Patent Application
20130153355
Various embodiments of the disclosure relate to a hydraulic or wet clutch assembly having channels with ports in the inner hub of the clutch assembly for thermal management of the clutch assembly.
Hydraulically actuated clutches, or wet clutches, use coolant flow for thermal management of the clutch plates as they generate heat from friction during operation of the clutch. In the past, thermal management of the wet clutch included increasing the coolant volumetric flow rate to the clutch to increase heat transfer away from the clutch plates. However, this may be inefficient and also result in poor cooling uniformity and thermal management of the plates in the clutch pack.
In one embodiment, a wet clutch assembly includes an inner housing supporting a series of splines. The splines rotate with an input torque member to the clutch assembly. An outer housing rotates with an output torque member from the clutch assembly. A clutch pack is interposed between the inner and outer housing. The clutch pack selectively transfers torque from the input member to the output member. The clutch pack has a series of plates supported by the splines. Each spline defines a single aperture in fluid communication with at least one plate of the clutch pack. Apertures on adjacent splines are offset.
In another embodiment, a dual clutch assembly is provided. A first clutch is configured to selectively transfer torque from an input torque member to a first output torque member of the clutch assembly. The first clutch has a first series of plates and a first series of cooling channels. Each cooling channel defines a single port that is in fluid communication with at least one plate. Ports on adjacent cooling channels are offset from one another. A second clutch is configured to selectively transfer torque from the input torque member to a second output torque member of the clutch assembly. The second clutch has a second series of plates and a second series of cooling channels. Each cooling channel defines a single port in fluid communication with at least one plate. Ports on adjacent cooling channels are offset from one another.
In yet another embodiment, an inner housing for a clutch is provided with a generally cylindrical housing formed about a longitudinal axis. A first series of cooling channels is supported by the housing and configured for flow along the longitudinal axis. Each cooling channel in the first series defines a single aperture on an outer surface of the housing at a first position along the axis. A second series of cooling channels is supported by the housing and configured for flow along the longitudinal axis. Each cooling channel in the second series defines a single aperture on the outer surface of the housing at a second position along the axis.
The above aspects of the disclosure and other aspects are described below with reference to the attached drawings.
A detailed description of the illustrated embodiments of the present invention is provided below. The disclosed embodiments are examples of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale. Some features may be exaggerated or minimized to show details of particular components. The specific structural and functional details disclosed in this application are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art how to practice the invention.
In
The first input shaft 12 is in communication with an output member 18, such as a flywheel, of an engine or other prime mover through a first main clutch 20 and a second main clutch 22. In one embodiment, the first main clutch 20 is used to establish even speed gearing (second, fourth, and reverse gearing) through input shaft 12. The second input shaft 42 may be connected to flywheel 18 using the second main clutch 22 to establish odd speed gearing (first, third, and fifth).
The hydraulically actuated clutches 20, 22, or wet clutch, is shown in a dual clutch arrangement in a transmission 10 for use in a powertrain system. Alternatively, the clutch 20 may be used in other types of torque transmission arrangements as are known in the art including small, medium, and heavy duty powertrain systems. The hydraulically actuated clutch 20 has improved thermal management of the plates in the clutch pack by controlling the coolant flow path that provides for use in high thermal event connections. For example, a high thermal event may include a dual clutch system with both clutches 20, 22 slipping, such as when one clutch is engaging while the other is disengaging. The use of the clutches 20, 22 in a dual clutch transmission is provided for illustrative purposes, and should not be viewed as limiting the disclosure.
In some embodiments, the first and second main clutches 20, 22 are of a normally “on” type, with the on or engaged state caused by a spring biasing force, or the like, under a normal condition, and with the off or disengaged state caused by a command to engage a hydraulic or electric actuator. Engagement and disengagement of first and second main clutches 20, 22 may function automatically under the control of a vehicle system controller (VSC), and without the intervention of a user driver, such that the transmission 10 operates as an “automatic” transmission.
