U.S. patent application number 14/154592 was filed with the patent office on 2015-07-16 for infinitely variable transmission with controlled coasting.
This patent application is currently assigned to Caterpillar Inc.. The applicant listed for this patent is Caterpillar Inc.. Invention is credited to Joshua Callaway, Steven J. Juricak, Corwin E. Storer.
Application Number | 20150198246 14/154592 |
Document ID | / |
Family ID | 53521006 |
Filed Date | 2015-07-16 |
United States Patent
Application |
20150198246 |
Kind Code |
A1 |
Callaway; Joshua ; et
al. |
July 16, 2015 |
Infinitely Variable Transmission with Controlled Coasting
Abstract
A system for driving a machine is provided. A user input device
inputs a desired throttle setting for the machine. The system
includes an infinitely variable transmission having a transmission
ratio that is adjustable. At least one sensor determines an
inclination of the machine relative to a reference plane. A
controller is configured to determine and apply a variable rate
limit upon change in the transmission ratio based on the
inclination of the machine when the desired throttle setting is
reduced more than a predetermined amount and to adjust the rate
limit based on the difference between an actual engine speed and a
desired engine speed.
Inventors: |
Callaway; Joshua; (Cary,
NC) ; Juricak; Steven J.; (Cary, NC) ; Storer;
Corwin E.; (Bartonville, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Caterpillar Inc. |
Peoria |
IL |
US |
|
|
Assignee: |
Caterpillar Inc.
Peoria
IL
|
Family ID: |
53521006 |
Appl. No.: |
14/154592 |
Filed: |
January 14, 2014 |
Current U.S.
Class: |
701/65 |
Current CPC
Class: |
F16H 2059/663 20130101;
F16H 61/66 20130101; E02F 9/2253 20130101; F16H 61/42 20130101 |
International
Class: |
F16H 61/66 20060101
F16H061/66 |
Claims
1. A system for driving a machine comprising: a user input device
for inputting a desired throttle setting for the machine; an
infinitely variable transmission having a transmission ratio that
is adjustable; at least one sensor configured to determine an
inclination of the machine relative to a reference plane; and a
controller in communication with the user input device to receive
information relating to the desired throttle setting and the sensor
to receive information relating to the inclination of the machine;
the controller being in communication with the infinitely variable
transmission and configured to control the transmission ratio, the
controller being configured to determine and apply a variable rate
limit upon change in the transmission ratio based on the
inclination of the machine when the desired throttle setting is
reduced more than a predetermined amount.
2. The system according to claim 1 wherein the controller is
configured such that the rate limit determined by the controller is
different when the sensor determines the machine is traveling down
an incline as compared to the rate limit determined by the
controller when the sensor determines the machine is traveling up
an incline.
3. The system according to claim 2 wherein the rate limit
determined by the controller is relatively lower when the sensor
determines the machine is traveling down an incline than the rate
limit determined by the controller when the sensor determines the
machine is traveling up an incline.
4. The system according to claim 2 wherein the controller is
configured such that the rate limit determined by the controller
varies depending upon a degree of incline determined by the
sensor.
5. The system according to claim 1 further including an engine and
wherein the infinitely variable transmission comprises a
hydrostatic transmission including a hydraulic pump operatively
connected to the engine and a hydraulic motor operatively connected
to the hydraulic pump.
6. The system according to claim 5 further including an engine
speed sensor configured for determining an actual speed of the
engine.
7. The system according to claim 6 wherein the controller is
configured to determine a desired engine speed based on the desired
throttle setting and to adjust the rate limit based on a difference
between the actual engine speed and the desired engine speed when
the desired throttle setting is reduced more than a predetermined
amount.
8. The system according to claim 7 wherein the controller is
configured such that the rate limit determined by the controller is
lower when the difference between the actual engine speed and the
desired engine speed is relatively higher than when the difference
between the actual engine speed and the desired engine speed is
relatively lower.
