Hybrid transmission

This disclosure is related to hybrid transmission devices to transfer mechanical power for a powertrain system.

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

Powertrain systems use transmission devices to transfer tractive torque between one or more torque generative devices and an output member connected to a driveline. A hybrid transmission device transfers torque between multiple torque generating devices and an output member, with the multiple torque generating devices configured to generate power by converting potential energy to mechanical power. The hybrid transmission device and torque generating devices can also operate to react vehicle kinetic energy to create storable potential energy.

One of the torque generating devices can include a reciprocating piston internal combustion engine. A transmission device transfers mechanical power in the form of speed and torque from the engine to a driveline. The hybrid powertrain system can permit engine operation that is somewhat independent from the power output from the transmission, deriving additional power to meet requirements from other torque-generating devices. This permits engine operation that is optimized for emissions and fuel efficiency. A power-split transmission can use differential gearing to achieve a continuously variable torque and speed ratio between input and output. An electrically variable transmission can use the differential gearing to send a portion of the transmitted power to one or more torque generating devices, with a remainder of the power sent through a parallel torque path to a driveline. One form of differential gearing includes a planetary gear set.

A hybrid transmission is configured to transfer mechanical power to an output member and includes an input member, an output member, and a transmission case circumscribing first and second differential gear sets, each differential gear set including a plurality of meshingly engaged rotatable elements. The first differential gear set is configured with four nodes for transferring mechanical power, and the second differential gear set is configured with three nodes for transferring mechanical power. Two of the four nodes of the first differential gear set are continuously interconnected to two of the three nodes of the second differential gear set. A first torque transfer clutch is configured to selectively connect the input member to an internal combustion engine. First and second brake devices are configured to selectively interconnect elements of the first and second differential gear sets, the transmission case, the input member, and the output member.

One or more embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a two-dimensional schematic diagram of a powertrain system in accordance with the present disclosure; and

FIGS. 2-10 are two-dimensional schematic diagrams exemplifying embodiments of a hybrid powertrain system in accordance with the present disclosure.

Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same, FIG. 1 schematically illustrates a hybrid powertrain system 5 including the hybrid transmission 10 configured to transfer mechanical power between an input member 12 and an output member 14 . Preferably the input member 12 can be selectively connected to an internal combustion engine 20 , e.g., via application of a first clutch 22 . The hybrid powertrain system 5 further includes first and second torque machines (M 1 ) 50 and (M 2 ) 60 . In one embodiment the first and second torque machines 50 and 60 include electric motor/generator devices that interact with a power inverter device to convert electric power to mechanical power in a mechanical power generating mode and to convert vehicle kinetic energy to electric power in an electric power generating mode. When the first and second torque machines 50 and 60 include electric motor/generator devices, they each include a stator that preferably connects to a transmission case 16 and an associated rotor. The first torque machine 50 preferably generates a torque output sufficient to spin the engine 20 from a stopped position under cold operating conditions and provide output torque to the second torque machine 60 that is transferred to the output member 14 . In one embodiment, the first torque machine 50 has a maximum torque output of 50 kW. The second torque machine 60 preferably generates a torque output to provide tractive torque to the output member 14 that is preferably connected to a driveline including vehicle wheels. In one embodiment, the second torque machine 60 has a maximum torque output of 100 kW. Torque output from the first and second torque machines 50 and 60 can be in the form of tractive torque that can be transferred through the hybrid transmission 10 to the driveline to propel the vehicle in either a forward or reverse direction. Torque output from the first and second torque machines 50 and 60 can be in the form of reactive torque that can be transferred through the hybrid transmission 10 to react torque from the driveline.

The hybrid transmission 10 includes a first differential gear set 30 and a second differential gear set 40 . The first differential gear set 30 includes four nodes X 1 , X 2 , X 3 and X 4 including connecting points through which mechanical power in the form of torque and rotational speed can be transferred between the differential gear set 30 and other elements as described herein. The first differential gear set 30 includes a planetary gear set that includes at least one sun gear, and is shown including two sun gears, designated as S 11 and S 12 respectively. The first differential gear set 30 includes at least one carrier gear set C 1 including a plurality of planet gears (not shown) and at least one ring gear designated as R 1 . The ring gear(s) R 1 circumscribes the associated coaxial inner sun gear(s) S 11 and S 12 , separated by the associated carrier gear set C 1 including planet gears that simultaneously meshingly engage both the ring gear(s) and the sun gear(s) to rotate in concert to transfer torque across the four nodes X 1 , X 2 , X 3 and X 4 .

