Claim construction plays a crucial role in patent infringement cases. It helps to define the scope of a patent by interpreting the language of the claims in light of the complete specification. This process determines the boundaries of the patent holder’s exclusive rights and plays a key role in assessing patent infringement and validity.

The recent decision of the Division Bench of the Delhi High Court in Jay Switches India Pvt Ltd vs Sandhar Technologies Ltd & Ors. [FAO(OS) (COMM) 6/2025] underscores the significance of claim construction.

In the instant case, the Plaintiff alleged infringement of their patent rights in Indian patent number 427110, entitled “Air Tight Fuel Cap”, that disclosed a fuel cap designed to maintain the required air pressure within a fuel tank of a motor vehicle and prevent fuel spillage during the movement of the motor vehicle. The Plaintiff contended that the Defendants’ impugned fuel cap deployed an identical solution as claimed in the suit patent to prevent leakage by limiting free space between the beams and the MCP.

The central issue in the case revolved around the interpretation of the “length” of the main circular plate (MCP) and how it related to the “predetermined distance” (PD) in the suit patent. The relevant extracts from the patent application of the suit patent are set out as follows:

Claim 1. A fuel cap (1) to be secured intermittently to a fuel filler neck attached to an inlet of a feed oil pipe, comprising:

….

characterized in that each of the said locking projection (52) of the cylindrical locking member (5) is provided with a pair of beams on an inner surface thereof that terminate at a predetermined distance from a bottom end of the locking projections (52), and

the said predetermined distance being equal to 10% to 100% of the length (l) of the main circular plate (241) separating the middle portion (23) of the cylindrical body (2) from the bottom portion (24) of the cylindrical body (2).

Claim 2. The fuel cap (1) as claimed in claim 1, wherein the main circular plate (241) comprises of a pair of engagement projections (242) engaged within predetermined distance provided in the locking projections (52).

Complete Specification: …. This predetermined distance is equal to 10% to 100% of the length of the main circular plate 241 dividing middle and bottom portion of the cylindrical body 2. Further, the main circular plate 241 is provided with a pair of engagement projections 242 that engage within the locking projections 52. More particularly, these engagement projections 242 engage within the predetermined distance provided in the locking projections 52. Thus, this engagement of engagement projections 242 in the locking projections 52 helps in right fitment of fuel cap 1 on to the mouth of the fuel filler neck. More particularly, the circular seal member 33 tightly abuts the mouth of the fuel filler neck, thus leaving no space for any release of air pressure present within the fuel tank or the fuel itself A seal ring 4 which has a rectangular cross section is accommodated on top surface of the main circular plate 241. More particularly, the lower end of the trunk portion 31 which rests on top surface of the main circular plate 241 has a step 311 towards its inner surface so as to accommodate a seal ring 4. … … … The trunk portion 31 of the body cover 3 is encompassed by a coiled spring 7. More particularly the coiled spring 7 is encased inside the locking member 5. More precisely, the coiled spring 7 rests between upper surface of the main circular plate 241 and lower surface of a step 51 provided on inside surface near to top edge of the locking member 5. … … … The contraction of coiled spring 7 is responsible for axial movement of locking member 5 with respect to cylindrical body 2, thus urging the circular seal member 33 to fit tightly against the mouth of the fuel filler neck.”

Claim 1 specified that the PD should be between 10% to 100% of the length of the MCP (241). The Plaintiff argued that the PD in claim 1 should be interpreted to mean 10% to 100% of the length of the MCP (241) including the engagement projections (EP) (242). The Plaintiff argued that dependent claim 2, when read in conjunction with independent claim 1, indicated that the MCP and the EP formed a single unit, and, therefore, MCP should be understood to include both, the MCP and the EP. Additionally, the Plaintiff argued that the EP was the functional part of the MCP that interacted with the PD, while the rest of the MCP was a non-functional part. According to Plaintiff, the Defendants had infringed both claim 1 and claim 2, as only a minor alteration to the non-functional part of the MCP was made in the impugned product, while the functional part, the EP, remained unchanged. 

Notably, the MCP in the suit patent was denoted by reference numeral “241”, while the EP was referred to as “242”. The Plaintiff argued that the use of different reference numerals was merely for identification purposes and should not be interpreted as indicating separate elements.