9. A machine comprising: a user input device for inputting a
desired throttle setting for the machine; an engine; an engine
speed sensor configured for determining an actual speed of the
engine; an infinitely variable transmission having a transmission
ratio that is adjustable; and a controller in communication with
the user input device to receive information relating to the
desired throttle setting and the engine speed sensor to receive
information relating to the actual engine speed, the controller
being in communication with the infinitely variable transmission
and configured to control the transmission ratio, the controller
being configured to determine a desired engine speed based on the
desired throttle setting and to determine and apply a variable rate
limit upon change in the transmission ratio based on a difference
between the actual engine speed and the desired engine speed when
the desired throttle setting is reduced more than a predetermined
amount.
10. The machine according to claim 9 wherein the controller is
configured such that the rate limit determined by the controller is
lower when the difference between the actual engine speed and the
desired engine speed is relatively higher than when the difference
between the actual engine speed and the desired engine speed is
relatively lower.
11. The machine according to claim 9 further including at least one
sensor configured to determine an inclination of the machine
relative to a reference plane and wherein the controller is in
communication with the sensor and configured to adjust the rate
limit based on the inclination of the machine when the desired
throttle setting is reduced more than a predetermined amount.
12. The machine according to claim 11 wherein the controller is
configured such that the rate limit determined by the controller is
different when the sensor determines the machine is traveling down
an incline as compared to the rate limit determined by the
controller when the sensor determines the machine is traveling up
an incline.
13. The machine according to claim 12 wherein the rate limit
determined by the controller is relatively lower when the sensor
determines the machine is traveling down an incline than the rate
limit determined by the controller when the sensor determines the
machine is traveling up an incline.
14. The machine according to claim 13 wherein the controller is
configured such that the rate limit determined by the controller
varies depending upon a degree of incline determined by the
sensor.
15. A method for controlling deceleration of a machine having an
engine and an infinitely variable transmission having a
transmission ratio, the method comprising the steps of: determining
when a desired throttle setting input by an operator is reduced
more than a predetermined amount; determining a variable rate limit
of change on the transmission ratio based on at least one of an
inclination of the machine or a difference between a desired engine
speed based on the desired throttle setting and an actual engine
speed; and applying the rate limit of change to adjustment of the
infinitely variable transmission in response to the reduction in
the desired throttle setting.
16. The method according to claim 15 wherein the rate limit is
different when the machine is traveling down an incline as compared
to the rate limit determined when the machine is traveling up an
incline.
17. The method according to claim 16 wherein the rate limit is
relatively lower when the machine is traveling down an incline than
the rate limit when the machine is traveling up an incline.
18. The method according to claim 16 wherein the rate limit varies
depending upon a degree of incline.
19. The method according to claim 15 wherein the rate limit is
lower when the difference between the actual engine speed and the
desired engine speed is relatively higher than when the difference
between the actual engine speed and the desired engine speed is
relatively lower.
20. The method according to claim 15 wherein the rate limit is
based on both an inclination of the machine and a difference
between a desired engine speed based on the desired throttle
setting and an actual engine speed.
Description
TECHNICAL FIELD
[0001] This patent disclosure relates generally to infinitely
variable transmissions for mobile machines and, more particularly,
to infinitely variable drive transmissions and methods for
controlling infinitely variable drive transmissions that provide
controlled coasting of mobile machines.
BACKGROUND
[0002] Many mobile machines used in industries such as mining,
construction and farming utilize infinitely variable transmissions,
such as a hydrostatic drive transmission. A hydrostatic drive
transmission utilizes a hydraulic pump and hydraulic motor
combination to provide continuously variable torque and speed to
the drive train of the machine. Such transmissions can provide
certain advantages over mechanical transmissions including improved
fuel economy.
[0003] A potential issue with hydrostatic drive transmissions is
that they can provide an operator with a different "feel" under
certain operating conditions than a traditional mechanical
transmission. One example of a circumstance where a hydrostatic
drive transmission can provide a different feel is when an operator
reduces the throttle when the machine is in motion. In such
circumstances, the machine will coast a certain distance as the
engine slows down. Machines with hydrostatic transmissions are
typically configured to decelerate in the same manner regardless of
the load or engine speed. As a result, a machine with a
displacement controlled hydrostatic drive transmission will coast a
similar distance no matter whether the machine is travelling on
flat ground, uphill or downhill when the operator reduces the
throttle. This can be unintuitive to an operator who may be used to
operating machines with traditional mechanical transmissions that
generally coast more when travelling downhill than they coast when
travelling uphill or on flat ground.
