GB2042112A - Brake pressure modulating valves - Google Patents

Abstract

An anti-skid modulating valve i) of the kind shown in Figure 1 with an inlet 7 and an outlet 8 to a brake cylinder. An expander piston is moved to the right by a spring 10 to close valve 5 and expand the volume of the chamber 9, so reducing the brake pressure. The piston is normally held in the position shown by a solenoid 6. In the modification according to the invention (Figure 2), the piston is in two parts 3a and 3b. A spring 12 urges them apart, causing detents 11 to lock the part 3a to the housing 13. When the solenoid 6 is energised, the parts 3a, 3b move together against the force of the spring 12, and if the solenoid is subsequently de-energised, the composite piston can move to the right to reduce the brake pressure. <IMAGE>

Description

Pressure reducer in an antilocking device of a braking system The invention relates to a pressure reducer in an antilocking devive of a braking system.

Directly acting braking systems, provided with an automatic control of the braking moment /by means of an antislide governor, reduce pressure in a wheel member of a brake by pumping liquid out of the brake back to a main cylinder by means of an action member. This pumped quantity -if a back "kick" of a brake pedal should not come in question- must be forced into an accumulator, which simultaneously serves as a pressure limiter, so that an action member may not work against an uncontrolled high pressure, which may be provided in the main cylinder by a driver.

There is a drawback in such a system, viz. that it must also comprise an accumulator with a pressure limiter besides an action member. An other disadvantage resides in the fact that the action member must always work against pressure provided by a driver upto the pressure value adjusted by a limiter.

There are also known antislide governors provided with action members controlled electromagnetically and working on the principle of delivery against the main brake cylinder. It is necessary, for a good function of these governors, that a piston of the action member, after ending each antilock period, may take its initial position. This effect is reached, as to hitherto known governors in fact in two ways. One way resides in applying a spring pushing the piston of the action member into the initial position. The application of this spring requires a bigger dimension of a control electromagnet of the action member, because its effect onto the piston must surpass, besides a pressure effect of the brake liquid provided by pushing down the brake pedal, also a force effect of this spring.The other way resides in applying a freely seated piston of the action member, which takes its initial position only by an effect of different pressure on both sides of the piston, what makes in practice a considerable problem, because a perfect tightness of a stop valve must be ensured.

If there exists any untightness, liquid penetrates in the brake space, what causes that the piston does not return into its initial position, when the antilock period is over, but it returns by a stoke being diminished by the value corresponding with the volume of penetrated liquid. This process repeats at a repeated antilock period upto the condition, when it is in fact impossible to relieve the brake; in this way the antilock governor is put out of operation. In this case it is necessary to relieve and to push down again the brake pedal, what decreases an active safety. The said drawback may also take place if it concerns an embodiment of relieving pistons provided with a spring, especially of the dimension of the spring is not sufficient or if the initial characteristic of the spring is changed, e.g. by a fatigue of material.

Other known devices, which may be taken as a previous stage of the invention, may be characterized as an action member for an antislide governor controlled electromagneticly and working on the principle of a delivery against the main brake cylinder, where the relieving piston is carried out as a differential one, its function surface subjected to pressure from the main cylinder is larger than its function surface subjected to pressure from the wheel brake cylinder, and the space between the action surfaces of the cylinders is connected to atmosphere.

The action member for an antislide governor according to the invention ensures always a correct function of an antilock mechanism, because the relief piston of the action member takes always its initial position after the anitlock period is over. This effect is got only by applying a relief differential piston. The action member of an antilock system of this device is put into function by switching on the electrical current.

The aim of the invention is to provide a device having an only member, which enables, during an ordinary braking, a free passage or liquid from the main cylinder to the brake and back, so that-after an impulse from the governor- the passage from the main cylinder is closed /the brake pedal is stiff/ and liquid from the brake is put back into this member, so that pressure in the brake falls down. If the impulse from the governor disappears, liquid is pushed back into the brake and the passage to the main cylinder is open again.

