In 1922, when locomotives of the E series were being constructed in Germany and Sweden under the order of the Soviet government, V. I. Lenin wrote: "It is highly desirable not to miss the opportunity of utilizing any available funds... for acquiring much more beneficial diesel locomotives."
In 1924–1925, two diesel locomotives were imported from Germany into our country. Along with the domestic Shch-el 1 machine (see "TM" No. 1, 1979), they underwent trial runs over several years. Their operation enabled railway workers to gain valuable experience.
Despite economic challenges, the Soviet government and the People's Commissariat for Transport (NKPS) sought to establish a robust scientific and production foundation for the development of new locomotives. To this end, in 1927, a laboratory for diesel locomotives was founded at the Moscow Higher Technical School named after N. E. Bauman, with significant funds allocated for the purchase of necessary instruments and equipment. Professor A. N. Shelest was appointed to lead the laboratory. That same year, a design bureau was established at the Kolomna Machine-Building Plant named after V. V. Kuybyshev, headed by engineer B. S. Pozdnyakov. The bureau's task was to develop blueprints for new diesel locomotives.
At that time, the Kolomna machine builders received their first order from the NKPS for two locomotives equipped with 600-horsepower diesel engines and electric transmissions. These machines were intended for secondary lines and shunting operations. They were expected to match the power and tractive force of the renowned "Ovechka" steam locomotive series Ov (see "TM" No. 1, 1974). Hence, they were pre-assigned the designation O9L.
By the 1920s, leading economists, railway experts, and engineers already understood that diesel locomotives were the most economically advantageous option for shunting operations, regardless of the mainline traction type—steam, diesel, or electric. They also determined the optimal power range for shunting locomotives to be 400–600 horsepower. This is why the NKPS specification for the Kolomna plant included a 600-horsepower diesel engine. While this specification and the locomotive's work output were clear, opinions diverged on the drivetrain configuration.
Such disagreements were understandable. In the 1920s, a variety of diesel locomotives with electric, mechanical, and hydraulic transmissions were being built worldwide, alongside designs incorporating direct and pneumatic drives. Complex machines were also created, combining steam boilers, turbines, and electric transmissions similar to those used in the Shch-el locomotive. In short, diesel locomotive engineers had no shortage of ideas.
Deciding on the drivetrain type—individual or group—was particularly challenging. In the first approach, each drive axle is powered by its own electric motor, sometimes even two. In the second, the locomotive is equipped with a single electric motor. This motor, via a gearbox, turns a crankshaft linked to a group of drive wheels using a rod mechanism, resembling a steam locomotive.
Since the optimal solution was unknown, the NKPS tasked the Kolomna plant with conducting experimental testing. Thus, two diesel locomotives were ordered: both equipped with the same diesel-generator group but differing in drivetrain—one with an individual electric drive and the other with a single electric motor and group drive rod mechanism.
The diesel locomotive with an individual drive was designed with a 0-40-0 axle arrangement and an axle load of 16 tons. However, it was not possible to meet the specified weight of 94 tons. Therefore, to distribute the full locomotive weight of 98.7 tons onto the rails, the designers added a pivoting bogie at the front of the machine, resulting in a modified 1-40-0 axle arrangement. The leading axle bore a weight of 14.3 tons, while each driving axle carried 21.1 tons.
The primary engine was a six-cylinder, four-stroke, non-compressor diesel engine of German manufacture. All electric motors on this diesel locomotive were connected in parallel. During acceleration, the generator initially produced partial power, gradually increasing the excitation of the traction motors, and subsequently the generator reached full power as its excitation increased.
To ensure smoother and more reliable deceleration, the locomotive employed two braking systems: electric and pneumatic. The electric system operated at higher speeds, while the pneumatic system functioned at lower speeds. The braking process for a moving train was conducted in two stages. Initially, the driver set the controller to the "braking" position, causing the traction motors to switch to generator mode and be loaded with resistors. This converted the train's kinetic energy into electrical energy, which was then dissipated as heat in the resistors. Once the speed dropped to 20–25 km/h, further deceleration to a complete stop was achieved using the pneumatic braking system.
The diesel locomotive with the 1-40-0 axle arrangement was manufactured at the end of 1930 and was designated Oel 7. In November 1931, the Kolomna plant completed the second machine with a group drive, designated Oel 6. This locomotive had a design weight of 100 tons and an adhesion weight of 72 tons, with a 1-4-1 axle arrangement.
On November 6, 1931, the Oel 6 diesel locomotive arrived in Moscow. A celebratory rally was held at the Kazan Station, attended by K. E. Voroshilov, S. K. Ordzhonikidze, and other prominent party and government figures. In his speech, A. A. Andreyev, the People’s Commissar for Rail Transport, announced that the Oel series diesel locomotives had been approved for operation. In 1933, a second locomotive with a 1-40-0 axle arrangement was built and designated Oel 10.
The Oel 7 diesel locomotive underwent trial runs along the October Railway in 1931. Later, it, along with the other shunting locomotives of the series, was sent to the Ashgabat Railway. In the waterless region, the advantages of these locomotives became particularly evident. For example, their average daily mileage was 1.5–2 times higher than the norm for steam locomotives. Moreover, the machine with the individual drive operated more smoothly, accelerated faster, broke down less often, was easier to repair, and was generally more practical than the group-drive models.
The experimental Oel series diesel locomotives served on the Ashgabat Railway until the late 1940s, when they were replaced by more advanced locomotives.
OLEG KURIKHIN, Candidate of Technical Sciences