U.S. patent application number 09/802042 was filed with the patent office on 2001-09-20 for automatic transmission of vehicle.
Invention is credited to Nishimura, Nobuyuki, Shimizu, Tetsuya.
Application Number | 20010023385 09/802042 |
Document ID | / |
Family ID | 18594127 |
Filed Date | 2001-09-20 |
United States Patent
Application |
20010023385 |
Kind Code |
A1 |
Nishimura, Nobuyuki ; et
al. |
September 20, 2001 |
Automatic transmission of vehicle
Abstract
An automatic transmission arrangement includes TMCU (9) for
automatically shifting a transmission (3) according to a gear
position change signal issued from a manual shift switch (29a).
TMCU (9) also automatically disengages a clutch (2) when automatic
shifting takes place, and automatically engages the clutch (2) when
accelerator pedal depression (8) exceeds a predetermined value in a
clutch disengaged condition. TMCU (9) further decides a most
appropriate gear in accordance with a current vehicle running
condition, selects a higher one of the most appropriate gear and a
predetermined start gear as a target gear, and shifts the
transmission (3) to the target gear regardless of the gear position
change signal from the manual shift switch (29a) when the
accelerator pedal depression (8) exceeds a prescribed amount in the
clutch disengaged condition, and then engages the clutch (2).
Inventors: |
Nishimura, Nobuyuki;
(Kawasaki-shi, JP) ; Shimizu, Tetsuya;
(Kawasiki-shi, JP) |
Correspondence
Address: |
McCormick, Paulding & Huber LLP
CityPlace II
185 Asylum Street
Hartford
CT
06103-3402
US
|
Family ID: |
18594127 |
Appl. No.: |
09/802042 |
Filed: |
March 8, 2001 |
Current U.S.
Class: |
701/51 ;
701/55 |
Current CPC
Class: |
F16H 2061/023 20130101;
F16H 61/70 20130101; F16H 61/702 20130101; B60W 30/1819 20130101;
F16H 59/18 20130101; B60W 10/111 20130101; F16H 59/40 20130101;
B60W 30/182 20130101; F16H 59/56 20130101; F16H 61/0248 20130101;
B60W 2540/16 20130101; B60W 10/02 20130101; B60W 2540/10 20130101;
F16H 63/46 20130101; B60W 10/10 20130101 |
Class at
Publication: |
701/51 ;
701/55 |
International
Class: |
G06F 019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 14, 2000 |
JP |
2000-076370 |
Claims
What is claimed is:
1. An automatic transmission apparatus comprising: a first
controller for automatically shifting a transmission according to a
gear position change signal issued from a manual shift switch; a
second controller for automatically disengaging a clutch when
automatic shifting takes place, and for automatically engaging the
clutch when accelerator pedal depression exceeds a predetermined
value in a clutch disengaged condition; and a third controller for
deciding a most appropriate gear in accordance with a current
vehicle running condition, for selecting a higher one of the most
appropriate gear and a predetermined start gear as a target gear,
and for shifting the transmission to the target gear regardless of
the gear position change signal from the manual shift switch when
the accelerator pedal depression exceeds a prescribed amount in the
clutch disengaged condition, and then engaging the clutch.
2. The automatic transmission apparatus as in claim 1, wherein the
most appropriate gear is decided in a map from current accelerator
pedal depression and a rotation speed of an output shaft of the
transmission.
3. The automatic transmission apparatus as in claim 1, wherein the
gear position change signal is issued from the manual shift switch
in response to a shift lever movement.
4. The automatic transmission apparatus as in claim 1, wherein the
clutch is disengaged when a rotation speed of an input shaft of the
transmission drops below a value near an engine idling rotation
speed.
5. The automatic transmission apparatus as in claim 4, wherein the
value near an engine idling rotation speed is 450 rpm.
6. The automatic transmission apparatus as in claim 1, wherein the
predetermined value is 5% of an entire accelerator pedal
stroke.
7. The automatic transmission apparatus as in claim 1, wherein the
clutch is a mechanical friction clutch.
8. An apparatus comprising: means for automatically shifting a
transmission according to a gear position change signal issued from
a manual shift switch; means for automatically disengaging a clutch
when automatic shifting takes place, and for automatically engaging
the clutch when accelerator pedal depression exceeds a
predetermined value in a clutch disengaged condition; and means for
deciding a most appropriate gear in accordance with a current
vehicle running condition, for selecting a higher one of the most
appropriate gear and a predetermined start gear as a target gear,
and for shifting the transmission to the target gear regardless of
the gear position change signal from the manual shift switch when
the accelerator pedal depression exceeds a prescribed amount in the
clutch disengaged condition, and then engaging the clutch.
9. The apparatus as in claim 8, wherein the most appropriate gear
is decided in a map from current accelerator pedal depression and a
rotation speed of an output shaft of the transmission.
10. The apparatus as in claim 9, wherein the gear position change
signal is issued from the manual shift switch in response to a
shift lever movement.
11. The apparatus as in claim 10, wherein the clutch is disengaged
when a rotation speed of an input shaft of the transmission drops
below a value near an engine idling rotation speed.
