Such a windscreen wiper device is generally known. This prior art windscreen wiper device is designed as a so-called "flat blade" or "yokeless blade", wherein no use is made of several yokes pivotally connected to each other, but wherein the wiper blade is biassed by the carrier element, as a result of which it exhibits a specific curvature. The object of the invention is to provide an improved windscreen wiper device.

In order to accomplish that objective, a windscreen wiper device of the type referred to in the introduction is characterized according to the invention in that said groove extends in downward direction beneath the longitudinal strip for forming a longitudinal hollow channel defined by said longitudinal strip and a bottom of said groove, wherein a height of said hollow channel at the location of a middle longitudinal plane of said wiper blade perpendicular to the windscreen to be wiped is defined by: wherein W is a width of the longitudinal strip, and

wherein H is a height of the hollow channel at the location of a middle longitudinal plane of said wiper blade

perpendicular to the windscreen to be wiped.

First of all, the present windscreen wiper device can be used for large varieties of windscreens to be wiped mutually differing in their curvatures. Indeed, the hollow channel or "gap" between the longitudinal strip and the bottom of the groove generates a flexibility of said bottom and thus a variation of the position of the wiping element in a

direction perpendicular to the windscreen to be wiped, so that these differences in curvature may be compensated.

Secondly, any tolerances in windscreen shapes may thus be compensated as well.

According to the invention the height of said "gap" may vary, dependent on the pressure exerted by the oscillating arm on the wiper blade. Thus, the wiper blade being made of a flexible material, particularly rubber, may deform in accordance with said pressure, so that the "gap" between the longitudinal strip and the bottom of the groove may decrease in case of an increase of said pressure or may increase in case of a decrease of said pressure. Hence, the wiper properties are improved, as hazing is avoided at a location of a centre of the wiper blade at high pressures exerted by the oscillating arm. Extensive experiments and tests have made clear that the above defined range for the height of the "gap" at the location of the middle longitudinal plane of said wiper blade perpendicular to the windscreen to be wiped, is very advantageous. When the height of said "gap" is larger than indicated, the stability of the wiper blade is negatively affected, as tests have shown that - besides a vertical movement of the wiping element - also a rotational movement thereof will be generated. Such a rotation will negatively influence the so-called "attack angle" of the wiping element on the windscreen to be wiped. Consequently, the wiping properties will be damaged. In the event that the height of said "gap" is smaller than indicated, the

variation of the position of the wiping element in a

direction perpendicular to the windscreen to be wiped, i.e. the vertical movement of the wiping element, will be too small to have any positive effect on the repartition of the pressure on the wiping element, as exerted by the

oscillating arm. In a preferred embodiment of a windscreen wiper device in accordance with the invention said groove extends in upward direction above the longitudinal strip for forming a

longitudinal hollow channel defined by said longitudinal strip and an upper surface of said groove.

In another preferred embodiment of a windscreen wiper device according to the invention said wiper blade is provided with a spoiler at a side thereof facing away from a windscreen to be wiped.

The invention will now be explained more in detail with reference to figures illustrated in a drawing, wherein figure 1 is a perspective, schematic view of a

preferred embodiment of a windscreen wiper device according to the invention, with and without an

oscillating arm, respectively; and figures 2 through 5 show several cross-sectional views of a wiper blade as used in a windscreen wiper device of figure 1. Figure 1 shows a preferred variant of a windscreen wiper device 1 of the flat blade type according to the invention. Said windscreen wiper device 1 is built up of an elastomeric wiper blade 2 comprising a central or middle longitudinal groove 3, wherein a central or middle longitudinal strip 4 made of spring band steel is fitted in said longitudinal groove 3 (see figures 2 through 5) . Said strip 4 forms a flexible carrier element for the rubber wiper blade 2, as it were, which is thus biassed in a curved position (the curvature in operative position being that of a windscreen to be wiped) . An end of said strip 4 and/or an end of said wiperblade 2 may be connected on either side of the