[0004] U.S. Pat. No. 8,070,651 discloses a work machine coast
control system with an infinitely variable transmission. The
control system is configured to determine a driver demand regarding
deceleration of the machine at a time of coasting accompanied by an
accelerator releasing operation. The controller is further
configured to control the transmission to decelerate the vehicle
according to the determined drive demand regarding deceleration.
The control system does not provide any adjustment of the coasting
of the machine based on the slope on which the machine is
operating.
SUMMARY
[0005] In one aspect, the disclosure describes a system for driving
a machine. The system includes a user input device for inputting a
desired throttle setting for the machine. An infinitely variable
transmission is provided that has a transmission ratio that is
adjustable. At least one sensor is configured to determine an
inclination of the machine relative to a reference plane. A
controller is in communication with the user input device to
receive the desired throttle setting and the sensor to receive
information relating to the inclination of the machine. The
controller is in communication with the hydraulic motor and the
hydraulic pump and is configured to control the transmission ratio.
The controller is configured to determine and apply a variable rate
limit change in the hydrostatic transmission ratio based on the
inclination of the machine when the desired throttle setting is
reduced more than a predetermined amount.
[0006] In another aspect, the disclosure describes a machine
including a user input device for inputting a desired throttle
setting for the machine. The machine includes an engine and an
engine speed sensor configured for determining an actual speed of
the engine. The machine includes an infinitely variable
transmission having a transmission ratio that is adjustable. A
controller is in communication with the user input device to
receive the desired throttle setting and the engine speed sensor to
receive the actual engine speed. The controller is in communication
with the infinitely variable transmission and configured to control
the transmission ratio. The controller is configured to determine a
desired engine speed based on the desired throttle setting and to
determine and apply a variable rate limit upon change in the
transmission ratio based on a difference between the actual engine
speed and the desired engine speed when the desired throttle
setting is reduced more than a predetermined amount.
[0007] In yet another aspect, the disclosure describes a method for
controlling deceleration of a machine having an engine and an
infinitely variable transmission with an adjustable transmission
ratio. The method includes the step of determining when a desired
throttle setting input by an operator is reduced more than a
predetermined amount. A rate limit of change of the hydrostatic
transmission ratio is determined based on at least one of an
inclination of the machine or a difference between a desired engine
speed based on the desired throttle setting and an actual engine
speed. The rate limit of change is applied to adjust the
transmission ratio in response to the reduction in the desired
throttle setting.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a schematic side view of an exemplary machine
suitable for use with an infinitely variable transmission of the
present disclosure.
[0009] FIG. 2 is a schematic view of an infinitely variable
transmission according to the present disclosure.
[0010] FIG. 3 is a flow chart illustrating one method of
controlling coasting of an infinitely variable transmission
according to the present disclosure.
DETAILED DESCRIPTION
[0011] This disclosure generally relates to an apparatus and method
for providing controlled coasting of a mobile machine having an
infinitely variable transmission. With particular reference to
FIGS. 1 and 2, an exemplary machine 10 having an engine 12 and an
infinitely variable transmission is shown. In this case, the
infinitely variable transmission is a hydrostatic drive
transmission 14 (see FIG. 2) that can transmit power from the
engine 12 to a load, such as one or more traction devices 16, that
propel the machine in response to input received via operator input
devices. In the embodiment of FIG. 1, the traction devices 16
comprise wheels. Alternatively, the traction devices may embody a
track located on a side of the machine, a belt, or any other driven
traction device.
[0012] In addition to transmitting power to the traction devices
that propel the machine, the hydrostatic transmission 14 also may
be used to transmit power to other loads such as, for example, an
implement that is connected to the machine. In this case, the
machine 10 includes a bucket 17 that is supported by a boom 19 (see
FIG. 1) that is mounted to the body of the machine. The implements
carried by the machine may be utilized for a variety of tasks,
including, for example, loading, compacting, lifting, brushing, and
include, for example, buckets, compactors, forked lifting devices,
brushes, grapples, cutters, shears, blades, breakers/hammers,
augers, and others.
