Method for controlling reverse shift restriction in drive range of automatic transmission vehicle

The present invention relates to a method for controlling a reverse shift restriction in a drive "D" range of a vehicle having an automatic transmission. The method for controlling a reverse shift restriction in a drive "D" range of a vehicle's automatic transmission, comprising the steps of generating a frequency signal representative of the vehicle speed and direction. Next, determination of whether creeping is occurring is necessary. The automatic transmission is controlled based on said determination said frequency signal.

FIELD OF THE INVENTION 
The present invention relates to a method for controlling the hydraulic 
pressure of an automatic transmission to prevent reverse motion of a 
vehicle while the automatic transmission is in a Drive position. 
Additionally, the method for controlling the hydraulic pressure provides 
optimal control of a kick down band during automatic downshifting. 
BACKGROUND OF THE INVENTION 
Generally, electronics control an automatic transmission system of a 
vehicle through precisely controlling various valve actuators. Certain of 
these valves control the hydraulic pressure associated with the planetary 
gear sets, thereby providing precise shift control for stationary and 
moving vehicles. In other words, various engine sensors transmit signals, 
relating to operating conditions of the vehicle, to a transmission control 
unit ("TCU"). Based on these operating conditions, the TCU controls both 
shift mode hydraulic pressure and a damper clutch of the automatic 
transmission to optimize the performance of the vehicle. 
The TCU controls various solenoid valve actuators to control the automatic 
transmission pressure. In other words, the TCU generates a control signal 
for each solenoid valve. The control signal corresponds to an open/shut 
position of the solenoid valve. The position of the valves control the 
hydraulic pressure within the hydraulic control system, which improves 
shift quality of the transmission system. 
To achieve the above described control, detection of the vehicle's running 
condition, by each input sensor, should be accurate, and TCU should be 
programmed precisely. By this method, the automatic transmission maintains 
the hydraulic pressure to achieve the optimal running state of the vehicle 
under all road and operating conditions. Maintaining this condition 
requires a minimal amount to no effort on the part of the driver. By 
adding a control logic, which does not exist in a manual transmission, the 
automatic transmission is able to accomplish this optimal running state. 
The transmission control system, of the prior art, generally has 6 shift 
modes (or ranges), e.g., a parking "P" range, a reverse "R" range, a 
neutral "N" range, a drive "D" range, a second "2" range, and a low "L" 
range. Additionally, the "D" range provides first through fourth forward 
speed ratios, the "2" range the first and second forward speed ratios, and 
the "L" range the first forward speed ratio. That is, the driver can 
select one of the shift modes by shifting a shift selector lever between 
the modes, "D", "2", or "L". A shift operation occurs when the vehicle is 
placed in a mode other then "P" or "N". 
The TCU controls the forward and reverse speed ratios of the "R", "D", "2", 
and "L" ranges by controlling the hydraulic control system. The TCU 
generates the control signal necessary to control the hydraulic pressure 
based on various engine sensors, including engine rpms and throttle 
position. In particular, the vehicle's running condition is detected by 
various sensors, and the detected signals are transmitted to the TCU, such 
that each speed ratio in one of the "D", "2", and "L" ranges is determined 
in accordance with a shift pattern programmed in the TCU. When the 
automatic transmission vehicle is in a forward driving state, the 
vehicles's running conditions that the TCU uses to control hydraulic 
pressure include both engine rpms from a vehicle speed sensor ("PG-B"), 
and a throttle opening sensor's voltage from a throttle position sensor 
("TPS"). The TCU then determines the speed ratio in response to the rmp 
and throttle position signals. 
In the conventional automatic transmission, as described above, the 
transmission control system is designed to drive forwardly when the shift 
selector lever is in the "D" range. However, the signal supplied to the 
TCU does not have a direction of motion detector. Therefore, it is 
possible for the vehicle to inadvertently reverse while the shift selector 
lever is in the "D" range. For example, a vehicle stopped on a gradient 
may roll backwards with the shift selector still in a "D" range. The TCU 
would measure the backwards roll and assume that the vehicle was in 
forward motion. This phenomenon is generally known as creeping. That is, 
in this state, the inadvertent reversing of the vehicle cannot be 
prevented by the TCU as long as the driver does not depress the brake. The 
conventional automatic transmission, therefore, has a limitation of being 
unable to control creeping in the "D" range. 
This is caused because the conventional automatic transmission is 
constructed such that the creep control programmed in the TCU can prevent 
inadvertent reversing on a road having a gentle gradient but cannot 
prevent the same on a road having a steep gradient. In other words, when 
the throttle position and engine rpm indicate a stopped state, the TCU 
applies pressure to the kick down band which prevents the automatic 
transmission planetary gears from turning. This pressure is capable of 
preventing the gears from turning on flat as well as gentle gradient. When 
the road is steeply sloped upward, relatively higher hydraulic pressure 
should engage respective clutches and brakes to prevent the vehicle from 
reversing. However, there is no control logic which can achieve this in 
the conventional automatic transmission. 
