Title:
Rocker arm system for engine valve actuation
Kind Code:
A1


Abstract:
Systems and methods for actuating engine valves are disclosed. The systems may include primary and auxiliary rocker arms disposed adjacent to each other on a rocker arm shaft. A rocker arm coupling assembly may be disposed between the auxiliary rocker arm and the primary rocker arm. The coupling assembly may include a piston having a curved surface disposed in a bore formed in the primary rocker arm, and a slot having a second radius of curvature formed in the auxiliary rocker arm. The piston may be selectively hydraulically locked into an extended position between the primary and auxiliary rocker arms so as to selectively transfer one or more auxiliary valve actuation motions from the auxiliary rocker arm to the primary rocker arm.



Inventors:
Usko, James N. (North Granby, CT, US)
Sledesky, Stephen (East Hartford, CT, US)
Waldburger, David (Coventry, CT, US)
Application Number:
11/128328
Publication Date:
12/15/2005
Filing Date:
05/13/2005
Primary Class:
Other Classes:
123/90.2, 123/90.27
International Classes:
F01L1/02; F01L1/18; F01L1/26; F01L1/34; F01L9/02; F01L13/06; (IPC1-7): F01L1/34; F01L1/02
View Patent Images:



Primary Examiner:
CHANG, CHING
Attorney, Agent or Firm:
KELLEY DRYE & WARREN LLP (Parsippany, NJ, US)
Claims:
1. A system for actuating an engine valve comprising: a rocker arm shaft; a means for imparting primary valve actuation motion; a primary rocker arm disposed on the rocker arm shaft, said primary rocker arm being adapted to actuate an engine valve and receive motion from the means for imparting primary valve actuation motion; a means for imparting auxiliary valve actuation motion selected from the group consisting of: engine braking motion, exhaust gas recirculation motion, and brake gas recirculation motion; an auxiliary rocker arm disposed on the rocker arm shaft adjacent to the primary rocker arm, said auxiliary rocker arm being adapted to receive motion from the means for imparting auxiliary valve actuation motion; and a rocker arm coupling assembly disposed between the auxiliary rocker arm and the primary rocker arm, said coupling assembly being adapted to selectively transfer one or more auxiliary valve actuation motions from the auxiliary rocker arm to the primary rocker arm.

2. The system of claim 1, wherein said coupling assembly comprises: an actuator piston disposed in a bore formed in said primary rocker arm; and a slot formed in said auxiliary rocker arm for selectively receiving said actuator piston.

3. The system of claim 2, wherein said actuator piston is disposed in said auxiliary rocker arm, and said slot is formed in said primary rocker arm.

4. The system of claim 2, wherein said actuator piston includes a curved surface to facilitate engagement with said slot.

5. The system of claim 2, wherein said slot includes a curved surface to facilitate engagement with said piston.

6. The system of claim 1, wherein said primary rocker arm comprises an exhaust rocker arm, and said auxiliary rocker arm comprises an intake rocker arm.

7. The system of claim 1, further comprising: a control valve; and a lash piston disposed in a bore formed in said primary rocker arm.

8. A system for actuating an engine valve comprising: a rocker arm shaft; a means for imparting primary valve actuation motion; a primary rocker arm disposed on the rocker arm shaft, said primary rocker arm being adapted to actuate an engine valve and receive motion from the means for imparting primary valve actuation motion; a means for imparting auxiliary valve actuation motion; an auxiliary rocker arm disposed on the rocker arm shaft adjacent to the primary rocker arm, said auxiliary rocker arm being adapted to receive motion from the means for imparting auxiliary valve actuation motion; and a coupling assembly, comprising: an actuator piston disposed in a bore formed in said primary rocker arm; and a slot formed in said auxiliary rocker arm for selectively receiving said actuator piston, wherein said actuator piston includes a curved surface to facilitate engagement with said slot.

9. The system of claim 8, said coupling assembly being adapted to selectively transfer one or more auxiliary valve actuation motions from the auxiliary rocker arm to the primary rocker arm.

10. The system of claim 8, wherein said actuator piston includes a curved surface to facilitate engagement with the slot.

11. The system of claim 8, wherein said primary rocker arm comprises an exhaust rocker arm, and said auxiliary rocker arm comprises an intake rocker arm.

