THROTTLE RAMP RATE CONTROL SYSTEM FOR A VEHICLE
[0001] The present invention relates to a system and method for controlling a prime
mover of a vehicle, and, more specifically, a system and method for controlling the
throttle ramp rate of a prime mover during the launch of a vehicle.
Background of the Invention
[0002] During the launch of a motor vehicle, the vehicle operator adjusts a throttle of the
vehicle, typically by depressing an accelerator pedal, in order to increase the running
speed of the engine. Increasing the engine speed increases the amount of torque
generated by the engine, which subsequently causes the wheels to turn. The rate at which
the speed of the engine can be increased is known as the throttle ramp rate. In some
vehicles, only one or two throttle ramp rates may be available, such as a low throttle ramp
rate for when a desired engine speed is relatively low, and a high throttle ramp rate for
when a desired engine speed is relatively high. Furthermore, these throttle ramp rates
may be constant in value. Figure 1 is a graph of engine speed over time, and depicts a
constant throttle ramp rate as used in the prior art.
[0003] A constant value high throttle ramp rate is sufficient for vehicles that maintain a
uniform weight. However, for vehicles such as commercial trucks, the effective vehicle
weight can vary drastically depending on the type and amount of cargo being carried. As
a result, one constant high throttle ramp rate is inadequate, as it often leads to excessive
acceleration of the engine when the vehicle is light, resulting in jerky starts, or
insufficient acceleration of the engine when the vehicle is heavy, resulting in a slow and
labored launch of the vehicle.
Summary of the Invention
[0004] The present invention, according to one embodiment, includes a system and
method of controlling the fueling of an engine during a vehicle launch. The system and
method accomplish this by determining a target engine speed, along with determining
whether there is a high throttle demand upon the engine. The default high throttle ramp
rate can then be adjusted according to a calculated amount of offset that is based upon an
estimated weight of the vehicle.
Brief Description of the Drawings
[0005] Figure 1 is a graph depicting a typical throttle ramp rate of a conventional vehicle.
[0006] Figure 2 is a simplified schematic illustration of an exemplary or illustrative
vehicle drive-train system that incorporates the throttle ramp rate control system
according to an embodiment of the invention.
[0007] Figure 3 is a flow chart depicting the steps taken in the adjustment of a throttle
ramp rate for an engine of a vehicle.
[0008] Figure 4 is a graph depicting an example of the type of throttle ramp rates
available according to an embodiment of the invention.
[0009] Figure 5 is a graph depicting an example of the type of throttle ramp rates
available according to another embodiment of the invention.
Description of the Preferred Embodiment
[0010] Figure 2 is a schematic illustration of an exemplary vehicle drive-train system 20
that incorporates a throttle ramp rate control system according to an embodiment of the
present invention. In system 20, a multi-gear transmission 22 having a main transmission
section 24, which may or may not be connected in series with a splitter-type auxiliary
transmission section 26, is drivingly connected to a prime mover 28 by clutch 30. Prime
mover 28 can be one of many different types, including, but not limited to, a heat engine,
electric motor, or hybrid thereof. For illustrative purposes, prime mover 28 will be
presumed to be an internal combustion engine 28 for the remainder of this discussion.
[0011] Engine 28 includes a crankshaft 32, which is attached to an input member 34 of
clutch 30. Clutch 30 can be any type of clutch system, although in practice, will likely be
of the type commonly utilized in vehicle drive-trains, such as, for example, frictional
clutches including centrifugal clutches or position controlled clutches. For the remainder
of the discussion, clutch 30 will be assumed to be a centrifugal friction clutch.
[0012] Input member 34 of centrifugal friction clutch 30 frictionally engages with, and
disengages from, an output member 36, which is attached to an input shaft 38 of
transmission 22. The clamping force and torque transfer capacity of centrifugal friction
clutch 30 is a function of the rotational speed (ES) of the engine 28 and clutch input
member 34.
[0013] Vehicle drive-train 20 also includes at least one rotational speed sensor 42 for
sensing engine rotational speed (ES), sensor 44 for sens ing input shaft rotational speed
(IS), and sensor 46 for sensing output shaft rotational speed (OS), and providing signals
indicative thereof. The engaged and disengaged states of clutch 30 may be sensed by a
position sensor, or alternatively, determined by comparing the speed of the engine (ES) to
the speed of the input shaft (IS). A sensor 47 is also provided for sensing a throttle pedal
operating parameter, such as throttle position, and providing an output signal (THL)
indicative thereof.
