WO1999004479A1

WO1999004479A1 - Motor cooling methods and apparatus

Info

Publication number: WO1999004479A1
Application number: PCT/US1998/014088
Authority: WO
Inventors: Joe Kent Hammer; Ronald Lowell Ziegler
Original assignee: Crown Equipment Corporation
Priority date: 1997-07-16
Filing date: 1998-07-08
Publication date: 1999-01-28
Also published as: AU8293598A

Abstract

Motor (50, 110, 300) cooling is preformed using a pair of cooling fans (151, 350; 120, 320), one (151, 350) on the top of the motor and one on the bottom of the motor. A shroud (380) is placed around the top of the motor enclosing the top fan and directing air into the motor to flow over a brush-commutator assembly (135, 390) of the motor and over armature and field windings (440, 445) of the motor. The shroud engages the motor at a location above openings (165, 410) which vent a portion of the cooling air (170, 425) outside the motor below the brush-commutator assembly with the remaining air (175, 430) being vented out the bottom of the motor. An air scoop or duct (200) may be attached to the shroud with an inlet communicating with the outside of a motor compartment (40) within which the motor is enclosed to draw cooler air from outside the motor compartment, thus providing additional cooling effect.

Description

MOTOR COOLING METHODS AND APPARATUS

BACKGROUND OF THE INVENTION The present invention relates in general to fork lift trucks and, more particularly, to an improved method and apparatus for cooling electric motors used for operation of the trucks wherein cooling air, preferably from outside a motor compartment of a truck, is drawn into the top of a motor housing by fans located at both ends of the motor with a portion of the cooling air being vented outside the housing after flowing over a commutator-brush assembly and the remaining cooling air being vented out the bottom of the motor. Electric motors used in fork lift trucks are typically direct current motors having high torque capability that are positioned within motor compartments located above a driven wheel or wheels of the trucks. These motors are used for both traction and to drive hydraulic pumps. The motors normally include motor housings with each motor having a commutator-brush assembly at one end of the motor, typically at the top of the motor, within the housing. At the other end of the motor, an internal fan is mounted on a shaft of the motor to draw cooling air into the motor housing during operation of the motor. Since the brushes, as well as the windings within the motor, can get extremely hot during operation, air inlet ventilation openings are located near the brushes, and the cooling fan draws air into the motor housing adjacent the brushes and exhausts it out the bottom of the motor. This air cools the motor to maintain its temperature below certain critical temperature limits in order to prevent damage to the motor. Present day electric motor design, including the provision of ventilation openings located near the brush-commutator assembly, does not provide adequate cooling of the brushes to enable optimum motor performance. Air drawn into the motor by operation of the existing fan flows into the motor housing, but a significant portion of that air bypasses the brushes and flows directly down the inside of the housing and therefore does not provide optimum cooling of the brushes.

SUMMARY OF THE INVENTION In the present invention, sufficient cooling air is directed over the brush- commutator assembly to allow a given motor to operate at higher horsepower output while maintaining motor temperature below the critical limits. This allows higher power output, or higher production from the motor, without the need for a larger, more expensive motor.

To accomplish the purposes of this invention, namely, to provide additional cooling of existing motors, a second fan is added at the end of the motor opposite the existing fan, preferably near the brush assembly where a great proportion of the heat of the motor is generated. In some embodiments of the invention, particularly in combination with traction motors where a brake assembly is typically attached to the upwardly extending shaft of the motor, the fan is made a part of brake assembly, and therefore it provides additional surface area for cooling the brake as well as for enhancing the movement of air into the motor and across the brushes. In another embodiment of the invention, a radial fan is attached to the top of the motor.

Additional openings are formed in the upper end cap of the motor, above the brush assembly, to provide air inlets to more effectively direct cooling air across the brush assembly. The existing air inlets on the motor housing are modified to permit cooling air to enter above the brush assembly. Some cooling air exits the motor housing below the brush assembly and the remainder of the cooling air passes through the motor and exits at the bottom of the housing.