The second first differential gear set 40 preferably includes a planetary gear set including elements including a sun gear S 2 , a carrier gear C 2 set including a plurality of planet gears, and a ring gear R 2 .

The first differential gear set 30 continuously interconnects with the second differential gear set 40 at each of two separate nodes, i.e., connecting points through which mechanical power is transferred. The input member 12 mechanically couples to an element of the second differential gear set 40 that couples to an element of the first differential gear set 30 that couples to the output member 14 . Alternative differential gear sets can include bevel gears or other gear sets arranged such that the rotational speed of at least one element of the gear set is a weighted average of rotational speeds of two other elements.

The first and second differential gear sets 30 and 40 continuously interconnect at two nodes on each of the first and second differential gear sets 30 and 40 . The continuous interconnections include the ring gear R 1 of the first differential gear set 30 fixedly connected to the sun gear S 2 of the second differential gear set 40 , preferably using a first interconnecting member 37 , and the sun gear S 11 of the first differential gear set 30 fixedly connected to the ring gear R 2 of the second differential gear set 40 preferably using a second interconnecting member 47 .

The hybrid transmission further includes the first clutch 22 , a first brake 26 , a second brake 28 , and the transmission case 16 .

The first differential gear set 30 includes the four nodes X 1 , X 2 , X 3 and X 4 . The first node X 1 includes a connecting point to selectively ground rotation of one of the elements of the first differential gear set 30 to the transmission case 16 for torque multiplication, preferably by applying the second brake 28 .

The second node X 2 includes a connecting point to selectively ground rotation of an element of the first differential gear set 30 to the transmission case 16 , preferably by applying the first brake 26 . The action of applying the first brake 26 further includes grounding rotation of the first interconnecting member 37 , thus grounding rotation of the sun gear S 2 of the second differential gear set 40 and any elements connected thereto, e.g., the engine 20 or the first torque machine 50 .

The third node X 3 includes a connecting point to transfer power between another of the elements of the first differential gear set 30 and the output member 14 . The fourth node X 4 includes a connecting point to transfer power between another of the elements of the first differential gear set 30 and the second torque machine 60 . The fourth node X 4 further includes a connecting point to transfer power between another of the elements of the second differential gear set 40 and the second torque machine 60 .

The second brake device 28 can be applied to ground rotation of the second sun gear S 12 to the transmission case 16 to enable operation of the second torque machine 60 at low speed.

The first brake device 26 can be applied to ground rotation of the first torque machine 50 to the transmission case 16 to enable a launch maneuver using the second torque machine 60 .

The first clutch device 22 can be applied to spin the engine 20 to crank and start the engine 20 and to enable torque transfer between the engine 20 and the first differential gear set 30 to generate electric power through the first torque machine 50 and to provide tractive power through the second differential gear set 40 .

In one embodiment, a second clutch device (shown as 24 in FIGS. 2-10 ) can be applied to lock rotation of selected elements of the first and second differential gear sets 30 and 40 to maximize torque transfer from the engine 20 and the first and second torque machines 50 and 60 to the output member 14 through the hybrid transmission 10 .

The hybrid transmission 10 can transfer torque between the input member 12 , the first and second torque machines 50 and 60 , and the output member 14 across the first, second, third and fourth nodes X 1 , X 2 , X 3 and X 4 of the first differential gear set 30 by applying selected ones of the first clutch 22 and brakes 26 and 28 , and selectively applying the second clutch 24 . Specific operating states of the hybrid powertrain system 5 including the hybrid transmission 10 can be described with reference to Table 1, below:

wherein the ‘x’ indicates that the corresponding clutch or brake is applied and the terms (+) and (−) indicate a rotational direction. When the engine 20 is ‘Off’, the engine 20 is unfueled and not spinning or otherwise rotating. When the engine 20 is ‘On’, the engine 20 is fueled and spinning.