[0014] The terms "engaged" and "disengaged" as used in connection with clutch 30 refer
to the capacity, or lack of capacity, respectively, of the clutch 30 to transfer a significant
amount of torque. Mere random contact of the friction surfaces, in the absence of at least
a minimal clamping force, is not considered engagement.
[0015] Engine 28 may be electronically controlled by an electronic controller 48 that is
capable of communicating with other vehicle components over an electronic data link
(DL) operating under an industry standard protocol such as SAE J-1922, SAE J-1939,
ISO 11898 or the like. Engine controller 48 includes an output for selectively
transmitting a command signal to engine 28, while engine 28 includes an input that
selectively receives the command signal from engine controller 48. Engine controller 48
further includes at least one mode of operation for controlling engine fuelling, thereby
controlling the engine speed (ES) of engine 28
[0016] A shift actuator 50 may be provided for automated or semi-automated shifting of
the transmission main section 24 and/or auxiliary section 26. A shift selector 51 allows
the vehicle driver to select a mode of operation and provide a signal GRt indicative
thereof. One example of such a transmission system is the AutoShift™ series of
transmission systems by Eaton® Corporation. Alternatively, a manually operated shift
lever 52 having a shift knob 54 thereon may be provided, which is manually manipulated
in a known shift pattern for selective engagement and disengagement of various shift
ratios.
[0017] System 20 further includes a control unit 60, and more preferably an electronic
control unit (ECU), such as a microprocessor-based electronic control unit that
communicates by one or more data links. ECU 60 may receive input signals 64 from
sensors 42, 44 and 46 and processes the signals according to predetermined logic rules to
issue command output signals 66 to system actuators, such as engine controller 48, shift
actuator 50, and the like. Alternatively, one or more signals from sensors 42, 44 and 46
may be directed to engine controller 48, which may then supply ECU 60 with the
necessary data. Then, through communication over a data link, ECU 60 can work with
engine controller 48 to command operation of engine 28.
[0018] ECU 60 and engine controller 48 may be electrically coupled to throttle sensor 47
to receive one or more output signals THL. Output signal THL corresponds to one or
more throttle operating parameters, including, but not limited to, throttle position, throttle
application rate, and acceleration of throttle application. For illustrative purposes, the
throttle ramp rate control system according to the embodiments discussed below will act
in response to receipt of an output signal THL corresponding to throttle position.
However, it will be appreciated that the invention is not limited to the ECU 60 receiving
signals from throttle sensor 47, and that the invention can be practiced by ECU 60
receiving signals from any component that is capable of detecting the desired fueling or
throttle rate of engine 28, such as engine controller 48.
[0019] Application of the throttle ramp rate control system will now be explained with
reference to the flow chart of Figure 3. The first step 100 involves determining a target
engine speed (EST) that engine 28 should be operating at depending on one or more
parameters, including the current fueling or throttle rate. As indicated previously, ECU
60 receives a signal THL from throttle sensor 47, the signal, in this embodiment,
representing throttle position. Based on characteristic maps of preferred engine fueling
routines programmed into ECU 60 and/or engine controller 48, a predetermined target
engine speed (EST) that corresponds to the indicated throttle position is obtained.
[0020] The next determination, as illustrated in option box 110, is whether a high throttle
demand is present during the launch of a vehicle. For purposes of this application, a
vehicle launch occurs when clutch 30 is moved from a disengaged state to an engaged
state, resulting in the accelerated movement of a vehicle that initially was stationary or
traveling at near-zero velocity. In the present embodiment, the assessment of whether a
high throttle demand is present is made by ECU 60. Specifically, ECU 60 monitors
signal THL that is output by throttle sensor 47 and which corresponds to throttle position.
When the position of the throttle surpasses a predetermined point, ECU 60 considers a
high throttle demand to be present. For illustrative purposes, consider the following
example where the throttle is controlled by the acceleration pedal of a vehicle. Once a
driver depresses the acceleration pedal past a certain point, which corresponds to a certain
percentage of total possible pedal movement, for example 90%, ECU 60 considers a high
throttle demand to exist.
