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This invention relates to motor vehicle transmission controls employing an
output speed sensor for speed ratio selection, and more particularly to a
diagnostic control for responding to a perceived failure of such sensor.
BACKGROUND OF THE INVENTION
Speed ratio selection in a motor vehicle automatic transmission is
conventionally determined as a function of vehicle speed and engine
throttle position or torque. When the ratio selection is electronically
controlled, the vehicle speed information is derived from a sensor, such
as an electromagnetic speed pickup, which generates an electrical speed
signal corresponding to the output speed of the transmission.
A potential shortcoming of any such system is that a loss of the vehicle
speed signal results in an immediate selection of the first or starting
ratio and disables further ratio selection. This shortcoming has been
recognized and various approaches have been suggested to minimize the
likelihood of such an occurrence. Some systems include circuits for
detecting an abrupt loss of the output speed signal; others employ
multiple redundant sensors. See, for example, the U.S. Pat. Nos.
4,363,973, Kawata et al. and 4,523,281 Noda et al.
One problem in this regard is that loss of the output speed signal may not
be detectable when the vehicle is in a normal idle condition. Indeed, at
least one system employs a logical comparison of the output speed signal
with various other signals when the vehicle is at rest for the purpose of
detecting an inconsistency. See the Stahl U.S. Pat. No. 4,495,457.
However, speed sensor related failures are not the only reason for an
apparent loss of the output speed signal. An apparent loss of the output
speed signal can also occur when there is a transmission line or operating
pressure failure, or merely a failure of the starting ratio of the
transmission. In the case of a starting ratio failure, the transmission
may be capable of continued operation in a higher ratio; disabling further
operation of the transmission, in such case, may result in an unnecessary
walk-home situation for the occupants of the vehicle.
SUMMARY OF THE PRESENT INVENTION
The present invention is directed to a diagnostic control effective when
there is an apparent loss of the output speed signal for determining if
failure is real, and if so, the cause of the failure. The transmission
controller, according to this invention, monitors the input speed of the
transmission in relation to a threshold speed indicative of normal vehicle
movement or engine speed flare. If the threshold speed is exceeded for at
least a predetermined time and no signal from the output speed sensor is
observed, a failure is verified and the diagnostic control is initiated.
When the diagnostic control is initiated, the transmission controller is
caused to successively upshift the transmission through its various
forward speed ratios while monitoring the transmission input speed to
detect the occurrence of an upshift-related reduction thereof. If the
shifting fails to produce a reduction in the transmission input speed by
the time the transmission has been shifted to the highest available speed
ratio, a total transmission failure is indicated and a manual back-up mode
is activated. If the shifting produces a decrease in the transmission
input speed, a total failure of the transmission is ruled out and the
diagnostic control determines if the failure is transmission or sensor
related. If the output speed signal is still absent and the input speed is
high enough to generate vehicle motion, a speed sensor related failure is
indicated. If the output speed signal indicates normal vehicle movement,
the diagnostic control is terminated and all forward ratios lower than the
current ratio are indicated as failed. Further control functions are
provided for avoiding an improper detection of a shift-related input speed
reduction due to operator manipulation of the engine torque setting
(throttle).
The diagnostic control method of this invention thus provides a reliable
indication of both the existence of a failure and the cause of the
failure. The information concerning the cause of the apparent output speed
signal loss enables the transmission controller to take appropriate action
and to avoid an unnecessary disabling of the transmission or degradation
of its operation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1a and 1b schematically depict a computer based electronic
transmission control system according to the teachings of this invention.
FIGS. 2-5 graphically depict the operation of the diagnostic control method
of this invention for an output speed sensor related failure, a starting
ratio failure, a steady throttle operating pressure failure, and an
unsteady throttle operating pressure failure, respectively.
