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 This application is a continuation-in-part of International Application No. PCT/GB2002/005498 filed Dec. 6, 2002. The International application published in English on Jun. 12, 2003 as WO 2003/047387.
 This invention relates to cordless hairdryers of the type comprising a rechargeable battery to power a motor that drives a fan, and a gas canister to supply gas to a catalyst for flameless combustion and which provides heat to the air driven by the fan.
 The concept of such a hairdryer is well known, (see for example, U.S. Pat. No. 5,009,592, U.S. Pat. No. 4,635,382, U.S. Pat. No. 4,800,654, U.S. Pat. No. 4,903,416 DE-A-3103843) but no commercial product has yet been launched on the market. The reasons for this are complex and are connected with, among other things, the inefficiency of batteries and the inability to convert the potential energy in the gas to heat in the air in an efficient way.
 One of the problems addressed by the invention is to ensure that electronic or electrical failure does not compromise product safety, especially in view of the proximity of the gas reservoir and electrical components.
 Burners for such hairdryers are preferably of the flameless type, employing a catalyst that supports combustion of the fuel at a lower temperature than would be the case in the absence of the catalyst.
 Catalytic burners are safer, but sensitive, however, to changes in airflow and are easily extinguished; Preferably, two burners are present so that if one goes out the other can relight the extinguished one, before any safety mechanism cuts-off the fuel supply and necessitates restarting of the hairdryer.
 However, the very nature of hairdryers means that their airflow is frequently disturbed, in use, by the manipulations imposed by the user. Sometimes the outlet of the hairdryer will be blocked,,temporarily, by being held too close to the head, or even to thick wedges of hair. At other times, all exit resistance is suddenly removed, so that gushes of air pass through the hairdryer. Unfortunately, to get the air hot for hair drying, it needs to come into contact with the burner. Indeed, the residence time of the air in the hairdryer is very short, given that the quantity of air required by a satisfactory hair dryer is in the order of 10 to 20 litres per second.
 One approach is for the burner to heat a good heat conductor which is shaped into fins so that the air, passing over the fins becomes heated. However, there are few conductors that can conduct the heat fast enough for this application. Ideally, the air needs to come into direct contact with the burners and the hot exhaust gases to get sufficient heat quickly enough. But that is the nub of the problem: because instantaneous significant variations in airflow will over-cool, over-heat, or extinguish the burner, it is difficult to achieve the desired result without rendering the hairdryer too sensitive to such fluctuations.
 Another approach is to heat plates disposed in front of the burners as disclosed in U.S. Pat. No. 5,155,925, but this disturbs the air flow significantly.
 It is an object of the present invention to provide a hairdryer that overcomes the difficulties experienced, or at least mitigates their effects.
 In accordance with the invention there is provided a hairdryer comprising:
 a housing, defining an air passage;
 a battery, adapted to power a motor and a fan driven by the motor to drive air down the air passage;
 a burner, in the air passage and in the form of a sleeve enclosing at its open end a catalyst; and
 a combustible gas supply flow to the burner;
 wherein a first, coned baffle is provided to deflect combusted gas exiting the burner so as to mix with air after flowing around the burner; and
 a second baffle is provided to shroud the burner and prevent air that flows in the passage around the second baffle and burner from cooling the burner.
 With this arrangement of heating the air by mixing the airflow with combusted gas after its exit from the burner, and by shrouding the burner so that there is no danger of the burner being cooled by the airflow, the risk that flameless combustion might be terminated is eliminated.
 Preferably, the sleeve is finned behind the burner to shed heat, conducted from the burner, through radiation and convection to the surrounding airflow.
 Said second baffle may extend from a fin of the sleeve, ideally the one closest to the burner.
 The burner may include a catalyst in the form of a coil of platinum coated wire.
 The first baffle preferably comprises a ceramic block that leaves an annular space in the air passage through which the combusted gas and air flow. Preferably, the first baffle is truncated at its rear end in the direction of air and combusted gas flow to create turbulence in the flow to ensure complete mixing of the air and combusted gas.
 Preferably, a third baffle is disposed upstream of the burner and creates a tubular flow of the air driven by the fan. Said third baffle may comprise the motor being arranged in the air passage downstream of the fan.
 Preferably, the fan is a radial fan drawing air axially through an end opening of the housing and expelling the air radially from the fan against shrouds that deflect the air into a tubular flow. Said shrouding may comprise the housing itself.