[0021] If a high throttle demand is not present, engine 28 is not expected to quickly reach
a high engine speed (ES). Accordingly, the rate at which the engine ramps up, or the rate
at which engine speed (ES) reaches a target speed (ESt), need not be that high. As a
result, the throttle ramp rate control system, as depicted in box 120, applies a default or
predetermined low throttle ramp rate to engine 28.
[0022] Alternatively, if a high throttle demand is present, engine 28 is expected to
quickly reach a high target engine speed (ESt). In this circumstance, the throttle ramp
rate control system will attempt to modify a default high throttle ramp rate based on the
vehicle's weight. If only the weight of the vehicle is taken into account, an estimate of
gross vehicle weight (GVW) may be appropriate. However, if the vehicle is a heavy duty
truck or the like, which may include a trailer, then the appropriate weight to consider is
the gross combined weight (GCW), which takes into account both the GVW and the
weight of the trailer. For the remainder of the discussion, it will be assumed that the
weight of a vehicle is properly represented by its gross combined weight (GCW).
[0023] The GCW can be estimated by various direct or indirect methods. For example,
one method of directly estimating GCW is through the use of sensors incorporated into
the vehicle. Alternatively, GCW may be indirectly estimated through mathematical
derivation. Automated vehicle systems using GCW as a control parameter and/or having
logic for determining GCW may be seen, for example, by reference to U.S. Patent Nos.
5,490,063 and 5,491,630, the disclosures of which are incorporated herein by reference in
their entirety. As described in these references, data such as vehicle acceleration is
monitored, and then through multiple reiterations of the mathematical formula, a value
for mass, which corresponds to GCW, can be derived. The system can be designed so
that the mathematical derivation process may be performed by ECU 60, or alternatively,
by another vehicle component possessing the computational capability. For example,
AutoShift™ transmission systems by Eaton® Corporation possess the ability to estimate
the weight of a vehicle. Accordingly, if the present invention is incorporated into a
vehicle that utilizes an AutoShift™ transmission, the throttle ramp rate control system
may retrieve the GCW data from the AutoShift™ system. For the remainder of this
discussion, it will be assumed that GCW is estimated by mathematical derivation.
[0024] If GCW is estimated by mathematical derivation, it may be necessary to verify or
validate the data to assure that it is reasonably accurate. This is because multiple stages
of data may need to be collected and multiple reiterations of the deriving mathematical
formula carried out. For example, it may require on the order of fifty ("50") calculations
before a reasonably accurate estimate of GCW is obtained, and each calculation may
require new vehicle operating data before it can be carried out. Further, it may be that
vehicle operating data can be obtained only during certain times or during certain actions,
such as when the transmission 22 is shifted from a lower to higher gear. As a result, a
reasonably accurate estimate of GCW may not be available until a certain amount of time
has passed or until the transmission 22 has shifted through a certain number of gears.
[0025] To assure that a reasonably accurate estimate of GCW is obtained, the throttle
ramp rate control system verifies or validates the estimated GCW at step 130 by
confirming that either enough time has passed or a sufficient number of appropriate
actions have occurred in order for the required number of calculations to be carried out.
If a vehicle is in a launch state and there is a high throttle demand, but the estimated
GCW cannot be validated at 130 for the reasons noted above, then the system applies a
default high throttle ramp rate (see step 140) to engine 28.
[0026] If an estimated GCW can be obtained and validated at 130, the system continues
on to step 150 and, based upon preprogrammed logic rules, determines the appropriate
throttle ramp rate to apply taking into account the weight of the vehicle (GCW). The new
throttle ramp rate, adjusted for the weight of the vehicle (GCW), is then expressed as an
amount of offset that must be added or subtracted to the default high throttle ramp rate.
Consider the following example, provided for illustrative purposes, where it is assumed
that the default high throttle ramp rate is 100 rpm/sec. A truck incorporating the throttle
ramp rate control system according to the present embodiment normally weighs 18,000
lbs., but upon being loaded, weighs 70,000 lbs. Upon validating an estimated weight of
the truck, the system determines that a high throttle ramp rate of 130 rpm/sec is
appropriate, and that the default ramp rate of 100 rpm/sec needs to be supplemented with
an offset of 30 rpm/sec.
[0027] Before the adjustment to the default ramp rate is finalized, the system undergoes
an error checking process. Specifically, at step 160, a determination is made on whether
the calculated amount of offset falls within a predetermined range. This predetermined
range is defined by empirically decided first and second maximum offset values that
correspond, respectively, to the maximum amounts that the default high ramp rate can be
increased by, for example, +50 rpm/sec, or reduced by, for example, -50 rpm/sec.