12. The apparatus as in claim 11, wherein the value near an engine
idling rotation speed is 450 rpm.
13. The apparatus as in claim 12, wherein the predetermined value
is 5% of an entire accelerator pedal stroke.
14. The automatic transmission apparatus as in claim 13, wherein
the clutch is a mechanical friction clutch.
15. A method comprising the steps of: A) automatically shifting a
transmission according to a gear position change signal issued from
a manual shift switch; B) automatically disengaging a clutch when
automatic shifting takes place, and automatically engaging the
clutch when accelerator pedal depression exceeds a predetermined
value in a clutch disengaged condition; and C) deciding a most
appropriate gear in accordance with a current vehicle running
condition, selecting a higher one of the most appropriate gear and
a predetermined start gear as a target gear, and shifting the
transmission to the target gear regardless of the gear position
change signal from the manual shift switch when the accelerator
pedal depression exceeds a prescribed amount in the clutch
disengaged condition, and then engaging the clutch.
16. The method as in claim 15, wherein the most appropriate gear is
decided in a map from current accelerator pedal depression and a
rotation speed of an output shaft of the transmission.
17. The method as in claim 16, wherein the gear position change
signal is issued from the manual shift switch in response to a
shift lever movement.
18. The method as in claim 17, wherein the clutch is disengaged
when a rotation speed of an input shaft of the transmission drops
below a value near an engine idling rotation speed.
19. The method as in claim 18, wherein the value near an engine
idling rotation speed is 450 rpm.
20. The method as in claim 19, wherein the predetermined value is
5% of an entire accelerator pedal stroke.
Description
CROSS REFERENCES TO RELATED APPLICATION
[0001] The instant application claims priority under 35 USC 119 of
Japanese Patent Application No. 2000-76370 filed on Mar. 14, 2000,
the entire disclosure of which is incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an automatic transmission
loaded on a large vehicle such as a tractor-trailer.
[0004] 2. Description of the Related Art
[0005] Recently, many large vehicles such as tractor-trailers,
trucks and lorries are equipped with an automatic clutch and
automatic transmission in order to lighten a driver's burden. A
controller associated with the automatic transmission selects a
most appropriate transmission gear position in accordance with
vehicle speed from a map, and the transmission is automatically
shifted up and down in response to acceleration and deceleration of
the vehicle.
[0006] Some of such automatic transmissions are further equipped
with a manual mode which allows a driver to manually shift the
transmission according to a shift lever movement. In the manual
mode, unless the driver shifts the transmission with the shift
lever, a current transmission gear position is maintained. The
shift lever movement made by the driver only causes the
transmission gear position change.
[0007] Generally, such automatic transmissions have an automatic
clutch device, which automatically disengages and engages a
friction clutch by an actuator.
[0008] In the manual mode, the conventional arrangement has a
following problem. For example, when a vehicle is decelerated to a
low speed while a relatively high speed gear is being maintained,
the clutch is automatically disengaged to avoid engine stalling,
and the disengaged condition is kept. After that, when an
accelerator pedal is stamped to accelerate the vehicle, the clutch
is automatically engaged. However, since the transmission gear
position is high, the engine stalls upon clutch engagement or the
clutch excessively slips. This hinders smooth driving, and damages
the clutch.
SUMMARY OF THE INVENTION
[0009] An object of the present invention is to prevent an engine
from stalling and a clutch from being damaged when a vehicle is
accelerated after deceleration when a transmission is in a manual
mode.
[0010] According to one aspect of the present invention, there is
provided an automatic transmission apparatus including a controller
for automatically shifting a transmission according to a gear
position change signal issued from a manual shift switch. This
controller (or second controller) also automatically disengages a
clutch when automatic shifting takes place, and automatically
engages the clutch when accelerator pedal depression exceeds a
predetermined value in a clutch disengaged condition. The
controller (or third controller) further decides a most appropriate
gear in accordance with a current vehicle running condition,
selects a higher one of the most appropriate gear and a
predetermined start gear as a target gear, and shifts the
transmission to the target gear regardless of the gear position
change signal from the manual shift switch when the accelerator
pedal depression exceeds a prescribed amount in the clutch
disengaged condition, and then engages the clutch.
[0011] The most appropriate gear may be decided in a map from
current accelerator pedal depression and a rotation speed of an
output shaft of the transmission.
[0012] The gear position change signal may be issued from the
manual shift switch in response to a shift lever movement.
[0013] The clutch may be disengaged when a rotation speed of an
input shaft of the transmission drops below a value near an engine
idling rotation speed.
[0014] Other objects, aspects and advantages of the present
invention will become apparent to those skilled in the art to which
the invention pertains from the subsequent detailed description and
the appended claims, taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 illustrates a flowchart of stall and clutch excessive
wear prevention control according to the present invention;
[0016] FIG. 2 illustrates an engine drive power transmitting system
of a vehicle to which the present invention is applied;
[0017] FIG. 3 illustrates an automatic transmission employed in the
system shown in FIG. 2;
[0018] FIG. 4 illustrates an automatic clutch device employed in
the system shown in FIG. 2;
[0019] FIG. 5 illustrates a shift up map; and
[0020] FIG. 6 illustrates a shift down map.
