Brake fluid pressure controller

Abstract: An arrangement for preventing the master cylinder (1) of a brake system from getting damaged even if the brake fluid in the master cylinder reservoir is sucked up into the brake circuit during traction control. A wheel brake pressure control valve (5) is provided in the main line (3). The system also includes a discharged fluid reservoir (6) for storing fluid discharged from the control valve (5), a pump (7) for returning the fluid stored in the discharged fluid reservoir (6) into the fluid return point (8) of the main line (3), a traction control changeover valve (16) for checking any fluid flow from the fluid return point (8) toward the master cylinder (1), and an intermediate reservoir (12) provided in the supply line (11) branching from the main line (3) and adapted to communicate with the main line (3) during normal braking. The system further includes a relief valve (15) provided in a connecting line (14) branching from the main line (3) to check any fluid flow from the connecting line (14) toward the intermediate reservoir (12) during traction control. Another changeover valve (13) is provided to open and close communication between the intermediate reservoir (12) and the discharged fluid reservoir (6).

Description: This invention relates to a brake fluid pressure controller having both the functions as an antilock controller and a traction controller. An antilock controller in the simplest form is known as a fluid return type. It comprises a wheel brake fluid pressure control valve including a discharge valve and provided in a main fluid line extending from the master cylinder to wheel brakes, a discharged fluid reservoir for temporarily storing the brake fluid discharged from the discharge valve, and a circulation pump for sucking up brake fluid in the discharged fluid reservoir and returning it to the main fluid line. If it is desired to add the traction control function to this device, the simplest and most efficient way to do so is to use the circulation pump as a pressure source for the traction control. In order to use the pump for this purpose, it is necessary to supply brake fluid to the inlet port of the pump. There are several known methods for supplying brake fluid to the pump inlet. These methods are roughly classified into two types. In one type, a fluid supply line is provided which extends directly from a reservoir of the master cylinder to the pump inlet. In the other type, such a fluid supply line branches from the main fluid line connecting the outlet of the master cylinder to a wheel brake. The latter arrangement is more advantageous because the entire device can be more easily mounted on the wheel and because there is no need to return brake fluid from the inlet of the master cylinder to its reservoir. In the latter arrangement in which the fluid supply line branches from the main fluid line, it is necessary to provide a traction control changeover valve to check the fluid flow from the point at which the fluid discharged from the pump flows into the main fluid line, toward the master cylinder during traction control, and provide a shutoff valve to check the fluid flow from the fluid supply line toward the discharged fluid reservoir during a normal braking mode (while pressure is being applied to the master cylinder). One problem with the latter arrangement is that the amount of brake fluid supplied to the pump tends to be limited due to intake resistance at the inlet of the master cylinder, flow resistance in the piping from the master cylinder to the brake fluid pressure controller, and flow resistance in the shutoff valve for closing the fluid supply line during normal braking, so that the brake fluid pressure may not rise quickly at the initial stage of traction control. One way to solve this problem is to provide an intermediate fluid reservoir in the fluid supply line, as disclosed in the European patent application EP-A-539 898 (see especially Fig. 4). The arrangement including such an intermediate fluid reservoir has the following problems. Such an intermediate fluid reservoir is so adapted that when the fluid pressure in the intermediate fluid reservoir drops below the atmospheric pressure, its volume will decrease, so that the internal fluid pressure is always kept substantially equal to the atmospheric pressure. Upon completion of traction control, its volume increases by the force of a spring or the resilience of a rubber member until it becomes equal to the initial volume. Thus, if the traction control continues for a long time, brake fluid in the reservoir of the master cylinder may be drawn through the fluid supply line into the intermediate fluid reservoir during traction control because of the tendency of the intermediate reservoir to get back to high-volume side. If a brake is applied while the brake fluid in the reservoir of the master cylinder is being sucked into the intermediate reservoir during traction control, a greater amount of brake fluid