STEERING CIRCUIT WITH BYPASS VALVE
CROSS REFERENCE TO RELATED APPLICATIONS
[00011 This application is being filed on 23 April 2013, as a PCT Intemalional
Patent application and claims priority to U.S. Patent Application Serial No. 61/640,215
filed on 30 April 2012, the disclosure of which is hereby incorporated herein by reference.
BACKGROUND
[00021 In many ccoff-highwayv~e~h icles, such as tractors, combines, loaders, line
painting vehicles, sweepers, pavers, marine vehicles, etc., hydraulic steering circuits are
utilized to control an actuator that steers the vehicle. In these hydraulic steering circuits,
hydraulic steering control units are used to assist the driver in steering the vehicle by
providing additional force to the steered wheels.
SUMMARY
[OOO~I An aspect of the disclosure relates to a steering circuit. The steering circuit
includes a reservoir. A fluid pump includes an inlet that is in fluid communication with
the reservoir and an outlet. An actuator is in selective fluid communication with the fluid
pump. A steering control unit defines a fluid inlet port that is in fluid communication with
the outlet of the fluid pump, a fluid outlet port that is in fluid communication with the
outlet of the fluid pump, and frrst and second control ports in fluid communication with
the actuator. The steering control unit includes a proportional valve assembly that has an
open-center neutral position. The open-center neutral position provides fluid
communication between the fluid inlet port and the fluid outlet port. The steering control
unit further includes a fluid meter in fluid communication with the proportional valve
assembly. A pressure relieving valve provides fluid communication between the outlet of
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the fluid pump and thc reservoir when a pressure of the fluid at the outlet of the fluid
pump exceeds a threshold value. A bypass valve provides selective fluid co~nmunication
between the outlet of the fluid pump and the reservoir. The bypass valve is disposed in
parallel to the pressure relieving valve.
[0004] Another aspect of the present disclosure relates to a steering circuit. The
steering circuit includes a reservoir, a fluid pump having an inlet in fluid communication
with the reservoir and an outlet, an actuator in selective fluid communication with the
fluid pump and a steering control unit. The steering control unit defines a fluid inlet port
that is in fluid communication with thc outlet of the fluid pump, a fluid outlet pump that
is in fluid communication with the reservoir, and first and second control ports in fluid
communication with the actuator. The steering control unit includes a proportional valve
assembly and a fluid meter. The proportional valve assembly has an open-center neutral
position that provides fluid communication between the fluid inlet port and the fluid
outlet port. The fluid meter is in fluid communication with the proportional valve
assembly. A pressure relieving valve provides fluid communication between the outlet of
the fluid pump and the reservoir when a pressure of the fluid at the outlet of the fluid
pump exceeds a threshold value. The steering circuit further includes a flow path
disposed in parallel to the pressure relieving valve. The flow path provides selective fluid
communication between the outlet of the fluid pump and the reservoir.
[ooosl Another aspect of the present disclosure is related to a method of operating
a bypass valve in a steering circuit. The method includes providing a reservoir, a fluid
pump having an inlet in fluid communication with the reservoir and an outlet, an actuator,
a steering control unit in selective fluid communication with the actuator, wherein the
steering control unit includes a proportional valve assembly, having an open-center
neutral position that provides fluid communication through the proportional valve
assembly between the fluid pump and the reservoir when the proportional valve assembly
is in the neutral position, and a fluid meter in fluid communication with the proportional
valve assembly, a bypass valve, which is disposed in parallel to the proportional valve of
the steering unit, providing selective fluid communication between the outlet of the fluid
pump and the reservoir. The method further includes receiving a first signal that indicates
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that the actuator is at a travel limit. The bypass valve is actuated to an open position so
that fluid is communicated from the outlet of the pump to the reservoir through the bypass
valve. A second signal is received that indicates the actuator is being moved in a
direction away from the travel limit. The bypass valve is actuated to the closed position.
DRAWINGS
[00061 FIG. 1 is a schematic representation of a steering circuit having exemplary
features of aspects in accordance with the principles of the present disclosure.
[OOO~I FIG. 2 is a cross-sectional view of an exemplary steering control unit
suitable for use with the steering circuit of FIG. 1.