[0028] If the calculated amount of offset falls within the allowable range, it is considered
reasonable. The high throttle ramp rate is then adjusted accordingly at step 180 by
adding the offset to the default ramp rate. The system may then pass on the adjusted high
throttle ramp rate to other vehicle systems at step 190 for further processing and
implementation.
[0029] If the calculated amount of offset falls outside the allowable range, it is set to be
equal to the closer of the two empirically determined maximum offset values. For
illustrative purposes, consider an example where the ramp rate offset is calculated to be
+60 rpm/sec, but the allowable offset range is between -50 rpm/sec and +50 rpm/sec.
Upon such a determination, the calculated offset value is set at step 170 to be equal to the
closer of the two maximum offset values. Thus, the previously calculated offset value of
+60 rpm/sec would be reduced to +50 rpm/sec. The high throttle ramp rate is then
adjusted accordingly as previously described. In this manner, the system assures that
damage will not occur due to an attempt to generate a high throttle ramp rate that is either
too small or too great in value.
[0030] Unlike conventional vehicles that rely on a single default high throttle ramp rate,
the system of the present invention, as described above, allows for a high throttle ramp
rate to be adjusted based on the weight (GCW) of the vehicle. This adjustability allows
the system to obtain any one of a multitude of high throttle ramp rates. This is further
demonstrated in Figure 4, which depicts a graph of engine speed over time. For
illustrative purposes, assume line B of Figure 4 represents the ramp rate of conventional
systems, or alternatively, the default ramp rate of the present embodiment. By then
determining and applying an offset value to the default ramp rate, an adjusted ramp rate
of lower value (line A) or higher value (line C) may be obtained.
[0031] According to a further embodiment of the invention, adjustments based on an
estimated weight of the vehicle (GCW) are made to the default high throttle ramp rate
only when the state of the vehicle approaches near or reaches a predefined point in the
clutch engagement process. According to the current embodiment, this predefined point
is set at or near what is known as the "touch point", which represents the moment at
which clutch 30 begins to engage, and thus transmit torque. As further emphasized in the
graph of Figure 5, the default high throttle ramp rate is applied without adjustment until
the state of the vehicle approaches or comes reasonably close to approaching the "touch
point", represented by point A. At that time, acceleration of engine 28 can continue on at
the current rate (C), or proceed at a lesser ramp rate (B) or greater ramp rate (D) by
addition of the calculated offset to the default ramp rate. This allows for advantages such
as quicker initiation of vehicle acceleration by allowing a higher ramp rate to be applied
for a portion of time, but then apply a slower, adjusted ramp rate once clutch engagement
begins. This reduces the chance of a difficult vehicle launch, along with the possibility of
damage due to overly rapid acceleration of engine 28.
[0032] Although certain preferred embodiments of the present invention have been
described, the invention is not limited to the illustrations described and shown herein,
which are deemed to be merely illustrative of the best modes of carrying out the
invention. A person of ordinary skill in the art will realize that certain modifications and
variations will come within the teachings of this invention and that such variations and
modifications are within its spirit and the scope as defined by the claims.
We Claim:
1. A method of controlling fueling of an engine (28) during a vehicle launch,
comprising the steps of:
(a) determining (110) whether there is a high throttle demand upon
said engine (28);
(b) calculating a throttle ramp rate offset (150) based on an estimated
weight of said vehicle when said high throttle demand is present;
(c) adjusting a default high throttle ramp rate (140) based upon said
calculated throttle ramp rate offset;
(d) checking (160) whether said calculated throttle ramp rate offset is
reasonable; and
(e) correcting (170) said calculated throttle ramp rate offset if
determined to be unreasonable.
2. The method as claimed in claim 1, wherein said step of checking whether
said calculated throttle ramp rate offset is reasonable comprises
comparing said calculated throttle ramp rate offset to at least one
predetermined offset value.
3. The method as claimed in claim 1, comprising the step of validating said
estimated vehicle weight.
4. The method as claimed in claim 3, wherein said step of calculating said
throttle ramp rate offset is performed if said estimated vehicle weight is
determined to be valid.
5. The method as claimed in claim 3, wherein said estimated vehicle weight
is held to be valid after a predetermined number of reiterative calculations
of said estimated vehicle weight are performed.