FIGS. 6, 7a-7c, and 8a-8b depict flow diagrams representative of suitable
program instructions executed by the computer based controller of FIG. 1
for carrying out the diagnostic routine of this invention. FIG. 6 depicts
a main loop or executive program; FIGS. 7a-7c depict the diagnostic
routine of this invention; and FIGS. 8a-8b depict shift point selection
and ratio failure routines.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring now to FIGS. 1a and 1b, the reference numeral 10 generally
designates a motor vehicle drivetrain including an engine 12 and a
parallel shaft transmission 14 having a reverse speed ratio and four
forward speed ratios. Engine 12 includes a throttle mechanism 16
mechanically connected to an operator manipulated device, such as an
accelerator pedal (not shown), for regulating engine output torque, such
torque being applied to the transmission 14 through the engine output
shaft 18. The transmission 14 transmits engine output torque to a pair of
drive axles 20 and 22 through a torque converter 24 and one or more of the
fluid operated clutching devices 26-34, such clutching devices being
applied or released according to a predetermined schedule for establishing
the desired transmission speed ratio.
Referring now more particularly to the transmission 14, the impeller or
input member 36 of the torque converter 24 is connected to be rotatably
driven by the output shaft 18 of engine 12 through the input shell 38. The
turbine or output member 40 of the torque converter 24 is rotatably driven
by the impeller 36 by means of fluid transfer therebetween and is
connected to rotatably drive the shaft 42. A stator member 44 redirects
the fluid which couples the impeller 36 to the turbine 40, the stator
being connected through a one-way device 46 to the housing of transmission
14. The torque converter 24 also includes a clutching device 26 comprising
a clutch plate 50 secured to the shaft 42.
The clutch plate 50 has a friction surface 52 formed thereon adaptable to
be engaged with the inner surface of the input shell 38 to form a direct
mechanical drive between the engine output shaft 18 and the transmission
shaft 42. The clutch plate 50 divides the space between input shell 38 and
the turbine 40 into two fluid chambers: an apply chamber 54 and a release
chamber 56. When the fluid pressure in the apply chamber 54 exceeds that
in the release chamber 56, the friction surface 52 of clutch plate 50 is
moved into engagement with the input shell 38 as shown in FIG. 1, thereby
engaging the clutching device 26 to provide a mechanical drive connection
in parallel with the torque converter 24. In such case, there is no
slippage between the impeller 36 and the turbine 40. When the fluid
pressure in the release chamber 56 exceeds that in the apply chamber 54,
the friction surface 52 of the clutch plate 50 is moved out of engagement
with the input shell 38 thereby uncoupling such mechanical drive
connection and permitting slippage between the impeller 36 and the turbine
40. The circled numeral 5 represents a fluid connection to the apply
chamber 54 and the circled numeral 6 represents a fluid connection to the
release chamber 56.
A positive displacement hydraulic pump 60 is mechanically driven by the
engine output shaft 18 through the input shell 38 and impeller 36, as
indicated by the broken line 62. Pump 60 receives hydraulic fluid at low
pressure from the fluid reservoir 64 and supplies pressurized fluid to the
transmission control elements via output line 66. A pressure regulator
valve (PRV) 68 is connected to the pump output line 66 and serves to
regulate the fluid pressure (hereinafter referred to as line pressure) in
line 66 by returning a controlled portion of the fluid therein to
reservoir 64 via the line 70. In addition, pressure regulator valve 68
supplies fluid pressure for the torque converter 24 via line 74. While the
pump and pressure regulator valve designs are not critical to the present
invention, a representative pump is disclosed in the U.S. Pat. No.
4,342,545 to Schuster issued Aug. 3, 1982, and a representative pressure
regulator valve is disclosed in the Vukovich U.S. Pat. No. 4,283,970
issued Aug. 18, 1981, such patents being assigned to the assignee of the
present invention.
