Patent Application
20060100060
1. Field of the Invention
The invention relates to automotive vehicle powertrains, including a hybrid electric vehicle powertrain, with an engine connected driveably to torque input elements of multi-ratio transmission gearing without a hydrokinetic torque converter.
2. Background Art
In a conventional multiple-ratio power transmission mechanism for automotive vehicle powertrains, a hydrokinetic torque converter typically is disposed between an internal combustion engine and torque input elements of multiple-ratio gearing, which establishes multiple torque flow paths to vehicle traction wheels. The torque converter provides a torsional dampening effect that modifies dynamic disturbances during ratio shifting. It also effects smooth and improved launch performance of the vehicle from a standing start.
These advantages of a torque converter are partially offset by an inherent torque converter inefficiency, which results in a power loss manifested by a high operating temperature of the hydrokinetic torque converter fluid. This necessitates the use of an oil cooler. Further, the torque converter has a substantial rotary mass, including the mass of its hydraulic fluid, which adds to the gross weight of the transmission assembly. It also requires significant packaging space in the powertrain assembly.
Attempts have been made to eliminate the torque converter from the transmission to avoid inherent hydrokinetic power losses in the converter that reduce overall transmission efficiency. A control system for a converterless transmission of this type is disclosed in U.S. Pat. No. 6,299,565, which describes a strategy for obtaining maximum smoothness during a vehicle launch, as well as transient damping by a slipping wet clutch. The clutch is allowed to slip during engagement and disengagement of transmission ratio controlling friction elements.
A converterless transmission control system is disclosed also in U.S. Pat. No. 6,217,479, which discloses a strategy for slipping a friction element of a clutch and brake system for multiple-ratio gearing to achieve torsional isolation that normally would be provided by a hydrokinetic torque converter.
U.S. Pat. Nos. 6,176,808 and 6,585,066 disclose a converterless transmission in a hybrid electric vehicle powertrain wherein a high voltage induction motor is situated between an engine and multiple-ratio gearing. The motor is used to provide added vehicle launch performance and to reduce undesirable torsional vibrations during vehicle launch and during transmission ratio shifting. The rotor of the motor provides a rotary mass that achieves a flywheel effect analogous to the flywheel effect provided by a rotary torque converter in a conventional hydrokinetic torque converter transmission. U.S. Pat. No. 6,585,066 further discloses a slipping wet clutch in the power flow path between the engine and torque input elements of the gearing. The wet clutch complements the function of a damper assembly in transmission power flow paths, such as the power flow paths described in the '808 patent, by attenuating peak torque fluctuations during vehicle launch and during ratio shifts.
In a powertrain of the kind disclosed in the prior art references mentioned above, which are owned by the assignee of the present invention, a shift of the automatic transmission is characterized by two distinct shift phases, commonly referred to as a torque phase and an inertia phase. A power-on upshift, for example, experiences a torque phase when the capacity of the oncoming friction element is increased to control the shift. The output torque is changed to the upshifted torque while the speeds remain at the downshifted values. The torque phase is followed by an inertia phase in which the speeds of the engine and the transmission components are decreased to the upshifted values.
Normally, the torque phase is controlled using an open loop control system that is either event-based or time-based. Speed sensors within the transmission can detect the start of the inertia phase. When a speed ratio change is detected, the shift control system typically begins closed loop control of the oncoming friction element.
In a conventional transmission, only an input speed sensor and an output speed sensor are required since it is necessary only to obtain repetitive values of the speed ratio during the inertia phase to control shift events. The speed sensors determine the overall transmission ratio. Since the only event that is being controlled at any given instant is the shift event, the overall ratio is an indicator of the progress of the shift event. Thus, the speed ratio, or its derivative, is used as a control variable for closed loop control of the inertia phase and as a trigger for initiating other control events during the shift interval.
In a converterless multiple-ratio transmission of the kind previously discussed, such as the pre-transmission hybrid transmissions of the '066 patent and the '808 patent, it may be necessary, while a shift event is taking place, to control dynamic events other than the shift event. One example of a dynamic event that would be controlled during a shift event is disclosed in co-pending U.S. patent application Ser. No. 10/838,489 filed May 4, 2004, entitled “Torsional Isolation of a Converterless Automatic Transmission Through Slip Control of Friction Clutch.” That co-pending patent application is assigned to the assignee of this invention.