A shroud is placed over the upper portion of the motor and the newly installed fan. Air is drawn into the shroud through a central opening by action of the fan, and the air is then directed into the motor housing and across the brush assembly.

In some cases, an optional air scoop or duct is attached to the shroud with an inlet communicating with the outside of the motor compartment to draw air from outside the motor compartment. This air is generally significantly cooler that the air inside the motor compartment, thus providing additional cooling effect.

It is therefore an object of the present invention to provide methods and apparatus for cooling a motor by providing additional cooling air which is directed across the motor's brush assembly.

It is a further object of the present invention to provide extra cooling for a direct current motor by positioning the air inlet and outlet openings to maximize the flow of cooling air over the brush assembly.

It is a still further object of this invention to provide a shroud to enhance the flow of cooling air over the brush assembly of a direct current motor.

It is another object of this invention to provide a supplemental fan to increase the air flow through the motor, and particularly across the brush and commutator assembly.

It is an additional object of this invention to provide cooling air for a traction motor used in a fork lift vehicle by bringing in cooling air from outside the motor compartment. Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a lift truck showing a traction motor for the truck with a motor cooling shroud of the present invention attached thereto; Fig. 2 is a side view of a prior art traction motor;

Fig. 3 is a side view of the traction motor of Fig. 1 ; Fig. 4, similar to Fig. 3, shows the addition of a duct for bringing in outside cooling air; Fig. 5 is a perspective view of an embodiment of the invention including a duct having an accordion fold;

Fig. 6 is a perspective view of a pump motor embodying the present invention; Fig. 7 is a plan view of the motor of Fig. 6 with a shroud removed to reveal a fan; and

Fig. 8 is a partially sectioned side view of the motor of Fig. 6.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, and particularly to Figs. 1 - 3, a rider reach truck 10 includes a power unit 15 which includes an operator's compartment 20, a battery compartment 30, and a motor compartment 40.

A battery in the battery compartment 30 supplies power to a traction motor 50 located in the motor compartment 40 and connected to a steerable wheel 55 located at the left rear corner of the power unit 15 and to hydraulic motors (not shown) which supply power to several different systems within the truck 10. The traction motor 50 has been modified in accordance with the present invention to include a shroud 180 as shown in Fig. 3 and as fully described hereinafter. A caster wheel 56 is mounted at the right rear corner of the power unit 15. A pair of outriggers 60 support the front end of the truck 10.

In the operator's compartment 20 are mounted a steering tiller (not shown) for controlling the direction of travel of the truck 10 and a control handle 67 for controlling the speed of travel and the forward and reverse direction of travel of the truck as well as fork height, fork extension, and fork tilt and side-shift.

A mast assembly 70 mounted to the front of the truck 10 includes an overhead guard 75. A pair of forks 80 are carried on a fork carriage mechanism 85 which is carried on extendable mast elements 90.

Reference is now made to Fig. 2, which illustrates a prior art motor cooling system. A traction motor 110 for a fork lift truck has a central rotating shaft 115, a bidirectional cooling fan 120 mounted to the shaft at the lower end of the motor, a brake mechanism 125 attached to the shaft at the upper end of the motor, and a plurality of ventilation holes 130 through a motor housing. The holes 130 are located near the top of the motor in the vicinity of a brush assembly (not shown) but located generally at 135. The brake mechanism 125 is provided with cooling fins 150 to aid in dissipating the heat generated in braking the motor (and the truck which it is moving).

During operation of the motor 110, the fan 120 causes air, illustrated by the arrows 140, to be drawn into the motor through the ventilation holes 130. The air passes across the brush assembly inside the motor, as well as the internal motor windings, and exits through openings formed in the lower end of the motor. In the present invention, one embodiment of which is illustrated in Fig. 3 wherein like elements are identified by the same reference numerals as in Fig. 2, several improvements have been made to the prior motor cooling system. These improvements include the placement of ventilation openings 155, 165 in the motor housing, the addition of a shroud 180, and a second or additional bidirectional cooling fan 151 is added to the first bidirectional cooling fan 120.