The hybrid powertrain system 5 can operate in one of a plurality of operating states by operating the engine 20 in one of the On and Off states, and operating one or both the first and second torque machines (M 1 ) 50 and (M 2 ) 60 , and applying selected ones of the clutches 22 and 24 and brakes 26 and 28 . The vehicle operating states include vehicle launch (Launch), low speed electric vehicle operation (EV Low Speed), high speed electric vehicle operation (EV High Speed), highway operation in an electrically-variable transmission mode (EVT Highway), a fixed gear mode with electric power assist (Fixed Gear-Electric Power Assist), and reverse (Reverse). Operation in the fixed gear mode with electric power assist (Fixed Gear-Electric Power Assist) is effected by simultaneously locking first and second clutches 22 and 24 to lock rotation of the first and second differential gear sets 30 and 40 to maximize power transfer between the first and second torque machines 50 and 60 , the engine 20 , and the output member 14 . Fixed gear operation is characterized by a fixed ratio between rotational speed of the engine 20 via the input member 12 and rotational speed of the output member 14 .

FIGS. 2-10 show embodiments of the hybrid transmission 10 described in FIG. 1 , including the input member 12 , the output member 14 , first and second differential gear sets 30 and 40 , the first and second clutches 22 and 24 , the first and second brakes 26 and 28 , and the transmission case 16 . Like numerals refer to like elements throughout the embodiments. In each embodiment, the second differential gear set 40 includes a sun gear 42 , a carrier gear set 44 , and a ring gear 46 . The carrier gear set 44 connects to the engine 12 when clutch 22 is applied.

FIG. 2 shows an embodiment of the hybrid transmission 10 A including the input member 12 , the output member 14 , first and second differential gear sets 30 A and 40 , the first and second clutches 22 and 24 , the first and second brakes 26 and 28 , and the transmission case 16 . Like numerals refer to like elements throughout the embodiments. The first differential gear set 30 A includes two coaxial sun gears including a first sun gear 32 A and a second sun gear 32 A′, a carrier gear set 34 A, 34 A′ including a complex planet gear set, and a ring gear 36 A. The first sun gear 32 A and the second sun gear 32 A′ rotate independently, or rotate synchronously when clutch 24 is applied.

The two interconnections between the first and second differential gear sets 30 A and 40 in this embodiment include the ring gear 36 A fixedly connected to the sun gear 42 using a first interconnecting member 37 A, and the first sun gear 32 A fixedly connected to the ring gear 46 using a second interconnecting member 47 A.

The first node X 1 includes the connecting point between the first differential gear set 30 A and the transmission case 16 , which includes selectively applying the second brake device 28 to ground rotation of the second sun gear 32 A′ to the transmission case 16 in this embodiment.

The second node X 2 includes the connecting point to selectively ground rotation of the ring gear 36 A of the first differential gear set 30 A and thus ground rotation of the first torque machine 50 and the sun gear 42 of the second differential gear set 40 . This includes selectively applying the first brake 26 to ground rotation of the ring gear 36 A and the first interconnecting member 37 A to the transmission case 16 in this embodiment.

The third node X 3 includes a connecting point to transfer power between the carrier gear set 34 A′ of the first differential gear set 30 A and the output member 14 in this embodiment.

The fourth node X 4 includes a connecting point to transfer power between the first sun gear 32 A of the first differential gear set 30 A and the second torque machine 60 in this embodiment.

FIG. 3 shows another embodiment of the hybrid transmission 10 B including input member 12 , output member 14 , first and second differential gear sets 30 B and 40 , the first and second clutches 22 and 24 , the first and second brakes 26 and 28 , and the transmission case 16 . Like numerals refer to like elements. The first differential gear set 30 B includes two coaxial sun gears including a first sun gear 32 B and a second sun gear 32 B′, a carrier gear set with rotationally connected coaxial elements 34 B and 34 B′, and a ring gear 36 B. The first sun gear 32 B and the second sun gear 32 B′ rotate independently.

The two interconnections between the first and second differential gear sets 30 B and 40 in this embodiment include the carrier gear set 34 B fixedly connected to the sun gear 42 using a first interconnecting member 37 B, and the first sun gear 32 B fixedly connected to the ring gear 46 using a second interconnecting member 47 B.

The first node X 1 includes the connecting point to transfer power between the first differential gear set 30 B and the transmission case 16 , which includes selectively applying the second brake device 28 to ground rotation of the ring gear 36 B to the transmission case 16 in this embodiment.