DETAILED DESCRIPTION OF THE INVENTION
[0021] While the present invention will be described in connection
with a preferred embodiment thereof, it should be understood that
it is not intended to limit the invention to that embodiment.
[0022] An embodiment of the present invention will now be described
with reference to the accompanying drawings.
[0023] Referring first to FIG. 2, illustrated is an automatic
transmission 3 according to the present invention, which is
installed in a tractor-trailer with a diesel engine 1. The
transmission 3 is coupled with the engine 1 via a clutch 2, and an
output shaft 4 (FIG. 3) of the transmission 3 is connected to a
propeller shaft (not shown) to drive rear wheels (not shown). The
engine 1 is electronically controlled by an engine control unit
(ECU) 6. Specifically, ECU 6 reads a current engine revolution
speed and engine load from outputs of an engine rotation sensor 7
and accelerator opening sensor (accelerator pedal depression
sensor) 8, and determines primarily from these outputs timing of
fuel injection and an amount of fuel injection from a fuel
injection pump 1a.
[0024] As illustrated in FIG. 3, a flywheel 1b is mounted on a
crankshaft of the engine 1, and a ring gear 1c is formed along the
periphery of the flywheel 1b. As the teeth of the ring gear 1c pass
by the engine revolution speed sensor 7, the sensor 7 outputs
pulses. ECU 6 counts the number of the pulses per unit time to
calculate the engine revolution speed.
[0025] Referring back to FIG. 2, the clutch 2 and transmission 3
are automatically controlled by a transmission control unit (TMCU)
9. ECU 6 and TMCU 9 are connected to each other over a bus and
communicate with each other.
[0026] As illustrated in FIGS. 2, 3 and 4, the clutch 2 is a
mechanical friction clutch, and includes the flywheel 1b (input
part of the clutch), a driven plate 2a (output part of the clutch),
and a pressure plate 2b for frictionally contacting the driven
plate 2a with the flywheel 1a and leaving the driven plate from the
flywheel. The clutch 2 has a clutch booster 10 to cause the
pressure plate 2b to move in an axial direction. The clutch 2 is
generally disengaged and engaged in an automatic manner to lighten
a driver's burden. When the clutch 2 should be operated delicately,
e.g., when the vehicle is moved backward at a very slow speed, and
when the clutch 2 should be disengaged suddenly, e.g., in an
emergency case, it is also possible to disengage and engage the
clutch 2 manually upon stamping of a clutch pedal 11. Thus, this is
a so-called selective automatic clutch. A clutch stroke sensor 14
is provided for detecting a stroke of the clutch itself (i.e.,
position of the pressure plate 2b), and a clutch pedal stroke
sensor 16 is provided for detecting how deep the clutch pedal 11 is
stamped. These sensors are connected to TMCU 9.
[0027] As best illustrated in FIG. 4, the clutch booster 10 is
connected to an air tank 5 via two air pipes "a" and "b" as
indicated by the solid line, so that the clutch booster 10 is
pneumatically activated by the air pressure supplied from the air
tank 5. One of the air pipes "a" is used for automatic clutch
disengagement and engagement, and the other air pipe "b" is used
for manual clutch disengagement and engagement. The air pipe "a" is
divided to two branch lines a1 and a2. On the first branch line a1,
provided in series are two electromagnetic valves MVC1 and MVC2 for
automatic disengagement and engagement. On the second branch line
a2, provided is an electromagnetic valve MVCE for emergency case.
At a position where these branch lines a1 and a2 meet, a double
check valve DCV1 is provided. The air pipe "b" has a hydraulic
valve 12 which is associated with the clutch booster 10. Another
double check valve DCV2 is provided at a position where the air
pipes "a" and "b" encounter. Each of the double check valves DCV1
and DCV2 is a three-way valve which is activated by differential
pressure.
[0028] The electromagnetic valves MVC1, MVC2 and MVCE are turned on
and off under the control of TMCU 9. When turned on, the
electromagnetic valve connects its upstream side to the downstream
side. When turned off, the electromagnetic valve blocks up the air
so that the upstream side is disconnected from the downstream side,
and the downstream side is released to the atmosphere. First, the
automatic clutch operation will be described. The electromagnetic
valve MVC1 is simply turned on and off in accordance with on and
off of an ignition key. When the ignition key is in an off
position, i.e., the vehicle is stopped, the electromagnetic valve
MVC1 is turned off and interrupts the air pressure of the air tank
5. The electromagnetic valve MVC2 is a proportional control valve
and able to arbitrarily control an amount (or flow rate) of air to
be fed and discharged. This is necessary to control a speed of
clutch disengagement and engagement. When both the electromagnetic
valves MVC1 and MVC2 are turned on, the air pressure of the air
tank 5 causes the double check valves DCV1 and DCV2 to switch so
that the air pressure is applied to the clutch booster 10. This
disengages the clutch. In order to engage the clutch, the
electromagnetic valve MVC2 is only turned off. This releases the
air pressure of the clutch booster 10 from the electromagnetic
valve MVC2.
