Digital pump with multiple outlets

Abstract

A pump system for coupling a positive displacement pump capable of supplying flow sequentially to a number of different volumes at different pressures. In some embodiments the pump output is coupled to multiple volumes that may be at the same or different pressures. The output of the pump is cycled between each such volume by on-off valves to maintain the required pressure in each volume, with the output of the pump being returned to its input when necessary to vent excess flow capacity. A controller may be used to control the on-off valves responsive to pressure sensors for each volume. In other embodiments the output of the pump is through on-off valves coupled to actuators as well as to a by-pass valve, and the valves are operated at high speed and with a duty cycle to provide controlled actuator velocities. Various embodiments are disclosed.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of pump systems.

2. Prior Art

A common method for dividing flow from a single pump is to provide the required flow for all of the loads at the highest required pressure and bleed the lower pressure flows from the high pressure volume through valves to the lower pressure volumes. Having to supply all of the flow at the highest required pressure, rather than at the required pressure for each load, is power inefficient. Also the power lost goes into the fluid being pumped, and may require special cooling if excessive temperatures are to be avoided. A more efficient alternative is to provide separate pumps for each pressure, though this is less attractive from a manufacturing and maintenance point of view.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a pumping system in accordance with the present invention.

FIG. 2 is a diagram of one stage of an exemplary multiple actuator system that may be controlled by the system of FIG. 1.

FIG. 3 is a block diagram of an exemplary control system for the pumping system of FIG. 1.

FIG. 4 is a block diagram of an exemplary control system for the pumping system for an actuator system using one of more actuators in accordance with FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a fixed displacement pump capable of supplying flow sequentially to a number of different volumes at different pressures. Adding a valve or series of valves to the pump outlet allows the pump to be sequentially connected to a number of different control volumes, each at a different pressure. When the pump is not connected to a control volume, it can be connected back to a sump or to its own inlet. The percentage of time that the pump spends connected to a particular volume can be utilized to regulate the pressure in that control volume. Using this methodology, the fixed displacement pump will on average look like a variable flow pump to each of the control volumes.

There are two basic advantages to using this system, namely hydraulic efficiency and mechanical simplicity. (The word “hydraulic” as used herein is used in a general sense to mean a liquid, such as conventional hydraulic fluid, engine oil, fuel and/or other hydrocarbon and non-hydrocarbon liquids.) At any given time, the pump is connected to only one control volume. The pressure rise across the pump is equal to the control volume pressure and the power required to drive the pump is proportional to the pump flow rate times the pressure rise. As the valves are sequenced and the pump is connected to different control volumes, the pump supplies only the necessary flow at the required pressure for each control volume. Any excess pump flow not used in any of the pressurized control volumes is simply routed back to the tank (and pump input) at a very low pressure. The system can be built using very simple components, a fixed displacement pump and a series of “on-off” (“on”=open and “off”=closed) valves. This potentially replaces a variable displacement pump and a series of pressure reducing valves. The possible valving combinations to redirect the pump flow are numerous, and well within the skill of one skilled in the art.

Thus the present invention uses a fixed displacement pump to control pressures in multiple volumes simultaneously using valves to sequentially connect the pump to each volume, as shown on FIG. 1. In some applications the pressures may be similar or the same. For instance, the present invention could be used to provide actuation pressure to multiple actuators to control the position of the actuators, with actuator return being provided by any of various means, such as by way of example, a spring, by gravity or by the provision for hydraulic return also powered by the same pump. One stage of an exemplary multiple actuator system so controlled may be seen in FIG. 2.

The digital pump with multiple outlets of the present invention may also be advantageously used to pressurize multiple rails in engine applications. By way of example, in a diesel engine designed to include a hydraulic engine valve actuation (HVA) system, the HVA system may operate from one rail and the diesel injectors may operate from a second rail at a substantially higher pressure. The present invention may be used to pressurize both rails in an energy efficient manner.