The transmission shaft 42 and a further transmission shaft 90 each have a
plurality of gear elements rotatably supported thereon. The gear elements
80-88 are supported on shaft 42 and the gear elements 92-102 are supported
on shaft 90. The gear element 88 is rigidly connected to the shaft 42, and
the gear elements 98 and 102 are rigidly connected to the shaft 90. Gear
element 92 is connected to the shaft 90 via a freewheeler or one-way
device 93. The gear elements 80, 84, 86 and 88 are maintained in meshing
engagement with the gear elements 92, 96, 98 and 100, respectively, and
the gear element 82 is coupled to the gear element 94 through a reverse
idler gear 103. The shaft 90, in turn, is coupled to the drive axles 20
and 22 through gear elements 102 and 104 and a conventional differential
gear set (DG) 106.
A dog clutch 108 is splined on the shaft 90 so as to be axially slidable
thereon and serves to rigidly connect the shaft 90 either to the gear
element 96 (as shown) or the gear element 94. A forward speed relation
between the gear element 84 and shaft 90 is established when dog clutch
108 connects the shaft 90 to gear element 96, and a reverse speed relation
between the gear element 82 and shaft 90 is established when the dog
clutch 108 connects the shaft 90 to the gear element 94.
The clutching devices 28-34 each comprise an input member rigidly connected
to a transmission shaft 42 or 90, and an output member rigidly connected
to one or more gear elements such that engagement of a clutching device
couples the respective gear element and shaft to effect a driving
connection between the shafts 42 and 90. The clutching device 28 couples
the shaft 42 to the gear element 80; the clutching device 30 couples the
shaft 42 to the gear elements 82 and 84; the clutching device 32 couples
the shaft 90 to the gear element 100; and the clutching device 34 couples
the shaft 42 to the gear element 86. Each of the clutching devices 28-34
is biased toward a disengaged state by a return spring (not shown).
Engagement of the clutching device is effected by supplying fluid pressure
to an apply chamber thereof. The resulting torque capacity of the
clutching device is a function of the applied pressure less the return
spring pressure.
The circled numeral 1 represents a fluid passage for supplying pressurized
fluid to the apply chamber of clutching device 28; the circled numeral 2
and letter R represent a fluid passage for supplying pressurized fluid to
the apply chamber of the clutching device 30; the circled numeral 3
represents a fluid passage for supplying pressurized fluid to the apply
chamber of the clutching device 32; and the circled numeral 4 represents a
fluid passage for directing pressurized fluid to the apply chamber of the
clutching device 34.
The various gear elements 80-88 and 92-100 are relatively sized such that
engagement of first, second, third and fourth forward speed ratios are
effected by engaging the clutching devices 28, 30, 32 and 34,
respectively, it being understood that the dog clutch 108 must be in the
position depicted in FIG. 1 to obtain a forward speed ratio. A neutral
speed ratio or an effective disconnection of the drive axles 20 and 22
from the engine output shaft 18 is effected by maintaining all of the
clutching devices 28-34 in a released condition. The speed ratios defined
by the various gear element pairs are generally characterized by the ratio
of the turbine speed N.sub.t to output speed N.sub.o. Representative
N.sub.t /N.sub.o ratios for transmission 14 are as follows:
FIRST--2.368, SECOND--1.273 THIRD--0.808, FOURTH--0.585 REVERSE--1.880
Shifting from a current forward speed ratio to a desired forward speed
ratio requires that the clutching device associated with the current speed
ratio (off-going) be disengaged and the clutching device associated with
the desired speed ratio (on-coming) be engaged. For example, a shift from
the first forward speed ratio to the second forward speed ratio involves
disengagement of the clutching device 28 and engagement of the clutching
device 30.
The fluid control elements of the transmission 14 include a manual valve
140, a directional servo 160 and a plurality of electrically operated
fluid valves 180-190. The manual valve 140 operates in response to
operator demand and serves, in conjunction with directional servo 160, to
direct regulated line pressure to the appropriate fluid valves 182-188.
The fluid valves 182-188, in turn, are individually controlled to direct
fluid pressure to the clutching devices 28-34. The fluid valve 180 is
controlled to direct fluid pressure from the pump output line 66 to the
pressure regulator valve 68, and the fluid valve 190 is controlled to
direct fluid pressure from the line 74 to the clutching device 26 of
torque converter 24. The directional servo 160 operates in response to the
condition of the manual valve 140 and serves to properly position the dog
clutch 108.