Even speed gearing, such as second speed input gear 24, fourth speed input gear 26 and reverse input gear 28, are connected to the first input shaft 12 such that they rotate with the shaft 12. Similarly, odd speed gearing, such as a first speed input gear 30, third speed input gear 32, and fifth speed input gear 34, are connected to the second input shaft 14 such that they rotate with the shaft 14. The number of gears and arrangement of the gears as shown on the first and second input shafts 12, 14 is not limited to the illustration of
Output gearing is connected to countershaft 16 to selectively engage the input gearing as described above. A first speed output gear 36, third speed output gear 38, fifth speed output gear 40, reverse output gear 42, second speed output gear 44, and fourth speed output gear 46 are connected to countershaft 16 to rotate with the countershaft 16. The number of output gears provided on countershaft 16 is not limited in number or arrangement, and may vary with the number and arrangement of input gears.
A final drive pinion gear 48 is also connected to the countershaft 16 to rotate with the countershaft 16. The final drive pinion 18 is meshed with a rotational output member 50, such as a final drive ring gear. For example, transmission 10 output rotation from drive pinion 48 to output member 50 may be distributed to vehicle wheels through a drive shaft and a differential.
The transmission 10 has axially moveable clutches 52, 54, 56, and 58, such as synchronized single or double acting dog-type clutches, that are splined to countershaft 16 to rotate with the countershaft. The clutches 52, 54, 56, 58 may be moved in an axial direction to fix one of the output gears to the countershaft 16 for rotation with the countershaft. In another embodiment, the clutches 52, 54, 56, 58 may be provided on the first and second input shafts 12, 14 to engage and disengage gears on the input shafts 12, 14 for rotation with the input shafts.
The transmission 10 also includes axially moveable input shaft clutches 60 and 62, such as synchronized single acting dog-type clutches, that are splined to the first input shaft 12 to rotate with the shaft 12. The clutch 60 may be moved in an axial direction with respect to the main clutch assembly 64 to fix first input shaft 12 for rotation with second input shaft 14. Similarly, clutch 62 may be moved in an axial direction to fix the first input shaft 12 for rotation with output member 50.
For example, during vehicle launch and acceleration, the first and second main clutches 20, 22 are initially disengaged and clutch 52 is moved to fix the first speed output gear 36 to countershaft 16. When the clutch 52 is engaged, power or torque from a prime mover and input 46 may be transmitted to countershaft 16 by engaging the second main clutch 22. The power applied to second input shaft 14 is transmitted from the flywheel 46 through the second clutch 22 to the second shaft 14. Power is then transmitted through the first speed input gear 58 on the second shaft 14 to the first speed output gear 36 on the countershaft 16. The output gear 36 transmits power to the final drive pinion 48 and rotational output member 50 so that a first speed ratio is established in transmission 10.
As the vehicle accelerates and a second speed ratio is desired, clutch 56 is engaged while the first main clutch 20 is disengaged, such that the second speed output gear 44 is fixed to countershaft 16 and no power is being transmitted from flywheel 46 to the first input shaft 12 at this point. The currently engaged second main clutch 22 is disengaged after the clutch 56 is engaged, while simultaneously or nearly simultaneously engaging the first main clutch 20. This causes the power to change paths from the second input shaft 14 to the first input shaft 12, with a corresponding change in gearing ratio. Power applied to the first input shaft 12 is transmitted through the second speed input gear 24 to countershaft 16 through second speed output gear 44, and then to the final drive pinion 48 and rotational output member 50 to establish a second speed ratio in the transmission 10. This process may be repeated, with the selective activation of the appropriate clutch, in the same manner for up-shifting through the remaining gear ratios, in a reverse manner for down-shifting from one gear ratio to another, or for shifting into reverse gear using an idler gear 63.
The main clutch assembly 64 has an input housing 100, connected to and rotating with the output member 18. The output member 18 is connected to and rotates with an input hub 102 that is rotated by the prime mover or engine about rotational axis 101. The input housing 100 is connected to a main hub 104 that may operate as a rotating manifold to direct coolant fluids to the clutches 20, 22.