The controller for the system of FIG. 1 may be of a rather conventional configuration such as the basic processor based controller system of FIG. 3. The inputs to the controller are the pressures in the various volumes (FIG. 1) and the outputs are the control signals to valves 1 through n and to the bypass valve. Note that the valves preferably should be operated so that only one valve is kept open at any one time, but that two valves are momentarily at least partially open on switching the pump outlet to a different destination so that a high pressure spike is not created and/or the possibility of damage to the pump by its attempting to pump to a closed system is avoided. The underlap in valve actuation is preferably chosen so that both a pressure spike and backflow are minimized or eliminated. Also while the controller typically cycles sequentially through the various pressure sensor outputs to determine whether the pressure in the respective volume is low, it does not necessarily actuate the valves in the same sequence. By way of example, there may only be one volume that is using the pressurized fluid at any one time, so that only one such volume will need fluid replenishment, so that the respective valve will be opened, and then closed and the bypass valve opened as the respective target pressure is reached. If no volume needs fluid replenishment, then the bypass valve will remain open, even though the pressure sensors are being sequentially monitored. Also note that tolerances may be set for the pressure in each volume, which tolerances may be the same or different, volume to volume. By way of example, one might want to keep the pressure in one volume rather constant, say within 1%, for repeatability of the devices serviced by that pressure, while the pressure in another volume could vary substantially, say 10%, because that volume is only used to actuate a non-critical actuator. Consequently the percentage pressure drop in a volume to cause the respective valve to be opened may be different for different volumes. One might even set priorities between volumes, and still sequentially interrogate all volumes. If a volume with a more critical pressure limit was found to need fluid replenishment, then the output of the pump could be changed to that volume, even if the prior volume being replenished had not reached the shut off pressure for that volume. Thus while pressure sensing is preferably a sequential process, pumping to the various volumes may well not be a sequential process. Appropriate control by the controller will allow use of the minimum size pump possible to meet the overall fluid flow requirements of the system.

The pressure sensors used may be linear or non-linear sensors and may sense from zero pressure or be biased so as to only sense around the respective target pressure or pressures, as desired. In some applications, simple pressure switches may be used, with or without the switches or the controller providing some hysteresis or dead zone around the target pressure to avoid unnecessary valve cycling (also perhaps useful when using other pressure sensors). Also possible are the use of some linear and/or nonlinear sensors and one or more pressure switches in the same system, depending on the number of separate volumes to be pressurized and the specific requirements thereof. If pressure switches are used, the controller may monitor all switches simultaneously as a multi-bit parallel input, and in the event of more than one control volume being below the respective target pressure, couple flow to each such volume on a predetermined priority (predetermined order) basis.

Finally, it should be noted that the desired pressures, and perhaps the pressure tolerances or other parameters such as which of the n volumes are active at any time (need their pressure maintained) may also be provided as other inputs to the controller, as shown in FIG. 3. As one example, a parameter responsive to fluid temperature may be used to vary the pressures maintained to compensate for changes in fluid viscosity with temperature. As another example, another input may be time or a time related parameter, such as crankshaft angle in an engine system, so that fluid pressures may be maintained before the fluid under pressure is needed from the respective volume, but may be delayed at other times to maintain other pressures in the system.

The control of a pump system like that of FIG. 2 may be somewhat different, as shown in FIG. 4. Such a system typically may include multiple hydraulic actuators of the general type shown in FIG. 2, each controlled by an on-off Supply valve and an on-off Vent valve as shown. Such an actuation system may be used when the actuator return force is provided by some other source, such as by way of example, by gravity, a spring or compressed air. Note that in addition to the by-pass on-off valve, one half of the other plurality of on-off valves are operated (on) one at a time and phased so that two are partially on during the transition between valves to limit or eliminate a pressure spike in the system. The remaining on-off valves are coupled to a low pressure vent, and each is preferably off before the respective actuator is coupled to the pump output.

In other cases, a hydraulic return may also be provided for some or all actuators in the system merely by duplicating the control valve valving system for the actuator, but operative to actuate the actuator in the opposite direction, the four control valves being operated in pairs to vent one side of the actuator piston and to pressurize the other side of the actuator piston to cause actuator motion when desired. Venting of one side may precede or be phased with the pressurization of the other side of the actuator, but may not follow the pressurization of the other side since one and only one on-off valve connected to the positive displacement pump is on at any one time.

In the control system of FIG. 4, assume for simplicity, all actuators are the same size, so all have the same linear velocity for the same fluid flow rate (this is for convenience in the explanation and not a limitation of the invention). Also assume that the control inputs call for the operation of actuators 1 and 2, each at a rate of 3 feet per second, with all other actuators remaining stationary. Also assume that the positive displacement pump has a pumping rate equivalent to 10 feet per second for one such actuator. To get the desired 3 feet per second velocity from the first and second actuators and to hold all other actuators stationary, the controller would hold all vent valves V vent closed (off), and would cycle actuator valve Avalve#1 on and off, then cycle actuator valve Avalve#2 on and off, then cycle the Bypass valve on and off, then repeat this sequence. The desired average velocities for actuators 1 and 2 are obtained by operating these three valves with a relative on-time of 1, 1 and 4/3. Alternatively, one might us a sequence of Avalve#1 on and off, Bypass valve on and off, Avalve#2 on and off, Bypass valve on and off, then repeat the sequence. Now the relative on times would be 1, 2/3, 1 and 2/3. Note that this type of control may be used for control of a single actuator or multiple actuators in excess of two as described. In the event, the Control inputs called for a combined actuator motion exceeding the pumping rate of the fixed displacement pump, priorities may be set so that higher priority actuators receive most or all their flow rate needs at the expense of lower priority actuators.