[0013] While the hydrostatic drive transmission 14 is illustrated
in connection with a wheel loader, the arrangement disclosed herein
has universal applicability in various other types of machines
having hydrostatic drive or other infinitely variable transmissions
as well. In this regard, the term "machine" may refer to any
machine that performs some type of operation associated with an
industry such as mining, construction, farming, transportation, or
any other industry known in the art. For example, the machine 10
may be an earth-moving machine, such as a wheel loader, track
loader, bulldozer, excavator, dump truck, backhoe, motor grader,
material handler or the like.
[0014] The engine 12 (see FIG. 2) may be configured to produce a
power output and may include an internal combustion engine. For
example, the engine 12 may include a diesel engine, a gasoline
engine, a gaseous fuel-powered engine, or any other type of engine
apparent to one skilled in the art. The engine 12 may produce a
rotational mechanical output received by the hydrostatic drive
transmission 14.
[0015] To allow an operator to input commands relating to a desired
throttle setting for the machine, an operator input device 18
(shown schematically in FIG. 2) may be located within an operator
station of the machine 10, for example, in close proximity to an
operator's seat. By adjusting the desired throttle setting, the
operator may adjust the speed and acceleration of the mobile
machine. Manipulation of the operator input device 18 may generate
signals indicative of a desired throttle setting for the machine.
As described further below, the desired throttle setting may be
used to determine a desired engine speed as well as the speed or
acceleration of the machine. In one example, the operator input
device 18 may embody a pedal. In another example, the operator
input device 18 may embody a cruise control type button or switch
that can be engaged to set the machine at a desired throttle
setting or speed. It is contemplated, however, that the operator
input device 18 may embody additional or different control devices
such as, for example, joysticks, pedals, levers, switches, buttons,
wheels, and other control devices known in the art.
[0016] With additional reference to FIG. 2, the hydrostatic drive
transmission 14 may include a hydraulic pump 20 and a hydraulic
motor 22 coupled in a closed loop hydraulic configuration. The pump
20 may be mechanically driven by the engine 12, while the motor 22
may mechanically drive the traction device 16. A first passageway
24 may direct pressurized fluid discharged from the pump 20 to the
motor 22. A second passageway 26 may return used fluid from the
motor 22 to the pump 20. It is contemplated that, in some
embodiments, the functions of the first and second passageways 24,
26 may be reversed to thereby reverse the travel direction of the
traction device 16, if desired. While a hydrostatic transmission is
shown, the present disclosure is also applicable to other types of
infinitely variable transmissions such as electrically coupled
motors or toroidal transmissions.
[0017] The pump 20 may be a swashplate-type pump and include
multiple piston bores, and pistons held against a tiltable
swashplate 28. The pistons may reciprocate within the piston bores
to produce a pumping action as the swashplate 28 rotates relative
to the pistons. The swashplate 28 may be selectively tilted
relative to a longitudinal axis of the pistons to vary a
displacement of the pistons within their respective bores. The
angular setting of the swashplate 28 relative to the pistons may be
carried out by any actuator known in the art, for example, by a
servo motor. Although shown in FIG. 2 as producing only a
unidirectional flow of pressurized fluid, it is contemplated that
the pump 20 may be an over-center type pump or rotatable in
opposing directions to produce flows of fluid in opposing
directions, if desired.
[0018] The motor 22 may be a fixed or variable displacement type
motor fluidly coupled to the pump 20. The motor 22 may convert the
pressurized fluid from pump 20 into a rotational output of traction
device 16. As a variable displacement motor, the motor 22 may
include multiple piston bores and pistons (not shown) held against
a fixed or rotatable swashplate 30. The angle of the swashplate 30
may determine an effective displacement of the pistons relative to
the bores of the motor 22. The angular setting of the swashplate 30
relative to the pistons may be carried out by any actuator known in
the art, for example, by a servo motor. The respective
displacements of the pump and the motor may define a hydrostatic
transmission ratio.
