Wear limiters for centrifugal clutches

Abstract

The present invention relates to a wear limiter for a centrifugal clutch. Specifically, a centrifugal clutch for a transport refrigeration unit incorporating a wear limiter is provided. The centrifugal clutch includes a drum, a hub, at least two friction pad assemblies, and at least one spring (e.g., a vane or spiral) between each respective friction pad assembly. The wear limiter can be configured as part of the vane spring, as part of the friction pad assembly, and / or as a separate component. The wear limiter is configured to prevent a radially outwardly facing surface of at least one friction pad assembly from engaging an inwardly facing surface of the drum when the centrifugal clutch is in an extended position and the friction material of at least one friction pad assembly has worn to a wear thickness. This prevents the centrifugal clutch from engaging when the friction pads are worn.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 008879, filed April 13, 2020, the contents of which are hereby incorporated in their entirety. Background Art

[0003] Refrigerated trucks and trailers are commonly used to transport perishable goods, such as produce, meat, poultry, fish, dairy products, cut flowers, and other fresh or frozen perishable products. To keep the perishable goods contained, a transport refrigeration unit is typically mounted on the truck or trailer. The transport refrigeration unit can be driven mechanically (e.g., via a direct mechanical coupling or belt drive) or electrically. When mechanically driven, the transport refrigeration unit typically derives power from the vehicle's engine or from a separate engine within the transport refrigeration unit.

[0004] When the engine is not running or is not running at a high enough speed, the transport refrigeration unit is typically driven by a backup electric motor. Once the engine is running and at a high enough speed, the transport refrigeration unit switches from being driven electrically (e.g., by the backup electric motor) to being driven mechanically (e.g., by the vehicle engine or a separate engine within the transport refrigeration unit). To facilitate engagement of the engine (e.g., the vehicle engine or the separate engine) by the transport refrigeration unit, a clutch (e.g., a centrifugal clutch) is typically used. The clutch allows the engine to generate sufficient speed and torque before engaging to rotate the transport refrigeration unit's compressor. If the engine is not allowed to generate sufficient speed and torque, the initial resistance to rotation from the compressor may cause the engine to stall.

[0005] A conventional centrifugal clutch features a pair of friction pads mounted to a drive rotor or hub via a pivot post. To retract the friction pads and control the torque-speed curve, conventional centrifugal clutches typically use a biasing mechanism (e.g., one or more leaf or coil springs). As the engine generates speed and centrifugal force, the biasing mechanism is forced open, allowing the friction pads to extend radially outward toward the clutch drum. To engage the clutch drum and provide sufficient torque to allow the transport refrigeration unit's load to be driven by the engine, the friction pads must form sufficient contact with the clutch drum. To achieve this contact, the friction pads typically utilize a layer of friction material (e.g., a synthetic resin impregnated with metal, organic, or ceramic fibers) supported on a metal layer (e.g., steel). With repeated clutch use, this friction material layer wears (e.g., repeated clutch slipping causes wear of the friction material), and if worn far enough, this can expose the metal support.

[0006] Once the friction material on the friction pad wears to the point where the metal bearing is exposed, damage to the clutch and / or other components (e.g., the drum) can occur. Furthermore, since the drum is traditionally made of metal, the metal bearing, if it collides with the drum, can potentially cause product safety issues (e.g., by generating heat and / or sparks). Currently, there is no way to prevent metal-to-metal contact when the friction material on the friction pad wears to the point where the metal bearing is exposed.

[0007] Therefore, there remains a need for a centrifugal clutch that can prevent or at least mitigate metal-to-metal contact as the friction material on the friction pads wears. Summary of the Invention

[0008] According to one embodiment, a centrifugal clutch for a transport refrigeration unit is provided. The centrifugal clutch includes a drum, a hub, at least two friction pad assemblies, and at least one leaf spring. The drum includes an inward-facing surface. The hub is disposed within the drum. The hub is configured to be rotatably driven by an engine configured to power the transport refrigeration unit. The friction pad assemblies are connected to the hub. Each friction pad assembly includes a heel portion, a toe portion, and a radially outward-facing surface. The radially outward-facing surface includes friction material for contacting the inward-facing surface of the drum. The friction material has an installed thickness. At least one leaf spring is configured between each corresponding friction pad assembly. Each leaf spring includes an inward-facing surface. The inward-facing surface includes a wear limiter.