[00081 FIG. 3 is an alternate embodiment of a steering circuit having exemplary
features of aspects in accordance with the principles of the present disclosure.
[ooO91 FIG. 4 is a representation of exemplary modes of operation of the steering
circuit of FIG. 1.
[OOlO] FIG. 5 is a representation of a power steering mode of operation.
DETAILED DESCRIPTION
[OOll] Reference will now be made in detail to the exemplary aspects of the
present disclosure that are illustrated in the accompanying drawings. Wherever possible,
the same reference numbers will be used throughout the drawings to refer to the same or
like structure.
[0012] Referring now to FIG. 1, a steering circuit 10 of a vehicle is shown. The
steering circuit 10 could be utilized on a variety of off-highway type vehicles including
tractors, skid steers, backhoes, etc. The steering circuit 10 includes a fluid pump 12, an
actuator 14 and a steering control unit 16.
[0013] The fluid pump 12 includes an inlet 18 and an outlet 20. In the depicted
embodiment, the fluid pump 12 is a fixed displacement pump. In one embodiment, the
fluid pump 12 is a gear pump. The inlet 18 of the fluid pump 12 is in fluid
communication with a reservoir 22. The outlet 20 of the fluid pump 12 is in selective
fluid communication with the actuator 14 via the steering control unit 16.
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[0014] In the depicted embodinlent, the actuator 14 is a cylinder. The actuator 14
includes a piston rod 24 that is slidably disposed in a piston bore 26. The actuator 14
includes a first port 28 and a second port 30. The piston rod 24 extends or retracts in
response to fluid supplied to the fust and sccond ports 28,30.
[OOlS] Referring now to FIGS. 1 and 2, the steering control unit 16 includes a
proportional valve assembly 32. The steering control unit 16 defines a fluid inlet port 34,
a fluid outlet port 36, a first control port 38 and a second control port 40. The fluid inlet
port 34 is in fluid communication with the outlet 20 of the fluid pump 12 via a first flow
path 42. The fluid outlet port 36 of the steering control unit 16 is in fluid communication
with the reservoir 22 via a second flow path 44. The f i t and second control ports 38,40
are in fluid communication with the first and second ports 28,30 of the actuator 14 via
third and fourth flow paths 46, 48, respectively. The proportional valve assembly 32 is
disposed between the fluid inlet port 34 and the first and second control ports 38,40.
[0016] In the subject embodiment, the proportional valve assembly 32 includes a
rotary valve (e.g., a spool) 50 and a follow-up valve member (e.g., a sleeve) 52. The
rotary valve 50 rotates within a bore 54 of the follow-up valve member 52 as a result of
actuation of a steering actuation member 56 (e.g., a steering wheel, a joystick, etc.). In one
embodiment, the actuation of the steering actuation member 56 is manual. The
proportional valve assembly 32 is movable from a neutral position N to a right turn
position R or a left turn position L through the actuation of the steering actuation member
56.
[0017] In the right turn position R, fluid from the fluid inlet port 34 is
communicated to the first control port 38 through a fluid meter 58 of the steering control
unit 16 while fluid from the second control port 40 is communicated to the fluid outlet
port 36 through the fluid meter 58. In the left turn position L, fluid from the fluid inlet
port 34 is communicated to the second control port 40 through the fluid meter 58 while
fluid from the first control port 38 is communicated to the fluid outlet port 36 through the
fluid meter 58.
[0018] In the subject embodiment, the fluid meter 58 is a gerotor gear set. The
gerotor gear set includes a star 60 eccentrically disposed in a ring 62. The fluid meter 58
functions as a metering device that measures the proper amount of fluid to be fed to the
appropriate control port 38,40 of the steering control unit 16 in response to rotation of the
steering actuation member 56. The fluid meter 58 also functions as a follow-up device
that provides follow-up movement to the follow-up valve member 52 of h e proportional
valve assembly 32. For example, pressurized fluid flowing through the proportional valve
assembly 32 in response to rotation of the rotary valve 50 flows through the fluid meter 58
causing orbital and rotational movement of the star 60 within the ring 62. Such
movement by the star 60 causes follow-up movement of the follow-up valve member 52
of the proportional valve assembly 32 by means of a drive shaft 64. The drive shaft 64
has a first end 66 that is engaged with the star 60 and an oppositely disposed second end
68 that is engaged with the follow-up valve member 52 via a pin.
