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1. WO2000015457 - DRIVING MEANS

Note: Text based on automatic Optical Character Recognition processes. Please use the PDF version for legal matters

[ EN ]

DRIVING MEANS

The present invention concerns a power supply for vehicles and/or machines.

BACKGROUND OF THE INVENTION
Most types of work vehicles and machines (that power hydraulic apparatus) often have intense workloads requiring high torques or pressures during relatively short periods.

In all cases when an internal combustion engine is used (and also for a normal dc or ac electrical motor) it is necessary to rev the motor to obtain the desired torque. This means that the hydraulic pump must be over-dimensioned with respect to the flow and normally the fluid is pumped around the hydraulic system to no purpose except when the hydraulic valve is opened all the way and during very short periods handles the full pressure and flow. Normally this happens relatively seldom and during very short periods, for example for a few seconds.

To get the desired torque rotation or flow the internal combustion motor is therefore revved or gunned but only a part of the power is utilised during a short time while for the rest of the time the hydraulic fluid is pumped around and is shunted past the main hydraulics via the pressure valve and back to the tank without performing any work and with the result that the hydraulic fluid is warmed up and must be cooled.

Translated to the internal combustion engine the situation is that the engine operates for the most part without purpose while consuming a relatively large amount of fuel and also contaminating the environment with exhaust gases unnecessarily.

It should also be noted that a hydraulic system does not need more fluid and pressure than it consumes while an internal combustion engine cannot work in parallel with the hydraulic pump with respect to rotation rate and torque since the technical conditions for this are of opposite character.

One can therefore say that an internal combustion engine is not especially well suited for powering a hydraulic pump, especially when it comes to periodic workloads (intermittent use).

Through GB 1 365 511 and SE 392 454B an energy recovery system is already known in which a battery driven electric motor (for example a dc motor with permanent magnets) powers a hydraulic pump which in turn pumps the hydraulic fluid to a hydraulic piston cylinder. To make use of the accumulated potential energy on lowering a load the hydraulic fluid under pressure is allowed to operate on the hydraulic pump which then functions as a hydraulic motor which in turn powers the electric motor which then functions as a generator.

The international patent application WO 97/47884 describes an apparatus for pressurising a fluid for powering hydraulic devices in aircraft. The permanent magnet motor of the apparatus is connected to a secondary pump, a piston pump, a transmission between the permanent magnet motor and the piston pump and electronic controls for the permanent magnet motor so that part of the hydraulic fluid can be used as a coolant which flows through the electronic controls and the permanent magnet motor. Because of its special purpose the construction is very complicated and expensive to make as well as very high speed and thus not applicable as a power supply for vehicles or machines.

SUMMARY OF THE INVENTION
The object of the invention is to make a power supply for vehicles and/or machines that
• is simple, inexpensive and light weight in its construction,
• is made of standard components,
• does not require revving up to achieve the necessary power,
• consumes little energy in operation and production
• is very protective of the environment
• is optimally energy effective
• makes possible a considerably simpler hydraulics control system
• can support very high torque loads intermittently - coupled directly to a permanent magnet motor' s torque curve (and is powered by normal storage batteries).

These objects have been achieved through the characteristics given in the patent claims.

BRIEF DESCRIPTION OF THE DRAWINGS
In the following the invention will be described in detail in an exemplification with reference to the attached drawings showing an exemplification.

Fig. 1 shows a block diagram of the power supply according to the invention.

Fig. 2 shows a circuit diagram of the motor controls.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
The power supply according to the invention includes an electric energy source 11 that can be one or more storage batteries especially if the power supply is to be used in a mobile work machine, boat or other vehicle, for example. Number 12 indicates a dc electric motor the speed of which can be controlled by an electronic control unit 13 and other controls 13 a. The electric motor 12 powers a hydraulic pump 14 which via a control valve 15 pumps hydraulic fluid to a hydraulic operating device 16 which can be a piston-cylinder, a hydraulic motor or the like which carries out the actual work with one or more simultaneous functions.

