CONTROLLED HYDRAULIC SYSTEMS

There is herein described a controlled hydraulic systems for operating machinery. More particularly, there is described a controlled hydraulic system (200) comprising a variable drive ratio device (214) interposed between a prime mover (210) and a fixed displacement pump (112) for controlling the operating speed of the pump (212) and hence the output flow in the hydraulic system.

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Description
FIELD OF THE INVENTION

The present invention relates to controlled hydraulic systems for operating machinery. More particularly, the present invention relates to a controlled hydraulic system comprising a variable drive ratio device interposed between a prime mover and a fixed displacement pump for controlling the operating speed of the pump and hence the output flow in the hydraulic system.

BACKGROUND OF THE INVENTION

Many fixed displacement hydraulic pumps are connected directly to a variable speed prime mover, for instance a diesel engine, and as such the rotational speed of the pump, and hence its output flow, is almost directly proportional to the rotational speed of the prime mover.

In practice, this means that the speed of operation of any selected service on a machine being driven by such a principle is proportional to the speed of the prime mover. In the case of a diesel engine its low idle speed is approximately ⅓ of its high idle speed and as such it will take approximately three times as long to operate a service when the engine is running at low idle when compared to the time taken to operate the same service when the engine is running at high idle.

Further to this, hydraulic pump flow is only required when a service is required to be operated but with a fixed displacement pump the flow is continuous whether the flow is required or not.

In some applications the prime mover has a fixed speed, for instance an electric motor, and it can sometimes be advantageous to be able to vary the output flow from the fixed displacement pump.

There are a number of prior art systems for controlling hydraulic systems. However, many of these types of systems describe a hydraulic metering mode transitioning technique for a velocity based control system. However, there are a number of fundamental differences to these types of prior art systems and the present invention. For example, in the prior art the process selects which metering mode to use at any point in time which involves determining a parameter (such as a hydraulic load) which denotes an amount of force acting on the actuator. In contrast, in the present invention the parameter which is selected is operating speed. Moreover, in the prior art there is use of pressure transducers in a number of locations which are sensed. The present invention is different in that pressure transducers are used to monitor the pressures at different parts of the circuit in order to adjust spool position and maintain a specific pressure difference and hence maintain an operating speed of an actuator. Devices in the prior art also use the fact that cylinders acting as actuators are asymmetric in the head area and are different to rod area when apportioning flow is concerned. This does not happen in the present invention. A further significant difference is that prior art devices relate to monitoring pressure difference across the actuator.

It is an object of at least one aspect of the present invention to obviate or mitigate at least one or more of the aforementioned problems.

It is a further object of at least one aspect of the present invention to provide an improved controlled hydraulic system for operating machinery.

It is a yet further object of at least one aspect of the present invention to provide a hydraulic system comprising a variable drive ratio device interposed between a prime mover and a fixed displacement pump for controlling the operating speed of the pump and hence the output flow.

It is a further object of at least one aspect of the present invention to provide an improved method for controlling a hydraulic system.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a controlled hydraulic system comprising:

a prime mover;

a pump; and

a variable drive ratio device interposed between the prime mover and the pump;

wherein the variable drive ratio is capable of controlling the operating speed of the pump and hence the output flow in the hydraulic system.

The present invention therefore resides in the provision of a controlled hydraulic system comprising a variable drive ratio device interposed and/or positioned between a prime mover and a pump for controlling the operating speed of the pump and hence the output flow in the hydraulic system.

Typically, the prime mover may be of a fixed or variable speed and may, for example, be a diesel engine or an electric motor. By mounting the variable ratio drive between the prime mover and the pump means that the speed of the pump may be controlled independently or substantially independently of the prime mover speed. Diesel engines typically run between a minimum speed of about 650-750 rpm and a maximum speed of about 2200-2300 rpm. (Electric motors run at about 960, 1500, or 3000 rpm).

The variable ratio drive may be any suitable variable ratio drive unit. For example, a pump flow with a minimum engine speed of about a 3:1 ratio may be used (assuming that the engine has appropriate torque capability at low engine speed). The variable ratio drive may also be able to substantially limit the flow output when flow is not required in order to limit power wastage (potentially about a 1:3 ratio).

In particular embodiments, the pump may be a fixed displacement pump such as an external gear pump, an internal gear pump, a vane pump or any other such pump capable of delivering a fixed output flow in relation to its input drive speed.

