Motor vehicles – Steering gear – With fluid power assist
Reexamination Certificate
2002-02-21
2002-12-31
DePumpo, Daniel G. (Department: 3611)
Motor vehicles
Steering gear
With fluid power assist
C180S423000
Reexamination Certificate
active
06499557
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a power steering including a flow control valve for controlling a flow introduced toward a power cylinder.
2. Description of Related Art
A flow control valve installed in this type of power steering has a spool which is mounted inside a main body and has one end facing one of pilot chambers which is communicated with a pump port at all times and the other end facing the other pilot chamber incorporating a spring. A fixed orifice is formed downstream from the other pilot chamber. Pressure oil is introduced through the fixed orifice into a steering valve for controlling a power cylinder.
on the other hand, movement positions of the spool is controlled with pressure balance between both pilot chambers wherein pressure upstream from the orifice is set as pilot pressure of the one pilot chamber and pressure downstream from there is set as pilot pressure of the other pilot chamber.
It is configured to use the movement position of the spool for distribution of the pressure oil between a control flow rate QP of the flow for introducing the amount of discharge from a pump into the steering valve and a return flow rate QT for making the flow circulation-return toward a tank or a pump.
The above spool is designed to be maintained in a constant state of differential pressure after and before the fixed orifice, to supply a constant control flow rate QP to the steering valve for controlling the power cylinder at all times.
In such conventional power steering, a constant control flow rate QP is supplied from the flow control valve to the steering valve for controlling the power cylinder at all times. In other words, regardless of vehicle speed or steering conditions, the control flow rate QP is continuously supplied to the steering valve at a constant control flow rate QP at all times.
However, if the control flow rate QP is defined regardless of the vehicle speed or a steering status, for example, when a relation of QP with respect to the flow rate QM required by the power cylinder becomes QP>QM, the need for returning the resulting surplus flow rate to a tank through the above steering valve arises.
As described above, returning the surplus flow rate to the tank through the steering valve results in increase of a pressure loss in the circuit. Put another way, the pump is required to continue consuming the driving torque to make up for the amount of pressure loss. Therefore, as driving torque increases, energy consumption increases.
Moreover, since the control flow rate QP is set in accordance with the maximum required flow rate for the power cylinder, under present circumstance, some surplus flow rate is often returned to the tank. Thus, the conventional system has a problem associated with increase of energy consumption.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a power steering which in capable of reducing an energy loss to a minimum by controlling a control flow rate QP as travelling conditions or a steering status of a vehicle.
The present invention is predicated on configuration in which: a spool is mounted in a main body and has one of ends facing one of pilot chambers which communicates with a pump port at all times and the other end facing the other pilot chamber incorporating a spring. An orifice is provided downstream from the one pilot chamber. Pressure oil is introduced through the orifice into a steering valve for controlling a power cylinder. A movement position of the spool is controlled with a pressure balance between both the pilot chambers when pressure upstream from the orifice is set as a pilot pressure of the one pilot chamber and pressure downstream from the orifice is set as a pilot pressure of the other pilot chamber. The pressure oil is distributed between a control flow rate QP for introducing the amount of discharge from a pump toward the steering valve, and a return flow rate QT for making the pressure oil circulation-return toward a tank or the pump.
Based on the above power steering, a first invention features as follows: the orifice is a variable orifice controlling the degree of its opening in accordance with an excitation current of a solenoid. Also, a controller is provided for controlling the excitation current of the solenoid for the variable orifice. The controller is connected with a steering torque sensor, and calculates or stores a solenoid current instruction value I
T
in response to a steering torque signal from the steering torque sensor. Further, a solenoid current instruction value I
S
for standby is added to the solenoid current instruction value I
T
. Then the excitation current I of the solenoid SOL for the variable orifice is controlled based on the added instruction value.
According to the power steering of the first invention, the control flow rate QP can be controlled by means of detecting the steering torque. Therefore, the control flow rate QP is appropriately secured to accomplish an energy-saving type control.
Also, when the steering wheel is held stationary, the control flow rate QP can be appropriately secured by means of the steering torque thereby to allow the vehicle to resist a self-aligning torque.
Further, the standby flow rate can be secured even when the solenoid current instruction value I
T
based on the steering torque is zero, for example, in travel of the vehicle in a straight line. Therefore, the power steering can be prevented from seizure, and is capable of handling disturbances caused by a kick back or the like, and further sufficient response can be ensured.
In any of times when the steering wheel is turned, when the steering wheel is held stationary, and when the vehicle travels in a straight line, the control flow rate QP is appropriately secured not to increase torque for driving the pump P more than necessary thereby to attain the accurate energy-saving control.
In the power steering, a signal of the steering torque, the vehicle speed or the like has been conventionally used for controlling a steering reaction force on the output side or controlling sensitivity of the steering valve. However, the present invention has been made under the theme of energy savings and therefore uses a signal of the steering torque, the vehicle speed or the like to control the control flow rate QP, which has not been seen in prior art.
Moreover, in the present invention, the steering torque is directly detected thereby to obtain a more accurate value without need of other sensors or calculating means.
The present invention approaches the subject of energy savings and has the principal feature in that a signal of the steering torque, the vehicle speed or the like is used.
A second invention has configuration in which the controller is connected to a vehicle speed sensor, and calculates or stores a solenoid current instruction value I
V
in response to a vehicle speed signal from the vehicle speed sensors while multiplying the solenoid current instruction value I
T
by the solenoid current instruction value I
V
, and adding the solenoid current instruction value I
S
for standby to the multiplied value.
A third invention has configuration in which the controller is connected to a vehicle speed sensor, and calculates or stores a solenoid current instruction value T
V
in response to a vehicle speed signal from the vehicle speed sensor, while setting the solenoid current instruction value I
V
in response to the vehicle speed signal as a threshold value based on the solenoid current instruction values I
T
, and adding a solenoid current instruction value under the set threshold value to the solenoid current instruction value (I
S
) for standby.
A fourth invention has configuration in which the controller multiplies characteristics of the excitation current I of the solenoid and the control flow rate QP determined by the degree of opening of the variable orifice, and characteristics of the steering torque and the solenoid current instruction value I
T
together, to allow the steering torque and the control flow rate Q
Amano Norimasa
Kozuma Fumihide
Shima Naoto
Shimizu Noboru
Takai Masashi
DePumpo Daniel G.
Kayaba Industry Co. Ltd.
Steinberg & Raskin, P.C.
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