effectively prevented.
[0029] In a similar manner, failure of return spring 14 results in a displacement of lever
13 in the direction of arrow B under the action of transmission belt 11. The resulting
slack in transmission belt 11 around drum 6 results in rotation of the drum at a reduced
speed or even in stoppage of the drum.
[0030] In this case, slider element 16 is also displaced in the direction of arrow B by
the action of spring 21, whereby plane surface portion 22 is again cause to release
button 18. This results in button 18 and dontact 19 assuming their rest positions
as above descriebd, so that motors 8 and 26 and heater element 27 with thermostat
28 are again disconnected from the electric power supply.
[0031] Shown in fig. 2 is a laundry dryer equipped with a safety device in a second embodiment
of the invention. In this figure, the above described elements of the dryer are designated
by the same reference numerals as in fig. 1.
[0032] In the second embodiment, the safety device essentially comprises two breaker switches
29 and 30-facing each other over a short spacing and fixedly mounted in the machine
adjacent motor 8 and lever 13, and a slider element 31 carried by a support 32 secured
to the machine in a position adjacent switches 29 and 30.
[0033] Each breaker switch 29 and 30 is provided with a spring-loaded button 33 and 34,
respectively, cooperating with a normally closed electric contact 35 and 36, respectively,
said contacts being connected to the electric circuitry of the machine in a manner
to be described.
[0034] Slider element 31 is adapted to slide back and froth between a pair of parallel horizontal
guides 37 and 38 of support 32, and is connected to lever 13 by a compression spring
39.
[0035] Slider element 31 is further provided with a projection 40 located at a position
between the buttons of the two breaker switches so as to be able to selectively actuate
one or the other thereof.
[0036] The dimensions of projection 40 are selected so as to permit limited displacement
of slider element 31 under the resilient action of transmission belt 11 on tension
roll 12 and lever 13 during rotation of drum 6 withou projection 40 coming into contact
with one of the two buttons.
[0037] As shown in fig. 4, contacts 35 and 36 are connected in series with each other and
with program unit 23 of the machine, the program unit being in turn connected to the
electric components of the machine in the above descriebd manner.
[0038] During normal operation of the dryer, slider element 31 does nos act on contacts
35 and 36, so that they remain closed during the operating cycle of the dryer, permitting
the electric components of the machine to be supplied with electric power by program
unit 23.
[0039] In the case of rupture of transmission belt 11 or failure of return spring 14, slider
element 31 is displaced in the direction of arrow A or B, respectively, under the
action of lever 13 as described above.
[0040] As a result, projection 40 actuates the respective button 33 or 34, respectively,
causing the respective contact 35 or 36 to open, as shown in dotted lines, so as to
disconnect the electric components of the machine from the power supply.
[0041] Displacement of slider element 31 in one or the other direction thus results in the
flow of heated air through the drum being interrupted, so as to prevent overheating
and burning of the laundry from occurring.
[0042] The safety device according to the invention is of a simple and reliable type and
may be employed in combination with conventional safety devices protecting the machine
against electric failure, resulting in a laundry dryer thus being effectively protected
against any failure of its electric and mechanical components.
1. A laundry dryer comprising a blower driven by an electric motor and at least one
heater element for circulating heated air within a drum containing the laundry to
be dried, said drum being rotatively driven by a second electric motor via at least
one transmission belt extending around said drum and a belt pulley of said second
motor and kept under tension by means of at least one tensioning roll carried by a
spring loaded lever pivotally mounted in the lower rearward portion of the machine,
characterized by actuator means cooperating with said lever (13), said heater element
(27) and said motors (8, 26) so as to control the connection and disconnection, respectively,
of said heater element (27) and said motors (8, 26) to the electric power supply of
the machine in response to the position assumed by said lever (13).
2. A laundry dryer according to claim 1, characterized in that said actuator means
comprise a slider element (16) and a breaker switch (15) having a contact (19) for
controlling said heater element (27) and said motors (8, 26), said slider element
(16) being connected to said lever (13) by a spring (21) and comprising a plane surface
protion (22) adapted to actuate said contact (19) to its closed or open position.
3. A laundry dryer according to claim 1, characterized in that said actuator means
comprise a slider element (31) and two breaker switches (29, 30) having their contacts
(35, 36) connected in series with one another for controlling said heater element
(27) and said motors (8, 26), said slider element (31) being connected to said lever
(13) by a spring (39) and having a projection (40) disposed between said breaker switches
(29, 30) for actuating one or the other thereof to its open or closed position.
4. A laundry dryer according to the preceding claims, substantially as described with
reference to the accompanying drawings and for the stated purposes.