The pump may be driven by an electric motor or a variable speed electric motor.

The ratio of the variable ratio drive may be controlled by any suitable type of remote means. For example any of the following may be used:

    • (1) The input to control the pump speed may be determined by varying the speed of the prime mover such that pump output flow remains constant within prescribed operating limits of all components within the system over a wide range of prime mover speeds;
    • (2) The input to control the pump speed may be determined by other requirements, for instance the need to drive selected services at a specific speed, requiring a specific flow; and
    • (3) The input to control the pump speed may be determined by whether there is a demand for flow.

Methods of controlling the variability of the variable speed drive may include:

    • (1) Electro-, hydraulic or electro-hydraulic signaling into the unit based on sensors relating to engine speed;
    • (2) Electro-, hydraulic or electro-hydraulic signaling into the unit based on sensors relating to actuator operating speed; and
    • (3) Electro-, hydraulic or electro-hydraulic signaling into the unit based on sensors relating to control valve selection.

The variable ratio drive may therefore be envisaged as essentially a variable speed drive where the variability may be infinite between its upper and lower limits or alternatively it may be variable in discrete steps between its upper and lower limits. For example, the input to output ratio may be less than or greater than about 1:1.

It should be noted that any form of motor and/or engine may be used as the prime mover such as an electric motor or a diesel engine and may be used as a variable or fixed speed prime mover. The present invention may therefore provide a prime mover such as a drive from a transmission of a diesel engine which may be of variable speed, variable torque and/or variable energy consumption.

The present invention may therefore address the problem of facilitating the use of hydraulic systems by a user. The hydraulic system may be in a variety of machinery and vehicles. In particular, the hydraulic system may be in earth moving vehicles, construction equipment vehicles, mechanical handling equipment and the like, and also power units (which may use an electric motor as a prime mover).

To control a hydraulic system which forms part of a hydraulic apparatus requires a certain flow of hydraulic fluid in the hydraulic system. In certain circumstances the system may comprise a flow control device. During this flow, the pressure difference across one orifice (e.g. a spool metering notch), at least one orifice, three orifices or a plurality of orifices may be fixed. The orifices may be spool metering notches.

The hydraulic system may also comprise one reservoir, at least one reservoir or a plurality of reservoirs for hydraulic fluid. The hydraulic fluid may, for example, be any suitable oil-based flowable material/liquid. There may also be a system of cables for the hydraulic fluid to flow around to allow the hydraulic system to function. The system of cables (e.g. hydraulic pipework) may form a circuit for the hydraulic fluid.

In particular embodiments, in the hydraulic system there may be a steady state condition and there may be a fixed spool position. During the fixed spool position there may be a fixed flow across one orifice, at least one orifice, three orifices or a plurality of orifices. There may also be a fixed pressure difference across one orifice, at least one orifice, three orifices or a plurality of orifices. However, in practice the conditions may constantly change and an operator will be continually changing lever positions in order to control spool position so that the flow across all selected spools may be maintained under conditions of changing pressure and flow influences.

The orifices used in the hydraulic system may be any suitable type of valves such as poppet valves or spool valves. Spool valves are simpler than poppet valves. Both poppet valves and spool valves may be independently controlled. By using simple valves such as poppet valves also allows the different components of the hydraulic system to be separated which may simplify manufacturing processes. Poppet valves may be used, but spool valves are preferred. For reference, the three metering elements which are all on one spool, and are therefore mechanically linked, may be split into separate elements and controlled individually (i.e. the different elements may be independently controlled).

To control a hydraulically operated apparatus at a certain speed may require a certain flow of hydraulic fluid. At this flow, the pressure difference across one orifice (e.g. a spool metering notch), at least one orifice, three orifices or a plurality of orifices may be fixed. However, problems for a user may then occur if the conditions change and it requires action from an operator to maintain the operating speed of the selected service. The present invention may use pressure monitors on at least one side or either side of any selected orifice(s). In particular, there may therefore be pressure monitors on either side of one orifice, at least one orifice, three orifices or a plurality of orifices. The orifices may be spool metering notches.

In particular embodiments, the hydraulic system may be remotely controlled thereby providing a remote interactive control system.