 Preferably, there are a plurality of said burners in the air passage, arranged with their longitudinal axes parallel. In this event, when there are two burners, the first baffle comprises a ridge parallel a line joining said longitudinal axes, and a hip at each end substantially on the longitudinal axis of the respective burner.
 In accordance with another aspect of the present invention there is provided a hairdryer comprising:
 a) a housing;
 b) a fan mounted in the housing, driven by a battery powered motor and creating an airflow in through an air inlet of the housing, along an airflow passage through the housing and out through an air outlet of the housing;
 c) a burner in the housing in the airflow passage;
 d) a gaseous fuel supply for the burner;
 e) a baffle element adjacent the burner to separate the airflow passage into a first passage in contact with the burner, whereby the air flow in said first passage is heated to a first temperature, and a second passage separated from the burner; and
 f) an exit baffle before said air outlet and arranged to mix the airflows exiting said first and second passages so that said mixed air has an exit temperature less than said first temperature.
 Preferably, a shroud is behind the burner with respect to said airflow to protect the burner from direct impacts from said airflow.
 Accordingly, this aspect of the present invention is characterised by the airflow being divided, so that only a proportion of the total airflow passes the burner and, as a result, that air gets much hotter than suitable for drying hair. However, since there is a much smaller flow over the burner, changes in total airflow have much less impact on the airflow over the burner. Moreover, beyond the burner, the hot air mixes with the remaining air and is cooled in the process, while at the same time warming the air that flows down the second passage separated from the burner, so that mixed air at a suitable hair-drying temperature exits the housing.
 Preferably, said baffle element is a baffle sleeve surrounding the burner dividing the airflow passage into said first passage, being annular and delimited internally by the burner and externally by the baffle element, and said second passage, being annular and delimited internally by the baffle element and externally by the housing.
 Preferably, pressure enhancement means increases the pressure of the airflow in the first passage, slowing it down. Said pressure enhancement means may comprise an aerofoil section of said baffle element encouraging more airflow into said second passage than said first passage. When said baffle element is a sleeve, a longitudinal section of the wall of the sleeve is said aerofoil.
 According to another aspect of the invention, there is further provided a hairdryer comprising a burner, a fuel reservoir storing fuel, an electromechanical, biased closed, solenoid valve for controlling fuel supply from the reservoir, and an electronic valve control circuit, wherein pulse width modulation of the on/off period of the valve regulates the heat level of the burner. Preferably the control circuit includes a valve control element that is electrically isolated from the control circuit; for example it can be opto-isolated. The control circuit may include one or more condition sensors, for example an under-temperature or over-temperature sensor.
 According to another aspect of the invention there is provided a hairdryer, preferably a cordless hairdryer, comprising a burner, a flow passage, and at least one baffle diverting flow in the passage, in which a condition sensor is provided in conjunction with the baffle. Preferably the condition sensor is an under-temperature or over-temperature sensor. Preferably the baffle shrouds the burner, preventing airflow from cooling the burner and/or deflects combusted gas exiting the burner so that it mixes with air flowing around the burner.
 Embodiments of the invention are further described hereinafter, by way of example, with reference to the accompanying drawings, in which:
 Referring to
 A cross element
 Each burner
 Air is drawn into the port
 Finally, the combusted gases exit the burners
 A second baffle
 The fins
 Returning to the second baffle
 As noted already, there are two burners
 The baffle
 As discussed above, in overview the hairdryer includes a gas burner and gas reservoir and a fan. In addition, as discussed in more detail below, a control circuit and a battery for powering the fan are provided. A first baffle deflects combusted gas exiting the burner so that it mixes with air flowing around the burner. A second baffle shrouds the burner, preventing airflow from cooling the burner.
 Referring to
 Referring to
 The arrangement of
 Referring to
 Referring lastly to
 Turning in more detail to other aspects of the invention, control and safety circuits control the motor speed, burner level, burner ignition and provide safety shutdown in the case of various failure modes. As the controls and burner are likely to be physically remote, purely mechanical controls and safety features are less desirable. As an electrical power source is available (for the motor), at least part of the gas control system is preferably electrically powered and/or sensed. This provides the most versatile method of control, is the least involved and risky from a development point of view, and allows controls almost identical to a standard corded hairdryer.