The manual valve 140 includes a shaft 142 for receiving axial mechanical
input from the operator of the motor vehicle in relation to the speed
range the operator desires. The shaft 142 is also connected to an
indicator mechanism 144 through a suitable mechanical linkage as indicated
generally by the broken line 146. Fluid pressure from the pump output line
66 is applied as an input to the manual valve 140 via the line 148 and the
valve outputs include a forward (F) output line 150 for supplying fluid
pressure for engaging forward speed ratios and a reverse (R) output line
152 for supplying fluid pressure for engaging the reverse speed ratio.
Thus, when the shaft 142 of manual valve 140 is moved to the D4, D3, or D2
positions shown on the indicator mechanism 144, line pressure from the
line 148 is directed to the forward (F) output line 150. When the shaft
142 is in the R position shown on the indicator mechanism 144, line
pressure from the line 148 is directed to the reverse (R) output line 152.
When the shaft 142 of manual valve 140 is in the N (Neutral) or P (Park)
positions, the input line 148 is isolated, and the forward and reverse
output lines 150 and 152 are connected to an exhaust line 154 which is
adapted to return any fluid therein to the fluid reservoir 64.
The directional servo 160 is a fluid operated device and includes an output
shaft 162 connected to a shift fork 164 for axially shifting the dog
clutch 108 on shaft 90 to selectively enable either forward or reverse
speed ratios. The output shaft 162 is connected to a piston 166 axially
movable within the servo housing 168. The axial position of the piston 166
within the housing 168 is determined according to the fluid pressures
supplied to the chambers 170 and 172. The forward output line 150 of
manual valve 140 is connected via line 174 to the chamber 170 and the
reverse output line 152 of manual valve 140 is connected via the line 176
to the chamber 172. When the shaft 142 of the manual valve 140 is in a
forward range position, the fluid pressure in the chamber 170 urges piston
166 rightward as viewed in FIG. 1 to engage the dog clutch 108 with the
gear element 96 for enabling engagement of a forward speed ratio. When the
shaft 142 of the manual valve 140 is moved to the R position, the fluid
pressure in chamber 172 urges piston 166 leftward as viewed in FIG. 1 to
engage the dog clutch 108 with the gear element 94 for enabling engagement
of the reverse speed ratio. In each case, it will be remembered that the
actual engagement of the second or reverse speed ratio is not effected
until engagement of the clutching device 30.
The directional servo 160 also operates as a fluid valve for enabling the
reverse speed ratio. To this end, the directional servo 160 includes an
output line 178 connected to the electrically operated fluid valve 186.
When the operator selects a forward speed ratio and the piston 166 of
directional servo 160 is in the position depicted in FIG. 1, the passage
between lines 176 and 178 is cut off; when the operator selects the
reverse gear ratio, the passage between the lines 176 and 178 is open.
The electrically operated fluid valves 180-190 each receive fluid pressure
at an input passage thereof from the pump 60, and are individually
controlled to direct fluid pressure to the pressure regulator valve 68 or
respective clutching devices 26-34. The fluid valve 180 receives line
pressure directly from pump output line 66, and is controlled to direct a
variable amount of such pressure to the pressure regulator valve 68 as
indicated by the circled letter V. The fluid valves 182, 186 and 188
receive fluid pressure from the forward output line 150 of manual valve
140, and are controlled to direct variable amounts of such pressure to the
clutching devices 34, 32 and 28 as indicated by the circled numerals 4, 3
and 1, respectively. The fluid valve 186 receives fluid pressure from the
forward output line 150 and the directional servo output line 178, and is
controlled to direct a variable amount of such pressure to the clutching
device 30 as indicated by the circled numeral 2 and the circled letter R.
The fluid valve 190 receives fluid pressure from line 74 of pressure
regulator valve 68, and is controlled to direct a variable amount of such
pressure to the release chamber 56 of the clutching device 26 as indicated
by the circled numeral 6. The apply chamber 54 of the clutching device 26
is supplied with fluid pressure from the output line 74 via the orifice
192 as indicated by the circled numeral 5.