The main hub 104 supports a pump drive gear 106 and a pair of hydraulic piston systems 108. The hydraulic piston systems 108 each include a piston housing 110, an apply piston 112, a spring pack 114, an oil guide 116, and a balancing piston 118. The hydraulic piston systems 108 may or may not be symmetrical based on the desired sizing of the clutches and the packaging requirements for the clutch assembly 64. The hydraulic piston systems 108 are shown as opposed pistons, although other configurations may also be used.
The main hub 104 and input housing 100 also support an inner housing 120 for the first clutch 20 and an inner housing 122 for the second clutch 22. The inner housings 120, 122 are additionally supported by a support disk 124 extending from the main hub 104. In the embodiment shown, a series of separator plates 126, or reaction plates, for each clutch 20, 22 are supported by the inner housings 120, 122, such that the separator plates 126 rotate with the main hub 104. Each inner housing 120, 122 has channels and ports formed into it to direct coolant between the separator plates 126.
The clutches 20, 22 also each have a series of friction plates or disks 128 that are interposed or interleaved between the separator or clutch plates 126. The friction plates 128 for the first clutch 20 are supported by a first outer housing 130. The friction plates 128 for the second clutch 22 are supported by a second outer housing 132. The friction plates 128 may have grooves, such as a pattern of waffle grooves, or other patterns on the surface to move coolant fluid. Together, the separation plates 126 and friction plates 128 form a clutch pack.
The friction plates 128 move with respect to the separator plates 126 of the first clutch 20 when the clutch 20 is disengaged or slipping. The first outer housing 130 rotates with a mating spline 13 that is connected to the first shaft 12. The rotating hub 104 transfers rotation and power through an engaged clutch 20 and to the outer housing 130, mating spline 13, and first shaft 12. When the clutch 20 is engaged, the friction plates 128 and the separator plates 126 of the first clutch are stationary and locked with respect to one another, or may be slipping such that the plates 126, 128 are moving with respect to one another under friction.
The friction plates 128 move with respect to the separator plates 126 of the second clutch 22 when the clutch is disengaged or slipping. The second outer housing 132 rotates with a mating spline 15 that is connected to the second shaft 14. The rotating hub 104 transfers rotation and power through an engaged clutch 22 and to the outer housing 132, the mating spline 15, and second shaft 14. When the clutch 22 is engaged, the friction plates 128 and the separator plates 126 of the second clutch are stationary and locked with respect to one another, or may be slipping such that the plates 126, 128 are moving with respect to one another under friction.
The support manifold 134 supplies fluid to main hub 104 that supplies fluid to the first and second clutch 20, 22 through ports in the main hub 104. As the main hub 104 rotates, fluid contained in the main hub 104 tends to rotate and will be accelerated away from the axis 101. High-pressure circuits control piston movement while low-pressure circuits provide fluid for clutch cooling. The high-pressure fluid biases the respective pistons 112 and acts against the biasing force of springs 114. Additionally, the low-pressure fluid fills the chambers adjacent to balancing pistons 118. Low-pressure fluid for cooling flows under the spring seat of the oil guide 116 and then flows axially between the oil guide 116 and the spines of the inner housing 120, 122 until reaching port 136 shown in
The contacting frictional surfaces of various friction plates 126, 128 in each clutch 20, 22 may reach different temperatures during operation if not cooled adequately and uniformly. When the distribution of fluid through the clutch pack is not uniform, the friction plates receiving the least fluid may be vulnerable to overheating and wear. Prior art designs may result in low flow (or non-uniform flow) to the farthest plates 128 in a clutch, and may require increasing the volumetric flow rates to adequately cool the clutch, Alternatively, non-uniform flow in the prior art may result in overheating some of the plates within the clutch during higher thermal events even with increased volumetric flow rates.
