JPH0313109B2 - - Google Patents

Description

Claim 1: A brake control system 10 for operating a spring-based pressure release brake 11 between an engaged state and a released state that respectively stop and permit rotation of a rotatable member 12, comprising: a pump 16; a control valve 19 having an inlet 18 connected to and an outlet 22 connected to the working chamber 14 of the brake;
a control valve movable between a first position in which the control valve closes the inlet from the outlet and a plurality of operating positions in which the control valve controllably adjusts communication between the inlet and the outlet; a metering pump 23 with its inlet connected to the working chamber 14 of the brake, said metering pump being drivingly connected to the rotatable member 12; and an outlet 26 of the metering pump connected to the control valve 19. A metering pump inlet 24 and a metering pump outlet in a brake control system that includes a conduit connecting to the inlet 18 and a pressure maintenance device 29 that typically maintains the pressure in the conduit 28 at a predetermined pressure level sufficient to release the brake. a pressure relief device 36 for relieving pressure in the outlet 26 of the metering pump 23 at a pressure level below said predetermined pressure level when fluid flow therethrough is below a predetermined flow rate so as to reduce the operating pressure difference between the metering pump 23 and the predetermined pressure level; A brake control system characterized by having:

2. Said pressure relief device 36 for relieving the pressure in the outlet 26 is connected to the relief valve 37 and the relief valve and metering pump 23.
A brake control system (10) as claimed in claim 1, including a conduit (38) connecting the outlet (26) of the conduit and a restriction orifice (39) in the conduit.

3. The brake control system 10 of claim 2, wherein said predetermined flow rate is established by said orifice 39.

4. The brake control system 10 of claim 3, wherein a portion of the fluid in the outlet 26 of the metering pump 23 passes through the conduit 28 when the rate of flow through the outlet exceeds a predetermined flow rate.

TECHNICAL FIELD This invention relates generally to brake control systems for spring-based pressure release brakes on winches, and more particularly to apparatus for reducing the normal outlet pressure of a metering pump at low winch operating speeds.

BACKGROUND OF THE INVENTION Winches used on pipe laying machines and the like commonly have hydraulic release brakes that can be operated to control the lowering of a supporting load by controlling the rotation of the winch's cable drum. Brake control systems often include an accumulator coupled between a pump and a control valve to provide an auxiliary source of pressurized hydraulic fluid to release the brake to lower a suspended load when the pump is not operating. has. The accumulator is filled to a predetermined pressure determined by a relief valve. In order to achieve a stable lowering of the suspended load, the fluid pressure in the working chamber of the brake must be kept constant. This is often accomplished by a metering pump driven by the winch drum to pump fluid out of the working chamber at a rate proportional to the rotational speed of the drum and at essentially the same rate as the flow rate through the control valve. A constant pressure is thus maintained at a given position of the control valve. In order to maintain the fluid when the accumulator is used as a source of fluid pressure and to keep the accumulator pressure in normal operation, the metering pump returns the fluid to the inlet of the control valve in a regenerative manner and thereby at least produces an initial reduction in braking force. Fluid must be pumped against a pressure established by the relief valve that is substantially higher than the required pressure.

Some examples of such brake control systems were introduced in 1977.
No. 4,048,799 issued to Gaughran et al. on September 20, 1981, and U.S. Pat.

One of the problems associated with such brake control systems is the problem of internal leakage between the inlet and outlet of the metering pump due to the pressure differential between the inlet and outlet.
At very slow rates of descent and relatively high pressures,
Internal leakage within the metering pump reduces its efficiency such that the amount of fluid pumped from the working chamber is less than the amount of fluid delivered to the working chamber by the control valve. Therefore, the fluid pressure in the working chamber continues to increase for a given setting of the control valve, thereby causing the brake to release more than desired and causing the load to drop at an unexpected rate. As a result, the control system does not provide the precise low speed control required to lower heavy loads. Internal leakage does not pose a problem at medium or high drop rates where the fluid flow required to maintain a constant pressure in the working chamber is greater than the internal leakage of the metering pump.