The hydraulic system may comprise a controller such as a joystick controller, an electronic control package and/or a main control valve. There may also be a pressure monitor across an orifice or a series of pressure monitors across (e.g. on both sides) of a plurality of orifices. Pressure monitors may therefore be positioned on one side and/or both sides of any orifice(s). The joystick controller may be connected to the electronic control package which may allow the joystick controller to send a signal to the electronic control package. The electronic control package may then send a signal to a valve. This may allow the output signal from the electronic control package to be modified and changed in response to any change in signal from the pressure monitors on at least one or both sides of an orifice.

The hydraulic system according to the present invention may therefore allow a user to automatically use a controller (e.g. a given joystick position) to constantly modify spool position in response to any change in the pressure loss or increase across a selected orifice and thereby maintain the required flow and actuator speed. In the present invention, the system allows a user to select the desired operating speed of the service. The system may then monitor and control that operating speed (by modifying spool position) until such time as the input from the joystick is changed. This may be performed automatically.

The hydraulic system according to the present invention may allow monitoring of the flow and in some situations it may be possible to link this into the Engine Management System to control engine speed and hence pump flow, thereby reducing unused flow to a minimum.

The present invention may also use pressure transducers to monitor the pressures at different parts of the circuit in order to adjust spool position and maintain a specific pressure difference and hence maintain an operating speed of an actuator.

According to a second aspect of the present invention there is provided a method of controlling the operating speed of a pump and hence the output flow in a hydraulic system, the method comprising:

providing a prime mover;

providing a pump; and

providing a variable drive ratio device interposed between the prime mover and the pump.

The method of controlling the operating speed may comprise using a pressure monitor across an orifice or a series of pressure monitors across (e.g. on both sides) of a plurality of orifices as defined in the first aspect.

The pressure monitors form a sensing system and are capable of sensing pressure in the hydraulic system and transmitting this information to facilitate a user in using the hydraulic system and hence in the operation of a hydraulic machine.

According to a third aspect of the present invention there is provided machinery and/or a vehicle comprising a hydraulic system according to the first aspect.

Typically, the machinery may be earth moving vehicles, construction equipment vehicles, mechanical handling equipment and the like, and also power units (which may use an electric motor as a prime mover).

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 is a schematic representation of a pump mounted directly onto a prime mover according to the prior art;

FIG. 2 is a schematic representation of a variable speed drive interposed between a prime mover and a pump according to an embodiment of the present invention;

FIG. 3 is a representation of a diesel engine which has variable speed (i.e. the rpm on the x-axis) with resulting variable torque (as represented by ‘A’), variable power (as represented by ‘B’) and variable energy consumption (as represented by ‘C’);

FIG. 4 represents a hydraulic system according to the present invention and shows how the flow and input power is variable against rpm;

FIG. 5 is a representation of an open centre hydraulic circuit according to an embodiment the present invention;

FIG. 6 is a representation of a meter showing different notch positions in an apparatus according to an embodiment the present invention;

FIG. 7 is a representation of remote interactive control system according to an embodiment the present invention;

FIG. 8 is a flow chart which illustrates the operation of a remote interactive control system according to an embodiment of the present invention; and

FIG. 9 is a schematic representation of a remote interactive control system according to a further embodiment of the present invention.

 BRIEF DESCRIPTION

Generally speaking, the present invention resides in the provision of a controlled hydraulic system comprising a variable drive ratio device interposed between a prime mover and a fixed displacement pump for controlling the operating speed of the pump and hence the output flow in the hydraulic system.

FIG. 1 represents the prior art situation where the prior art apparatus, generally designated 100, comprises a prime mover 110 and a pump 112 mounted directly onto the prime mover 110. The prime mover 110 may be of a fixed or variable speed and may be a diesel engine or an electric motor. The pump 112 is mounted such that the drive between the prime mover 110 and the pump 112 is direct. This means that the speed of the pump 112 changes in proportion to the speed of the prime mover 110.

FIG. 2 is a general representation of apparatus according to the present invention generally designated 200. As shown in FIG. 2, a variable ratio drive 214 is mounted between a prime mover 210 and a pump 212 (e.g. a fixed displacement pump). The prime mover 210 may be of a fixed or variable speed and may be a diesel engine or an electric motor. By mounting the variable ratio drive 214 between the prime mover 210 and the pump 212 means that the speed of the pump 212 can be controlled independently of the prime mover 210 speed. The variable ratio drive 214 may be any suitable variable ratio drive unit.