The second node X 2 includes the connecting point to selectively ground rotation of the carrier gears 34 B and 34 B′ of the first differential gear set 30 B and ground rotation of the first torque machine 50 via the sun gear 42 of the second differential gear set 40 . This includes selectively applying first brake 26 to ground rotation of the first interconnecting member 37 B and the carrier gears 34 B and 34 B′ to the transmission case 16 in this embodiment.

The third node X 3 includes a connecting point to transfer power between the second sun gear 32 B′ of the first differential gear set 30 B and the output member 14 in this embodiment.

The fourth node X 4 includes a connecting point to transfer power between the first sun gear 32 B of the first differential gear set 30 B and the second torque machine 60 in this embodiment.

FIG. 4 shows another embodiment of the hybrid transmission 10 C including the input member 12 , the output member 14 , the first and second differential gear sets 30 C and 40 , the first and second clutches 22 and 24 , the first and second brakes 26 and 28 , and the transmission case 16 . Like numerals refer to like elements. The first differential gear set 30 C includes a single sun gear 32 C, a complex carrier gear set 34 C that rotationally connects to a first ring gear 36 C and a second ring gear 36 C′. The first ring gear 36 C and the second ring gear 36 C′ rotate independently.

The two interconnections between the first and second differential gear sets 30 C and 40 in this embodiment include the carrier gear set 34 C fixedly connected to the sun gear 42 using a first interconnecting member 37 C, and the sun gear 32 C fixedly connected to the ring gear 46 using a second interconnecting member 47 C.

The first node X 1 includes the connecting point to transfer power between the first differential gear set 30 C and the transmission case 16 , which includes selectively applying the second brake device 28 to ground rotation of the first ring gear 36 C to the transmission case 16 in this embodiment.

The second node X 2 includes the connecting point to selectively ground rotation of the carrier set 34 C of the first differential gear set 30 C and thus ground rotation of the first torque machine 50 and the sun gear 42 of the second differential gear set 40 . This includes selectively applying the first brake 26 to ground rotation of the first interconnecting member 37 C to the transmission case 16 in this embodiment.

The third node X 3 includes a connecting point to transfer power between the second ring gear 36 C′ of the first differential gear set 30 C and the output member 14 in this embodiment.

The fourth node X 4 includes a connecting point to transfer power between the sun gear 32 C of the first differential gear set 30 C and the second torque machine 60 in this embodiment.

FIG. 5 shows another embodiment of the hybrid transmission 10 D including the input member 12 , the output member 14 , first and second differential gear sets 30 D and 40 , the first and second clutches 22 and 24 , the first and second brakes 26 and 28 , and the transmission case 16 . Like numerals refer to like elements. The first differential gear set 30 D includes rotationally connected first and second sun gears 32 D and 32 D′, coaxial, independently rotating first and second carrier gear sets 34 D and 34 D′ that are rotatably connected to rotationally connected ring gears 36 D and 36 D′.

The two interconnections between the first and second differential gear sets 30 D and 40 in this embodiment include the first carrier gear set 34 D fixedly connected to the sun gear 42 using a first interconnecting member 37 D, and the first and second sun gears 32 D and 32 D′ fixedly connected to the ring gear 46 using a second interconnecting member 47 D.

The first node X 1 includes the connecting point to transfer power between the first differential gear set 30 D and the transmission case 16 , which includes selectively applying the second brake device 28 to ground rotation of the ring gears 36 D and 36 D′ to the transmission case 16 in this embodiment.

The second node X 2 includes the connecting point to selectively ground rotation of the first carrier set 34 D of the first differential gear set 30 D and thus ground rotation of the first torque machine 50 and the sun gear 42 of the second differential gear set 40 . This includes selectively applying the first brake 26 to ground rotation of the first interconnecting member 37 D to the transmission case 16 in this embodiment.

The third node X 3 includes a connecting point to transfer power between a planet gear of the second carrier gear set 34 D′ of the first differential gear set 30 D and the output member 14 in this embodiment.

The fourth node X 4 includes connecting points to transfer power between the first and second sun gears 32 D and 32 D′ of the first differential gear set 30 D and the second torque machine 60 in this embodiment.