[0009] According to additional or alternative embodiments, the centrifugal clutch defines an extended position and a retracted position.

[0010] According to additional or alternative embodiments, the centrifugal clutch is in the extended position when the hub is rotatably driven at 400 RPM or greater.

[0011] According to additional or alternative embodiments, the wear limiter is configured to prevent the radially outwardly facing surface of the at least one friction pad assembly from engaging the inwardly facing surface of the drum when the centrifugal clutch is in the extended position and the mounting thickness is worn to the wear thickness.

[0012] According to additional or alternative embodiments, the worn thickness is approximately 10% of the installed thickness.

[0013] According to additional or alternative embodiments, a centrifugal clutch is configured to transfer torque from an engine to a compressor within a transport refrigeration unit.

[0014] According to another aspect of the present disclosure, a centrifugal clutch for a transport refrigeration unit is provided. The centrifugal clutch includes a drum, a hub, at least two friction pad assemblies, and at least one leaf spring. The drum includes an inward-facing surface. The hub is disposed within the drum. The hub is configured to be rotatably driven by an engine configured to power the transport refrigeration unit. The friction pad assemblies are connected to the hub. Each friction pad assembly includes a heel portion having a wear limiter, a toe portion, and a radially outward-facing surface. The radially outward-facing surface includes friction material for contacting the inward-facing surface of the drum. The friction material has an installed thickness. At least one leaf spring is configured between each corresponding friction pad assembly. Each leaf spring includes an inward-facing surface.

[0015] According to additional or alternative embodiments, the centrifugal clutch defines an extended position and a retracted position.

[0016] According to additional or alternative embodiments, the centrifugal clutch is in the extended position when the hub is rotatably driven at 400 RPM or greater.

[0017] According to additional or alternative embodiments, the wear limiter is configured to prevent the radially outwardly facing surface of the at least one friction pad assembly from engaging the inwardly facing surface of the drum when the centrifugal clutch is in the extended position and the mounting thickness is worn to the wear thickness.

[0018] According to additional or alternative embodiments, the worn thickness is approximately 10% of the installed thickness.

[0019] According to additional or alternative embodiments, a centrifugal clutch is configured to transfer torque from an engine to a compressor within a transport refrigeration unit.

[0020] According to another aspect of the present disclosure, a centrifugal clutch for a transport refrigeration unit is provided. The centrifugal clutch includes a drum, a hub, at least two friction pad assemblies, at least one spring, and at least one wear limiter. The drum includes an inward-facing surface. The hub is disposed within the drum. The hub is configured to be rotatably driven by an engine configured to power the transport refrigeration unit. The friction pad assemblies are connected to the hub. Each friction pad assembly includes a heel portion, a toe portion, and a radially outward-facing surface. The radially outward-facing surface includes friction material for contacting the inward-facing surface of the drum. The friction material has an installed thickness. At least one spring is configured between each corresponding friction pad assembly. At least one wear limiter is configured between each corresponding friction pad assembly.

[0021] According to additional or alternative embodiments, the centrifugal clutch defines an extended position and a retracted position.

[0022] According to additional or alternative embodiments, the centrifugal clutch is in the extended position when the hub is rotatably driven at 400 RPM or greater.

[0023] According to additional or alternative embodiments, the wear limiter is configured to prevent the radially outwardly facing surface of the at least one friction pad assembly from engaging the inwardly facing surface of the drum when the centrifugal clutch is in the extended position and the mounting thickness is worn to the wear thickness.

[0024] According to additional or alternative embodiments, the worn thickness is approximately 10% of the installed thickness.

[0025] According to additional or alternative embodiments, a centrifugal clutch is configured to transfer torque from an engine to a compressor within a transport refrigeration unit.

[0026] According to additional or alternative embodiments, the wear limiter has at least one of a rod configuration and a spring configuration.

