Patent Application
20110319226
1. Field of the Invention
This invention relates generally to control of friction clutches and brakes of an automatic transmission, particularly providing a range of output in responsive to a control command input.
2. Description of the Prior Art
A torque converter is a fluid coupling, which produces a hydrokinetic drive connection between an impeller, connected to a power source such as an internal combustion engine, and a turbine, connected to an input shaft of an automatic transmission. The torque converter usually includes a bypass clutch, a friction control element which alternately mechanically connects the impeller and turbine and releases the impeller to drive the impeller hydrokinetically.
The transmission produces a range of speed ratios, whose magnitude depends on the operating gear, which depends on the selective engagement and disengagement of friction clutches and brakes.
In typical electro-hydraulic control of these control elements of the torque converter and transmission, the relationship between the electrical command signal, usually current, and torque transmitting capacity of the control element is substantially linear. However, in some vehicle applications wherein an engine is capable of producing very high output torque, a linear relationship results in poor clutch resolution during light load vehicle drive conditions.
If control element gain is high while the engine is producing high output torque, during low engine torque conditions control sensitivity over the control element is low increasing the probability of transmitting torque disturbances in the driveline. Good torque converter bypass clutch control under both heavy and light torque load conditions is necessary for good performance and fuel economy.
A need exists in the industry, therefore, for a technique that provides control element sensitivity and gain enhancement for improved control over a large range of torque transmitting capacity through the control element.
A device for multiple producing gains includes a control element having variable torque capacity, a source of control pressure, and a spring applying to the control element a first force due to said pressure and a variable second force opposing said pressure, producing a first gain when control pressure is relatively low, and a second gain greater than the first gain when control pressure is relatively high.
The multiple gain device produces torque transmitting capacity in the friction control element that is compatible with engine torque produced when a vehicle is heavily loaded or towing, yet the device produces, superior converter clutch control, resolution and gain as required under light road load conditions, without compromising fuel economy.
The device provides clutch sensitivity and gain enhancement control over a large range of torque conditions.
The assembly reduces seal drag by minimizing the number piston seals, eliminates need for a spring to release the clutch 86, and minimizes the required axial length of the assembly.
The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art.
The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which:
Referring first to
The torque converter assembly 10 includes a lockup clutch 24 located within a torque converter housing 25, which is secured to the impeller 12. The lockup clutch 24 alternately engages and disengages a drive connection between the housing 25 and a torsion damper 26. A turbine hub 27 is secured by a spline 29 to the transmission input shaft 28. Turbine torque is transmitted through the damper 26 to the transmission input shaft 28. The damper 26 may incorporate dual or single-stage compression springs 30, 32.
When lockup clutch 24 is fully engaged or slipping, i.e., while there is a speed difference between its input and output (housing 25 and input shaft 28), damper 26 attenuates transitory torque fluctuations between the engine crankshaft 14 and input shaft 28. When the clutch is disengaged, the hydrokinetic connection between impeller 12 and turbine 16 attenuates transient torque disturbances.
The lockup clutch 24 is alternately engaged and disengaged in accordance with the magnitude of clutch apply pressure in a hydraulic passage 34 communicating with a first and second pistons 36, 38. A hub 40, contacting input shaft 28 and thrust bearing 41, supports piston 36 for axial displacement on a radial outer surface of the hub. Seals 42, 44 prevent fluid leakage from passage 34 and permit axial movement of piston 36 relative to hub 40. Piston 36 supports piston 38 for axial displacement on a radial outer surface. Seals 44, 46 prevent fluid leakage from passage 34 and permit axial movement of piston 38 relative to piston 36. Piston 38 is formed with a flange 48, which extends radially inward toward a longitudinal axis 50 and over a surface of piston 36, thereby providing a blocking surface that limits independent rightward displacement of piston 36 relative to piston 38.
A Belleville spring 52 bears against piston 36 and applies a continuous force rightward displacement of piston 36 relative to piston 38. Pistons 36, 38 are closed pistons 40, sealed by O-rings 42, 44, 46.
When actuating pressure in passage 34 is low or absent, clutch 24 is disengaged, i.e., turbine 16 and impeller 12 are hydrokinetically connected and mechanically disconnected. When clutch 24 is engaged, the turbine and impeller are mechanically connected and hydrokinetically disconnected.