6. The method as claimed in claim 5, wherein vehicle data required for said
reiterative calculations of said estimated vehicle weight is obtained when a
transmission of said vehicle sifts from a lower gear to a higher gear.
7. The method as claimed in claim 1, wherein said adjustment of said default
high throttle ramp rate based upon said calculated throttle ramp rate
offset does not occur until an operating state of a clutch of said vehicle
approaches a predefined state.
8. The method as claimed in claim 7, wherein said predefined state of said
clutch is when said clutch begins to transmit torque.
9. The method as claimed in claim 1, comprising the step of selecting a
default low throttle ramp rate when it is determined that there is an
insufficient high throttle demand upon said engine.
10.The method as claimed in claim 1, wherein said high throttle demand is
determined by an operating parameter of a throttle of said vehicle.
11. The method as claimed in claim 1, wherein said estimated weight of said
vehicle is a gross combined weight of said vehicle.
12.The method as claimed in claim 1, comprising the step of determining a
target engine speed for said engine of said vehicle.
13. A system (20) of controlling fueling of an engine during a vehicle launch
by carrying-out the method as claimed in claim 1, the system comprising:
(a) an engine (28);
(b) a transmission section (24);
(c) a clutch (30) connecting said engine (28) to said transmission
Section (28)
(d) a throttle sensor (47) for monitoring one or more throttle
operating parameters; and
(e) a control unit (60), in communication with at least said throttle
sensor (47) and said engine (28), for detecting a high throttle
demand and obtaining an estimated weight of said vehicle;
wherein upon detecting said high throttle demand, said control unit
(60) adjusts a default high throttle ramp rate based upon said
estimated weight of said vehicle.
14.The system as claimed in claim 13, wherein said detection of said high
throttle demand is based upon a positional state of an accelerator pedal.
15.The system as claimed in claim 13, wherein said control unit adjusts said
default high throttle ramp rate by adding an offset amount, said offset
amount based upon said estimated weight of said vehicle.
16. The system as claimed in claim 15, wherein said control unit confirms
that said offset amount is reasonable by comparing said offset amount to
at least one predetermined offset value.
17. The system as claimed in claim 16, wherein said control unit reduces said
amount of offset upon determining that said offset amount is outside a
predetermined range.
18. The system as claimed in claim 13, wherein said estimated vehicle weight
is obtained by mathematical derivation using sensor readings.
19.The system as claimed in claim 13, comprising an engine control unit (48)
communicating with said control unit (60) by at least one data link,
wherein said engine control unit directly controls an operation of said
engine based upon instructions generated by said control unit.
20.The system as claimed in claim 13, wherein said control unit delays
adjusting said default high throttle ramp rate until said clutch approaches
a predefined operating state.
21. The system as claimed in claim 20, wherein said predefined operating
state is when said clutch begins to transmit torque.
22.The system as claimed in claim 13, wherein said clutch is one of a non
frictional clutch and a frictional clutch.
23.The system as claimed in claim 22, wherein said frictional clutch is a
centrifugal clutch.
24. The system as claimed in claim 22, wherein said frictional clutch is a
position controlled clutch.
25. A system of controlling powering of a prime mover during a vehicle launch
by carrying out the method as claimed in claim 1, the system comprising:
(a) a prime mover (28);
(b) a transmission system (24);
(c) a clutch (30) connecting said prime mover (28) to said
transmission system (24);
(d) a throttle sensor (47) for monitoring one or more throttle
operating parameters; and
(e) a control unit (60), in communication with at least said throttle
sensor (47) and said prime mover (28), for detecting a high
throttle demand and obtaining an estimated weight of said vehicle;
wherein upon detecting said high throttle demand, said control unit
(60) adjusts a default high throttle ramp rate based upon said
estimated weight of said vehicle.
26. The system as claimed in claim 25, wherein said prime mover is a motor.

The invention relates to a method of controlling fueling of an engine (28) during
a vehicle launch, comprising the steps of (a) determining (110) whether there is
a high throttle demand upon said engine (28); (b) calculating a throttle ramp
rate offset (150) based on an estimated weight of said vehicle when said high
throttle demand is present; (c) adjusting a default high throttle ramp rate (140)
based upon said calculated throttle ramp rate offset; (d) checking (160) whether
said calculated throttle ramp rate offset is reasonable; and (e) correcting (170)
said calculated throttle ramp rate offset if determined to be unreasonable.