[0027] According to additional or alternative embodiments, the spring is at least one of a leaf spring and a coil spring. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The subject matter which is regarded as the present disclosure is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The following description of the drawings is not to be construed as limiting in any way. Referring to the drawings, like elements are numbered alike:

[0029] Figure 1 is a perspective view of a truck having a transport refrigeration unit according to one aspect of the present disclosure.

[0030] Figure 2 is a perspective view of a transport refrigeration unit according to one aspect of the present disclosure.

[0031] Figure 3 According to one aspect of the present disclosure, a centrifugal clutch Figure 2 A perspective view of the power train of a transport refrigeration unit is shown in FIG.

[0032] Figure 4 According to one aspect of the present disclosure Figure 3 Exploded view of the centrifugal clutch shown in .

[0033] Figure 5 According to one aspect of the present disclosure Figure 3 An assembled view of the centrifugal clutch is shown in FIG.

[0034] Figure 6 According to one aspect of the present disclosure Figure 3 A partially assembled view of a centrifugal clutch is shown in FIG, wherein two leaf springs are constructed between two friction pad assemblies, each leaf spring including a wear limiter.

[0035] Figure 7 According to one aspect of the present disclosure Figure 3 A partially assembled view of a centrifugal clutch is shown in FIG, wherein two leaf springs are configured between two friction pad assemblies, each friction pad assembly including a wear limiter.

[0036] Figure 8 According to one aspect of the present disclosure Figure 3 A partially assembled view of a centrifugal clutch is shown in FIG, wherein two leaf springs and two wear limiters are constructed between two friction pad assemblies.

[0037] Figure 9 According to one aspect of the present disclosure Figure 3 A partially assembled view of a centrifugal clutch is shown in FIG, wherein two leaf springs and two wear limiters are constructed between two friction pad assemblies. DETAILED DESCRIPTION

[0038] It is crucial to prevent the metal bearings of the friction pad assembly (e.g., of a centrifugal clutch in a transport refrigeration unit) from contacting the metal surface of the drum in order to prevent or at least mitigate product safety issues. If the friction material on one or more friction pads wears away to the point where the metal bearings are exposed, the metal bearings could come into contact with the metal surface of the drum if the centrifugal clutch is fully extended. When these two metal surfaces come into contact with each other, heat and / or sparks may be generated, which could pose a product safety concern.

[0039] To help prevent metal-to-metal contact when the centrifugal clutch is in the extended position, a transport refrigeration centrifugal clutch having a wear limiter is provided. In some cases, the wear limiter may be configured as part of a leaf spring (e.g., extending from an inward-facing surface of the leaf spring), as part of a friction pad assembly (e.g., extending from a heel of a friction pad assembly), and / or as a separate component (e.g., spanning between two friction pad assemblies). Regardless of the specific configuration, the wear limiter is configured to prevent the radially outward-facing surface of at least one friction pad assembly from engaging the inward-facing surface of the drum when the centrifugal clutch is in the extended position and the friction material of at least one friction pad assembly has worn to a wear thickness. To prevent metal-to-metal contact, the wear limiter may limit how far the centrifugal clutch can extend (e.g., preventing the centrifugal clutch from extending beyond a point where the friction material is considered to have a wear thickness).

[0040] Now referring to the drawings, Figure 1 An exemplary transport refrigeration unit 200 mounted to a refrigerated truck 100 is shown in FIG. The transport refrigeration unit uses a centrifugal clutch to facilitate the transfer of engine power (e.g., a vehicle engine or a separate engine within the transport refrigeration unit) to the load of the transport refrigeration unit. Figure 2A standalone transport refrigeration unit 200 is shown in FIG. The transport refrigeration unit 200 includes a compressor 500 ( Figure 3 ), condenser (not shown), evaporator coil (not shown) and evaporator fan (not shown). Figure 3 As shown in FIG, the transport refrigeration unit 200 (eg, the compressor 500 of the transport refrigeration unit 200 ) may be driven by a separate engine 700 (eg, a diesel engine) within the transport refrigeration unit 200 .