Through analysis of the hydraulic pump's 14 need of high torques/pressures from zero revolutions and the requirement that the power source 12 for the hydraulic pump not consume more energy than exactly that required from one revolution to for example 3000 rpm it can be shown that a permanent magnet electric motor, in the following called a PM-motor, is the perfect power source for a hydraulic pump. A primary characteristic of a PM-motor is that it has essentially the same torque at one revolution as for example at 3000 rpm (that is, effectively a straight torque curve). A further characteristic of a PM-motor is its high efficiency (95-99%) and its small size and weight which makes it especially suitable for mobile equipment.

During development and a large number of tests it has been determined that the PM-motor coupled to a hydraulic pump makes it possible to save easily 60-80% of the energy or fuel in a work machine compared to a normal internal combustion engine since the PM-motor at for example 3000 revolutions does not consume more electricity or energy than corresponds to its load. For example the PM-motor then has a storage battery with continuous support charging from a generator 20. Tests with a multi-use miniloader have shown that it only uses 20-30% of a diesel motor's energy for corresponding work tasks without optimising the system for the tests to be carried out.

The electronic control unit 13 that can reverse the motor includes a programmable microprocessor 21 specially designed for permanent magnet motors. It can control the motor's speed, torque and breaking power smoothly and cost effectively. In the circuit diagram according to fig. 2 number 22 indicates a main breaker, 23 a key breaker and 24 a current controller, for example a potentiometer with which the amount of current can be set continuously or in steps, for example from 150 A to 240 A.

If the power supply is used in a mobile unit there can also be an electric charging unit 17 for the batteries 11. The charging can take place either directly by attaching a cable 18 to the mains or by starting a secondary motor 19, for instance an internal combustion engine that powers the electric generator 20. It is also possible to use the PM-motor as a charging generator. When using the internal combustion motor it is important that it operate optimally (at its best efficiency) with respect to the generator with minimal losses. Because of the PM-motor's high torque at low rotations it is possible to use the hydraulic system without bypassing the hydraulic fluid since the hydraulic valve 15 is an on-off valve with the sole purpose of directing the hydraulic fluid to the right operating device 16. The extra flow is completely controlled by the controls 13a which control the rotation rate of the PM-motor very exactly.

Other immediate advantages of this are that the hydraulic fluid is kept at a much lower temperature as it is not pumped around unnecessarily. Further, simple, inexpensive hydraulic valves 15 can be used. Depending on the exact control of the flow and pressure all types of work, such as manoeuvring, can be carried out with significantly greater precision and exactness. Because use of this technique saves as much as 60-80% of the energy it is easily possible to power a normal average sized work machine for a whole working day with a battery package (standard automobile lead batteries) of for example 100-200 Ah at 72 volts.

The hydraulic system can also be supplemented by a accumulator tank (not shown) for high pressure and flow for longer times. The pressure in the accumulator tank is built up during low flow periods.

This technique means that a very small PM-motor can replace a much larger internal combustion engine in situations that require high pressures periodically also for longer times.

The accumulator tank can also be automatically pressurised statically using a pressure sensor while little fluid volume is being consumed. A practical example of such an arrangement can be a mobile crane, for example, that lifts heavy loads for short times requiring high pressures for short times. In this imagined situation for example a 12 kW PM-motor equipped with an appropriate hydraulic pump can replace a diesel motor rated at more than 300 kW. In this example it is important that the useful volume of the accumulator tank be chosen correctly in terms of size and pressure.

The technical examples given can be correspondingly applied to tractors, power shovels, lifters, motorcycles, trucks, busses, cars, boats, etc, that is, situations where large forces are required for relatively short times, for example for lifts, starts and/or accelerations.

The investment cost of a power supply according to the invention can be reduced significantly compared to a corresponding internal combustion engine while large amounts of fuel can be saved at the same time. This is advantageous both for pocket books and the environment.

By choosing a hydraulic pump 14 and a PM-motor 12 that can be inverted the flow of the hydraulic fluid can be reversed and the hydraulic pump 14 made to function as a hydraulic motor and the PM-motor 12 as a PM-generator. In this way useable energy, such as potential energy or the braking energy of vehicles or hydraulic machines, can be used for example to recharge the batteries. The temporarily inverted hydraulic pump 14 in the form of a hydraulic motor can be used to brake the vehicle.