In a powertrain with a torsional isolation control strategy, for example, multiple clutches can be slipping so that the overall transmission ratio may not be indicative of the status of the shift event. Using transmission ratio percent shift complete as a control parameter, therefore, can cause errors by the shift controller, which can adversely affect shift quality. It is desirable, therefore, to use a strategy for controlling shift events that will accommodate accurate control of at least one additional simultaneous event.
The invention comprises a converterless transmission and control strategy that makes it possible to control simultaneously at least two events during a ratio shift interval to achieve maximum smoothness and to attenuate torsional vibrations during both vehicle start up and ratio shifting. The invention uses multiple speed sensors, in addition to the usual input and output speed sensors, so that the slip speed of several friction elements in the powertrain can be determined at each instant during the shift event under all circumstances. By knowing the slip speed for each friction element, the exact status of a shift event can be separated from the status of other control events that occur simultaneously during the ratio shift interval.
Unlike prior art shift control strategies that require an overall ratio as a control parameter during a shift event, the strategy of the present invention avoids errors created when multiple clutches are slipping by using the added speed information from the multiple speed sensors. The slip speed of the oncoming friction element is used as a control parameter rather than overall speed ratio.
The slip speed of the oncoming friction element is captured at the beginning of the shift. It is stored in random access memory of an electronic transmission controller and accessed by a central processor unit (CPU) in the controller to compute instantaneous states of a shift during a shift event. The control strategy will cause the slip speed of an oncoming friction element during a ratio change to progress to a zero value at the end of a shift event. Based on this information, the transmission controller determines slip speed triggers and a closed loop shift profile at the beginning of every shift event. The shift then proceeds in a manner similar to other closed loop shifts found in prior art control systems, but it is independent of other simultaneous transmission control events.
At the beginning of a ratio shift, the actuating pressure for an oncoming friction element is increased during a torque phase of the shift to effect rapid filling of a pressure actuator for the oncoming friction element. The slip speed of an actuator for an off-going friction element is detected at the beginning of an inertia phase of the shift. Slip speed of the oncoming friction element is controlled during the inertia phase of an upshift using closed loop control triggered by detection of a slip speed change for the oncoming friction element. Slip speed of the oncoming friction element is controlled during the inertia phase of a downshift using closed loop control triggered by detection of off-going friction element slip speed.
At the end of closed loop control, the pressure on the actuator for the oncoming friction element is increased as slip speed of the oncoming friction element becomes approximately zero.
a is a schematic line diagram of the transmission shown in
b is a chart showing the clutch and brake engagement and release pattern for the transmission illustrated in
a is a time plot of speed ratio during a power-on upshift event;
b is a time plot of pressure on the off-going friction element during a power-on upshift;
c is a time plot of a slip speed of an oncoming friction element during a power-on upshift;
d is a time plot of the slip speed of an off-going friction element during a power-on upshift;
a is a time plot of the speed ratio during a power-on downshift;
b is a time plot of the pressures on the off-going friction element during a power-on downshift;
c is a time plot of the slip speed for the oncoming friction element during a power-on downshift;
d is a time plot of the slip speed of an off-going friction element;
A converterless transmission capable of incorporating the strategy and control method of the invention is shown in
The engine 10 includes a crankshaft 14 journalled at 16 in end wall 18 of the engine housing. An intermediate housing 20 is located between the end wall 18 of the engine 10 and wall 22 for the transmission 12.
The intermediate housing encloses a stator 24 of an electric motor. The stator and the stator windings are secured to an interior machined surface 26 of the housing 20. A rotor assembly 28 is situated within the stator and separated from the stator by an air gap designated by numeral 30.
A slipping wet clutch cylinder 32 is secured to the rotor assembly 28. A bearing support shaft 34 rotatably supports the clutch cylinder 32 and is secured by bolts 36, or by other suitable fastening techniques, to the transmission wall 22.
An annular piston 38 is situated within the clutch cylinder 32 and cooperates with the cylinder to define a pressure chamber in communication with fluid pressure passage 40 in the support shaft 34. Passage 40 communicates with passage structure extending to a control valve body, shown generally at 42, which is secured to the upper side of transmission housing 44.
A slipping wet clutch disc assembly 46 has clutch plates secured to the cylinder 32. Internally splined clutch discs are carried by clutch element 48, which in turn is connected, preferably by drive splines, to the hub 50 of a spring damper assembly 52. A damper drive plate 54 is connected directly to the hub 50. Damper housing 56 is connected directly to crankshaft drive plate 58. The hub of drive plate 58 is secured directly, preferably by bolts 60, to the end of crankshaft 14.
