Portable pump

Abstract

Disclosed is a portable pump including a reciprocating air compressor arrangement with a crank driving a connecting rod and a piston within a cylinder, the connecting rod being connected to the crank and piston, the crank actuating the piston in a reciprocating motion within and relative to the cylinder, an electric motor having a drive shaft mounted to the crank and rotatable about a drive shaft axis, the drive shaft axis being at least substantially coaxially aligned with an axis of rotation of the crank, a control unit communicating with the electric motor to control the pump, a power supply communicating with the control unit to power the control unit and electric motor, a common housing containing the electric motor, reciprocating air compressor arrangement, control unit, and power supply, and an outlet fluidly connected to the reciprocating air compressor arrangement for fluidly engaging with an pumpable object.

Claims

1. A gearless portable pump capable of inflating a bicycle tire to 100 psi, comprising: a reciprocating air compressor arrangement comprising: a crank that drives a connecting rod and a piston within a cylinder, the connecting rod having a first end and a second end, the first end of the connecting rod connected directly to the crank and the second end of the connecting rod connected directly to the piston, with the crank provided to actuate the piston in a reciprocating motion within and relative to the cylinder so as to compress air within the cylinder; a brushless electric motor having a drive shaft mounted directly to the crank, with the drive shaft rotatable about a drive shaft axis, and with the drive shaft axis at least substantially coaxially aligned with an axis of rotation of the crank; a control unit in electrical communication with the electric motor to control operation of the pump; a power supply comprising a rechargeable battery in electrical communication with the control unit to supply power to the control unit and electric motor; the electric motor, the reciprocating air compressor arrangement, the control unit and the power supply each contained within a common housing; and an outlet fluidly connected to the reciprocating air compressor arrangement for fluidly engaging with an object to be pumped; wherein the reciprocating air compressor arrangement has an inner cylinder diameter (d, in mm), a stroke (s, in mm) and a piston clearance at top dead center (c, in mm), which meet the following design criteria:
1500<d.sup.2(s4.2c)<3800 wherein the piston clearance at top dead center is a clearance between a top of the air compressor cylinder and the piston.

2. The gearless portable pump according to claim 1, wherein the clearance at the top dead center (c) is between 0.2 and 1.0 mm.

3. The gearless portable pump according to claim 1, wherein the inner cylinder diameter (d) is between 12.0 and 20.0 mm.

4. The gearless portable pump according to claim 1, wherein the piston stroke (s) is between 10.0 and 14.0 mm.

5. The gearless portable pump according to claim 1, wherein the rechargeable battery has a nominal voltage of between approximately 7 and 12 volts, a C rating of at least approximately 25, and a capacity of between approximately 200 and 600 mAh.

6. The gearless portable pump according to claim 1, wherein the electric motor is a brushless DC motor having a motor diameter of between approximately 25 and 35 mm, a torque range of between approximately 100 and 300 mNm, and capable of operating at a speed of at least 550 rpm/V when subjected to a compressor load.

7. The gearless portable pump according to claim 1, wherein the pump has a total weight of less than 400 grams.

8. The gearless portable pump according to claim 1, wherein the housing has a length of between approximately 55 and 95 mm, a height of between approximately 50 and 70 mm, and a width of between approximately 30 and 45 mm.

9. The gearless portable pump according to claim 1, wherein the outlet is provided on or mounted to the housing.

10. The gearless portable pump according to claim 9, wherein the outlet comprises a collar extending outwardly from the housing, the collar comprising a valve receiving bore for receiving a valve of the object to be pumped.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) It will be convenient to hereinafter describe a preferred embodiment of the invention with reference to the accompanying figures. The particularity of the figures is to be understood as not limiting the preceding broad description of the invention.

(2) FIG. 1 is a schematic side view of the portable pump according to the present invention.

(3) FIG. 2 shows a typical pressure versus volume (PV) diagram for a reciprocating air compressor;

(4) FIG. 3 shows an isometric view of the portable pump shown in FIG. 1.