Each of the fluid valves 180-190 includes a spool element 210-220, axially
movable within the respective valve body for directing fluid flow between
input and output passages. When a respective spool element 210-220 is in
the rightmost position as viewed in FIG. 1, the input and output passages
are connected. Each of the fluid valves 180-190 includes an exhaust
passage as indicated by the circled letters EX, such passage serving to
drain fluid from the respective clutching device when the spool element is
shifted to the leftmost position as viewed in FIG. 1b. In FIG. 1b, the
spool elements 210 and 212 of fluid valves 180 and 182 are shown in the
rightmost position connecting the respective input and output lines, while
the spool elements 214, 216, 218 and 220 of the fluid valves 184, 186, 188
and 190 are shown in the leftmost position connecting the respective
output and exhaust lines.
Each of the fluid valves 180-190 includes a solenoid 222-232 for
controlling the position of its spool element 210-220. Each such solenoid
222-232 comprises a plunger 234-244 connected to the respective spool
element 210-220 and a solenoid coil 246-256 surrounding the respective
plunger. One terminal of each such solenoid coil 246-256 is connected to
ground potential as shown, and the other terminal is connected to an
output line 258-268 of a control unit 270 which governs the solenoid coil
energization. As set forth hereinafter, the control unit 270
pulse-width-modulates the solenoid coils 246-256 according to a
predetermined control algorithm to regulate the fluid pressure supplied to
the pressure regulator 68 and the clutching devices 26-34, the duty cycle
of such modulation being determined in relation to the desired magnitude
of the supplied pressures.
While the fluid valves 180-190 have been illustrated as spool valves, other
types of valves could be substituted therefor. By way of example, valves
of the ball and seat type could be used. In general terms, the fluid
valves 180-190 may be mechanized with any three-port pulse-width-modulated
valving arrangement.
Input signals for the control unit 270 are provided on the input lines
272-284. A position sensor (S) 286 responsive to movement of the manual
valve shaft 142 provides an input signal to the control unit 270 via line
272. Speed transducers 288, 290 and 292 sense the rotational velocity of
various rotary members within the transmission 14 and supply speed signals
in accordance therewith to the control unit 270 via lines 274, 276, and
278, respectively. The speed transducer 288 senses the velocity of the
transmission shaft 42 and therefore the turbine or transmission input
speed N.sub.t ; the speed transducer 290 senses the velocity of the drive
axle 22 and therefore the transmission output speed N.sub.o ; and the
speed transducer 292 senses the velocity of the engine output shaft 18 and
therefore the engine speed N.sub.e.
The position transducer 294 is responsive to the position of the engine
throttle 16 and provides an electrical signal in accordance therewith to
control unit 270 via line 280. A pressure transducer 296 senses the
manifold absolute pressure (MAP) of the engine 12 and provides an
electrical signal to the control unit 270 in accordance therewith via line
282. A temperature sensor 298 senses the temperature of the oil in the
transmission fluid reservoir 64 and provides an electrical signal in
accordance therewith to control unit 270 via line 284.
The control unit 270 responds to the input signals on input lines 272-284
according to a predetermined control algorithm as set forth herein, for
controlling the energization of the fluid valve solenoid coils 246-256 via
output lines 258-268. As such, the control unit 270 includes an
input/output (I/O) device 300 for receiving the input signals and
outputting the various pulse-width-modulation signals, and a microcomputer
302 which communicates with the I/O device 300 via an address-and-control
bus 304 and a bidirectional data bus 306. Flow diagrams representing
suitable program instructions for carrying out the control functions of
this invention and for developing such pulse-width-modulation outputs are
depicted in FIGS. 6-8.
FIGS. 2-5 illustrate the operation of the diagnostic control of this
invention under different vehicle operating conditions. For each case, the
turbine speed N.sub.t, the throttle position TPS, and the output speed
N.sub.o are depicted on a common time base.