12. The system of claim 8, further comprising: a control valve; and a lash piston disposed in a bore formed in said primary rocker arm.

13. The system of claim 8, the auxiliary valve actuation motion selected from the group consisting of: engine braking motion, exhaust gas recirculation motion, and brake gas recirculation motion.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

This application relates to and claims priority on U.S. Provisional Application No. 60/570,814, filed May 14, 2004 and entitled “Rocker Arm System for Engine Valve Actuation,” a copy of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to systems and methods for actuating valves in internal combustion engines. In particular, the present invention relates to systems and methods for actuating valves using a one or more rocker arms.

BACKGROUND OF THE INVENTION

Internal combustion engines typically use either a mechanical, electrical, or hydro-mechanical valve actuation system to actuate the engine valves. These systems may include a combination of camshafts, rocker arms, and push rods that are driven by the engine's crankshaft rotation. When a camshaft is used to actuate the engine valves, the timing of the valve actuation may be fixed by the size and location of the lobes on the camshaft.

For each 360 degree rotation of the camshaft, the engine completes a full cycle made up of four strokes (i.e., expansion, exhaust, intake, and compression). Both the intake and exhaust valves may be closed, and remain closed, during most of the expansion stroke wherein the piston is traveling away from the cylinder head (i.e., the volume between the cylinder head and the piston head is increasing). During positive power operation, fuel is burned during the expansion stroke and positive power is delivered by the engine. The expansion stroke ends at the bottom dead center point, at which time the piston reverses direction and the exhaust valve may be opened for a main exhaust event. A lobe on the camshaft may be synchronized to open the exhaust valve for the main exhaust event as the piston travels upward and forces combustion gases out of the cylinder. Near the end of the exhaust stroke, another lobe on the camshaft may open the intake valve for the main intake event at which time the piston travels away from the cylinder head. The intake valve closes and the intake stroke ends when the piston is near bottom dead center. Both the intake and exhaust valves are closed as the piston again travels upward for the compression stroke.

The above-referenced main intake and main exhaust valve events are required for positive power operation of an internal combustion engine. Additional auxiliary valve events, while not required, may be desirable. For example, it may be desirable to actuate the intake and/or exhaust valves during positive power or other engine operation modes for compression-release engine braking, bleeder engine braking, exhaust gas recirculation (EGR), or brake gas recirculation (BGR). FIG. 8 illustrates examples of a main exhaust event 600, and auxiliary valve events, such as a compression-release engine braking event 610, a bleeder engine braking event 620, exhaust gas recirculation event 630, and brake gas recirculation event 640, which may be carried out by an exhaust valve using various embodiments of the present invention to actuate exhaust valves for main and auxiliary valve events. An example of a main intake event 650 which may be carried out by an intake valve is also shown.

With respect to auxiliary valve events, flow control of exhaust gas through an internal combustion engine has been used in order to provide vehicle engine braking. Generally, engine braking systems may control the flow of exhaust gas to incorporate the principles of compression-release type braking, exhaust gas recirculation, exhaust pressure regulation, and/or bleeder type braking.

During compression-release type engine braking, the exhaust valves may be selectively opened to convert, at least temporarily, a power producing internal combustion engine into a power absorbing air compressor. As a piston travels upward during its compression stroke, the gases that are trapped in the cylinder may be compressed. The compressed gases may oppose the upward motion of the piston. As the piston approaches the top dead center (TDC) position, at least one exhaust valve may be opened to release the compressed gases in the cylinder to the exhaust manifold, preventing the energy stored in the compressed gases from being returned to the engine on the subsequent expansion down-stroke. In doing so, the engine may develop retarding power to help slow the vehicle down. An example of a prior art compression release engine brake is provided by the disclosure of the Cummins, U.S. Pat. No. 3,220,392 (November 1965), which is hereby incorporated by reference.

During bleeder type engine braking, in addition to, and/or in place of, the main exhaust valve event, which occurs during the exhaust stroke of the piston, the exhaust valve(s) may be held slightly open during remaining three engine cycles (full-cycle bleeder brake) or during a portion of the remaining three engine cycles (partial-cycle bleeder brake). The bleeding of cylinder gases in and out of the cylinder may act to retard the engine. Usually, the initial opening of the braking valve(s) in a bleeder braking operation is in advance of the compression TDC (i.e., early valve actuation) and then lift is held constant for a period of time. As such, a bleeder type engine brake may require lower force to actuate the valve(s) due to early valve actuation, and generate less noise due to continuous bleeding instead of the rapid blow-down of a compression-release type brake.

