Pressure regulating device for a spring-applied brake

Abstract

Pressure regulating device for a spring-applied brake (12), comprising a control valve arrangement (26, 32) that regulates the flow of hydraulic fluid from a pressure source (22) to the spring-applied brake (12) and the flow of hydraulic fluid from the spring-applied brake to a tank (18), and comprising a safety device (36, 38) that limits the pressure in the spring-applied brake to a preset value in the event of a malfunction, characterized in that the control valve arrangement has a normally closed supply valve (26) between the pressure source (22) and the spring-applied brake (12) and a normally open drain valve (32) between the spring-applied brake and the tank (18), and that the safety device has a normally open switching valve (36) that connects the spring-applied brake (12) to the tank (18) via a downstream pressure relief valve (38) in parallel to the drain valve (32).

Description

[0001] The invention relates to a pressure control device for a spring-applied brake, comprising a control valve arrangement that regulates the flow of hydraulic fluid from a pressure source to the spring-applied brake and the flow of hydraulic fluid from the spring-applied brake to a tank, and comprising a safety device that limits the pressure in the spring-applied brake to a preset value in the event of a malfunction.

[0002] Rail vehicles such as trams are often equipped with electro-hydraulic spring-applied brakes capable of generating sufficient braking force even in the event of a power failure. The brake is pre-tensioned into its braking position by spring force, and to release the brake or modulate the braking pressure, a suitable pressure must be built up in the spring-applied brake using the control valve assembly. If, due to a power failure or other malfunction, the control valve assembly no longer functions correctly, the pressure in the spring-applied brake should be limited by the safety device so that the vehicle is brought to a standstill by braking.

[0003] A pressure regulating device of the type mentioned above is known in practice, in which the regulating valve arrangement is formed by an electronically controlled proportional valve. The safety device is formed by a 3 / 2-way valve which, when energized, connects the regulating valve arrangement to the spring-applied brake and, upon switching to the de-energized state, disconnects this connection and instead connects the spring-applied brake to the tank via a pressure relief valve. The pressure relief valve is set to close as soon as the pressure in the spring-applied brake has dropped to the desired minimum pressure.

[0004] In the known pressure regulating device, the proportional valve, typically a piston spool valve, inevitably exhibits a certain amount of leakage. This necessitates the inclusion of a leakage control valve in the line to the tank. When energized, this valve captures the leakage flow and is only open when de-energized. This requires additional installation space in the vehicle. The space requirement is further increased by the relatively large dimensions of the valves used in the pressure regulating device. Firstly, the valve flow cross-sections, and consequently the valve bodies, must be large enough to ensure the hydraulic system functions even at low temperatures and with correspondingly high viscosity of the hydraulic fluid. Secondly, the valve coils must be dimensioned to ensure reliable switching at the operating voltage supplied by the vehicle. This also results in certain minimum dimensions for the coils.

[0005] The object of the invention is to create a pressure regulating device that can be used flexibly in different vehicle systems without compromising operational safety.

[0006] This problem is solved according to the invention by the control valve arrangement comprising a normally closed supply valve between the pressure source and the spring-applied brake and a normally open discharge valve between the spring-applied brake and the tank, and by the safety device comprising a normally open switching valve that connects the spring-applied brake to the tank via a downstream pressure relief valve in parallel with the discharge valve. Dividing the function of the control valve arrangement into two separate valves allows the use of a robust and virtually leak-free switching valve in the safety device instead of a 3 / 2-way valve. This switching valve requires comparatively little installation space and, moreover, eliminates the need for an additional leakage protection valve.Reducing the required installation space increases the design freedom when installing the pressure regulating device in different vehicle environments.

[0007] Advantageous embodiments and further developments of the invention are specified in the dependent claims.

[0008] While a switching operation of the control valve can, in principle, be achieved simply by disconnecting or reconnecting the valve coil to the supply voltage, it is more practical to control the control valve via an electronic ballast. The control valve, for example a poppet valve, requires only a small holding current in the closed state (the normal operating state). The ballast allows the current to be controlled or regulated so that a high initiation current is provided only when the valve is switched, while the current flow is reduced to the comparatively small holding current after switching to the closed state. This reduces not only the power consumption but also the heat generation of the pressure regulating device.