FIG. 2 represents the start up of a vehicle having an output speed sensor
related failure. The failure may be due, for example, to a failed sensor,
electrical connector, or wire. Although the output speed signal N.sub.o
remains at zero, the vehicle responds to the throttle movement in a normal
manner beginning at time t.sub.0 and the turbine speed begins to increase.
The control unit 270 monitors the turbine speed in relation to the
reference speeds REF2 and REF1. When the turbine speed exceeds REF2 at
time t.sub.1, the control unit 270 increases the transmission line
pressure to a maximum value MAX to prevent clutch slippage, if possible.
The reference REF1 is indicative of either normal vehicle movement or
NEUTRAL flaring (racing) of the engine 12, and is chosen such that turbine
speed will still be in excess of REF2 following an upshift to the next
ratio. Thus, when the turbine speed exceeds the reference REF1 at time
t.sub.2 (vehicle speed indication still zero), a failure is verified and
the diagnostic control is initiated. After a predetermined delay, the
diagnostic control initiates a 1-2 upshift, which causes a normal
pull-down or reduction of the turbine speed N.sub.t. The control unit 270
senses the pull-down at time t.sub.3, and deduces the existence of an
output speed sensor related failure.
Had the throttle position TPS been reduced in the course of the diagnostic
control depicted in FIG. 2, a shift-related pull-down of the turbine speed
could not be reliably sensed. To avoid an improper diagnosis under such
conditions, the control unit 270 monitors the throttle position and the
speed ratio SRTC across the torque converter 24. If a throttle tip-out
(reduction) is detected in the course of a diagnostic upshift while the
speed ratio SRTC is indicative of positive torque transmission, the
transmission 14 is returned to the previously engaged ratio and the
diagnostic control is reinitiated. This control is graphically illustrated
for the vehicle operating condition depicted in FIG. 5.
If the speed ratio SRTC indicates that no significant torque is being
transmitted through torque converter 24, throttle tip-outs are irrelevant,
and the diagnostic control is permitted to continue the upshift sequence
to determine which, if any, of the forward speed ratios are available.
This feature permits successful prompt completion of the diagnostic
routine in situations where one or more of the lower forward ratios are
not available, and the operator modulates the throttle position at each
occurrence of engine flaring.
FIG. 3 represents the start up of a vehicle having a failed starting
(FIRST) ratio. This failure may be due, for example, to a failed actuator
or clutch. In this case, the engine 12 is unrestrained and the throttle
movement starting at time t.sub.0 causes the turbine speed N.sub.t to
flare. However, the vehicle is stationary and the output speed signal
remains at zero. When the turbine speed N.sub.t rises above the reference
speed REF2, the line pressure is set to the maximum value MAX, as
indicated above. Shortly after time t.sub.1 when the turbine speed rises
above the reference REF1, the control unit 270 initiates a diagnostic 1-2
upshift. This brings the turbine speed substantially to zero and causes an
increase in the output speed signal as oncoming clutch for SECOND ratio
begins engaging and the vehicle begins to move. The control unit 270
senses a nonzero output speed signal with the turbine speed less than
REF2, and flags all forward ratios lower than the engaged ratio--FIRST, in
the present example--as failed.
FIGS. 4 and 5 represent the start up of a vehicle having a loss of the
transmission operating pressure. This failure may be due, for example, to
a failed servo valve, actuator, or pump. As in the example illustrated in
FIG. 3, the engine 12 is unrestrained and the throttle movement starting
at time t.sub.0 causes the turbine speed to flare. Meanwhile, the vehicle
remains stationary and the output speed signal N.sub.o remains at zero.
In the example of FIG. 4, the throttle position is maintained steady, and
shortly after time t.sub.1 when the turbine speed N.sub.t rises above the
reference speed REF1, the control unit 270 initiates a diagnostic 1-2
upshift. Due to the pressure loss, the shift does not occur and there is
no turbine speed pull-down. At such point, the control unit 270 initiates
a diagnostic 2-3 upshift. This shift also fails to occur and the control
unit 270 sequentially upshifts the transmission in the above manner until
the highest ratio (FOURTH) is commanded. Since no ratio can be engaged,
the control unit 270 deduces at least partial loss of operating pressure
and enters a back-up hydraulic mode in which hydraulic valving directs
whatever fluid pressure is available to a default clutch.