The possibilities in this example mean that when we have a monofunction system the system can be run in both directions. For mulitfunction a secondary system of electrical or hydraulic motors is needed. Other advantages that can be achieved with the system coupled to a vehicle are that locking of the wheels (braking) or their rotation speed can be controlled using the pressure control of the hydraulic fluid and charging of the batteries at the same time using an accumulator tank. This can additionally replace ABS technology. There is also the possibility of including 4WD for starting vehicles or when it is needed.

Potential energy in mobile cranes, power shovels and other piston cylinder apparatus can also be used in a return phase delivering energy to the system. An elevated, hanging load on a crane, for example, returns almost as much energy when the load is lowered. The same situation obtains for power shovels, loaders, etc.

"Brake energy" can also be used in connection with wind power units and water turbines which results in optimal energy generation. The situation with potential and braking energy often presupposes high voltage and high performance batteries to take up the energy either directly or indirectly using an accumulator (pressure) tank.

The power source according to the invention can be used also for fast planing or displacement boats. By using a PM-motor as a supplementary power source (booster) at the planing threshold large energy expenditures can be achieved for relatively short times. Further the marine engine can be used without reversal since backing can also be carried out by the system, the PM-motor or the reduced hydraulics. As an example one can power a normal 20-30 foot pleasure boat for example for 2-4 hours at 4-8 knots with a 100 amp-h/72 volt battery package with an energy expenditure of 8- 15 horsepower from a PM-motor. The advantage of this equipment is that also the power supply is practically silent and the speed can be varied continuously in both directions. Additionally, in the power supply one has a very dependable backup motor for emergencies, fishing or military use. In this example one can use the PM-motor with or without a hydraulic system depending on the specific needs. As the system is coupled to a marine engine it comprises a very powerful generator function for dc or ac current.

The technical solution described for boats also entails very simple installation as only one way of coupling to the internal combustion engine (for the backup motor and for manoeuvring) is needed when the hydraulic motor is coupled directly to the boat's transmission or propeller axle. Neither is it necessary to have a start motor and generator for the marine engine. The system can easily be integrated with the oil lubrication system of the internal combustion engine and can thus improve the lubrication system of the internal combustion engine for a stable, controlled oil pressure from start for a long chosen time after a stop for controlled cooling of the motor. The marine engine's oil pump can also be eliminated.

When the system is integrated with an internal combustion engine it is appropriate to use it to power other units such as water pumps and cooling pumps which usually have low efficiencies depending on the different rotation speed regions of the internal combustion engine which in turn make over-dimensioned pumps that do not work (pump) according to cooling needs but according to the different speeds of the internal combustion engine unnecessary.

Other interesting application needs can be gas turbines and jet motors which on starting need quick acceleration so that the compressor function of the gas turbine begins to work and provide the desired pressure.

In a corresponding way electricity can be generated from the gas turbine/jet motor when it is in operation and a separate APU/generator is made unnecessary.

Finally one can also consider coupling jet motors in parallel through hydraulics in a larger system and thereby significantly increase the dependability of operation. In this exemplification one can consider an "advanced" battery package which should in principle provide an electrical limited backup motor function during for example landings.

In the above mentioned examples and tests a 72 volt 12 kW PM-motor (air cooled) was used but it is clearly possible to use 12, 24, 36 volt motors and higher depending on force and torque. The hydraulic pumps used had flows of 40-100 litre/min and a pressure of 200-350 bar. Control electronics is necessary for the PM-motor and is programmed for the desired function and application.

The weight of the above mentioned equipment is about 20-25 kg including the PM-motor, pump and control electronics. The storage battery used was 6 optima "Yellow Top" 55 Ah/t (110 Ah/t) with a battery weight of 110 kg.

LIST OF REFERENCE NUMBERS

11 storage battery
12 permanent magnet motor (PM-motor) or PM-generator 13 electronic control unit
13a controls
14 hydraulic pump
15 control valve
16 operating device
17 charging unit
18 mains cable
19 internal combustion engine
20 generator
21 microprocessor
22 mains breaker
23 key breaker
24 current controller