[0029] If abnormality occurs in either the electromagnetic valve
MVC1 or MVC2 during clutch disengagement and that electromagnetic
valve is turned off, the clutch is suddenly engaged in opposition
to the driver's intent. Thus, if such abnormality is detected by an
abnormality diagnosis circuit of TMCU 9, the electromagnetic valve
MVCE is immediately turned on. This causes the air pressure passing
through the electromagnetic valve MVCE to switch the double check
valve DCV1 to the opposite side so that the air pressure is
supplied to the clutch booster 10. As a result, the clutch
disengaged condition is maintained and the sudden clutch engagement
is prevented.
[0030] Next, the manual mode will be described. The hydraulic
pressure is fed from and returned to the master cylinder 13 upon
stamping and releasing of the clutch pedal 11. The hydraulic
pressure is fed to the hydraulic valve 12 via an oil line 13a as
indicated by the broken line to open and close the hydraulic valve
12 and in turn to feed and release the air pressure to and from the
clutch booster 10 for manual disengagement and engagement of the
clutch 2. As the hydraulic valve 12 is opened, the air pressure
passing therethrough causes the double check valve DCV2 to switch
so that the air pressure reaches the clutch booster 10. It should
be noted that when the automatic clutch disengagement and
engagement interferes with the manual clutch disengagement and
engagement, priority is given to the manual disengagement and
engagement.
[0031] As illustrated in FIG. 3 in detail, the transmission 3 is a
basically "always engaged" type of multi-stage transmission, and
has sixteen forward gear positions and two backward gear positions.
The transmission 3 has a splitter assembly 17 as an auxiliary
transmission on its input side, a range gear assembly 19 as another
auxiliary transmission on its output side, and a main gear assembly
18 between these two auxiliary gear assemblies. The transmission 3
transfers a drive power of the engine 1 from the input shaft 15 to
the splitter 17, main gear assembly 18, range gear assembly 19 and
output shaft 4 in this order.
[0032] A gear shift unit GSU is provided for automatically shifting
the transmission 3. GSU includes a splitter actuator 20, main
actuator 21 and range actuator 22 for shifting the splitter
assembly 17, main gear assembly 18 and range gear assembly 19
respectively. Like the clutch booster 10, these actuators are also
pneumatically driven under the control of TMCU 9. A current gear
position of each of the gear assemblies 17, 18 and 19 is detected
by an associated gear position switch 23 (FIG. 2). The rotation
speed of the countershaft 32 is detected by a countershaft rotation
sensor 26, and that of the output shaft 4 is detected by an output
shaft rotation sensor 28. These detection signals are fed to TMCU
9.
[0033] The automatic transmission described above also possesses a
manual mode so that the transmission can be shifted up and down in
response to a shift lever movement caused by the driver. In the
manual mode, as illustrated in FIG. 2, a gear position change
signal issued from a shift lever unit 29 located next to a driver'
seat triggers disengagement and engagement of the clutch 2 and gear
position change of the transmission 3. Specifically, when the
driver moves a shift lever 29a of the shift lever unit 29, a shift
switch installed in the shift lever unit 29 is turned on to output
the gear position change signal to TMCU 9. Upon receiving this
signal, TMCU 9 selectively and/or cooperatively causes the clutch
booster 10, splitter actuator 20, main gear actuator 21 and range
gear actuator 22 to operate so as to perform a series of shift up
(or down) operations (clutch disengagement, gear disengagement,
gear engagement and clutch engagement). TMCU 9 also causes a
monitor 31 to display a current gear position. Therefore, the shift
switch incorporated in the shift lever unit 29 is a manual shift
switch of the invention. This manual shift switch is turned on by
the shift lever movement in this embodiment.
[0034] In the shift lever unit 29, "R" represents reverse, "N"
neutral, "D" drive, "UP" shift up, and "DOWN" shift down. Next to
the driver' seat, also provided are a mode switch 24 for switching
of shift mode between the manual mode and automatic mode, and a
skip switch 25 for switching between gear-by-gear shifting and
every other gear shifting.
[0035] In the automatic shift mode, if the shift lever 29a is in
the D range, the transmission is automatically shifted up and down
in accordance with the vehicle speed. It should be noted that even
in the automatic shift mode, if the driver moves the shift lever
29a to UP or DOWN, the transmission is manually shifted. In the
automatic shift mode, if the skip switch 25 is turned off (normal
mode), the transmission gear position change takes place one gear
at a time. This is advantageous when a tractor tows a trailer with
a relatively heavy load. When the skip switch 25 is turned on (skip
mode), the gear position change occurs every other gear (e.g., from
first gear to third gear). This is advantageous when the tractor
does not tow the trailer or tows the trailer with a relatively
light load.
