GB2598729A

GB2598729A - Control system for an automatic transmission of a vehicle

Info

Publication number: GB2598729A
Application number: GB2014134.7A
Authority: GB
Inventors: Alexander Poyntz Owen Thomas; Timothy Paul; Wardle Roger
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2020-09-09
Filing date: 2020-09-09
Publication date: 2022-03-16
Anticipated expiration: 2040-09-09
Also published as: GB202014134D0; DE102021209956A1; GB2598729B

Abstract

A control system for controlling an automatic transmission of a vehicle. The transmission includes a torque converter and the control system comprises a processor configured to determine a modified shift point 552 of the automatic transmission in dependence upon a scheduled shift point and to determine a level of slip of the torque converter. The control system is then arranged to output the modified shift point 560. This provides a shift point which is more consistent between the slip and locked operating condition of the torque converter.

Description

CONTROL SYSTEM FOR AN AUTOMATIC TRANSMISSION OF A VEHICLE

TECHNICAL FIELD

The present invention relates to a control system for an automatic transmission of a vehicle.

Aspects of the invention relate to a control system, a vehicle a method, a computer program and a non-transitory, computer-readable storage medium.

BACKGROUND OF THE INVENTION

Automatic transmissions that automatically change gear ratios as a vehicle moves have been used in vehicles in particular automobiles for some time. The most common type of automatic transmission is a hydraulically operated transmission. This type of transmission typically includes a torque converter, a planetary gear train and hydraulic control. The torque converter transmits and decouples the engine power to the planetary gears thereby allowing the vehicle to start from rest without stalling or a slipping clutch. The planetary gear train comprises planetary gearsets, clutches and brakes to provide various gear ratios. The different gear ratios provide different speeds of rotation of the output shaft depending on which gears are engaged in torque transmission. The clutches and brakes are used to effect gear changes.

The hydraulic control uses automatic transmission fluid sent under pressure by an oil pump to control the various clutches and brakes.

The torque converter typically includes three elements, an impeller, a turbine and a stator.

The impeller is rotationally connected to the engine output by a flex plate. The turbine is connected to the transmission input shaft and provides the output from the torque converter. The stator is located between the impeller and turbine to redirect oil flow returning from the turbine to the impeller, this redirection provides a torque multiplication across the torque converter. The stator is connected to a fixed stator shaft by a one-way clutch. Many torque converters also include a lockup clutch that locks the impeller and turbine together to eliminate slip and therefore improve efficiency.

In some conditions, such as when the transmission is warming up, it is undesirable to lock the torque converter. The inefficiency of the torque converter may be used to quickly warm the transmission fluid and improve the overall efficiency of the transmission while also improving the control response and smoothness of the transmission. When the transmission has reached the desired operating temperature, the lockup clutch is engaged to improve efficiency as further warming is not needed.

The transmission is controlled to shift gears based on shift maps with a shift depending on accelerator pedal position and vehicle speed. The change in control of the lockup clutch from unlocked when warming to locked results in an inconsistent experience for the driver. A shift point at a particular vehicle speed will have differing engine speed depending on whether the lockup clutch is locked or open. Due to the characteristic of the torque converter this speed difference will change depending on the engine torque applied. It is undesirable to create a shift map based on engine speed because of the change in engine speed with torque and because the vehicle has a higher inertia it provides a more stable speed signal.

The present invention therefore aims to mitigate the issues associated with known systems.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a control system, a method, a vehicle, a computer program and a non-transitory, computer-readable storage medium as claimed in the appended claims.

Aspects of the present disclosure relate to a control system for controlling an automatic transmission of a vehicle, the automatic transmission including a torque converter, the control system comprising a processor configured to: determine a modified shift point of the automatic transmission in dependence upon a scheduled shift point and a level of slip of the torque converter, and output the modified shift point.

In an embodiment the processor is further configured to: determine that torque converter slip is occurring, determine a value indicative of a level of slip of the torque converter, obtain the scheduled shift point indicative of the point at which the automatic transmission is currently scheduled to shift, and determine the modified shift point using the scheduled shift point and the value indicative of the level of slip of the torque converter.

In an embodiment the control system is configured to receive a signal indicative of the current throttle pedal position, and wherein the scheduled shift point is obtained using the current throttle pedal position and a shift map of throttle pedal position, wheel speed and gear shift points.

In an embodiment the value indicative of torque converter slip is determined in dependence upon an input speed of the torque converter and an output speed of the torque converter.

In an embodiment the value indicative of torque converter slip is determined in dependence upon a speed ratio across the torque converter.

In an embodiment the value indicative of torque converter slip is determined in dependence upon a speed difference across the torque converter.

In an embodiment the processor is configured to subtract the value indicative of torque converter slip divided by the gear ratio from the scheduled shift point to determine the modified shift point.

In an embodiment the modified shift point is reached prior to the scheduled shift point.

In an embodiment the processor is configured to control the automatic transmission to change gear according to the modified shift point.

