US 4,965,735 AGrant
Method of Determining the Shift Lever Position of an Electronic Automatic Transmission System
Issue Date:1990-10-23
•8 Claims
•2 Drawing Sheets
Abstract
A method of determining the shift lever position of an electronic automatic transmission system by identifying the mode of transmission operation selected by the driver of the vehicle to provide hysteresis between the park, reverse, neutral, overdrive, drive and low positions and to permit limited operation of the controller without functioning PRNODDL sensors.
Metadata
Assignee
- Chrysler Corporation
Inventors
- Gerald L. Holbrook
- Maurice B. Leising
Application Information
Application Number:US 1886150
Filing Date:1988-04-29
Priority Date:1988-04-29
Art Unit:234
Classifications
IPC:
B60K 4104
Field of Search:
36474424.1866
Patent Drawings (2 sheets)
Description
Background of the Invention
1. Field of the Invention
The present invention relates to an automatic transmission primarily intended for motor vehicle use, and more particularly to a method of determining the shift lever position selected by the driver of a transmission that is controlled electronically and hydraulically.
2. Description of Related Art
Generally speaking, land vehicles require three basic components. These components comprise a power plant (such as an internal combustion engine) a power train and wheels. The internal combustion engine produces force by the conversion of the chemical energy in a liquid fuel into the mechanical energy of motion (kinetic energy). The function of the power train is to transmit this resultant force to the wheels to provide movement of the vehicle
The power train s main component is typically referred to as the "transmission". Engine torque and speed are converted in the transmission in accordance with the tractive-power demand of the vehicle. The vehicle's transmission is also capable of controlling the direction of rotation being applied to the wheels so that the vehicle may be driven both forward and backward.
A conventional transmission includes a hydrodynamic torque converter to transfer engine torque from the engine crankshaft to a rotatable input member of the transmission through fluid-flow forces The transmission also includes frictional units which couple the rotating input member to one or more members of a planetary gearset. Other frictional units, typically referred to as brakes, hold members of the planetary gearset stationary during flow of power. These frictional units are usually brake clutch assemblies or band brakes. The drive clutch assemblies can couple the rotating input member of the transmission to the desired elements of the planetary gearsets, while the brakes hold elements of these gearsets stationary. Such transmission systems also typically provide for one or more planetary gearsets in order to provide various ratios of torque and to ensure that the available torque and the respective tractive power demand are matched to each other.
Transmissions are generally referred to as manually actuated or automatic transmissions. Manual transmissions generally include mechanical mechanisms for coupling rotating gears to produce different ratio outputs to the drive wheels.
Automatic transmissions are designed to take automatic control of the frictional units, gear ratio selection and gear shifting. A thorough description of general automatic transmission design principals may be found in "Fundamentals of Automatic Transmissions and Transaxles," Chrysler Corporation Training Manual No. TM-508A. Additional descriptions of automatic transmissions may be found in U S. Pat. No. 3,631,744, entitled "Hydromatic Transmission," issued Jan. 4, 1972 to Blomquist, et al., and U.S. Pat. No. 4,289,048, entitled "Lock-up System for Torque Converter," issued on Sept. 15, 1981 to Mikel, et al. Each of these patents is hereby incorporated by reference.
In general, the major components featured in such an automatic transmission are: a torque converter as above-mentioned; fluid pressure-operated multi-plate drive or brake clutches and/or brake bands which are connected to the individual elements of the planetary gearsets in order to perform gear shifts without interrupting the tractive power; one-way clutches in conjunction with the frictional units for optimization of power shifts; and transmission controls such as valves for applying and releasing elements to shift the gears (instant of shifting), for enabling power shifting, and for choosing the proper gear (shift point control), dependent on shift-program selection by the driver (selector lever), accelerator position, the engine condition and vehicle speed.