[00191 The proportional valve assembly 32 of the steering control unit 16 has an
open-center configuration. The open-center configuration provides fluid communication
through the proportional valve assembly 32 between the fluid inlet port 34 and the fluid
outlet port 36 of the steering control unit 16 when the proportional valve assembly 32 is in
the neutral position N.
[0020] The steering circuit 10 includes a conventional pressure relieving valve 70
disposed upstream of the proportional valve assembly 32. m e pressure relieving valve 70
is downstream of the outlet 20 of the fluid pump 12 and upstream of the fluid inlet port 34
of the steering control unit 16. In the subject embodiment, the pressure relieving valve 70
is adapted to communicate fluid from first flow path 42 to the second flow path 44 when
the pressure of the fluid at the outlet 20 of the fluid pump 12 exceeds a threshold value
(e.g., a pressure setting, etc.) of the pressure relieving valve 70. In the subject
embodiment, the pressure relieving valve 70 is adapted to communicate fluid from outlet
20 of the fluid pump 12 to the reservoir 22 when the pressure of the fluid at the outlet 20
of the fluid pump 12 exceeds the threshold value of the pressure relieving valve 70.
[0021] The steering circuit 10 further includes a bypass valve 72 (e.g., directional
valve, check valve, flow regulator valve, sequencing valve, etc.). The bypass valve 72 is
adapted to provide fluid communication between the outlet 20 of the fluid pump 12 and
the reservoir 22 when certain conditions are met regardless of the fluid pressure at the
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outlet 20 of the fluid pump 12 so that fluid from the fluid pump 12 can bypass the steering
control unit 16. The bypass valve 72 is disposed in a parallel with the pressure relieving
valve 70 of the steering control unit 16.
[00221 'The bypass valve 72 includcs a fluid inlet 74 and a fluid outlet'76. The
fluid inlet 74 is in fluid communication with the first flow path 42 at a location between
the outlet 20 of the fluid pump 12 and the fluid inlet port 34 of the steering control unit
16. The fluid outlet 76 of the bypass valve 72 is in fluid communication with the
reservoir 22. In the depicted embodiment, the fluid outlet 76 of the bypass valve 72 is in
fluid communication with the second flow path 44 at a location between the fluid outlet
port 36 of the steering control unit 16 and the reservoir 22.
[00231 In one embodiment, the bypass valve 72 is a proportional valve. In a first
position (shown in FIG. I), fluid communication between the fluid inlet 74 and the fluid
outlet 76 of the bypass valve 72 is blocked. In the second position, fluid communication
between the fluid inlet 74 and the fluid outlet 76 is open and unrestricted. In the depicted
embodiment, the bypass valve 72 is biased to the first (i.e., closed) position.
[00241 In the subject embodiment of FIG. 1, the bypass valve 72 is an electrohydraulic
valve. The bypass valve 72 includes a solenoid 78. The solenoid 78 is adapted
to receive a signal 80 from a controller 82. In response to the signal 80, the solenoid 78
actuates the bypass valve 72 to the second (i.e., open) position.
[00251 In the subject embodiment, the steering circuit 10 includes an actuator
position sensor 84 and a steering actuator sensor 86. In the depicted embodiment, the
actuator position sensor 84 is adapted to provide the position of the actuator 14. In one
embodiment, actuator position sensor 84 detects when the actuator reaches an end or stop
position. In another embodiment, the actuator position sensor 84 is a King Pin angle
sensor.
[00261 The steering actuator sensor 86 is adapted to provide infonnation related to
the actuation of the steering actuation member 56. In one embodiment, the steering
actuator sensor 86 is adapted to provide information regarding the position of the steering
actuation member 56 and/or the rotation direction of the steering actuation member 56
and/or the RPM of the steering actuation member 56.
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~10271 In another embodiment, the steering circuit 10 may include a sensor that
senses the amount of flow being communicated to the actuator 14. In another
embodiment, the steering circuit 10 may include a sensor that senses the pressure of the
fluid being cornrnuiicated to the actuator 14.
