Pressure washer

Abstract

A high pressure washer (100) is described comprising: - a pump (40) and an electric motor (50) configured to drive the pump (40), where said pump (40) is connected to an inlet duct (15) of a liquid to be pressurised and to a delivery duct (20) of a liquid pressurised by the pump (40), - an electronic circuit (200) to control the power supply of said electric motor (50); - wherein said electronic circuit (200) comprises an electronic control unit (60) operatively connected to said electric motor (50); characterised in that said electronic circuit (200) is configured to vary the rotation speed of the motor (50) by varying the waveform of the current supplying the motor (50) in order to change the flow rate of the liquid pressurised by the pump (40) in the delivery duct (20).

Description

[0001] PRESSURE WASHER

[0002] TECHNICAL FIELD

[0003] The present invention relates to a pressure washer, that is a high-pressure washing device, for cleaning surfaces by generating a jet of liquid under pressure.

[0004] PRIOR ART

[0005] As is known, high pressure washing devices, or pressure washers, comprise a high pressure pump suitable for drawing a washing fluid, for example water, whose delivery duct is connected to a flexible hose connected to a dispensing lance of pressurised liquid. The dispensing lance generally comprises an elongated body equipped with a handle to which a dispensing wand supporting a dispensing nozzle at the free end thereof can be removably associated.

[0006] The dispensing lance then comprises a trigger which is placed at the handle and actuates a tap adapted to allow or interrupt the flow of the washing fluid from the pump to the dispensing nozzle.

[0007] The fluid sent to the lance is placed under pressure by a motor pump, that is a pump to which at least one electric motor is mechanically connected with the aim of supplying the pump with the mechanical energy to pressurise the fluid.

[0008] In known pressure washers, the pressure of the fluid delivered by the pump is regulated downstream of the pump, e.g. by activating a bypass to divert a portion of the pressurised fluid flow.

[0009] In this known solution, the pump always delivers the maximum fluid flow rate, and therefore the flow rate regulation dissipates hydraulic energy that is still supplied by the pump.

[0010] From the above, it can be seen that in systems of the known type there is an unnecessary waste of hydraulic energy, and consequently of electrical energy absorbed by the motor to drive the pump, so ultimately there is undue consumption of power by the electric motor driving the pump.

[0011] The aim of this invention is to overcome the drawbacks of the prior art by providing a high pressure washer that offers improved energy performance.

[0012] A further aim of the invention is to provide a high pressure washer that offers a plurality of operating modes available to the user.

[0013] Finally, another object of the present invention is to improve the versatility and ease of use of high pressure washers, all within the framework of a simple, rational and robust construction solution.

[0014] These objects are achieved by the features of the invention set forth in the independent claim. The dependent claims outline preferred and / or particularly advantageous aspects of the invention.

[0015] DISCLOSURE OF THE INVENTION

[0016] The invention, particularly, makes available a high pressure washer comprising:

[0017] - a pump and an electric motor configured to drive the pump, where said pump is connected to an inlet duct of a liquid to be pressurised and to a delivery duct of a liquid pressurised by the pump;

[0018] - an electronic circuit to control the power supply of said electric motor;

[0019] - where said electronic circuit comprises an electronic control unit operatively connected to said electric motor; characterised in that said electronic circuit is configured to vary the rotation speed of the motor by varying the waveform of the current supplying the motor in order to change the flow rate of the liquid pressurised by the pump in the delivery duct.

[0020] This solution makes it possible to adjust the motor speed and thus the flow rate of the pressurised fluid in such a way as to achieve significant energy savings.

[0021] According to an embodiment of the invention, the electronic control unit is configured to vary the waveform of the current supplying the motor by interrupting the alternating current supplying the motor for a predetermined time interval starting from a reference signal.

[0022] A high pressure washer is made available that allows the water flow rate to be regulated easily and effectively.

[0023] An aspect of the invention provides that the electronic circuit comprises a zero-crossing circuit, configured to generate the electrical reference signal whenever the sinusoidal waveform of the motor supply current crosses zero and to make said signal available to the electronic control unit.

[0024] An advantage of such a solution is that the zero-crossing circuit allows the zero crossing of the motor's AC power supply waveform to be monitored in order to have a reference point for synchronising the motor speed regulation.