The ratio of the variable ratio drive 214 may be controlled by any suitable type of remote means. For example any of the following may be used:

    • (1) The input to control the pump speed may be determined by varying the speed of the prime mover such that pump output flow remains constant within prescribed operating limits of all components within the system over a wide range of prime mover speeds;
    • (2) The input to control the pump speed may be determined by other requirements, for instance the need to drive selected services at a specific speed, requiring a specific flow; and
    • (3) The input to control the pump speed may be determined by whether there is a demand for flow.

Methods of controlling the variability of the variable speed drive may include:

    • (1) Electro-, hydraulic or electro-hydraulic signaling into the unit based on sensors relating to engine speed;
    • (2) Electro-, hydraulic or electro-hydraulic signaling into the unit based on sensors relating to actuator operating speed; and
    • (3) Electro-, hydraulic or electro-hydraulic signaling into the unit based on sensors relating to control valve selection.

The present invention therefore relates to the positioning/interposing of a variable ratio drive 214 between a prime mover 210 and a pump 212. The variable ratio drive 214 is essentially a variable speed drive where the variability may be infinite between its upper and lower limits or alternatively it may be variable in discrete steps between its upper and lower limits. For example, the input to output ratio may be less than or greater than 1:1.

There are a number of situations where the present invention may be of use. These include, but are not limited to, the cases described below:

Case 1: An Input to Output Ratio of Less than 1:1

If the flow is not required then the variable speed drive would potentially assume a pump drive speed close to zero so that the pump delivered either no or a minimal amount of flow. Alternatively, we may use the situation where the ratio could vary between 1:3 and 3:1.

Case 2: An Input to Output Ratio of Less than 1:1

If the system requires less flow than that the pump is delivering due to the speed it is being driven at then the ratio can be adjusted in order to reduce the pump speed and hence reduce the flow.

Case 3: An Input to Output Ratio of 1:1

Normal situation where flow required relates directly to speed of prime mover.

Case 4: An Input to Output Ratio of Greater than 1:1

If the system requires more flow than the pump is delivering due to the speed it is being driven at then the ratio can be adjusted in order to increase the pump speed and hence the flow.

Case 5: An Input Ratio of Less than, Equal to, or Greater than 1:1

Where the pump is being driven by fixed speed prime mover and there is a requirement to vary the output flow which can be achieved by varying the pump speed.

Case 6: Engine Running at Low Speed

This applies to where an engine running at a lower speed has a torque limit. The torque limit controls the ratio of the variable speed drive such that high flow is available as long as the associated pressure requirement together with that flow does not exceed the torque limit. In such a case the ratio, and so the pump flow, would adjust to ensure that the pump demand remained within the available torque limit.

It should be noted that any form of motor and/or engine may be used as the prime mover such as an electric motor or a diesel engine and may be used as a variable or fixed speed prime mover.

The present invention may therefore provide a prime mover such as a drive from a transmission of a diesel engine which is of variable speed, variable torque and/or variable energy consumption. The apparatus of the present invention may therefore be seen as an energy transformer which may comprise a converter such as a variable ratio drive which may provide constant speed output with variable torque. In this regard we refer to FIG. 3 which is a representation of a diesel engine which has variable speed (i.e. the rpm on the x-axis) with resulting variable torque (as represented by ‘A’), variable power (as represented by ‘B’) and variable energy consumption (as represented by ‘C’).

FIG. 4 represents a hydraulic system according to the present invention and shows how the flow and input power is variable against rpm. The present invention addresses the problem of facilitating the use of hydraulic systems by a user. The hydraulic system may be in a variety of machinery and vehicles. In particular, the hydraulic system may be in earth moving vehicles, construction equipment vehicles, mechanical handling equipment and the like, and also power units (which may use an electric motor as a prime mover).

To control a hydraulic system which forms part of a hydraulic apparatus requires a certain flow of hydraulic fluid in the hydraulic system. During this flow, the pressure difference across an orifice (e.g. a spool metering notch) is fixed. To illustrate this function we refer to FIG. 5 which is a representation of an open centre hydraulic circuit, generally designated 500 with an oil reservoir 510. During a steady state condition there will be a fixed spool position. There will be a fixed flow across each orifice and a fixed pressure difference across each orifice. However, in practice the conditions will constantly change and the operator will be continually changing lever positions in order to control spool position so that the flow across all selected spools is maintained under conditions of changing pressure and flow influences. As shown in FIG. 5, position P2 is a meter in centre notch position 514 which may increase in size with spool selection. Position P1 is an open centre notch 512 which reduces in size with spool selection. Position P3 is a meter out centre notch 516 which increases in size with spool selection.