[0019] The machine 10 may be equipped with a plurality of sensors
or sensing devices that gather data from various components and
systems and generate signals that are directly or indirectly
indicative of various machine parameters associated with the
performance and operating conditions of the machine. Sensors may be
associated with, for example, the engine 16 and may include an
engine speed sensor 32 configured to determine the operating speed
of the engine. Sensors may also be provided that can be used to
monitor the output ratio of the hydrostatic transmission. Other
sensors may automatically gather real-time data such as the
operation of engine 16, the position of and load on the work
implements, fluid pressure, flow rate, temperature, contamination
level, and/or viscosity, fluid (i.e., fuel, oil, water, etc.)
levels and consumption rates, electric current and/or voltage
levels, engagement status of the parking brake, loading levels
(e.g., payload value, percent of maximum allowable payload limit,
payload history, payload distribution, etc.), and other desired
information. In addition, various sensors may be associated with
the machine 10 that may be used to determine machine travel
characteristics (e.g., speed, acceleration, torque, slip rate,
etc.) as well as the position and orientation of machine 10. Such
sensors may include a sensor 34 that is configured to determine the
inclination of the machine relative to a reference plane. A
combination of multiple sensor inputs may also be used to provide a
signal indicative of machine incline.
[0020] A controller 36 may be provided to facilitate operation of
the machine including the hydrostatic drive transmission 14. As
schematically shown in FIG. 2, the controller 36 may be in
communication with the operator input device 18 to receive
information relating to the desired throttle setting, the pump 20,
the motor 22, the engine 12, the engine speed sensor 32 to receive
the actual engine speed and the sensor 34 to receive information
relating to the machine incline. The controller 36 may be further
configured to generate control signals for regulating operation of
the pump 20 and the motor 22. More particularly, the controller 36
may be configured to control displacement of the pump 20 and the
motor 22 by, for example, controlling a pump actuator device (e.g.,
a solenoid and spool valve) to vary the displacement of the pump
20. Additionally, the pump actuator device may provide information
to the controller about actual or commanded displacement of the
pump 20. Similarly, the displacement of the motor 22 may also be
controlled by a motor actuator device. The motor actuator device
may also provide information to the controller about actual or
commanded displacement of the motor 22. The controller 36 may
control displacement of the pump 20 and motor 22 based on
information received from the operator input device 18 and the
various sensors. Through adjustment of the displacements of the
pump 20 and motor 22, the controller 36 can control the hydrostatic
transmission ratio. The controller 36 may be in communication with
the operator input device 18, the engine speed sensor 32, the
sensor 34 for determining machine incline, the pump 20 and the
motor 22 via control lines, which may carry digital, analog, or
mixed types of signals. Alternatively, communication with the
various components may be implemented by mechanical or hydraulic
lines.
[0021] The controller 36 may be a single controller or may include
more than one controller disposed to control various functions
and/or features of the machine 10. For example, the machine may
include separate controllers for the hydrostatic transmission and
for the engine. The term "controller" is meant to be used in its
broadest sense to include one or more controllers and/or
microprocessors that may be associated with the machine 10 and that
may cooperate in controlling various functions and operations of
the machine. The functionality of the controller 36 may be
implemented in hardware and/or software without regard to the
functionality. The controller 36 may rely on one or more data maps
relating to the operating conditions of the machine 10 that may be
stored in the memory of controller 36. Each of these maps may
include a collection of data in the form of tables, graphs, and/or
equations. The controller 36 may use the data maps to maximize the
efficiency of the machine 10.
[0022] The controller 36 may embody a single microprocessor or
multiple microprocessors. Numerous commercially available
microprocessors may be configured to perform the functions of the
controller 36. It should be appreciated that the controller 36 may
readily embody a general machine microprocessor capable of
controlling numerous machine functions. Various other circuits may
be associated with the controller 36, such as power supply
circuitry, signal conditioning circuitry, data acquisition
circuitry, signal output circuitry, signal amplification circuitry,
and other types of circuitry known in the art.