[0025] According to an embodiment of the invention, the zero-crossing circuit comprises two diodes each of which is connected via the anode to an AC power supply source, while the cathode of each of the diodes is connected to a common node, in turn electrically connected to a contact of the control unit.

[0026] An advantage of this solution is that it provides a zero-crossing circuit that is inexpensive and easy to implement.

[0027] According to an embodiment of the invention, the electronic circuit comprises a Triac, electrically connected to the electric motor, and equipped with a gate connected to the electronic control unit, whereby the conduction of said Triac is delegated to the electronic control unit according to said time interval.

[0028] An advantage of this solution is a simple and effective control of the Triac's conduction and interdiction status and thus of the electric motor's power supply.

[0029] According to another embodiment of the invention, the electronic control unit is configured to send the conduction signal to the Triac at the end of the time interval, wherein said time interval is calculated from the zero crossing of the sinusoidal waveform of the motor supply current signalled by said zero-crossing circuit.

[0030] An advantage of this embodiment is the fact that, during the time interval, the electric motor is not activated, as the Triac is in a non-conducting state, resulting in a lower water flow rate and consequent energy savings.

[0031] According to yet another embodiment of the invention, an optoelectronic isolator is interposed between the electronic control unit and the Triac.

[0032] An advantage of this embodiment is that the optoelectronic isolator electrically isolates the portion of the electronic motor control circuit operating in direct current from the portion of the motor control circuit operating in alternating current.

[0033] According to a further embodiment of the invention, a protective snubber is associated with the Triac.

[0034] An advantage of this embodiment is that the snubber has the function of an electrical transient suppressor circuit.

[0035] According to a further embodiment of the invention, the electronic circuit comprises further means of activating a bypass function to bypass the control of the electronic control unit upon the variation of the alternating current supply waveform of the motor.

[0036] An advantage of this embodiment is that a user can bypass the effect of the electronic control circuit, i.e. the interruption of the alternating current supplying the motor for a predetermined time interval, by means of said activation means, thus ensuring that the motor driving the pump is continuously supplied with 100% power.

[0037] According to an aspect of the invention, said activation means comprise a switch the switching of which generates a control signal at the input to the electronic control unit, wherein said electronic control unit is configured, upon receipt of the control signal, to continuously power the motor.

[0038] An advantage of this embodiment is its simplicity, which is particularly economical and effective.

[0039] According to a different aspect of the invention, the activation means of the by-pass function comprise a switch, associated with a pressure switch, the switching of which is controlled according to the actuation of a trigger of the dispensing lance, said control unit being programmed to detect the number of switching operations of said switch and activate the by-pass function when the number of switching operations of the switch is equal to a predetermined number (Ns) in a predetermined time interval (At).

[0040] This embodiment of the activation means has the advantage of allowing the user to activate the by-pass function directly from the dispensing lance extremely quickly.

[0041] According to another aspect of the invention, the control unit is programmed to activate the bypass function for a predetermined time interval within the control unit itself.

[0042] This aspect of the invention has the advantage that the operator does not have to manually deactivate the by-pass function.

[0043] BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Further features and advantages of the invention will be more apparent after reading the following description provided by way of non-limiting example, with the aid of the accompanying drawings.

[0045] Figure 1 is a schematic view of the high pressure washer according to a first embodiment of the invention;

[0046] Figure 2 is a diagram illustrating a first embodiment of an electronic circuit controlling the motor of the high pressure washer in figure 1 ;

[0047] Figure 3 is a schematic view of the pressure washer according to a second embodiment of the invention;

[0048] Figure 4 is a diagram illustrating an electronic circuit controlling the motor of the high pressure washer of figure 3, in accordance with the second embodiment; Figure 5 is a schematic view of the high pressure washer according to a third embodiment of the invention;

[0049] Figure 6 is a diagram illustrating an electronic circuit controlling the motor of the pressure washer of figure 5, in accordance with the third embodiment;

[0050] Figure 7 is a diagram illustrating a first operating step of the high pressure washer circuit of the invention; and

[0051] Figure 8 is a diagram illustrating a second operating step of the high pressure washer circuit of the invention.

[0052] DETAILED DESCRIPTION OF THE FIGURES

[0053] With particular reference to figure 1 , the reference numeral 100 generally indicates a high pressure washer, or a high pressure washing device.