The present invention is directed to overcoming one or more of the problems as described above.

DISCLOSURE OF THE INVENTION According to the present invention, there is provided a brake control system for operating a spring-based pressure release brake between an engaged state and a disengaged state that respectively stop and permit rotation of a rotatable member, comprising: a pump; a control valve having an inlet connected to the pump and an outlet connected to the working chamber of the brake, the control valve being capable of controlling a first position in which the inlet is closed from the outlet and communication between the inlet and the outlet; a control valve movable between a plurality of operating positions for adjusting the control valve; and a metering pump having an inlet and an outlet connecting said inlet to an operating chamber of a brake, said metering pump being driveable to a rotatable member. a metering pump connected thereto, a conduit connecting the outlet of the metering pump to the inlet of the control valve, and a pressure maintenance device that normally maintains the pressure in the conduit at a predetermined operating pressure level sufficient to release the brake. a metering pump outlet at a pressure level below said predetermined pressure level when fluid flow therethrough is below a predetermined flow rate so as to reduce the operating pressure difference between the metering pump inlet and the metering pump outlet; A brake control system is provided which is characterized by having a pressure relief device for releasing pressure therein.

As explained above, when the pressure difference between the inlet and outlet of the metering pump is small, leakage in the fluid metering section within the pump causes the metering pump to pump a predetermined amount of fluid to be metered to the inlet. However, according to the present invention, when the fluid flow through the metering pump is less than a predetermined flow rate and the pressure difference between the inlet and outlet of the metering pump is small, the brake is applied. A pressure relief device is provided to relieve the pressure at the outlet of the metering pump to a pressure level lower than that maintained by the pressure maintenance device sufficient to relieve the pressure difference between the inlet and outlet of the metering pump. The metering pump is capable of discharging a predetermined metered amount of fluid to the outlet, since the metering pump never decreases below a certain point. Therefore, the metering pump can flow an amount of fluid that accurately corresponds to the rotation of the rotatable member, and the pressure in the brake operating chamber is prevented from increasing abnormally due to a decrease in the discharge efficiency of the metering pump. . Therefore, the brake is prevented from being released more than necessary and the load is prevented from dropping at an unexpected speed.

[Brief explanation of the drawing]

The single drawing is a schematic illustration of an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, a brake control system, designated generally by the reference numeral 10, stops and permits rotation of rotatable member 12, respectively, during engaged and disengaged states. Spring utilization pressure release brake 1
Activate 1. Brake 11 typically includes a spring 13 that provides an engagement force and an actuation chamber 14 for receiving pressurized fluid to compress spring 13 to release the brake. The rotatable member 12 may be a rotatable member of a winch, such as a winch drum or a member associated with the rotation of a winch drum.

The brake control system 10 includes a pump 16 having its inlet connected to a reservoir 17 and its outlet connected via a conduit 20 and a check valve 21 to an inlet 18 of a control valve 19. Outlet 2 of control valve 19
2 is connected to the working chamber 14 of the brake. Control valve 19 is movable between a neutral position in which it closes inlet 18 from outlet 22 and a plurality of different operating positions in which it controllably adjusts communication between the inlet and outlet.

Metering pump 23 has an inlet 24 and an outlet 26 and is drivingly connected to the rotatable member via a clutch 27. Inlet 24 is brake 11
It is connected to the working chamber 14 of. Outlet 26 is connected via conduit 28 to inlet 18 of control valve 19 .

Means 29 are provided for normally maintaining the pressure in conduit 28 at a predetermined operating level. The pressure maintaining means 29 is a conduit 20 between the pump 16 and the check valve 21.
a relief valve 30 connected to the conduit 28 , a check valve 31 disposed in the conduit 28 , and an accumulator 32 connected to the conduit 28 between the check valve 31 and the inlet 18 . Another relief valve 33 is connected to the conduit 28 between the check valve 31 and the inlet 18 so that the conduit 28
Release excess pressure inside. The conduit 34 is the relief valve 30
and 33 are connected to reservoir 17.