[0009] Another advantage is that the ballast allows for flexible adaptation to the different supply voltages provided by the vehicle. Even if the available operating voltages vary from vehicle type to vehicle type, valves with identically dimensioned coils can then be used in the different vehicle types, resulting in rationalization effects through the standardization of components.

[0010] The control units or drivers for the supply and drain valves can also include adjustable voltage converters, which transform the voltage supplied by the vehicle into the voltages required by the coils. Robust two-way poppet valves can then be used as the supply and drain valves, their coils designed for operation at a fixed voltage of, for example, 12V. These valves are characterized by their small size and are largely insensitive to particle contamination of the hydraulic fluid. Overall, this further reduces the required installation space. At the same time, the requirements for the vehicle's electrical system are relaxed, allowing identical pressure regulating devices to be used in a wider range of vehicle types.

[0011] In one embodiment, control units are provided for the switching valve, the supply valve, and the drain valve. The switching valve control unit and the supply valve control unit are powered via a common interface, while the drain valve control unit is powered via a separate interface. If the common interface fails, the pressure in the spring-applied brake is not reduced to zero, which would result in the vehicle braking fully. Instead, the pressure only drops to a value determined by the pressure relief valve, at which point the vehicle is safely brought to a stop.

[0012] The following section explains an exemplary embodiment in more detail with reference to the drawings.

[0013] They show: Fig. 1 a hydraulic diagram of a pressure control device according to the invention; and Fig. 2 a current / time diagram of a ballast for a switching valve in the pressure regulating device.

[0014] Fig. Figure 1 shows the essential components of a hydraulic device 10 that controls the hydraulic pressure of a spring-applied parking brake 12 of a rail vehicle. A pump 16, driven by a brushless motor 14, draws hydraulic fluid from a tank 18 and delivers it via a check valve 20 to a pressure accumulator 22, which forms a pressure source for the pressure control device. A pressure relief valve 24, connected between the pressure accumulator 22 and the tank 18, limits the pressure in the pressure accumulator to a mechanically adjustable value.

[0015] The pressure accumulator 22 is connected to the inlet of a normally closed supply valve 26, the outlet of which is connected to the spring-applied brake 12. The supply valve 26 is designed as a two-way poppet valve and can be controlled by a power driver 28 in an electronic control unit 30 such that the flow rate to the spring-applied brake 12 varies continuously.

[0016] The outlet of the supply valve 26 and the spring-applied brake 12 are connected to the inlet of a normally open drain valve 32, the outlet of which is connected to the tank 18. The drain valve 32 can be controlled by a control device 34 so that the flow rate of the hydraulic fluid from the spring-applied brake also varies continuously.

[0017] In normal driving operation, the supply valve 26 is open and the release valve 32 is closed, so that the maximum pressure supplied by the pressure accumulator 22 is present at the spring-applied brake 12, and thus the spring-applied brake is fully released. During a braking operation, the pressure in the spring-applied brake 12 is regulated by the control of the supply valve 26 and the release valve 32 so that the spring-applied brake provides the required braking force.

[0018] The outlet of the supply valve 26 and the spring-applied brake 12 are connected to the inlet of a normally open switching valve 36, the outlet of which is connected to the tank 18 via a pressure relief valve 38. A control unit 40 keeps the switching valve 36 closed during driving and also during braking. The control units 40 and 28 for the switching valve 36 and the supply valve 26 are supplied with power via a common interface X2. In the event of a power failure, the switching valve 36 opens while the supply valve 26 closes, so that the hydraulic fluid from the spring-applied brake 12 flows through the pressure relief valve 38 into the tank until the closing pressure of the pressure relief valve is reached. This closing pressure, which also determines the remaining pressure in the spring-applied brake 12, can be manually adjusted to ensure that the vehicle is braked with a safe deceleration.As long as the X1 interface remains intact, a wear-prone and potentially dangerous emergency stop can be prevented.

[0019] The control unit 34 for the drain valve 32 is supplied with operating voltage via a separate interface X1. In the event of a voltage failure, the drain valve 32 opens, and the pressure in the spring-applied brake 12 drops at a rate determined by the flow cross-section of the drain valve 32. This also brings the vehicle to a standstill in this case.