The efficiency of the clutch or efficiency of the cooling process decreases if the temperatures vary between frictional disks within a clutch pack. The frictional disk may degrade and the clutch performance may decrease if the thermal load and temperature on a frictional disk is too high over time. The thermal management of the frictional disks in a clutch may be determined. Modeling, such as computational fluid dynamics, may be used to model and estimate whether the clutch plates are being adequately cooled by the coolant. Testing, such as through high duty cycles on the clutch, may be used to verify the modeling results and for additional data. Various embodiments use inner housings 120, 122 with cooling ports strategically positioned to more evenly distribute flow to the frictional plates 128 and reduce the amount of temperature variation between clutch plates. The size of the coolant pump for the manifold 134 may be reduced after the amount of temperature variation between clutch plates is reduced, also leading to higher efficiencies.
An embodiment of the inner housing 120 is illustrated in
Each spline 138 has a port 136 positioned at an axial location along the length of the spline 138. The number of ports 136 may vary depending on the number of plates in the clutch pack that are used with the inner housing 120. In the embodiment shown, there are three axial positions for the ports 136. The inner housing 120 supports six separator plates and six friction plates such that any given port supplies coolant to the two friction plates it is adjacent to. The ports 136 are elongated in shape or cross section, and may be a rounded rectangle, an ellipse, or the like. Of course, the ports 136 may be shaped differently to provide coolant to greater or fewer plates, and may be circular, polygonal, complex polygonal, or other shape as is known in the art. The ports 136 may have equivalent cross-sections to one another for the coolant to pass through. Of course, in other embodiments, the area of the ports may vary compared to one another.
In the embodiment shown, a first series of ports 144 are positioned at a first axial position 146 of the inner housing 120. A second series of ports 148 are positioned at a second axial position 150 of the inner housing 120. A third series of ports 152 are positioned at a third axial position 154 of the inner housing 120. The axial positions 146, 150, 154 are offset by an equidistant amount, however, other amounts of offset are also contemplated.
Each series of ports may have the same number of ports, or a different number. For example, each series of ports may have nine ports, twelve ports, or any other number. Flow is radially distributed to the plates by providing coolant to the plates from multiple ports in the series arranged around the circumference of the inner housing.
The ports in each series are sequentially positioned radially about the inner housing. For example, on three consecutive splines 138 there is a port from the first, second and third series of ports 144, 148, 152, as shown. The pattern repeats itself about the circumference of the inner housing 120. In other embodiments, other positioning arrangements may be used for the ports 138.
The inner surface of each spline 138 forms a channel for coolant flow. Coolant flows along the interior surface of the spline 138 until reaching the port 136 on the spline 138. Coolant flows through the port 136 and to the clutch pack. Coolant flows by centrifugal forces along the channel as the inner housing 120 rotates with the clutch hub 104.
The ports in the inner housing are positioned and offset such that the first series of ports 144 provides coolant to the first and second plates 158, 164. The second series of ports 148 provides coolant to the third and fourth plates 170, 176. The third series of ports 152 provides coolant to the fifth and sixth plates 182, 188. For example, the third series of ports 152 provide a dedicated flow path for coolant to the fifth and sixth plates 182, 188. The coolant flowing through the splines 138 defining the third series of ports 152 may only flow to the fifth and sixth plates 182, 188 thereby increasing flow uniformity to the plates and improved thermal management. In the embodiment shown, each pair of plates receives approximately a third of the coolant flowing through the main clutch 20. The number of ports for the example shown has the number of series of ports, or axial positions for the ports, equal to half of the total number of friction plates. In other embodiments, the main clutch 20 may have greater or fewer plates, greater or fewer axial port positions, and differing ratio of plates to axial positions.
In prior art systems, with more than one port on a spline, the normalized axial flow to the fifth and sixth plates 182, 188 may fall near zero as the coolant exits the channel through an earlier port, leading to non-uniform flow and varying temperatures in the plates in a clutch undergoing high thermal events.
An example of a prior art system having three axial port locations with the first and third axially positioned ports on the same spline, and the second axially positioned port on a different spline is also displayed on
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments that are not explicitly illustrated or described.
One or more embodiments have been described as providing advantages or being preferred over other embodiments and/or over prior art with respect to one or more desired characteristics. As such, any embodiments described as being less desirable relative to other embodiments with respect to one or more characteristics are not outside the scope of the claimed subject matter.