The control system of the automatic transmission is typically hydraulically operated through the use of several valves to direct and regulate the supply of pressure. This hydraulic pressure control will cause either the actuation or deactuation of the respective frictional units for effecting gear changes in the transmission. The valves used in the hydraulic control circuit typically comprise spring-biased spool valves, spring-biased accumulators and ball check valves. Since many of these valves rely upon springs to provide a predetermined amount of force, it will be appreciated that each transmission design represents a finely tuned arrangement of interdependent valve components. While this type of transmission control system has worked well over the years, it does have its limitations. For example, such hydraulically controlled transmissions are generally limited to one or a very small number of engines and vehicle designs. Therefore, considerable cost is incurred by an automobile manufacturer to design, test, build, inventory and repair several different transmission units in order to provide an acceptable broad model line for consumers.
Additionally, it should be appreciated that such hydraulically controlled transmission systems cannot readily adjust themselves in the field to compensate for varying conditions such as normal wear on the components, temperature swings and changes in engine performance over time. While each transmission is designed to operate most efficiently within certain specific tolerances typical hydraulic control systems are incapable of taking self-corrective action on their own to maintain operation of the transmission at peak efficiency.
However, in recent years, a more advanced form of transmission control system has been proposed, which would offer the possibility of enabling the transmission to adapt itself to changing conditions In this regard, U.S. Pat. No. 3,956,947. issued on May 18, 1976 to Leising, et al., which is hereby incorporated by reference, sets forth a fundamental development in this field. Specifically, this patent discloses an automatic transmission design which features an "adaptive" control system that includes electrically operated solenoid-actuated valves for controlling certain fluid pressures. In accordance with this electric/hydraulic control system, the automatic transmission would be "responsive" to an acceleration factor for controlling the output torque of the transmission during a shift from one ratio of rotation (between the input and output shafts of the transmission) to another. Specifically, the operation of the solenoid-actuated valves would cause a rotational speed versus time curve of a sensed rotational component of the transmission to substantially follow along a predetermined path during shifting.
3. Objects of the Present Invention
It is one of the principal objects of the present invention to provide a significantly advanced electronically controlled transmission which is fully adaptive. By fully adaptive, it is meant that substantially all shifts are made using closed-loop control (i.e., control based on feedback). In particular, the control is closed loop on speed, speed ratio, or slip speed of either N.sub.t (turbine of the torque converter) and N.sub.e (engine) or a combination of N.sub.t and N.sub.o (output) which will provide the speed ratio or slip speed. This transmission control is also capable of "learning" from past experience and making appropriate adjustments on that basis.
Another object of the present invention is to provide an automatic transmission in which the shift quality is maintained approximately uniform regardless of the engine size, within engine performance variations or component condition (i.e. The transmission control system will adapt to changes in engine performance or in the condition of the various frictional units of the transmission)
It is a more specific object of the present invention to provide a method of determining the shift lever position to identify the mode of transmission operation selected by the driver to provide hysteresis between the park, reverse, neutral overdrive, drive and low (PRNODDL) positions and to permit limited operation of the controller without functioning PRNODDL sensors.
This application is one of several applications filed on the same date, all commonly assigned and having similar Specification and Drawings, these applications being identified below.
Commonly assigned application Ser. No. 187,772, filed Apr. 29, 1988 now U.S. Pat. No. 4,875,391 has been printed in its entirety. The Figures and the entire specification of that application are specifically incorporated by reference. For a description of the above copending applications, reference is made to the above mentioned U.S. Pat. No. 4,875,391.
Summary of the Invention
To achieve the foregoing objects, the present invention provides a comprehensive four-speed automatic transmission system. While this transmission system particularly features a fully adaptive electronic control system, numerous other importance advances are incorporated into this unique transmission system, as will be described below in detail.