[0041] Figure 3 The power train 300 of the transport refrigeration unit 200 is depicted. The power train 300 of the transport refrigeration unit 200 may include a centrifugal clutch 400, a compressor 500, an electric motor 600, a separate engine 700 (e.g., within the transport refrigeration unit 200), and an alternator 800. The centrifugal clutch 400 may drive the load in the power train 300, which may be comprised of the compressor 500, the electric motor 600, and the alternator 800. For example, the centrifugal clutch 400 may not engage the engine 700 until the engine 700 generates sufficient speed and torque. As an alternative to being driven by the engine 700, the compressor 500 may be driven by the electric motor 600, such that the centrifugal clutch 400 does not transmit any torque to the engine. By using the centrifugal clutch 400, the transport refrigeration unit 200 can gradually apply the load in the powertrain 300 to avoid unexpected stalling of the engine 700, which could occur if the load in the powertrain 300 is applied to the engine 700 before the engine 700 has developed sufficient speed and torque.

[0042] Figure 4 , an exploded view of the centrifugal clutch 400 of the transport refrigeration unit 200 is shown in FIG. The centrifugal clutch 400 includes a drum 410, a hub 420, at least two friction pad assemblies 430, and at least one spring (e.g., a leaf spring or a coil spring) 440 configured between each respective friction pad assembly 430. The drum 410 includes an inwardly facing surface 411. The hub 420 is configured to be disposed within the drum 410. The hub 420 is configured to be rotatably driven by the engine 700 within the transport refrigeration unit 200. For example, the hub 420 may be connected to a flywheel 450 such that the hub 420 can be rotatably driven within the drum 410. In some cases, the drum 410 is disposed between the hub 420 and the flywheel 450, with a bearing 460 at the intersection of the flywheel 450 and the drum 410. The friction pad assemblies 430 are connected to the hub 420 using, for example, one or more shafts 470 and / or bushings 480. Each friction pad assembly 430 includes a radially outwardly facing surface 431 (at the Figure 6-9), which includes friction material for contacting the inward-facing surface 411 of the drum 410. When installed, the friction material of each friction pad assembly 430 may have an installed thickness. However, repeated or undesired use of the friction pads 430 may cause the friction material to become worn (e.g., resulting in the friction material having a worn thickness).

[0043] A spring (e.g., a leaf spring or coil spring) 440 can help pull the friction pad assembly 430 inward, away from the inward-facing surface 411 of the drum 410, until the engine 700 generates sufficient speed for the centrifugal force of the friction pad assembly 430 to overcome the force of the leaf spring 440, causing the outward-facing surface 431 to contact the inward-facing surface 411. The friction therebetween generates torque to drive the compressor 500. When the friction pad assembly 430 is pulled away from the inward-facing surface 411 of the drum 410 (e.g., keeping the friction material from contacting the inward-facing surface 411 when the friction material has no wear thickness), the centrifugal clutch 400 can be referred to as being in a retracted position. When the friction pad assembly 430 is extended outward toward the inward-facing surface 411 of the drum 410 (e.g., allowing the outward-facing surface 431 to contact the inward-facing surface 411 when the friction material has no wear thickness), the centrifugal clutch 400 can be referred to as being in an extended position.

[0044] The centrifugal clutch 400 can move from a retracted position to an extended position relative to the speed of the engine 700. This may be due, at least in part, to the increase in centrifugal force generated as the speed of the engine 700 increases. For example, as the speed of the engine 700 increases, the rotational speed of the hub 420 and the friction pad assembly 430 increases, which may result in an increase in centrifugal force. Each spring (e.g., a leaf spring or a coil spring) 440 can be designed to resist a certain amount of centrifugal force so that the centrifugal clutch 400 is in the extended position, driving the load in the powertrain 300, only when the engine 700 has reached the desired speed. The point at which the centrifugal clutch 400 is designed to engage the engine 700 may depend on many factors, including, but not limited to, the size of the compressor 500 and / or the specific cooling load required by the design of the transport refrigeration unit 200.