Additionally, the conventional TCU sensor is designed to generate a 
frequency signal proportional to the vehicle speed so as to identify the 
current vehicle speed. However, the conventional TCU design does not 
discriminate the change between forward and reverse states of the vehicle. 
That is, when the vehicle is reversed in a state where the shift selector 
lever is in the drive "D" range, the TCU takes the vehicle's reverse speed 
for the forward speed and controls the hydraulic control system according 
to this misidentification. 
The creep control of the conventional automatic transmission and the 
conventional vehicle speed sensor will be described hereinafter with 
reference to FIGS. 1, 2A and 2B. 
As shown in FIG. 1, the conventional method of creep control includes, at 
step s1, calculating the rotating speed of a transfer drive gear and, at 
step s10, calculating the rotation speed of a vehicle speed reed switch. 
These signals constitute the frequency signal. Next, step 12, the method 
determines if the shift operation is performed or not. As described above, 
a shift operation exists when the vehicle shift selector lever is in a 
position other then "P" or "N". At step s14, the method transmits a signal 
relating to the frequency signal generated in steps s1 and s10 to a shift 
control part, in the cases where the shift operation is performed. Step 
s16, the TCU determines whether creep is occurring, based on industry 
standard methods. Step s16 is only performed when the shift operation is 
not performed. Step s18, transmitting the signal to a control routine, 
such that normal control occurs when creeping does not occur; and 
transmitting the signal to a creep control routine when creeping occurs, 
step s20. 
As described above, the conventional creep control method has a drawback in 
that it does not consider the rotating direction of the transfer drive 
gear, that is, the driving direction of the vehicle. Thus, the TCU can 
inadvertently control hydraulic pressure based upon rolling backwards. 
The inadvertent control signal is generated because the conventional TCU 
has no ability to sense the direction of motion of a vehicle. Referring to 
FIGS. 2A and 2B, there are shown a structure of a conventional vehicle 
speed reed switch (speed sensor) and an output wavy pattern, produced by 
the speed reed switch, induced into the TCU, respectively, illustrating a 
structural problem of the sensor. The symmetrical design of vehicle speed 
reed switch, as shown in FIG. 2A, produces a wavy pattern, used as the 
vehicle speed signal, induced into the TCU, incapable of indicating 
vehicle direction. In other words, the wavy pattern is the same regardless 
of the rotating direction of the transfer drive gear, as shown in FIG. 2B. 
The vehicle speed is measured by the rotational speed of the transfer 
drive gear. As FIGS. 2A and 2B show, the TCU cannot discriminate vehicle 
direction, i.e., between forward and reverse driving states, based on the 
wavy pattern produced by the vehicle speed reed switch. 
More in detail, when the system determines the following 4 conditions are 
satisfied, then the system determines creep is occurring and that creep 
control is necessary. In the prior art, when it is determined creeping is 
occurring, the creep control achieves the second speed and generates a 
pressure control solenoid valve duty ratio of 68.8%. The 4 conditions 
indicating creep are: 
1) The manual selecting signal should be in the "D" or "2" range; 
2) The rotation speed of the transfer drive gear is lower than 460 rpm; 
3) The idle switch is ON (i.e., the accelerating pedal should not be 
pressed); and 
4) The throttle opening voltage is lower than 0.94 V. 
FIG. 3 shows a pressure control solenoid valve duty output during the creep 
control. As shown in FIG. 3, when the rotation speed of the transfer drive 
gear is lower than 460 rpm, the creep duty ratio is maintained constantly 
at 68.8%. 
Further, when satisfying one of the following 4 conditions, the vehicle 
exits the creep state: 
1) The manual selecting signal relays being in the P, R, N, or L range; 
2) The rotation speed of the transfer drive gear is higher than 460 rpm; 
3) The idle switch is OFF, (i.e., the accelerating pedal should not be 
pressed); and 
4) The throttle opening voltage should be higher than 0.94 V. 
As described above, the conventional creep control method in the "D" range 
of the automatic transmission is performed without consideration of the 
rotating direction relayed by the vehicle speed sensor. It is desirous to 
identify the vehicle direction to more accurately control the hydraulic 
press. 
SUMMARY OF THE INVENTION 
The advantages and purpose of this invention will be set forth in part from 
the description, or may be learned by practice of the invention. The 
advantages and purpose of the invention will be realized and attained by 
means of the elements and combinations particularly pointed out in the 
appended claims. 
To attain the advantages and in accordance with the purpose of the 
invention, as embodied and broadly described herein, the present invention 
provides improved methods for controlling an automatic transmission of a 
vehicle. Specifically, the present invention provides a method of 
controlling the automatic transmission of a vehicle, comprising the steps 
of generating a frequency signal representing both a speed of the vehicle 
and a direction of motion of the vehicle. From the frequency signal, 
determining whether creeping is occurring and controlling the automatic 
transmission based on the results of the determination.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in FIG. 4, a method for controlling a reverse shift restriction in 
a "D" range of a vehicle's automatic transmission according to a preferred 
embodiment of the present invention comprises calculating the rotation 
speed of a transfer drive gear, step s100, and identifying a rotating 
direction of the transfer drive gear and determining the corresponding 
vehicle direction, in accordance with a vehicle speed reed wavy pattern, 
step s200. Step s300 calculates from the rotation speed of the transfer 
drive gear the corresponding vehicle speed. Step s400 determines whether a 
shift operation is being performed. A shift operation is identified 
whenever the shift selector lever is something other than "P" or "N" mode. 
