Agricultural machine comprising a safety system with improved triggering kinematics

An agricultural machine includes a hitching support, at least one tool or group of tools, at least one support arm which is connected to the hitching support by a first joint and to the tool or tool group, and which is mounted so as to pivot about a transfer axis between operational and raised positions, and a safety device making it possible to carry out a safety movement under the effect of pressure. The safety device includes a lift connected to the hitching support by a second joint. The second joint is offset relative to the first joint in the direction of travel. The safety movement can include a second movement phase during which the lift is able to move the tool or the group of tools away from the ground.

The present invention relates to the field of mounted, drawn or pushed agricultural machines, particularly of the type that glide resting on the ground in the normal use, such as harvesting, mowing or plant-treatment machinery.

The invention relates more specifically to an agricultural machine of the type mentioned hereinabove with a safety system having improved triggering kinematics.

Whatever their exact nature, the agricultural machines to which the invention relates all have in common the fact that during work they normally travel in a direction of forward travel and that they each comprise:a hitching support,at least one tool or group of tools having, in the work position, an extension transverse to the direction of forward travel and projecting laterally with respect to the hitching support,at least one mounting arm connected to the hitching support via a first articulation, and to the tool or the group of tools considered, said mounting arm being mounted with the ability to pivot about an axis referred to as the transfer axis, substantially parallel to the plane of the ground when the machine is hitched, and about which the tool or the group of tools can be transferred alternately between a working position in which it at least partially rests on the ground and at least one raised position, in which it is distanced from the ground, anda safety device by means of which the tool or the group of tools considered can perform a safety movement under the effect of sufficient pressure exerted thereon in an opposite direction to the direction of forward travel, this safety movement comprising at least a first phase of movement of which at least one component is a rotation toward the rear, this being with respect to the direction of forward travel, and about the first articulation.

Specifically, when they are being used, these machines may strike a stone, a stump or a similar obstacle protruding from the ground and firmly set therein, possibly hidden by the plant matter. In order to avoid damage to the tool or the group of tools, to the hitching support and/or to the connections between these elements, as a result of a brutal impact, the safety device in the known way causes the tool or the group of tools to pivot toward the rear in order to absorb the shock, compensate for the forward travel of the machine with respect to the obstacle, and give said tool or group of tools more time to overcome the obstacle, by passing over it by sliding or after being raised.

Numerous solutions are already known that allow this function to be achieved.

In these known machines, the aforementioned transfer axis also determines the transport position and potential intermediate positions such as, for example, a windrowing position in the case of a mower or a swather.

Such agricultural machines are known for example from documents FR 2 384 431, EP 2 189 053 and EP 2 926 643.

A constructional variant of such machines, in which the transfer axis is a vertical axis (the transport position being obtained by folding toward the rear, parallel to the direction of forward travel), is known from document EP 0 679 327.

Documents FR 2 384 431 and EP 2 189 053 further disclose the presence of additional means which, in addition to causing the tool or the group of tools to pivot toward the rear, also cause it to lift off the ground when the pressure exerted by the obstacle is sufficient and persists despite the folding-back.

Similarly, and more specifically in relation to a mower, document EP 2 926 643 also discloses additional means leading to a lifting, but of the frontal part of the tool or of the group of tools only, which lifting is intended to make it easier to pass over the top of the obstacle, which is often small in size.

However, these known solutions for safety systems are complex in construction, require several different active components or else perform actions that are difficult to control with precision.

It is an object of the present invention to overcome at least the chief disadvantages mentioned hereinabove.

To that end, the invention proposes, for an agricultural machine of the type defined hereinabove, in which the safety device comprises at least one lifting means connected to the hitching support by a second articulation and to the tool or to the group of tools, or to the mounting arm, by a third articulation, planning that the first articulation directly connects the mounting arm to the hitching support, that the second articulation is offset relative to the direction of forward travel with respect to the first articulation, and that the safety movement may comprise a second phase of movement that is consecutive to the first phase and in which the lifting means is in an end-stop state in which, if the pressure persists in the context of this second phase of movement, it exerts on the tool or the group of tools considered an upwardly-directed force so as to distance said tool or group of tools considered from the ground.