[0054] The high pressure washer 100 comprises a box-like casing 10, for example made of plastic material, to which a handle and / or wheels (not illustrated) are preferably associated for moving the high pressure washer itself.

[0055] The high pressure washer 100 comprises a single inlet duct 15 of the fluid to be pressurised, for example a single inlet duct 15 of the fluid to be pressurised, adapted to be connected to a source of fluid to be pressurised, for example a tank or a water network. This inlet duct is at least partially contained inside the casing 10.

[0056] The high pressure washer 100 also comprises a delivery duct 20 of the pressurised fluid, for example a single delivery duct 20 of the pressurised fluid, and a dispensing lance 25 to which said delivery duct 20 is fluidically connected, for example by means of a flexible hose. The delivery duct 20 is for example at least partially contained in the casing 10.

[0057] The dispensing lance 25 comprises a body equipped with a handle 37 to which, for example, a dispensing wand 30 is associated in a removable way, which is equipped at one free end thereof with a dispensing nozzle 32.

[0058] Any other cleaning tool can be associated with the dispensing lance 25, as an alternative to the wand, such as a rotating brush.

[0059] The dispensing lance 25 may comprise a trigger 35 that is movable between a first position, in which the dispensing lance does not dispense pressurised fluid, and a second position, in which the dispensing lance dispenses pressurised fluid.

[0060] In particular, the trigger 35 is placed at the handle 37 of the dispensing lance 25 and actuates a valve between a first position, in which it allows the flow of the pressurised fluid from the delivery duct 20 to the dispensing nozzle, and a second position, in which it interrupts the flow of the pressurised fluid from the delivery duct 20 to the dispensing nozzle 32.

[0061] The high pressure washer further comprises a pump 40, connected at the inlet to the inlet duct 15 and at the outlet to the delivery duct 20, preferably with a fixed displacement.

[0062] The high pressure washer 100 also includes an electric motor 50 configured to drive the pump 40 operatively connected to the fluid inlet duct 15 and the fluid delivery duct 20. That is, the electric motor 50 is mechanically connected to the pump 40 to actuate it so as to pressurise the fluid coming from the inlet duct 15. Overall, the electric motor 50 and the pump 40 form a motor pump of the high pressure washer 100.

[0063] The electric motor 50 is adapted to be electrically connected to an electrical energy source, i.e. to the electrical distribution network and / or to a battery, e.g. housed inside the casing 10.

[0064] The high pressure washer 100 also comprises an electronic circuit 200, equipped with an electronic control unit 60, and described in more detail with reference to figure 2 below; the circuit 200 is electrically connected to the motor 50 to control its operation.

[0065] The high pressure washer 100 also includes a pressure switch 70, located on the delivery duct 20, e.g. downstream of the pump 40 (i.e. between the pump 40 and the dispensing lance 25), where the aforementioned pressure switch 70 has a movable rod 72 against the force of a spring 74, so that it can selectively act on an electric switch 75.

[0066] In turn, the electrical switch 75 is preferably in the form of a normally closed (NC) switch wherein in the normally closed position, the electrical switch 75 is connected, via the electronic circuit 200, to the power supply circuit of the motor 50 controlling the pump 40; the electrical switch 75 may also assume a second open position wherein it is connected to a common ground node of the circuit at a predetermined voltage (equal to zero).

[0067] In particular, the electric switch 75 of the pressure switch 70 on the delivery duct 20 is normally closed (NC) when the delivery pressure of the pump 40 is below a predetermined calibration value Pth, and opens automatically when the pressure exceeds the calibration value Pth.

[0068] Opening the electrical switch 75 of the pressure switch 70 causes the pump 40 to stop, providing a Total Stop function and occurs, for example, when the dispensing lance 25 is closed, resulting in an increase in pressure upstream thereof. Figure 1 also shows the power supply line 1 10, which comprises two cables, one of which, L, is the power line and the other, N, is the neutral phase.

[0069] The cables L and N are connected to a manually operated two-pole switch 90, from which the power supply cable of the electric motor 50, which drives the pump 40, derives.

[0070] Figure 2 is a diagram illustrating a possible embodiment of an electronic circuit 200 controlling the motor 50 of the high pressure washer 100 of figure 1 .

