GB2256982A - Interference supressing arrangement for two-speed windscreen wiper motor. - Google Patents

Description

2 2) 6 '1 ') 2 I- MOTOR CIRCUIT The present invention relates to a motor

circuit of the type used, for example, to drive vehicle windscreen wipers.

Most windscreen wiper motors cause interference to the vehicle radio, principally by disturbing the vehicle supply voltage. In order to suppress this interference, it is common to provide, next to each relevant motor brush, a capacitor for suppressing noise in the Long Wave and Medium Wave frequency bands (commonly 15OkHz to 30OkHz, and 60OkHz to 1.6MHz respectively) and a choke for suppressing noise in the Short Wave frequency band. In order to suppress Long Wave and Medium Wave noise adequately, the capacitor should normally have a is capacitance of between 1.0 and 2.2pF, which makes it physically large.

A twospeed motor, for use in providing the conventional low and high wiping speeds, has three brushes, a ground brush connected to ground and two supply brushes, each placed at a suitable angle to the commutator ring relative to the ground brush so as to provide respectively the low or high wiping speed. This type of motor can cause interference at each of its two speeds, and thus has two capacitors and two chokes, one capacitor and one choke for each of the supply brushes.

In one known arrangement, the capacitors and chokes are placed on a brush plate inside the motor casing. Although this provides a compact unit, the capacitors in particular are limited in size due to the restricted space inside the motor casing. As a consequence the capacitance is also limited, sometimes reducing the effective Long Wave and Medium Wave noise suppression.

An arrangement of this type is shown in Figure 1 and is described in further detail below.

In another known arrangement, the capacitors and chokes are placed on the outside of the motor casing, either directly on the casing or in a separate container or compartment mounted on the casing. The capacitors and chokes are connected to their respective brushes by short leads passing through appropriate openings in the motor casing.

Although the size of the capacitors and chokes is less limited with this arrangement, it is still limited to an extent due to the restricted space in which the motor is usually positioned. This arrangement also makes the motor unit more difficult to assemble, and therefore more expensive.

The present invention seeks to provide an improved motor circuit.

Accordingly, an aspect of the present invention provides a motor circuit comprising an electric motor including a ground brush connected to ground and at least one supply brush; supply connecting means adapted to be connected to a d. c. power supply; a switch connected to the supply connecting means and to the supply brush or brushes; and an interference suppression capacitor connected to the supply connecting means and to ground.

With this arrangement, it is only necessary to have a single interference suppression capacitor irrespective of the number of supply brushes as, in use, the capacitor will always be connected to the appropriate supply brush.

The capacitor (or capacitors) can also be used to suppress noise from the switch, and also from the parking switch, which is not possible with the prior art arrangements.

Furthermore, as it has been realised that it is not necessary to place the capacitor (or capacitors) in or on the motor casing, the capacitor can conveniently be placed at a distance from the motor, for example in a part of the circuit where space is less restricted. This allows the use of larger capacitors, more able to provide better noise suppression. It has been found that this can more than offset any loss in suppression that may be caused by placing the capacitor (or capacitors) at a distance from the motor.

Additionally, the removal of the capacitors from within the motor casing frees space within the casing, which can simplify considerably the design of the brush plate and positioning of the chokes.

The appropriate value of capacitance to provide the desired noise suppression and to take into account the length of wire between the capacitor and the brushes can readily be found by the skilled person.

Preferably, the capacitor is disposed adjacent the supply connecting means. A capacitor of appropriate value could be supplied with the wiper assembly.

In another embodiment, for use with a motor circuit comprising a timer unit for providing an intermittent wipe facility, the interference suppression capacitor is disposed in the timer unit. Alternatively, when used with a motor circuit comprising a motor gearbox, the interference suppression capacitor is disposed in the motor gearbox. With either of these embodiments, the capacitor can be fitted within one of the units of the wiper motor assembly, so that the assembly can be supplied in a form in which it is not necessary to handle a loose capacitor.

Advantageously, the motor circuit comprises a single interference suppression capacitor.