[00281 In the subject embodiment, the controller 82 receives inputs from the
sensors 84,86. In response to the inputs from the sensors 84,86, the controller outputs
the signal 80 to the solenoid 78.
~ 2 9 1 Referring now to FIG. 3, an alternate embodiment of a steering circuit 210
is shown. In FIG. 3, the components and features of the steering circuit 210 that are the
same as those in the steering circuit 10 will have the same reference numerals and will not
be further described. New components and features will have a reference number greater
than 200.
[00301 The steering circuit 210 includes the fluid pump 12, the actuator 14 and the
steering control unit 16. The steering circuit 210 further includes a bypass valve 272 that
is in selective fluid communication with the outlet 20 of the fluid pump 12 and the
reservoir 22. The bypass valve 272 is disposed in parallel with the pressure relieving
valve 70. The bypass valve 272 functions similarly to the bypass valve 72. In the
depicted embodiment, however, the bypass valve 272 is actuated manually. The bypass
valve 272 includes an actuation member (e.g., button, lever, etc.) 273. By actuating the
actuation member 273, the bypass valve 272 can be actuated between the first position
and the second position.
[00311 Referring now to FIGS. 1 and 4, the steering circuit 10 has a plurality of
modes of operation 100. In the depicted embodiment, the steering circuit 10 includes a
power steering mode 102, a neutral mode 104 and an assist mode 106. In one
embodiment, the mode of operation would be selectable by the operator.
[00321 Referring now to FIGS. 1,4 and 5, an exemplary embodiment of the power
steering mode 102 will be described. The power steering mode 102 would likely be
selected by an operator when the steering actuation member 56 is going to be actuated.
roo331 In step 107 of the power steering node 102, the controller 82 evaluates
whether the actuator 14 is at a travel limit (e.g., fully extended, fully retracted, abutting a
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mechanical stop, etc.). In step 107, the controller 82 evaluatcs the signal from the
actuator position sensor 84 to determine if the actuator 14 is at a travel limit. If the
actuator 14 is not at a travel limit, the bypass valve 72 is actuated to the first position (i.e.,
the closed position) in step 108 so that fluid communication between the fluid inlet 74
and the fluid outlet 76 of the bypass valve 72 is blocked. In this position, the fluid from
the outlet 20 of the fluid pump 12 is communicated to the proportional valve assembly 32
of the steering control unit 16.
[00341 If the actuator 14 is at a travel limit, the bypass valve 72 is actuated to the
second position (i.e., the open position) in step 110 so that fluid communication between
the fluid inlet 74 and the fluid outlet 76 of the bypass valve is open. With the bypass
valve 72 in the second position, fluid from the outlet 20 of the fluid pump 12 is
communicated to the reservoir 22 through the bypass valve 72.
[00351 In a conventional steering circuit, the pressure of the fluid from the pump
outlet would increase when the steering actuator (e.g., cylinder) reached the travel limit.
The pressure would increase until it exceeded the setting of a pressure relief valve at
which point the pressure relief valve would open allowing fluid to be communicated to
the reservoir. As the pressure of the fluid in the conventional steering circuit would be at
the pressure relief valve setting, the pump would require more energy to operate. In
addition, the temperature of the fluid in the conventional steering circuit would increase
as it flowed over the pressure relief valve. In the steering circuit 10 described herein, the
pressure of the fluid at the outlet 20 of the fluid pump 12 is below the setting of the
pressure relieving valve 70 when the actuator 14 is at a travel limit due to the open flow
path to the reservoir 22 through the bypass valve 72. As a result, the power consumed by
the pump is low. In addition, since the fluid does not pass through the pressure relieving
valve 70 when the actuator 14 is at the travel limit, less heat is generated as compared to
the conventional steering circuit.
[0036] In step 112, the controller 82 receives a signal from the steering actuator
sensor 86. If the direction of actuation of the steering actuation member 56 is in a
direction away from the travel limit, the bypass valve 72 is actuated to the first position
(i.e., the closed position) in step 114.
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[00371 Referring now to FIGS. 1 and 4, the neutral mode 104 will be described.