The transmission control system includes a microcomputer-based controller which receives input signals indicative of engine speed, turbine speed, output speed (vehicle speed), throttle angle position, brake application, predetermined hydraulic pressure, the driver selected gear or operating condition (PRNODDL), engine coolant temperature, and/or ambient temperature. This controller generates command or control signals for causing the actuation of a plurality of solenoid-actuated valves which regulate the application and release of pressure to and from the frictional units of the transmission system. Accordingly, the controller will execute predetermined shift schedules stored in the memory of the controller through appropriate command signals to the solenoid-actuated valves and the feedback which is provided by various input signals.
Another primary feature of the present invention is to provide an adaptive system based on closed-loop control. In other words, the adaptive control system performs its functions based on real-time feedback sensor information, i.e., the system takes an action which affects the output, reads the effect, and adjusts the action continuously in real-time. This is particularly advantageous because the control actuations can be corrected as opposed to an open loop control in which signals to various elements are processed in accordance with a predetermined program.
In accordance with one aspect of the present invention, the controller is programmed to determine the shift lever position of the driver selected gear or operating mode of the transmission to provide hysteresis between the PRNODDL positions, and to provide limited operation of the transmission in the event the PRNODDL sensors, which determine the driver selected gear or operating conditions are not operating properly.
Brief Description of the Drawings
Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiment, the appended claims and in the accompanying drawings in which:
FIGS. 20A and 20B are flow charts of the shift lever position methodology according to the present invention.
Shift Lever Position Methodology
The transmission control logic relies on the Shift Lever Position (SLP) methodology to identify the mode of transmission operation selected by the driver to provide hysteresis between the PRNODDL positions, and to permit limited operation of the transmission controller 3010 without functioning PRNCDDL contact switch sensors (NS.sub.1, NS.sub.2, RL.sub.1, RL.sub.2) by utilizing pressure switch data from the pressure switches 646, 648 and 650 (FIGS. 5A-L) to identify the three hydraulic modes of operation (i.e. reverse R, neutral N and drive D) In the SLP nethodology, P, R, N, and OD (overdrive) PRNODDL codes are accepted as being valid without regard to pressure switch data since the corresponding hydraulic porting (park and neutral are identical) condition must occur first. Testing for SLP position (checking pressure switch input) is only done with temporary or invalid codes present since this is the area where hydraulic porting changes occur.
Referring to FIGS. 20A and 20B, the shift lever position (SLP) methodology is shown. At the beginning in block 1800, the methodology advances to diamond 1802 and determines whether the PRNODDL code (PC) from the sensors (NS.sub.1, NS.sub.2, RL.sub.1, RL.sub.2) is equal to a code for park P, neutral N or a temporary code (T.sub.1) stored in memory in the transmission controller 3010. If PC is equal to park, reverse or a temporary code, the methodology advances to block 1804 and sets the shift lever position (SLP) 606 (FIGS. 5A-L) equal to neutral. If PC is not equal to park, neutral or a temporary code, the methodology advances to diamond 1806 and determine whether PC is equal to reverse R or overdrive OD. If PC equals reverse or overdrive, the methodology advances to block 1808 and sets the SLP 606 equal to PC. If PC is not equal to reverse or overdrive, the methodology advances to diamond 1810 and determines whether PC is in drive D or low L. If PC is drive or low, the methodology advances to diamond 1812 and determines whether SLP 606 is reverse or neutral. If SLP 606 is not reverse or neutral, the methodology advances to diamond 1813 and determines whether a neutral to first gear (N-1) shift is in progress by looking for a flag. If a neutral to first gear shift is not in progress, the methodology advances to block 1808 previously described and sets SLP 606 equal to PC.