[0036] On the other hand, when the manual shift mode is selected,
the gear position change is effected completely according to the
driver's intention. When the shift lever 29a is in the D range, no
gear position takes place and a current gear position is
maintained. Only when the driver operates the shift lever 29a to UP
or DOWN, the transmission 3 is shifted up or down. If the skip
switch 25 is turned off, the gear position change occurs one gear
by one gear. If the skip switch 25 is turned on, the gear position
change occurs every other gear. In this mode, the D range is an H
(hold) range to keep a current gear position.
[0037] An emergency shift switch 27 is also provided in the
vicinity of the driver' seat. In case an electromagnetic valve of
GSU fails, for instance, the driver presses an ON button and turns
a knob to shift the transmission 3.
[0038] As illustrated in FIG. 3, the transmission 3 includes the
input shaft 15, main shaft 33 and output shaft 4 that are arranged
coaxially, and a countershaft 32 that extends below and in parallel
to these shafts. The input shaft 15 is coupled to the driven plate
2a of the clutch 2. The input shaft 15 and main shaft 33 are
supported such that they can rotate relative to each other.
[0039] Next, the structures of the splitter assembly 17 and main
gear assembly 18 will be described. A split high gear SH is
rotatably mounted on the input shaft 15. Main gears M4, M3, M2, M1
and MR are rotatably mounted on the main shaft 33 in this order
from the front. These gears SH, M4, M3, M2 and M1 except for the
gear MR always mesh with counter gears CH, C4, C3, C2 and C1 fixed
on a counter shaft 32 respectively. The gear MR always meshes with
an idle reverse gear IR, and the idle reverse gear IR always meshes
with a counter gear CR secured on the counter shaft 32.
[0040] The gears SH, M4, . . . mounted on the input shaft 15 and
main shaft 33 have splines 36 for selection of themselves. In the
vicinity of these splines 36, provided are first to fourth splines
37 to 40 fixed to the input shaft 15 and main shaft 33. First to
fourth sleeves 42 to 45 always engage with the first to fourth
splines 37 to 40 such that they can slide back and forth. By
selectively sliding the first to fourth sleeves 42 to 45 to cause
them to engage with and disengage from the splines 36 of the gears,
a particular transmission gear is selected or the transmission is
brought into a neutral condition (geared in and out). Movement of
the first sleeve 42 is made by the splitter actuator 20, and those
of the second to fourth sleeves 43 to 45 are made by the main
actuator 21.
[0041] In this manner, the splitter assembly 17 and main gear
assembly 18 have an "always-engaged" type structure that is
automatically shifted up and down by the associated actuators 20
and 21. It should be noted that a spline portion of the splitter
assembly 17 has an ordinary mechanical synchronization unit, but a
spline portion of the main gear assembly 18 does not. Because of
this, a so-called synchronization control is performed to match the
engine revolution speed with the gear rotation speed so that the
shifting can be made without the synchronization unit. Here, not
only the main gear assembly 18 but also the splitter gear assembly
17 have a neutral position so as to prevent rattle noise of gears.
The detail of the neutral position of the splitter gear assembly
can be found in Japanese Patent Application No. 11-319915 or
corresponding U.S. patent application Ser. No. ______ filed on Nov.
7, 2000, entitled "MULTI-STAGE TRANSMISSION OF VEHICLE" (Attorney
Docket No. 5616-0027, ISZ-US-89), the entire disclosures of which
are incorporated herein by reference.
[0042] Next, the range gear assembly 19 will be described. The
range gear assembly 19 has a planetary gear mechanism 34 and is
shiftable to a high or low position. The planetary gear mechanism
34 includes a sun gear 65 secured on the rear end of the main shaft
33, a plurality of planetary gears 66 meshing with the outer
periphery of the sun gear, and a ring gear 67 having inner teeth in
mesh with the planetary gears 66. The planetary gears 66 are
rotatably supported by a common carrier 68 that is connected to the
output shaft 4. The ring gear 67 has a tubular portion 69 that is
rotatably fit over the output shaft 4. The tubular portion 69 and
the output shaft 4 constitute a double shaft structure.
[0043] A fifth spline 41 extends from the tubular portion 69.
Closely behind the fifth spline 41, provided is an output shaft
spline 70 extending from the output shaft 4. In close front of the
fifth spline 41, provided is a stationary spline 71 fixed to the
transmission casing. A fifth sleeve 46 always meshes with the fifth
spline 41 such that it can slide back and forth. Movement of the
fifth sleeve 46 is controlled by the range gear actuator 22. Spline
portions of the range gear assembly 19 have synchronization
mechanisms.
[0044] When the fifth sleeve 46 moves forwards, it engages with the
fixed spline 71 so that the fifth spline 41 is coupled to the fixed
spline 71. This causes the ring gear 67 to be secured on the
transmission casing and the output shaft 4 is caused to rotate at a
reduction ratio greater than one. This is the low gear
position.
[0045] On the other hand, if the fifth sleeve 46 moves backwards,
it engages with the output shaft spline 70 so that the fifth spline
41 is coupled with the output shaft spline 70. As a result, the
ring gear 67 and carrier 68 are fixed relative to each other, and
the output shaft 4 is directly rotated at a reduction ratio of one.
This is the high gear position.