[0071] The electronic circuit 200 acts as a driver circuit for the motor 50 and can be subdivided into a DC portion operating in direct current and an AC portion operating in alternating current.

[0072] The electronic circuit 200 comprises a Triac 210 (or thyristor), electrically connected to the motor 50, and equipped with a control gate connected to the electronic control unit 60. Specifically, the Triac is switched on by the electronic control unit 60 to control the electric current supply, via the Triac 210, to the motor 50 in the manner described below. A protection circuit is also associated with the Triac 210 to protect the Triac 210 from electrical transients. In the illustrated example, the protection circuit can be provided with a snubber circuit 220, which is known in itself.

[0073] Between the electronic control unit 60 and the Triac 210 an optoelectronic isolator 250 is interposed whose function is to electrically isolate the DC portion of the electronic circuit 200 of the motor 50 operating in direct current from the AC portion of the electronic circuit 200 operating in alternating current and which is an electronic component that transfers electrical signals between the two portions of the circuit using a light signal.

[0074] The electronic circuit 200 comprises a DC power supply circuit 201 of the electronic control unit 60. In the illustrated embodiment, this power supply circuit 201 comprises a transformer 240, a high voltage winding 241 of which is connected to the two-pole switch 90, while the low voltage winding 242 is connected to a rectifier 243 which generates a DC voltage signal to supply the electronic unit 60. Preferably the output of the rectifier is connected to the electronic control unit via a voltage regulator 244

[0075] In the embodiment illustrated, the rectifier 243 is provided with a Greatz diode bridge, the output of which is connected to the voltage regulator 244, which in turn is electrically connected to the control unit 60. Other embodiments of the invention, not illustrated, may provide for different solutions of the DC power supply circuit of the electronic control unit 60. For example, a variant could involve the use of an analog / digital (AC / DC) converter, the AC (alternating current) side of which is connected to the mains voltage via the two- pole switch, while the DC (direct current) side is connected to the control unit 60 to provide the energy required to power the control unit and possibly also to generate a reference signal at each zero crossing of the voltage.

[0076] A zero-crossing circuit 245 is connected to the ends of the low-voltage winding 242 of the transformer 240, electrically connected to the control unit 60 and adapted to generate a reference signal at the zero crossing of the sinusoidal waveform of the supply current of the motor 50.

[0077] Said zero-crossing circuit 245 may comprise two diodes 246 and 247, each of which is connected via the anode to an AC power source, while the cathode of each of the diodes is connected to a common node 248, which in turn is electrically connected to a contact of the control unit 60.

[0078] In the embodiment illustrated, the zero-crossing circuit 245 may comprise two diodes 246 and 247, each of which is connected via the anode to a respective end of the low voltage winding 242 of the transformer, while the cathode of each of the diodes is connected to a common node 248, which in turn is electrically connected to a contact of the control unit 60. The common node 248 is connected to ground via a voltage stabiliser 249.

[0079] The change of state of the two diodes 246 and 247 from the interdiction state to the conduction state, and vice versa, which occurs at the zero crossing of the supply current of the motor 50, i.e. at the transition from the negative half-wave of the supply current to the positive half-wave, and vice versa, generates a rectified half-wave signal which is made available to the electronic control unit 60 and is used by it as a reference signal of the zero crossings of the sinusoidal waveform of the supply current of the motor 50.

[0080] The electronic control unit 60 is programmed and configured to power the electric motor only after a preset time interval D depending on the reference signal generated by the zero crossing circuit 245. In the embodiment illustrated each time the sinusoidal AC waveform of the power supply to the motor 50 crosses zero, a change of state of the two diodes takes place and the reference signal, acquired by the electronic control unit 60, is generated, which is used by the electronic control unit 60 as the starting instant for the calculation of the time interval D at which the power supply to the motor 50 is interrupted. Fig. 8 shows the waveform of the motor power supply current in which it can be seen that each time the current passes from the negative half-wave to the positive half-wave, and vice versa, there is an interruption of the motor supply for a time interval D.

[0081] The value of the time interval D is set in the electronic control unit 60, e.g. equal to 1 ms, but can also be set to different values.

