Low viscosity functional fluid composition

A brake fluid comprising a functional fluid, wherein the functional fluid comprises

• (A) from 70 to 90 wt.-% of alkoxy glycol according to formula (I)
• CH3—O—(CH2—CH2—O)n—H (I)
• wherein n is a number from 2 to 5, with the proviso that in at least 30 wt.-% of all compounds according to formula (I) n is 3, and that 15 to 65 wt.-% of all compounds according to formula (I) have n=4 or 5, and
• (B) less than 1.0 wt.-% of alkoxy glycol according to formula (II)
• R1—O—(CH2—CH2—O)m—H (II)
• wherein
• R1 is a C2 to C8 alkyl residue,
• m is a number from 2 to 6,
• (C) from 8 to 25 wt.-% of at least one compound according to formula (III)
• H—O—(CH2—CH2—O)k—H (III)
• wherein k is a number of 2 or higher, with the proviso that in at least 80 wt.-% of all compounds according to formula (III) k is 2 or 3,
• (D) at least one additive, selected from the group consisting of corrosion inhibitors, alkalinity agents, aging protection agents, defoamers and lubricants, the lubricants being selected from the group consisting of propylene oxide containing alkylene oxide polymers that are optionally substituted with a C1 to C4 alkyl group, triglycerides, castor oil, ricinoleic acid, and ethoxylates of castor oil or ricinoleic acid, and mixtures thereof, and
• wherein the fluid comprises at most 3 wt.-% of an ester between boric acid and a glycol or alkylpolyglycol compound.

A method of operating a vehicular brake, the method comprising transmitting hydraulic pressure by a functional fluid, wherein the functional fluid comprises

• (A) from 70 to 90 wt.-% of alkoxy glycol according to formula (I)
• CH3—O—(CH2—CH2—O)n—H (I)
• wherein n is a number from 2 to 5, with the proviso that in at least 30 wt.-% of all compounds according to formula (I) n is 3, and that 15 to 65 wt.-% of all compounds according to formula (I) have n=4 or 5, and
• (B) less than 1.0 wt.-% of alkoxy glycol according to formula (II)
• R1—O—(CH2—CH2—O)m—H (II)
• wherein
• R1 is a C2 to C8 alkyl residue,
• m is a number from 2 to 6,
• (C) from 8 to 25 wt.-% of at least one compound according to formula (III)
• H—O—(CH2—CH2—O)k—H (III)
• wherein k is a number of 2 or higher, with the proviso that in at least 80 wt.-% of all compounds according to formula (III) k is 2 or 3,
• (D) at least one additive, selected from the group consisting of corrosion inhibitors, alkalinity agents, aging protection agents, defoamers and lubricants, the lubricants being selected from the group consisting of propylene oxide containing alkylene oxide polymers that are optionally substituted with a C1 to C4 alkyl group, triglycerides, castor oil, ricinoleic acid, and ethoxylates of castor oil or ricinoleic acid, and mixtures thereof, and
• wherein the fluid comprises at most 3 wt.-% of an ester between boric acid and a glycol or alkylpolyglycol compound.