If SLP 606 is reverse or neutral at diamond 1812, or PC does not equal drive or low at diamond 1810, or a neutral to first gear shift is in progress, the methodology advances to diamond 1814 and determines whether PC equals an invalid code (I) stored in memory. If PC is an invalid code, the nethodology advances to diamond 1816 and determines whether a PRNODDL FAIL (PF) flag has been set. If PF has not been set, the methodology advances to block 1817 and determines whether a count n on a counter is greater than a predetermined value such as 15. If the count n is greater than the predetermined value, the methodology advances to block 1818 and sets PF. If the count n is not greater than the predetermined value, the methodology advances to block 1819 and increments the count n. The methodology then advances to diamond 1821. If PC is not an invalid code at diamond 1814, the methodology advances to block 1820 and sets the count n on the counter equal to a predetermined value such as zero. The methodology then advances to diamond 1821. If PF was previously set at diamond 1816 or once the PF flag has been set at diamond 1818, the methodology advances to diamond 1821 and determines whether SLP 606 is reverse. If SLP is reverse, the methodology advances to block 1822 and turns ON the low/reverse clutch solenoid-actuated value 636. The methodology then advances to diamond 1823 and determines whether the low/reverse pressure switch 650 is equal to one or pressurized. If the low/reverse pressure switch 650 is equal to one, the methodology advances to block 1824 and sets SLP 606 equal to neutral. This occurs because the low/reverse pressure switch 650 is pressurized or producing a signal equal of one (See FIG. 5A) only when the transmission 100 is not in reverse gear and the low/reverse clutch 310 is being applied. If the low/reverse pressure switch 650 is not equal to one, the methodology advances to block 1837 to be described.
If SLP 606 is not reverse at diamond 1821, the methodology advances to diamond 1826 and determines whether SLP 606 is equal to neutral. If SLP is neutral, the methodology advances to block 1827 to set an SLP test flag. The methodology then advances to diamond 1828 and determines whether the overdrive pressure switch 646 is equal to one or pressurized. If the overdrive pressure switch 646 equals one, the methodology advances to block 1824 and sets a count Z on a counter equal to a predetermined value such as 43. The methodology then advances to block 1830 and sets SLP 606 equal to overdrive OD. This occurs because the overdrive clutch 304 is being applied when the overdrive pressure switch 646 is pressurized or producing a signal equal to one (See FIG. 5H). If the overdrive pressure switch 646 does not equal one, the methodology advances to diamond 1832 and determines whether the low/reverse solenoid-actuated valve 656 is ON, the pressure switches 646, 648 and 650 are not pressurized or are equal to zero (See FIG. 5C) and N.sub.e is greater than a predetermined value, i.e. 500 r.p.m. If that criteria is true, the methodology advances to block 1834 and sets SLP 606 equal to reverse. If that criteria is not true, the methodology returns.
At diamond 1826, if SLP 606 is not neutral, the methodology advances to diamond 1836 and determines whether the engine speed N.sub.e is less than a predetermined speed, i.e. 500 r.p.m. If engine speed N.sub.e is less than the predetermined speed, the methodology advances to block 1837 and decrements the count Z on the counter by a predetermined value. The methodology then advances to block 1838 and clears the SLP test flag. The methodology then returns. If engine speed N.sub.e is not less than the predetermined speed, the methodology advances to diamond 1839 and determines whether a shift is in progress or occurring by looking for a flag. If the shift is in progress, the methodology advances to diamond 1840 and determines whether a neutral to first gear shift is in progress as previously described. If a neutral to first gear shift is not in progress, the methodology advances to block 1837 previously described. If the shift is not in progress, or a neutral to first gear shift is in progress, the methodology advances to diamond 1841 and determines whether the LU switch valve 614 is being applied as a result of the low/reverse element solenoid-actuated valve 636 being energized or on the low/reverse pressure switch 650 equals one and both the two/four 648 and overdrive 646 pressure switches equal zero. If that criteria is true, the methodology advances to block 1842 and sets SLP 606 equal to neutral. If that criteria is not true, the methodology advances to diamond 1843 and determines whether the transmission 100 is presently in fourth gear by calculating speeds. If the transmission is presently in fourth gear, the methodology advances to diamond 1844 and determines whether the pressure switches 646, 648 and 650 equal zero. If the pressure switches equal zero, the methodology advances to block 1842 previously described. If all the pressure switches 646, 648 and 650 do not equal zero, the methodology advances to block 1837 previously described.