[0082] The electronic control unit 60 can be programmed with a bypass function to override the control on the variation of the motor supply AC waveform, so that the motor can be supplied continuously, i.e. without interrupting the motor power supply for a predetermined time interval D. The bypass function is activated by the user through appropriate activation means. In addition, the control unit can be programmed to activate the bypass function only for a predetermined time interval.

[0083] In accordance with the first embodiment of the invention, illustrated in Figs. 1 and 2, the means of activating the bypass function include the switch 75 associated with the pressure switch 70. In particular, the switching of the switch is controlled by the user by actuating the trigger of the dispensing lance. In fact, every time the user operates the trigger of the dispensing lance, the pressure of the fluid inside the delivery duct decreases. A decrease in the pressure value, detected by the pressure switch, causes the switching of the switch 75.

[0084] The electronic control unit 60 is electrically connected to the switch 75 when the switch is in the NC position and is programmed to detect the number of switch operations, i.e. the number of trigger actuations of the dispensing lance, and to activate the bypass function whenever the number of switch operations, in a predetermined time interval At, is equal to a predetermined value Ns, stored in the control unit 60.

[0085] Activation of the bypass function provides, as mentioned above, a continuous supply of power to the motor without any control over the supply current waveform, allowing the motor to run at 100% of its power. Preferably, the control unit is programmed to activate this bypass function for a preset time interval tboost, after which the bypass function is deactivated by the control unit itself. Other embodiments of the invention may provide that the deactivation of the by-pass function always takes place according to the number of switching operations of the switch 75 associated with the pressure switch 70.

[0086] The second embodiment of the invention, illustrated in Figs. 3 and 4, differs from the first embodiment with regard to the activation means of the bypass function.

[0087] This bypass function, in accordance with the second embodiment of the invention, is activated by the user by acting on a switch 150, located for example on the casing 10 of the high pressure washer 100, the switching of which, i.e. the transition from an open position to a closed position, has the function of generating a control signal for the electronic control unit so that it activates the bypass function by interrupting the control on the variation of the waveform of the alternating current supplying the motor, so as to allow the motor to be continuously supplied.

[0088] In the particular embodiment illustrated, the switch 150 is provided as a push-button whose pressure generates a control signal made available to the electronic control unit which is configured, upon receipt of said signal, to continuously power the motor 50 for a time tboost pre-set within the control unit itself by interrupting the control (of the electronic control unit 60) on the variation of the waveform of the alternating current supplying the motor.

[0089] It should be noted that the circuit 200 also includes a heat sink 170 known per se.

[0090] Figs. 5 and 6 illustrate a third embodiment of the invention which differs from the previous embodiments of the invention in that it comprises a pressure switch 80 instead of the pressure switch 70. The function of the pressure switch 80 is to control the switching of a switch 85 designed to cut off the power supply to the electric motor 50 when the lance is not delivering fluid under pressure. As shown in Figs. 4 and 5, the difference between the second and third embodiments of the invention consists of the fact that, in the second embodiment, the interruption of the power supply to the electric motor 50 is controlled by the control unit 60 via the T riac 210, whereas in the third embodiment of the invention the switch 85 is placed and acts directly on the power supply line of the motor 50 by interrupting at least one of the phases. In particular, the electrical switch 85 of the pressure switch 80, which is located on the delivery duct 20, is normally closed (NC) when the delivery pressure of the pump 40 is below a predetermined calibration value Pth, and opens automatically when the pressure exceeds the calibration value Pth.

[0091] The switching of the electric switch 85, from the closed position to the open position, of the pressure switch 80 causes the interruption of the power supply to the motor and the consequent stopping of the motor 50, and thus of the pump 40, guaranteeing the Total Stop function and occurring, for example, when the dispensing lance 25 is closed, resulting in an increase in pressure upstream thereof.

[0092] The operation of the high pressure washer 100 according to the invention is as follows.

[0093] In idle conditions, the two-pole switch 90 is open and the dispensing lance 25 does not dispense fluid.

[0094] In this configuration, the motor 50 is idle and the pump 40 is also idle.

[0095] The switch 75 of the pressure switch 70 is in the closed position (NC), as the delivery pressure of the pump 40 is zero.

[0096] When the operator wants to start the high-pressure cleaner, he operates the two-pole switch 90 in order to power the motor 50.