In the example of FIG. 5, a throttle position tip-out occurs shortly after
the diagnostic upshift command. Since the speed ratio SRTC indicates that
no significant torque is being transmitted through the torque converter
24, the diagnostic upshifting is permitted to continue despite the
throttle tip-outs. When the highest or FOURTH ratio has been commanded,
and no turbine speed pull-down observed, the loss of transmission
operating pressure is indicated and the hydraulic back-up mode is
activated.
The flow diagrams depicted in FIGS. 6-8 represent program instructions to
be executed by the microcomputer 302 of control unit 270 in mechanizing
the diagnostic control of this invention. The flow diagram of FIG. 6
represents a main or executiee program which calls various subroutines for
executing particular control functions as necessary. The flow diagrams of
FIGS. 7a-7c and 8a-8b represent subroutine functions pertinent to the
present invention.
Referring now more particularly to FIG. 6, the reference numeral 340
designates a set of program instructions executed at the initiation of
each period of vehicle operation for initializing the various registers,
timers, etc. used in carrying out the control functions of this invention.
Following such initialization, the instruction blocks 342-350 are
repeatedly executed in sequence as designated by the flow diagram lines
connecting such instruction blocks and the return line 352.
Instruction block 342 serves to read the various input signals applied to
I/0 device 300 via the lines 272-284, to update (increment) the various
control unit timers, and to perform output speed drop-out logic. The
output speed drop-out logic functions to detect a sudden loss of the
output speed signal N.sub.o and to set a DROP-OUT flag whenever a sudden
loss is detected. A sudden drop-out can occur in normal operation (as in
hard braking on a slippery road surface), and a set DROP-OUT flag
indicates merely a potential output speed sensor related failure. Until
the vehicle is brought to a stop, the diagnostic routine is disabled, and
further shifting is carried out in accordance with an estimation of the
output speed N.sub.o, based on the turbine speed N.sub.t and ratio R. Once
the vehicle has been brought to a stop, execution of the diagnostic
routine is enabled to determine if an output speed sensor related failure
has in fact occurred.
Instruction block 344 performs the diagnostic control of this invention and
is set forth in greater detail in the flow diagrams of FIGS. 7a-7c as
indicated at block 344. Instruction block 346 determines the desired speed
ratio, R.sub.des, and is set forth in greater detail in the flow diagram
of FIGS. 8a-8b as indicated at block 346.
Instruction block 348 serves to determine pressure commands for both the
pressure regulator valve PRV and the clutching devices 26-34 for shifting
and nonshifting modes of operation, based primarily on the transmission
input torque and the desired speed ratio. Instruction block 350 converts
the clutching device and PRV pressure commands to a PWM duty cycle based
on the operating characteristics of the various actuators (empirically
determined) and energizes the actuator coils 246-256 accordingly.
Referring now to the flow diagrams of FIGS. 7a-7c, the blocks generally
designated by the reference numeral 360 are first executed to determine if
execution of the diagnostic routine is appropriate. The decision blocks
362-364 determine if the vehicle has been brought to a stop and the
starting or FIRST ratio engaged. If so, the instruction block 366 is
executed to clear the DROP-OUT flag (if set) and execution of the
diagnostic routine is permitted. If either of the decision blocks 362-364
are answered in the negative, the execution of instruction block 366 is
skipped and the decision block 368 is executed to determine if the
DROP-OUT flag is set. If the DROP-OUT flag is not set, the diagnostic
routine is permitted to be executed as indicated by the flow diagram line
370; if the DROP-OUT flag is set, execution of the diagnostic routine is
skipped, as indicated by the flow diagram line 372.
