CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national phase filing of International Patent Application No. PCT/EP2019/056897, entitled “BATTERY SAVING SYSTEM AND ELECTRICALLY POWERED MOBILITY DEVICE COMPRISING THE SAME” and filed on Mar. 19, 2019, which claims priority to European Patent Application No. 18169884.6 entitled “BATTERY SAVING SYSTEM AND ELECTRICALLY POWERED MOBILITY DEVICE COMPRISING THE SAME” and filed on Apr. 27, 2018, the entire contents of each application is herein incorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure generally relates to electrically powered mobility devices.

BACKGROUND

Electronic components usually consume energy even when they are switched off. Depending on the battery size and the energy consumption while the system is switched off, there is a risk that the battery/batteries will be drained when the device containing the battery/batteries is not in use.

For battery powered mobility devices that are not used on a daily basis this could become a major problem. In particular, it could be a problem for mobility devices of the kind where the idle current of a drive control system that controls the operation of the device is high is relation to the capacity of the battery/batteries. The situation is worsened in case the mobility device is left unused for a longer period of time without prior charging. This could result in a total battery drain, especially for batteries such as lead acid batteries which do not comprise any internal electronics. With lead acid batteries there is a risk of sulfation. Sulfation gradually degrades the battery/batteries, resulting in that they lose capacity. This risk increases when batteries are deeply discharged, i.e. when batteries are drained below the lowest recommended voltage.

SUMMARY

An object of the present disclosure is to provide a battery saving system which solves, or at least mitigates problems of the prior art.

There is hence according to a first aspect of the present disclosure provided a battery saving system for an electrically powered mobility device comprising a battery and a drive control system powered by the battery, wherein the battery saving system comprises: a current monitoring circuit configured to monitor a load current provided by the battery, wherein the current monitoring circuit is configured to determine whether a load current magnitude is below a load current threshold level, a timer circuit having a counter configured to successively count as long as the load current magnitude is below the load current threshold level, and to reset the counter in the event that the load current magnitude exceeds the load current threshold level, and a disconnecting switch configured to be operated between an open state and a closed state, wherein the timer circuit is configured to trigger the disconnecting switch to obtain the open state when the counter has reached a predetermined number to thereby disconnect the battery from the drive control system.

With an electrically powered mobility device is meant a mobility aid comprising an electric motor. Examples of such electrically powered mobility devices are mobility aids for small children with disabilities, hospital beds and lifting aids. The electric motor of devices of this type may only be used seldom, as the device does not necessarily form part of everyday life for its user. Such devices may have a drive control system which draws an idle current which is high in relation to the capacity of the battery/batteries. A further example of an electrically powered mobility device is an electrically powered wheelchair.

The battery saving system automatically disconnects/separates the battery from a drive control system and prevents the battery from being drained when not used. This is accomplished by monitoring the load current together with the timer circuit that allows the battery saving system to be idle until the counter reaches the predetermined number before disconnecting the battery from the drive control system with the disconnecting switch. The risk of sulfation may thereby be reduced.

One embodiment comprises a voltage monitoring circuit configured to monitor a battery voltage, wherein the current monitoring circuit is configured to monitor a charging current, and wherein the timer circuit is configured to reset the counter as long as at least one of a) the battery voltage is above a predetermined voltage threshold level and b) a charging current magnitude is above a predetermined charging current threshold level.

The counter is hence constantly reset as long as charging is in progress and one of the conditions a) and b) is fulfilled, enabling charging for any given length of time without disconnection of the battery from the battery charger.

The charging current can be differentiated from the load current since the two currents have opposite signs.

According to one embodiment the counter is configured to be activated when the battery voltage is below the predetermined voltage threshold level and the charging current magnitude is below the predetermined charging current threshold level.

According to one embodiment the disconnecting switch is configured to be set in the open state to disconnect the battery when the charging current magnitude is above a predetermined allowed charging current level.

According to one embodiment the predetermined allowed charging current level is higher than the maximum recommended battery charging current.