The additional bidirectional cooling fan 151 is placed on a rotor 127 of the brake mechanism 125. The fan 151 provides additional surface area for cooling as well as for movement of air across and through the motor 110. Additional openings 155 are placed in the motor housing above the brush assembly 135 to provide air inlets to the brush assembly/commutator section and to form a portion of a first passageway for directing cooling air from the fan 151 toward the brush assembly/commutator section. Air flows into the openings 155, as illustrated by arrows 160. Further openings 165 are provided below the brush assembly/commutator section to permit some of the air to exit immediately below the brushes, as represented by the arrows 170. Thus, the openings 165 form a portion of a second passageway for venting a portion of the cooling air from the brush assembly/commutator section to outside the motor 110. The remaining cooling air passes through the motor and exits through the existing openings in the bottom of the motor, as illustrated by arrows 175, via a third passageway. A shroud 180 is placed over the upper portion of the motor 110. The shroud 180 includes a central opening 185 in its upper surface into which cooling air is drawn, as shown by arrow 190. The lower end 195 of the shroud 180 is placed in contact with the motor housing below the openings 155 but above the openings 165. Thus, in operation, as the motor 110 rotates, air will be drawn into the opening 185 as a result of the action of both the fan 120, mounted at the lower end of the motor, and also the fan 151 , attached to the brake rotor 127 at the upper end of the motor 110. Air is drawn into the motor housing through the openings 155 above the commutator assembly. The air then flows across the brush assembly/commutator section, and a portion of the air exits through the openings 165, as shown by arrows 170, the remaining air flows across the motor windings due to operation of the fan 151 and the fan 120 and exits the motor though existing openings at the bottom of the motor housing, as shown by arrows 175.

The embodiment shown in Fig. 3 improves the cooling of the motor 110 significantly. For example, a motor configured as shown in Fig. 2, rated at 4.9 hp when running at critical temperature limits, whereas with the addition of the fan 151 , openings 155 and 165, and the shroud 180, the motor is rated at 6.6 hp when running the same critical temperature limits.

A further improvement is shown in Fig. 4 wherein like elements are identified by the same reference numerals as in Figs. 2 and 3. In this embodiment of the invention, a duct 200 has been added to the top of the shroud 180 in order to bring outside air into the motor. The motor 110 is typically located in a closed compartment above the driven wheels such as the motor compartment 40 of Fig. 1. This compartment contains not only the traction motor, but also other equipment, such as hydraulic pumps and associated motors, and electronic equipment. The ambient air within this compartment under typical operating conditions can be considerably higher than outside air temperature. Thus, by drawing cooling air from outside the compartment through louvers or openings 205 formed in the outer wall or door 210 of the compartment, the cooling of the motor 110 is improved further.

As a result, with a given motor in a typical fork lift application, with a motor configured as shown in Fig. 2, a lift truck would be able to sustain a power output at critical temperature limits that was equivalent to handling about 25 loads per hour. With the motor configured as shown in Fig. 3, the sustained level is about 45 loads per hour, and when configured as shown in Fig. 4, the sustained level is about 58 loads per hour. An alternate embodiment of the duct 200 of Fig. 4 is shown in the perspective view of Fig. 5. The duct 200 of Fig. 4 includes an upper housing 220, which is provided with an opening 225 that conforms to the opening 185 in the shroud 180, and an outwardly extending housing 230 that includes an opening 235 positioned adjacent the louvers or openings 205 in the outer wall or door 210. An accordion fold 240 allows the duct 200 to compress when pressed against the outer wall or door 210.