The mentioned drawbacks may be obviated by the pressure reducer in an antilock device of a braking system, enabling under ordinary conditions of braking a free passage of liquid and closing the passage, after having received an impulse from the governor, during the lasting of the impulse at a simultaneous pressure reducing in a part of the braking system to brake cylinders, a central portion of which is carried out as a differential piston, the function surface of which, subjected to pressure from the main brake cylinder, is larger than its function surface subjected to the pressure from a wheel brake cylinder according to the invention, the principle of which resides in a central portion being carried out in two parts, the outer part of which forms a hollow cylinder, in which an axially movable inner part is situated, being sprung with respect to the outer part by means of a spring and being ended by a conical surface, linking up to a cylindrical step of the inner part and marking a guidewayfor balls, leaning against it, and being pushed against the outer part of the central portion by means of a holding-down element and spring.The relation between the spring force and weight of the inner part of the central portion is represented by an equation F/m2 < 30.S/mand m = m1 + m2, whereF means a force of a spring S means a piston surface m1 means weight of the outer part of the central portion m2 means weight of the inner part of the central portion With respect to hitherto known embodiments the pressure reducer according to the invention is put into function by switching off electrical current - what accelerates the governing process - and more over, only one piston is here as an action member by which several-parts systems of hitherto known embodiments /accumulator and action member/ are replaced.

In order that the invention may be clearly understood and readily carried into effect, a preferred embodiment thereof is, by way of example, hereinafter more fully described and illustrated in the accompanying drawing, in which Figure 1 shows a principle of a pressure reducer in an axial section; Figure 2 shows an embodiment for ensuring a free passage of liquid even at a fall-out of electrial current.

Figure 3 shows the detail of the cylindrical step between the inner part of the core and its cylindrical face.

According to the principle of a pressure reducer shown in Figure 1, the device consists of a body 1 having a shape of a cylinder. In the said body 1 there moves a piston 2, which transits in a central portion 3 /as to its right part/and in a push button 4/as to its left part/ carrying on its end a valve 5. A solenoid 6 is arranged round the central portion 3 in the body 1. The valve 5 controls the passage of liquid delivered into the body 1 through an inlet hole 7 from the main cylinder, and flowing away through an outlet hole 8 after passing a chamber 9. The passage is controlled by the said valve 5 forced down to the seat by means of a spring 10.

The device works in this principle arrangement as follows: If current passes the solenoid 6, the central portion 3 /the core/ is pulled by a magnetic force into the body 1 /towards left/and the piston 2 connected to it by means of the push button 4 forces the valve 5 from the seat, and liquid may freely pass the inlet hole 7 from the the main cylinder through the chamber 9 to the to the outlet hole 8 and from there to the brake. If there is pressure in the brake, and current in the solenoid 6 is switched off, the magnetic force between the central portion 3 and body 1 disappears, the piston 2 is forced to right by pressure existing in the chamber 9, and by functioning the spring 10, the valve 5 bears against the seat, and in this way the passage from the main cylinder is closed.In the chamber 9 and in the brake connected to it the pressure falls down without limits, because the piston 2 may be freely pushed out of the body 1 /towards right. if electrical current is switched on into the solenoid 1 again, the magnetic flow between the core 3 and body 1 pushes the piston 2 to the left and pressure in the chamber 9, and of course in the brake as well, rises to the initial value. If the core 3 bears against the face of the body 1, the valve 5 is open again by means of the push button 4 and pressure of the main cylinder affects the brake again.

To ensure a free passage of liquid through the device according to the invention even at a fall-out of electrical power, it is possible to arrange an other aditional device, working on an inertion principle, which in a standstill condition /the solenoid is not under current/ ensures mechanically the core in an extreme left position, but it allows at disappearing the current of the solenoid - after its previous exciting - a free movement of the core to the right, and in this way the pressure reducing in the brake.