windscreen wiper device 1 to respective connecting pieces or "end caps" 5. In this embodiment, the connecting pieces 5 are separate constructional elements, which may be form- locked, as well as force-locked to both ends of said strip 4/said wiper blade 2. In another preferred variant, said connecting pieces 5 are in one piece with the strip 4 made of spring band steel. The windscreen wiper device 1 is furthermore built up of a connecting device 6 for connecting an oscillating wiper arm 7 thereto. The oscillating wiper arm 7 can be pivotally connected to the connecting device 6 about a pivot axis near one end. The preferred embodiment of figure 1 according to the invention comprises a spoiler or "air deflector" 8 which is made in one piece with the rubber wiper blade 2 and which extends along the entire length thereof. The connecting device 6 with the wiper blade 2 is mounted onto the oscillating arm 7 as follows. A joint part 9 being already clipped onto the connecting device 6 is pivoted relative to the connecting device 6, so that said joint part 9 can be easily slided on a free end of the oscillating arm 7. During this sliding movement a resilient tongue 10 of said joint part 9 is initially pushed in against a spring force and then allowed to spring back into a hole 11 of said oscillating arm 7, thus snapping, that is clipping the resilient tongue 10 into the hole 11. This is a so-called bayonet-connection. The oscillating arm 7 together with the joint part 9 may then be pivoted back in a position parallel to the wiper blade 2 in order to be ready for use. By subsequently pushing in again said resilient tongue 10 against the spring force (as if it were a push button) , the connecting device 6 and the joint part 9 together with the wiper blade 2 may be released from the oscillating arm 7. Dismounting the connecting device 6 with the wiper blade 2 from the oscillating arm 7 is thus realized by sliding the connecting device 6 and the joint part 9 together with the wiper blade 2 in a direction away from the oscillating arm 7. The connecting device 6 comprises two cylindrical protrusions 12 extending outwards on either side of said connecting device 6. These protrusions 12 pivotally engage in identically shaped cylindrical recesses 13 of the plastic joint part 9. Said protrusions 12 act as bearing surfaces at the location of the pivot axis in order to pivot the joint part 9 (and the oscillating arm 7 attached thereto) about the pivot axis near one end of the oscillating arm 7. Although not shown in figure 1, but fully understood by a skilled person, said oscillating arm 7 is connected to a mounting head fixed for rotation to a shaft driven by a small motor. In use, the shaft rotates alternately in a clockwise and in a counter-clockwise sense carrying the mounting head into rotation also, which in turn draws said oscillating arm 7 into rotation and by means of said

connecting device 6 moves said wiper blade 2. With reference to figures 2 through 5 the wiper blade 2 comprises a wiping element 14. Said wiping element 14 consists of two tilting web grooves 15 defining a strip-like tilting web 16 between them, as well as a downwardly

extending wiping lip 17 on the tilting web 16. Said wiping lip 17 rests with its free end on a windscreen to be wiped. In action said wiping lip 17, as if it were a hinge, tilts in its oscillation reversal positions.

As can be seen in figures 2 through 5, the central groove 3 extends in downward direction beneath the longitudinal strip 4 for forming a longitudinal hollow channel 18 defined by said longitudinal strip 4 and a bottom 19 of said groove 3. Said central groove 3 also extends in upward direction above the longitudinal strip 4 for forming a longitudinal hollow channel 20 defined by said longitudinal strip 4 and an upper surface 21 of said groove 3. This is realized for

facilitating insertion of said longitudinal strip 4 inside said groove 3 and for reducing the amount of raw material used in order to minimize costs and weight.

The magnitude of said pressure is dependent, for example, on the curvature of a windscreen to be wiped, the curvature of the longitudinal strip 4, as well as on the force of a spring mounted between the mounting head and the oscillating arm 7. In case a relatively low pressure is exerted by the oscillating arm 7, that is by the longitudinal strip 4 on the wiper blade 2, the height H or "gap" of the hollow channel 18 may increase. The flexible bottom is in that case bent outwardly, so that the wiping element 14 is in that case in a position facing away from the longitudinal strip 4. The wiping element 14 is allowed to follow its normal oscillatory movement. In a situation when a relatively high pressure is exerted by the longitudinal strip 4 on the wiper blade 2. In that particular case the height H or "gap" of the hollow channel 18 may decrease. The flexible bottom is in that case bent inwardly, so that said wiping element 14 is forced into a position facing towards the longitudinal strip 4. In other words, due to the resiliency of the bottom 19 of the groove 3, said wiping element 14 is allowed to move in a direction perpendicular to a windscreen to be wiped, dependent on the pressure exerted by the longitudinal strip 4 on the wiper blade 2.

With reference to figure 5, according to the invention the height H of said hollow channel 18 at the location of a middle longitudinal plane of said wiper blade 2

perpendicular to the windscreen to be wiped is defined by:

— W < H < - W,

40 5 wherein W is a width of the longitudinal strip 4, and wherein H is a height of the hollow channel 18 at the location of the middle longitudinal plane of said wiper blade 2perpendicular to the windscreen to be wiped. As can be seen from figure 5, the width W of the longitudinal strip 4 is measured from one exterior

longitudinal side of the longitudinal strip 4 to the other exterior longitudinal side of the longitudinal strip 4. The height H or "gap" of the hollow chamber 18 is measured at the location of the middle longitudinal plane of said wiper blade 2 perpendicular to the windscreen to be wiped from the bottom 19 of said hollow channel 18 to the longitudinal strip 4.

The invention is not restricted to the variants shown in the drawing, but it also extends to other preferred embodiments that fall within the scope of the appended claims.