Motor vehicles – Steering by driving
Reexamination Certificate
1999-07-07
2001-04-17
Johnson, Brian L. (Department: 3618)
Motor vehicles
Steering by driving
C180S417000, C180S441000, C180S442000
Reexamination Certificate
active
06216806
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to a supplemental steering system and more specifically to a supplement steering system for a machine or vehicle operable for providing supplemental steering through steering input controlled differential brake application when an emergency condition such as a low pressure condition in a primary or main steering system or an engine stalling condition is present.
BACKGROUND ART
There are many types of supplemental steering controls known in the art. Many of the known supplemental steering controls use a pressure storage device such as an accumulator to store pressurized fluid that can be used to provide pressurized fluid for steering in the event the main steering control fails. In other steering systems, a steering control valve having a HMU (hand metering unit) is used during emergency conditions. In these systems, the HMU is used to provide pressurized fluid to steer the machine in the event the main steering pump flow is lost.
In other steering control systems, a differential steer mechanism is used to provide the steering of the machine. In many of these differential steering units, individual steer motors are connected to the differential steer mechanism and operate to either increase or decrease the speed of the respective outputs that provide the driving force to the machine. By increasing or decreasing the speed of one of the outputs relative to the other output, the machine turns in the direction of the slowest output speed. In differential steered machines, each of the outputs are always under a continuous driving force, even when the machine is being steered. By using two different steering motors connected to the respective outputs, during an emergency steering control it is possible to provide stored pressurized fluid to one or the other of the steering motors to steer the machine. Since fluid motors normally require a volume of pressurized fluid to provide the force on a continuous basis to provide the needed differential between the two outputs, it is many times not practical to try to store the needed pressurized fluid.
In other differential steer machines, a single fluid motor is connected to the differential steer mechanism. In these differential steer mechanisms, the single steer motor provides an input into the differential steer mechanism to increase the speed of one of the outputs and simultaneously decrease the speed of the other of the outputs. When the single steer motor is not receiving pressurized fluid to cause rotation of its output, the drive outputs from the differential steer mechanism are mechanically locked together by the non-rotating fluid motor. As noted above, with respect to the differential steer mechanism having two steering motors, it is not practical to use accumulators for storage of pressurized fluid for emergency steering since the volume of pressurized fluid needed for a longer duration of emergency steering is too large.
It has also been known to provide a complete redundant emergency steering control but these systems are normally cost prohibitive. In machines not having differential steering mechanisms, it is well known to use brakes on the drive outputs to individually slow one output relative to the other in order to steer the machine. In these machines, when the one drive output is braked, the power is transferred across a standard differential to the other drive output.
In machines having differential steer mechanisms with only one steering motor, attempting to brake one output is not successful since both outputs are under a continuous driving force. Consequently, the machine will not respond to attempts to steer by braking since the non-rotating fluid motor has the two outputs locked together. In these differential steered machines, even attempts to install larger brakes of very high capacity will not provide adequate steering by braking. Even if it did provide some steer control, the size of the brakes would be cost prohibitive.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
DISCLOSURE OF THE INVENTION
In one aspect of the present invention, a supplemental steering system is provided for a vehicle having a first brake actuable for slowing rotation of a first drive output or wheel, a second brake actuable for slowing rotation of a second drive output or wheel, a brake actuator including a reservoir of brake fluid adapted for connection to the first and second brakes for directing the brake fluid under pressure to the first and second brakes, and a main or primary steering system. The brake actuator includes a port connected in fluid communication with a first port and a second port of a supplemental steering control valve, the supplemental steering control valve including a valve body defining a bore divided into a first chamber and a second chamber, the first port communicating with the first chamber and the second port communicating with the second chamber. The supplemental steering control valve further includes a piston located in the bore connected to a steering input and having a neutral position generally equidistant between the first and second chambers, a first brake port communicating the first chamber with the first brake, and a second brake port communicating the second chamber with the second brake. The piston is movable in a first direction a predetermined distance into the first chamber to close the first port such that further movement of the piston in the first direction will urge brake fluid in the first chamber through the first brake port to actuate the first brake, and the piston is movable in a second direction a predetermined distance into the second chamber to close the second port such that further movement into the second chamber will urge brake fluid contained therein through the second brake port to actuate the second brake.
According to another aspect of the invention, the present supplemental steering system includes a second valve, the second valve including a first port connected in fluid communication with the first brake port, a second port connected in fluid communication with the second brake port and a signal input connected in communication with a suitable signal source for operating the valve, a signal source operable for generating a signal representative of a predetermined fluid pressure condition in the primary or main steering system, the second valve being operable to allow fluid flow therethrough between the first port thereof and the second port thereof when the signal representative of the predetermined fluid pressure condition is present, and to prevent flow between the first port thereof and the second port thereof when the signal is absent. The signal can be a fluid signal or an electrical signal, and the predetermined fluid pressure condition is preferably representative of a normal operating condition for the primary or main system. The absence of the predetermined condition is indicative of an emergency condition, such as a low pressure condition in the primary steering system, such as a low charge pump pressure indicative of a failure such as a leak, or a broader problem such as an engine stall or shut down or the like.
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U.S. application Ser. No. 09/093,203 filed Jun. 8,
Burrrows J. W.
Caterpillar Inc.
Haverstock Garrett & Roberts
Johnson Brian L.
Yeagley Daniel
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