Exhaust gas recirculation (EGR) systems may allow a portion of the exhaust gases to flow back into the engine cylinder during positive power operation. EGR may be used to reduce the amount of NOx created by the engine during positive power operations. An EGR system can also be used to control the pressure and temperature in the exhaust manifold and engine cylinder during engine braking cycles. Generally, there are two types of EGR systems, internal and external. External EGR systems recirculate exhaust gases back into the engine cylinder through an intake valve(s). Internal EGR systems recirculate exhaust gases back into the engine cylinder through an exhaust valve(s). Embodiments of the present invention primarily concern internal EGR systems.

Brake gas recirculation (BGR) systems may allow a portion of the exhaust gases to flow back into the engine cylinder during engine braking operation. Recirculation of exhaust gases back into the engine cylinder during the intake stroke, for example, may increase the mass of gases in the cylinder that are available for compression-release braking. As a result, BGR may increase the braking effect realized from the braking event.

A valve actuation system may be adapted to provide one or more of the auxiliary valve events described above, in addition to providing main valve events. Moreover, the motion imparted by a valve train element to produce a main valve event may be used to provide an auxiliary valve event. For example, a main intake event lobe on a camshaft may be used to additionally actuate one or more valves for an EGR event. In valve actuation systems providing both main and auxiliary valve events, packaging, cost, reliability, and/or performance are design factors that may be considered.

SUMMARY OF THE INVENTION

Responsive to the foregoing challenges, Applicant has developed an innovative system for actuating an engine valve. In one embodiment of the present invention, the system comprises: a rocker arm shaft; a means for imparting primary valve actuation motion; a primary rocker arm disposed on the rocker arm shaft, the primary rocker arm being adapted to actuate an engine valve and receive motion from the means for imparting primary valve actuation motion; a means for imparting auxiliary valve actuation motion selected from the group consisting of: engine braking motion, exhaust gas recirculation motion, and brake gas recirculation motion; an auxiliary rocker arm disposed on the rocker arm shaft adjacent to the primary rocker arm, the auxiliary rocker arm being adapted to receive motion from the means for imparting auxiliary valve actuation motion; and a rocker arm coupling assembly disposed between the auxiliary rocker arm and the primary rocker arm, the coupling assembly being adapted to selectively transfer one or more auxiliary valve actuation motions from the auxiliary rocker arm to the primary rocker arm.

Applicant has further developed a system for actuating an engine valve comprising: a rocker arm shaft; means for imparting primary valve actuation motion; a primary rocker arm disposed on the rocker arm shaft, the primary rocker arm being adapted to actuate an engine valve and receive motion from the means for imparting primary valve actuation motion; means for imparting auxiliary valve actuation motion; an auxiliary rocker arm disposed on the rocker arm shaft adjacent to the primary rocker arm, the auxiliary rocker arm being adapted to receive motion from the means for imparting auxiliary valve actuation motion; and a coupling assembly, comprising: an actuator piston disposed in a bore formed in the primary rocker arm; and a slot formed in the auxiliary rocker arm for selectively receiving the actuator piston, wherein the actuator piston includes a curved surface to facilitate engagement with the slot.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to assist the understanding of this invention, reference will now be made to the appended drawings, in which like reference characters refer to like elements.

FIG. 1 is a schematic view of a valve actuation system according to a first embodiment of the present invention.

FIG. 2 is a schematic view of a valve actuation system according to a second embodiment of the present invention.

FIG. 3 is an overhead view of a valve actuation system according to the embodiment of the present invention shown in FIG. 1.

FIG. 4 is an overhead view of a valve actuation system according to the embodiment of the present invention shown in FIG. 2.

FIG. 5A is a partial side view of a valve actuation system in a first operating mode according to an embodiment of the present invention.

FIG. 5B is a partial side view of a valve actuation system in a second operating mode according to an embodiment of the present invention.