FIGS.1to7are a simplified illustration of an agricultural machine1moving normally in a direction of forward travel A during work, and comprising:a hitching support2,at least one tool or group of tools3having, in the work position, an extension transverse to the direction of forward travel A and projecting laterally with respect to the hitching support2,at least one mounting arm4connected to the hitching support2via a first articulation L1, and to the tool or to the group of tools3considered, said mounting arm1being mounted with the ability to pivot about an axis AT referred to as the transfer axis, substantially parallel to the plane of the ground S when the machine1is hitched, and about which the tool or the group of tools3can be transferred alternately between a working position in which it at least partially rests on the ground S and at least one raised position, in which it is distanced from the ground S,a safety device5by means of which the tool or the group of tools3considered can perform a safety movement under the effect of sufficient pressure P exerted in an opposite direction to the direction of forward travel A, this safety movement comprising at least a first phase of movement of which at least one component is a rotation toward the rear, this being with respect to the direction of forward travel A, and about the first articulation L1.

Furthermore, said safety device5comprises a lifting means6connected to the hitching support2by a second articulation L2and to the tool or to the group of tools3, or to the mounting arm4, by a third articulation L3. This lifting means6advantageously has a determined range of operation. Within this range, the lifting means6is positively active, and possibly controllable.

In addition, the second articulation L2is offset relative to the direction of forward travel A with respect to the first articulation L1and the first articulation L1directly connects the mounting arm4to the hitching support2.

Furthermore, the safety movement may comprise a second phase of movement that is consecutive to the first phase and in which the lifting means6is in an end-stop state in which, if the pressure P persists in the context of this second phase of movement, it exerts on the tool or the group of tools3considered an upwardly-directed force so as to distance said tool or group of tools3considered from the ground S. In addition, said tool or group of tools may potentially continue its rearward rotation (if the pressure P persists). The pressure P may be exerted on the tool or the group of tools3or on the mounting arm4.

By virtue of the above measures, the invention proposes a simple, robust, economical and reliable solution for bringing about a safety clearance movement when the tool or the group of tools3encounters, as the machine is moving forward, an obstacle that it can neither move aside nor overcome in the normal working position.

By providing two phases of safety movement the invention makes it possible to provide a graduated response with two levels, in terms of action, for overcoming the obstacle while continuing to move forward, this being dependent on the significance (size, weight, resistance to being pulled out, etc.) of the obstacle encountered. In addition, by assigning it an additional function by exploiting a (constructively defined) specific state, this being in relation to an arrangement with a particular configuration in terms of positions and connections, the invention may advantageously, where appropriate, make use of a means that already exists on the machine1to contribute to achieving the second phase of the safety movement. Finally, the movement away from the ground is a direct and exclusive result of constructional arrangements (end-stop state, arrangement, structure, dimensions and fixing of the lifting means6, etc.) and is achieved automatically and progressively from the moment at which the end-stop state is reached, and without the need for a command.

What is meant herein by an end-stop state is, in the case of a lifting means6that can be deformed or folded with a change (an increase or a decrease) to at least one dimension, a configuration reached by said means6at the end of the first phase of the safety movement and in which any additional modification in the same direction is rendered (physically) impossible, the means6then behaving like a connection element that is rigid and nondeformable with respect to an additional modification to said at least one dimension.

Thus, when the lifting means6reaches the end-stop state, the first phase of the safety movement comes to an end and the second phase of the safety movement begins. Furthermore, when the safety movement is in its second phase, the lifting means6is in an end-stop state. In the end-stop state, if the pressure P persists, the lifting means6exerts on the tool or the group of tools3considered an upwardly directed force or stress which allows said tool or group of tools3considered to be moved progressively away from the ground S in addition to potentially continuing to rotate this tool or group of tools rearward.

As a preference, the second articulation L2is, in the normal working position, also offset relative to the ground S with respect to the first articulation L1.

Advantageously, the lifting means6is configured to, on the one hand, allow a variation in the distance D between the second and third articulations L2and L3over a determined range of lengths and, on the other hand, reach an end-stop state in which said distance D exhibits a maximum or minimum value, and in which said lifting means6exerts an upwardly directed force.

This upward stress (with respect to the plane of the ground) progressively causes the tool or the group of tools3to move away from the ground during the course of the second phase of the safety movement, in the event of the pressure P persisting and as the machine1advances.

The minimum or maximum value for the distance D is reached when the lifting means reaches its end-stop state, at the end of the first phase of the safety movement.