FIG. 6 shows another embodiment of the hybrid transmission 10 E including the input member 12 , the output member 14 , first and second differential gear sets 30 E and 40 , the first and second clutches 22 and 24 , the first and second brakes 26 and 28 , and the transmission case 16 . Like numerals refer to like elements. The first differential gear set 30 E includes sun gear 32 E, carrier gear set including planet gears 34 E and 34 E′ rotationally connected to first and second ring gears 36 E and 36 E′ respectively. The first and second ring gears 36 E and 36 E′ rotate independently, and can be rotationally fixed by applying clutch 24 .

The two interconnections between the first and second differential gear sets 30 E and 40 in this embodiment include the first ring gear 36 E fixedly connected to the sun gear 42 using a first interconnecting member 37 E, and the sun gear 32 E fixedly connected to the ring gear 46 using a second interconnecting member 47 E.

The first node X 1 includes the connecting point to transfer power between the first differential gear set 30 E and the transmission case 16 , which includes selectively applying the second brake device 28 to ground rotation of the second ring gear 36 E′ to the transmission case 16 in this embodiment.

The second node X 2 includes the connecting point to selectively ground rotation of the first ring gear 36 E of the first differential gear set 30 E and the first torque machine 50 and the sun gear 42 of the second differential gear set 40 . This includes selectively applying first brake 26 to ground rotation of the first interconnecting member 37 E to the transmission case 16 in this embodiment.

The third node X 3 includes a connecting point to transfer power between the carrier gear set 34 , 34 E′ of the first differential gear set 30 E and the output member 14 in this embodiment.

The fourth node X 4 includes a connecting point to transfer power between the sun gear 32 E of the first differential gear set 30 E and the second torque machine 60 in this embodiment.

FIG. 7 shows another embodiment of the hybrid transmission 10 F including the input member 12 , the output member 14 , first and second differential gear sets 30 F and 40 , the first and second clutches 22 and 24 , the first and second brakes 26 and 28 , and the transmission case 16 . Like numerals refer to like elements. The first differential gear set 30 F includes sun gear 32 F, compound, complex carrier gear set including interconnected first, second and third carrier gear sets 34 F, 34 F′, 34 F″, and ring gears 36 F and 36 F′.

The two interconnections between the first and second differential gear sets 30 F and 40 in this embodiment include the first ring gear 36 F fixedly connected to the sun gear 42 using a first interconnecting member 37 F, and the sun gear 32 F fixedly connected to the ring gear 46 using a second interconnecting member 47 F.

The first node X 1 includes the connecting point to transfer power between the first differential gear set 30 F and the transmission case 16 , which includes selectively applying the second brake device 28 to ground rotation of the third carrier gear set 34 F″ to the transmission case 16 in this embodiment.

The second node X 2 includes the connecting point to selectively ground rotation of the ring gear 36 F of the first differential gear set 30 F and the first torque machine 50 and the sun gear 42 of the second differential gear set 40 . This includes selectively applying the first brake 26 to ground rotation of the first interconnecting member 37 F to the transmission case 16 in this embodiment.

The third node X 3 includes a connecting point to transfer power between the first and second carrier gear sets 34 F and 34 F′ of the first differential gear set 30 F and the output member 14 in this embodiment.

The fourth node X 4 includes a connecting point to transfer power between the sun gear 32 F of the first differential gear set 30 F and the second torque machine 60 in this embodiment.

FIG. 8 shows another embodiment of the hybrid transmission 10 G including the input member 12 , the output member 14 , first and second differential gear sets 30 G and 40 , the first and second clutches 22 and 24 , the first and second brakes 26 and 28 , and the transmission case 16 . Like numerals refer to like elements. The first differential gear set 30 G includes sun gear 32 G, carrier gear sets 34 G and 34 G′, and first and second ring gears 36 G and 36 G′.

The two interconnections between the first and second differential gear sets 30 G and 40 in this embodiment include the second ring gear 36 G′ fixedly connected to the sun gear 42 using a first interconnecting member 37 G, and the sun gear 32 G fixedly connected to the ring gear 46 using a second interconnecting member 47 G.

The first node X 1 includes the connecting point to transfer power between the first differential gear set 30 G and the transmission case 16 . This includes selectively applying the second brake device 28 to ground rotation of the first ring gear 36 G to the transmission case 16 in this embodiment.