(5) FIG. 4 shows the portable pump of in FIG. 1 when engaging a bicycle tyre valve.

(6) FIG. 5 is a photograph of the portable pump of FIG. 1, when shown in a size comparison with two conventional CO2 canisters and a canister adaptor.

DETAILED DESCRIPTION

(7) FIGS. 1 and 3 to 5 show a portable pump 100 according to the present invention.

(8) The portable pump 100 includes a power supply 102, and an electric motor 104 having a drive shaft 106 that connects directly to a reciprocating air compressor 108. In this regard, the drive shaft 106 is rigidly mounted to the crank 122, with the rotation axes of the drive shaft 106 and the crank aligned along X-X (shown in FIG. 1).

(9) A control unit 110 is provided, which is in electrical communication with the electric motor 104, and the power supply 102. The power supply 102, electric motor 104, drive shaft 106, reciprocating air compressor arrangement 108 and control unit 110 are all contained within a housing 112.

(10) The control unit 110 may be a printed circuit board that consists of control circuitry that turns the motor ON and OFF via switch 114, and monitors the battery's voltage.

(11) The reciprocating air compressor arrangement 108 includes a number of components which allow for the portable pump 100 to be miniature in size. The reciprocating air compressor arrangement 108 includes a cylinder 116, as well as a piston 118 connected to a connecting rod 120. The connecting rod 120 is connected to a crank 122 which is driven directly by the motor's drive shaft 106, rather than the drive shaft 106 driving the crank 122 via a gear assembly.

(12) The piston 118 preferably further includes a sealing arrangement (not shown) which ensures compressed air is maintained within the cylinder 116 during the compression process.

(13) In operation, the portable pump 100 is turned on by a user via switch 114. Once turned on, the electric motor 104 starts running which, in turn, rotates the drive shaft 106. The rotating drive shaft 106 turns/rotates the crank 122, causing the connecting rod 120 and piston 118 to reciprocate axially within the cylinder 116. One-way valves (not shown) located on the top surface of the piston 118 as well as inside the compressor head 124 ensure that air is compressed inside the cylinder 116 and forced through the outlet 126. This process is carried out many times a second as the piston 118 axially reciprocates within the cylinder 116.

(14) Advantageously, the arrangement of the portable pump 100 allows it to be manufactured small enough so that it can be mounted directly onto a tyre valve. Indeed, the pump 100 can be considered to be of a miniature size when compared to existing pump designs. This means that no additional hose or fittings are required to transfer the compressed air to the tyre, as the pump can fit between most conventional 700 mm diameter bicycle wheel spoke configurations and directly onto the tyre valve, thereby further reducing the size and weight of the pump 100. The pump 100 is manufactured without a gearbox or outlet hose, and so this enables the pump 100 to be of a very small size when compared to existing pump designs. The pump 100 has a length only in the order of approximately 55 to 95 mm, a height of only approximately 50 to 70 mm and a width of only approximately 30 to 45 mm. These small dimensions allow the pump to fit easily into a cyclist's jersey pocket.

(15) For a high pressure, direct-drive (i.e. no gearing) portable/miniature pump to be realised, the compressor's compression ratio needs to be optimised so that a small, brushless motor can be utilised, while achieving a pump up time of less than 1 minute. The diameter of the brushless motor must be small enough so that it fits inside the pump, and therefore motor diameters ranging from 25-35 mm need to be considered. At the time of writing, low cost 25-35 mm diameter brushless DC motors that are fitted with rare earth, permanent magnets can achieve motor torques ranging from 100 to 300 mNm. Therefore, the compressor should be designed so that it can be driven by a motor that can produce this level of torque.

