Patent Application
20150266464
1. Field of the Invention
This invention relates generally to controlling torque modulation during a transmission gear change in response to a signal representing slow torque modulation, wherein the torque modulation is performed by a fast actuator.
2. Description of the Prior Art
When a transmission upshift is performed, inertia is transmitted through the powertrain to the driven vehicle wheels. But when a transmission downshift is performed, toque produced by the operative vehicle power source must be modulated and vehicle kinetic energy must be absorbed or dissipated. Preferably, in a hybrid electric vehicle kinetic energy is transmitted to the vehicle's powertrain where it can be regenerated and stored as electric energy in an onboard electric storage battery.
Use of slow torque modulation for torque reduction during gear shifting will be directed by a command signal toward the slow actuator, i.e., the power source having the slower response time to the signal for torque reduction. Use of the fast torque modulation for torque reduction will be directed by a command signal toward the faster actuator. Potential exists to capture energy from the faster actuator (using the electric machine in a modular hybrid powertrain). But since the slow torque modification is directed toward the slow actuator path, the opportunity to collect this energy may be reduced.
A method for controlling torque modification during a gearshift includes modifying transmission input torque during the gearshift using an actuator having slower and faster responses to a request for slow input torque modification, fulfilling the request using the slower response provided the faster response is unable to fulfill the request, and fulfilling the request using the faster response, provided the faster response can provide the requested torque modification.
The method recovers more energy if the fast actuator is an electric machine, thereby compensating for lost energy during other gearshift events.
The method uses a slow torque modulation request to evaluate whether there is enough capability and authority in the fast actuator to perform the request. If there is sufficient capability/authority, then the fast actuator is used via to provide the request in enough time to satisfy the slow torque modulation request. Since the fast actuator responses faster to the request, sufficient time is available to evaluate this decision and perform the request.
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:
The torque converter 20 is a hydraulic coupling that produces a hydrokinetic drive connection between an impeller, which is driveably connected to the engine 12 when clutch 14 is closed, and a turbine, which is driveably connected to the driven wheels 30.
The torque converter lock-up clutch 22 alternately opens and closes a drive connection between the torque converter's turbine and the shaft 38.
A vehicle equipped with this powertrain 10 can produce electric drive and hybrid electric drive and can charge the battery 36 either by regenerative braking, i.e., recovering and converting kinetic energy of the vehicle during a braking event to electric energy that can be stored in battery 36, or by using the engine to charge battery 36.
During regenerative braking, torque is transmitted from the wheels 30 to the electric machine 16. To recoup most of the kinetic energy using regenerative braking, the torque converter clutch 22 should be kept locked while vehicle speed is slowing.
The control strategy coordinates operation of the torque converter clutch 22 and the electric machine 16 during a vehicle braking event, whether engine 12 is running or the engine is stopped. If engine 12 is running, its crankshaft is connected to the electric machine 16; therefore, the torque converter's impeller speed can not drop below the engine idle speed. If engine 12 is stopped, the electric machine 16 can be running at speeds lower than the nominal engine idle speed. If the transmission's hydraulic system line pressure is provided by the mechanical oil pump 18, the minimal impeller speed should be determined by the minimal pressure that the pump should generate in this case.
Referring to
The variation during the downshift of the extent to which the gearshift is completed is represented by graph 46 (Sft_pct_complete).
The gearshift phases that occur during the downshift include (i) start shift phase 48 wherein the oncoming transmission control element is prepared for engagement by rapidly pressurizing its hydraulic servo briefly to remove dimensional clearances and then reducing that pressure; (ii) torque transfer phase 50, wherein torque carried by the offgoing transmission control element is decreased and transferred to the oncoming transmission control element; (iii) ratio change phase 52, wherein the transmission speed ratio changes; shift end phase 54, wherein the oncoming control element is fully engaged and pressure in the offgoing element is vented; and gear shift termination phase 56.
Graph 58 shows the variation of servo pressure in the oncoming transmission control element during the downshift.
Graph 60, representing a slow actuator response to an input torque reduction request, includes a stepwise torque reduction 61 and a ramp reduction when triggered by shift percent complete 46, followed by another stepwise reduction 62 and a stepwise increase 63 to the original input torque magnitude, when input torque response exceeds the requested input torque 64.
Graph 65, representing a fast actuator response to an input torque reduction request, includes a stepwise torque reduction 66, followed by a ramped linear increase 67, and a stepwise increase 68 to the original input torque magnitude, when input torque response exceeds the requested input torque 64.
The steps of the algorithm shown in
At step 76, controller 72 computes the capability of powertrain 10 to produce a fast modification of input torque, and at step 78 the controller computes the capability of the powertrain to produce a slow modification of input torque. After a gearshift in transmission 24 begins at step 80, transmission controller 74 triggers a request for a slow torque modification of input torque.
Slow to fast torque input torque modification is evaluated at step 84.
A test is performed at step 86 to determine whether powertrain 10 is able to produce fast input torque modification in response to the request for slow input torque modification produced at step 82.
If the result of test 86 is logically negative, a slow actuator is promptly given lead time to react to the request for slow input torque modification so that the slow input torque modification is ready when needed to compensate for inertia effects at step 88.
If the result of test 86 is logically positive, a test is performed at step 90 to determine whether a request for fast input torque modification has been triggered by transmission controller 74 at step 92. The requests triggered at step 82 and 92 allow inertia effects of the gearshift to be compensated by reduction or increase of input torque. A slow actuator requires addition time, whereas a fast actuator does not require additional time.
If the result of test 90 is negative, control returns to step 90.
If the result of test 90 is positive, a fast modification of input torque is produced at step 94. As illustrated, the step 94 results from the fast modification of input torque or the slow to fast torque modification of input torque.
When internal combustion engine 12 is producing input torque, adjusting the throttle opening is slow actuation, whereas adjusting ignition timing or spark is fast actuation. In a hybrid electric powertrain, switching the electric machine 16 to operate as a motor produces fast input torque modification in response to a request for increased input torque. Switching the electric machine 16 to operate as a generator produces fast input torque modification in response to a request for input torque reduction.
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.