In performing the diagnostic routine, the decision block 374 is first
executed to determine if the MASTER FAIL flag is set, indicating that
there has been a loss of the transmission operating pressure. If so,
further execution of the diagnostic routine is not required and the flow
diagram portion 376 of FIG. 7c is executed to clear the various diagnostic
shift control flags and counters, as indicated by the circled numeral 3.
The decision block 378 determines if the OUTPUT SPEED SENSOR FAILED flag is
set. As indicated below, this flag is set by the control unit 270 to
indicate an output speed sensor related failure in the presence of a
vehicle operating condition, such as depicted by the graphs of FIG. 2. If
the flag is set, further execution of the diagnostic routine is not
required; the instruction block 380 of FIG. 7b is executed to clear the
MASTER FAILURE flag and the flow diagram portion 376 of FIG. 7c is
executed as indicated above to clear the various diagnostic shift control
flags and counters.
If the OUTPUT SPEED SENSOR FAILED flag is not set, the decision block 382
is executed to determine if the output speed signal N.sub.o is at or near
zero. If not, vehicle movement is indicated and the blocks 384-388 are
executed to determine which, if any, forward ratios have failed. If the
DIAGNOSTIC SEQUENCE START flag is set and the diagnostic requirements
(turbine speed pull-down, no throttle tip-out, etc.) have been met, the
instruction block 388 is executed to flag all forward ratios lower than
the currently engaged ratio R.sub.des as failed. Thereafter, the
instruction block 380 and the flow diagram portion 376 are executed to
complete the diagnostic routine. If the diagnostic requirements are not
met, the remainder of the routine is skipped. If the DIAGNOSTIC SEQUENCE
START flag is not set, diagnostic shifting has not occurred; this
represents a normal mode of operation and the instruction block 380 and
the flow diagram portion 376 are executed to complete the diagnostic
routine.
If the output speed signal N.sub.o is substantially zero, there may be a
system failure and the decision block 390 is executed to determine if a
transmission ratio shift is in progress. If so, the remainder of the
diagnostic routine is skipped. If not, the decision block 392 of FIG. 7b
is executed to determine if the turbine speed N.sub.t is greater than or
equal to the reference speed REF2. If the turbine speed N.sub.t exceeds
the reference REF2, the blocks 394-400 are executed to set the
transmission line pressure P.sub.L to a maximum value MAX and to time a
predetermined interval using a register referred to as the DIAGNOSTIC
COUNTER. So long as the turbine speed N.sub.t exceeds the reference REF2,
the DIAGNOSTIC COUNTER is incremented by the instruction block 396. When
the count in the DIAGNOSTIC COUNTER exceeds a count indicative of a
predetermined interval, such as 100 milliseconds (as determined at
decision block 398), the instruction block 400 is executed to set the
DIAGNOSTIC SEQUENCE START flag. If the turbine speed N.sub.t subsequently
falls below the reference speed REF2 the execution of blocks 394-400 is
skipped, as indicated by the flow diagram line 402.
The instruction block 404 is then executed to determine if the DIAGNOSTIC
SEQUENCE START flag has been set. If the DIAGNOSTIC SEQUENCE START flag is
not set, the instruction block 380 and the flow diagram portion 376 of
FIG. 7c are executed as described above to clear the various diagnostic
shift flags and exit the diagnostic routine.
If the DIAGNOSTIC SEQUENCE START flag is set, the flow diagram portion
comprising the blocks 408-425 is executed to determine if a diagnostic
shift request is appropriate. The decision block 408 is first executed to
determine if the DIAGNOSTIC UPSHIFT REQUEST flag is set. If not, the flow
diagram portion 410 of FIG. 7c is executed to initiate a diagnostic
upshift as indicated by the circled numeral 5.
If the DIAGNOSTIC UPSHIFT REQUEST flag is set, the blocks 414-420 are
executed to analyze the shift. The decision block 414 first determines if
the turbine speed N.sub.t is greater than or equal to the reference speed
REF2 defined in reference to FIGS. 2-5. If the | | |