If the transmission 100 is not presently in fourth gear, the methodology advances to diamond 1845 and determines whether count Z equals a predetermined value such a zero. If Z does not equal zero, the methodology advances to block 1837 previously described. If Z equals zero, the methodology advances to diamond 1846 and determines whether the transmission 100 is presently in first gear by speed calculations, the low/reverse pressure switch 650 equals one and turbine speed N.sub.t is greater than a predetermined r.p.m., or the pressure switches 646, 648 and 650 equal zero, or the low/reverse pressure switch 650 equals one and a neutral to first gear shift is in progress. If any of that criteria is not true, the methodology advances to diamond 1847 and determines whether the SLP test flag has been set. If the SLPT flag has not been set, the methodology advances to block 1837 previously described. If the SLP test flag has been set, the methodology advances to block 1848 and sets Z equal to a predetermined value such as 43. The methodology then advances to block 1838 previously described. If any of the criteria in diamond 1846 is true, the methodology advances to block 1849 and sets the SLP test flag and starts or continues a SLP timer (SPT). The methodology then advances to diamond 1850 and determines whether the time on the SLPT timer is greater than a predetermined time period. If the time on the SLPT timer is not greater than the predetermined time period, the methodology returns. If the time on the SLPT timer is greater than the predetermined time period, the methodology advances to diamond 1851 and determines whether the transmission 100 is operating in first gear by performing speed calculations. If the transmission 100 is not operating in first gear, the methodology advances to block 1852 and sets SLP 606 equal to neutral. The methodology then advances to block 1838 previously described. If the transmission 100 is operating in first gear, the methodology advances to diamond 1854 and determines whether the low/reverse pressure switch 650 equals one. If the low/reverse pressure switch 650 does not equal one, the methodology advances to block 1856 and sets 606 equal to reverse (See FIG. 5C). The methodology then advances to block 1838 previously described. If the low/reverse pressure switch 650 does equal one, the methodology advances to block 1852 and sets SLP 606 equal to neutral (See FIG. 5A). The methodology then advances to block 1838 previously described.
The present invention has been described in an illustrative manner. It is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.
Obviously, any modifications and variations are possible in light of the above teachings. Therefore, the subject invention may be practiced otherwise than as specifically described.
Claims
What is claimed is:
1. In a vehicle having an engine and a transmission including an input member, an output member, a gear assembly for changing the ratio of torque between the input member and output member, a plurality of friction elements for shifting the gear assembly, sensors providing signals indicative of measurement data for predetermined conditions, a controller having memory for processing and storing the signals and predetermined values and providing signals to control the friction elements, at least one sensor sensing the position of a manually operated shift lever to select between a plurality of predetermined operating modes the transmission such as park, reverse, neutral, overdrive, drive and low (PRNODDL) and temporary intermediate positions and providing a code (PC) of each predetermined operating mode, a method of identifying a plurality of operating modes of the transmission and allowing operation of the transmission with temporary or invalid PC by utilizing fluid pressure and speed sensor data, said method comprising the steps of: generating a PC by a plurality of sensors indicative of the shift lever position; setting the current shift lever position by the controller equal to PC when PC equals at least one of a plurality of predetermined PC codes and conditions exist; otherwise, checking the fluid pressure by the controller of at least one of a plurality of pressure sensors associated with predetermined friction elements and checking speed relationships by the controller of at least one of a plurality of speed sensors to identify the predetermined mode of operation of the transmission; identifying the predetermined mode of operation of the transmission without PC and setting the current shift lever position equal to the identified predetermined mode of operation of the transmission; and controlling the transmission using the current shift lever position.