than the brake fluid sucked into the brake circuit in an amount corresponding to the stroke of the brake pedal during a normal braking mode will be sucked into the brake circuit. If, in this state, the brake pedal is released, the cup seal in the master cylinder (in the case of a conventional master cylinder) or the rubber seal of center valve (in the case of a center-valve type master cylinder) will be gnawed by the side port when passing therethrough. Such a problem could occur with any type of master cylinder, including the abovementioned conventional type, a center-valve type single master cylinder, conventional + conventional type, center valve + center valve type, or center valve + conventional tandem master cylinder, and other types (e.g. tilt-valve type). An object of the present invention is to provide a brake fluid pressure controller in which excess brake fluid is prevented from being supplied into the brake circuit. The present invention achieves this object with the features of claim 1. The brake fluid pressure controller according to the present invention includes a traction control valve and further comprises an intermediate fluid reservoir which communicates with the main fluid line at least during normal braking mode, and a second changeover valve provided between the fluid supply line and the discharged fluid reservoir for shutting off fluid communication between the fluid supply line and the discharged fluid reservoir during traction control. This intermediate fluid reservoir is so arranged that when the internal pressure of the intermediate fluid reservoir drops below the atmospheric pressure, its volume will decrease until its internal pressure becomes substantially equal to the atmospheric pressure, that said intermediate fluid reservoir communicates with the fluid supply line while the volume of the intermediate fluid reservoir is smaller than its initial volume, and that the volume of the intermediate fluid reservoir increases while the fluid pressure of the reservoir of the master cylinder is being applied to the intermediate fluid reservoir. During traction control, the second changeover valve completely shuts off fluid communication between the pump inlet and the fluid supply line. Thus, the pump can suck up only the fluid in the intermediate fluid reservoir and the discharged fluid reservoir. It will never suck up fluid in the reservoir of the master cylinder. According to this invention, an intermediate fluid reservoir is provided in the fluid supply line. With this arrangement, it is possible to eliminate the influence of the intake resistance at the inlet of the master cylinder and the flow resistance in the piping from the master cylinder to the brake fluid pressure controller. This makes it possible to supply brake fluid to the pump with higher efficiency. Thus, it is possible to raise the brake fluid pressure sufficiently quickly at the initial stage of traction control while keeping the structure of the entire controller as simple as possible. According to this invention, fluid communication between the pump inlet and the fluid supply line is completely shut off during traction control. Thus, there is no possibility of the brake fluid in the reservoir of the master cylinder being sucked into the pump during traction control. Thus, it is possible to prevent damage to the master cylinder. Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which: Fig. 1 is a circuit diagram of First Embodiment; Fig. 2 is a circuit diagram of Second Embodiment; Figs. 3A and 3B are circuit diagrams of Third Embodiment; and Fig. 4 is an enlarged vertical sectional view of an embodiment of the intermediate fluid reservoir. Fig. 1 shows a three-position control ABS (antilock brake system). In this arrangement, the main fluid line communicates with the fluid supply line at all times. The traction control changeover valve used in this embodiment is a two-port, two-position valve provided between a branching point at which the fluid supply line branches from the main fluid line and a fluid return point at which the fluid discharged from the pump returns to the main fluid line. A master cylinder 1, which is operated by a brake pedal, has two fluid outlets 2 (a booster may be added to the master cylinder). Since two lines from the two outlets are identical, we will describe only one of them. A wheel brake fluid pressure control valve 5 having a discharge valve is provided in a main fluid line 3 through which the outlet 2 communicates with a wheel brake 4. This valve 5 may be a three-position type which can be changed over among three positions, i.e. pressure-increase, pressure-hold and pressure-decrease positions. Otherwise, it may be a two-position type that lacks the pressure-hold position. In many cases, check valves are provided parallel to this control valve to allow quick brake pressure reduction when the brake pedal is slackened during antilock control (though not shown in the drawings). While the wheel brake fluid pressure