FIG. 6 is a typical representation of apparatus 600 according to the present invention which shows a meter out notch 610, an open centre notch 612 and a meter in notch 614. A value housing 616 and a valve spool 618 is also shown.

There are a number of problems with open center systems. For example, for a given spool position the operating speed of an actuator will vary due to:

    • (1) Any change in the load on the actuator (by varying the pressure requirement) i.e. as is typical on many machines due to changing mechanical advantage;
    • (2) Any change in the input flow to a valve i.e. as may occur during changes in the engine speed;
    • (3) How many spools are selected i.e. selecting more spools affects the operating conditions of the first selected spool.

To control a hydraulically operated apparatus at a certain speed requires a certain flow of hydraulic fluid. At this flow, the pressure difference across an orifice (e.g. a spool metering notch) is fixed. However, problems for a user then occur if the conditions change and it requires action from an operator to maintain the operating speed of the selected service. The present invention uses pressure monitors on at least one or both sides of any selected orifice. For example, we refer to FIG. 7 which is a representation of remote interactive control system 700 of the present invention. The system 700 comprises a joystick controller 710, an electronic control package 712, a main control valve 714 and a pressure monitor 716 across an orifice. Pressure monitors may therefore be positioned on at least one or both sides of any orifice. The joystick controller 710 is connected to the electronic control package 712 which allows the joystick controller 710 to send a signal to the electronic control package 712. The electronic control package 712 may then send a signal to a valve. This allows the output signal from the electronic control package 712 to be modified and changed in response to any change in signal from the pressure monitors on at least one or both sides of an orifice. The purpose of the orifice is to meter the flow between the pump and a selected service in order to control the speed of operation of that selected function. On an open centre valve there are typically 3 orifices which perform this action as depicted in FIG. 5 and FIG. 6. The open centre orifice progressively closes the flow path from the pump back to the oil reservoir in order to raise pressure, the meter in orifice progressively opens in order to allow that pump flow out to the selected function, and the meter out orifice progressively opens in order to allow oil from the opposite side of the selected function to return back to the oil reservoir. Movement of the valve spool within the valve housing therefore progressively moves this set of 3 orifices, changing the area of each simultaneously, in order to control the selected function. If the spool is selected in the opposite direction a similar set of 3 orifices achieve the same purpose in order to reverse the direction of operation of the selected function.

In practice, these metering orifices will frequently be designed to suit a specific function in terms of their individual rate of change of opening with regard to spool position. The proposal with the new system is that these 3 orifices are separated and as such can be controlled individually for improved machine control.

FIG. 8 is a flow chart which illustrates the operation of the remote interactive control system 700 according to the present invention. The system 700 may therefore allow a user to automatically for a given joystick position to constantly modify the spool position in response to any change in the pressure loss or increase across a selected orifice and thereby maintain the required flow and actuator speed. This is in contrast to prior art techniques with both open centre and load sense where a user selects the spool position in order to control the operating speed of the service. In the present invention, the system allows a user to select the desired operating speed of the service. The system may then monitor and control that operating speed (by modifying spool position) until such time as the input from the joystick is changed.

In a prior art open centre system any flow not required is passed through the centre of the valve and back to the tank. In contrast, the present invention will allow monitoring of the flow and in some situations it may be possible to link this into the Engine Management System to control engine speed and hence pump flow, thereby reducing unused flow to a minimum.

FIG. 9 is a representation of a remote interactive control system 900 according to the present invention. The system 900 comprises joystick controls 910, an electronic control package 912; a series of spool valves 920,930,940,950 and a reservoir 918 of oil. In a selected position, oil is diverted inside the spool valves 920,930,940,950 to the selected service and returning oil is diverted back to the reservoir 918. On either side of the spool valves 920,930,940,950 there are pressure monitors 922,924; 932,934; 942,944; 952,954 which monitor the flow through an orifice in the spool valves 920,930,940,950.