According to another aspect of the present invention, there is provided a motor circuit comprising an electric motor including a ground brush connected to ground and at least. one supply brush; supply connecting means adapted to be connected to a d.c. power supply; a switch connected to the supply connecting means and to the supply brush or brushes; and an interference suppression capacitor disposed adjacent the switch.

Some embodiments of the invention are described below, by way of illustration only, with reference to the accompanying drawings, in which:Figure 1 shows a prior art windscreen wiper motor circuit; Figure 2 shows a first embodiment of windscreen wiper motor circuit; Figure 3 shows another embodiment of windscreen wiper motor circuit; and Figure 4 shows a third embodiment of windscreen wiper motor circuit.

Referring first to Figure 1, a prior art windscreen wiper motor circuit includes a two-speed motor 10 which comprises a ground brush 12, a low motor speed supply brush 14 and a high motor speed supply brush 16. The output shaft (not shown) of the motor 10 is connected to a gear box 18, of conventional form, which includes a park switch 20 connected between a timer unit 22 and either ground or a positive d.c. power supply V+. The timer unit 22, which is also of conventional form, provides an intermittent wiping facility.

The supply brushes 14,16 of the motor and the timer unit 22 are connected to respective terminals of a switching circuit 28 by respective conductors 24,26,32. The switching circuit 28, which is actuated by a driver-operated switch 30 movable between an off position 0, an intermittent wipe position I, a low speed position L and a high speed position H, acts to connect the appropriate conductor 24,26,32 to the power supply V +, which is typically the vehicle battery (not shown). When the switch 30 is switched to the intermittent wipe position I. the conductor 32 is connected to the power supply V+ to feed power to the motor 10 via the timer unit 22. In this mode, the timer unit 22 controls the supply of power to the motor 10 so as to stop the motor 10 for a predetermined period each time the wiper blades reach the park position, monitored by the state of the park switch 20. As this intermittent wipe feature is well known in the art, it will not be described further. 20 In the low speed or high speed position, the switching circuit 28 connects the appropriate conductor 24,26, and thereby the appropriate supply brush 14,16, to the power supply V+ to cause the motor to rotate continually at a low or high speed. The circuit also includes first and second interference suppression capacitors Cl,C2 for suppressing noise, caused by rotation of the motor, in the Long Wave and Medium Wave frequency bands. The capacitors Cl,C2 are placed within the motor 30 casing and are connected between their respective conductor 24,26 and the motor casing, which acts as electrical ground. Two chokes (not shown), for suppressing noise in the Short Wave frequency band, are also provided in the motor casing and are 35 connected in series between a respective supply brush 1 14,16 and conductor 24,26.

In practice, the capacitors Cl,C2 and the chokes are fitted on the brush plate (not shown) of the motor.

A washer motor 50 for driving a water pump of a windscreen washing mechanism, is also provided, being connected to the power supply V+ via a driver-operated washer switch 52. This is of conventional form.

Referring now to the first embodiment of circuit shown in Figure 2, it can be seen that the principal parts of this circuit are the same as those of the circuit of Figure 1. However, in this embodiment, the capacitors Cl and C2 of the circuit of Figure 1 are replaced by a single capacitor C3 connected to, and located adjacent, conductor 34 which couples the switching circuit 28 to the power supply V+. The other terminal of capacitor C3 is connected to ground.

When the switching circuit 28 connects one of the conductors 24,26,32 to the power supply V+, the capacitor C3 will also become connected to that conductor to provide the required noise suppression.

It will thus have the equivalent effect as the capacitors Cl,C2 of the circuit of Figure 1. 1 In choosing the appropriate capacitance for the capacitor C3, it is necessary to consider both the frequencies which are to be suppressed and also the length of conductor between the capacitor C3 and the chokes, to prevent the occurrence of electrical oscillation caused by the extra length of conductor between these components. However, since in practice the length of the conductor between the capacitor C3 and the chokes will be considerably less than the wavelength of the noise to be suppressed by the 1 capacitor C3, the selection of the appropriate capacitance is not difficult.