Damper springs 62 are situated between the damper drive plate 54 and the damper housing 56. They are arranged in a circular fashion about the axis of the hub 50, thereby providing a resilient connection between the crankshaft and the clutch element 48 in known fashion.
The input shaft for the transmission is shown at 64. Although the transmission illustrated in
Input shaft 64 is connected through a drive spline 66 to clutch cylinder 68 for forward drive friction clutch 70. When clutch 70 is engaged, a driving connection is established between shaft 64 and sun gear 72 of a first planetary gear unit 74. A ring gear 76 is connected driveably to carrier 78 of gear unit 80. Carrier 78 is adapted to be braked by selectively engageable low-and-reverse brake 82.
A sun gear 84 is connected driveably to the transmission input shaft 64 through a reverse clutch 86. The ring gear 88 of the gear unit 80 is driveably connected to the carrier 79 for the gear unit 74.
A direct clutch assembly 90 connects the torque input shaft 64 with the clutch cylinder 68. Clutch cylinder 68 also is connected to the sun gear 72 through the clutch 70, as mentioned earlier. Clutch 90 also connects the shaft 64 to the ring gear 76.
The ring gear 88 of gear unit 80 defines a sprocket for a chain drive, indicated generally at 92. The driven sprocket of the chain drive, shown at 94, is rotatably mounted in the transmission housing on the axis of output shaft 96. It is connected driveably to a sun gear 98 of final drive gearset 100. The ring gear 102 of the final drive gearset 100 is connected directly to the transmission housing.
The carrier of the gearset 100 is connected to differential carrier 104 of a differential gear unit 106. Differential pinions are carried by the carrier 104. They mesh driveably with side gears carried by torque output shaft 96 and a companion output shaft 110. Each output shaft is connected to vehicle traction wheels through a universal joint assembly and axle half-shafts, not shown.
A friction brake band 108 surrounds a brake drum that forms a part of the reverse clutch 86. The brake drum is connected driveably to sun gear 84 of gear unit 80.
A sun gear speed sensor 84′ is disposed in close proximity to the brake drum for reverse clutch 86. The brake drum is surrounded by brake band 108, which is engaged during second and fourth ratio to anchor sun gear 84. The speed of sun gear 84 is equal to the speed of the brake drum to which it is directly connected.
The speed sensor 84′ may be a proximity-type inductance sensor that develops a voltage pulse signal as a trigger element carried by the adjacent brake drum passes a magnetic flux field of the sensor. The voltage pulses created by the sensor for each revolution of sun gear 84 are sensed by a transmission controller. Each pulse time interval is compared by the controller to the number of clock ticks generated by the controller during the pulse time interval. The number of clock ticks within successive voltage pulses is an indicator of sun gear speed.
A carrier speed sensor 78′ is disposed in close proximity to a rotary member of reverse brake 82, which is connected directly to carrier 78. Speed sensor 78′ functions in a manner similar to speed sensor 84′. It provides an instantaneous value for the speed of carrier 78 in each control loop of the transmission controller during a transmission ratio shift interval. Together with the usual input and output speed sensors, the speed sensors 84′ and 78′ provide the speed information needed by the controller to compute slip speeds of an oncoming friction element and an off-going friction element during power-on upshifts and downshifts and power-off upshifts and downshifts.
For a complete description of the gearing and the clutches and brakes of the transmission 12, reference may be made to the previously mentioned Patent U.S. Pat. No. 4,938,097. That description is incorporated in this disclosure by reference.
b shows a clutch and brake engagement and release sequence to establish four forward-driving ratios and a single reverse ratio. The clutches and brakes are identified in
To establish the first gear ratio in the forward-drive range, the forward clutch FC and the low-and-reverse brake L/R are engaged. The forward clutch remains applied for operation in each of the first three forward-driving ratios.
A ratio change to the second forward-driving ratio is obtained by releasing low-and-reverse brake L/R and by applying brake band 2/4. An upshift to the third ratio is obtained by releasing brake band 2/4 and applying clutch DC. Fourth ratio, which is the top forward-drive ratio, is obtained by releasing the forward clutch FC and applying reaction brake 2/4.