2. A method as set forth in claim 1 including the steps of: checking whether the PC is equal to at least one of park, neutral and a temporary code by comparing the codes to each other; if PC is equal to either one of park, neutral and a temporary code, concluding that the shift lever position is neutral; if PC is not equal to either one of park, neutral and a temporary code, checking whether PC is equal to either one of reverse and overdrive; and if PC is either one of reverse and overdrive, concluding that the shift lever position is equal to PC.
3. A method as set forth in claim 2 including the steps of: if PC is not either one of reverse and overdrive, determining whether PC is equal to at least one of drive and low; if PC is equal to at least one of drive and low, determining whether the shift lever position is equal to either one of reverse and neutral; and if the shift lever position is not at least one of reverse and neutral, concluding that the shift lever position is equal to PC.
4. A method as set forth in claim 3 including the steps of: determining whether a neutral to first shift is in progress; if PC is invalid, determining whether a PRNODDL FAIL (PF) flag has been set; if the PF flag has not been set, setting the PF flag; if PC is not invalid and if the PF flag has been set, determining whether the shift lever position is reverse; determining whether a predetermined pressure sensor is equal to a predetermined logical state from a signal by the sensor; and if the predetermined pressure sensor is equal to the predetermined logical state, concluding that the shift lever position is neutral.
5. A method as set forth in claim 4 including the steps of: if the shift lever position is not reverse, determining whether the shift lever position is equal to neutral; if the shift lever position is neutral, determining whether another pressure sensor is equal to a predetermined logical state from a signal by the sensor; and if the predetermined pressure sensor is equal to a predetermined logical state, concluding that the shift lever position is overdrive.
6. A method as set forth in claim 5 including the steps of: if the predetermined pressure sensor does not equal the predetermined logical state, determining whether a predetermined solenoid-actuated valve is in a predetermined operating state, the pressure sensors are equal to a predetermined state and the engine speed is greater than a predetermined speed; and if the predetermined solenoid-actuated valve is in the predetermined operating state, the pressure sensors are equal to a predetermined logical state and the engine speed is greater than the predetermined speed, setting the shift lever position to reverse.
7. A method as set forth in claim 6 including the steps of: if the shift lever position is not neutral, determining whether the engine speed is less than a predetermined speed by comparing the speeds to each other; if the engine speed is not less than the predetermined speed, determining whether a shift is in progress; if the shift is in progress, determining whether a neutral to first gear shift is in progress; if the shift is not in progress or a neutral to first shift is in progress, determining whether a predetermined controller logic state exists and a plurality of predetermined pressure sensors are equal to a predetermined logical state; if the controller logic does not equal the predetermined logical state and all predetermined pressure sensors are equal to a predetermined logical state, determining whether the transmission is presently in fourth gear by comparing speeds from the input sensors; if the controller logic equals the predetermined logical state and all predetermined pressure sensors equal the predetermined logical state, setting the shift lever position equal to neutral; if the transmission is presently in fourth gear, determining whether the pressure sensors equal a predetermined logical state; if all the pressure sensors equal the predetermined logical state, setting the shift lever position equal to neutral; determining whether the time on a timer is greater than a predetermined time period; if the time on the timer is greater than the predetermined time period, determining whether the transmission is presently operating in first gear; if the transmission is not presently operating in first gear, setting the shift lever position equal to neutral; if the transmission is presently operating in first gear, determining whether the predetermined pressure sensor equals to a predetermined logical state; if the predetermined pressure sensor does not equal to the predetermined logical state, setting the shift lever position equal to reverse; and if the predetermined pressure sensor equals the predetermined logical state, setting the shift lever position equal to neutral.