Conversely, the Defendants argued that the PD in claim 1 should be interpreted to mean 10% to 100% of the length of the MCP (241) alone, excluding the EP (242). They contended that the language in claim 1 specifically referred to the MCP’s length without mentioning the EP. The Defendants further argued that the inclusion of the EP from claim 2 could not modify the description of the MCP’s length in claim 1. They also pointed out that the complete specification consistently differentiated between the MCP and the EP. The Defendants also highlighted the voluntary amendment made during prosecution, wherein the PD was initially described as 10-100% of the MCP (242), which was amended to specify that the MCP was to be identified with the numeral 241 and not 242. They also pointed to the Plaintiff’s stance during pre-grant oppositions, where the PD was defined in relation to the MCP (241), and the inventive step was based on the configuration and function of the MCP (241) and the distance between the bottom end and the beams. Based on this interpretation, the Defendants claimed that the PD in the impugned product was 120% of the length of the MCP (not including the EP), which was beyond the 100% limit specified in the suit patent. The Defendants thus argued their product did not fall within the scope of the suit patent.

The single Judge, in its decision, had emphasized that patent claims must be read in conjunction with the complete specification and understood as ordinary English sentences, without adding or subtracting from them and without considering the subjective intent of the patentee. The Court also reiterated that the expression “characterized” used in the claim language describes the crux of the invention. Additionally, the Court highlighted that the reference numerals or signs used in technical drawings aid in the understanding of technical features but they do not limit the scope of the claim.

In its analysis, the Court carefully examined the distinction between the terms MCP and EP used in the suit patent. The Court observed that the range of 10% to 100% in claim 1 referred specifically to the length of the MCP identified by the reference numeral “241”. The Court noted that this numerical reference when viewed in conjunction with the technical drawing of the patent, referred exclusively to the MCP because the reference to “242”, which corresponded to the EP, appeared only in claim 2. Additionally, claim 2 did not include any reference to the range of 10% to 100% or the specific relationship between the PD and the MCP’s length, which was a key feature of claim 1. The Court further clarified that the Plaintiff’s interpretation of the MCP and EP as a single unit was not supported by the language of claim 1. The term “MCP” in claim 1 was followed by the specific reference to the middle and bottom portions of the cylindrical body, and this reference did not encompass the EP, which was discussed separately in claim 2, and, therefore, the Court dismissed the Plaintiff’s contention that the two claims must be read together. The Court also explained that these numerical references aided in understanding the technical features of the claim and were not to be disregarded.

The Court noted that the term MCP and EP were used in a separate and distinct manner in the complete specification, wherein MCP (241) was described as a structural component of the fuel cap, whereas the EP (242) was described as an attachment to the MCP, serving a locking function. The Court also rejected the Plaintiff’s argument that the MCP was a non-functional part of the suit patent, emphasizing that as per the complete specification, the MCP played an important structural role in the invention, particularly in housing and aligning key elements necessary for the airtight sealing mechanism.

The Court further highlighted that prosecution history acts as an important aid in claim construction. It was noted that during prosecution, the Plaintiff had amended claim 1 by inserting the letter “l” in the context of the MCP alone and not the EP. Notably, this amendment was made pursuant to the pre-grant opposition filed by the Defendant in respect of lack of clarity with regards to the claimed range. This, the Court remarked, negated the Plaintiff’s argument that the length referred to in claim 1 included the EP. Additionally, the Court noted that the Plaintiff had made a submission during the pre-grant opposition that the expression “length” was used in the context of a “circular plate” to refer to the thickness of the circular plate. Considering that an EP is not a “circular plate”, the Court concluded that the expression “length” in claim 1 referred to the thickness of the MCP alone, and not the EP referred in claim 2.  

The Court held that the claims in the suit patent were ambiguous, and determination of the patent’s scope was a matter to be decided at the trial stage, where a more thorough examination could take place.  

In view of the aforesaid, it was held that the Plaintiff failed to make out a prima facie case for the grant of interim injunction. The Division Bench upheld this reasoning and declined to interfere with the judgement passed by the single Judge.