FIG. 6 is a cross-sectional view of the valve actuation system shown in FIG. 3 along section lines 6-6 according to an embodiment of the present invention.

FIG. 7 is a detailed view of a rocker arm coupling assembly according to an embodiment of the present invention.

FIG. 8 is a valve lift diagram depicting a number of different and exemplary main and auxiliary engine valve events, one or more of which may be produced with an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Reference will now be made in detail to an embodiment of the present invention, an example of which is illustrated in the accompanying drawings. With reference to FIG. 1, a system for actuating engine valves is shown.

The valve actuating system includes at least two rocker arms disposed on a rocker shaft (500, as shown in FIGS. 3 and 4). The at least two rocker arms may include a primary rocker arm 100 and an auxiliary rocker arm 200. The primary rocker arm 100 and the auxiliary rocker arm 200 may be pivoted about the rocker shaft as a result of motion imparted to them by motion imparting means 150 and 250, respectively. The motion imparting means 150 and 250 may comprise a camshaft and/or another suitable motion imparting device, such as, for example, a push tube or equivalent valve train element. The rocker arms 100 and 200 are adapted to actuate one or more engine valves 400 to produce an engine valve event by contacting the valve directly, through a pin, or through a valve bridge 410 (as shown in FIGS. 2, 5A, and 5B).

The engine valves 400 comprise poppet-type valves that are used to control communication between the combustion chambers (e.g., cylinders) in an engine and aspirating (e.g., intake and exhaust) manifolds. The system may further include a rocker arm coupling assembly 300 disposed between the primary rocker arm 100 and the auxiliary rocker arm 200 so as to selectively transfer one or more valve actuation motions from the auxiliary rocker arm 200 to the primary rocker arm 100.

In one embodiment of the present invention, the primary rocker arm 100 may comprise an exhaust rocker arm and the auxiliary rocker arm 200 comprises an intake rocker arm. The exhaust rocker arm 100 may be adapted to actuate one or more exhaust valves to produce a main exhaust event, and an auxiliary valve event, such as, an engine braking event, an exhaust gas recirculation (EGR) event, and/or a brake gas recirculation event (BGR). The intake rocker arm 200 is adapted to actuate one or more intake valves to produce an engine valve event, such as, for example, a main intake event. In one embodiment of the present invention, the exhaust valve actuated by the exhaust rocker arm 100 and the intake valve actuated by the intake rocker arm 200 are in the same engine cylinder. It is contemplated, however, that the engine valves may be in different engine cylinders. FIG. 3 is an overhead view of a valve actuation system having a primary rocker arm (exhaust rocker arm) 100, and an auxiliary rocker arm (intake rocker arm) 200.

In an alternative embodiment, as shown in FIG. 2, the primary rocker arm 100 may comprise a dedicated rocker arm. The dedicated rocker arm 100 may be adapted to actuate one or more exhaust valves to produce an auxiliary valve event, such as, an engine braking event, an exhaust gas recirculation (EGR) event, and/or a brake gas recirculation event (BGR). In this embodiment, the valve actuation system may further comprise an exhaust rocker arm 175 adapted to actuate one or more exhaust valves to produce an engine valve event, such as, for example, a main exhaust event. The exhaust rocker arm 175 may be pivoted about the rocker shaft as a result of motion imparted to them by motion imparting means 170. FIG. 4 is an overhead view of a valve actuation system having a primary rocker arm (dedicated rocker arm) 100, an auxiliary rocker arm (intake rocker arm) 200, and an exhaust rocker arm 175.

In one embodiment of the present invention, the primary rocker arm 100 may actuate one or more engine valves 400 to produce an engine braking event. FIGS. 5A and 5B are side views, of the valve actuation system according to an embodiment of the present invention. With reference to FIGS. 5A and 5B, a cam 150 may include a main exhaust event lobe 152, and an engine braking lobe 155, such as a bleeder braking lobe (shown in FIGS. 5A-B) or a compression release braking lobe. The depictions of the lobes on the cam 150 are intended to be illustrative only, and not limiting. It is appreciated that the number, combination, size, location, and shape of the lobes may vary markedly without departing from the intended scope of the present invention. For example, in conjunction with the embodiment of the present invention shown in FIG. 3, the cam 150 imparting motion to the primary rocker arm 100 may comprise a dedicated cam for braking that does not include a main exhaust event lobe.