[0046] As described above, the transmission 3 has two gear
positions (high and low gear positions) in the splitter assembly
17, four gear positions in the main gear assembly 18, and two gear
positions (high and low) in the range gear assembly 19 when in the
forward mode. In sum, the transmission 3 can be shifted from the
first to the sixteenth gear positions (2.times.4.times.2=16). In
the backward mode, the transmission 3 has two gear positions (high
and low) upon switching of the splitter assembly 17.
[0047] Next, the actuators 20, 21 and 22 will be described. Each
actuator includes one or more pneumatic cylinders activated by the
air pressure from the air tank 5, and a plurality of
electromagnetic valves for switching between application and
releasing of the air pressure to and from the pneumatic cylinders.
These electromagnetic valves are selectively operated by TMCU 9 so
that the pneumatic cylinders are selectively activated.
[0048] The splitter actuator 20 includes a pneumatic cylinder 47
and three electromagnetic valves MVH, MVF and MVG. The pneumatic
cylinder 47 has a double piston. When the splitter assembly 17
should be in a neutral condition, the electromagnetic valve MVH is
turned on, the electromagnetic valve MVF is turned off and the
electromagnetic valve MVG is turned on. When the splitter assembly
17 should be shifted to the high gear position, the electromagnetic
valve MVH is turned off, the electromagnetic valve MVF is turned
off and the electromagnetic valve MVG is turned on. In order to
shift the splitter assembly 17 to the low gear position, the
electromagnetic valve MVH is turned off, the electromagnetic valve
MVF is turned on and the electromagnetic valve MVG is turned
off.
[0049] The main gear assembly actuator 21 includes a pneumatic
cylinder 48 for gear selection, another pneumatic cylinder 49 for
shifting, three electromagnetic valves MVC, MVD and MVE associated
with the first pneumatic cylinder 48 and two electromagnetic valves
MVB and MVA associated with the second pneumatic cylinder 49. The
first pneumatic cylinder 48 has a double piston and the second
pneumatic cylinder 49 has a single piston.
[0050] When the electromagnetic valve MVC is turned off, the
electromagnetic valve MVD is turned on and the electromagnetic
valve MVE is turned off, the first pneumatic cylinder 48 is moved
downwards in the drawing so that the third and fourth gears and N3
(neutral position between the third and fourth gears) of the main
gear assembly can be selected. When the electromagnetic valve MVC
is turned on, the electromagnetic valve MVD is turned off and the
electromagnetic valve MVE is turned on, the first pneumatic
cylinder 48 is moved into the neutral condition so that the first
and second gears and N2 (neutral position between the first and
second gears) of the main gear assembly can be selected. When the
electromagnetic valve MVC is turned on, the electromagnetic valve
MVD is turned off and the electromagnetic valve MVE is turned off,
the first pneumatic cylinder 48 is moved upwards in the drawing so
that the reverse gear and N1 of the main gear assembly are
selectable.
[0051] The second pneumatic cylinder 49 is brought into the neutral
condition when the electromagnetic valve MVA is turned on and the
electromagnetic valve MVB is turned on. This allows selection of
N1, N2 and N3 of the main gear assembly. When the electromagnetic
valve MVA is turned on and the electromagnetic valve MVB is turned
off, the pneumatic cylinder 49 is moved to the left in the drawing
so that the second, fourth and reverse gears can be selected. When
the electromagnetic valve MVA is turned off and the electromagnetic
valve MVB is turned on, the pneumatic cylinder 49 is moved to the
right so that the first and third gears of the main gear assembly
can be selected.
[0052] The range gear actuator 21 includes a pneumatic cylinder 50
with a single piston, and two electromagnetic valves MVI and MVJ.
The pneumatic cylinder 50 is moved to the right in the drawing when
the electromagnetic valve MVI is turned on and the electromagnetic
valve MVJ is turned off. This shifts the range gear assembly to the
high gear position. On the other hand, the pneumatic cylinder 50 is
moved to the left in the drawing when the electromagnetic valve MVI
is turned off and the electromagnetic valve MVJ is turned on to
shift the range gear assembly to the low gear position.
[0053] In order to brake the countershaft 32 for the
above-mentioned synchronization control, the countershaft 32 is
equipped with a countershaft brake 27. This brake 27 is a wet
multiple plate type brake and actuated by the air pressure from the
air tank 5. Application and non-application of the air pressure is
switched by an electromagnetic valve MV BRK. When the
electromagnetic valve MV BRK is turned on, the air pressure is
applied to the countershaft brake 27 to apply a brake force to the
counter shaft. When the electromagnetic valve MV BRK is turned off,
the air pressure is allowed to escape from the countershaft brake
27 so that no brake force acts on the countershaft. More detail of
the counter shaft brake can be found in Japanese Patent Application
No. 2000-83274 or corresponding U.S. patent application Ser. No.
______ filed on Jan. 23, 2001, entitled "LUBRICATION SYSTEM FOR
COUNTERSHAFT BRAKE" (Attorney Docket No. 5616-0032, ISZ-US-94), the
entire disclosures of which are incorporated herein by
reference.