(16) To determine the required motor torque, one must consider the pressure-volume (PV) diagram of a reciprocating compressor, as shown in FIG. 2. The swept volume (V.sub.bV.sub.d) and the clearance volume (V.sub.d) can be calculated using:

(17) $\begin{array}{cc}{V}_b-V_d={\left(\frac{d}{2}\right)}^{2}s& \left(1\right)\\ V_d={\left(\frac{d}{2}\right)}^{2}c& \left(2\right)\end{array}$

(18) Where d is the diameter of the cylinder, s is the stroke of the piston, and c is the clearance of the piston from the top of the cylinder when the piston is at top-dead centre. From Equations (1) and (2) V.sub.b is easily determined. Assuming that the compression and expansion of air is a reversible polytropic process (PV.sup.n=constant) Equation (2) can be used to determine V.sub.a, and therefore the induced volume (V.sub.bV.sub.a) can be calculated using:

(19) $\begin{array}{cc}{V}_b-V_a={}_c{\left(\frac{d}{2}\right)}^2\left[s+c-{c\left(\frac{P_d}{P_a}\right)}^{\frac{1}{n}}\right]& \left(3\right)\end{array}$

(20) where .sub.c is the efficiency of the compressor and n is the polytropic index. Equation (3) can then be substituted into Equation (4), which calculates the mass flow rate (m) of air entering the compressor:

(21) $\begin{array}{cc}m=\frac{P_a\left(V_b-V_a\right)}{\mathrm{RT}}& \left(4\right)\end{array}$

(22) Where is the motor speed (in Hz), R is Boltzmann's gas constant (in J/kgK) and T is the temperature of the air entering the cylinder.

(23) The indicated power (IP) of the compressor can then be calculated using the following equation:

(24) $\begin{array}{cc}\mathrm{IP}=\left(\frac{n}{n-1}\right)\mathrm{mR}\left({T\left(\frac{P_d}{P_a}\right)}^{\frac{\left(n-1\right)}{n}}-T\right)& \left(5\right)\end{array}$

(25) Once IP is known, the mean effective pressure (P) acting on the top surface of the piston can be calculated using the following equation:

(26) $\begin{array}{cc}P=\frac{\mathrm{IP}}{\left(V_b-V_d\right)}& \left(6\right)\end{array}$

(27) Finally, an estimate of the required motor torque () can be calculated using:

(28) $\begin{array}{cc}=\frac{P{d}^{2}s}{8}& \left(7\right)\end{array}$

(29) Substituting Equations (1-6) into Equation (7) yields the following:

(30) $\begin{array}{cc}=\frac{d^2{P}_a{}_c}{8T_i}\left(\frac{n}{n-1}\right)\left(s+c-{c\left(\frac{P_d}{P_a}\right)}^{\frac{1}{n}}\right)\left({T_i\left(\frac{P_d}{P_a}\right)}^{\frac{\left(n-1\right)}{n}}-T_i\right)& \left(8\right)\end{array}$

(31) Assuming ambient conditions, Equation (8) can be simplified to the following design equation, which can be used to optimise the compressor's critical dimensions d, s and c to ensure the chosen brushless motor can provide sufficient torque:
1500<<3800(9)

(32) Where =d.sup.2(s4.2c) (dimensions in mm). Equation (7) assumes the chosen brushless motor can provide motor torques ranging from 100-300 mNm.

(33) Further to this, the pump must be able to pump up tyres fast enough so that the pumping process is not laborious for the user. Ideally, a standard-sized road bike tyre should be able to be pumped from 0 psi to 100 psi in less than one minute. An estimate of tyre pump up times (t) can be determined from the pumps free air delivery (FAD):

(34) $\begin{array}{cc}t=\frac{V_t\left(P_d-P_a\right)}{P_a\mathrm{FAD}}& \left(10\right)\end{array}$

(35) Where V.sub.t is the tyre volume and
FAD=(V.sub.bV.sub.a)

(36) Substituting Equations (3) and (10) into Equation (11), and assuming ambient conditions, the following equation can be used to estimate a pump up time for a given value of (in mm units) and motor speed .sub.rpm (in revolutions per minute):

(37) $\begin{array}{cc}t=\frac{540{10}^6}{{}_{\mathrm{rpm}}}& \left(12\right)\end{array}$

(38) As the brushless motor is not geared, its speed will reduce significantly with increasing tyre pressure during pumping. However, the inventors found that by increasing the clearance (c) to a value ranging from the usual 0-0.2 mm size for a highly efficient compressor out to 0.2-1.0 mm, the reduction in motor speed was less. This reduction easily accounted for lower values due to larger clearances, and fast pump up times were maintained. Further to this, the large range in allowable clearances makes the compressor easier to manufacture with higher yields.