The system may include a lash piston 120 disposed in a bore formed in the primary rocker 100 and in selective contact with the cam 150. A spring 126 biases the lash piston 120 away from the cam 150. The system may include a plunger 122 extending into the lash piston bore, and a locking nut 124. The locking nut 124 may be adjusted to extend the plunger 122 a desired distance within the bore, and, correspondingly, adjust the position of the lash piston 120 relative to the cam 150. The lash piston 120 may include a surface 128 suitable for contacting and following the motion of the cam 150.

The rocker arm shaft 500 may include one or more internal passages for the delivery of hydraulic fluid, such as engine oil, to the rocker arms mounted thereon. Hydraulic fluid may be selectively supplied to the primary rocker arm 100 by a fluid supply valve (not shown), such as a solenoid valve, to initiate engine braking operation.

A control valve 110 may be disposed in a bore 112 formed in the primary rocker arm 100. The control valve 110 controls fluid communication between the passage in the rocker shaft 500 and the lash piston 120 through a hydraulic passage 105 formed in the primary rocker arm 100. A spring 114 biases the control valve 110 into a first position, as shown in FIG. 5A, wherein the control valve is seated in a detent 505 on the rocker shaft 500. In this position, the control valve 110 substantially prevents fluid communication to the lash piston 120, and holds the primary rocker arm 100 in position on the rocker shaft 500.

When engine braking is desired, a supply valve, such as, for example, a solenoid valve (not shown), is activated and hydraulic fluid is supplied through the rocker shaft 500 to the control valve bore 112. The hydraulic pressure created by the fluid causes the control valve 110 to actuate from the first position, as shown in FIG. 5A, corresponding to a non-braking operating mode, to a second position, as shown in FIG. 5B, corresponding to braking operating mode. With the control valve 110 in this position, hydraulic fluid is permitted to flow through the hydraulic passage 105 to the lash piston 120.

The intake rocker arm 200 may include a cam roller 210 for following the motion of an intake cam 250 (not shown). The motion from the intake cam 250 may be used to actuate an intake valve to provide a main intake event. The motion from the intake cam 250 also may be transferred to the primary rocker arm 100 through the coupling assembly 300 such that the primary rocker arm 100 actuates the exhaust valve 400 to provide an auxiliary valve event, such as an EGR valve event.

In one embodiment of the present invention, with reference to FIG. 6, the rocker arm coupling assembly 300 may comprise an actuator piston 310 disposed in a bore 320 formed in the primary rocker arm 100, and a slot 330 formed in the intake rocker arm 200 that selectively receives the piston 310. A spring 340 biases the piston 310 in the bore 320 away from the slot 330. It is contemplated that the piston 310 may be disposed in a bore formed in the auxiliary rocker arm 200 and the slot 330 formed in the primary rocker arm 100 without departing from the scope of the present invention.

Hydraulic fluid may be selectively supplied from a passage in the rocker arm shaft 500 (not shown) to the bore 320 through a hydraulic passage 360 formed in the primary rocker arm 100. The hydraulic fluid may be selectively supplied by a fluid supply valve (not shown), such as, for example, a solenoid valve. The hydraulic pressure created by the fluid in the bore 320 causes the piston 310 to translate against the bias of the spring 340 and extend into the slot 330. A mechanical stop 350 limits the travel of the piston 310 within the bore 320.

A partial detailed view of the coupling assembly 300 according to an embodiment of the present invention is shown in FIG. 7. The piston 310 may include a slot engagement portion having a curved surface 315. The slot 330 may include a piston engagement portion having a curved surface 335 with a centerline 336. When the piston 310 is engaged in the slot 330, rotation of the auxiliary rocker arm 200 causes rotation of the primary rocker arm 100. The piston surface 315 and the slot surface 335 may facilitate receipt of the piston 310 into the slot 330, and, accordingly, transfer of the auxiliary valve actuation motion from the auxiliary rocker arm 200 to the primary rocker arm 100. The location of the piston 310 and the slot 330 may be varied depending on the desired engine valve lift.