[0045] In some cases, centrifugal clutch 400 is not in the extended position until hub 420 is rotatably driven at 400 RPM or greater. For example, centrifugal clutch 400 may not be in the extended position until hub 420 is rotatably driven at at least 400 RPM, at least 500 RPM, at least 600 RPM, at least 700 RPM, at least 800 RPM, at least 900 RPM, at least 1000 RPM, at least 1100 RPM, at least 1200 RPM, at least 1300 RPM, at least 1400 RPM, at least 1500 RPM, or at least 1600 RPM. For example, in some cases, if hub 420 is not rotatably driven at at least 400 RPM, friction pad assembly 430 will not engage inwardly facing surface 411 of drum 410, meaning that compressor 500 may not be driven by engine 700. To cover centrifugal clutch 400 during this rotation, plate 490 may be used. An assembled view of the centrifugal clutch 400 with the plates 490 is shown in FIG. Figure 5 Shown in.

[0046] To ensure that engine 700 can be engaged by centrifugal clutch 400, it is important that engine 700 has generated sufficient speed. If engine 700 does not generate sufficient speed, there will not be enough friction between friction pad assembly 430 and inward-facing surface 411 of drum 410 to provide sufficient torque to drive the load in powertrain 300 so that drum 410 rotates at the same speed as engine 700. In this situation, clutch 400 is said to be slipping and not fully engaged. Slipping of clutch 400 may cause the friction material on friction pad assembly 430 to wear (e.g., reduce the thickness of the friction material). However, it is expected that even normal use (e.g., without slipping) may cause friction material wear on friction pad assembly 430, which may be unavoidable. When friction material wear exceeds a certain threshold, friction pad assembly 430 may need to be replaced so that friction pad assembly 430 can engage inward-facing surface 411 of drum 410.

[0047] As described above, as the friction material wears, it is particularly important to prevent the friction pad assembly 430 from engaging the inward-facing surface 411 of the drum 410 to prevent metal-to-metal contact from occurring. To help prevent the radially outward-facing surface 431 of the friction pad assembly 430 from engaging the inward-facing surface 411 of the drum 410 when the centrifugal clutch is in the extended position and the friction material wears to a wear thickness, at least one wear limiter 401 may be installed within the centrifugal clutch 400. The wear limiter 401 may be configured as part of the leaf spring 440, as part of the friction pad assembly 430, and / or as a separate component. It should be appreciated that the centrifugal clutch 400 may incorporate multiple wear limiters 401 having the same or different configurations.

[0048] Figure 6 , a partially assembled view of a centrifugal clutch 400 is shown having two friction pad assemblies 430, each including a heel 432 and a toe 433, and two leaf springs 440 with wear limiters 401. It is contemplated that each leaf spring 440 may be constructed as a unitary structure (e.g., formed from a single continuous sheet of metal), for example, with the wear limiter 401 being integral with the leaf spring 440. The wear limiter 401 of each respective leaf spring 440 may be configured to engage the heel 432 of the friction pad assembly 430 when the centrifugal clutch 400 is in the extended position. To prevent the radially outward-facing surface 431 of the friction pad assembly 430 from engaging the inward-facing surface 411 of the drum 410 when the friction material of the friction pad assembly 430 has a worn thickness, the wear limiter 401 may be configured to extend radially inward, thereby limiting the radial distance that the centrifugal clutch 400 may be extended (e.g., to prevent the friction material from contacting the inward-facing surface 411 of the drum 410 when the friction material has a worn thickness). For example, the wear limiter 401 may prevent the spring 440 from flattening beyond a certain degree.

[0049] Figure 7 , a partially assembled view of a centrifugal clutch 400 is shown having two friction pad assemblies 430, each friction pad assembly 430 including a heel portion 432 and a toe portion 433, and two leaf springs 440. As shown, each heel portion 432 includes a wear limiter 401. It is contemplated that the heel portion 432 and the wear limiter 401 can be constructed as a unitary structure (e.g., formed from a continuous sheet of metal), for example, wherein the wear limiter 401 is integral with the heel portion 432. The wear limiter 401 from each respective heel portion 432 can be configured to engage an inwardly facing surface 441 of the leaf spring 440 when the centrifugal clutch 400 is in the extended position. To prevent radially outwardly facing surfaces 431 of friction pad assemblies 430 from engaging inwardly facing surfaces 411 of drum 410 when the friction material of friction pad assemblies 430 has a worn thickness, wear limiters 401 may be configured to extend radially outwardly to limit the radial distance that centrifugal clutch 400 can extend (e.g., to prevent friction material from contacting inwardly facing surfaces 411 of drum 410 when the friction material has a worn thickness). For example, wear limiters 401 may prevent spring 440 from flattening beyond a certain extent.