[0023] The control system, including the controller 36 and the
associated sensors, may be configured to provide controlled or
adjusted deceleration or coasting of the machine 10 when an
operator signals for a reduction in the desired throttle setting of
more than a predetermined amount through the operator input device
18. For instance, where the operator input device 18 is an
accelerator pedal, the controlled coasting of the machine 10 may be
applied when an operator removes his foot from the accelerator
pedal. More specifically, the controller 36 may be configured to
adjust the deceleration or coasting of the machine 10 in such
circumstances so as to mimic the coasting behavior of a standard
mechanical transmission in which the machine coasts more when
traveling down an incline, coasts less when traveling up an incline
and coasts an intermediate amount when traveling on even or level
ground. Such coasting behavior can be more intuitive to an operator
because it is consistent with their experiences with conventional
mechanical transmissions.
[0024] The controlled or adjusted coasting of the machine 10 can be
accomplished by configuring the controller 36 to limit the rate at
which the machine 10 decelerates, and thereby how much the machine
10 coasts, through adjustment of the hydrostatic transmission 14
based on the inclination of the machine as determined by the sensor
34. More specifically, the rate at which the machine 10 decelerates
can be adjusted by configuring the controller 36 to limit the rate
at which the hydrostatic transmission ratio changes. The controller
36 may also be configured to adjust the rate limit on changes in
the hydrostatic transmission ratio based on a difference between a
desired speed of the engine 12 (as determined from the desired
throttle setting) and the actual speed of the engine 12 (as
determined by the engine speed sensor 32). The adjustment of the
rate limit based on the difference between the desired engine speed
and the actual engine speed can be performed in place of or in
addition to the adjustment of the rate limit based on inclination
of the machine 10.
[0025] Referring to FIG. 3 of the drawings, a schematic flow
diagram is provided that includes various steps that may be
included in the control system and implemented by the controller 36
to provide controlled or adjusted machine coasting. In an initial
step 38, the operator uses the operator input device 18 to reduce
the desired throttle setting. If the desired throttle setting is
reduced more than a predetermined amount the controller 36 may be
configured to control or adjust the deceleration or coasting of the
machine. One step (step 40 in FIG. 3) involved in that process is
determining a desired engine speed command based on the desired
throttle setting entered by the operator in step 38. A propel
command for the hydrostatic transmission is also determined based
on the throttle command input by the operator in step 42. The
propel command can represent a desired transmission ratio of the
hydrostatic transmission.
[0026] In step 44, the machine incline is determined. This step can
be performed by the sensor 34 and communicated to the controller
36. Alternate methods also could be used to determine machine
incline. The machine incline data produced by the sensor 34 can
include whether the machine 10 is traveling up an incline, down an
incline or traveling on level ground and a measurement of the angle
of inclination of the machine relative to a reference plane. In
step 46, the controller 36 takes the machine incline data and
determines a rate limited propel command based on the machine
incline. In particular, the rate limited propel command can be an
adjustment applied to the propel command from step 42 in which the
rate of change of the hydrostatic transmission ratio is limited to
a determined amount. For example, the controller 36 may be
configured such that when the sensor 34 determines that machine is
traveling down an incline, the rate limit on the propel command is
set low so that the propel command (i.e., the transmission ratio)
does not change significantly despite the operator reducing the
desired throttle setting. This allows a longer coast for the
machine 10 after the operator reduces the throttle command.
Conversely, the controller 36 may be configured such that when the
sensor 34 determines that the machine 10 is travelling up an
incline, the rate limit is set relatively higher which allows the
propel command (i.e., the transmission ratio) to change more
rapidly resulting in a faster deceleration of the machine 10 as
compared to when traveling down an incline. Accordingly, the
machine 10 coasts a shorter distance when traveling up an incline
as compared to when traveling down an incline.
[0027] The rate limit adjustment of the propel command may be
further adjusted based on the amount of incline determined by the
sensor 34 and the controller 36. For example, the rate limit may be
set lower when the machine 10 is traveling down steeper inclines
than when traveling down more gradual inclines. Similarly, the rate
limit may be set higher when traveling up a steeper incline than
when traveling up a more gradual incline. To this end, the
controller 36 could include a map or the like that contains
different rate limits for different machine inclinations.