A further aspect of the present disclosure relates to a vehicle comprising an automatic transmission including a torque converter, and a control system according to any previous aspect or embodiment.

A further aspect of the present disclosure relates to a method of controlling an automatic transmission of a vehicle, the automatic transmission including a torque converter, the method comprising: determining a modified shift point of the automatic transmission in dependence upon a scheduled shift point and a level of slip of the torque converter, and outputting the modified shift point.

In an embodiment the method further comprises: determining that torque converter slip is occurring, determining a value indicative of a level of slip of the torque converter, obtaining the scheduled shift point indicative of the point at which the automatic transmission is currently scheduled to shift, and determining the modified shift point using the scheduled shift point and the value indicative of the level of slip of the torque converter.

A further aspect of the present disclosure relates to a computer program that, when run on a processor, performs a method according to any one of the above method aspect or embodiment.

A further aspect of the present disclosure relates to a non-transitory, computer-readable storage medium storing instructions thereon that when executed by one or more processors causes the one or more processors to carry out the method aspect or embodiment.

Within the scope of this application it is expressly envisaged that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible.

The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows schematic illustration of a vehicle according to an embodiment of the invention in side view; Figure 2 shows a schematic illustration of a powertrain of the vehicle according to an embodiment the invention in plan view; Figure 3 shows a schematic illustration of a control system according to an embodiment of the invention; Figure 4 shows a gear shift map describing an embodiment of the invention; and Figure 5 shows a flow chart describing an embodiment of the invention.

DETAILED DESCRIPTION

A control system of an automatic transmission in a vehicle in accordance with an embodiment of the present invention is described herein with reference to the accompanying Figures.

Figure 1 shows a vehicle 100 according to an embodiment of the present invention. The vehicle 100 may be two-wheel drive or four-wheel drive and includes an automatic transmission. The vehicle may be a hybrid vehicle including an internal combustion engine and an electric drive motor.

Figure 2 shows a powertrain 200 according to an embodiment of the present invention. The powertrain 200 comprises an internal combustion engine 210, a torque converter 220, a transmission 230, a final drive 240 and driving wheels 252 and 254. The engine 210 provides torque to drive the torque converter 220 by means of flex plate 212. Drive passes from the flex plate 212 to the torque converter impeller 222 and the torque converter provides hydrodynamic drive to the turbine 224, drive then leaves the torque converter through the transmission input shaft 232 into the transmission 230. The torque converter has a lockup clutch 226 which driveably connects the impeller to the turbine when controlled to engage. The transmission 230 provides a range of selectable gear ratios and the output from the transmission passes to the prop shaft 234. The prop shaft 234 drives the final drive 240 which may contain a differential and drives side shafts 242 and 244 which themselves drive wheels 252 and 254.

Figure 3 shows a control system 300 according to an embodiment of the present invention.

The control system comprises a plurality of control modules, input signals and controlled outputs. While an embodiment is shown, the functions of individual modules may be combined or distributed across controllers on a network. Similarly, the embodiment shows an arrangement of sensors and controlled outputs, these may be substituted by equivalent signals without departing from the invention. Signals between controllers are also shown in the embodiment and these may be carried by a network such as a CAN network linking a plurality of controllers.

The control system 300 comprises an engine control module (ECM) 310 which accepts signals from an accelerator pedal 314 and an engine speed sensor 312. These are used by the controller to determine fuel injection and, in a gasoline engine, the ignition timing. The engine speed and pedal position signals are sent to the transmission control module (TCM) 320.

In this embodiment an anti-lock braking system (ABS) controller 330 is shown which receives signals from wheel speed sensors 332, 334, 336 and 338. From these signals a vehicle speed is calculated which is sent to the TCM 320.

The TCM 320 receives signals from the ECM 310 and the ABS 330 and additionally receives speed sensor signals indicative of the input and output speeds 322 and 323. The TCM may derive the vehicle speed from the ABS signal or the output shaft speed signal. It is also possible for the engine to operate in a cruise control mode, so the accelerator pedal position does not correctly indicate the need for a gear shift. In this case a virtual pedal signal may be substituted by the ECM and transmitted to the TCM so that the correct gear may be selected. The TCM sends control signals to a hydraulic valve body 325 and the valve body sends hydraulic pressure to clutches and brakes 32710 329 in the transmission and torque converter to control gear selection and torque converter lockup.

Figure 4 shows a gear shift map describing an embodiment of the present invention. The X axis is wheel speed shown in rpm although this could equally conveniently be shown in kph or as an output shaft speed in rpm. The Y axis is the accelerator pedal position in % and the kickdown position is shown as 101%. Kickdown may be implemented as a separate switch or by an additional spring with the pedal position sensor showing the kickdown demand.