(39) Experiments carried out by the inventors showed that when utilising the following compressor dimensions: Inner cylinder diameter (d): 12-20 mm Stroke (s): 10-14 mm Clearance (c): 0.2-1.0 mm

(40) Brushless motors of 25-35 mm diameter when driven with 7-12 volts could easily achieve pump up times of less than 60 seconds, provided the brushless motors were designed to rotate at speeds equal to, or greater than 550 rpm/V under compressor load. The 7-12 volt voltage requirements allow the pump to be powered from either a 2-cell or 3-cell high discharge lithium battery.

(41) FIG. 3 shows the miniature pump 100 in isometric view. Charge port 128 allows the use of an external charger to charge the pump's internal battery. FIG. 4 shows the miniature pump 100 when engaged onto a valve 128 of a bicycle tyre 130 via the pump's outlet 126. As the unit is so small, it easily fits between the spokes 132 of the bicycle wheel without use of a hose. However, for wheel designs that did not allow for a direct connection (i.e. disc wheels), the pump's outlet 126 can be replaced by an optional hose.

(42) One of the main dimensional constraints of the pump 100 is the size of the rechargeable battery 102. The battery 102 must be small enough to fit inside the housing 112 of the pump 100, yet be able to provide enough current to pump up at least one bicycle tyre before a recharge is required. The battery 102 must also be able to handle the high currents required to drive the compressor arrangement 108, without affecting is performance, or worse, being damaged due to excessive current draw.

(43) The rate (C) at which a battery 102 can be safely discharged is dependent on both the maximum discharge current (I) that the battery experiences, and the battery's capacity (). These three variables are related as follows:
I=C(13)

(44) Experiments have shown that for the pump 100 to be realised, rechargeable batteries must be manufactured with C ratings of at least 25, otherwise the battery's capacity is significantly reduced after prolonged use.

(45) The amount of torque that a brushless motor can deliver is estimated as follows:

(46) 0$\begin{array}{cc}=\frac{30I}{\mathrm{Kv}}& \left(14\right)\end{array}$
Where Kv is the motor's speed (in units rpm/V). Substituting Equation (13) into Equation (14) and rearranging allows us to determine the minimum battery capacity requirements for the miniature pump:
[mAh]>4K(15)

(47) For brushes motors with torques of at least 100 mNm and speeds of at least 550 rpm/V, Equation (15) suggests the pump's battery must have a capacity of at least 200 mAh. At the time of writing, commercially available high-discharge lithium batteries with C ratings greater than 25, and with capacities ranging from 200-600 mAh were able to fit inside the housing 112 of the pump 100, assuming the dimensions of the housing 112 ranged from 55-95 mm in length, 50-70 mm in height and 30-45 mm in thickness. It was also determined that batteries of these capacities were able to pump up at least one road bike tyre to 100 psi without the need to be recharged.

(48) FIG. 5 has been provided for purely comparative purposes, to further highlight the small (ie. miniature) size of the pump 100. A cyclist carrying the pump 100 in a rear pocket of their jersey would require similar pocket space as when carrying two CO2 canisters C and the associated adaptor/connector A. Thus, the cyclist should be easily able to carry the pump 100 instead of the canisters and adapter.

(49) It is to be understood that various alterations, modifications and/or additions may be introduced into the construction and arrangement of the parts previously described without departing from the spirit or ambit of this invention.