By moving the capacitor C3 away from the motor 10, it is possible to place it in a position where there are less restrictions on space, so that in practice it is not restricted size-wise. This can allow a more appropriate capacitor to be chosen, which can more than offset any degradation in suppression which may be caused by the length of wire between the capacitor C3 and the supply brushes 14,16.

Furthermore, in its position in Figure 2, the capacitor C3 can also suppress noise caused by the switching circuit 28.

Another embodiment of circuit is shown in Figure 3. In this embodiment, an interference suppression capacitor C4 is placed within the timer unit 22. It is connected between a power supply terminal of the timer unit 22 and its casing, which acts as electrical ground. The capacitor C4 has the same effect as the capacitor C3 of Figure 2 since it is directly connected to the switching circuit 28 via line 56.

As with the embodiment of Figure 2, this embodiment also provides a large choice of capacitors since there is normally more free space in the typical timer unit and, of course, since it is only necessary to have a single capacitor.

A third embodiment of circuit is shown in Figure 4, in which a-single interference suppression capacitor CS is placed within the gearbox 18, in which there is usually more free space than in the motor 10. The capacitor CS is connected to the power supply terminal of the park switch 20 and to the case of the gearbox 18. which acts as electrical ground.

As with the other embodiments, the capacitor C5 is connected directly to the switching circuit 28 via line 56, for coupling with the conductors 24, 26.

As the capacitors C4,C5 of Figures 3 and 4 will be protected from the environment by the case of the timer unit 22 and the gearbox 18, respectively, caseless capacitors can be used.

It should be clear to the skilled person that the above-described embodiments can be used with other motors, not just motors for vehicle windscreen wipers.

Claims (8)

Claims:

1. A motor circuit comprising an electric motor including a ground brush connected to ground and at least one supply brush; supply connecting means adapted to be connected to a d.c. power supply; a switch connected to the supply connecting means and to the supply brush or brushes; and an interference suppression capacitor connected to the supply connecting means and to ground.

2. A motor circuit according to claim 1, wherein the capacitor is disposed adjacent the supply connecting means.

3. A motor circuit according to claim 1, comprising a timer unit for providing an intermittent wipe facility, the interference suppression capacitor being disposed in the timer unit.

4. A motor circuit according to claim 1, comprising a motor gearbox, the interference suppression capacitor being disposedIn the motor gearbox.

5. A motor circuit according to any preceding claim, comprising two supply brushes.

6. A motor circuit according to any preceding claim, comprising a single interference suppression capacitor.

7. A motor circuit comprising an electric motor including a ground brush connected to ground and at least one supply brush; supply connecting means adapted to be connected to a d.c. power supply; a switch connected to the supply connecting means and to the supply brush or brushes; and an interference suppression capacitor disposed adjacent the switch.

8. A motor circuit substantially as hereinbefore described with reference to and as illustrated in Figure 2, 3 or 4.

8. A motor circuit substantially as hereinbefore described with reference to and as illustrated in Figure 2, 3 or 4.

Amendments to the clairns have been fiL-d as fdkms Claims:

1. A motor circuit comprising an electric motor including a ground brush connected to ground and at least two supply brushes; supply connecting means adapted to be connected to a d.c. power supply; an interference suppression capacitor connected to the supply connecting means and to ground; and a switch adapted to connect the supply connecting means and the interference suppression capacitor to each of the supply brushes selectively.

2. A motor circuit according to claim 1, wherein the capacitor is disposed adjacent the supply connecting means.

3. A motor circuit according to claim 1, is comprising a timer unit for providing an intermittent wipe facility, the interference suppression capacitor being disposed in the timer unit.

4. A motor circuit according to claim 1, comprising a motor gearbox, the interference suppression capacitor being disposed in the motor gearbox.

5. A motor circuit according to any preceding claim, comprising two supply brushes.

6. A motor circuit according to any preceding claim, comprising a single interference suppression capacitor.

7. A motor circuit comprising an electric motor including a ground brush connected to ground and at least one supply brush; supply connecting means adapted to be connected to a d.c. power supply; a switch connected to the supply connecting means and to the supply brush or brushes; and an interference suppression capacitor disposed adjacent the switch.