Fluid-pressure and analogous brake systems – Speed-controlled – Odd condition or device detection
Reexamination Certificate
1998-12-02
2001-03-20
Schwartz, Christopher P. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Odd condition or device detection
C303SDIG001, C303SDIG002, C374S100000
Reexamination Certificate
active
06203123
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of detecting the temperature of brake fluid which is effective in controlling the brake fluid pressure in an automotive brake using electromagnetic on-off valves or a spool/valve type electromagnetic proportional pressure control valve, and a method of controlling the brake fluid pressure which makes it possible to control the brake fluid pressure to an ideal state while avoiding bad influences due to change in the viscosity of the brake fluid with change in the temperature.
Automotive brake systems are being sophisticated year after year. Recent brake systems include not only ABS's (antilock brake systems) but TCS's (traction control systems) and ASC systems (active safety control systems for correcting oversteering or understeering while the vehicle is turning by individually controlling the wheel brakes).
Such a brake system is shown in FIG.
3
. In this system, during normal braking, the fluid passage connecting a master cylinder
2
to a wheel cylinder
4
for producing braking force is open, so that brake fluid can freely flow therebetween.
When a brake pedal is in its ON position, if an electronic control unit (not shown) detects any lockup tendency of the vehicle wheel and produces a pressure reduction signal, the position of an electromagnetic changeover valve
5
changes over to disconnect the wheel cylinder
4
from the master cylinder
2
, while an electromagnetic on-off valve
9
opens to discharge fluid pressure from the wheel cylinder
4
into a reservoir
3
.
When the locking tendency of the wheel disappears as a result of the pressure reduction, the electronic control unit detects this fact and produces a pressure re-increase signal. In response to this signal, the electromagnetic on-off valves
8
and
9
are opened and closed, respectively, so that fluid pressure is supplied into the wheel cylinder
4
from a pump
6
. The wheel cylinder pressure thus rises again. Alternatively, the electromagnetic on-off valves
8
,
9
may be both closed to maintain the wheel cylinder pressure. During antilock control, the above operations are repeated until the vehicle comes to a stop or until the brake pedal
1
is released to prevent lockup of the vehicle wheel.
Traction control is similar to antilock control except that the brake pedal
1
is not trodded during traction control. If the electronic control unit detects slip of the vehicle wheel, the electromagnetic changeover valve
5
changes over and the electromagnetic valve
8
opens so that fluid pressure is supplied into the wheel cylinder
4
from an accumulator
7
. The wheel cylinder
4
is thus braked in spite of the fact that the brake pedal is not trodden. Then, pressure reduction and pressure re-increase operations are repeated to prevent slip of the vehicle wheel.
In a different arrangement, an electromagnetic proportional pressure control valve
10
shown in
FIG. 4
is used to introduce fluid pressure from the pump circuit into the wheel cylinder
4
and to discharge fluid pressure from the wheel cylinder
4
into the reservoir
3
.
This electromagnetic proportional pressure control valve
10
comprises a housing
11
, a spool
12
substantially liquid-tightly and slidably inserted in the housing, a reaction pin
13
inserted at one end of the spool
12
, a spool-biasing spring
14
, and an electromagnet
15
for biasing, i.e. pulling, the spool
12
in the direction opposite to the direction in which the spool is biased by the spring
14
.
The housing
11
has a first port
16
, a second port
17
, a third port
18
, a first fluid chamber
19
into which one end of the spool
12
protrudes, and a second fluid chamber
20
into which the other end of the spool
12
protrudes.
The spool
12
has a surface passage
21
, and an internal passage
22
kept in communication with the second port
17
. The internal passage
22
has one end open to the first fluid passage
19
, and at this end, the reaction pin
13
is substantially liquid-tightly inserted in the passage
22
. Thus, a difference equal to the sectional area of the reaction pin
13
is created between the areas for bearing fluid pressures that urges the spool
12
in opposite directions. The spool
12
is thus biased under a downward thrust which is equal to the above difference in area multiplied by the pressure at the second port
17
.
Between the spool
12
and the first port
16
, a first valve portion
23
is formed to open and shut off communication between the first and second ports
16
,
17
according to the position of the spool. Between the spool
12
and the third port
18
, a second valve portion
24
is formed to open and shut off communication between the second and third ports
17
,
18
according to the spool position. The degree of opening of each of the first and second valves
23
,
24
changes with the spool position.
With this electromagnetic proportional pressure control valve
10
, during a non-control state in which no current is supplied to the electromagnet
15
, the spool
12
is maintained in the illustrated position by the spring
14
. In this state, the first valve portion
23
is open, so that fluid pressure from the first port
16
flows into the second port
17
.
When the electromagnet
15
is energized, the spool
12
is pulled downward in the figure by the electromagnetic force until the upward force balances with the downward force.
The relation at the balancing point is given by the following formula (1). Until the first valve portion
23
closes, the pressure at the second port
17
and the spool moving distance increase as the exciting current I increases. When the current I further increases after the first valve portion
23
has been closed, the second valve portion
24
will open, thus communicating the second port
17
to the third port
18
. The pressure at the second port
17
thus drops.
Fpr+Fsol=Fsp (1)
Fsp: force of the spring
14
Fsol: driving force by the electromagnet
15
Fpr: thrust resulting from fluid pressure
Fpr in the above equation is given by:
(P2−P3)·S
wherein P2 is the pressure at the second port
17
(load pressure), P3 is the reservoir pressure, and S is the sectional area of the reaction pin
13
. On the other hand, Fsol equals b·I2 (b is a constant). Thus, the following relations are met:
(P2−P3)·S+b·I2=Fsp
∴P2=(Fsp−b·I2)/S+P3 (2)
Since Fsp, b, S and P3 are all constants, the pressure P2 is proportional to the current I. In the equation (I), (Fsp−Fsol) is the spool driving force by the driving means.
In the arrangement in which the electromagnetic on-off valves
8
,
9
shown in
FIG. 3
are used to introduce fluid pressure from the fluid pressure source (pump) into the wheel cylinder and discharge fluid pressure from the wheel cylinder into the reservoir, if the viscosity of brake fluid changes markedly, while the viscosity is extremely high, brake fluid flows at a slow rate, so that the amount of fluid that passes through the on-off valves decreases. This creates a difference between the pressure range when the fluid viscosity is low (shown by solid line
FIG. 5
) and the pressure range when it is high (chain line).
In the arrangement in which the spool-valve type electromagnetic proportional pressure control valve shown in
FIG. 3
is used to control brake fluid pressure, if the fluid viscosity is extremely high, the actual pressure P rises or falls only slowly as shown in
FIG. 6
, so that it takes a long time for the actual pressure P to reach the target pressure P(n). This means delay in response.
An object of this invention is to provide a method of detecting a brake fluid temperature as a basic data for control without a temperature sensor and a method of controlling brake fluid pressure which can control fluid pressure based on the detected data so that sufficiently accurate control is possible even if the fluid temperature is low and thus its viscosity is extremely high.
SUMMARY OF THE INVENTION
According to this i
Greenblum & Bernstein P.L.C.
Schwartz Christopher P.
Sumitomo Electric Industries Ltd.
Sy Mariano
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