According to one embodiment the disconnecting switch is configured to be set in the open state to disconnect the battery when the battery voltage is above a predetermined allowed voltage level.

Thus, the battery is protected against overcharging. This may prolong the lifetime of the battery by reducing the risk of gas being released to the atmosphere during battery gassing. If too much gas is lost, the battery will dry out, reducing the battery lifetime. At the same time the risk of explosion is reduced.

According to one embodiment the predetermined allowed voltage level is higher than the maximum recommended battery charging voltage.

One embodiment comprises a button configured to enable setting the disconnecting switch in the closed state and to reset the counter.

One embodiment comprises a power supply configured to be powered by the battery and configured to power the timer circuit, wherein the disconnecting switch is configured to disconnect the power supply from the battery when the disconnecting switch is in the open state, and wherein the button has a mechanical switch configured to be set in a closed position when the button is actuated, causing the power supply to connect to the battery and power the timer circuit.

The power supply may for example be a power converter, e.g. a DC-DC converter. The power supply may for example be series-connected with the disconnecting switch. The button may for example include a mechanical switch such as a momentary mechanical switch, which is parallel connected with the disconnecting switch. By pushing the button, the momentary mechanical switch may be set in a closed position, closing the circuit formed by the battery and the power supply. The power supply will thus be powered by the battery. The button may hence activate the power supply. The power supply may be configured to power the timer circuit. The power supply may be configured to power the current monitoring circuit and/or the voltage monitoring circuit. By activating the power supply, the disconnecting switch may be set in the closed state. For example, the power supply may be configured to power the timer circuit when activated, causing the timer circuit to trigger the disconnecting switch to obtain its closed state. For example, if the disconnecting switch comprises a semiconductor switch, such as a transistor, the timer circuit may send a signal to the semiconductor switch which sets the semiconductor switch in its closed state. The power supply will thus be fed from the battery via the disconnecting switch which is in the closed state. Moreover, the drive control system will be connected to and powered by the battery. The button may for example be a mechanical button, e.g. a push button such as a momentary push button, or a soft button.

There is according to a second aspect of the present disclosure provided a method of prolonging the life of a battery of an electrically powered mobility device comprising a drive control system powered by the battery, comprising: detecting a load current from the battery to the drive control system, determining whether a load current magnitude is below a load current threshold level, counting as long as the load current magnitude is below the load current threshold level, in case the load current magnitude exceeds the load current threshold level, resetting the counter, and operating a disconnecting switch to obtain an open state when the counter reaches a predetermined number to thereby disconnect the drive control system from the battery.

One embodiment comprises, during charging: detecting a battery voltage and a charging current, determining whether the battery voltage is below a predetermined voltage threshold level or the charging current is below a predetermined charging current threshold level, and resetting the counter as long as at least one of a) the battery voltage is above the predetermined voltage threshold level and b) the charging current is above the predetermined charging current threshold level.

One embodiment comprises operating the disconnecting switch to obtain an open state when the charging current magnitude is above a predetermined allowed charging current level to thereby disconnect the battery from a battery charger.

One embodiment comprises operating the disconnecting switch to obtain an open state when the battery voltage is above a predetermined allowed voltage level to thereby disconnect the battery from a battery charger.

There is according to a second aspect of the present disclosure provided a control system for an electrically powered mobility device comprising the battery saving system according to the first aspect. The control system may be a supervisory control system which includes the drive control system. The supervisory control system may include further control functions than those of the drive control system which are directed to drive control. The supervisory control system may for example additionally be configured to control the seating system and any other function not related to drive control.

The control system may be configured to control the operation of the disconnecting switch based on the state of the timer circuit, in particular the counter.

There is according to a third aspect of the present disclosure provided an electrically powered mobility device comprising: a battery, a drive control system, and a battery saving system according to the first aspect.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to “a/an/the element, apparatus, component, means, etc.” are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, etc., unless explicitly stated otherwise.

