Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
1998-09-15
2001-06-19
Graham, Matthew C. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C137S625650, C251S129080, C303S117100
Reexamination Certificate
active
06247765
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of controlling fluid pressure on a load that is effective when e.g. automotive brake fluid pressure is controlled using a proportional pressure control valve or a flow-control valve.
From unexamined Japanese patent publications 1-261581 and 3-69877 and unexamined Japanese utility model publication 1-261581, as well as Japanese patent applications 9-133450 and 9-21611 filed by the applicant of this invention, proportional pressure control valves are known which have a drive means capable of electrically controlling the output and adapted to control the fluid pressure on the load to a value corresponding to the driving force of the drive means by moving a spool by the drive means to a position corresponding to the driving force of the drive means.
This type of proportional pressure control valves includes a housing having a first port connected to a fluid pressure source, a second port connected to a load, and a third port connected to a reservoir, a spool mounted in the housing, a first valve portion for opening and cutting off communication between the first and second ports depending on the position of the spool, and a second valve portion for opening and cutting off communication between the second and third ports.
Specifically, when the spool is moved to a point where the driving force of the drive means balances with a thrust produced by receiving in opposite directions the pressure at the second port on pressure receiving portions having different areas, the state of communication of the second port with the first or third port is changed over, and the degree of opening of the first or second valve portion is adjusted so that the pressure at the second port is controlled to a value corresponding to the driving force of the drive means.
FIG. 1
shows fluid pressure-fluid amount characteristics. As shown, automotive brakes consume a greater amount of brake fluid in a low-pressure region.
Thus, if a proportional pressure control valve of the above-described type is used to control automotive brake fluid pressure, control responsiveness worsens in the low-pressure region.
As shown in
FIG. 2
, in a region where a lesser amount of brake fluid is consumed (region where the pressure is higher than P
1
), pressure rise or fall per unit fluid amount is great, that is, the pressure rises and falls sharply. The actual pressure P thus approaches the target pressure P(n) quickly. But in a region where a large amount of brake fluid is consumed (region where the pressure is lower than P
1
), pressure rise or fall per unit fluid amount is small, that is, the pressure rises or falls only slowly. It thus takes a long time for the actual pressure P to reach the target pressure P(n). Responsiveness of control is thus no good.
Automotive brake systems have been sophisticated year after year. Some recent brake systems include not only an ABS (antilock brake control system) but a TCS (traction control system) and an ASC (active safety control) system. Such systems require high-precision control even in the low-pressure region.
An object of this invention is to improve responsiveness of control in such a low-pressure region.
SUMMARY OF THE INVENTION
According to this invention, there is provided a method of controlling a fluid pressure applied to a load wherein in controlling the fluid pressure applied to the load using a proportional pressure control valve of the above-described type, if, in a control fluid pressure range, there is a pressure region where the consumption of fluid is greater than in other regions, overshoot control is carried out to increase fluid pressure in the pressure region by adding a predetermined pressure to a target pressure for a predetermined time, and undershoot control is carried out to reduce fluid pressure in the pressure region by subtracting a predetermined pressure from a target pressure for a predetermined time.
Preferably, the system has both the functions of overshoot control during a pressure increase phase and undershoot control during a pressure reduction phase. But a system having only one of these functions would be advantageous.
Such accurate fluid pressure control may be carried out using flow control valves as disclosed in unexamined Japanese patent publication 6-221452. Such flow control valves comprise a housing having an inlet port and an outlet port, and a spool substantially liquid-tightly and slidably mounted in the housing so as to define first and second fluid pressure chambers at one and the other ends of the spool, a driving means for biasing the spool, the first and second fluid pressure chambers applying fluid pressure on the one and other ends of the spool and communicating with each other through a fluid passage having an orifice, a valve portion comprising a shoulder portion formed on the inner periphery of the housing and a shoulder portion formed on the outer periphery of the spool, the shoulder portions being movable into and out of sliding contact with each other to form and stop a fluid flow from the inlet port to the outlet port through the orifice, wherein the spool moves to a balancing point where a thrust applied to the spool due to a difference in pressure between the first and second fluid pressure chambers balances with the force of the drive means which is opposite in direction to the thrust, and fluid flows through the orifice toward the outlet port at a rate determined by the difference in fluid pressure and the sectional area of the orifice, whereby when a thrust applied to the spool due to a difference in pressure between the first and second fluid pressure chambers by an automatic opening degree adjusting function of the valve portion according to the position of the spool balances with the force of a drive means which is opposite in direction to the thrust, fluid flows through the orifice toward the outlet port at a rate determined by the difference in fluid pressure and the sectional area of the orifice. If two such flow control valves are used with the load connected to a fluid pressure source through one of the two flow control valves and to a reservoir through the other fluid flow control valve, to control the fluid pressure applied to the load, the same problems as mentioned above can occur. Thus, in this case, too, overshoot or undershoot control is carried out to improve responsiveness.
FIG. 3
shows the method of controlling the fluid pressure on the load by means of a proportional pressure control valve according to this invention.
First, an electronic control unit determines whether the target pressure P(n) is in a region where overshooting or undershooting control is needed (or whether P(n) is lower than P
1
). If the ECU determines such control is necessary, it adds, for pressure increase control, a predetermined pressure addP, to the target pressure P(n) for a predetermined time T
1
to control the proportional pressure control valve so as to achieve the new target pressure P(n) plus addp, and subtracts, for pressure reduction control, the predetermined pressure addP from the target pressure for a predetermined time T
2
to control the proportional pressure control valve so as to achieve the new target pressure P(n) minus addP. With this arrangement, the valve portions are opened to a greater degree than with conventional control arrangements both during pressure increase and pressure reduction. Thus, the actual pressure P rises and falls quickly, improving the responsiveness of control in the low-pressure region.
Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which:
REFERENCES:
patent: 4662605 (1987-05-01), Garcia
patent: 5439277 (1995-08-01), Higashi
patent: 5445446 (1995-08-01), Yamamuro
patent: 5495869 (1996-03-01), Hashida
patent: 5538336 (1996-07-01), Reuter et al.
patent: 5579807 (1996-12-01), Kohler
patent: 5636908 (1997-06-01), Yamamuro
patent: 5638861 (1997-06-01), Hashida
patent: 5778932 (1998-07-01), Alexander
patent: 5
Graham Matthew C.
Greenblum & Bernstein P.L.C.
Sumitomo Electric Industries Ltd.
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