Reverse drive is obtained by simultaneously applying reverse clutch RC and low-and-reverse brake L/R.
The invention comprises a control method and strategy for achieving high quality, power-on upshifts and power-on downshifts as well as power-off upshifts and downshifts. A description of the strategy for power-on upshifts will be described with reference to
a-2d show time plots of the relationship of speed ratio, slip speed, and friction element pressure for both an oncoming friction element and an off-going friction element as the speed ratio changes from a first ratio to a second ratio. The controller commands a power-on upshift at 130 in
As the actuator for the oncoming friction element is filling, the stroke of the actuator is completed without causing any significant torque capacity increase in the friction element. Concurrently, the off-going friction element pressure command is reduced, as shown at 140, to a level that is lower than the initial off-going friction element pressure command at 141. The pressure at 140 will hold the input torque at that instant in the shift interval after the stroke of the oncoming friction element is complete at time 142 in
The oncoming friction element pressure then increases or ramps up, as shown at 144. When the pressure on the oncoming friction element is sufficient to start the shift, the capacity of the oncoming friction element will be capable of accommodating input torque plus inertia torque. At that instant, the oncoming friction element slip speed will begin to decrease, as shown at 146, the amount of decrease being identified as delta_rpm at
The value delta_rpm can be used to trigger transmission closed loop control during the inertia phase of the shift, which occurs between time 148 and time 152, seen in
When the oncoming clutch slip speed decreases between time 148 and time 152, the pressure on the off-going friction element actuator is reduced, as shown at 154 in
Closed loop control of the oncoming friction element slip speed is performed by establishing a target slip speed trajectory, as shown at 160 in
During an early part of the inertia phase, beginning at time 148, the commanded slip speed is varied in value with a first slope. Later in the inertia phase, the slope decreases relative to the first slope. This is done to improve end-of-shift transients as the oncoming friction element stops slipping. The point at which the slope of the commanded slip speed changes is one of the several trigger points that the controller can establish based upon the speed information obtained from the independent speed sensors 84′ and 78′ seen in
After the speed change is completed, the oncoming friction element capacity is increased, as shown at 166, in order to have sufficient capacity to hold the combustion torque of the engine. Simultaneously, the pressure for the off-going friction element is reduced to zero as shown at 168 in
The characteristics of a power-on downshift are shown in
When the oncoming friction element is being stroked with a stroke pressure 172, the oncoming friction element has little or no capacity. The pressure of the off-going friction element is reduced as shown at 178. After a time delay following a command for a pressure reduction, the pressure of the off-going friction element begins to decrease, as shown at 180. This causes the off-going friction element to start slipping, as shown at time 182 in
The value of the slip speed at 184 is compared to a measured oncoming friction element slip speed shown at 186 in
A value of the oncoming friction element slip speed equal to zero represents a synchronous speed in ratio R3 at 176. Values of oncoming slip speed less than zero (e.g., the value at time 190 in
After the oncoming friction element slip speed reaches zero, the oncoming friction element pressure command continues to increase, as shown at 194, to a value that will hold the current input torque in the new ratio 176.
Power-off upshifts are performed in a manner similar to a power-on upshift described with reference to
During a power-off upshift, the trajectory of the oncoming friction element slip speed is always driven to zero to complete the shift. Likewise, power-off downshifts are performed in a manner similar to power-on downshifts. Thus, the off-going friction element slip speed is used to directly sense the start of oncoming clutch capacity, and oncoming friction element slip is controlled using closed loop control characteristics until zero slip speed is reached, thereby achieving a synchronous speed. Unlike a power-on downshift, oncoming friction element slip speed is used during power-off downshifts to trigger the closed loop control.
A desired slip trajectory is determined by the processor, as shown by the plot at 203 in
When the oncoming friction element slip speed is near zero, as shown at 206, the end of the shift is triggered, which brings the oncoming friction element pressure up to the maximum value, as shown at 208, the end of the shift being designated as an end mode plot 210.
The transmission ratio changes during closed loop control, as shown at 212. The initial ratio at the beginning of the shift is shown at 214 and the upshifted ratio is shown at 216. The plot for the input speed during the ratio change is shown at 218.
During a power-on downshift, as shown in
Although an embodiment of the invention has been described, it will be apparent to persons skilled in the art that modifications may be made without departing from the scope of the invention. All such modifications and equivalents thereof are intended to be covered by the following claims.