During the first phase of the safety movement, the lifting means6is in what is referred to as a slack state. In the slack state, the lifting means6allows a variation in the distance D between the second and third articulations L2and L3over a determined range of lengths.

In practice, the choice of lifting means6and the adjustment of its travel (the end of travel corresponding to the end-stop state) determine the circumstances that define the beginning of the second phase of the safety movement. The fact that the end-stop state is linked to the maximum admissible length of one element of the machine makes it possible reliably and simply to ensure that the tool or the group of tools3is moved away from the ground. An angle of inclination (pivoting about the articulation L1when viewed from above) of around 5° to 15° of the tool or of the group of tools3(more specifically of between 10° and) 11° toward the rear with respect to a plane perpendicular to the direction of forward travel A, or its normal working position, constitutes a good compromise for the choice of the end of the first phase and the start of the second phase of the safety movement.

As a preference, the invention may plan that, when the tool or the group of tools3is in the working position, the distance D varies between, on the one hand, a minimum value corresponding to the normal working position of the tool or of the group of tools3and, on the other hand, a maximum value. This maximum value may be achieved at the end of the first phase or during the course of the second phase of the safety movement. In the normal working position, no obstacle is exerting sufficient pressure P on the tool or the group of tools3or on the mounting arm4to trigger the safety movement.

In order to ensure that the tool or the group of tools is kept in the normal working position, in collaboration with the first articulation L1, the mounting arm4is also advantageously connected directly to the hitching support2via a fourth articulation L4offset forward with respect to the first articulation L1, in the direction of forward travel A. In addition, the fourth articulation L4is offset downward toward the ground S, with respect to the second articulation L2. As a preference, the fourth articulation L4is situated substantially the same distance away from the plane of the ground as the first articulation L1. As is apparent from the attached figures, the first articulation L1connects the mounting arm4directly to the hitching support2, and the fourth articulation L4(which also directly connects the mounting arm4to the hitching support2).

What is meant in the present document as a direct connection or assembly is an assembly between mounting arm4and hitching support2that has no additional intermediate component or element, namely other than the articulation L1and, where appropriate, the fourth articulation L4. When the aforementioned two articulations are present, the direct articulated connection between the support2and the arm4consists in a pivot connection about the transfer axis AT.

According to a first embodiment variant, evident fromFIGS.1to7, the machine1may comprise, where appropriate for each mounting arm4, a guide device7that allows a variation in the distance between the third articulation L3or a free end11of the mounting arm4, on the one hand, and the or a fourth articulation L4that connects the mounting arm4to the hitching support2, on the other hand. The free end11of the mounting arm4is situated at the opposite end to the hitching support2. The lifting means6is connected to the tool or to the group of tools3or to the mounting arm4by the third articulation L3, which is offset toward the free end11of the arm4.

According to a second embodiment variant that can be implemented as an alternative to or in combination with the aforementioned first variant, the machine1may comprise, where appropriate for each mounting arm4, a guide device7allowing a variation in the distance between the first articulation L1, on the one hand, and the third articulation L3or the free end11of the mounting arm4, on the other hand.

By providing such a device7, the mounting arm4has the ability to have an at least limited modification to its shape, allowing the two phases of the safety movement without compromising the prime functions of said arm4, namely to support, hold in position, and move between the various illustrated operational positions, the tool or the group of tools3.

The guide device7may also make it possible to limit the amplitude of the safety movement. When the second phase of the safety movement is reached, the tool or the group of tools3is in what is known as the triggered position.

According to one feature of the invention, that makes it possible to limit the number of articulated fixing points between the mounting arm4and the hitching support2, the invention may plan for the transfer axis AT to pass through the first articulation L1.

According to a preferred construction, the transfer axis AT is defined by collaboration between the first and fourth articulations L1and L4, or in other words, said articulations L1and L4together define said axis AT. It is then fixed with respect to the hitching support2. This hitching support2is intended to be connected to a tractor or similar vehicle, not depicted.

Thus, these two articulations L1and L4guide both the safety movement and the transfer movements between the working position on the ground and one of the other predetermined positions away from the ground (transport position, windrowing position).