8. In a vehicle having an engine and a transmission including an input member, an output member, a torque converter assembly for transmitting torque between the engine and the input member, a gear assembly for changing the ratio of torque between the input member and output member a plurality of friction elements for shifting the gear assembly, sensors providing signals indicative of measurement data for predetermined conditions, a controller having memory for processing and storing the signals and predetermined values and providing signals to control the friction elements, at least one sensor sensing the position of a manually operated shift lever to select between a plurality of predetermined operating modes of the transmission such as park, reverse, neutral, overdrive, drive and low (PRNODDL) and temporary intermediate position and providing a code (PC) for each predetermined operating mode, a method of identifying a plurality of operating modes of the transmission and allowing operation of the transmission by utilizing fluid pressure data, said method comprising the steps of: checking the fluid pressure to predetermined friction elements to determine the position of the shift lever; checking the position of the shift lever from PC; comparing the fluid pressure determined shift lever position to the PC shift lever position; and if the fluid pressure determined shift lever position does not equal the PC shift lever position, setting the shift lever position equal to the fluid pressure determined shift lever position; checking whether the PC is equal to at least one of park, neutral and a temporary code by comparing the codes to each other; if PC is equal to either one of park, neutral and a temporary code, concluding that the shift lever position is neutral; if PC is not equal to either one of park, neutral and a temporary code, determining whether PC is equal to either one of reverse and overdrive if PC is either one of reverse and overdrive, concluding that the shift lever position is equal to PC; if PC is not either one of reverse and neutral, determining whether PC is equal to at least one of drive and low; determining whether a neutral to first shift is in progress; if the shift lever position is not at least one of reverse and neutral, concluding that the shift lever position is equal to PC; if either one of PC does not equal drive or low, the shift lever position is either one of reverse and neutral, and a neutral to first shift is iu progress, determining whether PC is invalid; if PC is invalid, determining whether a PRNODDL Fail (PF) flag has been set; if the PF flag has not been set, setting the PC flag; if PC is not invalid and if the PF flag has been set, determining whether the shift lever position is in reverse; if the shift lever position is reverse, turning on a low/reverse clutch solenoid-actuated valve; determining whether low/reverse pressure sensor is equal to one; if the low/reverse pressure sensor is equal to one, determining that the shift lever position is neutral; if the shift lever position is not reverse, determining whether the shift lever position is equal to neutral; if the shift lever position s neutral, determining whether the overdrive pressure sensor is equal to one; if the shift lever position is neutral, setting the shift lever position test flag; determining whether the overdrive pressure sensor is equal to one; if the overdrive pressure sensor is equal to one, setting a predetermined variable to a predetermined value; determining that the shift lever position is overdrive; if the overdrive pressure sensor does not equal one, determining whether the low/reverse solenoid-actuated valve is on, the pressure sensors are equal to zero and the engine speed is greater than a predetermined value; if the low/reverse solenoid-actuated valve is on, the pressure sensors are equal to zero and the engine speed is greater than the predetermined value, setting the shift lever position to reverse; if the shift lever position is not neutral, determining whether the engine speed is less than a predetermined speed; if the engine speed is not less than the predetermined speed, determining whether a shift is in progress; if the shift is in progress, determining whether a neutral to first shift is in progress; if the shift is not in progress or a neutral to first shift is in progress, determining whether the low/reverse pressure sensor equals one and both the two/four and overdrive pressure sensors are equal to zero; if the low/reverse pressure sensor does not equal one and both the two/four and overdrive pressure sensors equal zero, determining whether the transmission is presently in fourth gear; if the low/reverse pressure sensor equals one and both the two/four and overdrive pressure sensors equal zero, setting the shift lever position equal to neutral; if the transmission is presently in fourth gear, determining whether the pressure sensors equal zero; if all the pressure sensors equal zero, setting the shift lever position equal to neutral; determining whether the time on a timer is greater than a predetermined time period; if the time on the timer is greater than the predetermined time period, determining whether the transmission is presently operating in first gear; if the transmission is not presently operating in first gear, setting the shift lever position equal to neutral; if the transmission is presently operating in first gear, determining whether the low/reverse pressure sensor equal one; if the low/reverse pressure sensor does not equal one, setting the shift lever position equal to reverse; and if the low/reverse pressure sensor equals one, setting the shift lever position equal to neutral.
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