When the required torque transmitting capacity of lockup clutch 24 is positive but relatively low, as when the engine output torque is low, the magnitude of clutch apply pressure in hydraulic passage 34 is a relative low, whereby piston 38 is maintained at a leftward position by the force of spring 52, and the low torque piston 38 is forced by actuating pressure rightward into contact with the clutch. The pressure force on piston 38 forces the discs and plates of clutch 24 into mutual frictional contact causing the clutch to fully engage or at least partially engage.
When the magnitude of engine output torque on crankshaft 14 is high, the required torque transmitting capacity of lockup clutch 24 is high and the magnitude of clutch apply pressure in hydraulic passage 34 is a relative high. In this case, the high torque piston 38 is urged rightward by actuating pressure against the force of spring 52, forcing the low torque piston 38 rightward into contact with the clutch 24 due to contact of piston 36 against flange 48 of piston 38. The pressure force on pistons 36, 38 forces the discs and plates of clutch 24 into frictional contact causing the clutch to fully engage.
Fluid contained in the torque converter 10 is supplied from the output of an oil pump 52 and is returned to an oil sump, to which an inlet of the pump is connected hydraulically. Two other oil passages interface with the torque converter providing cooling flow (hydrodynamic and clutch). When converter clutch cooling pressure is greater than bypass clutch control pressure, this pressure returns the piston 38. The pressure that applies the clutch is the difference between the control pressure and cooling pressure. This differential pressure times the piston area minus the spring force is the resultant clutch apply force. The torque capacity can be calculated using the clutch dimensions.
In
A Belleville spring 98 is fitted at its outer end with a lip seal 100 and at its inner end by a lip seal 102. The inner end of spring 98 is secured in position by contact with a shoulder 104. The outer end moves along axis 50 in response to actuating pressure 80 applied to surface 106 of spring 98. The Belleville spring 106 functions as both a spring and an actuating piston.
Actuating pressure 80 on spring 106 forces the discs and plates 92, 94 into mutual frictional contact, thereby engaging the control element 90. When actuating pressure is low, the low gain 72 is effective. When actuating pressure is high, the high gain 76 is effective.
The assembly of
TCCZ is control pressure produced by a torque converter solenoid, either a variable force solenoid or a PWM solenoid.
CLEX is output from valve 110 when the valve is exhausting. The circuit can exhaust directly to a sump, but it is preferable to use elevated vent pressure or a low pressure relief valve, such as a poppet valve, to keep the circuit filled and to avoid drain down.
CAPY is the torque converter clutch apply pressure, i.e., clutch piston pressure, or CAPY can be supplied to the clutches and brakes that produce gear shifting in a hydraulically controlled automatic transmission.
NDX is the feed to valve 110. NDX is preferably supplied from the transmission's a manual valve, which is controlled by the vehicle operator's manually control of the gear shifter. The manual valve only supplies feed in the neutral and drive positions of the gear shifter. But NDX can be directly supplied also from a source of transmission line pressure.
R is a pressure signal from the manual valve supplied when the gear shifter is moved to the reverse position. This R pressure forces CAPY to a low magnitude when the gear shifter is moved to the reverse position.
CRLZ is a pressure signal from a torque converter release circuit applied to the backside of the torque converter clutch piston. CRLZ pressure moves the regulator valve 110 a differential pressure regulator to improve performance. CRLZ pressure is preferred but can be vented in some applications.
In the low gain state 130, valve 110 functions as a pressure regulator, wherein control pressure TCCZ forces spool 114 rightward in chamber 112 against the force of spring 116. This movement opens communication between the hydraulic line that carries NDX pressure and flow to valve 110 and the line that carries CAPY pressure and flow to clutch 24. A pressure force is produced on the plunger 118 due to CAPY feedback pressure. Sleeve 124 remains in contact with shoulder 120 and does not move. In this state clutch piston pressure varies along graph 132.
As control pressure TCCZ increases, the balance of forces acting on sleeve 124, i.e., the force of spring 116 acting rightward on the sleeve, pressure force on plunger 118 acting rightward on the sleeve, and the force of spring 122 acting leftward on the sleeve, changes. When the force balance becomes equal, sleeve 124 has no force applied by shoulder 120. Therefore, any additional increase in control pressure TCCZ initiates the second state 134 and the higher gain 136.
As control pressure TCCZ increases in the second state 134, sleeve 124 shuttles rightward away from contact with shoulder 20, causing the force of spring 122 to participate in the regulation, changing the force balance of the regulating valve, and producing a larger change in CAPY pressure for a given increase in TCCZ control pressure. Gain 136 is therefore greater than gain 132 during operation in the second state.
In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.