As shown by the attached figures, the machine1comprises at least a first cylinder8for keeping the tool or the group of tools3in the normal working position in a controlled manner, this first cylinder8allowing the tool or the group of tools3to perform the first phase of the safety movement. Said first cylinder8may allow the tool or the group of tools3to perform the first phase of the safety movement, freely, or preferably while applying a predetermined resistive stress counter to said safety movement, this first cylinder8forming part of the safety device5. In the latter case, the end-of-travel position defines the end-stop state (no need for a specific end stop) and the entirety of the travel of the first cylinder8is exploited. The first cylinder8thus generates the resistive stress that keeps the tool or the group of tools3in the normal working position. This amounts to stating that the first cylinder8generates the resistive stress that keeps the distance D at its minimum value.

Advantageously, the second articulation L2is, in the normal working position, offset forward, relative to the direction of forward travel A, and upward, away from the ground S, with respect to the first articulation L1. In addition, the lifting means6in the end-stop state may advantageously be a tie capable of transmitting a pulling force between the tool or the group of tools3, on the one hand, and the hitching support2, on the other hand (preferably right from the start of the second phase of the safety movement).

Such a design is advantageous because it minimizes the overall bulk of the machine1, because it avoids shifting the center of gravity of the machine1toward the rear, and because it makes it possible to maintain a certain ground clearance corresponding to the distance between the machine1and the ground S in the windrowing position (in the case of a mowing or haymaking machine for example).

The safety device5may thus comprise either the first cylinder8(designed and arranged to be in an end-stop state at the end of the first phase of the safety movement—FIGS.1to5andFIG.7), or a connecting means6′ of the chain, cable or similar type (FIG.6—designed and arranged to be in an inextensible state at the end of the first phase of the safety movement). The end of the first phase of the movement corresponds to the distance D between the second and third articulations L2and L3during the course of the safety movement reaching its maximum value. Whether the lifting means6comprises the first cylinder8or a connecting means6′, it is relaxed and/or unable to transmit a pulling force in the normal working position and during the first phase of the safety movement.

Such a tie of the passive type (connecting means) may be mounted in parallel with a second, raising, cylinder10, without necessarily being fixed by the same articulations or sites to the mounting arm4and/or to the hitching support2.

By using the first cylinder8as lifting means6, the invention allows the safety device5to be reset remotely (from the towing vehicle, not depicted) (using a hydraulic pressure control).

Furthermore, given the arrangement of the lifting means (relative arrangement of the articulations L2and L3with respect to the articulations L1and L4), the safety device5is situated essentially above the mounting arm4and above the tool or the group of tools3.

In order to enjoy a certain freedom in the guided path of the tool or of the group of tools3, and thus allow the simultaneous combination of several elementary movements, during the two phases of the safety movement, while at the same time limiting the number of articulations and allowing said tool or group of tools to move toward and from the other functional positions (transport position, windrowing position, triggered position), it may advantageously be planned for each of the first, second and fourth articulations L1, L2and L4to allow, on the one hand, at least a limited rotation about an axis substantially parallel to the plane of the ground S and substantially parallel to the direction of forward travel A and, on the other hand, at least a limited rotation about an axis substantially perpendicular to the plane of the ground S.

As is evident from comparingFIGS.1and2, and more particularly in connection with a machine1equipped with a tool or with a group of tools3that is inclined forward in the normal working position (nose-down), provision may be made for the device7for guiding the or a mounting arm4considered to be configured to exert a force on the front of the tool or of the group of tools3, so as to tilt it upward by rotation about the first articulation L1, and to do so already during the first phase of the safety movement.

Such an arrangement (automatically forcing an upward pivoting) of course encourages the tool or the group of tools3to pass over small-sized protruding obstacles, during the first phase of the safety movement (FIG.2).

As a preference, the guide device7(for example of the toggle-joint type with two parallel pivot pins) is actively kept in the folded position under the effect of a controlled stress supplied by the first cylinder8(and/or by another additional cylinder14), that also keeps the tool or the group of tools3in the normal working position.

As also shown by the attached figures, the second articulation L2is situated closer to a midplane PM of the hitching support2, perpendicular to the plane of the ground S and parallel to the direction of forward travel A, than the first articulation L1. As a preference, each of the first, second and fourth articulations L1, L2and L4is a ball-jointed articulation. Such a design of the machine1advantageously allows the mounting arm4to accompany the upward tilting of the front of the tool or of the group of tools3as it pivots about the first articulation L1.