Although sump 17 is shown symbolically, this sump is typically the housing containing the winch drive mechanism, and fluid through conduit 34 is typically directed to the winch drive mechanism for lubrication.

The outlet 26 of the metering pump 23 at a pressure level lower than the predetermined operating level when the fluid flow therethrough is lower than the predetermined flow rate so that the operating pressure difference is reduced.
Means 36 are provided for relieving the pressure therein.
This pressure relief means 36 includes a relief valve 37 and a conduit 38 connecting the relief valve to the outlet 26 of the metering pump 23.
and a restriction orifice 39 disposed in the conduit 38. Conduit 41 connects relief valve 37 to conduit 34 .

In operation, hydraulic fluid is pumped through conduit 20, check valve 21 and conduit 28 upon initial activation of pump 16. With check valve 31 blocking fluid flow to outlet 26 of metering pump 23, accumulator 32 is filled to a pressure as determined by relief valve 30, which in this case is approximately 2600 kPa (375 psi). After the accumulator is filled, relief valve 30 opens and directs excess fluid through conduit 34 to reservoir 17.

To reduce the load supported by rotatable member 12, control valve 19 is moved from the illustrated neutral position to the operating position to pump pressurized fluid to pump 16.
to pressurize the working chamber 14 of the brake 11. This reduces the effective force of the spring 13, thereby causing the controllably rotatable member 12 to rotate under the influence of the load. The rotational speed of the rotatable member is controlled by controlling the fluid pressure in the working chamber. The pressure in the actuating chamber required to release the brake depends somewhat on the weight of the load being supported by the rotatable member. Rotatable member 12
On the other hand, the rotation of the metering pump 2 is carried out via the clutch 27.
Drive 3. Metering pump 23 then pumps fluid out of working chamber 14 at a flow rate proportional to the rotational speed of rotatable member 12 .

Fluid exiting metering pump 23 through outlet 26 can take one of two different flow paths depending on the flow rate. If the flow rate is below a predetermined flow rate, such as occurs when nudging the load into position, fluid passes through restrictor orifice 39, relief valve 37, conduit 41 and into sump 17. The relief valve 37 is connected to the conduit 2
It is set to open at a pressure lower than the 2600 kpa operating pressure normally maintained during the 8-day period. The pressure required to open the relief valve 37 is somewhat greater than the pressure required to release the brake and may be anywhere between 900 and 1100 kpa (130 and 160 psi) in the present invention. When rotatable member 12 is being rotated at a higher speed, metering pump 23 pumps fluid through outlet 26 at a higher flow rate. When the flow rate exceeds the capacity of orifice 39, which in the present invention is about 1.85 liters (0.5 gallons) per minute, sufficient pressure is created by the flow from the metering pump so that this fluid opens check valve 31. and a portion thereof returns through conduit 28 to inlet 18 of control valve 19 in a regenerative manner. In this state, a small portion of fluid still passes through orifice 39 and relief valve 37.

In view of the foregoing, it is readily apparent that the structure of the present invention provides an improved brake control system with a metering pump relief that provides precision control during low speed load drop-offs. This uses an additional relief valve and orifice connected in series to the outlet of the metering pump to relieve pressure in the outlet at a predetermined pressure level in response to fluid flow through it being below a predetermined flow rate. It is done by The pressure difference between the inlet and outlet of the metering pump is therefore reduced resulting in a drastic reduction of internal leakage within the metering pump at such low speeds. The metering pump is thus capable of pumping fluid out of the brake working chamber at a rate proportional to the rotational speed of the rotatable member in a conventional manner.

Other aspects, objects, and advantages of the invention can be obtained from a study of the drawings, disclosure, and appended claims.