The neutral mode 104 would be selected by an operator when the steering function is not
required. In one embodiment, the neutral mode might be selected if the vehicle is
stationary and auxiliary functibns of the vehicle are being used.
[0038] In the neutral mode 104, the bypass valve 72 is actuated to the first
position (i.e., the open position) in step 116. In the first position, fluid communication
between the fluid inlet 74 and the fluid outlet 76 of the bypass valve 72 is open.
[0039] Since the fluid pump 12 is in open fluid communication with the reservoir
22 in the neutral mode 104, movement of the rotary valve 50 will not result in movement
of the actuator 14 until a rotational limit of the rotary valve 50 has been reached. In one
embodiment, the rotational limit is 15 degrees. At this rotational limit, the rotary valve 50
gets mechanically coupled to the fluid meter 58, which operates as a pump. With the
fluid meter 58 operating as a pump, actuation of the steering actuation member 56 causes
fluid to be communicated to the control ports 38,40 of the steering control unit 16
through a check valve 90 and through the proportional valve assembly 32. This type of
steering is referred to hereafter as manual steering. The actuation force exerted on the
steering actuation member 56 in order to get movement from the actuator 14 during
manual steering is greater than the actuation force exerted on the steering actuation
member 56 in order to get movement from the actuator 14 during power steering.
[00401 Referring still to FIGS. 1 and 4, the assist mode 106 will be described.
The assist mode 106 would be selected by an operator when the operation of the vehicle
does not require frequent actuation of the steering actuation member 56. In one
embodiment, the assist mode 106 would be selected when the vehicle is operating in a
field (e.g., harvesting, planting, etc.).
[ow 11 In step 118 of the assist mode 106, the bypass valve 72 is actuated to a
third position between the first and second positions. The third position is an
intermediate position that allows restricted fluid communication between the fluid inlet 74
and the fluid outlet 76 of the bypass valve 72. With the bypass valve 72 in the third
position, fluid flows from the fluid inlet 74 to the fluid outlet 76 but the restriction in the
pathway between the fluid inlet 74 and the fluid outlet 76 causes the pressure of the fluid
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in the first flow path 42 to be higher than the pressure of thc fluid in the first flow path 42
when the bypass valve 72 is in the second position (i.e., the open position).
100421 In the assist mode 106, the steering control unit 16 can be actuated using
manual steering. Since the pressu;e of the fluid in the first flow path 42 in the assist mode
106 is higher than the pressure of the fluid in the first flow path 42 in the neutral mode
102, the actuation force exerted on the steering actuation member 56 in order to get
movement from the actuator 14 during manual steering in the assist mode 106 is less than
the actuation force exerted on the steering actuation member 56 in order to get movement
from the actuator 14 during manual steering in the neutral mode 104.
100431 Various modifications and alterations of this disclosure will become
apparent to those skilled in the art without departing from the scope and spirit of this
disclosure, and it should be understood that the scope of this disclosure is not to be unduly
limited to the illustrative embodiments set forth herein.
We claim:
1. A steering circuit comprising:
a reservoir;
a fluid pump having an inlet in fluid communication with the reservoir and an
outlet;
an actuator in selective fluid communication with the fluid pump;
a steering control unit defining a fluid inlet port that is in fluid communication
with the outlet of the fluid pump, a fluid outlet port that is in fluid communication with
the reservoir, and first and second control ports in fluid communication with the actuator,
the steering control unit including:
a proportional valve assembly having an open-center neutral position,
wherein the open-center neutral position provides fluid
communication between the fluid inlet port and the fluid outlet
port;
a fluid meter in fluid communication with the proportional valve assembly;
a pressure relieving valve providing fluid communication between the outlet of the
fluid pump and the reservoir when a pressure of the fluid at the outlet of the fluid pump
exceeds a threshold value; and
a bypass valve providing selective fluid communication between the outlet of the
fluid pump and the reservoir, the bypass valve being disposed in parallel to the pressure
relieving valve.
2. The steering circuit of claim 1, wherein the bypass valve is a proportional valve
having a fluid inlet and a fluid outlet, the bypass valve includes a first position in which
fluid communication between the fluid inlet and the fluid outlet is blocked and a second
position in which fluid communication between the fluid inlet and the fluid outlet is open.