[0028] In step 48, the actual engine speed is determined, such as
through the engine speed sensor 32 communicating with the
controller 36. The controller 36 then compares the actual engine
speed from step 48 to the desired engine speed from step 40 to
determine the difference therebetween in step 50. The difference
between the actual and the desired engine speeds is then applied by
the controller 36 in step 52 to adjust the rate limited propel
command that, in this case, is produced in step 46 based on the
machine inclination. As noted previously, the step 52 of applying a
rate limit to the propel command based on the difference between
the actual engine speed and the desired engine speed can be
performed instead of step 46 to provide a different type of
controlled coasting of the machine or in addition to step 46 as
shown in FIG. 3 to provide further adjusted coasting of the
machine.
[0029] In order to provide the engine speed adjustment to the rate
limit on the propel command determined in step 46, the controller
36 may be configured to provide a higher rate limit on the propel
command, and thereby provide more aggressive deceleration, when the
difference between the desired engine speed and the actual engine
speed is small, including when the difference is zero. For example,
when the operator reduces the throttle setting to zero, the further
deceleration of the machine 10 can be limited, so as to provide an
unusually long machine coast, when the engine 12 reaches its low
idle speed because reduced engine speed can no longer be used to
slow the machine. In such circumstances the actual engine speed,
i.e. the engine's low idle speed, matches the desired engine speed.
Accordingly, when the difference between the desired engine speed
and the actual engine speed is low or zero, the rate limit on the
propel command can be increased in order to allow the hydrostatic
transmission 14 to provide further deceleration of the machine 10
through appropriate adjustment of the hydrostatic transmission
ratio. Conversely, when the difference between the desired engine
speed and the actual engine speed is high, such as the time shortly
after the operator reduces the throttle command, only a small or no
adjustment in the rate limit may be performed by the controller 36
in step 52 because the reducing engine speed still can be used to
help decelerate the machine.
[0030] The rate limited propel command produced in steps 46 and/or
52 is then used by the controller to direct the displacement
settings of the pump 20 and/or motor 22 in steps 54 and 56. The
directed displacement settings for the hydraulic pump 20 and
hydraulic motor 22 are such that the desired hydrostatic
transmission ratio for the controlled coasting of the machine 10 is
produced.
INDUSTRIAL APPLICABILITY
[0031] The present disclosure is applicable to any type of mobile
machine having an infinitely variable transmission, including, for
example, an electric, toroidal or hydrostatic transmission. The
disclosure is particularly applicable to machines that are driven
in environments in which the coasting feel of a mechanical
transmission may be desirable. By adjusting the rate limits on the
propel command based on machine inclination, the control system of
the present disclosure allows a hydrostatic transmission to mimic
the coasting characteristics of a mechanical transmission in that
the machine will coast farther when traveling downhill than when
traveling uphill. This is in contrast to a typical hydrostatic
transmission with which a machine will coast the same distance when
traveling uphill and when traveling downhill.
[0032] The adjustment of the propel command based on the difference
between the desired and actual engine speeds also allows the
deceleration and coasting of machines with hydrostatic
transmissions to be more consistent with the coasting and
deceleration experienced with machines having mechanical
transmissions. One circumstance where the adjustment of the rate
limit based on the difference between the desired engine speed and
the actual engine speed can have a significant impact is when
decelerating or coasting on level ground. In particular,
hydrostatic transmissions can provide an unusually long coast when
operating on level ground because the deceleration slows
considerably once the engine reaches the low idle speed. Adjusting
the rate limit under such circumstances allows a hydrostatic
transmission to provide a more intuitive machine coast with a
uniform deceleration of the machine.
[0033] It will be appreciated that the foregoing description
provides examples of the disclosed system and technique. However,
it is contemplated that other implementations of the disclosure may
differ in detail from the foregoing examples. All references to the
disclosure or examples thereof are intended to reference the
particular example being discussed at that point and are not
intended to imply any limitation as to the scope of the disclosure
more generally. All language of distinction and disparagement with
respect to certain features is intended to indicate a lack of
preference for those features, but not to exclude such from the
scope of the disclosure entirely unless otherwise indicated.
[0034] Recitation of ranges of values herein are merely intended to
serve as a shorthand method of referring individually to each
separate value falling within the range, unless otherwise indicated
herein, and each separate value is incorporated into the
specification as if it were individually recited herein. All
methods described herein can be performed in any suitable order
unless otherwise indicated herein or otherwise clearly contradicted
by context.
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