Using valves that are very fast, such as solenoid actuated spool valves having a single solenoid, spring return or double solenoid valves, the motion obtained is usually quite smooth and the pressure fluctuations quite limited by the compressibility of the fluid used and the elasticity of the hydraulic system, thus simulating a constant velocity. On-off (Two way) valves generally in accordance with U.S. Pat. No. 5,640,987 may be used, the disclosure of which is hereby incorporated by reference, though the latching feature need not be used, and/or one solenoid may be replaced by a return spring.

If further smoothing is desired, normally some accumulator effect may be added, such as by providing more elasticity to the plumbing of the system.

Thus while certain preferred embodiments of the present invention have been disclosed and described herein for purposes of illustration and not for purposes of limitation, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.

Claims

1. A pump system comprising: a positive displacement pump having an input and an output; a plurality of on-off valves each having an input coupled to the output of the positive displacement pump; the outputs of the plurality of on-off valves each being coupled to a respective control volume to be pressurized; a bypass on-off valve also having an input coupled to the output of the positive displacement pump and having an output coupled to the input to the positive displacement pump; the plurality of on-off valves being sequenced so that the positive displacement pump is connected to different control volumes at different times to provide the necessary flow at a required pressure for each control volume; the by-pass on-off valve routing any excess pump flow back to the input to the positive displacement pump.

2. The pump system of claim 1 wherein one and only one of the plurality of on-off valves or the bypass valve is on at any one time.

3. The pump system of claim 2 wherein the turn off of one on-off valve and the turn on of the next on-off valve are phased so that one on-off valve is partially off as the next on-off valve is partially on.

4. The pump system of claim 2 wherein the turn off of one on-off valve and the turn on of the next on-off valve are phased to maintain flow from the positive displacement pump without a substantial pressure spike in the output of the positive displacement pump.

5. The pump system of claim 1 wherein each control volume includes a pressure sensor and wherein the plurality of on-off valves and the bypass on-off valve are controlled by a controller, the controller sequentially checking an output of each pressure sensor and controlling the plurality of on-off valves and the bypass on-off valve to provide the necessary flow at the required pressure for each control volume.

6. The pump system of claim 5 wherein the controller is responsive to at least one additional input.

7. The pump system of claim 5 wherein the pressure sensors are pressure switches.

8. The pump system of claim 5 wherein the pressure sensors are selected from the group consisting of linear and nonlinear pressure sensors.

9. The pump system of claim 8 wherein the pressure sensors are biased so as to only sense around the required pressures.

10. The pump system of clam 5 wherein the plurality of on-off valves provide the necessary flow at the required pressure for each control volume, each with a predetermined hysteresis around the required pressure.

11. The pump system of claim 10 wherein the hysteresis is imposed by the controller.

12. The pump system of claim 1 wherein the on-off valves are solenoid operated spool valves

13. A pump system for controlling one or more hydraulic actuators comprising: a positive displacement pump having a hydraulic fluid pumping rate; a controller coupled to receive actuator velocity control signals; a plurality of on-off valves; a bypass on-off valve having an input coupled to an output of the positive displacement pump and having an output coupled to an input to the positive displacement pump; a first half of the plurality of on-off valves each being configured to couple an output of the positive displacement pump to a hydraulic actuator input; a second half of the remaining plurality of on-off valves each being configured to couple a hydraulic actuator input to a low pressure vent, wherein each hydraulic actuator has a specific actuator velocity per unit hydraulic fluid flow rate; the controller being configured to sequentially and repetitively couple selected ones of the plurality of on-off valves on and off with a duty cycle selected to provide a fluid flow rate through the selected on-off valves to cause an actuator velocity responsive to the actuator velocity control signals.

14. The pump system of claim 13 wherein one and only one of the first half of the plurality of on-off valves or the bypass valve is on at any one time.

15. The pump system of claim 14 wherein the turn off of each of the first half of the on-off valves and the by-pass valve and the turn on of the next valve of the first half of the on-off valves and the by-pass valve are phased so that one on-off valve is partially off as the next on-off valve is partially on.

16. The pump system of claim 14 wherein the turn off of each of the first half of the on-off valves and the by-pass valve and the turn on of the next valve of the first half of the on-off valves and the by-pass valve are phased to maintain flow from the positive displacement pump without a substantial pressure spike in the output of the positive displacement pump.

17. The pump system of claim 13 wherein the on-off valves are solenoid operated spool valves