Referring now to Figs. 6, 7 and 8, a pump motor 300 is shown having a central rotating shaft 315. A unidirectional cooling fan 320, see Fig. 8, mounted on the shaft 315 at the lower end of the motor 300 forces air through louvers 335 formed in a base plate 330. For a pump motor configuration, the lower end of the motor shaft 315 is flush with the bottom end of the motor 300 and includes a splined opening to mate with a pump shaft. The embodiment of the pump motor 300 of Figs. 6-8 includes, in accordance with the present invention, a unidirectional fan 350 mounted on the upper end of the shaft 315. The fan 350 includes a pair of spaced apart circular plates 352 and 353, and several fan blades 355 mounted between the plates 352, 353. The upper plate 352 includes a centrally located opening 360. Air flows into the fan 350 axially and exits radially.

The motor 300 includes an exterior housing 310 and a removable top cover plate 365. Removal of the plate 365 provides access to the brush assembly 390. Typically, the brush assembly 390 includes four removable brushes 392 that are spring biased against a commutator 394 comprising a plurality of commutator segments. The cover plate 365 is normally solid in a conventional pump motor, but in the present invention, a plurality of openings 370 are formed in the cover plate, on the top thereof as illustrated, to allow air to flow downwardly, substantially axially into the brush assembly 390. A shroud 380 covers the fan 350 and the top portion of the motor 300, as shown. The shroud 380 is also provided with a centrally located top opening 385 which is coaxial with the opening 360.

A plurality of openings are formed circumferentially around the motor 300 at the level of the brush assembly 390. This is a conventional arrangement in the prior art motor. However, a band 400 surrounds these openings, and air is directed through an opening or a plurality of openings taking the form of slots 410 as illustrated, formed in the band 400, below the level of the brush assembly 390.

As shown is Fig. 8, the flow of air, represented by arrows 420, enters through the top opening 385 in the shroud 380, flows into the fan 350 which forces the air into the openings 370 in the cover plate 365, across the brush assembly 390 with some of the air, represented by arrows 425, flowing outwardly from the motor 300 through the slots 410, and some of the air, represented by the arrows 430, being directed down across rotating or armature windings 440 and field windings 445 due to operation of the fan 350 and the fan 320 where it exits through the louvers 335. Having thus described the invention of the present application in detail and by reference to preferred embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.

Claims

1. A method for cooling an electric motor (50, 110, 300) of the type including a housing (310), a set of field windings (445) in said housing, a rotating shaft (115, 315)) extending through said housing and provided with a commutator (394) having commutator segments connected to rotating windings (440), and a brush assembly (135, 390) mounted in said housing for supplying current to said rotating windings through said commutator segments, said method comprising the steps of: directing cooling air (190, 420) across said brush assembly (135, 390) and said commutator (394); venting a first portion of said cooling air (170, 425) outside said housing after said first portion of said cooling air passes at least partially across said brush assembly (135, 390) and said commutator (394); directing a second portion of said cooling air (175, 430) across said field windings and said rotating windings; and venting said second portion of said cooling air (175, 430) outside said housing after said second portion of said cooling air passes at least partially across said field windings and said rotating windings.

2. A method as claimed in claim 1 further comprising the steps of: providing a first cooling fan (151 , 350) at a first end of said rotating shaft (115, 315) to force cooling air (190, 420) into said motor housing at said one end of said rotating shaft; and providing a second cooling fan (120, 320) at a second end of said rotating shaft to force cooling air from said motor housing at said second end of said rotating shaft.

3. A method as claimed in claim 1 wherein said electric motor (50, 110, 300) is enclosed within a motor compartment (40), said method further comprising the step of providing said cooling air (190) from outside said motor compartment.