 Referring to the control and safety circuit block diagram shown as
 When the switch
 The over-temperature thermal switch
 The next components in the safety circuit
 Both the over-temperature and under-temperature switches comprise condition sensors which are provided on the baffle
 In order to initially light the burner
 Once the gas ignites, after a few seconds the under-temperature switch will close and the power supply
 In the case where the gas shut-off valve
 In the case where gas regulation is accomplished using a manual regulator valve
 Motor control is not critical to the safety of the hairdryer, and therefore can be controlled electronically, as failure leading to overheating is detected by the hardwired over-temperature switch (and airflow switch if necessary). However safety critical components such as the solenoid valve
 According to this arrangement, the safety critical circuits cannot be compromised by failure of the electronics. The use of optical isolation components to prevent any monitoring or control circuits of the electronics providing power or incorrectly enabling part of the safety circuit ensure this. Failure of the electronic control circuits may prevent operation of the hairdryer, but always in a fail-safe manner.
 The safety circuit shuts off the gas supply in the event of failure to ignite the gas burner (or subsequent extinguishing of the burner, either controlled or due to a failure), an over-temperature condition (due to failure of the fan/motor, blockage of airflow etc.) or airflow less than a minimum level.
 As regards motor control and electronic gas regulation, there are two embodiments presented regarding the gas regulation (to provide different heat settings) One uses a manual regulator valve
 The advantage of the electronic control of the solenoid valve is the reduction of mechanical parts (albeit at the increase of electronic control) and more freedom in the mounting position and type of controls.
 The electronic control circuit (ECC)
 A possible arrangement
 A single on/off slide switch
 Moving the switch to the “on” position
 The on/off slide switch
 The heat level is controlled by a switch (or manual regulator)
 After use the user moves the slide switch to the “off” position
 A “cool shot” options is also possible involving extinguishing and re-igniting the burner. Cold air operation is possible by switching the unit to “off”, then moving the switch to “on” without igniting the gas.
 As regards ignition of the burner, a preferred implementation is the electronic spark ignition system
 The cheaper alternative is a simple mechanical piezo-ignition system of any appropriate type. The piezo would be triggered once when the user moves the on/off/ignite switch
 Further safety and related aspects include the placement of the spark electrodes, chosen to further minimise the risk of ignition of gas products due to the build up of silicone on the spark electrodes.
 Also, to prevent hair ingress into the product a filter or grill is placed at the air inlet. This prevents hair being drawn in and becoming entangled with the fan and keeps other debris out.
 Furthermore, to prevent debris drawn into the hairdryer (eg. fluff, hair, etc.) from being ignited by the gas burners and ejected as burning or very hot particles, firstly the air inlet filter will prevent most particles from being drawn into the hairdryer, and secondly, the risk of any particles that are drawn in, coming into contact with a flame or a very hot surface is minimised by the product design. In particular, the gas burners are catalytic and therefore burn without a substantial flame at temperatures of approximately 500-800 C. (rather than 1300 C.). Furthermore, these hot catalytic surfaces are protected from the intake air to maintain combustion. Thus particles drawn through the product are not exposed to high temperatures capable of posing a hazard.
 Yet further, products that might reasonably be used with the hair dryer such as gels and hairsprays do not present a safety risk as a result of various features.
 For example, airflow is controlled through the product so that aerosols etc are less likely to come into contact with surfaces that are sufficiently hot to ignite thenm, the spark ignition source is appropriately placed, the operating temperature of the catalytic burners is reduced, and combustion occurs in a safe fashion with the hairdryer.
 The invention as described herein is hence simple to use and similar in use to existing corded dryers. It provides gas shutdown in the case of failure of the burners to ignite, or extinguishing for any reason, two (or more) levels of heat output and fan speeds, gas ignition, reduced airflow detection and gas shutdown, over-temperature detection and gas shutdown, under-temperature detection and gas shutdown (which may be used to detect ignition failure), battery low indicator and burner on indicator.
 A baffle element
 Behind the burner
 Longitudinally, the sleeve baffle
 The burner
 In any event, the air exiting the hairdryer
 It will be appreciated that features and components from the various embodiments can be combined or interchanged as appropriate without departing from the inventive concept. The individual components described, to the extent they are generic or off-the-shelf products, will be well known to the skilled reader and hence have not been described in detail.