However, as a variant (not depicted), the articulations L1and L4at least may be produced in the form of universal joints (with spiders), their vertical axes then being parallel to the two axes of pivoting of the toggle joints that constitute the guide device7. This variant nevertheless does not allow the upward pivoting of the front of the tool or of the group of tools3during the safety movement.

In connection withFIGS.1to3, it may be noted that the two successive phases of the safety movement take the following form:The first phase comprises a component of rotation with respect to the hitching support2toward the rear about the first articulation Ll. It comprises a pivoting about a vertical axis passing through L1. It also comprises a pivoting about an axis that is horizontal or parallel to the ground S, transverse to the direction of forward travel A and passing through L1, and it may also comprise a component of pivoting upward about the transfer axis AT.The second phase for its part comprises a pivoting about a vertical axis passing through L1, and a pivoting about an axis passing through L1and L2.

It will also be noted that the lifting means6forces the entirety of the tool or of the group of tools3to perform a pivoting about the axis passing through L1and L2.

In addition, during the safety movement, the tool or the group of tools3performs a rotation together with at least part of the mounting arm4. In general, the tool or the group of tools3performs the safety movement with respect to the hitching support2together with the mounting arm4. As is evident fromFIGS.2and3, the tool or the group of tools3performs the safety movement together with the lifting means6.

In order to adapt the position of the tool or of the group of tools3to suit the unevennesses of the terrain, the machine1may comprise a load-lightening means9relieving part of the force with which the tool or the group of tools3bears against the ground, said load-lightening means9advantageously consisting of an energy accumulator.

In order to limit unwanted triggerings of the safety device5and minimize the number of cylinders employed, provision is advantageously made for the first cylinder8that forms part of the lifting means6or that alone constitutes said means, to be connected to a pressure accumulator9′ in order to constitute the load-lightening means9(FIG.1D).

In that case, the first cylinder8and, where appropriate, the load-lightening means9, ensures that the tool or the group of tools3is kept in the normal working position, provides the resistive force that has to be overcome in order to trigger the first phase of the safety movement, and acts as a tie at the end of travel in order to automatically lift the tool or the group of tools3during the second phase of the safety movement, by movement about the ball-jointed connection that forms the first articulation L1. In addition, the load-lightening means9also makes it possible to reduce the force with which the tool or the group of tools3presses down on the ground, as the distance D between the second and third articulations L1and L3lengthens, thus making it easier to pass over small-sized obstacles without the need to trigger the second phase of the safety movement. In other words, during the first phase of the safety movement, made up of at least a rearward rotation about the first articulation L1of the tool or of the group of tools3with respect to the hitching support2, the load-lightening means9generates an upwardly directed torque on the arm4and about the transfer axis AT without necessarily separating the tool or the group of tools3from the ground S.

In order to be able to ensure the movement of the tool or of the group of tools3between the various customary positions needed for correct operation and transport of the machine1, the latter comprises, where appropriate for each tool or group of tools3, a second cylinder10known as the raising cylinder, configured to transfer the tool or the group of tools3considered alternately between the working position and at least one intermediate or final raised position, by pivoting about the transfer axis AT.

For preference, and in accordance with an embodiment that is practical, simple, and not very bulky, the second cylinder10, or raising cylinder, is constructionally associated with the lifting means6and is advantageously secured to and arranged coaxially in the extension of the first cylinder8that forms parts of said lifting means6and configured to be, at the end of the first phase of the safety movement, in a lengthened end-stop state.

According to one preferred embodiment of the invention that is evident fromFIGS.1to7, the or each mounting arm4comprises a first front constituent part4′ directly connected to the hitching support2by a or the fourth articulation L4and a second rear constituent part4″ connected directly to the hitching support2by the first articulation L1, said first and second constituent parts4′ and4″ being connected to one another by the or a guide device7. In this embodiment, the second part4″ comprises the free end11of the mounting arm4, and the third articulation L3.

In a variant, provision may also be made for the first front part4′, connected to the hitching support4by the articulation L4, to comprise the free end11and the articulation L3, to the detriment of the second rear part4″, connected to the hitching support2by the articulation L1.

Whichever is the constituent part of the arm4that bears the free end11and the articulation L3, the guide device7allows the mounting arm4to deform, so as to allow the mounting arm4to effect a rotation about L1without moving the fourth articulation L4, this deformation allowing the part4′ to be misaligned from the part4″. As a preference, this deformation makes it possible to form an angle (other than 180°) between the part4′ and the part4″.