4. Apparatus for cooling an electric motor (50, 110, 300) of the type including a housing (310), a set of field windings (445) in said housing, a rotating shaft (115, 315) extending through said housing and provided with a commutator (394) having commutator segments connected to rotating windings (440), and a brush assembly (135, 390) mounted in said housing for supplying electrical current to said rotating windings through said commutator segments, said apparatus comprising: a first cooling fan (151 , 350) mounted on a first end of said rotating shaft for drawing cooling air (190, 420) into said motor; a first passageway (155, 370) in said housing positioned to direct cooling air from said first cooling fan (151 , 350) toward said brush assembly and said commutator; a second passageway (165, 425) in said housing positioned to vent a portion of said cooling air (170, 425) from said brush assembly and said commutator to outside said housing; a third passageway in said housing positioned to direct cooling air (175, 430) over said field windings and said rotating windings; and a second cooling fan (120, 320) mounted on a second end of said rotating shaft opposite said first end to draw cooling air (175, 430) through said third passageway and vent said cooling air outside of said housing.

5. Apparatus for cooling an electric motor ( 300) of the type including a housing (310) with first and second end covers (365, 330), a set of field windings (445) in said housing, a rotating shaft (135, 390) extending through said housing and provided with a commutator (394) having commutator segments connected to rotating windings (440), and a brush assembly (390) mounted in said housing for supplying electrical current to said rotating windings through said commutator segments, said apparatus including: a first cooling fan (350) mounted on a first end of said rotating shaft for drawing cooling air into said motor; at least one opening (370) in said first end cover of said housing positioned to direct cooling air from said first cooling fan toward said brush assembly and said commutator; a shroud (380) surrounding said first cooling fan and coupled to said first end cover, said shroud directing cooling air from said first fan into said housing through said at least one opening; a passageway (400, 410) in said motor to vent a first portion of said cooling air (425) outside said housing after said cooling air has passed over at least a portion of said brush assembly and said commutator; and a second cooling fan (320) mounted on a second end of said rotating shaft opposite said first end for drawing cooling air into said motor and for passing a second portion of said cooling air (430) across said field windings and said rotating windings, said second cooling fan further providing for venting said second portion of said cooling air outside said housing.

6. Apparatus as claimed in claim 5 further comprising a band (400) surrounding openings formed circumferentially around said motor adjacent said brush assembly and said commutator, said band including openings and defining an outer portion of said passageway.

7. Apparatus as claimed in claim 5 wherein said motor (300) is enclosed within a motor compartment (40), said apparatus further comprising a duct (200) extending from said shroud (380) to a location adjacent an outer wall (210) of said motor compartment to draw cooling air from outside said motor compartment.

8. Apparatus as claimed in claim 7 wherein said duct (200) includes an accordion fold (240) so that said duct can compress when pressed against said outer wall (210) of said motor compartment.

9. Apparatus for cooling an electric motor (50, 110, 300) of the type including a housing (310), a set of field windings (445) in said housing, a rotating shaft (115, 315) extending through said housing and provided with a commutator (394) having commutator segments connected to rotating windings (440), and a brush assembly (135, 390) mounted in said housing for supplying electrical current to said rotating windings through said commutator segments, said apparatus including: a first passageway in said housing positioned to direct cooling air (190, 420) from a top portion of said housing toward said brush assembly and said commutator; a second passageway in said housing positioned to vent a first portion of said cooling air (170, 425) from said brush assembly and said commutator to outside said housing; and a third passageway in said housing positioned to direct cooling air (175, 430) over said field windings and said rotating windings and vent said cooling air outside of said housing.

10. Apparatus as claimed in claim 9 wherein said first passageway includes a first cooling fan (151 , 350).

11. Apparatus as claimed in claim 10 wherein said third passageway includes a second cooling fan (120, 320).

12. Apparatus as claimed in claim 9 wherein said first passageway includes a cooling fan (151 , 320).

13. Apparatus as claimed in claim 9 wherein said third passageway includes a cooling fan (120, 320).

14. Apparatus as claimed in claim 9 wherein said motor (50, 110, 300) is enclosed within a motor compartment (40), said apparatus further comprising a duct (200) extending from said first passageway to a location adjacent an outer wall (210) of said motor compartment to draw cooling air from outside said motor compartment.

15. Apparatus as claimed in claim 14 wherein said duct (200) includes an accordion fold (240) so that said duct can compress when pressed against said outer wall (210) of said motor compartment.