[0097] In this position, the pump 40 starts up and brings the delivery pressure to a value above the calibration value Pth.

[0098] The pressure switch 70 opens the normally closed (NC) switch 75 as the pressure exceeds the set value Pth and the stem 72 of the second pressure switch 75 moves against the spring 74 in the direction of the arrow G in figure 1 opening the normally closed (NC) switch 75 and the motor 50 stops.

[0099] When the operator wishes to dispense pressurised water, he / she opens the dispensing lance 25 with the trigger 35, and the water (or fluid) pressure upstream of the lance 25 decreases.

[0100] This causes the rod 72 of the switch 75 of the second pressure switch 70 to be pushed by its own spring 74 in the opposite direction to the arrow F in figure 1 , returning the switch 75 to the normally closed (NC) position and the motor 50 starts. When the operator wishes to interrupt the dispensing of pressurised water, he / she must simply release the trigger 35 by closing the dispensing lance 25, so that the pressure upstream of the lance rises above the set value Pth, and the normally closed (NC) switch 75 of the pressure switch 70 opens, in the manner described above, causing the motor 50 to stop.

[0101] Figure 7 is a diagram illustrating the sinusoidal waveform S of the supply current to the motor 50, i.e. a waveform comprising a plurality of positive half-waves interspersed with negative half-waves.

[0102] In particular, referring to a power supply with a frequency of 50 Hz, each sinusoidal wave has a duration of 20 ms (milliseconds), i.e. 1000 ms / 50 = 20 ms.

[0103] Due to the presence of the zero-crossing circuit 245 in the electronic circuit 200, every time the sinusoidal waveform S of the motor supply current 50 crosses the zero, the electrical reference signal P is generated and sent to the electronic control unit 60.

[0104] Since there are 2 zero crosses per cycle, there is a 10 ms period after each zero cross detection which can be managed as follows. With reference to figure 8, after every zero crossing of the power supply current to the motor 50 the electronic control unit 10 interrupts the power supply to the motor 50 for a predetermined time interval D. (as schematically represented by the dashed areas N in figure 5).

[0105] At the end of the time interval D, the electronic control unit 60 sends a current signal to the gate of the Triac 210, thus ensuring a predictable level of power attenuation of the motor 50, which, in the example, results in the motor 50 being supplied at 80% power. This process is repeated for both the positive half-wave and the negative half-wave of the supply current to the motor 50.

[0106] As a further example, we note that if instead the motor 50 is powered at the beginning of the 10 ms period, without applying any delay D, it will be powered at 100%. On the contrary, if the motor 50 is powered at the end of the 10 ms period, the motor remains switched off. If the chosen delay D is, for example, 5 ms, the motor 50 will only be powered at half power.

[0107] With reference to the second and third embodiments of the invention, the action on the switch 150 by the user generates an input control signal to the electronic control unit 60, which is configured in bypass function to bypass the control on the variation of the waveform of the alternating current supplying the motor, so as to allow the motor to be continuously powered. In the second and third illustrated embodiments, the control unit 60 can be programmed to activate the bypass function only for a predetermined time interval tboost.

[0108] In this case, the motor 50 will always be powered at 100%, providing a booster function on demand, for the preset time tboost within the control unit, e.g. 30 seconds.

[0109] Alternatively, as per the first embodiment illustrated, the activation of the bypass function can be delegated to the activation means comprising the trigger 35 of the dispensing lance 25.

[0110] In this case, whenever the movable trigger 35 of the dispensing lance 25 is activated, the fluid pressurised by the pump is dispensed by the lance 25 through the dispensing wand 30 and the dispensing nozzle 32, and at the same time, a pressure change occurs in the delivery duct 20. In this case, the pressure switch 70 records this pressure variation.

[0111] More specifically, the rod 72 of the first pressure switch 70 moves under the force of the spring 74 in the direction of the arrow F in figure 1 and acts on the electrical switch 75 in such a way as to move it from the first normally closed (NC) position in which it is connected to the electronic control unit 60, to the second position in which it is connected to the common ground node. The opening of the switch 75 is detected by the electronic control unit 60.