Kickdown provides a lower gear at most points in the map when the driver increases the pedal beyond a position indicated by an additional spring resistance to the pedal. The lines on the map show the shift demand for each upshift and downshift. For example, 1-2 is the line at which the transmission will shift up from 1st to 2nd gear and 4-3 is the line at which the transmission will shift down from 41b to 3dgear. This map is simplified for this embodiment, in a gearbox with more than 4 gears there would be a shift line for each upshift and each downshift.

Considering an acceleration from rest in 1st gear at 50% pedal demand. The first upshift line is encountered at 1400 rpm which commands an upshift from 1st to 2nd gear. Continued acceleration would reach the next upshift line at 1850 rpm so the transmission would then upshift from 2nd to 3rd. If the 50% throttle was maintained and the vehicle slowed because it encountered a hill the wheel speed would reduce. At 1750 rpm the 4-3 shift line would be crossed with no effect because the transmission has already selected 3rd gear. If the deceleration continued to 1250 rpm then the 3-2 shift line would be crossed, and the transmission would downshift from 3rd to 2sd gear. The vehicle may continue to decelerate to 1050 rpm and at this point the driver may increase the pedal depression. Moving vertically on the map the next shift line would be crossed at 1050 rpm and 75% pedal when the transmission would shift down from 2nd to Pt. In this way any change in pedal depression or wheel speed may lead to a gear shift when the appropriate shift lines are crossed.

Figure 5 shows a flow chart describing an embodiment of the present invention. The flowchart starts at 510 and proceeds to 520 where the turbine speed 524 is subtracted from the engine speed 522 to provide the torque converter slip speed 526. The flow continues to 530 where the speed slip 534 is calculated by dividing the torque converter slip speed 526 by the gear ratio 532. At step 540 the shift map 544 is used with the pedal position 524 to provide the wheel speed for the next shift 546. This is used in the main flow at 550 to provide the modified wheel speed for next shift 552 by subtracting the speed slip 534 from the wheel speed for next shift 546. The final step in the flow 560 is to change gear when the wheel speed reaches the modified wheel speed for next shift. The flow ends at 570.

At any point in the shift map there are adjacent lines for an upshift and for a downshift. Both speeds may be modified using this method to provide consistent shifts when the torque converter is unlocked. When the torque converter is locked then the engine speed and turbine speeds match so there is no torque converter slip and the wheel speed for next shift remains unmodified. This algorithm therefore has no effect when the torque converter is locked.

It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Claims

CLAIMS: 1. A control system for controlling an automatic transmission of a vehicle, the automatic transmission including a torque converter, the control system comprising a processor configured to: determine a modified shift point of the automatic transmission in dependence upon a scheduled shift point and a level of slip of the torque converter, and output the modified shift point.
2. A control system according to claim 1 wherein the processor is further configured to: determine that torque converter slip is occurring, determine a value indicative of a level of slip of the torque converter, obtain the scheduled shift point indicative of the point at which the automatic transmission is currently scheduled to shift, and determine the modified shift point using the scheduled shift point and the value indicative of the level of slip of the torque converter.
3. A control system according to claim 2 wherein the control system is configured to receive a signal indicative of the current throttle pedal position, and wherein the scheduled shift point is obtained using the current throttle pedal position and a shift map of throttle pedal position, wheel speed and gear shift points.
4. A control system according to any one of claims 2 to 3 wherein the value indicative of torque converter slip is determined in dependence upon an input speed of the torque converter and an output speed of the torque converter.
5. A control system according to any one of claims 2 to 4 wherein the value indicative of torque converter slip is determined in dependence upon a speed ratio across the torque 30 converter.
6. A control system according to any one of claims 2 to 5 wherein the value indicative of torque converter slip is determined in dependence upon a speed difference across the torque converter.
7. A control system according to any one of claims 2 to 6 wherein the processor is configured to subtract the value indicative of torque converter slip divided by the gear ratio from the scheduled shift point to determine the modified shift point.
8. A control system according to any one of claims 2 to 7 wherein the modified shift point is reached prior to the scheduled shift point.
9. A control system according to any one of claims 1 to 8 wherein the processor is configured to control the automatic transmission to change gear according to the modified shift point.
10. A vehicle comprising an automatic transmission including a torque converter, and a control system according to any one of claims 1 to 9.
11. A method of controlling an automatic transmission of a vehicle, the automatic transmission including a torque converter, the method comprising: determining a modified shift point of the automatic transmission in dependence upon a scheduled shift point and a level of slip of the torque converter, and outputting the modified shift point.
12. A method according to claim 11 wherein the method further comprises: determining that torque converter slip is occurring, determining a value indicative of a level of slip of the torque converter, obtaining the scheduled shift point indicative of the point at which the automatic transmission is currently scheduled to shift, and determining the modified shift point using the scheduled shift point and the value indicative of the level of slip of the torque converter.
13. A computer program that, when run on a processor, performs a method according to any one of claims 11 or 12.
14. A non-transitory, computer-readable storage medium storing instructions thereon that when executed by one or more processors causes the one or more processors to carry out the method of any one of claims 11 or 12.