More specifically, and according to an advantageous constructional variant evident fromFIGS.1to7, the or each mounting arm4may have an A-shaped structure of which the vertex is connected to the tool or to the group of tools3, for example via a fifth articulation L5, and of which the two legs12and12′ are connected, at their opposite ends from the vertex, to the hitching support2by the first articulation L1and by the or a fourth articulation L4, respectively.

As described above, the guide device7may be incorporated either into the front leg12′ (FIGS.1to7) or into the rear leg12of the A-shaped structure.

In the attached figures, these two legs12and12′ are rigidly connected by a crossmember. Of course, several crossmembers (or any other means of rigid attachment) may be envisioned.

Such a structure of mounting arm4is more particularly described and illustrated in French patent application No. 1760994 of Nov. 21, 2017, in the name of the Applicant Company, the various embodiment variants that form the subject matter of that patent application and, more generally, the entirety of the content thereof, being incorporated by reference into the present.

As is evident from the attached figures, the articulation L5is, for example, a pivot connection with an axis substantially parallel to the direction of forward travel A in the normal working position (absence of sufficient pressure P to move the group of tools3toward the rear—group of tools3extending in a direction substantially perpendicular to the midplane PM—FIG.1), achieving a pendular attachment of the tools3.

Furthermore, the articulation L3is situated above the mounting arm4such that the first cylinder8and second cylinder10are also positioned a pronounced distance above said arm4.

The tool or the group of tools3may for example comprise or consist of a conditioner or a conveyor.

The machine1may be of the mounted, semimounted or drawn type. In the latter two instances, a wheelset supports at least part of the weight of the machine1. In order notably to be able simply to provide a stress that causes the upward tilting of the front edge of the tool or of the group of tools3, using the rearward pivoting movement about the first articulation L1during the first phase of the safety movement, provision may, as shown in the attachedFIGS.1to5, be made for the two legs12and12′ each to have a curved or bowed shape, with portions that rise and fall with respect to the plane containing the two outer ends of said legs12and12′ and the vertex of the A-shaped structure, the guide device7being incorporated into one of said portions, this being dependent on the desired variation in distance.

According to a first variant evident fromFIGS.1to5, the guide device7consists of a mechanism of the toggle joint or scissors stay type comprising a link rod13connected in an articulated manner to or to the two constituent parts4′ and4″ of the mounting arm4considered using pivot connections with parallel axes.

In another alternative embodiment variant depicted inFIG.7, the second articulation L2is offset toward the rear, relative to the direction of forward travel A, and downward, closer to the ground S, with respect to the first articulation L1. In addition, the second articulation L2is situated further away from the midplane PM than the first articulation L1. The lifting means6may then comprise, or else consist of, a thrusting additional cylinder14exerting a torque forward and upward about the articulation L1so as to keep the tool or the group of tools3in a normal working position. The end-stop state of the lifting means6is then reached when the additional cylinder14is retracted all the way to the end of its travel. This additional cylinder14may also make it possible to increase the lightening of the load during the safety movement.

In the context of this other variant, the third articulation L3is advantageously situated (in the working position with respect to the plane of the ground) above the second articulation L2, whereas in the variants ofFIGS.1to6it is the articulation L2that is advantageously situated above the articulation L3.

AlthoughFIGS.1to7show a machine1with just one tool or group of tools3, said machine1may of course comprise two tools or groups of tools3arranged on either side of the hitching support2, preferably of identical forms and arranged symmetrically (with respect to the midplane PM), each one connected to the hitching support2by its own mounting arm4and each one associated with a safety device5.

In connection with a preferred application of the invention, the tool or the group of tools3consists of a mowing member or member for treating cut plant matter, or a group of such members, attached by means of a pivot connection L5, forming a or the fifth articulation with an axis substantially parallel to the direction of forward travel A in the normal working position, to the free end11of the support arm4which is the opposite end to the hitching support2, said machine1being of the mounted or drawn type.

Of course, the invention is not restricted to the embodiments described and depicted in the attached drawings. Modifications remain possible, notably from the viewpoint of the makeup of the various elements or through substitution of technical equivalents, without thereby departing from the field of protection of the invention.