Operation of an embodiment of the valve actuation system of the present invention will now be described. During positive power operation, when engine braking is not desired, hydraulic fluid is not supplied to the control valve bore 112 through the rocker shaft 500. The control valve 110 remains seated in the rocker shaft detent 505, in an “engine brake off” position, substantially preventing hydraulic fluid communication to the lash piston 120. Without sufficient hydraulic pressure acting on it, the lash piston 120 remains in a retracted position, as shown in FIG. 5A. As the cam 150 rotates, the engine braking lobe 155 does not come into contact with the lash piston 120, and accordingly, the engine braking valve motion is not transferred to the engine valve(s) 400. As the cam continues to rotate, the main exhaust event lobe 152 contacts the cam follower surface 128 of the lash piston 120 and causes the primary rocker arm 100 to rotate about the rocker shaft 500 in a counter-clockwise direction (relative to the view shown in FIG. 5A), and act on the engine valve 400 directly, through a pin, or through a valve bridge, as shown in FIG. 5A. The primary rocker arm 100 actuates the engine valve 400 to produce the main exhaust valve event.

During engine braking operation, hydraulic fluid is supplied to the control valve bore 112 through the rocker shaft 500. The hydraulic pressure causes the control valve 110 to translate in the bore 112 against the bias of the spring 114, as shown in FIG. 5B. With the control valve 110 in this “engine brake on” position, hydraulic fluid is permitted to flow through the hydraulic passage 105 to the lash piston 120. Under the pressure of the hydraulic fluid, the lash piston 120 extends from the primary rocker arm 100 taking up the lash between the piston and the cam 150. As the cam 150 rotates, the cam follower surface 128 of the lash piston 120 follows the entire motion of the cam 120, including the engine braking lobe 155. As a result, the engine braking valve motion is transferred to the engine valve(s) 400 through the rocker arm 100.

When auxiliary exhaust valve actuation is desired for EGR and/or BGR, for example, a solenoid supply valve (not shown) may be activated so as to provide hydraulic fluid through the rocker shaft 500 through the hydraulic passage 360 to the actuator piston bore 320. The hydraulic fluid pressure created in the bore 320 causes the piston 310 to translate against the bias of the spring 340 and extend into the slot 330. As auxiliary valve motion is applied to the auxiliary rocker arm 200, the auxiliary rocker arm 200 begins to rotate. Because the piston 310 is engaged in the slot 330, the rotation of the auxiliary rocker arm 200, in turn, causes the primary rocker arm 100 to rotate and actuate the exhaust valve 400. The timing of the auxiliary valve motion may be appropriate to provide an auxiliary valve event, such as an EGR or BGR event.

With reference to FIG. 7, the piston surface 315 and the slot surface 335 may facilitate receipt of the piston 310 into the slot 330, and, accordingly, transfer of the auxiliary valve actuation motion from the auxiliary rocker arm 200 to the primary rocker arm 100. For example, if the piston 310 extends towards the slot 330 after the auxiliary rocker arm 200 has begun to rotate under the influence of the cam 250, the piston surface 315 may contact the slot surface 335 to the right of the centerline 336. In this case, because of the curvature of the surfaces 315 and 335, the piston 310 may be pulled into position within the slot 330. If the piston surface 315 contacts the slot surface 335 to the left of the centerline 336, the piston 310 will not immediately engage the slot 330. During the next rotation of the cam 250, as the cam approaches lower base circle, the piston 310 will then engage the slot 330. The shape of the surfaces 315 and 335 also may prevent the piston from resting on the slot surface 335. This may reduce or eliminate unwanted additional valve lift, and stress loading on the auxiliary rocker arm 200.

It will be apparent to those skilled in the art that various modifications and variations can be made in the construction, configuration, and/or operation of the present invention without departing from the scope or spirit of the invention. For example, it is appreciated that the primary rocker arm 100 could be implemented as an intake rocker arm, or an auxiliary rocker arm, without departing from the intended scope of the invention. Further, where engine braking functionality is not required, it is contemplated that embodiments of the valve actuation system may be provided without the control valve 110 and/or the lash piston 120. In addition, the rocker shaft 500 may further include a hydraulic passage adapted to provide lubrication fluid to the one or more rocker arms. These and other modifications to the above-described embodiments of the invention may be made without departing from the intended scope of the invention.