The second node X 2 includes the connecting point to selectively ground rotation of the second ring gear 36 G′ of the first differential gear set 30 G and the first torque machine 50 and the sun gear 42 of the second differential gear set 40 . This includes selectively applying first brake 26 to ground rotation of the first interconnecting member 37 G to the transmission case 16 in this embodiment.

The third node X 3 includes a connecting point to transfer power between a planet gear of the carrier gear set 34 G of the first differential gear set 30 G and the output member 14 in this embodiment.

The fourth node X 4 includes a connecting point to transfer power between the sun gear 32 G of the first differential gear set 30 G and the second torque machine 60 in this embodiment, which is connected to the ring gear 46 of the second differential gear set 40 via the second interconnecting member 47 G.

FIG. 9 shows another embodiment of the hybrid transmission 10 H including the input member 12 , the output member 14 , first and second differential gear sets 30 H and 40 , the first and second clutches 22 and 24 , the first and second brakes 26 and 28 , and the transmission case 16 . Like numerals refer to like elements. The first differential gear set 30 H includes first and second sun gears 32 H and 32 H′, first and second carrier gear sets 34 H and 34 H′, and first and second ring gears 36 H and 36 H′. The first and second ring gears 36 H and 36 H′ are rotationally fixed.

The two interconnections between the first and second differential gear sets 30 H and 40 in this embodiment include the second carrier gear 34 H′ fixedly connected to the sun gear 42 using a first interconnecting member 37 H, and the second sun gear 32 H′ fixedly connected to the ring gear 46 using a second interconnecting member 47 H.

The first node X 1 includes the connecting point to transfer power between the first differential gear set 30 H and the transmission case 16 . This includes selectively applying the second brake device 28 to ground rotation of the first and second ring gears 36 H and 36 H′ to the transmission case 16 in this embodiment.

The second node X 2 includes the connecting point to selectively ground rotation of the second carrier gear 34 H′ of the first differential gear set 30 H and the first torque machine 50 and the sun gear 42 of the second differential gear set 40 . This includes selectively applying first brake 26 to ground rotation of the first interconnecting member 37 H in this embodiment.

The third node X 3 includes a connecting point to transfer power between the sun gear 32 H of the first differential gear set 30 H and the output member 14 in this embodiment.

The fourth node X 4 includes a connecting point to transfer power between the carrier gear 34 H′ of the first differential gear set 30 H and the second torque machine 60 in this embodiment, which is connected to the ring gear 46 of the second differential gear set 40 .

FIG. 10 shows another embodiment of the hybrid transmission 10 I including the input member 12 , the output member 14 , first and second differential gear sets 30 I and 40 , the first and second clutches 22 and 24 , the first and second brakes 26 and 28 , and the transmission case 16 . Like numerals refer to like elements. The first differential gear set 30 I includes first and second sun gears 32 I and 32 I′, compound carrier gear set 34 I and 34 I′, and ring gear 36 I.

The two interconnections between the first and second differential gear sets 30 I and 40 in this embodiment include the compound carrier gear set 34 I and 34 I′ fixedly connected to the sun gear 42 using a first interconnecting member 37 I, and the second sun gear 32 I′ fixedly connected to the ring gear 46 using a second interconnecting member 47 I.

The first node X 1 includes the connecting point to transfer power between the first differential gear set 30 I and the transmission case 16 . This includes selectively applying the second brake device 28 to ground rotation of the ring gear 36 I to the transmission case 16 in this embodiment.

The second node X 2 includes the connecting point to selectively ground rotation of the complex carrier gear set 34 I and 34 I′ of the first differential gear set 30 I and the first torque machine 50 and the sun gear 42 of the second differential gear set 40 . This includes selectively applying the first brake 26 to ground rotation of the compound carrier gear set 34 I and 34 I′ to the transmission case 16 in this embodiment.

The third node X 3 includes a connecting point to transfer power between the first sun gear 32 I of the first differential gear set 30 I and the output member 14 in this embodiment.

The fourth node X 4 includes a connecting point to transfer power between the second sun gear 32 I′ and the second torque machine 60 in this embodiment, which is connected to the ring gear 46 of the second differential gear set 40 .

The disclosure has described certain preferred embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.