3. The steering circuit of claim 1, wherein the bypass valve having a fluid inlet and a
fluid outlet, the bypass valve includes a first position that provides no fluid
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comn~unicationb etween the fluid inlet and the fluid outlet, a second position that
provides open fluid communication between the fluid inlet and the fluid outlet, and a third
position that provides restricted fluid communication between the fluid inlet and the fluid
outlet.
4. The steering circuit of claim 2, wherein the bypass valve is a directional valve.
5. The steering circuit of claim 2, wherein the bypass valve is configured for manual
actuation.
6. The steering circuit of claim 2, wherein the bypass valve is biased to the first
position.
7. The steering circuit of claim 2, wherein the bypass valve is an electro-hydraulic
valve.
8. The steering circuit of claim 7, further comprising:
a sensor;
a controller in communication with the sensor and the bypass valve, wherein the
controller actuates the bypass valve in response to a signal from the sensor.
9. The steering circuit of claim 8, wherein the sensor detects when the actuator
reaches an end position.
10. The steering circuit of claim 8, wherein the sensor monitors actuation of the
proportional valve assembly of the steering control unit.
11. A steering circuit comprising:
a reservoir;
a fluid pump having an inlet in fluid communication with the reservoir and an
outlet;
an actuator in selective fluid communication with the fluid pump;
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a steering control unit defining a fluid inlet port that is in fluid communication
with the outlet of the fluid pump, a fluid outlet port that is in fluid communication with
the reservoir, and first and second control ports in fluid communication with the actuator,
the steering control unit including:
a proportional valve assembly having an open-center neutral position,
wherein the open-center neutral position provides fluid
communication between the fluid inlet port and the fluid outlet
port;
a fluid meter in fluid communication with the proportional valve assembly;
a pressure relieving valve providing fluid communication between the outlet of the
fluid pump and the reservoir when a pressure of the fluid at the outlet of the fluid pump
exceeds a threshold value; and
a flow path disposed in parallel to the pressure relieving valve, the flow path
providing selective fluid communication between the outlet of the fluid pump and the
reservoir.
12. The steering circuit of claim 11, wherein the flow path provides restrictive fluid
communication between the outlet of the fluid pump and the reservoir.
13. The steering circuit of claim 12, wherein the flow path includes a bypass valve
that actuates between a first position and a second position.
14. The steering circuit of claim 13, wherein the bypass valve includes a third position
disposed between the first and second positions.
15. The steering circuit of claim 14, wherein the bypass valve is a proportional valve.
16. The steering circuit of claim 11, wherein the flow path includes a bypass valve
that is selected from the group consisting of an electrohydraulic valve, a proportional
valve, a directional valve, a check valve, a flow regulator valve, and a sequencing valve.
17. A method for operating a bypass valve in a steering circuit, the method
comprising:
providing a reservoir, a fluid pump having an inlet in fluid communication with
the reservoir and an outlet, an actuator, a steering con&ol unit in selective fluid
communication with the actuator, wherein the steering control unit includes a proportional
valve assembly, having an open-center neutral position that provides fluid communication
through the proportional valve assembly between the fluid pump and the reservoir when
the proportional valve assembly is in the neutral position, and a fluid meter in fluid
communication with the proportional valve assembly, a bypass valve providing selective
fluid communication between the outlet of the fluid pump and the reservoir, the bypass
valve being disposed in parallel to the proportional valve of the steering unit;
receiving a first signal that indicates that the actuator is at a travel limit;
actuating the bypass valve to an open position so that fluid is communicated from
the outlet of the fluid pump to the reservoir through the bypass valve;
receiving a second signal that indicates the actuator is being moved in a direction
away from the travel limit; and
actuating the bypass valve to a closed position.
18. The method of claim 17, wherein an actuator position sensor that provides the
position of the actuator provides the first signal.
19. The method of claim 18, wherein a steering actuator sensor that provides
information related to actuation of a steering actuation member provides the second
signal.
20. The method of claim 17, wherein the bypass valve is selected from the group
consisting of an electrohydraulic valve, a proportional valve, a directional valve, a check
valve, a flow regulator valve, and a sequencing valve.