control valve 5 is in the fluid discharge position, the wheel brake 4 communicates with a discharged fluid reservoir 6. A pump 7 sucks brake fluid in the discharged fluid reservoir 6 and feeds it toward a fluid return point 8 in the main fluid line. Though not shown, a combination of a fluid reservoir as a damper and a throttle is frequently used to avoid pulsation of the flow of fluid that has been discharged from the pump 7. We have so far described the basic construction of a fluid-return type antilock brake fluid pressure controller. In order that this system can be used as a traction control as well, the following elements are added. A fluid supply line 11 is provided which branches from the main fluid line 3 at a branch point 17 upstream of the fluid return point 8 and leads to an intermediate fluid reservoir 12. A second changeover valve 13 is provided in the fluid supply line 11 between the discharged fluid reservoir 6 and an intermediate fluid reservoir 12. A relief valve 15 is provided in a line 14 through which the intermediate reservoir 12 communicates with the main fluid line 3. It discharges brake fluid in the fluid communication line into the intermediate fluid reservoir if the pressure in the fluid communication line exceeds a maximum pressure necessary for traction control. A traction control changeover valve 16 including a shutoff valve is provided in the main fluid line 3 at a point between the branch point 17 and the fluid return point 8. As shown in Fig. 4, the intermediate fluid reservoir 12 accommodates a piston 20 and a spring 21 and has top and bottom openings through which its interior communicates with the fluid line 14 and the atmosphere, respectively. When the interior pressure drops below the atmospheric pressure, the piston 20 will be pushed up by the atmospheric pressure while pressing the spring. As a result, the effective reservoir volume decreases. The wheel brake fluid pressure control valve 5 in this embodiment is a three-port, three-position electromagnetic changeover valve which can be changed over among pressure-increase, pressure-hold and pressure-reduction positions. The second changeover valve 13 is a three-port, two-position pressure-responsive changeover valve. As the traction control changeover valve 16, an electromagnetic changeover valve is used. Though not shown, this system has an electronic control unit for controlling the control valve 5, changeover valve 16, and the pump 7, in response to wheel speed signals from wheel speed sensors. In this embodiment, during normal braking mode, the wheel brake fluid pressure control valve 5 is in the position shown in Fig. 1 in which the main fluid line 3 is shut off from the discharged fluid reservoir 6 and communicates with the wheel brake 4. During normal braking and antilock control mode, with the pressure from the master cylinder overcoming the bias by the spring force, the second changeover valve 13 takes the position shown in Fig. 1 in which the intermediate fluid reservoir 12 communicates with the fluid supply line 11. During traction control mode, the traction control changeover valve 16 is activated to close the main fluid line 3 between the points at which the fluid supply line 11 and the fluid line 14 connect with the main fluid line, respectively. In this state, the second changeover valve 13, triggered by the master cylinder pressure, will take a spring-biassed normal position where the intermediate fluid reservoir 12 is shut off from the fluid supply line 11 and communicates with the discharged fluid reservoir 6. Thus, in this state, the pump 7 sucks up fluid only from the intermediate fluid reservoir 12 and the discharged fluid reservoir 6. In other words, it will never suck up fluid from the reservoir of the master cylinder 1. In the second embodiment shown in Fig. 2, an electromagnetic changeover valve is used as the second changeover valve 13, while a pressure-responsive type changeover valve is used as the traction control changeover valve 16. Fig. 2 shows the state in which neither normal braking nor antilock or traction control operates. Otherwise, this embodiment is the same as the first embodiment. Thus, the same parts are denoted by the same numerals and their description is omitted. The controller of the third embodiment shown in Fig. 3 is a two-position control ABS. As the traction control changeover valve 16, a three-port, two-position electromagnetic changeover valve is used. As the second changeover valve 13, a pressure-responsive type changeover valve is used which is triggered by the master cylinder pressure. In this arrangement, the three-port, two-position traction control changeover valve 16 is connected so that the master cylinder 1 communicates with the wheel cylinder during traction control. Thus, it is possible to increase the brake pressure sharply when a sharp brake is applied during traction control. Fig. 3A shows the state during normal braking mode. Fig. 3B shows the state during traction control mode.