[0050] Figure 8 and Figure 9, a partially assembled view of a centrifugal clutch 400 having two friction pad assemblies 430 is shown, each friction pad assembly 430 including a heel 432 and a toe 433, and two leaf springs 440. As shown, the centrifugal clutch 400 includes two wear limiters 401 configured between each corresponding friction pad assembly 430 (e.g., spanning from the heel 432 of one friction pad assembly 430 to the toe of the other friction pad assembly 430). Figure 8 As shown in , in some cases, the wear limiter 401 is configured as a spring (e.g., as a drawbar spring). When configured as a spring, the wear limiter 401 may have a mechanism for limiting the expansion of the spring (e.g., a rod extending through the center of the spring). Figure 9 As shown in , in some cases, the wear limiter 401 is configured as a rod configuration. Regardless of whether the wear limiter 401 is configured as a rod configuration or a spring configuration, when the friction material of the friction pad assembly 430 has a worn thickness, the wear limiter 401 can prevent the radially outward-facing surface 431 of the friction pad assembly 430 from engaging with the inward-facing surface 411 of the drum 410 by limiting the radial distance that the centrifugal clutch 400 can extend (e.g., preventing the friction material from contacting the inward-facing surface 411 of the drum 410 when the friction material has a worn thickness).

[0051] Regardless of the configuration of the wear limiter 401, the wear limiter 401 is configured to prevent the radially outwardly facing surface 431 of at least one friction pad assembly 430 from engaging the inwardly facing surface 411 of the drum 410 when the centrifugal clutch 400 is in the extended position and the installed thickness has worn to the worn thickness. In some cases, the friction material of any given friction pad assembly 430 may be referred to as having a worn thickness when 10% of the friction material remains (e.g., meaning that in some cases, 90% of the friction material may be worn away from the friction pad 430 before it requires replacement). In some cases, the worn thickness may be between 1% and 10%, 1% and 15%, 1% and 20%, 1% and 30%, 1% and 40%, 1% and 50%, 10% and 15%, 10% and 20%, 10% and 30%, 10% and 40%, 10% and 50%, 15% and 20%, 15% and 30%, 15% and 40%, 15% and 50%, 20% and 30%, 20% and 40%, 20% and 50%, 30% and 40%, 30% and 50%, or 40% and 50% of the installed thickness. It should be appreciated that the friction material may be considered to have a worn thickness when less than 1% and greater than 50% of the friction material remains.

[0052] Although the present disclosure has been described with reference to one or more exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt particular situations or materials to the teachings of the present disclosure without departing from the basic scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiments disclosed as the best mode for carrying out the present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims.

Claims

1. A centrifugal clutch for a transport refrigeration unit, the centrifugal clutch comprising: a drum including an inwardly facing surface; a hub disposed within the drum, the hub configured to be rotatably driven by an engine configured to power the transport refrigeration unit; at least two friction pad assemblies connected to the hub, each friction pad assembly including a heel, a toe, and a radially outwardly facing surface, the radially outwardly facing surface including a friction material for contacting an inwardly facing surface of the drum, the friction material including a mounting thickness; as well as at least one leaf spring configured between each respective friction pad assembly, each leaf spring including an inwardly facing surface, the inwardly facing surface including a wear limiter, wherein the wear limiter is integral with the leaf spring, the wear limiter configured to prevent the radially outwardly facing surface of at least one friction pad assembly from engaging the inwardly facing surface of the drum when the centrifugal clutch is in the extended position and the installed thickness wears to the worn thickness, and wherein the wear limiter is configured to engage the heel when the centrifugal clutch is in the extended position.

2. The centrifugal clutch according to claim 1, characterized in that: When the hub is rotatably driven at 400 RPM or greater, the centrifugal clutch is in an extended position.

3. The centrifugal clutch according to claim 1, wherein: The worn thickness is approximately 10% of the installed thickness.

4. The centrifugal clutch according to claim 1, wherein: The centrifugal clutch is configured to transfer torque from the engine to a compressor within the transport refrigeration unit.

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