[0112] Thus, each time a trigger 35 is pulled, a signal is sent to the electronic control unit 60, so that it is possible to command the activation of the booster function according to the number of signals received from the control unit 60 within a reference time interval At .

[0113] In practice, a number of signals Ns, resulting from a variation of the lance trigger position, is predefined in the electronic unit 60 for a predetermined time interval At, which determines the setting of the time interval D. In particular, if the user presses and releases the lance trigger a certain number of times greater than or equal to the predefined number of signals Nswithin the reference interval At, the control unit 60 is configured to continuously power the motor 50, for a certain pre-set time tboost, for example 30 seconds, so that the booster function is active during this time interval.

[0114] The invention thus described allows a user to operate the pressure washer 100 by managing the speed of the motor 50 in at least two different modes.

[0115] The invention thus conceived is susceptible to several modifications and variations, all falling within the scope of the inventive concept. Moreover, all details can be replaced by other technically equivalent elements. In practice, the materials used, as well as the contingent shapes and sizes, can be whatever according to the requirements without for this reason departing from the scope of protection of the following claims.

Claims

CLAIMS1. A high pressure washer( O) comprising:- a pump (40) and an electric motor (50) configured to drive the pump (40), wherein said pump (40) is connected to an inlet duct (15) of a liquid to be pressurised and to a delivery duct (20) of a liquid pressurised by the pump (40),- an electronic circuit (200) to control the power supply of said electric motor (50);- wherein said electronic circuit (200) comprises an electronic control unit (60) operatively connected to said electric motor (50); characterised by the fact that said electronic circuit (200) is configured to vary the rotation speed of the motor (50) by varying the waveform of the current supplying the motor (50) in order to change the flow rate of the liquid pressurised by the pump (40) in the delivery duct (20).

2. The high pressure washer (100) according to claim 1 , wherein the electronic control unit (60) is configured to vary the waveform of the current supplying the motor (50) by interrupting the alternating current supplying the motor (50) for a predetermined time interval (D) starting from a reference signal.

3. The high pressure washer (100) according to claim 2, wherein said electronic circuit (200) comprises a zero-crossing circuit (245), configured to generate the electrical reference signal whenever the sinusoidal waveform of the motor supply current crosses zero and to make said signal available to the electronic control unit (60).

4. The high pressure washer (100) according to claim 3, wherein the zero-crossing circuit comprises two diodes (246, 247), each of which is connected via the anode to an AC power supply source, while a cathode of each of the diodes (246, 247) is connected to a common node (248), which in turn is electrically connected to a contact of the control unit (60).

5. The high pressure washer (100) according to claim 3, wherein said electronic circuit (200) comprises a Triac (210), electrically connected to the electric motor (50), and provided with a gate connected to the electronic control unit (60), wherein the electronic control unit (60) is configured to send a conduction signal to said Triac (210) according to said time interval (D).

6. The high pressure washer (100) according to claim 5, wherein the electronic control unit (60) is configured to send the conduction signal to the Triac (210) at the end of thetime interval (D), wherein said time interval (D) is calculated from the zero crossing of the sinusoidal waveform of the motor supply current (50) detected by said zero-crossing circuit (245).

7. The high pressure washer (100) according to claim 5, wherein an optoelectronic isolator (250) is interposed between the electronic control unit (60) and the Triac (210).

8. The high pressure washer (100) according to claim 2, wherein said electronic circuit (200) further comprises means for activating a bypass function to bypass the control of the electronic control unit (60) upon the variation of the waveform of the alternating current supplying the motor.

9. The high pressure washer (100) according to claim 8, where said activation means comprise a switch (150) the switching of which generates a control signal at the input to the electronic control unit (60), wherein said electronic control unit (60) is configured, upon receipt of the control signal, to continuously power the motor (50).

10. The high pressure washer (100) according to claim 8, wherein the activation means of the by-pass function comprise a switch (75), associated with a pressure switch (70), the switching of which is controlled according to the actuation of a trigger of the dispensing lance, said control unit (60) being programmed to detect the number of switching operations of said switch and activate the by-pass function when the number of switching operations of the switch is equal to a predetermined number (Ns) in a predetermined time interval (At).

11. The high pressure washer (100) according to claim 9 or 10, wherein the control unit is programmed to activate the bypass function for a predetermined time interval (tboost) within the control unit itself.

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