Claims: A brake fluid pressure controller comprising a wheel brake fluid pressure control valve (5) including a discharge valve provided in a main fluid line (3) extending from a master cylinder (1) having a master cylinder reservoir to a wheel brake (4), said master cylinder (1) having a master cylinder reservoir which is in the rest position of the master cylinder (1) in communication with said main fluid line (3), a discharged fluid reservoir (6) for temporarily storing the brake fluid discharged from said discharge valve, a pump (7) for sucking up the brake fluid in said discharged fluid reservoir (6) and returning it to the main fluid line (3) at a fluid return point (8) located between said master cylinder (1) and said wheel brake fluid pressure control valve (5), a traction control changeover valve (16) located between said fluid return point (8) and said master cylinder (1) for checking the fluid flow from said return point (8) toward the master cylinder (1), an intermediate fluid reservoir (12) of the type having a tendency to return to its state of maximum volume, a second changeover valve (13) which controls the fluid flow from a fluid supply line (11) branching from the main fluid line (3) to said intermediate fluid reservoir, a fluid communication line (14) branching from the main fluid line (3) at a point downstream of said traction control changeover valve (16) and leading to said intermediate fluid reservoir (12), and a relief valve (15) provided in said fluid communication line for discharging brake fluid in said fluid communication line (14) into said intermediate fluid reservoir (12) if the pressure in said fluid communication line (14) exceeds a maximum pressure necessary for traction control, characterized in that said fluid supply line (11) branches from the main fluid line (3) at a point upstream of said traction control changeover valve (16), that, at least during the normal braking mode, said second changeover valve (13) enables fluid communication between said intermediate fluid reservoir (12) and the main fluid line (3) via said fluid supply line (11) and shuts off fluid communication between said intermediate fluid reservoir (12) and said discharged fluid reservoir (6), and that, during the traction control mode, said second changeover valve (13) completely shuts off fluid communication between the intermediate fluid reservoir (12) and said fluid supply line (11) and permits fluid communication between said intermediate fluid reservoir (12) and said discharged fluid reservoir (6). A brake fluid pressure controller as claimed in claim 1, characterized in that said second changeover valve (13) permits fluid communication between said fluid supply line (11) and said intermediate fluid reservoir (12) during the normal braking mode and the antilock brake control mode. A brake fluid pressure controller as claimed in claim 1 or 2, characterized in that said intermediate fluid reservoir (12) is so arranged that when the internal pressure of the intermediate fluid reservoir (12) drops below the atmospheric pressure, its volume will decrease until its internal pressure becomes substantially equal to the atmospheric pressure, that said intermediate fluid reservoir (12) communicates with said fluid supply line (11) while the volume of said intermediate fluid reservoir (12) is smaller than its initial volume, and that the volume of said intermediate fluid reservoir (12) increases while the fluid pressure of the master cylinder reservoir is being applied to said intermediate fluid reservoir (12). A brake fluid pressure controller as claimed in claim 1 or 2, characterized in that said second changeover valve (13) is a pressure-responsive changeover valve triggered by the master cylinder pressure. A brake fluid pressure controller as claimed in claim 1 or 2, characterized in that said traction control changeover valve (16) is a pressure-responsive changeover valve triggered by the master cylinder pressure. A brake fluid pressure controller as claimed in claim 1 or 2, characterized in that said traction control changeover valve (16) is a three-port, two-position valve provided in the main fluid line (3) downstream of a point at which said fluid supply line (11) branches from the main fluid line (3) for selectively bringing the master cylinder (1) into communication with said fluid return point (8) from the pump (7) or said wheel brake (4).

Inventors: KOHNO TERUHISA, TAKATA KOJI, KOHNO, TERUHISA, TAKATA, KOJI, KOHNO, TERUHISA, C/O ITAMI WORKS OF, TAKATA, KOJI, C/O ITAMI WORKS OF
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LTD.
Application year: 1995
Main classification: B60T8
IPC codes: B60T8