[0020] Another interface, X3, provides the operating voltage for motor 14 via a further control unit 42. Control units 28, 34, 40, and 42 contain adjustable voltage converters that transform the supply voltages provided via interfaces X1-X3 into the voltages required by the consumers, namely motor 14 and the valve coils. This allows the pressure control device to be easily adapted to different vehicle types that provide different supply voltages.

[0021] The ballast 40 also has the function of regulating the current flow through the coil of the switching valve 36 depending on the time. Fig. Figure 2 shows possible current / time curves for a switching operation of the switching valve 36. Curves 44 and 46 in Fig. Figure 2 shows the current I flowing through the valve coils as a function of time t. Assume that at time t = 0 the command to release the brake arrives, so that the switching valve 36 must change from the de-energized, open state to the closed state. The ballast 40 then increases the current according to curve 44 until it reaches the value I1, which corresponds to the rated current of the coil. This rated current indicates the current required to ensure that the valve actually switches. The current then remains at this level for a certain time interval, until time t1. At the latest by time t1, the valve has reached its closed position. Since the air gap in the magnetic circuit of the valve has then practically decreased to zero, the coil has its maximum inductance, and a lower current, the so-called holding current, is sufficient to keep the valve in the closed position.The ballast 40 therefore reduces the current to a lower value I2, which corresponds to the holding current. During the time the valve remains closed, power consumption and heat generation are thus reduced. If, at time t2, the command is given to switch the control valve 36 back to the open position, the ballast reduces the current, and as soon as the current falls below a certain threshold, the valve returns to the open position by spring force.

[0022] Curve 46 in Fig. Paragraph 2 describes the case where over-excitation occurs during the valve's closing phase; that is, in the interval between t=0 and t=t1, the current is regulated to a closing current greater than the nominal current. In this case as well, after a time interval at least equal to the valve's closing time plus a certain reserve, the current is reduced back to the holding current I2.

Claims

[1] Pressure control device for a spring brake (12), with a control valve arrangement (26, 32) which controls the flow of hydraulic fluid from a pressure source (22) to the spring brake (12) and the flow of hydraulic fluid from the spring brake to a tank (18), and with a safety device (36, 38) which limits the pressure in the spring brake to a preset value in the event of a fault, characterized by that the control valve arrangement has a normally closed supply valve (26) between the pressure source (22) and the spring-loaded brake (12) and a normally open drain valve (32) between the spring-loaded brake and the tank (18), and that the safety device has a normally open switching valve (36) which connects the spring-loaded brake (12) to the tank (18) via a downstream pressure relief valve (38) parallel to the drain valve (32). [2] Pressure control device according to claim 1, wherein at least one electronic ballast (28, 34, 40) is provided for controlling the supply valve (26) and / or the discharge valve (32) and / or the switching valve (36). [3] Pressure control device according to claim 2, wherein a control device (30) is provided for generating setpoint values ​​for the current control of at least one of the ballasts (28, 34, 40). [4] Pressure control device according to claim 3, in which a ballast (28) for controlling the supply valve (26) and a ballast (34) for controlling the discharge valve (32) are provided and the control device (30) is designed to adapt the setpoint value for these ballasts (28, 34) so ​​that the desired pressure is established in the spring brake (12). [5] Pressure control device according to claim 3 or 4, in which a ballast (40) is provided for controlling the switching valve (36) and the control device (30) is designed to lower the setpoint value for this ballast (40) after a certain operating time required by the valve for switching. [6] Pressure control device according to one of claims 3-5, wherein the ballast (40) of the switching valve (36) and the ballast (28) of the supply valve (26) are supplied with energy through a common interface (X2) and the ballast (34) of the discharge valve (32) is supplied with energy through a separate interface (X1). [7] Pressure control device according to claim 6, wherein the opening pressure of the pressure relief valve (38) is mechanically adjustable. [8] Pressure control device according to one of the preceding claims, in which the supply valve (26), the discharge valve (32) and the switching valve (36) are designed as leak-free seat valves.

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