This additional device, shown in Figure 2, is provided with a two-parts core, consisting of an outer part 3a of the core and of an inner part 3b of the core. Several radial holes are arranged in the outer part 3a of the core in its hollow cylindrical part surrounding the inner part 3b of the core. In the said holes there are seated balls 11.Both parts of the core are -in a standstill condition /solenoid 6 without current/- pushed, one from the other, by means of a spring 12; the outer part 3a of the core is pushed to the left to the body 1, the inner part 3b of the core is pushed to the right, so that its conical face pushes the balls 11 radially, and the balls 11 lean against a cover 13 closing the body 1, and in this position they make impossible for the outer part 3a of the core and in this way also to it connected piston 2 and push button 4 to move to the right A free passage of liquid through the valve 5 from the main cylinder to the brake and back is ensured in this way /a braking at a fall-out of electrical power/.

The pressure reducer with an aditional device works as follows: If current is switched on into the solenoid 6, the inner part 3b is pulled to the left to the outer part 3a of the core and both parts are holded together by a magnetic force on the body 1/an ordinary braking/. If a fall-out of electrical power in the solenoid 6 comes in question during the function of the pressure reducer, and there is pressure in the chamber 9, the piston 2 together with both parts 3a and 3b is rapidly pushed to the right, and pressure in the brake diminishes. The balls 11 does not prevent this motion, as they are not radially pushed out and that is why they does not lock the outer part 3a of the core against the cover 13.There is a condition for the said function, viz. that the acceleration, which is affected by pressure of the piston 2 to both parts of the core 3a and 3b, may be greater than the acceleration which may be provided by the spring 12 of the inner part 3b of the core, so that both part of the core may stay connected during the movement to the right and that they may be not pushed one from the other. This condition may be reached, if the inner part 3b is sufficiently heavy and the spring 12 tiny. This requirement is followed, if the relation of the force of the spring 12 and of the weight of the inner part 3b corresponds with the equation: F/m2 < 30.S/mand m = m1 + m2 where F means a force ofthe spring S means an area of the piston m1 means a weight of the outer part of the core m2 means a weight of the inner part of the core If at the end of the function of the pressure reducer electrical power is switched on into the solenoid again, both parts 3a and 3b will be pulled to the left into the body 1 and the piston 2 increases again pressure in the brake to the initial value. After the outer part 3a of the core has beared against the face of the body 1, the valve 5 opens and the main cylinder will be connected to the brake, and an ordinary braking comes in question.The braking being at the end, the pressure in the chamber 9 disappears and electrical power is switched off in the solenoid 6. The spring 12 pushes both parts 3a and 3b one from the other, the balls 11 are radially pushed out against the cover 13 and so they lock the outer part of the core 3a and together with it also the piston 2 and valve 5 in a standstill position, so that the passage through the device is free.

An alternative design of a locking mechanism resides in the fact, that the inner part 3b of the core is provided with a cylindrical step, against which balls 11 bear in a locked position of the core. The balls are pushed against the outer part 3a of the core by means of a holder which is pushed by a spring against the body 1, and in this way the outer part 3a of the core is kept in the basic position, where it bears against the face of the body 1.

Although the invention is illustrated and described with reference to one preferred embodiment thereof, it is to be expressly understood that it is in no way limited to the disclosure of such a preferred embodiment but it is capable of numerous modifications within the scope of the appended claims.

Claims (3)

1. A pressure reducer in an antilock device of a braking system, enabling under ordinary conditions of braking a free passage of liquid and closing the passage after having received an impulse from a governor, during the lasting of the impulse at a simultaneous pressure reducing in a part of the braking system to brake cylinders, a core of which is carried out as a differential piston, the function surface of which, subjected to pressure from the main brake cylinder, is larger than its function surface subjected to the pressure from a wheel brake cylinder, comprising a core being carried out in two parts, the outer part of which forms a hollow cylinder, in which an axially movable inner part is situated, being sprung with respect to the outer part by means of a spring and being ended by a conical surface, linking up to a cylindrical step of the inner part and forming a guideway for balls, leaning against it, and being pushed against the outer part of the core by means of a holding-down element and spring.

2. A pressure reducer as in claim 1, wherein the relation between the spring force and weight of the inner part of the core is represented by an equation F/m2 < 30.S/mand m = m1 + m2 where F means a force of the spring S means a piston area m1 means a weight of the outer part of the core m2 means a weight of the inner part of the core

3. A pressure reducer in an antilock device of a braking system, substantially as described with reference to the accompanying drawings.