Next, as step s500, the signals representing the vehicle direction and 
speed are transmitted to a shift control part when step s400 determines 
whether a shift operation is being performed. When it has been determined 
that a shift operation is not being performed, step s600 determines 
whether creeping is occurring, in the conventional method. Step s700 
constitutes transmitting the signal to a normal control routine when 
creeping is not occurring, and, step s800, constitutes determining the 
direction creeping is occurring, in a forward or reverse direction (Vss). 
This determination is based on the direction of motion determined in step 
s200. Step s900 transmits the signal to the forward creep control routine 
when the creep direction is in the forward direction; and step s1000, 
transmits the signal to the reverse creep control routine when the creep 
direction is in a reverse direction. As described above, the present 
invention uses a creep control logic and sensor to control the forward and 
reverse state of the vehicle. This control automatically places the 
vehicle in a condition most suitable to a driver's intentions, thereby 
providing driving convenience to the driver 
That is, when the vehicle is inadvertently reversed while in a 
forward-running state, the TCU identifies this and suitably controls the 
automatic transmission. This control prevents the vehicle from further 
reverse motion even when the driver does not depress the brake pedal. In 
addition, because the TCU identifies the direction and power of the 
vehicle regardless of the shift selector lever position, the hydraulic 
pressure can be accurately controlled when the shift selector lever is 
being shifted between the ranges. Finally, because it is possible to 
accurately control creeping of the automatic transmission vehicle, the 
life of the parts of the automatic transmission (e.g., various clutches 
and brakes) is greatly increased. 
Referring to FIG. 6, there is a graph illustrating a pressure control 
solenoid valve (PCSV) duty output of a preferred embodiment of the present 
invention. As shown in FIG. 6, the creep state of the vehicle is 
controlled by varying the hydraulic pressure in accordance with the 
forward and reverse directions of the vehicle, and the same creep state is 
always maintained under any load conditions. Therefore, even on a steep 
slope, the rearward pushing of the vehicle can be prevented. 
Referring-to FIG. 5A, there is a diagram illustrating a vehicle speed reed 
switch 50. As shown in FIG. 5A, a plurality of reed sensors 52 are 
designed in an asymmetrical structure so as to be able to identify the 
forward and reverse directions of the vehicle. Thus, it can be shown that 
the output wavy pattern changes based on the rotating direction of the 
sensor. Thus, the TCU can identify which direction the vehicle is moving, 
forward or reverse, based upon the wavy pattern. This can be applied to 
another application where a control according to the rotating direction is 
required as well as in the automatic transmission vehicle. The sensor 
identifies direction by determining each output magnitude at predetermined 
time sections. Because of the asymmetrical design, the magnitude of the 
reed wavy pattern varies according to the rotating direction of vehicle 
speed reed switch 50. This magnitude and direction are checked by a 
microcomputer within the TCU, such that the forward and reverse driving 
directions of the vehicle can be identified in accordance with the 
variation rate of each output magnitude at each time section. FIG. 5B 
shows an output wavy pattern of vehicle speed reed switch 50 according to 
a preferred embodiment of the present invention. The following table shows 
an output wavy pattern according to the rotating direction of an 
embodiment of vehicle speed reed switch 50, illustrating an output 
magnitude depicted in FIG. 5B. 
______________________________________ 
Rotation/Term 
T1 T2 T3 . . . Tn 
______________________________________ 
A direction 
Medium Small Large . . . Medium 
B direction 
Medium Large Small . . . Medium 
______________________________________ 
Therefore, the creep control method of the automatic transmission vehicle 
according to the present invention has the advantages as follows: 
First, when the vehicle is inadvertently reversed while in a 
forward-running state on an uphill grade, because the TCU identifies this 
and suitably controls the automatic transmission, the vehicle is not 
further reversed even when the driver does not depress the brake pedal. 
Second, because the TCU can identify the forward and reverse driving 
states of the vehicle, the TCU engages the kick down band with an optimal 
hydraulic pressure according to the driving direct of the vehicle, thereby 
precisely controlling creeping of the vehicle at a flat road surface. 
Finally, because it is possible to accurately control the creeping of the 
automatic transmission vehicle is possible, the life of the parts of the 
automatic transmission(e.g., for example, various clutches and brakes) is 
greatly increased. 
While the invention has been described in connection with what is presently 
considered to be the most practical and preferred embodiments, it is to be 
understood that the invention is not limited to the disclosed embodiments, 
but, on the contrary, it is intended to cover various modifications and 
equivalent arrangements included within the spirit and scope of the 
appended claims.