[0054] Next, the automatic shift control will be described. TMCU 9
has a shift up map as illustrated in FIG. 5 and a shift down map as
illustrated in FIG. 6 in its memory. In the automatic shift mode,
TMCU 9 conducts the automatic shifting according to these maps. For
example, in the shift up map of FIG. 5, a shift up curve from an
n'th gear (n is an integer from one to fifteen) to an n+1'th gear
is determined from an accelerator pedal depression (accelerator
opening) (%) and output shaft rotation speed (rpm). In the map, a
single point is determined from current accelerator depression and
output shaft rotation speed. When the vehicle is accelerated, the
rotation speed of the output shaft 4 connected to wheels gradually
increases. Therefore, in the normal automatic shift mode, the
transmission is shifted up one gear by one gear every time a
current point passes over a nearest shift up curve. If the skip
mode is selected, the transmission is shifted up every other gear
as a current point passes over a shift up curve above the nearest
shift up curve.
[0055] As in FIG. 5, the shift down map of FIG. 6 has a shift down
curve from an n+1'th gear to an n'th gear, which is determined from
the accelerator pedal depression (%) and output shaft rotation
speed (rpm). A single point is defined from current accelerator
pedal depression and output shaft rotation speed. When the vehicle
is decelerated, the rotation speed of the output shaft 4 gradually
drops. In the normal automatic shift mode, therefore, the
transmission is shifted down one gear at a time as a current point
passes over a nearest shift down curve. In the skip mode, the
shifting down occurs every other gear.
[0056] In the manual mode, the driver can arbitrarily shift up and
down the transmission independently of these maps. In the normal
mode, a single gear position change operation made by the driver
causes the shifting by one gear. In the skip mode, the shifting
occurs by two gears upon a single gear position change
operation.
[0057] Current accelerator depression is detected by an accelerator
pedal sensor 8 (FIG. 2), and current output shaft rotation speed is
detected by the output shaft rotation speed sensor 28. TMCU 9
calculates a current vehicle speed from the current output shaft
rotation speed, and indicates it in a speedometer. In this manner,
the vehicle speed is indirectly determined from the output shaft
rotation speed. The output shaft rotation speed is proportional to
the vehicle speed.
[0058] Now, control for preventing the engine from stalling and
protecting the clutch according to the present invention will be
described. It should be assumed here that the driver stamps the
brake pedal to decelerate the vehicle while maintaining the current
gear position during the manual mode driving, and then stamps the
accelerator pedal to accelerate the vehicle. In the course of
deceleration, when the engine rotation speed drops close to the
idling rotation, the clutch is automatically disengaged since there
is a possibility of stalling. The clutch is maintained in the
disengaged condition until the accelerator pedal is depressed for
acceleration. However, if the driver depresses the accelerator
pedal when the gear position is high, the clutch is engaged with
the too high gear. This results in stalling and excessive slip and
wear of the clutch. The present invention prevents such
shortcoming. Specifically, when the accelerator pedal is stamped,
the transmission is automatically shifted down to an appropriate
gear position prior to clutch engagement regardless of the gear
position change signal from the manual shift switch. In other
words, even if the driver does not move the shift lever at all and
maintains the current gear position, the appropriate gear position
is automatically selected before the clutch is engaged.
[0059] Referring to FIG. 1, TMCU 9 determines at S101 whether the
current mode is a manual mode from the output of the mode switch
24. If the manual mode has been selected, the program proceeds to
S102. If not, the program advances to END. This is because stalling
and excessive clutch slip upon acceleration after deceleration
occur only in the manual mode. In the automatic mode, the
transmission is automatically shifted down in accordance with the
vehicle speed so that such problems would not occur. Whether the
skip mode is selected or not is out of question as far as the
engine stall and clutch excessive slip prevention is concerned.
[0060] At S102, it is determined whether the current shift lever
position is in the D (H in the manual mode) from the signal of the
shift lever unit 29. One of the conditions to perform the stall
prevention control is that the driver does not move the shift lever
for shifting up or down. If it is the D, the program proceeds to
S103. If not, the program proceeds to END to wait for completion of
shifting.
[0061] At S103, it is determined whether the rotation speed of the
input shaft 15 (or rotation speed of the clutch) is smaller than a
predetermined value (e.g., 450 rpm). If the input shaft rotation
speed is not smaller than 450 rpm, the program proceeds to S111. At
S111, the current gear position is memorized as a target gear
position for the next shifting. Thus, no shifting is effected. On
the other hand, if the input shaft rotation speed is less than 450
rpm, the program proceeds to S104. Here, the engine idling rotation
speed is 500 rpm, and the stall prevention control is performed
when the input shaft rotation speed becomes smaller than the idling
speed. This is because the clutch is surely disengaged in this
situation. Further, if the transmission was automatically shifted
down in spite of the rotation speed being not so low, the driver
might feel uncomfortable. Nevertheless, in actuality, the clutch is
disengaged during the deceleration when the input shaft rotation
speed becomes about 900 rpm, for instance, which is slightly higher
than the idling speed. In this manner, the stall prevention control
of the present invention is primarily applied when the clutch is
disengaged near the idling rotation.