In the prior art, it is conventional that spool valves having three orifices are machined onto the same component. Therefore, when an orifice needs to change area then the other two have to change at the same time. In the present invention, it becomes feasible to separate these various elements such that each of the orifices can be an individual component such as, for example, poppet valves or spool vales. It is preferred to use spool valves.

Whilst specific embodiments of the present invention have been described above, it will be appreciated that departures from the described embodiments may still fall within the scope of the present invention. For example, any suitable type of pressure monitors may be used to measure flow in the valves. Moreover, any suitable type of variable drive ratio may be used.

Claims

1. A controlled hydraulic system comprising:

a prime mover;
a pump; and
a variable drive ratio device interposed between the prime mover and the pump;
wherein the variable drive ratio is capable of controlling the operating speed of the pump and hence the output flow in the hydraulic system.

2. A controlled hydraulic system according to claim 1, wherein the prime mover is of a fixed or variable speed.

3. A controlled hydraulic system according to claim 1, wherein the pump is a fixed displacement pump.

4. A controlled hydraulic system according to claim 1, wherein the ratio of the variable ratio drive is capable of being controlled remotely.

5. A controlled hydraulic system according to claim 1, wherein the controlled hydraulic system comprises a flow control device.

6. A controlled hydraulic system according to claim 1, wherein the controlled hydraulic system comprises a system of cables capable of allowing the hydraulic fluid to flow.

7. A controlled hydraulic system according to claim 1, wherein there is provided a sensing system for measuring and/or sensing the pressure difference across one orifice (e.g. a spool metering notch), at least one orifice, three orifices or a plurality of orifices in the hydraulic system.

8. A controlled hydraulic system according to claim 1, wherein the hydraulic system comprise one orifice (e.g. a spool metering notch), at least one orifice, three orifices or a plurality of orifices which are formed from poppet valves.

9. A controlled hydraulic system according to claim 1, wherein the hydraulic system is remotely controlled thereby providing a remote interactive control system.

10. A controlled hydraulic system according to claim 1, wherein the hydraulic system comprises a controller (e.g. a joystick controller), an electronic control package and a main control valve.

11. A controlled hydraulic system according to claim 1, wherein the controller is connected to the electronic control package which is capable of allowing the controller to send a signal to the electronic control package which allows the output signal from the electronic control package to be modified and changed in response to any change in signal from the pressure monitors on at least one or both sides of an orifice.

12. A controlled hydraulic system according to claim 1, wherein a user is capable of automatically using a controller (e.g. a given joystick position) to constantly modify spool position in response to any change in pressure loss or increase across a selected orifice and thereby maintain the required flow and actuator speed.

13. A controlled hydraulic system according to claim 1, wherein a monitoring and/or sensing system is capable of continuously monitoring and sensing hydraulic flow and transferring this information to an Engine Management System to control engine speed and hence pump flow.

14. A controlled hydraulic system according to claim 1, wherein the hydraulic system comprises pressure transducers capable of monitoring the pressures at different parts of the hydraulic system in order to adjust spool position and maintain a specific pressure difference and hence maintain an operating speed of an actuator.

15. A controlled hydraulic system according to claim 1, wherein there is a pressure monitor across an orifice or a series of pressure monitors across (e.g. on both sides) of a plurality of orifices.

16. A method of controlling the operating speed of a pump and hence the output flow in a hydraulic system, the method comprising:

providing a prime mover;
providing a pump; and
providing a variable drive ratio device interposed between the prime mover and the pump.

17. A method of controlling the operating speed of a pump according to claim 16, wherein the method comprises comprise using a pressure monitor across an orifice or a series of pressure monitors across (e.g. on both sides) of a plurality of orifices in the hydraulic system.

18. A method of controlling the operating speed of a pump according to claim 17, wherein the pressure monitors are capable of forming a sensing system and are capable of sensing pressure in the hydraulic system and transmitting this information to facilitate a user in using the hydraulic system and hence in the operation of a hydraulic machine.

19-20. (canceled)

Patent History
Publication number: 20120070312
Type: Application
Filed: May 13, 2010
Publication Date: Mar 22, 2012
Applicant: David Brown Hydraulics Limited (Upton, Poole)
Inventor: Phil Godfrey (Dorset)
Application Number: 13/322,135
Classifications
Current U.S. Class: In Response To Pump Speed (417/42)
International Classification: F04B 49/00 (20060101);