[0062] The input shaft rotation speed is calculated from the
countershaft rotation speed detected by the countershaft rotation
speed sensor 26. TMCU 9 memorizes the numbers of teeth of the gears
in the transmission and respective gear ratios, and obtains the
input shaft rotation speed N1 from the equation shown below based
on the countershaft rotation speed N2, the number of the teeth Z1
of the split high gear SH (input gear) and the number of the teeth
Z2 of the counter gear CH (input counter gear).
N1=(Z2/Z1).times.N2
[0063] At S104, it is determined whether the current accelerator
pedal depression exceeds a predetermined value (e.g., 5%) from the
output of the accelerator pedal sensor 8. If the accelerator pedal
is stamped over 5%, TMCU 9 determines that the driver wants to
accelerate the vehicle so that the clutch is automatically engaged.
If the answer at S104 is yes, the program advances to S105. If no,
the program advances to S111.
[0064] At S105, it is determined whether the clutch is currently
disengaged from the output of the clutch stroke sensor 14. This
step is necessary because even if the clutch disengagement is
assumed from the answer at S103, there is a possibility that the
clutch is in actuality not disengaged due to interference with
other control and/or malfunctioning and abnormality. It should be
noted, however, that S105 is provided to just make sure that the
clutch is indeed disengaged. If the clutch is not engaged at S105,
the program proceeds to S106. Otherwise, the program proceeds to
S111.
[0065] At S106, the current gear position detected by the gear
position switch 23 is compared with a predetermined start gear
position (e.g., fourth or ninth gear) stored in TMCU 9. If the
current gear is higher than the predetermined start gear, it means
that the driver shifts down the transmission sufficiently during
the deceleration by his or her own intent. In such case, the stall
prevention control is not conducted. Therefore, the program
proceeds to S111. If the current gear is greater than the
predetermined gear, on the other hand, the program proceeds to
S107.
[0066] At S107, a most appropriate gear is selected in the shift up
map shown in FIG. 5 from the current accelerator pedal depression
detected by the accelerator pedal sensor 8 and the current output
shaft rotation speed detected by the output shaft rotation sensor
28. At the subsequent step, the selected most appropriate gear is
compared with the preset start gear. If the former is smaller than
the latter, the program proceeds to S109 to employ the preset start
gear as the target gear. If the answer at S108 is no, the program
goes to S110 to employ the selected most appropriate gear as the
target gear. In this manner, the higher one is used as the target
gear.
[0067] After deciding the target gear, the transmission is
automatically shifted to that target gear. Accordingly, appropriate
shift down occurs. After that, the clutch is automatically engaged
for subsequent acceleration of vehicle.
[0068] According to the stall prevention control of the present
invention, when the driver stamps the accelerator pedal to raise
the vehicle speed after deceleration, the transmission is first
automatically shifted down to a gear position suited to the vehicle
running condition and then the clutch is engaged. Therefore, the
engine will not stall and the clutch will not slip excessively upon
clutch engagement. This improves driver's comfort and protects the
clutch.
[0069] The higher one of the selected most appropriate gear and
preset start gear is utilized as the target gear for subsequent
acceleration of the vehicle since the transmission should be
shifted to a gear not smaller than the preset start gear. For
instance, if the vehicle is decelerated to a very slow speed while
the high gear position is maintained, the transmission might be
shifted down to a gear lower than the preset start gear (e.g.,
first or second gear) as far as the control is performed in
accordance with the shift down map. If it happens, the driver
experiences a shock upon clutch engagement and/or the engine
revolution speed suddenly and steeply rises, which also makes the
driver uncomfortable. In order to prevent such discomfort, a gear
at least equal to the predetermined start gear is used in the
present invention. If the vehicle is running at a certain speed
when the driver intends to accelerate the vehicle, the preset start
gear may be too low. In this case, the most appropriate gear
selected from the map is utilized. Accordingly, the driver does not
experience uncomfortable acceleration and clutch engagement.
[0070] It should be noted that the present invention is not limited
to the illustrated and described embodiment. For example, the most
appropriate gear is not determined necessarily from the accelerator
pedal depression and output shaft rotation speed. The vehicle speed
may be employed instead of the output shaft rotation speed. The map
used is not limited to the shift up map of FIG. 5. The manual shift
switch may be provided on or in a steering wheel.
[0071] It should also be noted that the transmission control unit 9
may be divided to three controllers such that a first controller
automatically shifts the transmission 3 according to a gear
position change signal issued from the manual shift switch 29a, a
second controller automatically disengages the clutch 2 when
automatic shifting takes place, and automatically engages the
clutch 2 when accelerator pedal depression exceeds a predetermined
value in a clutch disengaged condition, and a third controller
decides a most appropriate gear in accordance with a current
vehicle running condition, selects a higher one of the most
appropriate gear and a predetermined start gear as a target gear,
and shifts the transmission 3 to the target gear regardless of the
gear position change signal from the manual shift switch 29a when
the accelerator pedal depression 8 exceeds a prescribed amount in
the clutch disengaged condition, and then engaging the clutch
2.
* * * * *